U.S.A. Turbo expert talks.. (prob. worth a read)
02 January 2003, 02:57 AM
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Yes stainless works well 
Well i was putting a straight pipe on that was angle fitted and it lost mid range pull, so i started testing and was surprised at what i found, when the SWRT was here last year i asked them about it and they told me that it needs to be there for the sonic wave to bounce back and keep fresh charge from escaping from the exhaust valves on cam over lap, made sense as i had already seen the gains. I have repositioned many Apexi and HKS mufflers and the owners were blown away with how much more mid pull the car has. Like i said you might loose 2-3 kw at top end which for a drag car you need, but for a road car or circuit car torque is what pushes the car faster, HP is the ability to keep it going.
hey try it and you tell me !
I'm not here to sell anyone anything, I am just passing on my development work, I don't race my wrx anymore so i have no secrets
Michael
http://www.users.bigpond.net.au/msgofast/
[Edited by msgofaster - 2/1/2003 2:59:16 AM]
Well i was putting a straight pipe on that was angle fitted and it lost mid range pull, so i started testing and was surprised at what i found, when the SWRT was here last year i asked them about it and they told me that it needs to be there for the sonic wave to bounce back and keep fresh charge from escaping from the exhaust valves on cam over lap, made sense as i had already seen the gains. I have repositioned many Apexi and HKS mufflers and the owners were blown away with how much more mid pull the car has. Like i said you might loose 2-3 kw at top end which for a drag car you need, but for a road car or circuit car torque is what pushes the car faster, HP is the ability to keep it going.
hey try it and you tell me !
I'm not here to sell anyone anything, I am just passing on my development work, I don't race my wrx anymore so i have no secrets
Michael
http://www.users.bigpond.net.au/msgofast/
[Edited by msgofaster - 2/1/2003 2:59:16 AM]
02 January 2003, 10:20 PM
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When you split the gases with a second pipe the pipe that you will use to exhaust the WG gases WILL restrict your power by the fact that isn't big enough off the turbo.
We are talking about an OPEN mouth with a splitter as here in these pics,
http://www.users.bigpond.net.au/msgofast/exhaustsystems.html
This is what does work.
The splitter is into the back of the turbo, 22mm on a TDO4/5 and 32mm on a VF22,23,24,28,29,34 and 27mm on a VF30,35.
By way of the WG operation the gases are mixed in the back of the turbo pre splitter,The WG gas is directed into the flow of the main turbine gases, this is what reduces flow and increases lag, By stopping them from running into each other by using a splitter and having them blend together at the same direction will increase flow, by giving the path of BOTH gases room to expand will also reduce lag.
Does this help you to understand?
If you can grab a turbo and open the WG and take a look you will see where the gases are going and understand it easier too.
Michael
[Edited by msgofaster - 2/1/2003 10:22:04 PM]
We are talking about an OPEN mouth with a splitter as here in these pics,
http://www.users.bigpond.net.au/msgofast/exhaustsystems.html
This is what does work.
The splitter is into the back of the turbo, 22mm on a TDO4/5 and 32mm on a VF22,23,24,28,29,34 and 27mm on a VF30,35.
By way of the WG operation the gases are mixed in the back of the turbo pre splitter,The WG gas is directed into the flow of the main turbine gases, this is what reduces flow and increases lag, By stopping them from running into each other by using a splitter and having them blend together at the same direction will increase flow, by giving the path of BOTH gases room to expand will also reduce lag.
Does this help you to understand?
If you can grab a turbo and open the WG and take a look you will see where the gases are going and understand it easier too.
Michael
[Edited by msgofaster - 2/1/2003 10:22:04 PM]
25 January 2003, 11:21 AM
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The following excerpts are from Jay Kavanaugh, a turbosystems engineer at Garret, responding to a thread on www.impreza.net regarding exhaust design and exhaust theory:
“Howdy,
This thread was brought to my attention by a friend of mine in hopes of shedding some light on the issue of exhaust size selection for turbocharged vehicles. Most of the facts have been covered already. FWIW I'm an turbocharger development engineer for Garrett Engine Boosting Systems.
N/A cars: As most of you know, the design of turbo exhaust systems runs counter to exhaust design for n/a vehicles. N/A cars utilize exhaust velocity (not backpressure) in the collector to aid in scavenging other cylinders during the blowdown process. It just so happens that to get the appropriate velocity, you have to squeeze down the diameter of the discharge of the collector (aka the exhaust), which also induces backpressure. The backpressure is an undesirable byproduct of the desire to have a certain degree of exhaust velocity. Go too big, and you lose velocity and its associated beneficial scavenging effect. Too small and the backpressure skyrockets, more than offsetting any gain made by scavenging. There is a happy medium here.
For turbo cars, you throw all that out the window. You want the exhaust velocity to be high upstream of the turbine (i.e. in the header). You'll notice that primaries of turbo headers are smaller diameter than those of an n/a car of two-thirds the horsepower. The idea is to get the exhaust velocity up quickly, to get the turbo spooling as early as possible. Here, getting the boost up early is a much more effective way to torque than playing with tuned primary lengths and scavenging. The scavenging effects are small compared to what you'd get if you just got boost sooner instead. You have a turbo; you want boost. Just don't go so small on the header's primary diameter that you choke off the high end.
Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.
Again, less pressure downstream of the turbine is goodness. This approach minimizes the time-to-boost (maximizes boost response) and will improve engine VE throughout the rev range.
As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side.”
"As for the geometry of the exhaust at the turbine discharge, the most optimal configuration would be a gradual increase in diameter from the turbine's exducer to the desired exhaust diameter-- via a straight conical diffuser of 7-12° included angle (to minimize flow separation and skin friction losses) mounted right at the turbine discharge. Many turbochargers found in diesels have this diffuser section cast right into the turbine housing. A hyperbolic increase in diameter (like a trumpet snorkus) is theoretically ideal but I've never seen one in use (and doubt it would be measurably superior to a straight diffuser). The wastegate flow would be via a completely divorced (separated from the main turbine discharge flow) dumptube. Due the realities of packaging, cost, and emissions compliance this config is rarely possible on street cars. You will, however, see this type of layout on dedicated race vehicles.
A large "bellmouth" config which combines the turbine discharge and wastegate flow (without a divider between the two) is certainly better than the compromised stock routing, but not as effective as the above.
If an integrated exhaust (non-divorced wastegate flow) is required, keep the wastegate flow separate from the main turbine discharge flow for ~12-18" before reintroducing it. This will minimize the impact on turbine efficiency-- the introduction of the wastegate flow disrupts the flow field of the main turbine discharge flow.
Necking the exhaust down to a suboptimal diameter is never a good idea, but if it is necessary, doing it further downstream is better than doing it close to the turbine discharge since it will minimize the exhaust's contribution to backpressure. Better yet: don't neck down the exhaust at all.
Also, the temperature of the exhaust coming out of a cat is higher than the inlet temperature, due to the exothermic oxidation of unburned hydrocarbons in the cat. So the total heat loss (and density increase) of the gases as it travels down the exhaust is not as prominent as it seems.
Another thing to keep in mind is that cylinder scavenging takes place where the flows from separate cylinders merge (i.e. in the collector). There is no such thing as cylinder scavenging downstream of the turbine, and hence, no reason to desire high exhaust velocity here. You will only introduce unwanted backpressure.
Other things you can do (in addition to choosing an appropriate diameter) to minimize exhaust backpressure in a turboback exhaust are: avoid crush-bent tubes (use mandrel bends); avoid tight-radius turns (keep it as straight as possible); avoid step changes in diameter; avoid "cheated" radii (cuts that are non-perpendicular); use a high flow cat; use a straight-thru perforated core muffler... etc.”
"Comparing the two bellmouth designs, I've never seen either one so I can only speculate. But based on your description, and assuming neither of them have a divider wall/tongue between the turbine discharge and wg dump, I'd venture that you'd be hard pressed to measure a difference between the two. The more gradual taper intuitively appears more desirable, but it's likely that it's beyond the point of diminishing returns. Either one sounds like it will improve the wastegate's discharge coefficient over the stock config, which will constitute the single biggest difference. This will allow more control over boost creep. Neither is as optimal as the divorced wastegate flow arrangement, however.
There's more to it, though-- if a larger bellmouth is excessively large right at the turbine discharge (a large step diameter increase), there will be an unrecoverable dump loss that will contribute to backpressure. This is why a gradual increase in diameter, like the conical diffuser mentioned earlier, is desirable at the turbine discharge.
As for primary lengths on turbo headers, it is advantageous to use equal-length primaries to time the arrival of the pulses at the turbine equally and to keep cylinder reversion balanced across all cylinders. This will improve boost response and the engine's VE. Equal-length is often difficult to achieve due to tight packaging, fabrication difficulty, and the desire to have runners of the shortest possible length.”
"Here's a worked example (simplified) of how larger exhausts help turbo cars:
Say you have a turbo operating at a turbine pressure ratio (aka expansion ratio) of 1.8:1. You have a small turboback exhaust that contributes, say, 10 psig backpressure at the turbine discharge at redline. The total backpressure seen by the engine (upstream of the turbine) in this case is:
(14.5 +10)*1.8 = 44.1 psia = 29.6 psig total backpressure
So here, the turbine contributed 19.6 psig of backpressure to the total.
Now you slap on a proper low-backpressure, big turboback exhaust. Same turbo, same boost, etc. You measure 3 psig backpressure at the turbine discharge. In this case the engine sees just 17 psig total backpressure! And the turbine's contribution to the total backpressure is reduced to 14 psig (note: this is 5.6 psig lower than its contribution in the "small turboback" case).
So in the end, the engine saw a reduction in backpressure of 12.6 psig when you swapped turbobacks in this example. This reduction in backpressure is where all the engine's VE gains come from.
This is why larger exhausts make such big gains on nearly all stock turbo cars-- the turbine compounds the downstream backpressure via its expansion ratio. This is also why bigger turbos make more power at a given boost level-- they improve engine VE by operating at lower turbine expansion ratios for a given boost level.
As you can see, the backpressure penalty of running a too-small exhaust (like 2.5" for 350 hp) will vary depending on the match. At a given power level, a smaller turbo will generally be operating at a higher turbine pressure ratio and so will actually make the engine more sensitive to the backpressure downstream of the turbine than a larger turbine/turbo would. As for output temperatures, I'm not sure I understand the question. Are you referring to compressor outlet temperatures?
The advantage to the bellmouth setup from the wg's perspective is that it allows a less torturous path for the bypassed gases to escape. This makes it more effective in bypassing gases for a given pressure differential and wg valve position. Think of it as improving the VE of the wastegate. If you have a very compromised wg discharge routing, under some conditions the wg may not be able bypass enough flow to control boost, even when wide open. So the gases go through the turbine instead of the wg, and boost creeps up.
The downside to a bellmouth is that the wg flow still dumps right into the turbine discharge. A divider wall would be beneficial here. And, as mentioned earlier, if you go too big on the bellmouth and the turbine discharge flow sees a rapid area change (regardless of whether the wg flow is being introduced there or not), you will incur a backpressure penalty right at the site of the step. This is why you want gradual area changes in your exhaust."
“Howdy,
This thread was brought to my attention by a friend of mine in hopes of shedding some light on the issue of exhaust size selection for turbocharged vehicles. Most of the facts have been covered already. FWIW I'm an turbocharger development engineer for Garrett Engine Boosting Systems.
N/A cars: As most of you know, the design of turbo exhaust systems runs counter to exhaust design for n/a vehicles. N/A cars utilize exhaust velocity (not backpressure) in the collector to aid in scavenging other cylinders during the blowdown process. It just so happens that to get the appropriate velocity, you have to squeeze down the diameter of the discharge of the collector (aka the exhaust), which also induces backpressure. The backpressure is an undesirable byproduct of the desire to have a certain degree of exhaust velocity. Go too big, and you lose velocity and its associated beneficial scavenging effect. Too small and the backpressure skyrockets, more than offsetting any gain made by scavenging. There is a happy medium here.
For turbo cars, you throw all that out the window. You want the exhaust velocity to be high upstream of the turbine (i.e. in the header). You'll notice that primaries of turbo headers are smaller diameter than those of an n/a car of two-thirds the horsepower. The idea is to get the exhaust velocity up quickly, to get the turbo spooling as early as possible. Here, getting the boost up early is a much more effective way to torque than playing with tuned primary lengths and scavenging. The scavenging effects are small compared to what you'd get if you just got boost sooner instead. You have a turbo; you want boost. Just don't go so small on the header's primary diameter that you choke off the high end.
Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.
Again, less pressure downstream of the turbine is goodness. This approach minimizes the time-to-boost (maximizes boost response) and will improve engine VE throughout the rev range.
As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side.”
"As for the geometry of the exhaust at the turbine discharge, the most optimal configuration would be a gradual increase in diameter from the turbine's exducer to the desired exhaust diameter-- via a straight conical diffuser of 7-12° included angle (to minimize flow separation and skin friction losses) mounted right at the turbine discharge. Many turbochargers found in diesels have this diffuser section cast right into the turbine housing. A hyperbolic increase in diameter (like a trumpet snorkus) is theoretically ideal but I've never seen one in use (and doubt it would be measurably superior to a straight diffuser). The wastegate flow would be via a completely divorced (separated from the main turbine discharge flow) dumptube. Due the realities of packaging, cost, and emissions compliance this config is rarely possible on street cars. You will, however, see this type of layout on dedicated race vehicles.
A large "bellmouth" config which combines the turbine discharge and wastegate flow (without a divider between the two) is certainly better than the compromised stock routing, but not as effective as the above.
If an integrated exhaust (non-divorced wastegate flow) is required, keep the wastegate flow separate from the main turbine discharge flow for ~12-18" before reintroducing it. This will minimize the impact on turbine efficiency-- the introduction of the wastegate flow disrupts the flow field of the main turbine discharge flow.
Necking the exhaust down to a suboptimal diameter is never a good idea, but if it is necessary, doing it further downstream is better than doing it close to the turbine discharge since it will minimize the exhaust's contribution to backpressure. Better yet: don't neck down the exhaust at all.
Also, the temperature of the exhaust coming out of a cat is higher than the inlet temperature, due to the exothermic oxidation of unburned hydrocarbons in the cat. So the total heat loss (and density increase) of the gases as it travels down the exhaust is not as prominent as it seems.
Another thing to keep in mind is that cylinder scavenging takes place where the flows from separate cylinders merge (i.e. in the collector). There is no such thing as cylinder scavenging downstream of the turbine, and hence, no reason to desire high exhaust velocity here. You will only introduce unwanted backpressure.
Other things you can do (in addition to choosing an appropriate diameter) to minimize exhaust backpressure in a turboback exhaust are: avoid crush-bent tubes (use mandrel bends); avoid tight-radius turns (keep it as straight as possible); avoid step changes in diameter; avoid "cheated" radii (cuts that are non-perpendicular); use a high flow cat; use a straight-thru perforated core muffler... etc.”
"Comparing the two bellmouth designs, I've never seen either one so I can only speculate. But based on your description, and assuming neither of them have a divider wall/tongue between the turbine discharge and wg dump, I'd venture that you'd be hard pressed to measure a difference between the two. The more gradual taper intuitively appears more desirable, but it's likely that it's beyond the point of diminishing returns. Either one sounds like it will improve the wastegate's discharge coefficient over the stock config, which will constitute the single biggest difference. This will allow more control over boost creep. Neither is as optimal as the divorced wastegate flow arrangement, however.
There's more to it, though-- if a larger bellmouth is excessively large right at the turbine discharge (a large step diameter increase), there will be an unrecoverable dump loss that will contribute to backpressure. This is why a gradual increase in diameter, like the conical diffuser mentioned earlier, is desirable at the turbine discharge.
As for primary lengths on turbo headers, it is advantageous to use equal-length primaries to time the arrival of the pulses at the turbine equally and to keep cylinder reversion balanced across all cylinders. This will improve boost response and the engine's VE. Equal-length is often difficult to achieve due to tight packaging, fabrication difficulty, and the desire to have runners of the shortest possible length.”
"Here's a worked example (simplified) of how larger exhausts help turbo cars:
Say you have a turbo operating at a turbine pressure ratio (aka expansion ratio) of 1.8:1. You have a small turboback exhaust that contributes, say, 10 psig backpressure at the turbine discharge at redline. The total backpressure seen by the engine (upstream of the turbine) in this case is:
(14.5 +10)*1.8 = 44.1 psia = 29.6 psig total backpressure
So here, the turbine contributed 19.6 psig of backpressure to the total.
Now you slap on a proper low-backpressure, big turboback exhaust. Same turbo, same boost, etc. You measure 3 psig backpressure at the turbine discharge. In this case the engine sees just 17 psig total backpressure! And the turbine's contribution to the total backpressure is reduced to 14 psig (note: this is 5.6 psig lower than its contribution in the "small turboback" case).
So in the end, the engine saw a reduction in backpressure of 12.6 psig when you swapped turbobacks in this example. This reduction in backpressure is where all the engine's VE gains come from.
This is why larger exhausts make such big gains on nearly all stock turbo cars-- the turbine compounds the downstream backpressure via its expansion ratio. This is also why bigger turbos make more power at a given boost level-- they improve engine VE by operating at lower turbine expansion ratios for a given boost level.
As you can see, the backpressure penalty of running a too-small exhaust (like 2.5" for 350 hp) will vary depending on the match. At a given power level, a smaller turbo will generally be operating at a higher turbine pressure ratio and so will actually make the engine more sensitive to the backpressure downstream of the turbine than a larger turbine/turbo would. As for output temperatures, I'm not sure I understand the question. Are you referring to compressor outlet temperatures?
The advantage to the bellmouth setup from the wg's perspective is that it allows a less torturous path for the bypassed gases to escape. This makes it more effective in bypassing gases for a given pressure differential and wg valve position. Think of it as improving the VE of the wastegate. If you have a very compromised wg discharge routing, under some conditions the wg may not be able bypass enough flow to control boost, even when wide open. So the gases go through the turbine instead of the wg, and boost creeps up.
The downside to a bellmouth is that the wg flow still dumps right into the turbine discharge. A divider wall would be beneficial here. And, as mentioned earlier, if you go too big on the bellmouth and the turbine discharge flow sees a rapid area change (regardless of whether the wg flow is being introduced there or not), you will incur a backpressure penalty right at the site of the step. This is why you want gradual area changes in your exhaust."
26 January 2003, 11:59 AM
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Thanks for posting that Mr Minister. Really interesting and may clear up ideas in the minds of some of us. It all looks like commonsense in many ways but nothing like having it all confirmed by an engineer from Garret.
Les
Les
26 January 2003, 10:57 PM
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And what had I always told you? . . .
To be fair, the APS design only keeps the gasses seperate for something like 6-8" rather than 12-18". But in every other respect, it does seem to support that theory.
To be fair, the APS design only keeps the gasses seperate for something like 6-8" rather than 12-18". But in every other respect, it does seem to support that theory.
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28 January 2003, 09:33 AM
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Thanks!
This must rate as one of the most informative posts ever on ScoobyNet.
Especially the part about why a larger turbo is better than a smaller one at same boost was an eye opener...
This must rate as one of the most informative posts ever on ScoobyNet.
Especially the part about why a larger turbo is better than a smaller one at same boost was an eye opener...
30 January 2003, 12:32 PM
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I think you should re-read the article - an integrated wastegate makes for a big compromise from the outset. Given that (most ) of our cars are running integrated wg's, the d/p design is already flawed
Richard
) of our cars are running integrated wg's, the d/p design is already flawed Richard
30 January 2003, 09:55 PM
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HI Pete, You out there ?
Just thought it would be good to get your response to the above. I was wondering if the old ScoobySport (H & S) zorst turbo back agrees with the statments made by the fella above etc...
Thanks Pete,
Ray
Just thought it would be good to get your response to the above. I was wondering if the old ScoobySport (H & S) zorst turbo back agrees with the statments made by the fella above etc...
Thanks Pete,
Ray
30 January 2003, 11:04 PM
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Just remember, there's theory & there's practice. On top of that, the differences aren't going to be that big, or important, until you start getting to big power. Also, one solution doesn't suit all; keeping the flow seperate is 'advised' as being superior in the above post. Many people don't find this. I have found it correct - more fuel is required lower down the rpm range with the twin-dump, suggesting the system is more efficient. This is one of the rare downpipes where the wastegate flow rejoins the main flow a couple of feet down & at a soft angle, though... But the difference between this & a bellmouth? Minimal. The difference between either of them and the oem wastegate-blocking catted effort? Huge.
31 January 2003, 11:29 AM
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Any you guys read this,
http://www.users.bigpond.net.au/msgofast/exhaustsystems.html
Where do you think APS got the diea from? They were asked if they tried this years ago and to reply that " there is no gains we found"
The twin pipes don't work as it has been pointed out the WG only just opens and flow is directed into the main flows path using a IHI turbo, Mr Garret was smarter and turned the pivot point of the WG 90 deg so it opens and gas is mixed with the main flow and doesn't create turbulence. With the second pipe on twin pipes the flow from a IHI turbo and no divider will see most of the gases not even use the second pipe, so fit a divider and then you increase flow restriction as the gases expand into the back of the turbo, around the valve and then are forced back into a small pipe which all in turns adds to backpressure and less than perfect WG operation.
As for an exhaust to be as big as you can isn't totally true, might be ok if you are after the last kw at redline, what happens is you loose to much fresh charge out the exhaust valves on cam over lap, maybe you should check with Prodrive on this and i am sure you will get the same answer as i got
Open mouth is best WITH a divider/splitter that fit ALL the way into the back of the turbo, The difference in torque will blow you away guaranteed!
Some others reports are here,
http://www.mrtrally.com.au/forums/topic.asp?TOPIC_ID=4691&SearchTerms=splitter
ANY exhaust i have removed and fitted mine I have made gains, the biggest notice is low end power and mid range torque. I look at what some of your tune shops over there and what they sell makes me laugh
My V5 STI with nothing more than a cold air exhaust and small add ons makes 20 psi @3000rpm under full load with the std VF28 turbo and IC. I got gains of 66kw ATW with cold air , exhaust and retained the std air box, IC, engine and turbo.
http://www.users.bigpond.net.au/msgofast/STI.html
Don't take my word for it, copy it and make your own!
The TDO4 & 5 WG swings in the same direction as the VF, so yes there are big gains there too.
Splitter lengths are different between turbo's, TDO turbo's are only 22mm deep, VF turbo is 32mm deep bar the VF30/35 which is 27mm deep, you need to use 3mm flat plate or it WILL bend , it only protrudes into the dump pipe flange, so on a VF total length will be 44mm using a 12mm dump pipe flange plate.
The splitter needs to be in the edge of the step in the back of the turbo ( VF) with small 5mm radius on the corners and needs to be a reasonable snug fit.
The collector has to be 4" at the flange and down to 3" ideally over 12 " long in the tapper with a slow tapper, works well on a pre01 , but 01 on run a larger steering shaft and the tapper of the collector has to be made shorter, 5-6" , either way the tapper needs to be without a sharp reduction and 3" all the way to the tip. If you run a CAT it needs to be in the mid section, running them in the dump pipe kills low end power, look at the WRCar, they have there's at the end of the exhaust, deleted is even better
Some Jap tuners make systems that delete the rear S bend and places the muffler exit at an angle, this might be great for the last 4 kw in the top end , but you loose up to 15 kw in the mid range, if you have this type, place the muffler in the OEM position and add two 90 deg bends as per the OEM route and tell me how much better it pulls!
MS
[Edited by msgofaster - 1/31/2003 11:31:42 AM]
http://www.users.bigpond.net.au/msgofast/exhaustsystems.html
Where do you think APS got the diea from? They were asked if they tried this years ago and to reply that " there is no gains we found"
The twin pipes don't work as it has been pointed out the WG only just opens and flow is directed into the main flows path using a IHI turbo, Mr Garret was smarter and turned the pivot point of the WG 90 deg so it opens and gas is mixed with the main flow and doesn't create turbulence. With the second pipe on twin pipes the flow from a IHI turbo and no divider will see most of the gases not even use the second pipe, so fit a divider and then you increase flow restriction as the gases expand into the back of the turbo, around the valve and then are forced back into a small pipe which all in turns adds to backpressure and less than perfect WG operation.
As for an exhaust to be as big as you can isn't totally true, might be ok if you are after the last kw at redline, what happens is you loose to much fresh charge out the exhaust valves on cam over lap, maybe you should check with Prodrive on this and i am sure you will get the same answer as i got
Open mouth is best WITH a divider/splitter that fit ALL the way into the back of the turbo, The difference in torque will blow you away guaranteed!
Some others reports are here,
http://www.mrtrally.com.au/forums/topic.asp?TOPIC_ID=4691&SearchTerms=splitter
ANY exhaust i have removed and fitted mine I have made gains, the biggest notice is low end power and mid range torque. I look at what some of your tune shops over there and what they sell makes me laugh
My V5 STI with nothing more than a cold air exhaust and small add ons makes 20 psi @3000rpm under full load with the std VF28 turbo and IC. I got gains of 66kw ATW with cold air , exhaust and retained the std air box, IC, engine and turbo.
http://www.users.bigpond.net.au/msgofast/STI.html
Don't take my word for it, copy it and make your own!
The TDO4 & 5 WG swings in the same direction as the VF, so yes there are big gains there too.
Splitter lengths are different between turbo's, TDO turbo's are only 22mm deep, VF turbo is 32mm deep bar the VF30/35 which is 27mm deep, you need to use 3mm flat plate or it WILL bend , it only protrudes into the dump pipe flange, so on a VF total length will be 44mm using a 12mm dump pipe flange plate.
The splitter needs to be in the edge of the step in the back of the turbo ( VF) with small 5mm radius on the corners and needs to be a reasonable snug fit.
The collector has to be 4" at the flange and down to 3" ideally over 12 " long in the tapper with a slow tapper, works well on a pre01 , but 01 on run a larger steering shaft and the tapper of the collector has to be made shorter, 5-6" , either way the tapper needs to be without a sharp reduction and 3" all the way to the tip. If you run a CAT it needs to be in the mid section, running them in the dump pipe kills low end power, look at the WRCar, they have there's at the end of the exhaust, deleted is even better
Some Jap tuners make systems that delete the rear S bend and places the muffler exit at an angle, this might be great for the last 4 kw in the top end , but you loose up to 15 kw in the mid range, if you have this type, place the muffler in the OEM position and add two 90 deg bends as per the OEM route and tell me how much better it pulls!
MS
[Edited by msgofaster - 1/31/2003 11:31:42 AM]
31 January 2003, 01:20 PM
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Hi Mike,
I live in Nassau, Bahamas. I was thinking of welding in a splitter to my ScoobySport catless bellmouth downpipe. My car is a JDM STI-7. What turbo does my car run and what size plate do I need to well in, W X D X H ?
The ScoobySport downpipe is a 3" system that runs down to a 2.5" system, will I get good gains with a splitter even in this smaller diameter system ?
To cure the boost spiking I changed the factory restrictor from a .95mm (I think) to a 1.25mm. Peaks at 1.3 bar in 4th and holds about 1 bar.
Any other ideas suggestions.
I would like to have you sort a downpipe out for me but I am afraid the cost to send it here to The Bahamas would be very expensive so I would prefer to try and just add a splitter to my ScoobySport catless downpipe.
Cheers,
Ray
I live in Nassau, Bahamas. I was thinking of welding in a splitter to my ScoobySport catless bellmouth downpipe. My car is a JDM STI-7. What turbo does my car run and what size plate do I need to well in, W X D X H ?
The ScoobySport downpipe is a 3" system that runs down to a 2.5" system, will I get good gains with a splitter even in this smaller diameter system ?
To cure the boost spiking I changed the factory restrictor from a .95mm (I think) to a 1.25mm. Peaks at 1.3 bar in 4th and holds about 1 bar.
Any other ideas suggestions.
I would like to have you sort a downpipe out for me but I am afraid the cost to send it here to The Bahamas would be very expensive so I would prefer to try and just add a splitter to my ScoobySport catless downpipe.
Cheers,
Ray
31 January 2003, 08:50 PM
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Ray,
The V7 STI uses a VF30 and is 27mm deep to the back, so the splitter length will be 39mm long with 27mm protruding and the turbo is 60mm high in the back, hopefully the flange plate is also 60mm high, It maybe be large , but just center the splitter and weld it in, remember to use 3mm plate, I buy a length of 50 X 3 mm black plate and cut it up.
I will give you some specs for the location of the splitter in the flange too.
If you are looking at the flange opening there are 5 bolts that hold it on, there is 1 above and below the Waste Gate, if you measure from the top hole to the right 19mm going from the hole center this will mark the position of the top spot for the splitter. Off the bottom hole measure 22mm from hole center to splitter plate center. This is measuring towards the turbine side.
You will notice that the bottom hole under the WG is more to the left, more than 3mm and the plate doesn't look like it is square in the flange , but it does line up spot on with the step in the turbo.
I find that if i scribe a line to mark the protrusion length before i grind the radius on the corners on the splitter plate then you can use this line along with the lines you mark of the gasket face of the flange plate you can eye ball the line for protrusion , tack it in then make sure it sits right angle to the flange ( sits up straight) and then full welded with a nice fillet weld. This has been track tested in my own car for 3 yrs now and you need to use 3mm plate or it bends, first one was exhaust plate and it gets hot and bends.
The STI do have problems with over boost due to the mapping of the boost control in the ECU and there tinny exhaust. You would do good to Buy a Turbo XS MBC as these hold boost rock solid, they use a ball and spring and are more than just a shinny tap.
There are many guys that found they got more bottom end or mid range with 2.5" exhaust, this is mainly due to poor design in the dump pipe or the lack of the OEM S bends at the rear, You can still run 2.5 mid section , but now you will gain power right across the rpm with 3", how many people have fitted an exhaust and felt they lost power down low or at part throttle? This system makes GAINS EVERYWHERE, most are surprised at how much better it is off boost and how much quicker it comes on.
good luck
Michael
http://www.users.bigpond.net.au/msgofast/
MSR Rally Team
MSR Engineering
[Edited by msgofaster - 1/31/2003 8:55:44 PM]
The V7 STI uses a VF30 and is 27mm deep to the back, so the splitter length will be 39mm long with 27mm protruding and the turbo is 60mm high in the back, hopefully the flange plate is also 60mm high, It maybe be large , but just center the splitter and weld it in, remember to use 3mm plate, I buy a length of 50 X 3 mm black plate and cut it up.
I will give you some specs for the location of the splitter in the flange too.
If you are looking at the flange opening there are 5 bolts that hold it on, there is 1 above and below the Waste Gate, if you measure from the top hole to the right 19mm going from the hole center this will mark the position of the top spot for the splitter. Off the bottom hole measure 22mm from hole center to splitter plate center. This is measuring towards the turbine side.
You will notice that the bottom hole under the WG is more to the left, more than 3mm and the plate doesn't look like it is square in the flange , but it does line up spot on with the step in the turbo.
I find that if i scribe a line to mark the protrusion length before i grind the radius on the corners on the splitter plate then you can use this line along with the lines you mark of the gasket face of the flange plate you can eye ball the line for protrusion , tack it in then make sure it sits right angle to the flange ( sits up straight) and then full welded with a nice fillet weld. This has been track tested in my own car for 3 yrs now and you need to use 3mm plate or it bends, first one was exhaust plate and it gets hot and bends.
The STI do have problems with over boost due to the mapping of the boost control in the ECU and there tinny exhaust. You would do good to Buy a Turbo XS MBC as these hold boost rock solid, they use a ball and spring and are more than just a shinny tap.
There are many guys that found they got more bottom end or mid range with 2.5" exhaust, this is mainly due to poor design in the dump pipe or the lack of the OEM S bends at the rear, You can still run 2.5 mid section , but now you will gain power right across the rpm with 3", how many people have fitted an exhaust and felt they lost power down low or at part throttle? This system makes GAINS EVERYWHERE, most are surprised at how much better it is off boost and how much quicker it comes on.
good luck
Michael
http://www.users.bigpond.net.au/msgofast/
MSR Rally Team
MSR Engineering
[Edited by msgofaster - 1/31/2003 8:55:44 PM]
31 January 2003, 10:04 PM
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This is a great thread.MS,I d'ont understand why you think that bends in the exhaust(rather than angled like the Hiper) will improve the mid range torque.These major bends would rob the car of efficient flow would'nt they?
01 February 2003, 10:33 AM
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ms,thanks for the reply.I have a STi7 JDM MYO1 and am about to change the exhaust from 2.5" to 3".This might sound really stupid but is there no way(without major surgery) to completely seperate the wastegate gases from the turbo gases ie could'nt the wastegate gas be just be dumped to atmo under the car? Also the splitter design you describe involves it protruding into the turbo,have I understood that correctly? Is this because the gases are already mixing by the time they hit the downpipe? Apologies if I have misunderstood,I'm a little slow at these things.....
01 February 2003, 10:37 PM
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Thanks Michael I understand now.Not having looked inside the turbo it was difficult to envisage.I do have more questions though I'm afraid!! How did you decide how long the splitter needs to be into the DP to allow the gases to expand adequately.Also can you expand a little more about what you mean when you say 'the angled exhaust loses fresh charge capture on cam overlap'
Sorry to ask so many questions but this is a potentially very informative thread.
Many tahnks,Deep.
Sorry to ask so many questions but this is a potentially very informative thread.
Many tahnks,Deep.
01 February 2003, 11:31 PM
#29
Michael, very interesting!
I've got an open neck downpipe sitting here I was going to fit on my 94 WRX tommorrow, thing is would I benefit from putting the splitter in?. It's not tappered the same as your open neck downpipe(shorter from mouth to exhaust bore). Any advice, dimensions?
I have a HKS hiper system, and have taken the HKS downpipe(closed neck) off because I believed it to be causing boost creep at high revs, I was working on the theory that the WG gases couldn't flow enough compared to the less restricted exh turbine gases, does this sound feasable?, I asked this question many times but was told to check other things, I still believe this to be the case as the HKS d/p design effectively blocks the WG flow compared to the easy escape(combined with the extra flow of the hiper system) of the exh turbine gases thus causing the boost creep.
I imagine you are familiar with the design of the hks d/p?, but if not it is the same design as the standard subaru flat mounting plate to turbo with only the 3" bore d/p starting at a position in line with the turbine exit. Am I right to question this design?, people say if this was so the standard d/p would boost creep, but I'm working on the theory that the extra flow the no cat 3" bore hiper coupled with d/p behind turbine only would cause the creep because of WG gases hitting d/p plate and hitting flow of turbine gas(disrupting their exit)
sorry to ramble but it's been bugging me
James
I've got an open neck downpipe sitting here I was going to fit on my 94 WRX tommorrow, thing is would I benefit from putting the splitter in?. It's not tappered the same as your open neck downpipe(shorter from mouth to exhaust bore). Any advice, dimensions?
I have a HKS hiper system, and have taken the HKS downpipe(closed neck) off because I believed it to be causing boost creep at high revs, I was working on the theory that the WG gases couldn't flow enough compared to the less restricted exh turbine gases, does this sound feasable?, I asked this question many times but was told to check other things, I still believe this to be the case as the HKS d/p design effectively blocks the WG flow compared to the easy escape(combined with the extra flow of the hiper system) of the exh turbine gases thus causing the boost creep.
I imagine you are familiar with the design of the hks d/p?, but if not it is the same design as the standard subaru flat mounting plate to turbo with only the 3" bore d/p starting at a position in line with the turbine exit. Am I right to question this design?, people say if this was so the standard d/p would boost creep, but I'm working on the theory that the extra flow the no cat 3" bore hiper coupled with d/p behind turbine only would cause the creep because of WG gases hitting d/p plate and hitting flow of turbine gas(disrupting their exit)
sorry to ramble but it's been bugging me
James
02 February 2003, 02:17 AM
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OK Deep,
The splitter length is decided on what gave me the most power
I tried them running down inside the dump pipe but you loose top end power, and i have made them short as possible and this gave the best power, I have them 12mm long inside the exhaust as most exhaust us a 12mm thick flange plate and you need this much to be sure there is enough weld to hold it there.
The angled exhaust is very straight and doesn't provide a negative back pulse , IE no back pressure at low rpm, so boosted fresh charge is blown out the exhaust valves while both the inlet and exhaust valves are open ATDC on cam over lap or valve rock, more so than if you have the 2 90 deg bends before the rear muffler as per the OEM piping route.
Michael
http://www.users.bigpond.net.au/msgofast/
The splitter length is decided on what gave me the most power
I tried them running down inside the dump pipe but you loose top end power, and i have made them short as possible and this gave the best power, I have them 12mm long inside the exhaust as most exhaust us a 12mm thick flange plate and you need this much to be sure there is enough weld to hold it there.
The angled exhaust is very straight and doesn't provide a negative back pulse , IE no back pressure at low rpm, so boosted fresh charge is blown out the exhaust valves while both the inlet and exhaust valves are open ATDC on cam over lap or valve rock, more so than if you have the 2 90 deg bends before the rear muffler as per the OEM piping route.
Michael
http://www.users.bigpond.net.au/msgofast/