john banks

Have Magnex twin dump 3" dropping to 2.5" from the bottom of the downpipe at present, Magnex res centre and 6x4 BB but I need it bigger for my power goals.

Have heard a few Revolution 3" full systems and they are not too intrusive or restrictive it seems.

Car is a daily driver, and the minimum of noise increase would be nice, certainly cannot have some ridiculous drainpipe.

Anyone any other suggestions other than the Revolution?

Anyone running anything bigger than 3" that does not waken the dead?

Claudius

Isnt the decrease in the downpipe size a benefit in the sense that it "sucks" the air "out"?

How do you know you need a bigger downpipe?

john banks

I have not measured the exhaust back pressure, but I don't know any other c. 350 BHP cars that are aiming to get to 400-450 BHP this year that are running 2.5" systems. Maybe that sounds like I am a fashion victim, but the Garrett chap's posting http://www.scoobynet.co.uk/bbs/threa...hreadid=171018 and some other data suggest to me that 2.5" is inadequate for my goals. There is an argument that the gas is cooling by the bottom of the downpipe, but the exhaust at 1.45 bar at 7000 RPM is sounding like my PPP backbox did when I started pushing the boost up on that. I don't want this disastrous situation of lots of boost and poor power or torque that so easily afflicts Scoobies

[Edited by john banks - 1/26/2003 11:24:19 PM]

hades

The APS is 3" right through until the backbox, and you can specify it without the sports cat in the downpipe. I have one and you can't accuse mine of being silly loud (very similar noise figures to a prodrive kit), although I do have the sports cat in it. Whether dropping to 2.5" at the backbox will restrict at the sort of power you're looking for I don't know!

Think possibly the MRT is similar to the APS. Sure I've seen a couple of US exhausts at 3" too.

WREXY

Hi John.

The APS system passes the tough noise pollution laws that the EPA has set in Australia, so it shouldn't be loud at all. It is 3 inch all the way and I too am considering one.

In Australia, cars built after 1984 cannot be louder than 90db. They measure noise with a microphone from around 30-40cm behind the exhaust with revs held at around 4600rpm in neutral. The APS system has passed this test and it is certified.

Cheers,

Wrexy.

[Edited by WREXY - 1/27/2003 12:11:26 AM]

Claudius

Hi John

I'm not saying you should get a 2.5 inch inner diameter exhaust; I am asking if the downpipe getting smaller may have the effect of sucking the gas out as I have heard.

I am also saying that the exhaust must flow enough out, but not too much, or yopu will overspin the turbo, depending on what turbo you have, etc. You know?

nom

I think that the cat might make a big difference to the noise level, though. As the one without the cat won't be 'road legal' in Oz, I doubt that it's tested for noise level!

John - I've been trying to work out the same thing! There is a noticeable difference in shifting from 2.5" to 3", I have noticed. switching back to a 2.5" after a 3" is bleh. A good compromise system is BPM DP (the ceramic coated type) to a HKS Drager - not bad on cruise, gets a little noisy on boost, but that's OK. The BPM DP is noticeably quieter than the H&S one - don't know about the Magnex!
I've been thinking about using a 3" centre with a 'bubble chamber' in it (effectively an extra silencer, which apparently doesn't reduce flow...) and then getting a one-off BB designed/made that is a straight-through 3" type but set up to be as quite as possible rather than the usual "quiet on cruise but loud under boost and enhances the 'bubba-bubba' noise that we all like". Well, quiet on cruise is good if it was, loud under boost is of indifference and personally I don't really care about a 'bubba-bubba' noise that the car may or may not make.
It must be possible to do all these things, as there are road cars out there with the same power but a lot less noise (although maybe with a cat, but this is only a 3-6db reduction tops & the scoob is probably 12-15db louder than these cars).
I just have to get round to looking into it... Pat has apparently come up with a new design, but I don't know anything about it! Could be very interesting

Andy.F

Claudius, I am of the opinion that we want as little backpressure as possible at the turbine exit. The energy transfer at this point is due mainly to pressure ratio across the turbine creating expansion of the gasses. Minimise exit pressure and you can run less back pressure on the headers for the same boost. This equates to more power.
The pulse scavenging effect which I suspect you refer to when mentioning 'sucking out the gas' really only applies pre turbine.

Andy

[Edited by Andy.F - 1/27/2003 7:53:46 AM]

Claudius

Hmmm, not sure, Andy. Doesnt all that depend on how big the turbo is, how much it flows and how hot the gases get? A matter of pressure and temperature, you know?

nom

Idealy, you want high-speed (hot) flow on the turbo exhaust inlet, and a big hole on the turbo exhaust exit
So that'll be a post-turbo lowest-back-pressure-possible system, then.
Can't see how backing flow up through the turbo therefore slowing the flow therefore slowing the turbine could improve anything? Unless the turbo is the restriction in the system, I suppose, in which case the exhaust diameter is less important. But that's not the situation we're looking at here...

Andy.F

I'd agree with nom

Claudius -

Yes, there's more energy in the hot gas, that's one reason some cars run lower boost on a rolling road than they do on the road, the exhaust energy is less due to the lower temps achieved at turbine inlet.
I would not consider corking up the exhaust just to raise the temperature though
Can you explain your thinking behind the 'sucking out' virtue of a smaller pipe

Andy

WREXY

I was talking about the APS exhaust mentioned here.
http://www.airpowersystems.com.au/wrx/exhaust.htm

Further down the page, it mentions the EPA noise legality.

Cheers,

Wrexy.

nom

I imagine that the EPA regulation is bypassed, though, when there's no cat, as if there's no cat, the car isn't road legal, and therefore the EPA regulation isn't applicable?
I think, anyway, although I am probably talking poo here

Floyd

iTrader: (9)

I've heard cars with the cats removed from std centres and the noise doesn't increase noticeably. I don't think the cat makes much difference to noise, IMHO the majority of noise is quelled at the BB.

F

Pavlo

Mongoose isn't too bad, but then you have the problem of slip joints and not knowing how well your paticular one is going to fit.

So long as you have a resonator in the system, it should keep the noise down.

paul

Claudius

I know John has a different turbo from the standard one, but I dont remember which exactly, but nothing really big IIRC.

What I am saying is that if the exhaust is too big, then the turbo wont spin fast enough and not produce the optimum boost. So I suggested to measure how much or how little the exhaust flows.

Why wouldnt the turbo be the limiting factor (assuming the fuelling side is sorted)? Because you *think* that the exhaust is too big? Measure it!

john banks

Claudius I am extracting every last bit of power I can out of a small 16G TD05 (will be running it - ie mine not T-uk's - at 1.5 bar at 7000 RPM, 1.6 bar midrange) and then moving onto a 20G, as I said target is mid 400s BHP this year on a 2.5 litre.

nom

Still can't see how the exhaust (post-turbo bit) can effect the speed of the turbo wheel, other than negatively if it's too small . Sure, the 'upstream' part of the exhaust to the turbo wants to be as narrow as possible for highest flow speed (so restriction from diameter should only just become apparent slightly beyond the highest flow point wrt that entire system) to aid spool up, but post-turbo?

Pavlo

Exhaust down stream of turbo wants to be big as possible.

Any pulsing effects are mostly lost through turbo, and any pipe creates back pressure after turbine, effectively lowering the drive pressure.

Bigger is better, biggest is best!

And yes, this is not what you would be doing with a normally aspirated engine.

paul

Claudius

Tell me about it, I have the same piece of junk on my Evo! Going TD06 20G probably...

Claudius

nom and Pavlo, I dont know how to put it, sorry

Andy.F

Claudius

While we have your attention The Apexi PFC, can you retrofit them with MAP control instead of MAF or is it a different ECU for MAP use ?

(JB Sorry to stray off topic )

nom

Ah, now, the exhaust housing can be too big, certainly!
fits with that nicely

Anyway, back to the original question (ignoring the 'do you really need 3"' question! ). Anyone? Suggestions over the APS one? Anyone? Or are John & I the only ones in search of a 'silent but violent' solution?

john banks

"Silent but violent"

Claudius

Hi Andy

The PowerFC with MAP sensor capability is a different reference, I believe. I have a Denso MAP sensor plugged into the PowerFC and I think there are versions without the plug for the MAP sensor.

Claudius

Silent but violent, APS, 3 inch or not, etc....

Surely the bigger picture here is "how do we maximise John's engine output"?

What have you got in there anyway, John? Will it take a lot of power?

Scoty

WW2 bomber, sniger

John, Hayward and Scott will make you a custom 3 inch sytem.

S,M,G

John
I have done a LITTLE research here as per noise level, im going 3 inch after burner down pipe and centre with the old H/S back box instead of the A/B back box, check out scoobyworld site for db levels.
Steve

nom

I think the 'bigger picture' leads us to the same place. John's set-up is - I think - pretty similar to mine overall (slightly different kit but with the same 'feel') and I can tell you outright that he needs a 3" system. I changed from a H&S 3"-2.5" DP, straight-through centre & TSL BB to a BPM 3" DP & 3" 'afterburner' centre & BB (bubble centre to reduce noise) and the difference was vast. Huge. People in the car thought I'd done something serious to it since they were in it last, not just changed the exhaust! But it's loud! Too loud for me, so I'm not using it at the moment, although may give it a bash again if I'm feeling brave... (I am still using the BPM DP though, and unsuprisingly it's cack going into a 2.5" centre!)
The whole episode has left me with a strong desire to either have my ears changed to detachable models, or have the afterburner made much quieter somehow... I was going to approach H&S on this when less busy! I think there's a bit (not very big!) of a market for these 'silent but violent' type exhausts.

Claudius

I agree, I'd like something big but not loud. Dont need noise, just the performance