how much boost/power can a sti 8 engine run safely,running vf35,full decat,walbro,k+n panel filter.cheers guys.

 

With those mods you should be seeing a max of about 350bhp/torque with limiting factors to make over 400 being the MAF sensor, MAP sensor, Turbo, Injectors and intercooler and a couple of other bits depending on just how much more you're looking to make however, your engine will take a lot more with the right bits and quality remap, all still on the standard ECU.

An STi v8 will take 400-420bhp all day long no problem but i've heard of them genuinely taking over 500bhp long term. I've no doubts your engine would be living on borrowed time at 500+ but driven with some mechanical sympathy there's no reason why not. They are pretty strong.

 

My V7 made 340 bhp, to get more you'll need "headers" or Harvey's ported DEM manifolds...

dunx

 

Agree that the engine will take more than 400 but neither the MAF sensor nor MAP sensor will be a limiting factor.

 

Agree, got many customers running fmic, injectors (650cc),
MD321t turbo, ported or tubular headers and remap around 420 to 450bhp with standard maf and map sensors.

 

There are lots of cars running 450bhp on the std ECU. Very common indeed but that's just about the limit.

A std MAF sensor is only accurate up to 350-370g/s, we all know that, and gives you your 420-450bhp. Thereafter it is a limitiation. Even with a bigMAF tube, rescale and ECU hacks, to go over that you start losing a lot of resolution lower down the MAF scale which then affects normal everyday driving closed loop at around town and crusing speeds.

So long as you're running a turbo that moves enough air not to rely on big boost to make power the std MAP sensor will do, but for most people to make decent power their smaller turbos will be having to run a lot more boost, more often than not trying to operate outside of the std MAP sensors normal parameters and regularly triggering boost cut. I've done that on my own car.

There's not just the std MAP sensor to think about though, there is a boost limit hard coded onto the ECU as well which is just a couple of PSI over the limit of the std MAP sensor so ultimately regardless of MAP sensor the ECU is limited.

For a lot of owners that can't go to the expense of a much bigger/better turbo an uprated MAP sensor with their smaller turbo is another option and will keep them the safe side of their MAP sensor with a bit of scaling, allowing them to run boost to the limit of the ECU. In the USA there are owners running 20G's and making 420-430bhp but they are all running uprated MAP sensors because they are operating outside of the std MAP sensor's normal working parameters although not the ECU's.

There are limitations to the std MAF and MAP sensors even with all the ECU hacking and sensor rescaling you can muster. You're making out there's no limit when actually there is.

 

In answer to your original question, if your engine is in good condition, properly mapped with all supporting mods and no cat you will make as much as is possible to get out of a VF35 which subject to which rolling road you use to measure it on, is around 340 bhp so your STi 8 engine is good for well past what your VF35 can produce in my actual experience.

 

Simply the ecu will limit the maximum boost, and then you'll need a boost controller, but for more you need a bigger turbo really. I have seen a RR printout of 366 bhp on an "8".

IMHO.

dunx

 

Sorry Dunx but it is not the ECU that will limit the power. Beyond a certain point, as boost is increased the turbo is producing hot air as it is way outside its efficiency envelope. I don't have a compressor map for a VF35 but I guess it will not operate efficiently by 1.55/1.6 bar or there abouts. Beyond that point or some similar figure as you point out a turbo that can move more air is required.

 

You need less than 1.45bar to make a solid 350bhp on a VF35 peaking somewhere between 5500-6000rpm in 3rd gear and that takes you up to the 300g/s unhacked factory MAF limit. That's more than enough boost if the car has the right mods and is mapped properly with a factory STi TMIC.

Makes for a nicely quick car that will keep you happy for a while until you get used to it and then want more.

 

You sure? I'm still under 300g/s at 370bhp at 1.6bar on a VF36. At 340-350bhp, 1.4-1.5bar I'm at 270g/s. I'm on a JDM ECU so 300g/s doesn't worry me!

 

Absolutely sure

Airflow is roughly equivalent to Wheel BHP. 270g/s at a guesstimate is somewhere around 333bhp. 300g/s is at a guess 369bhp. Even using the guesstimate maths i think both of these figures are still a little bit over optimistic due to drivetrain loss figures used in the maths for me still being a bit too high. I use 16% loss as the maths suggest as general figure but even then i still think it's just a bit too high. Some dyno operators work on even higher loss figures at around 22% and give out much higher bhp readings. What is the right way??

I quote conservatively 350bhp at 300g/s because i genuinely feel that's much closer to the truth. Before any ECU hacks and with a properly rescaled MAF I maxxed mine out with a VF35. Big boost doesn't neccessarily mean more power although from very low down it can make a shed load of torque, but there's also the rest of the mapping to consider, and with an STi you have AVCS to play with as well.

Ultimately all that matters is how the car drives, and if the numbers really bother you, how much power you are putting down on the ground. People generally are far too hung up on engine BHP numbers that whichever way you glean them are all just guesses anyway.

If you want real engine bhp to brag about take the engine out and stick it on an engine Dyno. Guarantees a bullsh1t free figure. Then work out what it's putting down on the ground and you have real drivetrain loss numbers to work with. I've never heard of anyone doing that so any figure quoted is very much a guesstimate. However, there are good guesstimates and bad guesstimates.

 

Try 545bhp when I was on mine.

The limit isnt the ecu, the limit is the fact that they do not drive as smooth up there going on and off power as a proper aftermarket MAP based ecu. Therefore people take the decision of going to a ecu such as Syvecs or Simtek when looking for over 450bhp.

MAF sensor will read a lot more than that Francis and still be accurate. Ultimately it will read up to 5V and how that translates into a g/s time is down to how well you have put your maf tables together and the accuracy of the curve as well as a couple of other maps in the rom. The last figures I had out of mine were around 500g/sec and it was still my daily driver at that point.

It is very easy to change the boost cut levels.

Again It is very easy to change the boost cut levels and these 'hard coded' levels are there to be changed. Maybe your xml definitions are wrong.

There isnt.

I am sorry if it sound like I am disagreeing with everything you say Francis but there is so much misinformation there that I couldnt leave this as being possibly taken into SN myth.

 

I don't doubt that a VF35 can make a nice road car but 1.45 bar for a solid 350 bhp on a VF35 is optomistic or on a very optomistic dyno or both. My experience of VF35s is that they are generally around 340 bhp with all supporting mods and good ones are pushed to get to 350 bhp. Many cannot get anywhere near that. By comparison, VF34 is 350-360 bhp.
As highlighted, different rolling roads, different readings. I have used two rolling roads where the same development TD05 20G produced 420 and 422 bhp. 4th gear which is closest to 1:1 drive. However the same car did 448 bhp on another rolling road a few days later, in 4th gear, not only that you could vary the power figure by changing the gear you chose to run in.

 

You can make 700bhp from the standard ECU and use it as a daily runner if you like Duncan. I never said it cannot be done. You can have 650-700 g/s going through the MAF sensor but not many of us want to use MAF tubes the size of dustbin lids. The bigger the tube the less accurate it becomes and you can play with that MAF curve all you like.

The other reason they don’t run so well low down isn’t due to the accuracy of the MAF curve but it’s because you lose so much resolution at the bottom end of the curve thereby affecting closed loop running. At those sorts of levels they really can run rough until you’re on it!! I’ve already eluded to that.

You can change boost cut to any level you like but once you’ve exceeded the working parameters of your sensor you’ll get no further. There is a table on the ROM to change that parameter.

The ECU will read as much boost as you like however, there is a hard coded target boost limit on the ECU of 39.45psia or 24.95psi relative. That’s as much boost as the std ECU will let you make. Unless you go in and start changing the xml definitions, adding your own constraints to raise the limit changing the way it works out target boost, then that’s what it is. If your maths is that good and you’re 100% confident and sure you won’t **** a customers ECU that’s fine otherwise leave it as is. There’s nothing wrong with my ECU defs but how nice of you to ask.

You don’t have to be sorry about wanting to disagree, that’s absolutely fine and should be encouraged. It seems though that one-upmanship and generally pissing on someone’s parade (not that there was a parade) is the way things are done here by those that apparently know what they’re doing however, before you start playing those games make sure you have a good reason to **** on that parade. Sorry Duncan but there’s no misinformation or mythmaking here for you to massage your mythbusting prowess on.

In fact, the only SN Myth being generated and perpetuated here is the illusion that some established and well known tuners can actually put what they preach into practice.

I pulled the ROM off an Open Source tuned car today. The car was apparently mapped by a known tuner and only took a couple of hours to do from scratch. How thorough!! Not uncommon in this industry so i keep hearing!!

Suffice to say I was surprised at what I saw and not what i expected. The end result of this tune and the numbers it was making should make that tuner think again about asking people for money. I’ve seen PPP tunes drive smoother and make healthier figures than that with less mods!!

Ho Hum

 

Francis - the ecu gets fed a MAP voltage. The rom translates this voltage into a figure using a factor. Sure the table has a limit for what 'figure' can be put in but this isnt a limit in the actual boost that the car can or will produce - just a limit for the 'figure' in that table. You dont need to hack the xml to change this.

I was not wanting to **** on your parade or anyone else's.