Boost pressure...

[bradc]

Why do you think that?

[steelie600]

Well i'm not running an intercooler so i take it 13psi should be safe?

Yes you are its a big black thing behind the bumper

[Turbo_Steve]

its a big black thing behind

the bumper

Thank goodness for that - you had me worried there.

And entirely accurate!

[bradc]

There is little or no point in doing most mods to a VR4 without an ECU to support them. Once you've turned the boost up and freed up the exhaust system, you're only getting very marginal gains for your expenditure: the ECU is the next limitation as it actively stops you making more power. You can then fit a bigger intercooler to try and wring a bit more out of the turbos, but really, once you've remapped, you've got all you're going to get out of them wihtout upgrading to bigger ones.

I have to disagree with this. In NZ the standard power figure at the wheels on a VR-4 is around 160kw for a manual. At the last dyno day we had the cars with exhaust, boost and intercooler were running around 180-190kw at the wheels. I think that 20-30kw at the wheels which is around 25 to 37kw or so more at the engine is actually a very very good gain for such simple mods. It is also worth pointing out that one car in particular which was an auto. On the same day a 100% stock PFL auto made 140kw, this other car made 167kw which isn't bad for a PFL auto. It had the same exhaust + boost + intercooler. 27kw at the wheels is very impressive for such basic mods.

Furthermore in that very same car I went down to Levin in it and we averaged bang on 10l/100km which is 28.3mpg or there abouts over 1100km of driving.

[Ryan]

That's right Brad. Also, if these mods did not yield any performance gains, why would people continue doing them? The majority of people on this thread who have modified their VR-4's have not modified their ECU in any way/shape / form and yet see significant performance gains:

* Myself
* William
* Kenneth
* wintertide
* GroundControl

etc etc etc

[AlanDITD]

I have to disagree with this. In NZ the standard power figure at the wheels on a VR-4 is around 160kw for a manual. At the last dyno day we had the cars with exhaust, boost and intercooler were running around 180-190kw at the wheels. I think that 20-30kw at the wheels which is around 25 to 37kw or so more at the engine is actually a very very good gain for such simple mods. It is also worth pointing out that one car in particular which was an auto. On the same day a 100% stock PFL auto made 140kw, this other car made 167kw which isn't bad for a PFL auto. It had the same exhaust + boost + intercooler. 27kw at the wheels is very impressive for such basic mods.

Furthermore in that very same car I went down to Levin in it and we averaged bang on 10l/100km which is 28.3mpg or there abouts over 1100km of driving.

Yeah to be fair i would agree, Roughly speaking your talking about knocking 1second off your 1/4mile time with upped boost and a full exhaust with downpipes. Maybe more with intercooler hard pipes etc....then a remap possibly a touch more....dare i say 12's.....without nitrous..i would hope so.

1second isnt to be sniffed at thats a hell of a difference.

[bradc]

Unsure about 1/4 times Alan as not many of us have run quarter miles down here. But yes there is a massive power gain to be given by doing those three mods.

[AlanDITD]

Unsure about 1/4 times Alan as not many of us have run quarter miles down here. But yes there is a massive power gain to be given by doing those three mods.

Dude when i get the **** out of london im going to buy a manual galant VR4 and it will run a 12s 1/4 mile no nitrous!

[Turbo_Steve]

Let me rephrase, as you've all got the wrong end of the stick: I can see why what I have written may be misinterpreted:

here is little or no point in doing most mods to a VR4 without an ECU to support them. After you've turned the boost up and freed up the exhaust system, you're only going to get very marginal gains for your expenditure: the ECU is the next limitation as it actively stops you making more power. You can then fit a bigger intercooler to try and wring a bit more out of the turbos, but really, once you've remapped, you've got all you're going to get out of them wihtout upgrading to bigger ones.

Once you've put an exhaust on it and boost (theyre's your 1 second, Alan) the next thing you fit is probably the intercooler....and have to turn the boost down to avoid fuel cut. Every additional breathing mod you do brings the boost pressure down and down trying to avoid fuel cut: the turbos are flowing the same. They may be running a bit cooler.....but then the ECU isn't adjusting the fuelling or the ignition in response to it, so you're not gaining much at all, at least not against what you're spending out.

[bradc]

I disagree, the difference between 160kw and 180-190kw is pretty big.

We've had cars in NZ making around 175kw with 12psi and stock exhaust, so the remaining 5-15kw will be due to the intercooler and exhaust. The intercooler may not help a single run but it will keep the car in the best fuel map for much longer periods of time before the ecu pulls timing and dumps in fuel.

These same cars are going from 363nm of torque to anywhere from 420nm to 450nm which is a massive gain as well. Overall the area under the curve is greatly, vastly in fact increased.

[bradc]

Your second reply makes a bit more sense.

I agree, after boost, exhaust and intercooler there isn't much to be done to increase the power out of a VR-4 with stock ecu and turbos

[Turbo_Steve]

But you're changing the exhaust both times?
If you took a standard car and fitted an intercooler, and saw an extra 15Kw then I'd say fair enough.....but the exhaust makes a HUGE difference.

I've yet to get my intercooler warm at 12psi, because the car is moving quickly enough to cool it.

[bradc]

Thats true, a completely stock car won't see much gain from changing the intercooler because the stock one is capable of handling the heat.

But with increased boost the cars do knock quite a bit with the stock intercooler. Dickytim over here was running 14psi or so and after he installed an aftermarket intercooler found that his fuel economy was improved quite a bit and evoscan showed that it was spending most of it's time at 100 octane level, rather than dropping down to low 90's with the stock intercooler.

[SquattingDog]

Fuel cut has nothing to do with the fuel mixture. End or story.
The ECU looks at the amount of air being drawn by the engine, and if it's more than a specific mass (for a given set of parameters, load, TPS, RPMS whatever) it simply goes "NOPE" and stops fuelling to prevent any more boost.

Sorry to play the Necromancer here, but I just wanted to chime in on this (have been a little afk recently).

Correct me if I am wrong, but the ECU does not look at how much air, or mass of air before determining whether to cut the fuel, but more specifically the set load values at each RPM.

People keep saying it's to do with injectors and/or fuel pump - this is absolutely not correct (as stated above by Turbo_Steve). You could upgrade to a Walbro or better with 1000cc injectors and still "boost cut" (this is fuel, not boost cutting off) at the same boost level, simply because you are causing X load on the engine.

It would, however, be possible to run maybe 1 - 2psi more (maximum) with these upgrades, if indeed there was an issue with air/fuel running too lean and thus creating additional load on the engine. In my experience, this is not usually the case.

The colder the air being drawn in (eg the bigger the intercooler, and the better the flow from front-to-back of it; or with meth injection) - the lower the pressure of boost for the same amount of required fuel, as cold air is denser and lets the engine breathe better. This is why we fit intercoolers/meth to our cars. So yes, you should get the same performance at lower boost with a bigger intercooler (to an extent).

Further discussion welcome - I'm always learning too

[bradc]

Basically, yep!