racer135

iTrader: (2)

I have seen many toque curves and some looks like the shape 1 and others as shape 2. Note that there are not any numbers of torque we are taking just about the shape. Ignore the RPM values.



Is the curve shape for torque mainly defined by the boost profile and not the tune? I think shape 1 is mostly created by MBC on good fuel when using a big boost spike vs shape 2 which is more common with ECU Boost do to more flat curve and not necessarily a boost spike. Is this correct or is it created by the tune?

JordanS4

iTrader: (11)

shape 2 is holding more boost to redline, afr and timing prob affect it too.

Noize

iTrader: (24)

Boost, timing, fueling, and cam timing, turbo sizing, all of them effect it.

FWIW, I call shape 1 the "puke and die". When the IX came out and good Mivec tuning started popping up, you'd better and fatter torque curves since you can adjust the intake gear (like shape 2). Without optimizing it everywhere (like the VIII), it can only be optimized in one area. The factory cam gear settings on the VIII were optimized to the stock turbo at around 3000-4000rpm.

racer135

iTrader: (2)

The interesting thing is that some of the curves of some tuners are always the same no matter the mods on the car. Something similar to shape 1 so that's why I think it follows the boost curve.

JDMevoBOOST

iTrader: (37)

I think the reason you see some tuners tuning cars with similar curves is because once one person gets a setup right, people copy it because it worked. It's expensive to do all the testing on your own.

I know alot of the cali guys have similar setups with differing brands, but we all have similar results. FWIW on 91 my curves generally look like #1 and on E85 + more boost and more timing it looks like #2.

Kracka

iTrader: (49)

Boost, tune, fuel, turbo, etc. all effect the torque curve.

JohnBradley

iTrader: (30)

I would say in order: Boost (whether it spikes or just comes to a plateau), timing, cams/MIVEC. I have been able to keep consistent torque curves on both VIII and IXs. The intake manifold also plays an important role in the shape of the torque curve.

mitsuevo803

iTrader: (3)

Case closed

crcain

If you took the turbo off of your Evo and ran the car N/A (sinful, I know )... what would the powerband look like? And would peak torque occur at the moment the cams hit their sweet spot?

Ted B

iTrader: (6)

If the engine were suddenly made NA, the powerband would be significantly affected by the efficiency of the exhaust system, so that makes things a bit tougher to compare on equal footing. With the type of hardware typically used in larger turbo builds and an efficient exhaust, the NA torque curve would look more like a linear rise with a plateau somewhere in the 5500-6500 region and a gradual taper down from there.

mitsuevo803

iTrader: (3)

Do you mean from the lack of backpressure with say a 3 - 3.5 inch exhaust?

Ted B

iTrader: (6)

Be careful, because backpressure never does anything except rob power.

The most powerful NA engines have tuned, open-dump tubular manifolds that more or less result in zero backpressure. The reason why fitting a large exhaust can hurt an NA engine is because it can kill gas velocity. When this happens it is an issue of exhaust tuning, not an issue of backpressure.

mitsuevo803

iTrader: (3)

I never knew that. I knew that in turbo cars you wanted the least amount of backpressure possible after the turbo but I thought NA cars were different. Thanks!

turbo addict

iTrader: (2)

THNAK YOU! It is amazing how many people cant wrap their heads around this concept.

Ted B

iTrader: (6)

It's a very popular, widespread misconception, only because how a proper NA exhaust system works isn't something that can be easily gauged by the naked eye, just as one can't look at a saxophone and easily tell in what key it plays.

Engineering a good exhaust for a turbo engine is about as easy as fitting a dryer vent.

Engineering a good exhaust for an NA engine is like designing a musical instrument that plays a certain musical note when pulses of air are blown into it, and that ain't easy.