Contour Enthusiasts Group Archives Forums Modifications Forced Induction Please help me understand boost control!!!

Also depends on whether the pistons and rods are stock vs forged. Either way, rods can take more boost at lower rpms than they can take them at upper rpms. I'm not sure the exact formula, but stresses are not directly proportional at higher rpms. For instance the stresses on the rods at 6000rpms isn't twice as high as at 3000rpms, it's more like three times. That's why you don't see a lot of high rpm street cars aside from the Honda S2000 with it's 9000rpm redline. And even they recently put a bigger engine with a lower rpm because too many people were blowing engines because of oil starvation at high rpm/high side g's cornering.

So if you get the right kind of boost controller, you could set it to get 14psi from when it spools up, around 2500-3000rpms(depending on turbo/engine/etc..) to about 5000rpms then lower it to 8psi near the redline. While your peak HP may still only be as high as if you just ran 8psi, your TQ will be much higher and at the lowest rpm possible(and where you do the most driving).

I know the first turbo kit for the Focus used a aerocharger turbo that had built in boost controller that put out 12psi at 3000rpms and 240wtq, but by the redline lowered the boost to 9psi. It all depends on how you set it up, but I'd push the most boost down low you can run then lower it up high, especially if you're boosting a stock engine. And any mistakes and the engine is toast.

EDIT:
So your chart would look like this
2000-3000 RPM, run at 14psi
3000-4000 RPM, same
5000-6000 RPM, decrease to 10psi
6000-7000 RPM, decrease to 8psi

Most of your driving will be done under 4000rpms and will feel awesome on the street like that. Also on track, having a lot ot TQ down low could help pull you out of low speed corners easier.