I don't understand why 10 psi on a car with dp, cb, high flo cat, intake, and intercooler is quicker

than

a car with say just a dp, cb, and 12 lbs of boost consistently?

Could someone clear this up for me so I can better understand please? Thanks guys

 

This could be for hundreds of reasons.

The most generalized differences would be:
- Quality of tuning
- Driver skill
- Traction
- Intake and Exhaust restriction
- Condition of working parts
- Weight
- etc, etc.


If I had to guess, I would say the 10psi car would be running better because it's intake and exhaust are considerably less restricted than the 12psi car. Also, the intake air temps are going to be lower on a car with an aftermarket IC, so while the 10psi car may be running less pressure, it could be running more air.

On a side note, I hope the 10psi car has an aftermarket ECU.

 

Basically to break it down to physics, power is proportional to airflow and not air pressure. Boost is only a measure of air pressure, which, all else being equal, is proportional to air density. However, just because the air is denser doesn't mean more power, it has to move in order to get into the engine too, so what you really want is dense air+high velocity. By freeing up the intake and exhaust you improve air velocity by improving exhaust scavenging (exhaust) and reducing pumping losses (intake). Also, improving exhaust flow on a turbo motor makes it easier for the turbo to compress the air in the first place so it ends up being cooler, again that improves air density. Same goes for the intercooler, not only does it condense the air better, but it also reduces the pressure drop. Lower pressure drop both improves turbo efficiency and reduces pumping loses. Not to mention higher boost creates more heat, which at a certain point will completely overcome any benefit of the higher pressure by superheating the air and making it thus less dense, the opposite effect you are trying to achieve.

 

Good post Nathan!

 

Everyone bow down to Nathan. Excellent post that actually makes sense to all who will read it. Great job explaining and thanks for that.

 

awesome, thanks Nathan

Oh yeah, and I thought that as long as you keep boost to 10 psi you don't need an aftermarket ECU?

 

Wade has been doing a lot of testing with major mods and no ecu:

http://www.wvinter.net/~flanham/wlan.../3modrule.html

I would still recommend putting your car on a dyno just to be sure, but it appears the 3-mod rule should indeed be the 10psi rule.

 

if you are that 10psi car with aftermarket ic, exhaust, intake, i'd suggest getting some way to increase fuel still. If you hit a nice crisp cold night and decide to flog the car, there is a very good chance of running lean.

Danny

 

to simplify it even more...blow hotter air (less dence) through a straw at 12psi or a 3in tube (cold air) at 10psi. more air can be "pushed through" a 3in tube than a straw.
think of an engine as a big air pump.
nathan explained it well and i dont know how else to dumb it down. (no offence)