Boost quest.. ANY SMART COOKIES HERE?

[PorterzSupra]

Okay stock my car put out about 7.5 PSI in 5th gear at 3 grand at WOT but only put out about 4 PSI at higher PRM (4 grand and over) is this normal? I would imagine the boost would be if anything higher at higher RPM not lower because the exhaust turbin is spinning faster? Is this just just a case of the stock wastegate wasting my boost? lol ONE MORE QUESTION.... okay why do I get boost under a load but reving there is nothing, how does it know the difference between reving and driving?? -- Eric

 

[GrimJack]

This is normal. The turbo is spinning faster, but so is the engine, and with the stock turbo at higher RPMs, the engine can suck in more than the turbo can put out.

As for your second question, that's just the way turbos work. When you rev out of gear, the engine isn't really using much fuel, as there is no load on the engine. Without lots of fuel going in, there isn't much exhaust coming out, and turbos use that exhaust to spin up. This is the VERY simple explanation - if you are interested, a bit of work with Google will get you the technical explanations.

 

[mkIIIman089]

If the car is bone stock I'm not completely sure that is normal. My car since I've had it never had the stock DP on it, but I don't remember any fall off at high RPM at that low of a boost. 13psi now it falls off a lot at high RPM, but thats a lot more pressure for that same little turbo.

It could be a clogging DP cat and at high RPM you just cannot flow enough to keep it moving. So upgrading to an aftermarket downpipe could also resolve the problem.