Guru said:
Well the total price for our downpipe, Blitz SUS and the Turbo XS HPBC is $750. Now I would probably recommend and SBC-id instead of the manual boost controller. THis way you have a boost gauge in there. I'm doing that tomorrow.
As for the Noob's question, the reason the turbo is dying at higher RPM's is that the turbo can not deliver any more boost. It is completely maxed out at and starts delivery less and less boost. By redline I'm only getting around 13 PSI. The engine management is crucial to tune your AF mixtures and also your timing. It is crucial when changign turbos and of course fuel setups. We are doing some more tests tomorrow and will be sending our injectors and fuel rail to Japan for Power Enterprise to hopefully some up with a nice 800-880cc injector for us.

Save

CloNeGTS

· #23 · Jun 1, 2003

VF39......no one has come up with any kind of details on this baby as far as I can find.

Save

jeffsti

· #24 · Jun 1, 2003

shoeeater said:
NOOBIE ALERT!!!!

According to what I know about turbo's (not much) is that as the RPM increases the extra gas being pushed through the turbo should be able to increase the boost up to the desired level and keep it there as long as the turbo has enough waste gasses running through it? I know this obviously is not true because of those plots. Why does this happen?

You are right when you believe that with a higher RPM and more exhaust gases, the turbo should deliver more boost. This is the theory of a positive feedback system. But the problem that is occuring is that the turbo itself is too small to provide 17 psi at redline.

Even if you were to feed the turbo with even more exhaust gases, its just to physically small to provide the volume of air needed to hold boost stable at redline. At redline the engine is asking for more air than the turbo can flow.

When I had a turbo Eclipse, the stock turbo was very small also. I could boost that thing to 22 psi @ 4000 RPM, but at redline it would die down to 13 psi.

In order to hold a boost throughout the powerband, a turbo must continue to spin faster and faster as the RPMs increase.

A larger turbo will solve this problem, because it will be able to flow more air. It will also produce more lag because of inertia. It will take more exhaust gases to get the larger turbo moving. But once it does get going, it can provide unbelievable boost all the way to redline. You will notice how the torque curve will be flatter instead of dropping off before redline.

Jeff

See less See more

Save

Grant

· #25 · Jun 1, 2003

jeffsti said:
It will also produce more lag because of inertia. It will take more exhaust gases to get the larger turbo moving. But once it does get going, it can provide unbelievable boost all the way to redline. You will notice how the torque curve will be flatter instead of dropping off before redline.

Jeff

Its more than just inertia, larger turbos have large exhaust wheels and sometimes larger a/r exhaust housings. This means less exhaust velocity (worse spool), but better flow. IME, the hot side of the turbo has a much larger impact on spool than the size of the compressor wheel.

Plenty of small turbos can hold high boost, they just can't flow much. All things being equal, more boost (remember boost is just backpressure in the intake) means more exhaust pressure, PERIOD. If your wastegate spring gets blown open then it won't hold the boost, regardless of the turbo's effeciency. Of course less effecient turbos generate more backpressure, and restrictive exhaust and intake systems do as well. Turbines opperate off pressure ratios just like compressors, so ANY amount of backpressure at the turbine exit even worse than it would be on an NA engine.

Save

21 - 25 of 25 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

Top Contributors this Month