Originally posted by postal
Does any body have any experience measuring the back pressure on thier motors or have read up on this topic?
Thanks: Jason
Although I dont have a Buick (I have a 2.2L 16V Dodge) I am using what is basically the equivalent of the PT/GT61 on my car.
Making backpressure measurements is quite easy. Assuiming you already have an EGT port in your manifold, all it takes is a cheap pressure gauge (0-100 psi range is about right), some soft aluminum/copper tubing, some vacuum hose, and a compression fitting.
Basically, all I did was removed the EGT probe (which uses a 1/8" NPT thread) and inserted the compression fitting which has 1/8" NPT male threads on one side and a compression type fitting on the other. The compression fitting side goes to the tubing. Thhen, after a few feet of the tubing, I connected some standard rubber vacuum line to the tubing and ran that the rest of the way to the pressure gauge in the car. (Basically, you just need a few feet of the aluminum/copper tubing to handle the temperature close to the manifold).
Now, take your car out and flog it and compare the boost and backpressure gauges. This simple test will tell HUGE amounts of info.
I have used this test to determine when the turbo (especially the turbine side, but the compressor will play into it as well....thats another topic though) is too small. I have been shooting for something less than a 2:1 ratio on my car. The lower the ratio the better of course (i/e/ the more power youll make), but as with anything there are tradeoffs. If one sizes the turbo such that the ratio is very very small, the turbo may never even reach the desired boost level. The 2:1 ratio seems to be a good compromise for a street car to give reasonable spool and great top end power.
As for actual measurements, on my car at 25 psi boost, I measured 45 psi in the exhaust manifold with the PT/GT61 turbo. Thats a 1.8:1 ratio and is in my opinion pretty stinking sweet for a street car.
Its taken me a few turbos to get to this point though. Some past results were as follows (Which I also posted in the PT61 thread---
T3 55 trim compressor with 0.42 a/r housing paired to standard T3 turbine in 0.48 a/r housing
13 psi boost = 43 psi backpressure
T04E 50 trim compressor with 0.50 a/r housing paired to Stage 3 T3 turbine in 0.63 a/r housing
20 psi boost = 42 psi backpressure
Basically......power has shot through the roof with decreases in exhaust backpressure.