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04SVTGUY
06-20-2010, 01:23 PM
Just a quick question regarding the boost PSI on a stock Eaton on my 2004 Terminator.

Does the boost pressure change based on what gear you are in, or what the engine RPM's are? It seems to me that my boost pressure seems lower at higher gears or lower RPM's.

I currently have a 2.75" pulley with idler on an otherwise stock Eaton. Currently, when full boost is called for, it pegs the boost gauge at WOT in 1st, 2nd, and 3rd gears.

Calling for boost at 4th and higher gears doesn't seem to peg the gauge as much.

Is this normal?

Cheers!

Bob

ausie
06-21-2010, 02:43 AM
The boost of the supercharger is dependent on RPM and throttle position. I still have the stock pulley on my car which runs 8 to 10 psi. If you have free flowing exhaust, the boost will be lower due to drop in back pressure. So when you are in the higher gears, 4 -6, the boost will not be as quick to rise unless you are moving above 140MPH. 4 gear is a 1:1 ratio where as the 1,2,3 gears are torque multipliers which will generate higher RPM. The higher the gear the more load you place on the motor, so that will affect the boost gauge to some degree. What you are seeing is normal.

04SVTGUY
06-22-2010, 05:40 PM
Thank you for the response!

By the way, your car and mine could be twins! How do you find out what build number your car is? I know mine was made in 10/03.

Cheers!

Bob

ausie
06-29-2010, 09:38 AM
I found out my build number by calling SVT for which I had to provide the VIN number. At that time, they mailed out a certificate indicating build number.

One other thing I did not mention, fixed displacement superchargers such as the Eaton (roots) and the Lysholm twin screw (Whipple, Kenne Bell) will have an operating effeciency based on rotor speed. The faster it spins the more boost you get. However, there is a trade off in terms of discharge temperature as well as other factors that will effect boost at higher RPM. Too fast, the supercharger will overheat with may result in bearing failures, or worse such as rotor failure. I believe that FORD incorporated a boost purge or by-pass on overcharge at high RPMs. There is a way to prevent that by altering the vacuum lines on the by-pass valve which is one thing I have not done. I believe it is called "the boost by-pass mod".