Boost valve questions?

Sal Lubrano

Active Member
Apr 26, 2002
I have been reading the Principles book and well as many posts. Can some tell me if I am correct in my thinking. I see the stock boost valve in a brf is .471". When a .500 or a .555". valve is installed it allows for the pressure to rise much quickly and well as reach a higher value. Almost the same for the lo/rev boost valve when a larger valve is installed it will just push harder on the regulator holding it closed raising pressure. Does anyone know what the max line pressures would be if a stock spring and .471/.500/.555 boost valves were used? If a stiffer spring or shim is installed that will raise base line pressure. But since it is harder to compress wouldn't it have an effect on the boost valves?

Also I am having difficulty understanding the line bias valve. The book says it is fed by tv oil and regulates tv pressure (modulated tv oil) as engine torque varies? My question is how does it know when engine torque changes??

Thanks for all your time. Can't learn enough about these cars.
line pressures of 180,220,250 are typical with those valves. If the pump is a new GM or a finely reman'd unit then the pressures will be higher.
The amount of pull on the tv cable and the push it exerts on the tv plunger controls the volume of oil that exits the tv valve and enters the modulated tv upshift oil circuit.This is 0 psi at closed throttle and 90 psi at wide open.The tv limit valve feeds the tv valve 90 psi at then the tv system reregulates it.This is done in proportion to throttle angle.
Thank you Bison and Chris for the information. Greatly appreciated. Chris, I followed the information you wrote through the diagrams in the book and I just can not understand what is the purpose of the line bias valve. The book says it regulates pressure based on engine torque? It does not talk about it after that. What controls this valve? I see there is a spring in it but is there any other influence. How does this valve come in to play with the whole system?