Drive pressure guidelines.

[RonA]

I removed my tach from my gauge pod and installed a second 0-80psi boost gauge. I want to know if my top turbo is large enough. Say I run the boost measured at the intake up to 30 then 40 ,50 and finally 60 psi. At each of these intake boost levels I also log my exhaust manifold (drive) pressures. Does the relationship between these numbers assuming EGT's are within limits indicate whether your turbos are the proper size for your hp level. Say I am no more than 1 to 1 up to 45psi, 1. 1 to 1 at 50, 1. 2 at 55 and 1. 3 at 60, just as an example. Assume these are the best numbers obtained after adjusting the wastegate opening pressure. If a larger top turbo is used, say switching from a 35/12 to a 40/16, what would be the expected change.

Ron

 

[robertyoke]

from what I have seen so far it wont be a straight ratio like that. your boost will be lower than back pressure till the wastegate opends then boost will be higher for a bit, then as boost climes so will back pressure but your b. p. will clime faster than boost.

but even that will not stay constant because as your rpm's increase so will your b. p. , so at 1500 rpm 30 psi boost may be 30 psi b. p. but at 3000 rpm 30 psi boost may be 35 psi of back pressure.

If you flow enough past your top turbo then your bottom turbo becomes your restriction.

thats what I have seen so far, but I am sure someone with more experience will clear it up better than I can.