where is boost measured from?

[madwilly240]

Okay a turbo'd engine is always making boost, but where is it measured at. i know its pounds per square inch, but is it at the turbine, compressor, cylinder, where? or does the psi just stay the same throughout.

also, at idle, do you make less boost than at WOT?

[sanmiam]

Depends on the car and the setup. Putting it on the cold pipe would be a better way to do it IMHO because it accounts for the pressure drop in the intercooler, but it can be done either way. As for the boost thing:
IDLE = low RPM's, very little exhaust gas, turbo not spooled, very little boost
WOT = high RPN's, much more exhaust gas, turbo spooled, much higher boost

[Kreator]

From what i've been told, ideally, u'd want to measure it from somewhere inside the intake manifold. That way, you are actually measuring the real boost/vacuum your car sees. domestic aftermarket engines usually have a tap like that. Our cars (i think) don't.

So, the next closest to perfect is right at the TB. Now, at shifts you'll see some rise in boost, while your car is actually not seeing any of it.

The last and easiest (cuz all you need is a fitting, since turbos come with a threaded hole for it) is at the compressor outlet. That way you are reading what the turbo is producing, but it doesn't take in account any pressure drops along the way (like an ic).

Someone correct me if i'm wrong.

[Jim96SC2]

Just remember that if you use post I/C you will have to watch how you boost. Figure about 2lbs of boost lost via I/C. Now if you run 15lbs at the manifold it's 17lbs at the turbo, which is out of the compressor effeciency range.

EDIT: Sr's have a tap into the TB for boost relay information. I don't know if your talking about SR or KA. Either way if your insistant on it just get a brass fitting, some some of sealant (JB weld maybe?) and just drill the hole, press the fitting into it with some sealant on and WALLA! One pressure fitting.

[Jeff240sx]

Originally posted by Jim96SC2
Either way if your insistant on it just get a brass fitting, some some of sealant (JB weld maybe?) and just drill the hole, press the fitting into it with some sealant on and WALLA! One pressure fitting.

That's exactly what I did when my attempt at tapping the hole didn't work. JB Weld rules, but is butt ugly.
-Jeff

[Kreator]

Yep, same exact way i'm doing all the other hoses (pcv valve, vacm and another one i can't remember the name of). But for the boost, i thought why the f bother, if my compressor already has an outlet for boost reading and all i have in the path from the turbo to the TB is a tiny eclipse side mount.

[Jim96SC2]

Originally posted by Jeff240sx
That's exactly what I did when my attempt at tapping the hole didn't work. JB Weld rules, but is butt ugly.
-Jeff

Maybe soldering it would be cleaner looking then.

[Foxcolt]

why did you guys go through all that trouble?

Why didn't you just tee off the fpr?


I've got two boost gauges, autometer and AVC-r. One reads from the intake manny (tee'd off the FPR) and the other reads before the intercooler. Works pretty well.