what is the difference between turbo's that cause some to spool at cruise, and others do not?

My recently built DRZ system sees 10psi (before the TB) at any speed on the freeway. Its a cool "feature", but makes me nervous to have so much constant boost always present. I don't think it has much to do with turbo sizing vs engine sizing, because this is relatively a large turbo for the motor. My best theory is, its because the turbine/shaft/compressor wheel has so little mass (GT12)

I've had as much as 3psi on bigger turbo setups on bigger engines, but that took more than just cruising on the freeway. Either high speed (100+ mph) cruising or fighting a heavy head wind.

 

doesnt sound right to me. you have a bad boost guage or something?? you running 1/2" headers or something crazy?? what do you mean before the tb? is there vac in the intake at cruise?? if there is 10 psi boost in the intake pipe before the tb and vac in the intake, you are gonna kill you turbo in no time flat. you do know they make bov's to combat that problem when you let off the throt and there is this situation. they have them to protect your turbo.

 

if your boost gauge is before the TB, then yes, you can see boost. The engine is not actually seeing that boost though. I'd recomment moving the boost gauge to after the TB.

If your BOV is functioning, it will normally vent off that boost.

 

huh? what does chopping throttle have to do with boost at cruise?

Trust me, the system is quite free flowing, and it doesn't hit full boost til 6K RPM's.

The boost gauge is accurate, and I've never measured pressure after the TB (thats throttle body)

 

hmmm...now that you point this out, my previous systems I've built have mostly used boost reference after the TB. I would need to modify it to check it after the TB, but it would be interesting. I have no doubt there's a PSI drop over the TB, but that much??

 

yes it can make a noticable difference on the guage. if the throttle is only part open, i.e. under cruise, alot of the air flowing will deadhead against the throttleblade and cause your guage to read pressure when the engine is actually only seeing a fraction of that air

 

i agree 100%.go after the tb

 

wait do you have a bov on this thing? that def has to have a vac/boost ref after the TB

 

I should have put 2 and 2 together. I never considered that aspect of the BOV. I just assumed it was only to prevent surging. For this build, I have not installed a BOV...yet. Was planning on eventually doing it, but was going to wait until I lowered the CR and added an intercooler for higher boost

I would think though, that venting the pressure wouldn't be a good thing though, since you are throwing away pressure without removing the heat, which would decrease power and effficiency at partial throttle?

Learn something every day....

 

im not 100% on your last aspect but having the bov open at part throttle would prevent you from having boost at that point

 

does this apply with 2.3 svo.. cause i dont know where my factory boost gauge is connected.. maybe at the electronic boost controller? and the boost controller is hooked up at the turbo compressor in a T -with the waste gate