Why is it when some turbo'd cars are at a stand still, the motor can be revved up and it will blow off. But on other cars, you can rev it up all you want, but no BOV? Im guessing it has something to do with the type of turbo and motor... but i know someone knows for sure.

 

Well, on my car, it doesn't put enough of a load on the turbo to create boost pressure when I'm sitting still.

 

it mite not have a BOV it mite use a re-circulator?

 

are you sure the cars where you dont hear a blow off even has a BOV? hehe,..on my old SOHC-T setup,..i would keep my revs under 2500 RPMs because i didnt want some people knowing about my turbo setup...keeping it that low didnt build up enough pressure to release air,..or if i did,..i would blow off just slightly to where you couldnt hear it

 

the motor i was refering to that i heard the BOV when it was at a stand still was a new SRT-4. The car that i didnt hear the BOV when i revved it was my car when it was turbo'd :fawk: i might not have been getting the RPM's high enough.

 

I'd say that if they can rev sitting still and vent their BOV, then their turbo is just too small. :chuckles:

The car has to be able to build boost while the engine is not under load. The key to it is being able to move enough air, to burn enough gas, to spool X turbo, to build boost in the IC pipes (enough to make your BOV have enough + pressure to vent audibly). That's 2 2 2 much to follow, but that's the way it works. If your car isn't moving enough air and fuel through the intake and engine, it doesn't make enough exhaust gas to spool the turbo and build boost. Turbo efficiency has a lot to do with it, but there are a lot of other contributing factors involved.

Most cars with BOVs don't do this from the factory. Not that a car that normally doesn't do it can't do it, but you need to have a setup capable of it. Deisels don't have BOVs because they need detonation to run, so a BOV is pointless for them, but you can hack other things than a turbo to make this situation happen.

Just bolting a different BOV or boost controller on your car won't make it do this. A boost controller's job is to open the wastegate, and your wastegate will stay closed until you reach full boost, so it's pointless to think it would affect this. Some people will argue ball-n-spring versus needle valve... yadda yadda yadda... It won't matter.

The bov is going to open when the intake manifold pressure is lower than the intercooler pipe's pressure. In otherwords, if you ain't got boost enough to vent louder than your engine, you won't hear it. BUT! Some BOVs are designed like whistles to greatly exaggerate the sound of their operation. Like the HKS RFL. That's what I call a ricey BOV. Just because it's loud doesn't mean it's fast.

One easy way to make a car build boost when it's not under load is to put a huge downpipe and exhaust, and/or no cat :huh: on a car so that there's enough of a pressure drop after the turbo to make it spool with very little effort. If you can build over 5-7 pounds, you'll hear it with just about any BOV.

A giant turbo intake pipe with a big filter on it helps, too. So... any restriction you can take off the turbine wheels will make it easier for a car to spool a turbo. I'm not getting into intake velocity and pressure drops associated with overdoing the IC pipes. That's a whole 'nother thread.

Bigger turbos are harder to spool. This is where the "Not that a car that normally doesn't do it can't do it" comes in to play. Some cars with larger turbos and every other mod that still can't do this spray n2o at the track when the tree lights up, thus adding to the exhaust volume, and spooling the turbo. They're also usually equipped with tires that can handle that kind of setup and launch, so don't get any crazy ideas. It won't help you any on public pavement, just the track because you can't use those tires on the street.

My favorite way to do it is to install a shutterbox mechanism. With a shutterbox (studderbox, 2-stage, whatever), you'll have no problem spooling the turbo while stopped if your ignition system limits the engine RPMs instead of the throttle. You can stand on the gas without over-revving, thus, at the WOT fuel trim (more exhaust volume), and with the throttle plate open, there's nothing stopping you from moving air. In this condition, you'll build boost. It's frikkin' incredible with AWD.

 

Nice informative post Jafro :thumbup:
I learned a thing or two from it

 

:jawdrop: wow, thanks for all of the info man. Not only answered the question, but gave me some extra helpful info as well. :thumbup:

 

Also, don't forget... That Dodge has a 2.4L 4-banger. That's a big 4-banger. That thing will spool most turbos with ease.

 

damit dude, you are so the man. :goodjob: