correct me if im wrong...

[jesse0880]

in a previous thread, someone told me that when the car is in nuetral, the motor does not produce boost. ( this was brought on by my question about not hearing the turbo or bypass valve when in neutral). well, i have a few buddies with turbo'd cars such as a wrx and eclipse and when they rev their motors in nuetral, their blowoff valves can be heard, which means to me that there is pressure in the charge pipe.

my question is how is there no boost produce when in nuetral if the blowoff valve will open when in nuetral when the engine is rev'd? i believe i was told " when there is no load on the engine, there will be no boost"

this just isnt mechanically right to me. anyone care to explain.

[toyotaspeed90]

the only way that there would be no pressure built up in the system is if the wastegate is open.... and toyota didn't put in anything in the system to open the wastegate if in neutral

building boost using a turbo is all mechanical unless it's electronically controlled by a wastegate.... and when it's closed it's all mechanical anyways..... so the system doesn't care if the car is in neutral.....

you may not see as high of boost in neutral as the engine doesn't have a load on it like when driving, however....

[JekylandHyde]

It is possible to bring the car up to atmospheric pressure and/or maybe 1 psi or so if you rev the crap out of it ... that will be enough to make a blow off valve make it's noise.

Also, some BOVs work on a difference/change in pressure so even if you just alternate a huge amount of vacuum it can sound off.

You can build a lot more boost in nuetral if you are willing to bounce the engine off of the rev limiter. The cut in spark and/or fuel of the rev limiter will create a load on the engine resulting in boost.

The more important question, is why would you want to build boost in nuetral and who cares if you can hear a BOV while parked? That all serves no purpose whatsoever.

toyotaspeed90, no offense, but I do not understand/agree with most of what have written there. You can build boost with a wastegate open, in fact that is what limits boost - no eliminates it. Secondly, I've never heard of an "electronicaly controlled" wastegate. They are all opened by mechanic pressure. There are electronical boost controllers that prevent boost from getting to the wastegate, but the wastegate is still a mechanical piece.

[jesse0880]

that is what i don't get. the whole the no engine load, no boost deal. even if there is no load on the engine, isn't the motor still producing exhaust gases that would spin the turbo? is that the difference between being in nuetral and being in drive? the volume of exhaust?

[JekylandHyde]

There just is not enough volume to build boost.

When you are in nuetral, the engine is not working very hard ... even if you hit 7000 rpms.

What happens when you put it in gear and try to rev it?
The engine lags more, it has resistance, it has load.

If you are holding steady at 4000 rpms in 1st gear with the clutch in (basically the same as being in nuetral) and you let the clutch out ... are you still holding 4K? Nope ... rpms fall unless you give it more gas so the engine can work harder ... once the engien starts working harder, that is when you are going to process enough volume to make boost.

Does that make sense at all?

[jesse0880]

yep, thanks. that whole volume thing is what threw me off. its all clear as the sky