Boost only Under Load?

[dls93tsi]

This may be a stupid question for some of you, but I am wondering why the turbo will not spool if the engine is not under load from the tranny.

My 5-spd will not boost if I am just in neutral, but my friend's auto tsi will boost when in park and neutral. I was wondering why, if it has something to do with how much load is on the engine, or exhaust gas velocity or something. Im not an expert on the physics of this kind of thing, although I am tryin to learn.

Please dont post if you dont know what you are talking about. ( I like answers like Crankbender's...his tell me things I can use)

 

[DSMJim]

Most standard cars will not create boost in neutral because there is no laod on the engine. No load on the motor doesn't create much exhaust heat or pressure which keeps the motor from spooling. THe auto may have a lot more rotating mass on the crank causing it to spool the turbo because it takes more power for the engine to rev in neutral. I'm not really an auto guy so I can't give you a 100% answer here.

The standard car however is exactly as how you described it.. No load = no boost. There are guys who can create boost by reving the exhaust near redline then down to 5500 then upto 7500 again going up and down will cause the turbo to spool. I have a MSD ignition and at 5500rpm on the two step rev-limiter I can make 10-12psi of boost but I can put the gas to the floor and it will hold at 5500rpm putting load on the motor which causes the turbo to spool.

 

[RossY]

i have a 5spd and i build around 5 psi in neutral by just taking it to about 5500-6000rpm.

There was also a vid i saw not too long ago with a guy that built about 10psi just revving. can't remember if it was this site or not

 

[NOAHSR10]

http://www.members.aol.com/NOAHSR10/fc6251d6

 

[kpt4321]

Since we have no idea what any of the parts are on that car in the video, it's pretty useless.

I can build 25 psi at a 4500 rpm stutter if I retard the timing a lot. It's not hard to do, but also not a very good example of what really happens.

 

[Defiant]

Well, think it out. "Boost" is the same as "More Air Than The Motor Can Take In". So, if there's no load on the engine, and it "runs away from" the incoming charge -if the pistons are taking in all the air they're being fed, you'll never show boost in the plenum. Also, this is _very_ hard on the engine. Don't try to do it.

 

[kpt4321]

What is hard on the engine?