compressor surge???

[rkreigh]

when running 10-15 psi as 1/2-2/3 throttle the car pulls really well until it shifts into 4th and then it really stumbles.

I haven't been able to see whats going on with the scan master, but I wonder if the car is going into compressor surge.

here's the combo.

TE45, GN1, 72's, LS1 MAF, Trans +, Extender Extreme, 206 billet roller.

just starting running the car open loop and the idle is much smoother.

car runs really well except for the 4th gear stumble. almost sounds like air backing up the MAF too yet the throttle position is the same (hmmmm....)

I will try to get direct scan as I can't watch the scan master going fast!!!! thanks for any ideas.

 

[rkreigh]

anyone else have this??? the car really hesitates quite a bit, but only when shifting into 4th under boost, 10 psi or more.

thanks!!!

 

[UNGN]

4th gear isn't a close ratio shift. If you are letting the car shift itself, it WILL drop out of the power band on the 3-4 shift and the rpms may not be enough to keep the turbo spooled.

 

[TurboBob]

What kind of wastegate are you running?

It does sound like compressor surge. There are ways to
eliminate it tho. What happens at WOT?

Bob

 

[rkreigh]

Hi Bob!!! I'm running dual turbonetics wastegates on the cross over pipe with a bleeder valve plumbed in for "tuner style" boost control.

I know these waste gates are "old school" but I bought them 8 years ago when I had boost creep problems running one external wastegate with a very old T04 turbo long before I bought the TH down pipe. they still work well so I stuck with them.

the 4th gear stumble isn't really too much of a problem, I just want to make sure that's what's happening. I also have a front mount Eastern intercooler, and probably should invest in a blow off valve due to all the extra plumbing from the front mount.

by the way. Open loop rocks!!! the car runs better with the Extender Extreme chip than it ever has and the streetability with the 72s is nothing short of amazing.

bob, thanks for all the help, I still owe you direct scan traces but I've been car poor and trying to not spend any more cash on the race car.

FYI,

anyone who thinks the 72s aren't streetable should take a look at the trans + and the Extender Extreme setup, works very well and is EZ to use.

thanks a million Bob!!!

 

[TurboBob]

Glad you like the chip.....

What happens is that if the wastegate(s) are set for high boost (more than ~16) and you hold the boost down by backing out of the throttle the compressor goes into surge.

Some cars are more prone to it than others. It can be reduced by creative chip programming or adjusting the BstC (stock wastegates only).

Try turning the boost down and see if you can reduce/eliminate it. Then we can discuss how to prevent it.

Let me know.

Bob

 

[rkreigh]

thanks bob. I also found the compressor surges at only 10 psi at part throttle. almost any boost over 8 going into 4th even holding the throttle constant (checked the tps volts to be sure) I get a pretty pronounced stumble. but yes, the more the boost, the worse it gets. I think the long plumbing of the front mount and the big TE45 turbo contribute to this. my Cheetah didn't do this with the front mount. I really shouldn't be running boost into 4th gear anyway as the tranny isn't designed for much power in 4th. I already roasted a clutch drum before I rebuilt with the AC tranny and NL conv.

doesn't seem to happen anywhere else but 4th gear and obviously I need to get some traces done with DS to see what's going on.

have you ever heard of an OBD I package EASE??? I have that software for monitoring the vette ECMs on my ZR1s and I believe it may work on the buicks too.

I will see if it does and export a spreadsheet of the traces if I can get it to work. I believe it covers all the OBD GM from 86-96 but I will check and see.

not as accurate as direct scan because it reads the ALDL stream at the slower rate but it's better than nothing and I already own it!!!

thanks for the explanations, I will be heading to the dyno sometime soon to check out the A/F ratio on some race gas at around 23 psi and sneak up on the calibration.

thanks very much for all the help and the excellent work on the Extender Extreme!!!