I am trying to research the funtion and application of a blow off valve for the 87 Gn. I have been reading previous messages on GNTTYPE, but so far I have not found an actuall answer to the question, Is this something that I actually need on my car, or is it just for the sound? Some one please give me the straight answer! Thanks
Tom Redmond
onefast87GN
A BOV isn't an absolute necessity. It does reduce thrust wear on big turbos, and Bruce Plecan has found it really helps on his heavily modified relocated MAF project (he move the MAF to AFTER the turbo) .. he uses it to maintain spool up on throttle transition.
Ken Mosher,
In your opinion, do you think a daily drivin car should have one?
I guess my answer is no... with a stock turbo and nothing exotic done to the car as an assumption.
The blow off valve is used on many turbo'd except for the GN?T's. The blow-off valve is designed to vent the compressed air (ie boost) when you close the throttle. If this isn't done the compressed air hits the closed thottle body and tries to find another path, usually back through the turbo. This compressed air usually forces it's way though the turbo (this is the snorting noise you get on GN when you back off the throttle under full boost). This slows the turbo down, increasing lag when you get back on the throttle (and beats the turbo bearings a bit). On small cube motors with a manual trans this can really hurt performance as the turbo slows down on every shift and the small motor doesn't have the torque to make up for the turbo lag. Most factory applications vent the compressed air back into the air stream before the turbo to help keep the turbo spooled up. Some import guys will vent it to the atmosphere as they like the sound it makes (high pitched screeching noise on each shift). Most turbo systems don't use a hot-wire mass air flow sensor and therefore the air isn't exactly measured as it is calculated and this is the second main reason that many factory turbo cars use BOV's. The GN hot wire mass air flow meter actually measures the exact air going through it and the sound/pressure waves from the reversed air don't confuse it that much. Most cars measure the pressure going though them and the pressure waves from this can confuse them. The cars with blow off valves are programmed from the factory to take into account the air that went through them and they give the corresponding amount of fuel. If vented to the atmosphere they usually suffer from stalling when backing off the throttle as the car has the extra fuel for the air that was just dumped to the atmosphere. GN's are programmed the opposite way. You'll get no benefit from a BOV on a GN as we don't have manual tranny's and we have the torque of a bigger V-6 to help lag. Some think it helps turbo life, but the Garrett turbo's on the GN's seem to last longer then the Mits turbo's on my Eagle Talon and many other turbo'd cars (it has a factory BOV).
Guys, thanks for the input, and helping me not blow any more money on junk that I don't need on my car!
sincerely,
Tom Redmond
onefast87Gn