Over boosting??

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99 GTP

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United States
Indianapolis,In
I have a question about over boosting. I just bought my 99 GTP a month ago and the guy said he put a 3.4 pulley on it. No other mods besides the cai. Car do feel as fast as my buddys stock one could it be over boosting?? Im new into the supercharged world anybody have any answers?
 
Check online to see what the original pulley size is, you can then calculate about how much more boost you are getting.
 
So you asked GTP about a problem specific to your car because there was nothing anywhere else on the internet about this issue?
 
I know stop pulley size is 3.8 so I think the car is running lean. If it is over boosting what's things that could happen?
 
It could have detonation and the lean mixture wouldn't help it St all. You could have nice little holes blown right through the pistons. If you hear knocking just switch to a higher octane fuel.
 
Stock pulley size on a GTP is 3.8".

Engine knock is what you need to worry about when dropping pulley sizes.

Any exhaust mods? I would definately do those next. Atleast some ported manifolds and a downpipe. Absolute minimum, have an exhaust shop get rid of the u-bend if you haven't already.

Other than that, put in some colder plugs (I run copper Autolite 104's in my '97 GTP with a 3.4" pulley), and a 180° thermostat. Always run premium gas.
 
I have a 180 ts and some exhaust work headers are stock and I run 93 octain in it.. so could it over boost or do u think its good
 
before increasing the boost pressure there are many factors that need to be worked on.
do you have a boost pressure gauge?. if yes then take note of the pressure.
what condition is the motor in - has a leak down test been done?.
if an engine runs in a overboost enviroment for a while it would eventually start to damage internal parts such as blown headgaskets - burned exhaust valves - damaged piston ring grooves etc. etc..

if you increase dynamic pressure in an engine you also need to change the fuel ratio and ignition timing to compensate for the increased air.

you can look for damage by examining the sparkplugs - ceramic should be light brown in color - look for signs of aluminum speckels on the ceramic . if you find any this would point to piston damage.

there are so many things to look at.
good luck.
 
99 GTP
I have a 180 ts and some exhaust work headers are stock and I run 93 octain in it.. so could it over boost or do u think its good
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If you read the links that I posted, a 3.4" pulley is fine with intake/exhaust mods and high octane fuel. Any smaller than that, and the car will need a tune.

You should be fine.
 
I don't quite care what people say on the internet, more boost without tuning is not a good thing unless the car was already tuned MASSIVELY conservatively from the factory (too much fuel, not enough timing, etc)... And even then...
 
No i dont have a boost guage i am going to buy on and also a air fuel guage. Just dont want to lean it out. And i did check out the links thanks for that.. yea im going to have the head and supercharger and intake ported. Should i have it tuned after that??
 
Rotary Junkie
I don't quite care what people say on the internet, more boost without tuning is not a good thing unless the car was already tuned MASSIVELY conservatively from the factory (too much fuel, not enough timing, etc)... And even then...
Click to expand...

Depends on where you are getting your info. The links I posted are from a Grand Prix GTP tuner and the other from a site dedicated to the car. I'd say their info is pretty legit.

99 GTP
No i dont have a boost guage i am going to buy on and also a air fuel guage. Just dont want to lean it out. And i did check out the links thanks for that.. yea im going to have the head and supercharger and intake ported. Should i have it tuned after that??
Click to expand...

Yes.
 
99 GTP
I have a 180 ts and some exhaust work headers are stock and I run 93 octain in it.. so could it over boost or do u think its good
Click to expand...

Headers aren't stock on these cars, restrictive cast-iron manifolds are. If yours has headers, they are aftermarket.

Over-boosting isn't what to worry about. Engine knock is.

To safely run a 3.4", you would need a cai, 3" downpipe, 180° t-stat, and AL 104 or equivalent plugs.

A tune of the stock pcm wouldn't hurt, or you can get a replacement pcm like I did with a tune already loaded, such as DHP, Intense, etc.
 

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