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Still getting knock with 3.8" pulley and exhaust mods

97AutoXVette

97AutoXVette

New member
Recently installed K&N intake, PLOG, and ZZP 3" Catless DP on my 1999 GTP. There are no vaccuum leaks or anything like that and I replaced all the vac/boost lines to be sure. I have a lower temp T-Stat and the stock 3.8" supercharger pulley. Did some data logging yesterday and I am still seeing ~2 to 3 degrees of KR at WOT at different places in the RPM range. Anyone know why this is the case? Have you seen this regularly on stock GTPs with exhaust mods?? Figured I would have 0 KR after those mods without running more boost...
 


If this was the HP Tuners website, I'd say post the tune and scan so we can take a look at it.

But you can't paste those on the this forum. Without seeing the tune, there isnt anything I can do to suggest.
 
Fivefingerdeathpunch said:
If this was the HP Tuners website, I'd say post the tune and scan so we can take a look at it.

But you can't paste those on the this forum. Without seeing the tune, there isnt anything I can do to suggest.
Click to expand...

Understandable. The tune is pretty much stock as far as AFRs go, PE tables, MAF, etc.

LTFTs are a consistent +3.1% under WOT...
 


91parkave said:
Why wouldn't you add a little more fuel for your pe and see if the knock goes away first
Click to expand...

Think I should try that even though it's a stock pulley? I was under the impression they run them a little rich from the factory. Guess it would be a quick change though in the PE table and see how it works.
 
Stock tune 3in dp and stock pulley I saw up to 5 degrees of kr I wouldn't worry about it


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wa04compg said:
Stock tune 3in dp and stock pulley I saw up to 5 degrees of kr I wouldn't worry about it


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Click to expand...

Did you do anything to get rid of it? Think it is worth me dropping pulley size if I am already seeing KR with the stock pulley?
 
I would tune out your kr first before you think about dropping a pulley...was just making a point that stock tune stock gtp tend to have kr pretty normal it seems...flow mods may or may not make them go away


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My stock 97 when I first had it, saw upwards of 7*+ of KR from the factory. Seeing you only have 2-3* after a PLOG/DP combo, seems not to out of the ordinary. Add a little fuel and see if that cures the issue. I'd also replace the plugs as well. Since you're on a stock pulley, run AL606's since thats stock heat range. You want the hottest spark possible. When you drop pulley sizes, then swap to AL104 or even AL605's.
 


As of this afternoon, just saw up to 5.7* KR at WOT around 5,300 RPM.... Target AFR is 12.2 (set by me) in the PE table. I still need to swap plugs to see if that helps but gosh, 5.7* ?!?!?! Fuel trims are zero all the way across. Can plugs get rid of ~5* of KR? Maybe I should target lower AFRs in my PE table??
 
Do you have a wideband? Afr should be lower then that...most guys on here shoot for 11.2ish I think


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That's just target. I left the stock adder vs. time/RPM alone.. I'm tempted to zero out that table and make the target lower. Going to change plugs this afternoon and change the target and see how it does.
 
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