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spark plug gap range is best?

F

fst

New member
specs on my car:
98 grand prix gtp 8.5:1 compression ratio
65lb injectors
autolite 103 gapped at 0.036
ZZP Z7 turbo kit with T66
devils own controller 2bar with M7(?) nozzle
using -20*F washer fluid when lazy or 80/20 methanol/water mixture
17.5psi and 23* of timing

right now i see on the grand prix forums the turbo'd guys are running plug gaps in the 0.030-0.034. however they're not running methanol but larger size intercoolers. im running the default moderate sized intercooler 22x8x3.5". im using a NGK wideband and in order to run near knock-free my AFR is 10.0-10.2. my commanded AFR in the pcm is at 11.8.

my other question is what gap range should i consider running if i want to go to 18-20psi? i noticed when i try and run anything over 18psi at wide open throttle the car stutters and most likely is misfiring. i imagine im getting the misfire because of the add'l boost? again my AFR is still under 10.99.

any suggestions and advice is greatly appreciated!! TIA
 


i could try to lean it to 10.6-10.8. remember im also running methanol/alky injection which will add/richen my overall AFR.
 
exactly, you want your overall AFR to be where its supposed to be. you're now using the meth as a secondary fuel. your car will be tons faster with it being leaned out.
 
yea. however my main question is should i lower my gap or enlarge it if i want to go past 18psi? again, thsoe with no alky but with I/C run smaller gaps with more boost going in to prevent spark blowout. in my case of using both alky and I/C would going to a smaller gap could also cause spark blowout cause theres too much happening in the combustion chamber?
 


smaller gap prevents the spark from blowing out. if that is your issue then by all means go with a smaller gap. however, it sounds like youre drowning the car in fuel right now as well.
 
Your excess in fueling could also be fouling out your plugs...so I'd pull them and check them too.
 
i changed the recently a month ago anf the old plugs werent soaked but rather grayish-white. i'll have o double-check when i get the chance again. however, should i open the gap more then?
 
the plug gap being too small could be causing your rich condition. it COULD also be that you are running too rich (after meth and all) for the small gap.
In either case, widening the plug gap is easy, quick, and free. do that first
 


fst said:
specs on my car:
98 grand prix gtp 8.5:1 compression ratio
65lb injectors
autolite 103 gapped at 0.036
ZZP Z7 turbo kit with T66
devils own controller 2bar with M7(?) nozzle
using -20*F washer fluid when lazy or 80/20 methanol/water mixture
17.5psi and 23* of timing

right now i see on the grand prix forums the turbo'd guys are running plug gaps in the 0.030-0.034. however they're not running methanol but larger size intercoolers. im running the default moderate sized intercooler 22x8x3.5". im using a NGK wideband and in order to run near knock-free my AFR is 10.0-10.2. my commanded AFR in the pcm is at 11.8.

any suggestions and advice is greatly appreciated!! TIA
Click to expand...

I am the tech manager at Autolite, have alot of experience with these cars. I also agree with the other posters on your afr, fix that first. My coworker is a former owner of DHP. .028-.032 plug gap when running high boost with stock ignition to avoid blowing out the spark
 
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Also take into consideration stock valvetrain at 18+psi of boost. If you were to hop on a dyno I bet you would see some characteristics of valve float.

Get it in the 11.1-11.5ish afr range for the street, that way if your methanol fails, you should be able to tell and back off safely before it goes any leaner. You also should work on matching the commanded afr to your actual afr with the methanol if you are going to be using it all the time.
 
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