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Old 08-26-2010, 10:25 AM
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knocking issure, plugs fouling too fast

alright, iv got quite a few problems all related to ignition. first of all, the motor is a 355 with dart iron eagles, 74cc chambers for around 9:1 compression on flat tops, it has whipple supercharger, non inter cooled, but i do use methanol injection, i run about 10psi max. and its hard to keep it under 1psi during a average light acceleration, the blower is very over driven, the motor is always around 0 vacuum unless im just cruising.

ever since i swapped in my manual trans, i really can notice that i can feel the motor really loosing power when i get in a tall gear and the vacuum is low, basically during a normal acceleration. i can just feel the motor knocking when i hold on to the stick. i log it and sure enough my knock counts are high, in the 200s. the exhaust is loud so i cant hear anything, but i can feel it. i looked into my timing tables and they are very low, the knock sensor will say im knocking at 1500rpms with 10 degrees of timing, it will drop my timign to next to nothing and the knock sensor is still reading something, which i think is almost impossible, so i ruled it out as a false knock from leaky headers, noisy valve train, who knows, so i disabled knock retard. the motor runs better, but i still feel a knock and iv been really confused as to what more i can do wore the last week or 2, it may just be the motor breaking up as the motor gets very rich in the area that i suspect knock. so yesterday, i head off to school and my plugs are fouled after only 300 miles on them, i have a cylinder or 2 missing at low vacuum/low rpm. i pulled the plugs and they had some deposits, i cant tell if theres any real indicator of knock or not, heresa few pics

im completely lost as to what to do, these plugs are cr42ts (stock for this truck was xcr43ts) and i leave the gapped at .35 which is what they come at.

so after thinking about it extensively the only thing i have come up with is this. i know the proper thing to do with a blower is go colder on the plugs. but maybe thats just not the case here. im thinking my plugs are too cold, i think im not gettign a good burn and that the motor is filling up with carbon and im feeling either te motor breaking up from incomplete burn, or pre-ignition from all the carbon. what do you guys think? i was also thinking i need to go tigter on the gap to make them live longer.

as far as some history on the motor, im always tunign it, its always running a little rich. i normally change the plugs every 3 or 4,000 miles or they will become fouled. it is always a very dirty motor, always carboned up plugs but its always ran pretty good as long as you keep plugs in it. currently iv got a brand new set of plug wires in it, new coil, new distributor and module, but the cap and rotor are about 8,000 miles old. this is the first time iv only gotten 300 miles out of a set of plugs, the tuning has changed recently because i put a new 850cfm throttle body on, iv only got the tune roughed in.

i know this may take some time to read through but id really appreciate if someone could give me there opinion, i feel like theres nothing i can do to get this motor to accelerate smoothly thorough he lower rpm range.

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Old 08-26-2010, 03:59 PM
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thanks for the input. before i start rambling off engine specs let me say that i put new plugs in today, went back to the stock cr43ts and gaped them at .28 and the motor runs alot better, i dont feel any knock when i shift it into a taller gear anymore. however, the motor still needs work, i know the motor will fall apart if i continue to drive it in a poor state of tune.

im not lugging the motor like a diesel, im just accelerating at a normal pace around 1500-2000 rpms. 3rd gear is a big jump, if i wind it up to 2200 in 2nd, it still drops down to 1500 when i shift into 3rd. iv been accelerating in the 3000rpm range lately just to keep the vacuum low to reduce damage to my motor until i get things figured out.

ok, i can lower the boost, iv got a bigger pulley. ill probably go that route, but its hard to do that when i know i can run the motor out at wide open throttle at 9psi and have no issues with knock and no issues with having to run low timing, so would lowering my boost just be for the sake of low rpm driving?

the heads are actually 76cc(think i stated they were 74 earlier), this is just what theya re advertised at, didn't check them. block is 0 deck height with either .35 or .40 head gaskets, cant remember. and my compression ratio was done on a calculator, it comes up to 9.1 :1 to be exact. the idle is not fat at all, it idles around 17:1, the reason its fat when i accelerate if because i have kind of a delima with tuning this thing. the ecm only reads vacuum, so to deal with boost the fuel table is just tuned across the rpm range at the end of the table up the 0 vacuum row, so to get the air fuel ratio right at higher boost, it creates a rich condition when the motor is just touching on 0 vacuum. i just got a boost/vacuum referenced fuel pressure regulator going on the truck to solve this problem ,i shouldn't have any problem fixing this up, iv already got it going much better. iv also adjusted the timing curve a bit, i shouldn't have any problems getting it dialed in either. but you are correct, it is poorly tuned at the moment.

heres the cam im using, and im using that with 1.6 rockers. i can post a pic of the actual cam card if theres not enough info there for you. the motor is a 4 bolt main, 355cu, cast crank, forged lightweight pistons on 6" cast rods. trying to think what other dtails i can give you. its a stock auminum intake manifold, the blower is a 2.3 liter whipple which was just rebuilt. the blower is spinnign within its safe rpm limit, but right at that. i rev the motor to 5300rpms max because that is what spins the blower at its max speed. i spray 40%water and 60% methanol with a progressive controller, i run only 93 octane gas. i run 20w 50 motorcycle oil in the motor with the zddplus additive, oil pressure is about 40spi at idle and up to 70 driving. my highway crusi is about 2000 rpms at 60mph, my average cruise is around 75mph which is a little more then 2500rpms, i dont have any problems maintaining a nice cruise burning about 14 or 15:1 air fuel ratio, if i lay into it and try to pass, it will knock from what i can remember, it hard to keep it out of the boost. cruising down the highway at more then 80mph, i pretty much cruise at 0 vacuum, the rpms are up enough to were it runs great at this point, will pull hard all the way till 120mph.

any details i left out let me know. at this point im thinking lowering the boost is probably the best thing i can do. i really cant pull the heads off this thing, im going to college now and i live in an apartment complex, iv already almost been evicted for my truck, i work on it in the publix parking lot now. but if you think its an absolute must, then dont be afraid to tell me. i really wish i wouldnt have got these plugs now, ill probably switch them out for what you recommended soon. i really appreciate the input.

Last edited by chevy1500z71; 08-26-2010 at 04:09 PM.
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