fun_on_the_sand Posted July 14, 2006 Report Share Posted July 14, 2006 Guys, I had my engine ported and I added the cool head with 18cc domes. I am having this weird, knocking sound from the engine, I checked it and the cylinders are not hitting the head. THe sound is more like diesel engine kind of sound. Is that caused by the preignition due to lack of octane on high compresion? I tested the compresion and it is 197psi. I am using C-12 for fuel Quote Link to comment Share on other sites More sharing options...
dajogejr Posted July 14, 2006 Report Share Posted July 14, 2006 What curve is that dyna on? Quote Link to comment Share on other sites More sharing options...
chase@miamiatv.com Posted July 14, 2006 Report Share Posted July 14, 2006 its the cam's lol , my sleeper does the same thing and i checked the same thing you did ....... your guess is as good as mine Quote Link to comment Share on other sites More sharing options...
sheefreak Posted July 14, 2006 Report Share Posted July 14, 2006 Sounds like detonation, but c12 should be fine. Watch for spark plugs backing out. djogejr had a good question. Quote Link to comment Share on other sites More sharing options...
dajogejr Posted July 14, 2006 Report Share Posted July 14, 2006 C12 is rated at 108 Motor Octane... At 200 PSI and a good timing curve...it might be too much. You might have to use octane booster or get a fuel in the 115 range or so.... Try setting the dyna back to the stock setting. And don't run it like that for too long making that noise, bad things will happen!! You're not running a timing plate and/or a degree key, are you? Quote Link to comment Share on other sites More sharing options...
BigRed350x Posted July 14, 2006 Report Share Posted July 14, 2006 I get 112octane from a little local station around here for $6/gal. I run it at 50/50 with mine with no problems. I'm also at 7500ft though. Try to drop your timing down a little bit. I can run pump gas if I leave my timing at 0-4 Quote Link to comment Share on other sites More sharing options...
fun_on_the_sand Posted July 15, 2006 Author Report Share Posted July 15, 2006 What curve is that dyna on? I have it on the stock curve, i think is curve 4, should I try to advance te time chosing a diferente curve? C12 is rated at 108 Motor Octane... At 200 PSI and a good timing curve...it might be too much. You might have to use octane booster or get a fuel in the 115 range or so.... Try setting the dyna back to the stock setting. And don't run it like that for too long making that noise, bad things will happen!! You're not running a timing plate and/or a degree key, are you? No timing plate, just the CDI box I get 112octane from a little local station around here for $6/gal. I run it at 50/50 with mine with no problems. I'm also at 7500ft though. Try to drop your timing down a little bit. I can run pump gas if I leave my timing at 0-4 Quote Link to comment Share on other sites More sharing options...
fun_on_the_sand Posted July 15, 2006 Author Report Share Posted July 15, 2006 Sounds like detonation, but c12 should be fine. Watch for spark plugs backing out. djogejr had a good question. What is "back out" on a spark plug?? Quote Link to comment Share on other sites More sharing options...
Justintoxicated Posted July 15, 2006 Report Share Posted July 15, 2006 (edited) get some domes and lower your compression...Or find some Higher Octain fuel! C-12 is only rate @ 108 Edited July 15, 2006 by Justintoxicated Quote Link to comment Share on other sites More sharing options...
RILS Posted July 15, 2006 Report Share Posted July 15, 2006 I have it on the stock curve, i think is curve 4, should I try to advance te time chosing a diferente curve? No timing plate, just the CDI box What is your cranking compression? 200 psi is a bit high for my taste.Im running around 190 on 111octane with stk timing and havent had any problems.That just sound pretty high for 18s but every machine is diffrent.If I were you id pick up some 20cc domes and try to get it down around 175-185.With your compression that high your bottem end should be outstanding and your top suffering quite a bit.Other than that about all you can do is keep tring higher octane untill it quits detonating.I dont like running 190 but its not quite high enough for me to get another set of domes "I have 18s also" but if was as high as yours i would,most of the buliders Ive talked to dont like more than 185 on gas.What is your elevation? Quote Link to comment Share on other sites More sharing options...
fun_on_the_sand Posted July 15, 2006 Author Report Share Posted July 15, 2006 200 psi is a bit high for my taste.Im running around 190 on 111octane with stk timing and havent had any problems.That just sound pretty high for 18s but every machine is diffrent.If I were you id pick up some 20cc domes and try to get it down around 175-185.With your compression that high your bottem end should be outstanding and your top suffering quite a bit.Other than that about all you can do is keep tring higher octane untill it quits detonating.I dont like running 190 but its not quite high enough for me to get another set of domes "I have 18s also" but if was as high as yours i would,most of the buliders Ive talked to dont like more than 185 on gas.What is your elevation? Phoenix, almost see level. You think octane booster would be a quick fix for the weekend? Quote Link to comment Share on other sites More sharing options...
dajogejr Posted July 15, 2006 Report Share Posted July 15, 2006 Hell NO. If it's pinging on stock timing, the other settings are only more advanced (If I had a scanner at home, I'd post up the timing maps).. Quote Link to comment Share on other sites More sharing options...
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