Detonation

[DodgeT]

I'm stuck at 92 octane where I live and my 440 is having a hard time with it. It seems to want more advance, but I'm constantly fighting detonation if I get into it (and where's the fun in not doing that).

Even at around 5 degrees btdc I'm getting detonation - and it still seems to want more advance - of course it runs better around 10 - 15. Do I need to adjust the distributor springs or something? I shouldn't be much above 10.5 to 1 compression.

What additives are people using to boost their octane?

440, auto, N96
Comp Cams Xtreme Energy XE268H

 

[mentor70]

i would start with a compression test to check the cylinder pressure. if it is above 170 psi, then other that octane boost or race fuel or a cam change your stuck.

ive heard good things about this product:http://race-gas.com/

 

[DodgeT]

Low compression will cause detonation? I'm scared to check the compression now....Engine doesn't have 500 miles on it yet. How long before my rings are seated?

Like I said, it's fine unless I get into it.

 

[Photon440]

Toluene is a nice octane booster. It won't harm anything and has an octane (r+m)/2 rating of 114. Add a gallon per tank.

http://www.worldofchemicals.com/428...ive-for-racing-fuels-fuel-octane-booster.html

 

[SlinktRR]

Low compression will cause detonation? I'm scared to check the compression now....Engine doesn't have 500 miles on it yet. How long before my rings are seated?

Like I said, it's fine unless I get into it.

What is your total timing? You will probably have to shorten your advance curve in the distributor and run more initial. Break-in is whatever your builder tells you but usual is 500-1000, vary engine speeds and don't go over "x" RPM during the period. Then let er rip.

 

[DodgeT]

What is your total timing? You will probably have to shorten your advance curve in the distributor and run more initial. Break-in is whatever your builder tells you but usual is 500-1000, vary engine speeds and don't go over "x" RPM during the period. Then let er rip.

Changing the distributor curve is still an unknown science to me, but I will do some research. I've been fairly chill on the RPM's, and mostly just been driving a few miles at a time. I do stomp on it, but I don't go crazy with RPM's. Just changing them up. Thanks for the responses.

Also, as would be expected, when she is cold, no to little detonation...

 

[SlinktRR]

Changing the distributor curve is still an unknown science to me, but I will do some research. I've been fairly chill on the RPM's, and mostly just been driving a few miles at a time. I do stomp on it, but I don't go crazy with RPM's. Just changing them up. Thanks for the responses.

Also, as would be expected, when she is cold, no to little detonation...

Some distributors are easier than others. If its a new motor you should be able to get help from the builder, as detonation that you can hear clearly is trouble. Octane boost or backing off timing is a decent crutch until you figure it out. Too much cylinder pressure as mentor indicated can lead to detonation.

 

[DodgeT]

Some distributors are easier than others. If its a new motor you should be able to get help from the builder, as detonation that you can hear clearly is trouble. Octane boost or backing off timing is a decent crutch until you figure it out. Too much cylinder pressure as mentor indicated can lead to detonation.

Well, I moved across country and the rebuilder is 2000 miles away. And, it has been like 5 years. They may remember details if I call them I guess.

I've got 906 heads. Seems to me the compression ratio should have been around 10 or 10.5 to 1. When you say "detonation that you can hear clearly is trouble" what do you mean? I need to re-ring, change heads or something?

 

[Cranky]

Ring break in depends on ring type. Moly rings break in real fast and even regular rings will break in fairly quickly if things were done right. Pinging or detonation is harmful and the louder it is, the quicker damage can occur but your spark plugs will usually tell you the story. And yes, do a compression test to see what PSI it's making and is the first thing I would do. Doing that not only tells you the health of the engine but also how potent it is. High PSI is good but too high can cause your pinging. The higher it is, the better the gas should be and that cam might be producing too much cylinder pressure at low rpm for your static compression. You can make a low compression engine ping just as easily as you can a high compression engine but it's usually for different reasons. Having a good quench or squish distance is one key factor to having a good running engine that has high compression plus the cam is key too.

 

[lewtot184]

that 268 cam is ground on 110lsa with 4 degrees of advance ground into it. it closes the intake valve way too early and in my opinion too small for a 440. 10.5:1 is a no go with iron heads and no quench. cylinder pressure is probably well over 200psi. also check to make sure the plugs are dry. any oil seeping thru the intake or guides will cause detonation. i think the only hope is a mix of race gas.

 

[hunt2elk]

Any chance your harmonic balancer spun a bit and is giving you a false timing reading? I had that happen once.

 

[IQ52]

that 268 cam is ground on 110lsa with 4 degrees of advance ground into it. it closes the intake valve way too early and in my opinion too small for a 440. 10.5:1 is a no go with iron heads and no quench. cylinder pressure is probably well over 200psi. also check to make sure the plugs are dry. any oil seeping thru the intake or guides will cause detonation. i think the only hope is a mix of race gas.

Exactly what I was thinking,

 

[DodgeT]

that 268 cam is ground on 110lsa with 4 degrees of advance ground into it. it closes the intake valve way too early and in my opinion too small for a 440. 10.5:1 is a no go with iron heads and no quench. cylinder pressure is probably well over 200psi. also check to make sure the plugs are dry. any oil seeping thru the intake or guides will cause detonation. i think the only hope is a mix of race gas.

Hmmm...Okay. I got the whole compcams kit. Overall, I kind of like the setup, but race gas blends will get spendy. What cam do you recommend? I went 268 because I like my car to idle. Plus, I have loads of torque right now. Or, should aluminum heads be in my future? The rest of the engine is pretty stock. I need to look again, but I think my pistons are Sealed Power or something. It was a NAPA that did my machine work.

Basically, what will it take to run on 92 octane and be able to get into it? Opinions?

 

[dla4567]

I think before you start tearing apart your engine you should check cranking compression and total timing.

 

[lewtot184]

Hmmm...Okay. I got the whole compcams kit. Overall, I kind of like the setup, but race gas blends will get spendy. What cam do you recommend? I went 268 because I like my car to idle. Plus, I have loads of torque right now. Or, should aluminum heads be in my future? The rest of the engine is pretty stock. I need to look again, but I think my pistons are Sealed Power or something. It was a NAPA that did my machine work.

Basically, what will it take to run on 92 octane and be able to get into it? Opinions?

in my opinion, different pistons.

 

[DodgeT]

I put a fresher carb on today. It handles less advance better. I've got it down to less than 5 degrees now. I hear detonation when I am about 3/4 to 7/8 of the way to full throttle now. Much less than before I think. I will take some time and do a compression check one of these days when I feel like having burnt hands...

 

[SlinktRR]

I put a fresher carb on today. It handles less advance better. I've got it down to less than 5 degrees now. I hear detonation when I am about 3/4 to 7/8 of the way to full throttle now. Much less than before I think. I will take some time and do a compression check one of these days when I feel like having burnt hands...

Burned hands or a hole in your piston(s)? Thems ur choices. Its not that bad wear gloves. Harbor freight sells a compression kit for cheap, craftsman carries one. Just bump the starter. Better to have numbers than keep guessing, it will help the forum give you next steps to try.

Try finding race gas as lew indicated. If you're at 5 degrees and still pinging then the crutches are not going to get you around safely. Park it and find high octane gasoline, then enjoy it comfortably while planning your next move.

 

[Garys1969RR]

Try adding some E 85 into the mix. It's 105 octane and may help a little. Like 1 gallon into 5 gallons of premium. Also keep the engine as cool as possible. I removed my thermostat in my 13 to 1 C/R 451, and that really helped. But I am running 292 degrees total duration cam. Go to a cam that closes the intake valve later. Longer duration, or retard that one 4 degrees. Also slightly richer mixtures help. There are advance limiter plates you can put in to limit your total advance, so you can start with the right amount of initial advance. What does your detonation sound like? Is it a rattling sound?

- - - Updated - - -

Check the cranking compression pressure. Warm it up, then wait 30 minutes for the ex manifolds to cool off.

 

[Cranky]

With my 10.3 340 Cuda, it would run on 93 just fine so long as temps stayed at 180. 185 I'd start to hear it ping at full throttle but it wasn't easy to keep it there in the Houston summers but just 1 gallon of av gas on top of nearly a full tank did the trick.

 

[HEMI-ITIS]

Your trying to mask a problem and will end up with piston problems. 1st pull the plus and be CERTAIN there is no oil getting into the combustion chambers. 2nd,verify the timing and the damper. If they are where they belong you either have to use higher octane fuel or change the cam to bleed off some cylinder pressure. Do not load that engine until you rectify the situation or you WILL hurt those pistons!!!
Also,,,,,,driving so retarded:eusa_whistle: will make it run hotter and like dog pooooooimp: