440 detonation

[thrillbilly]

I have a question about spark knock/detonation.  The last few times I have driven my Charger, 440 and got on the gas hard at cruising speed, 60 or so.  I am getting spark knock.  I have ran 2 tanks of 93 through it, I was hoping it was crummy gas.  It does it when the outside temp. is fairly warm, 80+.  Car runs about 180 degrees.  What causes detonation?  Should I pull a couple of degrees of timing out?  How much damage does this do?  I let off of it when it does this.  Mopar performance dist.  recurved, initial around 14 deg.  34 deg. total at 2000.  Around 10:1 comp, aluminum heads 750 vac. secondary Demon carb.  Edelbrock Performer RPM.  I'm not exact on the cam, Comp cams Magnum I believe.  Thoughts, opinions?  Thanks.

[chargerbr549]

If you are running vacuum advance you might unhook it and see if that helps, if  it were me I would slow the advance rate down so its all in by 2800-3000 and up the advance to around 16 intial and 36 total, every car and combination is different so you might have to play around with it a little bit, also check that you aren't maybe running a little lean on your carb or possible a vacuum leak. 10 to 1 compression on aluminum heads doesn't sound extreme so that should be alright, hope this helps a little.

Kevin

[70charger_boy]

If you are running vacuum advance you might unhook it and see if that helps, if  it were me I would slow the advance rate down so its all in by 2800-3000 and up the advance to around 16 intial and 36 total, every car and combination is different so you might have to play around with it a little bit, also check that you aren't maybe running a little lean on your carb or possible a vacuum leak. 10 to 1 compression on aluminum heads doesn't sound extreme so that should be alright, hope this helps a little.

Kevin

  If that doesn't work then check to make sure it is not a rod bearing that is bad

[thrillbilly]

Thanks for the tips. The vac. advance is pluged off, it would get a surging at speed with it hooked up.  I can stand on it real hard from a stop and no knocking, it only happens when I am passing or proving a point to a tailgater...

[70charger_boy]

Thanks for the tips. The vac. advance is pluged off, it would get a surging at speed with it hooked up.  I can stand on it real hard from a stop and no knocking, it only happens when I am passing or proving a point to a tailgater...

Ok, so what RPM range are you at?  I'm willing to guess 1,700-2500 range?

[thrillbilly]

At 60 mph I am turning 2800 rpm.  Spark knock occurs at 3500 +

[chargerbr549]

Check to see if you either have the carb running too lean or maybe your fuel system might not be keeping up with your engine demand. Check to make sure that your fuel pressure at the carb doesn't fall much below 5lbs of pressure at all times if it does that might be whats causing your detonation.

Kevin

[Purple440]

thrillbilly I've had this same thing...ping at higher RPM but not low RPM.  I also have a Demon 750 v/c.  I don't have a solution for you but I've been told by multiple reliable sources that the Demon fuel curve is all over the place and you may just be going lean at that particular RPM range.  I'm throwing in a Holley next spring.

Do you have a descent fuel pump?  10:1 aluminum heads should be 9:1 according to the experts so I'd make sure you're not running lean at that RPM range.  Have you tried jetting up?  If you can post pics of your plugs the pro's around here will help you diagnose.

g/l 

[thrillbilly]

I haven't played with the jets much, plugs are always brown.  I have had this set up for a couple years now, and this is the first trouble that I have had like this.  I think I have a carter fuel pump, which puts out 6 psi. of pressure.  Ma;ybe a fuel pump upgrade is in order?

[Purple440]

So your plugs look the same now, after this problem started?

[thrillbilly]

I haven't pulled any since it started.  I have drove it to shows the past two weekends and had this problem.

[Purple440]

Well I'd check'm and make sure your timing is still where it should be.  I don't have experience beyond this so someone else will need to step in.  If you didn't change anything then it sounds like something is failing, like your fuel pump.

Check your plugs and do a fuel pressure test if you can.

g/l

- Doug

[firefighter3931]

Sounds like it's going lean on the secondaries. Check your rear bowl float level. 


Ron