Detonation problem

[Jakke]

I have detonation problem in my stroked 440.
Engine starts to detonate if get more than 28 deg. ignition adv.
Engine will not overheat, temperature stays 160-180 deg.
Engine detonates on hard acceleration and around 3000 rpm.

Here are my engine spec

Mopar 440 stroked to 496
-Stroke 4.15
-Bore 4.375
-Cam hydraulic roller ( crane )
o I 372/558, E 372/558
@ .05 timing
o intake: 19 BTDC, 49 ABDC, max lift 105 ATDC, duration 248
o exhaust 62 BBDC, 12 ATDC, max lift 115 BTDC, duration 254.0
CR 10.8:1
Heads
-Edelbrock RPM 88cc
-Crane roller rockers
Intake
-Edelbrock dual quad
-2x 600 cfm
Ignition
-MSD read to run distributor
-MSD 6AL box

What should I do?

[pcrmike]

If those eddy carbs are out of the box, I can bet they are too lean. I had a similar prob, and had to fatten them up some. :-)PCRMike

[ehostler]

Yep, I would say that you need to fatten up the jets.

[pcrmike]

Quickly. Before you damage the crowns and ring lands on the pistons. :-( PCRMike

[Jakke]

Yes carbs are Eddy's

I have lamba sensor and I have tuned engine to get richer mixture.

[pcrmike]

When you use a digital gauge with the stoichiometer (AF ratio) you need to have it solidly in the green (rich), but not maxed out, when at WOT. :-)PCRMike

[Jakke]

I think that fuel/air mixture is not the problem...

[pcrmike]

Okay, at that rate of compression, aluminum heads are good for the ratio, at that size of engine, the cam seems about right. Is it possible guys his plugs are a little on the hot side? Maybe a shorter tip? :-)PCRMike

[Dick]

Isn't anyone considering fuel quality/octane?

[aarracer]

Jakke

I would try some octane boost additive to rule out poor fuel .

Is the cam installed on it's reccommended centerline?

Cheers

AARRACER

[wilks3]

Can you even get 93 octane or race gas in Finland? Maybe try slowing the mechanical advance down some with heavier springs. Try a non-projected plug. I changed to NGK BR6S (stock #3522) eliminated what little ping I was getting.

[Jakke]

I use 99 octane fuel.

[ehostler]

If I recall correctly, you don't measure octane the same way we do. Plus, our blends cause different burn rates.

[Jakke]

Yes that is correct. Our 98 octane fuel matches your 93 octane fuel.

[BigBlockDude]

I have a built 440 ported iron heads, 9.5 comp, with same intake carbs. I have a Hughes cam, 228 232 @ .50, 524 540 lift. Would ping under a heavy load at around 2800-3000 rpm. As for the pinging I had to give it a short curve with stiff springs, so it comes in later. And about 30 degrees total timing. I have 17 initial now. It does not ping on 91. maybe try stiffer springs so full advance comes in at higher rpm.

[pcrmike]

Duh. Why didn't I think of that? A recurve for the dist would help a lot. (Now I feel stoopud) PCRMike

[cudabob496]

I don't know about detonation, but I would run a 180 thermostat, as your aluminum heads like heat. I did and my stroked 440 runs a lot better.

[Jakke]

Is it possible that wrong cam timing can cause detonation?

[aarracer]

Hi Jakke

Mother Mopar says, if you haven't installed the cam on the correct centerline, you CANNOT begin to diagnose any tuning problems correctly.
QUOTE "if you do not centerline your cam, then you do not get the full value of your investmentand and you probably won't achieve the desired improvement!
Obviously if you did not centerline the cam, you can not say for sure that your problems are with ignition or carb. Straight from "Mopar Engines Book" page 141/142!

Good luck

Cheers

AARRACER

[The_Dakota_Kid]

Have you verified true TDC with the markings on the balancer? I have had the stock ones slip, Also have you checked the accuracy of your timing light? That engine should NOT detenate @28 deg total timing. I have run that very same combo with the 84cc eddys with 92 octane pump fuel......this was with 32-34 deg total timing. I really think the guys are on to somthing, if the tdc checks out I would look into a lean condition.....does it surge at part throttle? I dont think changing the cams ICL will have a effect on the problem, unless its way out, in which you could tell in the performance.....Can youpost some pics of the plugs......I wouldnt run it any more untill this problem is resolved.....

[Jakke]

I will post some pics from the plugs and check those springs..

[Jakke]

I changed harder springs into distributor and detonation is gone.
Now max adv is 35 deg and no detonation.

Thank you all.