Tuning For Detonation

-
QuickDart360 said:
I have a similar issue with my hot 360. It will spark knock/detonate only after its driven for a while and in hot summer weather. Currently have rn12yc would rn9yc be a better choice? Otherwise car runs nice and crisp! Car has 3.91's out back a 9.5" FTI 3400-3600 stall converter. 292/508 mopar cam and higher compression kb107 pistons. Also 340 x heads.
Click to expand...
Where is the timing at now?
 
RustyRatRod said:
Maybe. Give me some more details. Cam specs, cranking compression number if you have it. Where is initial timing and total timing and when (RPM) does it get total timing? What intake manifold? If it's a dual plane, did you block the heat cross over?

In short, anything you can do to make the cooling system more efficient and to cool the intake charge will help a lot. Each individual step I took with mine helped. If I had to point to one step that helped the most, it was the thermostat.
Click to expand...
Yes sir! Timing is 15° timing and distributor is from Florida. Has timing limiter plate so total is if I recall 34 or 36°. Thermostat now is a Stewart 180° high flow all brass. Intake is a Victor 340 single plane works super! Cranking compression not sure.
 
QuickDart360 said:
meant distributor from FBO
Click to expand...

Can you get a cranking compression number? Without that, we're kinda shootin in the dark. And good on the Victor intake. You don't need manifold heat, so that's one less thing to do.
 
QuickDart360 said:
Yes sir! Timing is 15° timing and distributor is from Florida. Has timing limiter plate so total is if I recall 34 or 36°. Thermostat now is a Stewart 180° high flow all brass. Intake is a Victor 340 single plane works super! Cranking compression not sure.
Click to expand...

Oh and "how hot" does it run now? The hottest it gets. What's that number?
 
RustyRatRod said:
Oh and "how hot" does it run now? The hottest it gets. What's that number?
Click to expand...
I'll have to get back on that one. Inside temp gauge always shows 1/4 to 3/8 when its hottest day. I know probably not accurate. Radiator is copper/brass 3 row from The Paddock which is no longer around. Also distributor is still using vacuum advance. I hear some leave it off to help with knocking. Good idea?
 
carburetor is an 850 thermoquad that used to be on a race 440 Cuda. So its rejetted and no choke. Works good.
 
QuickDart360 said:
I'll have to get back on that one. Inside temp gauge always shows 1/4 to 3/8 when its hottest day. I know probably not accurate. Radiator is copper/brass 3 row from The Paddock which is no longer around. Also distributor is still using vacuum advance. I hear some leave it off to help with knocking. Good idea?
Click to expand...

The vacuum can very rarely has anything to do with detonation, because the vacuum drops off on acceleration. If you can get that cranking number, that'll help.
 
RustyRatRod said:
The vacuum can very rarely has anything to do with detonation, because the vacuum drops off on acceleration. If you can get that cranking number, that'll help.
Click to expand...
Actually I find it commonly does. If QuickDart is noticing detonation at light to mid throttle then yes its the problem of using vacuum advance with the FBO distributor's advance curve. A few of us have had similar issues with the MP distributors that used the YH advance.
If it only occurs when the throttle is at the floor or nearly at the floor, then yes it probably has nothing to do with vacuum advance.
Between half throttle and nearly full throttle its a toss up and having a vacuum gage and a knowing what the advance curves look is one way to pin it down.
 
My 340 @9.5 cranking only 155psi would momentarily ping if I abruptly stabbed the throttle from a cruise with vac advance hooked up @48. The vac advance cant drop off enough/in time for the big gulp of a/f and just a for a second.. makes what sounded like a single ping then it was good.
It was a 90's mopar replacement, not a performance adjustable type, made by Mallory for mopar and there were some bad ones that also were out of phase with the cap and spark scattered lighting off multiple cyls causing piston skirt scuffing in no.5 at or near bdc.
 
Last edited:
RustyRatRod said:
The vacuum can very rarely has anything to do with detonation, because the vacuum drops off on acceleration. If you can get that cranking number, that'll help.
Click to expand...
Not fast enough. It gets caught halfway home n bit in the *** by an unleashed dog called detonation.

I didnt realize you were running vac adv.
 
Instead of guessing on these 'Dizzy', find an old shop that has a Sun Dizzy machine and run it in.

Its like Guess 20 times or Spend $50 and know. I found a shop that had one. He showed me how to use it and allowed me to set the advances, go test it on the car and come back and tweek it for $50. I used one in Community Collage so I had the basics already. This was before the FBO plates so I was welding the slots and grinding. Changed many springs and a few advance cans too.

SunMachine.jpg
 
Last edited:
Mattax said:
Actually I find it commonly does. If QuickDart is noticing detonation at light to mid throttle then yes its the problem of using vacuum advance with the FBO distributor's advance curve. A few of us have had similar issues with the MP distributors that used the YH advance.
If it only occurs when the throttle is at the floor or nearly at the floor, then yes it probably has nothing to do with vacuum advance.
Between half throttle and nearly full throttle its a toss up and having a vacuum gage and a knowing what the advance curves look is one way to pin it down.
Click to expand...

Right, it's possible at part throttle. I need to reprogram that everybody might not have the same issue as I do. Mine only did it when the gas was plowed into real hard....kinda like what you'd do to a disease free pre plastic surgery young Pam Anderson.
 
RustyRatRod said:
I agree. I've read over and over slants don't like a ton of total timing. I really wanted to try about 20 initial and 30-32 total, but the plate is not offering that, even though it's marked to give those results. I have an email in to Don so we'll see what he says.
Click to expand...

My experience on all the FBO plates I have had. They are not really very accurate on the numbers you are getting the best I could get on my /6 and 2 small blocks. 10 was really more like 15.
 
Bewy said:
'One thing to understand is that detonation is not necessarily destructive'

And...

'If you've driven a car that has a lot of spark advance on the freeway, you'll hear it pinging. It can run that way for thousands & thousands of miles.'

These quotes are from a multipage Detonation/Pre-ignition article written by GM engineer A. W. Cline in 2000. You should be able to find the full article on the net.
Click to expand...
Good Gawd! Genital Motors...the same "4100" GM? The same CMPI GM? I could literally do about a hundred of those. We're not talking "100deg adv., 20:1 A/F extreme CAFE" retardedness here. Full-power detonation has killed more engines that actually make enough oats to kill themselves than anything else save poor building/parts.
 
Jim Kueneman said:
My experience on all the FBO plates I have had. They are not really very accurate on the numbers you are getting the best I could get on my /6 and 2 small blocks. 10 was really more like 15.
Click to expand...

Thanks for the input, Jim! I'm glad it wasn't "just me".
 
yellow rose said:
The MSD bushing ain’t worth a crap either. Several times I’ve had to make my own because I couldn’t get what I wanted with the several packages of bushing I have. Just straight crapola.
Click to expand...
@crackedback Rob offers some of those that MSD does not if you need some.
 
Doing OK on recovering. Just slow and still not allowed to lift anything.
 
You must log in or register to reply here.
-

Back
Top