Low RPM/High Load detonation
May 6th, 2011, 06:54 AM
#41
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I only pops at idle, or it did before the plug change...The idle is still just a bit rough but much smoother than before.
Doesn't the 160psi cranking pressure with a mild cam indicate moderate compression? Could it be too high?
Doesn't the 160psi cranking pressure with a mild cam indicate moderate compression? Could it be too high?
May 6th, 2011, 08:06 AM
#42
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I used to have this missing/popping condition at idle only. It's all but gone now with new, colder park plugs.
I guess I won't know for sure where my A/F ratio is until I install the A/F gauge...or at least eliminate it as a couse.
Peter
I guess I won't know for sure where my A/F ratio is until I install the A/F gauge...or at least eliminate it as a couse.
Peter
May 9th, 2011, 05:19 PM
#43
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Location: Columbus, OH
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My stock 425 is doing the same thing. I spent most of the day today putting and HEI system in it and getting it to run right. Its worse off than it was with the points. Ive tried everything i can think of. I had new fresh rebuilt mechanical quadrajet. Ive been talking to some guys and one suggest that he had seen a stretched timing chain that caused the distributor to do some funny stuff. Maybe ill try a chain but will like to hear what your fix is.
May 9th, 2011, 10:00 PM
#44
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No fix so far... colder plugs make no difference. I guess it's not pre ignition due to hot plugs glowing. I've noticed uneven plugs though. One is all carbon covered, black, and one is as if out of the box...the rest are OK. I don't know what the reason is.
I replaced my chain just recently. The idea was maybe the valve timing was off.
I also tried different coils, modules, wires, complete distributors....all the same.
Right now I drive with a TV cable bracket adjusted so that the kickdown from 3rd comes in earlier. Kinda helps but not always...It never knocks when in 1st or 2nd at high RPM... or in Drive on the highway at 80mph when I floor it. Only when I punch the gas at low rpm and the transmission in 3rd.
I replaced my chain just recently. The idea was maybe the valve timing was off.
I also tried different coils, modules, wires, complete distributors....all the same.
Right now I drive with a TV cable bracket adjusted so that the kickdown from 3rd comes in earlier. Kinda helps but not always...It never knocks when in 1st or 2nd at high RPM... or in Drive on the highway at 80mph when I floor it. Only when I punch the gas at low rpm and the transmission in 3rd.
May 9th, 2011, 11:12 PM
#47
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I'm just saying...you said you have a detonation problem but now we're finding out it's only when you punch it in 3rd gear at a low speed. Your 2.45 gear and a 1:1 ratio (3rd gear) don't make a good combination at low speed, you're bogging the engine down. No matter how little advance you have you're ASKING the engine to pop up to 2500-5000 rpm but the gearing won't allow it.
May 10th, 2011, 03:44 AM
#48
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What is going on, engine load wise, when it shifts? Is there a momentary increase in load? If so, I guess the stiff gearing is the reason...
I have almost eliminate the low rpm detonation by adjusting the detent cable. It will downshift sooner now. It still knocks as the transmission shifts if I give it too much gas from a stop though.
I have almost eliminate the low rpm detonation by adjusting the detent cable. It will downshift sooner now. It still knocks as the transmission shifts if I give it too much gas from a stop though.
Last edited by 455Eldorado; May 11th, 2011 at 09:56 AM.
May 10th, 2011, 08:33 AM
#49
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Here's the latest....with low initial timing, stiffest springs (blue) from the Crane kit and lots of vacuum advance connected to manifold vacuum...and re-adjusted TV cable...it runs without detonation so far (moderate driving). I haven't tested it up the hill yet though. I don't have the timing numbers, I did it by "ear" but my guess is I have less than 10° initial, the centrifugal starts at 1000rpm or so, and about 20° of vacuum advance for smooth idle. I had to use the Crane advance unit. That way I can adjust when the advance pulls unlike some other units where you can only adjust the amount of vacuum advance. In my case it works best if I adjust it to add advance sooner (with lower vacuum). That way I compensate for the late centrifugal advance...
It's not the best setup performance vise but not bad either...
It's not the best setup performance vise but not bad either...
Last edited by 455Eldorado; May 10th, 2011 at 08:36 AM.
May 10th, 2011, 04:15 PM
#53
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If you've got a cam with a usable range that starts at 1200, and a 2.41 (or whatever - I forget...) rear, then you need a converter with a higher than stock stall.
That's why you take the whole car into consideration when deciding on a cam.
- Eric
That's why you take the whole car into consideration when deciding on a cam.
- Eric
May 10th, 2011, 09:33 PM
#54
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The cam I have is very mild, I picked one for "towing power" because of the setup I have from a 350diesel. Usable range starts at 800RPM...and the converter has a stall speed just slightly higher than stock...
The car doesn't knock now at low rpm/high load. But it still does so at shift points. Moving the shift points higher ( it now downshifts sooner) also makes the transmission to shift at higher RPM (upshifts) when I hit the gas from a stop.
I'll try to find another final drive unit from 82-on with 3.xx gearing...
But than again, how come the 2.41diff. works with stock Olds 350 gas engine and Cadillac 6liter? Toronados and Buick Rivieras also use same differentials...
Peter
The car doesn't knock now at low rpm/high load. But it still does so at shift points. Moving the shift points higher ( it now downshifts sooner) also makes the transmission to shift at higher RPM (upshifts) when I hit the gas from a stop.
I'll try to find another final drive unit from 82-on with 3.xx gearing...
But than again, how come the 2.41diff. works with stock Olds 350 gas engine and Cadillac 6liter? Toronados and Buick Rivieras also use same differentials...
Peter
Last edited by 455Eldorado; May 10th, 2011 at 11:15 PM.
May 11th, 2011, 03:09 AM
#55
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Well, that all sounds right, then, which brings us back to whether you've really got the compression you think you have, and whether that cam was really ground the way the manufacturer claims.
It's a pain in the butt, but I kinda wonder whether putting a stock cam back in would fix the problem, regardless of what the company says on the cam card.
- Eric
It's a pain in the butt, but I kinda wonder whether putting a stock cam back in would fix the problem, regardless of what the company says on the cam card.
- Eric
May 11th, 2011, 10:34 PM
#57
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Actually, it is not exactly a 260H, it is a custom grind that derives from the 260H. I can't remember the duration values (similar to 260H) but the separation lobe is 112°. The CompCams came out with this cam to cure the condition. It runs very well, got rid of the smell, pulls strongly, idles smoothly, it's just this detonation that occurs with no previous warning. I don't get any "pinging" sound at any condition (pinging as a rattle or metalic sound). The detonation I have feels more like driving over a big hole on the road...It goes away as soon as I take my foot off of the accelerator.
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