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pinging under light load

10K views 56 replies 13 participants last post by  jimmywray600 
#1 ·
I am using MSD Streetfire ignition, I have 10 degrees base timing, 12* vacuum advance and 24*mechanical. Timing curve is all in at 3900 rpm which seems slow to me but at 2000rpm it is at 29* which seems to be quick, I would like to try and have the mechanical advance all in sooner but slower, anyone had this problem? I tried disconnecting the vacuum advance and the pinging was the same. It only seems to do it at low rpm under light load maybe it a bit lean transitioning into main jets, I will richen the idle circuit a little but I dont expect any change.
 
#2 ·
Compression ratio? Piston to deck clearance, head gasket thickness? What octane fuel are you using?
 
#3 ·
More info on engine, please. Sounds like the timing might be close, if not OK, and carb too lean. More info should help.

The questions above should establish the quench distance, which can have an adverse effect on things like pinging if it is radically wrong. If this is a new rebuild, the engine builder should know these things.
 
#9 ·
I had a fuel hose with a kink so fixed that but still pinging, I then released the fuel cap to make sure it had no vacuum and it was still pinging.
Maybe I should try bigger jets in the primaries? it is a 383 SBC with holley HP 750 carb, roller cam and AFR Aluminium 195 heads. If it is a lean condition I assume that it would ping regardless of how the timing is set? I will take the tank off soon to check that end out then maybe increase jet size or colder plugs, it is driving me mad!
 
#12 ·
If you are pinging at light load with only 29 or so degrees timing in something is way off the mark someplace.

Most well thought out N/A engines on pump gas will like closer to 40-50 degrees timing at light load (initial plus mechanical plus VA).

Of course this assumes ideal engine temps, tight squish, decent to excellent combustion chamber shapes....etc.

Do you have the cam specs of copy of the cam card?......
 
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#13 ·
You probably aren't on the mains at low RPM and light throttle either so jetting up isn't going to help. I'd pull the metering block off and blow air through all the passages just to rule the carb out but I don't think the problem is in the carb.

Unless you've made some modifications there is no way a Holley HP is lean on transition.
 
#14 ·
Your curve info is good for the most part. the late total mechanical is workable with the weights you are running, but is touchy to attain, because it involves "tailing" the straight ramps of the weights.

Tailing is adding a curvature to the end of the straight ramp of the weights, and is touchy to do, best with a bent sander, slowly, a little bit at a time. having a NON-DIAL BACK timing light and degree'd balancer will help.

Depending on the amount of metal removed to make the actual tail, the curve speed is increased, even when the springs are not changed.

Please remember, these mods are only for changing (speeding up) a part of the upper degrees available from a set of weights and center.

Weights 1 is a three set cuts info picture, stock, small change, then more degrees faster as rpm's rise above a certain point. Weights 2 are all 3 weights stacked on each other, pay particular attention to the straight part of the weight that interacts with the center plate. The more curvature, the faster the degrees activate as rpm's rise. It is possible to do this so the rate speeds up for only a very small amount of the actual curve.
 

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#16 ·
All depends on a few things.

Engine operating temperature, cast iron block, aluminum heads, 195 deg/F.

Timing curves and applications

Quench distance, if it isn't within the spec, expect pinging from lack of proper fuel mixture management and placement, in the upper ring, and quench areas

I have fixed engines that were extremely nicely built, proper just about everything, but too much, too little quench distance, and NOTHING stopped the pinging (and in most cases, over heating), UNTIL the quench distance was rectified.

Carburetiion wrong (too lean) in one specific area of the fuel curve
 
#21 ·
Complicated the first time, but, quench is easy to check with heads on.

With engine stopped, all spark plugs out, bring one cylinder close to TDC by rotating engine over by hand using breaker bar and socket on balancer center bolt.

Then, using dead soft plumber's solder, bent into a gradual 90 degree bend, insert the solder into a spark plug hole.

hand run the piston up and past TDC. Remove solder and measure existing quench distance.

Usng a .027 head gasket, and zero deck on the pistons, you would expect the .027 quench. Proper quench would be between .039 and .045.

So, with the .027 head gasket in place, the piston deck should end up being .017 down in the bore to get the right maximum quench.

Math:

.027 + .020 = .047 quench

.027 + .018 = .045, maximum quench

.027 + .012 = .039 minimum quench

There are variables, in that a company named Silv-O-Lite (still in Carson City, Nv) makes what is called a "De-STroked" piston for these engines. These particular pistons have the normal compression height (distance of the pin to the top deck) altered to ADD .020 to the stock compression height dimension. So, assuming what GM used, an .025 c/d, and the DeStroked pin position, the c/d would end up roughly .045 down into the bore at TDC.

It doesn't take much to figure out that the DeStroked piston makes it impossible to fit any head gasket to that engine and come out with a proper 1quench distance, as there have never been .000 thick head gaskets made.

For info, most GM engines used a compression height of between .020 and .025. This, added to the steel shim head gaskets they used on those engines, made the proper .039 to .045 quench, bolt it together. The problems started in two waves, the DeStroked pistons were first, then second, pack type ultra thick head gaskets. Assume a stock deck of .025, plus not the shim gasket, but a pack type of .055 thick, quench becomes a deadly .080. The DeStroked height down the bore, of .045, and the .055 head gasket made the quench an even more deadly .100 inch, PING CITY.

Why would they want to mess the quench up? Lack of knowledge, and to lower the compression ratio, to stop the pinging. IT NEVER WORKED, just made the situation far worse.

What was figured out to do was a nice end run, "ZERO DECK". A few savvy ngine builders thought to revise the thinking, modify the head gasket deck on the block to bring a stock c/h piston to be equal with the gasket surface, Zero Deck. then, select the pack gasket that makes the quench correct. ) deck height, .042 thick head gasket, perfect quench, done, works.

Getting the quench correct within its variable is essential to stop pinging in an engine that has disasteros quench. Engines with cast iron heads that are set to have the proper quench can usually run a half point more static compression than ones that don't. Aluminum heads and correct quench, usually, three quarters of a point of static compression.
 
#23 ·
Complicated the first time, but, quench is easy to check with heads on.

With engine stopped, all spark plugs out, bring one cylinder close to TDC by rotating engine over by hand using breaker bar and socket on balancer center bolt.

Then, using dead soft plumber's solder, bent into a gradual 90 degree bend, insert the solder into a spark plug hole.

hand run the piston up and past TDC. Remove solder and measure existing quench distance.

Usng a .027 head gasket, and zero deck on the pistons, you would expect the .027 quench. Proper quench would be between .039 and .045.

So, with the .027 head gasket in place, the piston deck should end up being .017 down in the bore to get the right maximum quench.

Math:

.027 + .020 = .047 quench


.027 + .018 = .045, maximum quench

.027 + .012 = .039 minimum quench

There are variables, in that a company named Silv-O-Lite (still in Carson City, Nv) makes what is called a "De-STroked" piston for these engines. These particular pistons have the normal compression height (distance of the pin to the top deck) altered to ADD .020 to the stock compression height dimension. So, assuming what GM used, an .025 c/d, and the DeStroked pin position, the c/d would end up roughly .045 down into the bore at TDC.

It doesn't take much to figure out that the DeStroked piston makes it impossible to fit any head gasket to that engine and come out with a proper 1quench distance, as there have never been .000 thick head gaskets made.

For info, most GM engines used a compression height of between .020 and .025. This, added to the steel shim head gaskets they used on those engines, made the proper .039 to .045 quench, bolt it together. The problems started in two waves, the DeStroked pistons were first, then second, pack type ultra thick head gaskets. Assume a stock deck of .025, plus not the shim gasket, but a pack type of .055 thick, quench becomes a deadly .080. The DeStroked height down the bore, of .045, and the .055 head gasket made the quench an even more deadly .100 inch, PING CITY.

Why would they want to mess the quench up? Lack of knowledge, and to lower the compression ratio, to stop the pinging. IT NEVER WORKED, just made the situation far worse.

What was figured out to do was a nice end run, "ZERO DECK". A few savvy ngine builders thought to revise the thinking, modify the head gasket deck on the block to bring a stock c/h piston to be equal with the gasket surface, Zero Deck. then, select the pack gasket that makes the quench correct. ) deck height, .042 thick head gasket, perfect quench, done, works.

Getting the quench correct within its variable is essential to stop pinging in an engine that has disasteros quench. Engines with cast iron heads that are set to have the proper quench can usually run a half point more static compression than ones that don't. Aluminum heads and correct quench, usually, three quarters of a point of static compression.
It is a complicated subject for sure, my block was decked but pistons still in the hole, I was aiming for perfect quench and got very close to the numbers you quoted, I think I have a lean issue and suspect the power valve is not opening quick enough
 
#22 ·
Ok the UK.So fuel octane in Europe and the UK is measured by a different system then over here in the USA.That's why 95 octane and aluminum heads are still experiencing pinging for you.Can you use an octane booster or is it not legal ? Check out this thread some good information about octane booster to help with shoddy petrol issues.

https://www.chevelles.com/forums/13...upreme-130-real-lead-octane-booster-back.html
one more to read
https://www.chevelles.com/forums/13-performance/733130-does-104-octane-boost-go-bad.html
and one more
 
#26 ·
I understand on the quench. The process is easy, once you have done it.I would school a firs timer to find a shop with an engine out of the car to learn the process from. A lot easier than leaning over a fender, etc. Becomes second nature after a couple of times. Even novices figure it all out.

Seriously, if the quench is out, and even if it is the only thing out, it can make for very frustrating issues not easily fixed, if at all.

YES, good call, do check the TDC, there are a few different timing scale to balancer combo's.

I agree, more than likely it has a lean issue, BUT, quench and timing must be correct before carburetion can be properly set.

Persevere, check the other stuff, confirm it, fix if needed, then go on to the carb.
 
#28 ·
Timing is set very conservatively, quench is as tight as I dare, I know the fuel is not terrific but my other motor runs okay, I did wonder if the roller cam causes the engine to gulp more air or if the power valve has been changed, I think they are 6.5 as standard I will open it up and see.
 
#29 ·
Respectfully, there is "no dare' in quench, it has a specific zone it needs to be in, or problems WILL ensue. .039 to .045 is the zone. Doesn't matter the engine, that is the spec to use.

Case in point, some years ago, about 3 decades ago, a friend of mine asked me to look into the pinging his 1959 Datsun 4 door (looks like a Tokyo taxi cab) had, that he couldn't get rid of, no matter what. It has a Ford 302 engine in it, and they are as good, when done right, as any other engine, including our small block Chevy.

I took the engine completely apart, measuring as I went, engine was assembled with good parts, very nice jog. ONLY problem was, pistons were Silv-O-Lite "Destroked" units. these pistons were made with the piston pin bore another .020 up the piston, to lower the deck another .020 down into the bore. This made the pistons sit .045 down in the bore. The head gaskets were pack type, .055 thick. This gave a quench distance of .100, way too big. He tried everything, different ignition curves, timing settings all the way back to TDC, jetting, name it.

The destroked pistons, and thicker pack type head gaskets ere designed to lower compression ratio, to run California low (miserable) octane fuels. What should have happened was to use a better piston with stock compression height, zero deck the block, and select a pack type head gasket between .039 and .045 thick.

Only thing wrong with it was the quench distance.

I did nothing more than have the block decked to zero deck for the destroked pistons, and put it back together with only a new gasket set with .042 head gaskets, no other mods, changes.

The engine still runs well, no issues, even on California disaster 87 octane unleaded, no pinging.
 
#30 ·
Threads like these are great. I learn so much reading them. :thumbsup:

The 327 I'm currently building has a quench of .044 thanks to Dave's willingness to share info. Standard deck, pistons .024 in the hole with .020 Mahle steel shim gaskets. I read Dave's advice on several older threads & he spent 30 minutes on the phone with me when he converted my points distributor to an HEI. Before that, I would've been content to use standard .041 Felpro MLS gaskets in the full gasket set. My 11:1 L79 with domed pistons would've ran like a dog & I never would've figured out why.
 
#31 ·
Usually pinging under a light load, such as starting up a grade, etc, tends to be either too much ignition lead..many times vacuum advance, too lean, too much compression / poor quality fuel or a combination. You indicated you had tried disconnecting the vacuum advance with no improvement. Any changes in power valve pretty worthless as these are intended to kick up the power circuit, if correctly chosen, and when we are driving we hopefully are driving on the cruise circuit and off the idle circuit and not yet into the power circuit (enrichment circuit). Does the pinging go away when you transition from the cruise circuit to the power circuit ( i.e. when you jump on the throttle ?). How do your plugs read ?? Carbon build up in the cylinder, mechanical issues such as pre-ignition from wrong head gasket, hot spots in the cylinder from poor combustion chamber shape, wrong reach plugs, etc. Do you want to try a thicker head gasket to see if lower compression helps ?? A few more variables to consider...FWIW. May wish to look up "lean throttle tip-in". GOOD LUCK
 
#32 ·
I said it earlier and it bears repeating- if you haven't made any changes to the IFR and/or the IAB and the carb doesn't have any blockages, there is no chance a 750HP is lean on the transition circuit.
 
#33 ·
Just thought of something,what plugs are you using ? AFR calls for a 3/4" reach, 14mm, gasket seat spark plug.Using shorter plugs will leave plug threads exposed causing problems.
here's AFR's recommended plugs :
From AFR site: Tuning and application/usage significantly influence the necessary heat range for optimal performance. Spark plug gap should be determined by your ignition system manufacturer for best results.

- 3/4" reach, 14mm, gasket seat

- Autolite #3924 or equivalent for normally aspirated, pump gas engines with a compression ratio between 9:1 and 11:1

- Autolite #3923 or equivalent for compression ratios between 11:1 and 13.5:1 or mildly boosted(8-12psi) applications running Race Gas

- Autolite #3922 or equivalent for engines with high compression, between 13.5:1 and 15:1, or high boost(10-18psi) applications running Race Gas
 
#35 ·
driver side spark plugs are all very sooty apart from cylinder #5 which is clean, I done a cranking compression test and got #1 @160, #3 @175, #5@175 and #7 @185. When idling the vacuum gauge flickers rapidly around 12". something appears to be different in cylinder #5, I am leaning toward a vacuum leak in the valley but want to rule everything else out first, the distributor cap looks good with less that 100 miles on it, wires are new but could be leaking to earth somewhere. it is making a pinging sound at WOT under load even though it is very rich and running 32* total timing, I am thinking it may be lean on one cylinder? would a stray spark create similar symptoms? one clean plug and the rest are sooty? I have already changed the plug.
 
#38 ·
If any of the wires are arcing to ground and/or one cylinder is misfiring then that plug would be gas wet,sooty but not white.Plugs that are white or light tan are lean.A good firing plug of the correct heat range will have a light brown color.
 
#36 ·
an update for anyone who is chasing similar problems, I fitted 73 jets and went on a cruise trying to not hit the gas pedal too hard. the result was #5 plug was white as snow but three other plugs were a bit cleaner than the rest, #7 #2 and #8, all these cylinders are fed from the passenger side plenum of the dual plane manifold I have, so as #5 is the whitest that has to be where the leak is right? I taken off the manifold and checked everything for flatness, sat it in there with no gasket and all looked fine, I notice that two of the bolt holes in the manifold have marks at the upper edge where the bolt threads have gouged in, it was only two of them but to be sure I elongated all the holes .030 toward the outside edge, put it all back together now waiting to road test, I suspect the bolts binding in the holes prevented the gasket sealing properly, will update after road test.
 
#37 ·
Just as a last post for me here, I would like to explain why quench is so sensitive.

Engines are quite a bit like human beings, and...robots, all combined as one disaster of an entity, metal, mineral, fluid, and a lot of other stuff with minds of their own, expected to act as one mind and body.

Quench is essential for piston deck cooling, and top ring sealing and cooling, when it is not correct, the engine suffers, pinging, detonation as a worse situation, cooling temp issues, the works.

But, the worst thing that occurs is heat expansion, not only in selected areas, but in all facets of operation, full engine. Take the actual physical sizing of the engine as it runs, and attains its heat. Ever changing, and final operating temps are a set deal, cast iron, 180, cast iron block/aluminum heads, 195, all aluminum, 200 deg/F. Not even running engine temps, like 160 on a full cast iron engine, will stop the physical "growth" of an engine, and clearances change as the temps change. Especially the crankshaft center to head deck length.

Lets look at this one, piston down in the bore .007, head gasket .027, total, .034. Too tight, mixture is pushed out of the quench areas, leaning them to detonation, or, less, pinging. Quench is designed to work with a heat expanded metal part assembly, change that final distance, or, area it should be operating in, problems endue. No engine stays at the cold set quench once it gets up to operating temperatures.

So, if the quench is off dead cold, it will be off when the engine is at full temps, no matter the engine temperature it is running at. Too cold, quench is also too small, too hot, quench is too large. At an incorrect operating temperature, amnd incorrect quench, that engine can be so far off, it isn't funny, and that no funny converts to the issues discussed in this topic. YES< other factors do come into play, and they all are as important as quench, but quench has caused more problems not easily solved than other issues.

Most of the changes I read about this engine are crutches to the hot engine quench not being correct. Thoise changes, such as 160 degree thermostat, really didn't help as much as thought.

Have a great day, everybody, I am going for my afternoon snack.
 
#39 ·
I was hoping to come back with good news, the plugs which are fed from the passenger side plenum of the dual plane manifold are still much leaner looking than the rest, #5 is pure white.
As #5 is the leanest by far I assumed that any vacuum leak is nearest to that cylinder, as I have just swapped the gaskets I thought I would test it, I fitted a plate on the manifold with an air line fitting in it, took off the valve rockers and connected the airline at about 10 psi and listened for the leaks, this proved inconclusive so I connected it to my vacuum pump, I pumped it up to 12 inches and it held pretty good, it took about 30 minutes to leak down, I am now thinking it is an issue with the carburettor, passenger side as cylinders 2,8,3 and 5 are leaner than the rest, blocked orifice ? Maybe the valve on #5 does not operate correctly when the engine is running, thus causing the other cylinders that share the same plenum to indicate lean also. The photo is plug #7, 5 and 3 from left to right
 

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#49 ·
Those white plugs sitting right next to plugs that are almost normal looking plugs are a classic picture of lean cylinders V. good cylinders plugs.Its great that you figured it out and just as great is that you posted back saying you fixed it. :hurray:

I am reasonably convinced that my ignition is not at fault so will start a new thread elsewhere
I should have verified my timing mark was correct, I had painted what I thought was the timing mark with white paint, it turned out that because I didnt have my reading glasses on I marked the wrong place, to confuse the matter the holley carb had a faulty metering block, air bleed on one side was oversized giving me lean plugs, it wasnt the lean condition causing the pinging it was the goofed up timing, after much messing about I went back to basics with a piston stop, the metering block was a little harder to diagnose, I had that off dozens of times before I noticed the oversized air bleed, I hope my mistakes are a help to others. It was a fresh build, I thought I was looking for one fault not realising that there was two faults.
I have a question about your balancer. About the balancer was the area that you painted and confused for the TDC mark a wide 1/8th inch cut in the outer ring of the balancer ?
 
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