I have a problem with A small block I recently put together. I'd like to get rid of the ping without having to go back in an put dished pistons in. When I told the engine builder what I was doing he was confident that I would have a compression ratio at or below 10:1.

After getting it put together I initially had a problem getting more than high 20s total advance. I set initial timing at 17 degrees and it ran fine, total advance at about 32 degrees. Since the temerature had gone up I started getting a ping under initial load. I backed the timing off to 15 and that helped a little. I then backed it off to 12 and found that total advance was now about 32 (perhaps the distributor need to break in a little). The ping is now hard to detect but now the engine bogs on initial load unless I start out at a highter RPM.

I recently went back and checked the CR with the calculator on here and it's telling my I have about 11:1.

Here is what I have:
Bore 4.030
Stroke 3.48
Cam Crane 272
Carb Holley 670 cfm
Intake RPM Airgap
HEI Proform
Gasket Felpro .041 (I believe)
Exhaust Stock Iron
Converter 2,500 Stall
Fuel 92 octane

I've thought about putting thicker head gaskets (.060) on and I've been told to try replacing the weights in the distributor.

Does anyone else have any better suggestions or comments on the above ideas.

TIA

Bob

You could lower the compression with larger chamber heads as a last resort. What heads are you using? Put the old distributor back in and see if that helps. The new one may be too aggressive for your combo.

What pistons and what is the chamber size? What is the LSA of the cam? Was the block decked? There is some info on Dynamic CR linked in my sig that might be helpful.

Sorry, I thought I had 64cc chamber vortecs up there. They have the "upgraded" springs and 1.5 rockers.

The cam card says: intake 27/65 & 272
Exhaust 67/25 & 272

Th timing section reads

Opens Closes Lift Duration
intake 3 BTC 33 ABDC 105 ATDC 216
exhaust 43 BBDC (7) BTDC 115 BTDC 216

It is a hydraulic cam.

The block was not decked.

T-man the old points distributor is much too worn out to be of any help.

Thanks

What kind of pistons, cast, hyper, or forged? I'm guessing you put flat tops in. With the gasket you specified (.041x4.166), a .025" deck, and 6cc valve pockets, I get 9.6 for the CR. With a 272º, 110º LSA cam advanced 4º (106 ICL), the DCR is 7.86. This DCR should not be a cause of any detonation issues.

One problem, but I'm not sure that is the cause of your problems, is the quench distance of .066". If the pistons are cast rebuilder type pistons (which are .020 short on pin height) the quench is .086". A wide quench distance like this could cause a pinging problem.

The bogging may be related to the pinging issue. More than likely the accelerator pump needs a larger squirter and some tuning. The pinging could also be caused by the carb being too lean. Try richening it up a couple jet sizes and see what happens.

In your situation, I'd say the most probably cause of pinging is either a lean condition, or too high of water temps, or both. That's where I'd start. The wide quench could be a cause, too. You could install a Fel-Pro .015" (x 4.100") shim gakset to correct the quench distance (provided you have the correct pin height pistons or the help out if the pistons are cast).

You should look at the distributor, too. It may need to be re-curved to get it right. If you get 32º total with both 17º initial and 12º initial, there appears be a problem with the distributor. With vortecs, about 34º total is about all you should need.

If you’re running a vacuum advance dist. try running it without and see if the ping goes away. If the vacuum advance is too high it will cause pinging on acceleration
32 degrees is pretty mild it shouldn't ping at 10:1 the bog sounds like it's from too little initial advance I would think 15-20 would be in the ball park then limit the total from there.

also to add...........need to graph your timming curve........go from idle till the total.........see if you have any spikes in sudden timming increases it should be a nice gental curve..........

i ran into this problem last summer my timming was good at idle and total...........but i never checked the curve..........i was doing everything to cure my problem even lowered the compression to 8.8 from 10.2 to still have it ping...........last thing i did was graph the curve and my problem was there along............it was spiking at 2000 rpms and thats were all my pinging started at............so this might be something to look into as well and maybe get a better dist. set up .............

figuring 4.03 bore, 3.48 stroke, .025 deck, .041 head gasket, -6cc valve notches in flattop piston and 64cc head I get about 9.7:1. Personally, my limit for street engines with iron heads and a small cam is 9:1. You can try to tighten up the quench a little by installing a thinner head gasket, but that also raises the CR some too. As I get it the new CR would be around 10.2:1. I don't know if the advatages of a tighter quench is going to offset gaining 1/2 point of CR or not. I wouldn't bet any of my own money on it.

ddeennis has a pretty good point about doing a detailed chack of the timing advance curve, I'd do that first. Can you check to see that the timing marks are right? It really at TDC when the zero mark lines up on the pointer? DO you have a dial-back timing light or a timing tape on the balancer?

Tom

While your fiddling with it Bob, check the plugs. If it isn't the curve as mentioned about, suspect your Holley is much too lean. Put a 105 PV in front and jet up just a freckle, AFTER the plugs confirm a lean reading.

OK, thanks all. I'm out of town until Friday. I'll see what I can do this weekend and get back to you folks with the results.

OK, I regapped the plugs to .45 and set timing back up to 17. With vacuum plugged total advance goes to about 35 degrees. I took the rpm up and saw no spikes in advanced timing. It appeared to go up smooth. (balancer is marked 0 to 50) With vacuum hooked up total timing goes above 45.

I drove the car with vacuum plugged and had no ping and only slight bog.

Any more suggestions?

I'm trying to eliminate the outside causes before I resort to pulling heads.

Thanks

You still haven't answered Pat's question.
What piston do you have? A part number would be nice. ;)
As was stated the rebulder pistons are "destroked" .020 which really screws the quench up with an undecked block.
They can end up about .050 in the hole.

Could you get a read on the plugs, or were they clean? Don't you think it can be attributed to the carburetor? I would jet up +2 and throw a higher rated power valve in, or at least increase the squirter size, as Pat mentions.

The floats are adjusted correctly, yes? Sometimes, the simplest things go overlooked...

I don't have an answer on the pistons except they are Hyperutetics. I'll have to check on them Monday. I didn't put bottom end together, just the top. Engine shop will be open then.

Gene, I think the carb might be right after the figuring out what to do about the dist. The plugs looked OK (nice and grey). I've got no black smoke from it but this motor does run warmer than the one I took out. I'll show you next week in Nashville.

You wouldn't get any smoke (unless disaster struck :( ) from a lean carb. A lean condition will make the engine run hotter than it should.

Bob, You have mail.

It's dreadfully hard to diagnose something like this over the internet , isn't it? Such a number of things it could be, including a dynamic compression ratio much too high ( although it doesn't calculate high???)

Certainly seems like a mis-metering carb, or weak ignition.

Well, I spoke to the engine builder and he told me the pistons were Seal Power/Speed Pro H345P Flat Top Hypereutectic pistons. He estimated CR at about 9.7 with 64cc heads. The block was not decked and he estimated the quench at between .20 and .25. (he put it together a few months ago) He suggested trying octane booster.

While I'm not having the problem right now. I'm going to start with having the dist. recurved and larger jets as been suggested. The little adjustments I've made have helped a great deal.

Thanks for all your suggestions, I'll keep you posted.

Bob, FWIW those pistons are listed in the SP catalog as having a minus 5 cc volume, due to them being a flat top with valve reliefs. The catalog lists a 9.24 CR with 64 cc heads (std bore-overbores slightly higher). The CR can vary though with actual deck height, head gasket thickness, and ACTUAL cc of the head comb chamber.

I get 9.72 SCR. You said the block was not decked so the deck height should be 9.025 with the pistons down the holes .025". Add the .041" gasket and you have a quench distance of .066". This could be the cause of the pinging. You can read up on quench here (http://www.speedomotive.com/Building%20Tips.htm). You could use a Fel-Pro .015" shim gakset to get the quench distance to .040". This should help.