421 pontiac PINGING, need help!

[1939coupe]

The Total Timing on the engine is 36 deg. 6 initial and 30 centrifical.
As for the Vac advance can, right now it addind about 6 deg. and I have it connected to Manifold Vac. I runs cooler at Idle this way.
Randy

[Bruce Dorsi]

The Total Timing on the engine is 36 deg. 6 initial and 30 centrifical.
As for the Vac advance can, right now it addind about 6 deg. and I have it connected to Manifold Vac. I runs cooler at Idle this way.
Randy

=====================
As you probably know, there are adjustable vacuum advance mechanisms on the market.  
....Perhaps, more vacuum advance and late centrifugal advance will eliminate the light-load ping, without affecting full-throttle performance??

I think there are also after-market ignition boxes that can use a knock-sensor to retard timing when needed.

It all boils down to how many $$$ you want to throw at the problem.

[C9]

The Total Timing on the engine is 36 deg. 6 initial and 30 centrifical.
As for the Vac advance can, right now it addind about 6 deg. and I have it connected to Manifold Vac. I runs cooler at Idle this way.
Randy

My book shows the timing figures for a 66 Pontiac 421 with three 2 barrels or one 4 barrel to be:

6 degrees BTDC initial.
22 degrees centrifugal, all-in @ 2300 rpm.
10 degrees vacuum, all-in @ 16" vacuum.

Disregarding vacuum, that gives you 28 degrees centrifugal all-in.
An entirely reasonable figure.
36 degrees all-in sounds like a Small Block Chevy timing figure.

Fwiw, I run a 455 Buick and all-in centrifugal timing on it is 32 degrees.
Some of the Buick guys running a more radical build than my mildy cammed, 9/1 compression engine run 32, 30 and 28 degrees all-in timing at the strip and on the street.

Ae you timing the engine with the vacuum advance line disconnected at the distributor?
And perhaps using a degreed balancer or timing tape to show you exactly where you're at?

If so, one small experiment you could try would be to set the initial timing at zero degrees (vac line disconnected).
That would give you 30 degrees all-in centrifugal timing.
Then, reconnect the vacuum line and take the car for a drive.
If the pinging goes away - and I'm betting it will - the next step would be to reinstall the original distributor weights and springs.
The factory distributor curve on these engines is a good choice for a performance engine whether factory stock, mildly cammed, low compression (9/1) or a more radical build.
Even with a radically built engine, this timing curve is a good one to start with.

Once you get things sorted out, you may be able to run the middle octane gas or even the 87 octane stuff.
Fwiw - the 87 works well in my 455 Buick winter and summer.

[1939coupe]

The only thing on the engine that is NOT stock is the Dist.
I'm running a Mallory Uni-light.
As for the amount of money I'm willing to Spend, I drive the car a lot and want to fix it RIGHT. I don't want to breakdown somewhere and find out the breakdown was caused by a Pinging or a Timing problem.
Randy

[Dr Flowgood]

1939 coupe,

Well the "right way"  is probably lowering the compression with dished pistons or larger combustion chamber heads  or both.  do you know what the compression ratio is rihgt now and what type piston , dished, flat ect  and combustion chamber size.    I have some friends that are pontiac nuts  Ill ask them what the largest chamber head would be.

Happy New year
Dj

[C9]

The only thing on the engine that is NOT stock is the Dist.

Mallory Uni-Lite's are easy to change the timing curve on.

Seems to me that'd be the easy way out - and the cheapest and the least work.

Get it back to baseline and see what you have as far as how well it runs.

[PeterR]

The following two links are to the same article posted in different forums.

Whilst the info does not specifically address Randys problem, it is very informative, and anyone who has followed the thread this far is bound to find it interesting reading.

http://www.streetrodstuff.com/Articles/Engine/Detonation/

http://www.germanmotorcars.com/Detonation.htm

[1939coupe]

1939 coupe,

Well the "right way"  is probably lowering the compression with dished pistons or larger combustion chamber heads  or both.  do you know what the compression ratio is rihgt now and what type piston , dished, flat ect  and combustion chamber size.    I have some friends that are pontiac nuts  Ill ask them what the largest chamber head would be.

Happy New year
Dj

My heads have a Casting Code of 092. And they are 1966 heads, so the Compression Ratio should be 10.5:1. And I know that the Pistons are Flat on top.
Thanks

[1939coupe]

The only thing on the engine that is NOT stock is the Dist.

Mallory Uni-Lite's are easy to change the timing curve on.

Seems to me that'd be the easy way out - and the cheapest and the least work.

Get it back to baseline and see what you have as far as how well it runs.

What step should I take first:
1- Cut back on initial timing (right now 6 deg.)?
2- Make Centrifical Adv. start coming in later than the present 1000 RPM?

I would rather NOT take initial timing out OR adjust my Vac can to put in Less than the 6 deg it is set for right now because the less Advance it has at Idle the Hotter the engine will run.
I just don't want to give up to much POWER.

[C9]

What step should I take first:
1- Cut back on initial timing (right now 6 deg.)?
2- Make Centrifical Adv. start coming in later than the present 1000 RPM?

I would rather NOT take initial timing out OR adjust my Vac can to put in Less than the 6 deg it is set for right now because the less Advance it has at Idle the Hotter the engine will run.
I just don't want to give up to much POWER.

Too much advance takes away from power as does not enough advance.

Limit the amount of centrifugal advance until you match the Pontiac factory recommended limit.  IE: 28 degrees total.

Even if you did spend lots of $$ on heads, pistons and the like, if you run too much advance you'll still have your problem.

Here's an address for Mallory tech instructions.
Just click on the style distributor you're running.

http://www.centuryperformance.com/mallory/mallorytech.asp

Note that there are two types of centrifugal limiting devices.
One - the older style Uni-Lite I believe - has bendable tabs.
The other has keys to set the advance and then lock it down.
I'm fairly sure the keys are available at Summit and the like.

Like my dad used to say, get it back to factory specs and go from there.
Worked every time for me....

[Crosley.In.AZ]

like C9 says , mayb start over again from tthe baseline with timing curve?

[1939coupe]

The following two links are to the same article posted in different forums.

Whilst the info does not specifically address Randys problem, it is very informative, and anyone who has followed the thread this far is bound to find it interesting reading.

http://www.streetrodstuff.com/Articles/Engine/Detonation/

http://www.germanmotorcars.com/Detonation.htm

Thank you very much for this Link. I learned a LOT about Detonation and how Timing and Cumbustion Chamber Design can be used to eliminate Detonation.

I also learned that Detonation (pinging) is NOT as bad as I thought.
I'm going to use the info in the article to alter my timimg curve.

Anyone who builds and works on there on engines should read this article.
Thanks again,
Randy

[HOTRODSRJ]

Randy......the real way to fix it right is find out not only what the static compression ratio is.....but more importantly do the arithmetic on dynamic compression ratios.  

Rereading the posts here I don't think you have a "load" of too much timing here even tho tweeking it first might show some improvement..certainly 30 is a more realistic target.   I have set ponchos up with both 400s and 455s to run over 30 degrees total....nary a problem on 92 octane but they have been engineered to run that way.  Just about every muscle car ( or big block from that era) that I have driven with the factory cams, heads and timing profiles ping under moderate and light loads with regular 92 pump gas.  It's the combination of compression ratio, cam profile, timing and lack of octane in today's fuel.

I also will admit that I don't know where the piston is sitting in the hole either with the 421.  And, yes I believe you have flat tops with reliefs.  I am guessing that your gasket is .028" which is pretty standard for these. This all figures in to dynamic compression ratios and there are plenty of online calculators to help you accomplish the correct values.

I recently did a 70 GTO almost with the very same issues.  3800 pound 1970 GTO, 400 +.030 over, factory dished pistons, stock 1.5 rockers, stock Q-jet, 3.55 rear gears, 4 speed, dual exhausts; stock point distributor used mostly for local shows, cruises and some road trips. The goal was to improve stock performance, at the same time lower 9.5 to 1 compression to run on pump gasoline. The engine came with the OEM "S" camshaft (068); 212/225 @.050" duration. The inherent problem with this engine was the lack of "overlap" that created a high DCR.  It pinged like a mother on pump gas under light and moderate load.

The results were spectacular!  The Edelbrock heads are a vast improvement and the power to the rear wheels was upped almost 100hp in combination with a newer comp cams, intake and HEI upgrade. Milage improved almost 25% too.  I personally think it's worth the cost....just on the fun factor.

Now....down to spending your money....hopefully smartly. I would suggest that you can do several things here with new heads and a different camshaft which will improve performance/power/torque, milage, and work all on pump gas if you do the homework.  The cam profile and heads in your engine is TERRIBLE with a capital T.....compared to today's OEM heads and performance cam grinds.  I will guarantee you if you do the Edelbrock RPM Performer head series with these........keep your quench design between .035 - .045 and dynamic compression ratio below 8.2 to one, (and you can keep your bottom end) you will be very satisfied with the outcome. But bottom line.....do your homework first.

Good luck with your problem here, I hope it comes out to your liking

[69byrd]

Don't know if you have found your answer yet.  But had the same issues with a .030 over 398. It sucks - I know.  Debated most of the solutions listed here... tried a few, as well.

I was told - the vacuum advance was primarily to promote better gas milage, and that the car would run fine (although Lopey )  without it.  

I disconnected the advance & drove the car like this for another year.  While this DID NOT totally eliminate the mid throttle pinging - it did reduce it greatly.  If you are running a quadrajet - also look into the setup of the rods - a little extra fuel at mid throttle, while a band-aid, can help too.

The best  solution - as stated earlier, is to reduce compression.

A set of 6x heads would be easy to come by, flow pretty well stock, and can be modded to flow like crazy.  The next step up would be 96 - these are a little more desireable ($400-500) because they have the larger exhaust valves.  

I was lucky enough to pick my 96's for $150 - added hardened seats & new valves for a total investment of less than half the price of the edelbrocks....

BTW the edelbrocks are around 87cc

Check out the Q&A on CLASSICALPONTIAC.COM - lots of compression talk going on there - from all the guys building 455's.

Good luck!

Chuck