Hi Guys,

I've got a 69 L36 that has recently developed some bad pinging. I pulled the distributor out and sent it off to a rebuilder who's rebuilding it. He had told me the shop that rebuilt the distributor before I owned the vehicle did a horrible job on it. However, he mentioned that even with a nicely rebuilt distributor the vehicle is going to still ping. Reason being is that the L36 has been bored .30 over and the compression has been jacked up to 10.75:1. When I had a compression test done on the vehicle the ratings out of each piston were in the 190s-210s. Therefore, I was told the only way to eliminate pinging is to run the car on race gas which I really don't want to do give it costs over $10/gallon in Southern California.

The thing that baffles me is that a good friend of mine has a 1966 L72 with the original motor, runs 91 in the car without octane boost and gets no pinging. That motor has a higher compression than my L36 (11:1) yet doesn't ping. Has the original heads (No aluminum).

Is there anything I can do to somehow stop this pinging OR am I truly forced to run this thing on 101 all day long?

Thanks!

 

My 69 L36 has the original heads and I have no problem with pinging running even 91 octane. Make sure somebody didn't change out the vacuum advance on the distributor as the original MS 360 12 can only produced about 12 degrees of advance and most now are higher which can cause pinging off idle. The original L36 distributor was set up with 26 degrees mechanical advance at the factory which was supposed to be all in by 3800 rpm and only 4 degrees initial. I am using a sleeve to restrict mechanical advance to 17 degrees and have it timed at 17 degrees initial for a total of 34 degrees all in by 3000 rpm now. With 34 degrees total I can run 91 octane all day long with no ping problem even though 94 octane is readily available here.

 

Set the timing correctly, curve the distributor to give you what you need, when you need it. You may need to limit your vac advance some.

There is a chance it could still ping for a variety of reasons, you'll need to eliminate them one by one... But a true 10.0-1 compression on iron heads is liveable. My 496 is 10.0-1, has 205-215 psi cranking pressure cold, and runs fine on 93 octane. Timing is set 33* total/locked out. When I run the vac advance, I do limit its travel to about 5*... more then 38* timing at cruise and I will get pinging.

I also have a 396 that is 10.0-1 with iron heads that runs well on 93 oct...but it has a pretty large cam in it, which helps with DCR and pinging.


Most of those "11-1" 427s never measure near that with the pistons .030-.040" down in the hole, ring leak by etc etc.

 

Thanks CanadaGrant! To clarify - I think the car is "knocking". Car sounded fine at idle but then when I drove it without even giving it much gas the sound would happen and progressively sound worse the more gas you gave the motor. I hoping that this new distributor will fix the problem and I can retime it to advance degrees you're talking about.

Before I yanked the distributor out a reputable Carb mechanic told me it had the following which I'm told was dangerous and way off the mark for stock:

Ignition initial timing at 15 degrees @ 650 RPM.
Full advance at 46 degrees @ 3,300 RPM

Carb mechanic told me the motor pulled little vacuum at idle and estimated that the cam in the motor was 240 degrees at .050.

 

If he really set your timing to 46* at 3300, that's your problem.... UNLESS, he set that with the vac advance connected (which you are not supposed to do).

Step 1, find a new mechanic.

 

My rebuilder shaved the heads rather than deck the block on my .30 over L36, then used a thicker head gasket. He dynoed the engine on 93 octane pump gas with ethanol, timing set at 34 and no death rattle. Pulled 408 hp...and 505 lbs/ft @ 3125. I now run the engine on 90 octane non-ethanol and mix it with 20-25% C12 race fuel at 108 octane. Total timing is at 36 degrees now, but I have had it up to 38 and still no detonation.

As others have said, you need to get your dizzy on a Sun machine and set it up. We ended up putting NOS original springs back in and swapping out the vacuum advance for a more friendly one. I can confirm the number, but think it is a B26.

 

I'm just praying I didn't hurt the motor - Drove it super super gently for like 5 mins just to get it home and have never started it since Christmas (When the knocking incident happened). You don't think I could have burned a hole in a piston from driving it super lightly for that amount of time could I? I'm planning on doing a compression test on the pistons after this rebuilt distributor gets dropped in just to be sure.

The carb guy told me that the amount of full advance was "what the motor needed" but he did acknowledge that full advance should be at 36* and that it was way off. Per your note I'm assuming the rebuilt distributor with proper timing should take care of all this....

 

Naw.... The engine will be fine...Take a lot more then light pinging at cruise to hurt one.

It'll be fine.

If you set the timing yourself, make sure to disconnect the vac advance and plug the vacuum source to it. Set the total timing to around 34-36* at 3500 or so and make sure the timing doesn't continue to advance at higher rpms then that.

After you tighten the distributor there, then check the timing at idle (initial timing) and hopefully it will at least be 15* or so.... If it is, you should be good to go.

Plug in the vacuum advance and check the timing at idle, it will likely be around 30* or so..... Then check the timing at 3000 or so and see what the total is with vac advance... It ill likely be around 50*...which is probably too much on today's gas. At that point, you'll need to limit the vacuum advance travel with a limiting plate, check timing again....rinse and repeat until you get it right.

I wouldn't personally run more then 40-42* total timing with vac advance at cruise....and even that might be too much.

 

Thanks AJ! You're a lifesaver! I'll respond to this post once I get the restored distributor back on my rig and start going at it.

Yeah - I'll be doing the timing in my house garage with a mechanic who did an unbelievable job on my family's 49 chevy pickup. Will let you know how it goes!

Thanks again everyone!

 

if, if the engine is supposed to be at 4 deg then the guy set you up right.
putting 11 more in at idle screwed the pooch.
now what was done to kick up the cr?
or is that stock?

 

 

Not true. Factory spec @ 4 deg BTDC is only for warranty considerations. Car will run fine there, but not at rated output of 390 hp. An initial setting of 15-16 reg BTDC at idle (with vacuum disconnected and plugged) is ideal for this engine...unless you are willing to accept less than what you paid for.

 

talking about the dist setup.
geez.
take 11 from 46 and it is proper. 36
his guy talk crap about how the dist was set.
IF, the dist was set for 4 deg then it was and is right.

he chose to change the idle deg.

RIF

 

The 4 deg shown on the emissions sticker is really just for that...where to set the initial timing for optimum emissions control.

 

If that thing really had 4* initial timing, it would run like complete ****..but it wouldn’t likely ping...

 

When I got my stock engine 69 it was timed at the factory 4 degrees initial. It really did run like **** and even though it had a tank full of 87 octane it still didn't ping. They did use a lot of centrifugal advance as the stock distributor was factory calibrated at 26 degrees so the max initial you want to use with the stock distributor setup is about 10 degrees to get your 36 total. I used limiter sleeves to reduce mechanical advance down to 17 degrees and upped my initial to 17 for a total of 34 degrees. Lighter springs make it all in at 3000 rpm. It likes lots of initial and runs very nice like that and can still run 91 octane with no pinging. I get a slight ping once in awhile on 91 octane if I up it to 36 total so 34 total works great for me.

 

AJ - Do you where I can find one of those limiting plates for the original tach drive distributor? Also - how does the plate work? Specifically where does it install into the distributor and how do you use it to limit vac advance? Apologies - all this is totally new to me.

 

This guy knows what he is doing....^^^

 

You can buy them, or you can make one for about $5... All you need is a small piece of sheet metal, a Dremel tool to cut and shape it....and some trial and error to get the desired degrees.








Or buy one here: scroll down
https://www.bartonekdragracing.com/w...b/ignition.htm

 

My 427/400 was curved like this and ran .060 TRW domes for about 10.25 to 1.......it would ping sometimes under a heavy load in 4th uphill.....but that was it. Ran strong on 93 swill.
Get the right curve and you will be happy.......OR......stick a larger can in it with more overlap to bleed off some of the compression. This is part of the reason why your buddies 67' does not ping.....the L36 does not have much cam in it......the L72 does....

Jebby