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1966 hardtop yellow black top factory auto with a/c 4v
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i have a 66 gto # matching 389 4barrel auto with factory a/c put a gm hei distributer in need to find a good timing for it so no ping it starts fine and runs good but pings on hard acceleration i run super it does not run hot or any thing anyone have any ideas where i should put the timing
 

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67 GTO
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Do you know where you are now as far as total timing, not including vacuum advance?

So many factors play into this....

What is the situation where it pings under hard accel? What rpms? 2000 rpms and mashing it, or is it pinging up top?

Need more info....
 

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Cameo Ivory 1967
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HEI's dont have adjustable timing curves, so just start retarding the timing two degrees at a time, until the pinging stops. That's all you can do with an HEI and that would put you at optimal timing.

The only mod for an HEI dizzy is to change springs and weights, which will change when and how the centrifugal comes in, but not how much.
 

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1967 400ci/TH400
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@armyadarkness - i have a similar issue on my '67 400ci/TH400. It's stock except for an Edelbrock intake manifold and 750CFM Brawler carburetor. Well, I also have an MSD 6AL ignition box with MSD blaster coil and MSD mechanical billet distributor. I set the advance to 6 degrees but still get pings at lower RPMs....up to about 2000-2500. I"m in TX, running 93 Octane with STP octane boost. The distributor does come with weights and springs of different sizes to change the timing curve. When i lived in CA, i just put about 5 gallons of 100 Octane racing fuel with 15 gallons of 91OCT....and didn't get pings. No racing fuel near me in TX. And it's my daily driver, so need a pragmatic solution.

Where do i start? Do i have too much advance? Seems like when i reduce the advance to 2 or 4 degrees, i get backfire..... Yes, i'm a rookie on timing so who knows what else i've messed up!

Thanks, Carl
 

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Cameo Ivory 1967
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3,377 Posts
@armyadarkness - i have a similar issue on my '67 400ci/TH400. It's stock except for an Edelbrock intake manifold and 750CFM Brawler carburetor. Well, I also have an MSD 6AL ignition box with MSD blaster coil and MSD mechanical billet distributor. I set the advance to 6 degrees but still get pings at lower RPMs....up to about 2000-2500. I"m in TX, running 93 Octane with STP octane boost. The distributor does come with weights and springs of different sizes to change the timing curve. When i lived in CA, i just put about 5 gallons of 100 Octane racing fuel with 15 gallons of 91OCT....and didn't get pings. No racing fuel near me in TX. And it's my daily driver, so need a pragmatic solution.

Where do i start? Do i have too much advance? Seems like when i reduce the advance to 2 or 4 degrees, i get backfire..... Yes, i'm a rookie on timing so who knows what else i've messed up!

Thanks, Carl
An MSD Billet should have come with centrifugal bushings. First clarify what dizzy you have and then we'll go from there.

If it is a Billet with bushings, then there are many tweaks that can be made, but even if not, there still may be a simple solution to your issue. I have a 67 400, TH400, with closed chamber 670 heads, and I have run from 12 to 16 degrees of initial, without issue.
 

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Cameo Ivory 1967
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@armyadarkness - i haven't changed what it came installed with figure 2 above: Blue stop bushing and 2 heavy silver springs.
Sometimes it's possible to be a tooth off on the dizzy, and then still keep the car running, poorly, by falsly advancing or retarding the timing, since you wouldnt be going from TDC.

I did this in my Vette, and it still ran well enough that I didnt realize it was wrong. Then on my GTO, I pulled the dizzy to replace it and the oild pump spun while the dizzy was out, so the new one went in wrong. Timing is actually very easy, but it can be a nightmare if you don't have it broken down simple, and sometimes forums hurt more than do good.

I would retrace my steps before trying anything. Set the engine at TDC, pull the dizzy cap and make sure that your rotor is pointing at plug number one, and that the firing order is right. If so, advance the timing until the engine runs best at idle. Once that is set, select the centrifugal bushing size which will bring it up to 36.

So if you can only get 6 degrees of initial, then you'd want a 30 degree centrifugal bushing, for a typical, optimum curve. If your engine cant handle 36, then you need to adjust accordingly.

SOOOOOOO... That being said, since the paper shows that your dizzy came with a 21 degree centrifugal bushing, then what should your base be set to for that bushing to give optimal timing?

If you said 15, then you understand how it works.

Also you could be missing springs, have all kinds of issues. Many great threads on this! But nothing takes the place of just clearing your mind and reading that manual!
 

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1967 400ci/TH400
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@armyadarkness - thanks! I thought i had it at TDC and pointing to number 1 cylinder....even used tape to mark etc.....had to move the oil pump shaft a bit for the new distributor to go in with a bit of the twist....but certainly something could have gone amiss. Will take your suggestion and retrace my steps.
 

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Cameo Ivory 1967
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The situation that you're describing, pinging at 6 degrees and backfiring when retarding, doesnt sound like normal pontiac response to timing. That's why I suspect that something is either set wrong or missing
 

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1967 400ci/TH400
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I'm not sure i would know the difference between pinging and valve train noise. I can hear it from inside when accelerating.....if i accelerate slowly, no pinging. The heads are 670s, YS engine. I have the idle set around 850rpm....it's an automatic and i added a brake booster so when i'm in Drive and have brake pedal on, it idles @ 550-600 rpm.

I'm not sure what you mean by the starter kick back.....it turns over great; i have the Hi-Torque starter from AMES installed.
 

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I'm not sure i would know the difference between pinging and valve train noise. I can hear it from inside when accelerating.....if i accelerate slowly, no pinging. The heads are 670s, YS engine. I have the idle set around 850rpm....it's an automatic and i added a brake booster so when i'm in Drive and have brake pedal on, it idles @ 550-600 rpm.

I'm not sure what you mean by the starter kick back.....it turns over great; i have the Hi-Torque starter from AMES installed.
Sometimes the pinging can be due to the vacuum advance can. It can be something like an additional 20 degrees more with high vacuum and then when you nail the gas, the addtional advance provided for by the vacuum advance does not retract fast enough so you are relying on the full mechanical advance pluse whatever advance is being added by the can at that instant. With the carb wide open, the vacuum drops so eventually all that extra 20 degrees goes away and you are running on just the weights/mechanical advance - with the problem being the advance can did not react fast enough.

There are different vacuum advance cans you can try and I recall the one you may want is called a "B-26". It only had 10 degrees of total vacuum advance, but also begins to operate at a lower engine vacuum and works better with big cams/low vacuum.

The other thing you can do is get the distributor set-up using the springs to get your total 34 degrees (Initial/balancer + dist, weights) to be all in at a higher RPM like 4,000 RPM's or even 4,500 RPM's. This stretches the weight's advance out over a broader range of RPM, ie instead of 34 degrees at 3,000 RPM's, you might only have 26 degrees at that RPM which effectively is the same as retarding the timing, but the weights will continue to add more timing as RPM's increase until you get your full advance of 34 degrees at 4,000 -4,500 RPM's.

So a lot of experimenting with Initial timing, mechanical timing, and the vacuum can. Most of this has been covered quite a bit in other posts if you do a search for it. (y)
 

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All good advice here. Now for a GM HEI get a

STandard Motor parts (SMP) VC 302 vacumn can.
Rock Auto part VC 302,
O’Reilly part BWD V 482,
Napa part # VC 1703

Standard makes them all but different retailers use different numbers.

The B26 is a very good can but for points dizzy’s.

this can will pull 10 degrees at low vacumn so you can use it effectively at idle on full manifold vacumn.

I think PJ is right if you are now hooked to full manifold vac your vac can may be pulling in 20 or even 25 degrees of timing, with your six base and maybe real high compression your Centrifigal comes on fast and you too much timing.

Also you may have to start low like a total of 32 base + Centrifigal to begin. That 10 degree vac can will help here as well. HEI’s were built with 384 different weight combinations to change the Centrifigal total, the MSD bushing system is very easy to work with. It comes close to doing what the chart says but sometimes just a little off so verify.

Like the bushing will say 21 but it could really be 23 on you package. They are plastic after all.
Try a 21 and set base at 11 to get 32 total with that new vac can and see where you go. Also agree with Army to make sure of the basics as you begin.

Remember heat contributes to pinging, so retared idle timing makes it hot. If you have no vac at idle 6 would be hot. So you have to play with it
 

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This spring inside this unit can be adjusted so that timing can pull in easy or harder under vacuum.
The cam piece is so you can make a stop , so you can limit the advance amount while pulling timing with vacuum
The springs are color coded so you can change the tension and raise or lower the rpm which mechanical pulls in timing . Keep the factory weights.
I saw an article that described how to make a mechanical stop for the mechanical advance for an HEI
The factory HEI is an excellent unit.It can easily be tuned. Try to learn it, understand it.
If you buy some super duper distributor , you will be out money and will likely be dissapointed.
There is notplug and play for what you need.
You are going to need a dial back timing light to sort it out. But it can easily be done, and the results will be well worth it. You just need to pick up some guidance .
My 389 has a crane unit.1 blue and 1 silver spring, and the vacuum stop is limited to 10 degrees total and it is set with a soft spring tension so it comes on pretty easy with ported vacuum. It will boil both rear tires from a dead stop with no pinging, on 91 octane.
I have the base tiing set at 14 degrees,10 total on the vacuum ( which dissapears at WOT) but the mechanical is set to be all in at 3200. it adds 20 degrees.
14 base plus 20 total mechanical at 3200 = 34. Pretty sweet
 

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The 670 heads are part of your trouble as the put the static CR at 10.5 to 1
that alone can cause a pinging problem. You should be able to tune around it
 
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