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the information i tried to highlight is that
an OE dist setup to run at 4 deg or 6 or 2 will not work
right when set to 14 deg.
if, the cr is low and carb jetted rich and cam cooperates
may not ping.
no one should just adv a dist and not understand what happened.
14 deg may be proper and best for your 350/427 regardless of what
cam was put in.
that is not the point.
point is dist controls spark and it needs to be at least measured for
adv curve.
just a warning for us that may not think about it.
glad OP is getting it fixed.
good example of what happens on a stock curve,,,,,,
pinging
I spoke with the distributor restored today and received some interesting news. I knew the shop/individual who owned the car before me had done an awful job on the distributor but apparently it gets worse - I was told the guts of the thing, specifically near the cam gear were spinning in the opposite direction - counter clockwise. Apparently whoever did the work a while back used Pontiac parts that spun counter-clockwise (supposedly this was how it was done during late 1950s). Restorer told me this would undoubtedly mess with the curves and make the thing impossible to time correctly. Therefore, I’m assuming this might explain why my motor had been pinging and knocking. Going to put some proper Chevy parts in the thing and get it right. I guess they just mickey moused it together and hoped for the best.
Last edited by Dammakins; Mar 28, 2018 at 09:24 PM.
I spoke with the distributor restored today and received some interesting news. I knew the shop/individual who owned the car before me had done an awful job on the distributor but apparently it gets worse - I was told the guts of the thing, specifically near the cam gear were spinning in the opposite direction - counter clockwise. Apparently whoever did the work a while back used Pontiac parts that spun counter-clockwise (supposedly this was how it was done during late 1950s). Restorer told me this would undoubtedly mess with the curves and make the thing impossible to time correctly. Therefore, I’m assuming this might explain why my motor had been pinging and knocking. Going to put some proper Chevy parts in the thing and get it right. I guess they just mickey moused it together and hoped for the best.
Wow....I do not see how or why somebody would or could do that.
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by Dammakins
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.
Drop me an e-mail and I'll send you all the info on them. I make them, and they're provided with complete instructions and photos for installation. They were featured by several magazines a while back and received very good reviews for their performance.
I spoke with the distributor restored today and received some interesting news. I knew the shop/individual who owned the car before me had done an awful job on the distributor but apparently it gets worse - I was told the guts of the thing, specifically near the cam gear were spinning in the opposite direction - counter clockwise. Apparently whoever did the work a while back used Pontiac parts that spun counter-clockwise (supposedly this was how it was done during late 1950s). Restorer told me this would undoubtedly mess with the curves and make the thing impossible to time correctly. Therefore, I’m assuming this might explain why my motor had been pinging and knocking. Going to put some proper Chevy parts in the thing and get it right. I guess they just mickey moused it together and hoped for the best.
To spin the distributer counter clockwise is impossible. The oil pump would be running backwards and you would have no oil pressure. Also the distributer gear would not match with the cam and it would not go in.
You need to set the mechanical max advance around 35 degrees and then see where the initial advance is. If the initial advance is less then 10 degrees at idle you could install a mechanical advance limit bushing to limit the advance. Between 10 to 15 degrees initial advance at idle combined with 35 degrees at full mechanical advance will give you near best performance. After this is done keep the vaccum advance disconnected and drive the car to see if it pings anymore? If pinging is gone you can then try the vacuum advance, and see what it does, if pinging is gone drive the car and enjoy. If pinging is still present with the vacuum advance hooked up then buy an adjustable advance canister and limit the vacuum advance until the pinging goes away.
If the engine still pinged with just the mechanical advance set 35 degree and no vacuum advance at all you need to check additional items. This could get long so first set the timing correcty and report back.
Last edited by bjankuski; Mar 30, 2018 at 08:09 AM.
Drop me an e-mail and I'll send you all the info on them. I make them, and they're provided with complete instructions and photos for installation. They were featured by several magazines a while back and received very good reviews for their performance.
To spin the distributer counter clockwise is impossible. The oil pump would be running backwards and you would have no oil pressure. Also the distributer gear would not match with the cam and it would not go in.
You need to set the mechanical max advance around 35 degrees and then see where the initial advance is. If the initial advance is less then 10 degrees at idle you could install a mechanical advance limit bushing to limit the advance. Between 10 to 15 degrees initial advance at idle combined with 35 degrees at full mechanical advance will give you near best performance. After this is done keep the vaccum advance disconnected and drive the car to see if it pings anymore? If pinging is gone you can then try the vacuum advance, and see what it does, if pinging is gone drive the car and enjoy. If pinging is still present with the vacuum advance hooked up then buy an adjustable advance canister and limit the vacuum advance until the pinging goes away.
If the engine still pinged with just the mechanical advance set 35 degree and no vacuum advance at all you need to check additional items. This could get long so first set the timing correcty and report back.
Maybe is misunderstood the restorer the other day. I know for sure that the thing was an absolute mess and was horribly done from the get go. I should get it back next week and will get her timed up and let you know how it goes. Excited to get it back - really hoping this fixes the recent issues I've been having with the car.
Maybe is misunderstood the restorer the other day. I know for sure that the thing was an absolute mess and was horribly done from the get go. I should get it back next week and will get her timed up and let you know how it goes. Excited to get it back - really hoping this fixes the recent issues I've been having with the car.
Are you using the original points distributor or is it something else you are putting together for it?
Are you using the original points distributor or is it something else you are putting together for it?
It's the original distributor with the Petronix ignitor set-up in it. The next thing I'm worried about in regards to that is the original braided spark plug wires I ordered. My understanding is that if you upgrade to Petronix II or III, you won't be able to use those wires because they're "solid core" wires. I ordered from Ecklers who I think sources them from Lectric limited and they confirmed their solid core. So I guess I have to stick with Petronix I vs II or III.
It's the original distributor with the Petronix ignitor set-up in it. The next thing I'm worried about in regards to that is the original braided spark plug wires I ordered. My understanding is that if you upgrade to Petronix II or III, you won't be able to use those wires because they're "solid core" wires. I ordered from Ecklers who I think sources them from Lectric limited and they confirmed their solid core. So I guess I have to stick with Petronix I vs II or III.
Try these. They are not solid core. I use them with my 69 427/390 and the Pertronix II.
For years I have done side jobs on Vettes and hot rods. Ignition timing is not rocket science. You set your max advance timing where you know it is all in at say 3500 rpm. In your case try 36 degrees with the vac adv plugged. Initial timing is immaterial and can only be changed by limiting the amount of mechanical advance. I am a firm believer in all advance in around 3000 - 3200 rpm and always use ported vac to vac advance. The all in timing people at low rpm like 2500 are for the smog years low compression motors that run fine on 87 gas
There is a possibility that some past owner changed your cam and you are just screwed. No amount of timing changes can fix a low duration cam in a high compression motor
If you are not into NCRS show car BS. Yank your distributer and coil and put them in a box where they belong
Then go buy a real easy to adjust digital dizzy with dials. You save money in the long run because you are not paying unqualified people $100 buck an hour. This is what I use on my two motors and I install them.
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
Hi Jebby,
The motor actually does have an aftermarket cam in it. The guy who rebuilt the original carb timed the motor and estimated the cam in it is in the realm of 240 degrees with 0.50 lift. When a shop ran a compression test on the motor they said the average in each cylinder is in the 180-200 realm. This is why they believed the compression in my motor had to be jacked up from the original spec. They estimated it is now in the 10.75:1 area.
I've been told because of the above, that the initial timing should be lower than 15* due to all the modifications. Thoughts?
The motor actually does have an aftermarket cam in it. The guy who rebuilt the original carb timed the motor and estimated the cam in it is in the realm of 240 degrees with 0.50 lift. When a shop ran a compression test on the motor they said the average in each cylinder is in the 180-200 realm. This is why they believed the compression in my motor had to be jacked up from the original spec. They estimated it is now in the 10.75:1 area.
I've been told because of the above, that the initial timing should be lower than 15* due to all the modifications. Thoughts?
240@ .050 is and largish cam.....and 180 is about the threshold for Pump 93.
I can see what you mean....backing down the timing is your only alternative.....
The honest, cheapest way to do it is to have the domes fly-cut and the assembly rebalanced.....
240@ .050 is and largish cam.....and 180 is about the threshold for Pump 93.
I can see what you mean....backing down the timing is your only alternative.....
The honest, cheapest way to do it is to have the domes fly-cut and the assembly rebalanced.....
Jebby
Do you think I have a chance to stop/minimize pinging if the timing can get kicked down? It's a bummer because I love the fact that the motor is powerful but it's now creating more issues than benefits - a mild cam would have been more appreciated. If only I could ask the former owner why these decisions were made.....
Estimating a cams duration & lift would be a great act for a circus side-show. Its just not do-able, too many varibles.
Estimating compression ratio using compression test data is just that, a guesstimate. Large carbon deposits on top of the pistons will throw your compression number a curve ball. And the cams intake valve closing event will determine the CR also.
You have to do a lot of algebra to get a true compression ratio and even then the heads have to be off to get true measurements.
If in fact, the CR is too high for your liking, changing to a thicker headgasket will keep your dynamic CR high, which is what you want, but will lower the static CR.
Nothing wrong with running a bompty-bompty cam on the street. You just have to do a little tweaking of the IGN timing. You will get it.
Last edited by HeadsU.P.; Apr 3, 2018 at 03:58 PM.
Do you think I have a chance to stop/minimize pinging if the timing can get kicked down? It's a bummer because I love the fact that the motor is powerful but it's now creating more issues than benefits - a mild cam would have been more appreciated. If only I could ask the former owner why these decisions were made.....
It is all you can do and the overall engine performance will suffer.....but you will be able to run it......
It is all you can do and the overall engine performance will suffer.....but you will be able to run it......
Jebby
if it’s simply a matter of losing a bit of hp I could care less. Ultimately I just want to be able to drive it, have the motor protected/not ping and be more reliable. If backing off the timing accomplishes those things then that’s good enough for me. Thanks for helping me out!
Last edited by Dammakins; Apr 4, 2018 at 02:56 PM.
You're on the right track. Ran my '70 LT-1 with a dist curve similar to those mentioned for 27 years. 190 psi cranking compression. Total timing at 3500 was 36 degrees on 98+ Octane, backed it down to 28 degrees total on 93 Octane. Very little vac advance, maybe 10 degrees. Never pinged either cruising or running hard. The 28 degree setting did cost it about 30 documented hp. Don't remember what the initial was cause I never set it that way. Between 4 and 12 I guess.So that would mean the distr had about 22-24 degrees in it, the rest was inital.
