Low compression engine = really high ignition timing?

[kerb12]

I'm noticing something weird with my '66 200... Idle isn't great at 12-14 degrees initial timing, and overall performance isn't that great either considering the amount of work I've done to it, so I hooked up a vacuum gauge and started turning the distributor to see where I would get highest vacuum - and the engine kept getting stronger and stronger until I hit about 45 degrees! I took the car out for a drive today with it set at 25 initial, and didn't get any pinging. I was weary about setting it higher, but I have a feeling it would have felt better if I did. It seems like my timing readings can't possibly be right, but I pulled the #1 plug and watched the piston to verify my timing marks are correct, and it looks good. This is with a stock DSII distributor from a '78 Fairmont.

I went back to re-calculate the C/R with my modified large log head, and if I used the equation right, I'm at 8.67:1. For some reason I thought the stock was 8.7:1 and I was ok, but the shop manual says 9.2:1, so I'm actually pretty low.

Could it be that my low compression is throwing the amount of timing advance I need way off?? It doesn't seem possible that over 25-45 degrees initial would even work, let alone be better...

A little engine background, it was recently rebuilt by a shop bored .030 over but otherwise stock, and they put a COMP 260h cam in. I put a DSII distributor in with an MSD 6a controller, headers, and then I swapped the stock head with a large log head with a direct mount Autolite 2v.

Any ideas? Am I safe driving with that high timing??

 

[wsa111]

You really need to check total advance with the vacuum advance disconnected.
If you need your distributor recurved or purchase one of mine already done advise.
Too much total can be fatal on pistons & performance. Bill

 

[rbohm]

there can be a number of reasons why you are running(seemingly) what seems to be excessive ignition timing. if your balancer ring has slipped, you could be reading more timing than you really have. or perhaps you are getting what is known as inaudible detonation. when you go to start your engine, does it tend to kick back a bit? if so then you in fact do have too much timing.

so take a good look at your plugs for signs of detonation, and check to see if your balancer is where it should be.

 

[JackFish]

You might have an issue there with the low compression due to the thicker head gaskets.
Were the heads shaved at all?
But yah I'd suspect the balancer.

 

[kerb12]

Hey Bill, this is Nick, I was actually talking to you over email about 2 weeks ago about getting one of your recurved ones. That's partly what set me down this path... I figured I would find my initial timing by turning the dist for highest vacuum reading at idle (with vacuum advance disconnected), and then listen for pinging on the high end to find what my total timing should be. Then I could get it recurved for those specs. Unfortunately though, those numbers are so high, I don't know if I should trust them so I'm weary about getting a new dist yet.

By the way, my idle vacuum is 15 in. if I'm in the 12-14 degree range, but I can get it up to 17 in. if I go into the 40's.

rbohm, no kicking when it starts. Actually starts better. I suspected the balancer too, but the timing marks line up when I'm watching the piston reach its highest. I'll pull all the plugs and check them though, that's a good idea.

JackFish, I'm running a Victor gasket (.044 compressed?) and the head was shaved .060 and measured at 54.5cc. For the calculation I used 3.71 bore, 3.126 stroke, .019 deck, and 6.5cc piston dish... which should be the stock numbers (with .030 bore). That gives just under 8.7:1. The head was built for a member here that was going to turbo it, that's why the compression is lower... I was hoping I could run it normal for a while though because I'm still undecided if I want to go turbo or not.

 

[hotroady]

Advancing initial timing wakes up low compression engines, might not be anything to worry about, but you could limit full centrifugal advance inside the distributor, to be safe. This can be done with distributor recurve.

 

[OpelGT+3point3]

I always run as much distributor advance as possible without pinging on accelleration. Plus I hook the vacuum advance to an off idle vacuum source. But it's possible that the cam isn't timed for best low end performance. A mild or stock cam can be dialed in with a compression tester. Trial and error; until you get the highest reading. Yours probably needs advanced..but that's a lot of work. Most V8's were retarded on the crank gear starting in 1971. I don't know if the six was or not, but I've seen most rebuilders use the later gears when they rebuild the older engines; losing power and mileage. We were swapping out crank gears and heads in the seventies to regain compression and cam timing advance. I've gained as much as 30 pounds by advancing cams. I gained power, mileage and throttle response. I never use a timing light. Every engine is different.