Timing

[Step]

I was reading through old threads trying to get some information about ignition timing for my 40, and I came across this from petepedlar back in Sept. of last year - "The timing was all in at 2500 with a ready to run MSD. One blue spring, one silver spring and the blue stopper. We broke in the cam at about 25 degrees and then put it up to 34 for the first pulls. We tried 36 & 38 and it liked 36 the best......." Is that 34 degrees of initial timing, with no vacuum advance? I'm running a MSD distributor with only mechanical, and I am at 18 degrees initial now, but am really searching for what might be correct. I've been up to 25 degrees initial, with no ping, and about 32 degrees total with all in by 3300, but still I am just hunting. Hence the research through old threads.

Jeff

 

[Fathead Racing]

Weight of the car, rear gear and what you are going to do with the car have a lot to do with the timing curve. My car is Hot street/strip 60 Impala with 4.56:1 gear. I have 18 to 20 dgs initial with 36 to 38 total all in by 2400 rpm. Add the vacuum advance that comes in at around 20" of vacuum and on the highway the engine sees 49 dgs advance.

 

[CDNpontiac409guy]

Jeff, I think the two most important factors are the actual compression ratio, and the fuel used.
With pump premium ( 92/93 octane ), and 10-10.5:1... 33/34 degrees total ( without vacuum advance of course ). If your compression is a little lower than that, you may be able to use 36.

I just dyno'd my 409 Stocker engine a few days ago. It's actual compression ratio ends up at about 11.4:1 ( stock crank, .074" over bore... 424 CID ). I have to use NHRA/IHRA race fuel.. in my case, I use VP C11. On the dyno, I found that as Fat just said... 36, even near 37 worked best for power. This was so, up to about 6200/6300 RPM, where it was quite apparent that that 1 or 2 degrees back "out", really helped peak HP... like about +12:eek:.

I've always found that strange... how an engine will actually require LESS ignition advance at high RPM, that it does in the mid range

Oh, I too, am running the MSD "ready to run" distributor, setup virtually identical to yours. Just a note... you might want to check the spark phasing to the distributor cap. Out of the box, mine was "sparking" JUST as the rotor tip was passing the distributor terminals. I solved the problem by relocating the "breaker plate, by cutting slots in the vacuum advance mounting holes.
I also use an MSD 6AL box, with a two step rev limiter.

 

[Fathead Racing]

[QUOTE=CDNpontiac409guy;

I've always found that strange... how an engine will actually require LESS ignition advance at high RPM, that it does in the mid range


Aubrey, it's all about swirl and tumble in the combustion chamber. The higher velocity the fuel/air mix enters the chamber the better the mix and combustion, that's why the engine wants to lay down at the higher rpms. You can buy a box that automaticly takes out 2 dgs at the higher rpms just for that reason!

 

[Step]

Thank you all, let me go one step further. I have a .060 over 409 running 10:1 Ross pistons with 6 Demon 98 two barrels on an Offenhauser manifold. The distributor is a MSD all mechanical, no vacuum advance, 6 AL ignition with no rev limiter, . The cam is 224 deg. @ .050 lift both intake and exhaust, with a .512 lift on 1.75 rockers, 110 deg. lobe separation. Trans is a 350, 3.89:1 rear end, 31" dia. rear tires, 2220 lb. T-bucket. I'm in California where the best gas one can get at the typical corner station is 91 octane unleaded, but I have gotten no ping on that so far. It is a street car, weekend cruises and the like. It gets jumped on, but is not raced at the strip. The carbs are running a little rich, and I am working my way through that problem, but I want to make sure I am not adding problems with poor timing. Does anyone think I would be better off going to a distributor with vacuum advance?

Jeff

 

[Skip FIx]

Aubrey and old 409 I bought in the 70s had a factory distributor with a choke type cable made into the advance bracket area the guy used the manually retard once in high gear.

 

[models916]

Try some booster

I use 1 Qt of Toulene for every 10 gals of premium in the tank. Not a lot of boost in octane, but something about it makes the engine sing. Sherwin Williams has it pretty cheap. I run 36 degrees all in at 2500. Will PING a little without some sort of booster.

 

[Fathead Racing]

Thank you all, let me go one step further. I have a .060 over 409 running 10:1 Ross pistons with 6 Demon 98 two barrels on an Offenhauser manifold. The distributor is a MSD all mechanical, no vacuum advance, 6 AL ignition with no rev limiter, . The cam is 224 deg. @ .050 lift both intake and exhaust, with a .512 lift on 1.75 rockers, 110 deg. lobe separation. Trans is a 350, 3.89:1 rear end, 31" dia. rear tires, 2220 lb. T-bucket. I'm in California where the best gas one can get at the typical corner station is 91 octane unleaded, but I have gotten no ping on that so far. It is a street car, weekend cruises and the like. It gets jumped on, but is not raced at the strip. The carbs are running a little rich, and I am working my way through that problem, but I want to make sure I am not adding problems with poor timing. Does anyone think I would be better off going to a distributor with vacuum advance?

Jeff

Hey Jeff, is the block passenger or truck? At 2200 lbs with a 3.89:1 gear you could get fairly aggessive with the timing with out detonation. The cam will make quite a bit of cylinder pressure at low rpm so rate of advance should be kept a little slower than usual, maybe 36 dgs all in by 3000 rpm. With that cam low end power should not be a problem. As a matter of fact with a car that light you could have a much more aggressive cam. If your builder paid attention to quench distance and dressed the pistons you should be A OK. I would run a vacuum advance, keeps the plugs cleaner and is set up correctly will give you a cleaner idle, especialy with your 6X2.

 

[Step]

Passenger car block.

Jeff

 

[Fathead Racing]

Sounds like the cam is Comp. magnum 268. What is converter stall? That car sounds like a hand full!

 

[Step]

It's a 2400 rpm stall converter, but in such a light car it acts like it is a lot lower. I have to really stand on the brakes at a red light to keep from rolling. Later in the summer I am going to switch to a higher stall, probably 2800. It can be a handful. I have no idea what it would do in the 1/4, but I do know that I don't want to be in it to try. The engine is running a little rich right now. I'll keep trying to see what I can do, and chime back in again when I get stuck. Thanks so far

Jeff