I have to be thankful first off that my engine is still running. I hope I did not pound the rod and main bearings into submission... For the past few weeks if not months I have been lamenting the weakness of my 430 and how it simply loses all pull by about 3750 rpm. I know it has the stock everything except HEI/curve/EverydayPerfcarb, but that shouldn't happen. Two days ago I was re-reading Larry's timing thread and thought I might as well add two-three more degrees of advance in to see if I'm missing any power in the upper ranges. I get home, start the car and drive it first to get the tires balanced and alignment done to find out that three out of four of my wheels are wobbling on the tire balancer and I likely need new rims. (Any offers? Any for sale?) Nevermind, I go about my day and finally get to timing the engine. I couldn't believe my eyes: at 800 rpm I had over 25 degrees of initial advance! I loosened the distributor and brought it back into the normal realm of 12* initial, 32* total. Due to reading more on Larry's thread I put it back in at 15* with a total of 35*. I then retune the idle, reset it. Tighten everything up and go for a drive. While the engine has not been changed, partswise, through this whole episode, I now have my top end back! Screams all the way to 5000 through the 2.25" glasspacks and no longer falls on its face. To think I was running nearly 45* of total timing, sheesh. Dodged a bullet in the long run The science behind having maximum cylinder pressure between 10*-15* ATDC is good until you feed it way too much timing, which is likely why it fell on its face at 3750 then picked up again at 5000 when the piston speed increased to a level where a leaner mixture could be burnt slower, delaying the maximum pressure back to about 10* again. This engine stuff is wild
I hope you are setting the initial, but also checking the total advance with the vacuum advance disconnected. With very light springs, there can be some mechanical advance in at idle speeds. Setting the initial timing with some mechanical advance in is inaccurate for obvious reasons. Lower the idle speed as much as possible to set the initial timing. Are you sure there is only 20* of mechanical advance in that HEI? Is it a TA Performance HEI?
It is an Everyday Performance HEI with 20*. And BQUICK I do mean ATDC. Why would you want maximum cylinder pressure occurring before the power stroke? That sounds like recipe for disaster.
I had a similar problem on my 1967 buick riviera, I had put in 14* initial timing and thought my bushing was a 19* which would have made my total advance 33* at 2500 rpm but to my surprise a week later I rechecked the total advance timing and it was 37 degrees. I almost killed my engine! So it’s good to check any time you mess with the distributor.
You've got that wrong. You want "advanced" timing which is BTDC. Retarded timing would be ATDC. You want more advanced timing as the rpm goes up because there is actually a delay between when the spark fires and the flame front moves across the combustion chamber and when the piston is at TDC for maximum pressure. As the rpm goes up you need to fire earlier to make sure it hits on time because everything is happening faster. If you fire late(retarded) as the piston is already moving down the bore you miss the opportunity for peak power. I rarely worry about initial timing. I just make sure it has the correct amount of total timing. If it lands somewhere between 12-18* initial it won't make much of a difference as long as fairly loose springs are installed(all in by 3000 rpm). Some cars may need slight changes to the curve for their setup.
When I was running a stock type distributor I would put one stiff spring on to check initial timing. Then you can have fun changing that spring with softer ones to get the curve you want. Should have full mechanical advance at 2200 to 2500 rpm.
OK. I re-read what you said and now I understand where you were going. That kind of technical talk went right over my head.
Depending on the fuel being used the burn rate can differ greatly but that is why we tune. The slower burn rate of a high octane allows us to advance the timing to get that mixture started sooner. But advancing too much can get the full burn going on the compression stroke costing power. Getting it just right to be making the burn atdc as the op states takes tuning. Lots of runs at the strip or a dyno session with some timing adjustments and probably some fuel adjustments to get max power. Then the fun can progress to getting that power to the ground.
