[Rich D]

looking for what the total timing should be on my motor. 495 stroker, Kauffman d ports, 85 cc. compression is 10.7. Mild hydraulic roller with plenty of vacuum. 93 octane fuel. I've read that they don't need much advance, like 30 to 32 but when the car was on the chassis dyno they said it had the most torque at 35 degrees. Anybody have something similar that could help. Thanks

[leeklm]

Not an expert here by any means, but thinking the settings from the best dyno runs would be appropriate. Of course a chasis dyno might be more accurate with full exhuast installed, etc.

We ran out of time when my 461 was on the engine dyno, and was at 32 deg mechanical advance. I have found that 28/29 degrees provides the best ET at the track. The vacuum advance then adds another 10 degrees at cruise speed.

I am at ~1,000 ft elevation, which I understand will make a difference as to what timing the engine likes.

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[steve25]

In reality unless your racing it your better off in terms of maxing out the life span of the motor by running it detuned a little bit like you would be by setting the timing at 32, especially since in your own words you have plenty of vacuum, and along with that I would have to assume a good steady idle.

Also note that the best timing setting for maximum Torque may not make the most peak HP anyway should that have been your goal by posting this question.

[Rich D]

Thanks guys. I was thinking that running it a couple degrees less would be safer for the motor. I plan on racing it a little but mostly show and cruise nights. I set it down to around 30- 31 degrees. Hope to try it at a local track soon. No roll bar so can't run faster then 11.5 anyway. Thanks again

[JLMounce]

My 85cc KRE D-'s like 32 degrees of timing. Adding more doesn't seem to add any snap to the engine or otherwise power output. At least nothing perceptible with the butt dyno.

My conversations with Jeff Kauffman when purchasing were that as the piston gets closer to 0 deck, the combustion chamber would continue to get more efficient and the need for more spark lead would reduce. He estimated most engines at zero deck would like around 30 degrees. I measured my pistons at .005 to .007 in the hole and he figured it would like 32 degrees. He was right on the money, at least for my engine.

[ta man]

Originally Posted by Rich D

Thanks guys. I was thinking that running it a couple degrees less would be safer for the motor. I plan on racing it a little but mostly show and cruise nights. I set it down to around 30- 31 degrees. Hope to try it at a local track soon. No roll bar so can't run faster then 11.5 anyway. Thanks again

Sounds like a great build, just go to the dragstrip on street nights or days..most tracks I go to are quite easy on tech on those days. The nice thing about the dragstrip is that good or bad any issues with the car will show up.
Also I see your in Colorado..so at a higher elevation a 11.5 is a pretty good achievement.

[mgarblik]

I was told decades ago, "the engine will tell you what it wants". If you trust the dyno and the timing light they were using, than 35 degrees is what this total combination wants to run it's best. I agree that using this number and taking 2 degrees out is a nice little safety cushion if you don't have any type of detonation sensor system. Have never seen an engine ruined by running a couple degrees less than optimum timing. Couple degrees too much advance, damage could happen.

[beemergary]

Bigger crank (stroke) with more advance your reaching a point of (firing) pushing down on almost a flat surface. Any closer and you will run backwards. Last 4.5 stroke I saw on dyno liked 30 degrees.

[leeklm]

"Also I see your in Colorado..so at a higher elevation a 11.5 is a pretty good achievement."

As a general rule, does an engine at higher elevation prefer more or less timing? I have been told elevation makes a difference- but was not sure in which direction.

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[Lee]

Originally Posted by mgarblik

I was told decades ago, "the engine will tell you what it wants". If you trust the dyno and the timing light they were using, than 35 degrees is what this total combination wants to run it's best. I agree that using this number and taking 2 degrees out is a nice little safety cushion if you don't have any type of detonation sensor system. Have never seen an engine ruined by running a couple degrees less than optimum timing. Couple degrees too much advance, damage could happen.

Agree with this.

35 seems like a lot for those heads, but maybe the elevation plays into that. Also, your "ZERO" may be off a bit, if it was not verified.

Find where the motor runs best, and leave it there.

[JLMounce]

Originally Posted by leeklm

"Also I see your in Colorado..so at a higher elevation a 11.5 is a pretty good achievement."

As a general rule, does an engine at higher elevation prefer more or less timing? I have been told elevation makes a difference- but was not sure in which direction.

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I think there’s a lot of myth, conjecture and hogwash on that subject. I think the answer is actually “it depends.”

The need for spark lead is dependent on the speed at which the fuel/air charge is burned. Mixture, compression, combustion chamber design etc all contribute.

An engine with higher static compression ratios, an EFI system that keeps the mixture in a fairly constant state with an efficient combustion chamber may see very close to the same burn rates at 5000 ft vs 2000 ft. In such a situation, advancing timing may be of no benefit.

On the other hand, your 71 Luxury LeMans with its 7.5:1 350, an out of tune carb and lazy combustion chambers with the pistons far down in the hole, may need some extra spark lead going from 2000 to 5000 ft.

I think that “rule of thumb” of 2-3* of extra advance at altitude comes from the idea that more timing = more power and that because you’ve lost dynamic compression in the thinner air, you can safely add timing. The lower cylinder pressures should theoretically slow down the mixture burn rate.

It makes sense on paper, but in practice you still have to find what the car wants. My KRE headed 455 likes 32 degrees. I was told it probably would like 31-32 and sure enough that’s what it likes. I’ve tried 34-35 degrees and I haven’t recorded any performance difference.

[Cliff R]

I think there’s a lot of myth, conjecture and hogwash on that subject. I think the answer is actually “it depends.”

I started taking my Honda 500 Quad out West Elk hunting a few years ago. It is the last year they used carburetors on them. I did some research and got dozens of different opinions on the subject or tuning it for 9000-12,000' operation instead of down here at 1200' where it spends most of its time.

Anyhow, although not directly related to what's going on here I did NOTHING to it, even after calling a couple of Honda dealerships in Colorado that recommended tuning them with different jets for 5000-6000', then leaner yet for 7000-10,000, then even leaner if I was going to be up over 10,000' a lot, etc, etc.

The only mod I did was to empty the tank and fill it up with low octane fuel once we got into Colorado and right before headed up to our hunting camp at 9600'.

The Honda Quad started instantly and ran FLAWLESSY the entire trip. I ran it up over 12,000' every day and back to 9600' and it never grumbled once. The only thing I did was to reach under the seat and turn the idle speed screw about 1/4 turn as it was idling a little to slow for my liking.

As this relates to N/A V-8 engines and tuning for high altitude I'm in the "it depends" category as well. I've sent hundreds of carbs out to customers who live and operate their vehicles over 5000's and have a pretty good grasp at this point what needs to be done with them. Even so each application is a little different and there are quite a few variables to the equation including what fuel they are going to use (octane), so nothing is cast in stone when it comes to high altitude tuning and more times than not you'll just have to jump in and figure things out on your own......FWIW......