All three together.
Continuing ignition timing debate from the 416 thread.
- Thread starter TT5.9mag
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28 vs 30 degrees
MobileCustoms
You can twist perceptions, reality won't budge
Thanks for that. So I think my grasp of what I mentioned is at least on the right track then. So if my my peak torque is a 4300rpm then I wouldn't want my timing to be all -in at that point. If my total timing is set for , say 35 degrees, is there a general number of degrees fewer than 35 that I'd want to shoot for at peak torque? I know each combo wants what it wants but I'm wondering what might be a decent number in general... like 30 degrees at peak torque rpm, then rely on stiffer springs to allow it to keep climbing more, to 35 as it approaches peak HP rpm?
30 vs 34 degrees
TT5.9mag
Two atmospheres are better than one
You absolutely have the concept. And the only answer to part two of your question is testing. Don’t settle on numbers for the sake of numbers. My bbc NA on the dyno wanted 43 degrees for max power. On boost at peak torque I have 23 in it, as an example.
TT5.9mag
Two atmospheres are better than one
Going by that graph, are you saying because the engine picked up everywhere changing from 30 to 34 that the concept isn’t valid? What happens if you put 40 in it? You may have arrived at the correct value for peak torque but haven’t yet got to peak hp. That’s all you can gleam from the graph alone.
You don’t grasp the why? I guess I’ll try it this way one time and then I just don’t give a ****.
If you have ever read the SuperFlow dyno manual you’d know this. If you don’t have a copy, get one. Then read it because I’m not going into that kind of detail here.
Everyone with a water brake dyno regardless of what data acquisition you use should read it. There is valuable information that I’m not going into here.
So take this for what it’s worth because I doubt anything I say to you will change your thinking.
Superflow says it takes 250 cycles to affect a change. That means a change in A/F ratio, timing, whatever. I’ve talked to people who say that’s a bit generous.
I do most of my testing at 300ish rpm/second. I know guys who never test at less than 600 rpm/second. I believe those power numbers are more accurate than the slower speeds, you can’t get enough data in a pull that fast.
That’s because it takes at least (according to SuperFlow and two of my mentors, one of which as I said has developed more testing protocols and has done and analyzed more dyno data from every conceivable dyno out there) 250 cycles to affect a change.
I believe it to be more like 300 cycles. Even if your software is sampling (or whatever they call it now) at 100 times a second you are still missing too many data points.
As a side note when I first worked with data loggers they were 5 samples per second. That’s horrible and you’d make tuning changes that went sideways or backwards because you were always at least late with the data.
The next up was 20 times a second and for a low 9 second car it was acceptable, but for a faster car you were in the same boat.
I have no idea what the sampling rate is for Pro Stock or fuel burners but I’m betting it’s over 100 times a second. For a 6.5 second pass you’d get about 700 data points. That’s pretty slow IMO.
It’s the same on a dyno. Because it takes 250 cycles to affect a change you can not, I say again CAN NOT use a sweep test to determine a timing curve.
You are not getting enough data to do it.
That’s why on sweep tests you can get too much if timing at peak torque and not see it.
If you steady state test at say 3000 rpm and even if you just do it every 1k after that to whatever peak rpm is, you’ll see it wants a curve. Every time.
And when you get the curve right the curve is almost always right. By that I mean in the car it may take more timing so if it wants X timing at peak power on the dyno, in the car it may take 2-4 degrees or more timing at peak for the best time slip, because the engine isn’t loaded the same in every gear, nor is it loaded like it is on the dyno.
But the shape of the curve will be the same.
I have a 395 inch small block I built that made 505 on my dyno, with OE iron heads and 2.02 valves. It’s a measured 11.xx:1 compression.
To get it happy I did a steady state test from 2500, then every 500 rpm after that to peak torque and after peak torque every 1k rpm.
The curve is 25 initial at a 1k idle at peak torque it’s at 30 and that’s at 5k. It tops out at 34 at 6500.
That is almost exactly 1.5-2.0 degrees per 1000 rpm. Bill Jenkins published that in 1975 and as crazy as it may seem, it’s just about spot on with all my testing.
I forget exactly how much power locked out timing cost this engine but it was at least 20/20. And it picked up from the bottom of the pull (2500) to peak rpm (6900).
It is grossly under valved and it’s severely under area for ports. Yet it made over 500 hp on bowl ported iron heads most guys would throw away.
So the upshot is you can’t sweep test for timing because it takes too many cycles to cause a change.
You go so fast that the engine always wants more timing because you don’t have enough time to let the engine tell you what it wants.
So you steady state the engine and move the timing around and watch the numbers. The engine will tell you exactly what it wants for timing and it’s a curve and it’s usually less total than locked timing.
What do you mean by a cycle?
This show exactly what I’m saying. It might be the best numbers you are getting but there is no way on this earth it wants 30 at peak torque and 30 at peak power.
You have compromised the tune up to make it half assed happy everywhere.
I’d be willing to bet (not sure what heads they are) that with a 2V carb it would want way more timing at peak rpm but if you give it more it will kill torque like a mother all around peak.
Give me a minute and I’ll dig out the Superflow manual and I’ll take a picture of it so you can read it for yourself.
TT5.9mag
Two atmospheres are better than one
I think this is a very powerful statement. I’ve seen motorhome 440s with 10 psi of boost so numb to timing changes that even on boost we ended up at 39 degrees. And peak torque was the same rpm as peak power. Weird stuff happens sometimes and each engine is different.
What’s the compression on the 602 crates with 2 barrels?
Ok, I had to find the Superflow book and my notebook.
Going off my memory I got it wrong. Superflow says 100 cycles and the other people I talk to said it’s 250 if not 300 cycles to affect a change.
SuperFlow is talking about how fuel behaves while testing. But the time is the same. And it affects ignition timing the same.
Cycles is rpm. It takes 100 cycles to affect a change. Again, that’s what SuperFlow says. I believe it to be at a minimum 250 cycles.
It’s the exact same with timing. When you are moving so fast, even at 300 rpm/second it’s too fast so the engine thinks it wants more timing than it does.
Going off my memory I got it wrong. Superflow says 100 cycles and the other people I talk to said it’s 250 if not 300 cycles to affect a change.
SuperFlow is talking about how fuel behaves while testing. But the time is the same. And it affects ignition timing the same.
Cycles is rpm. It takes 100 cycles to affect a change. Again, that’s what SuperFlow says. I believe it to be at a minimum 250 cycles.
It’s the exact same with timing. When you are moving so fast, even at 300 rpm/second it’s too fast so the engine thinks it wants more timing than it does.
I don’t know how to even begin to explain that engine other than to say it is an outlier of outliers.
Both with the amount of timing it wanted and how peak torque and power were at the same rpm.
Just weird but certainly not even remotely close to normal.
TT5.9mag
Two atmospheres are better than one
Agree. But a rising boost curve puts peaks in artificial places and does weird things with very low cylinder pressure.
TT5.9mag
Two atmospheres are better than one
Steve Morris just did a video with Holdener testing an LS with different cylinder heads and they ended up with wild timing numbers for a boosted LS and had hp/tq peaks at similar rpm. They were using a centrifugal blower with a rising boost curve. It’s always a combination of factors at play. Piston design, chamber design, and cylinder filling. Each one is a different animal.
I was going to watch that and forgot all about it.
Now I need to go find it and watch.
TT5.9mag
Two atmospheres are better than one
It didn't pick up everywhere at 34 deg. It lost everywhere until about 6900 on up where it almost made as much as 30 degrees. 28 degrees compared to 30 made a hair less (nearly the same) all up to about 6000 where it separates and starts making less the rest of the way up. I know those charts are hard to read on here. I added a graph below. Maybe that will help.
They whistle around 9.1 - 9.3. Just to make sure we are on the same page the dyno graphs I posted are of a spec motor not a 602 crate. Spec motor= 10.5 max comp. spec heads (stock replacement cast iron). Spec dual plane intake. Flat tappet, 2bbl. holley, 7400 rpm limit. Link to the specific rules below.
2025-Stock-Car-Rules.pdf https://share.google/UcGp9SqUSiO8Ui7gZ
Which is what I’d expect. You are saying your results match exactly what I’m saying. You just refuse to accept it.
Your locked timing is a compromise everywhere. 34 made less power everywhere and almost caught up at the very top of the power curve. That makes perfect sense.
28 and 30 are close until past peak torque and then it wants more timing so the 30 picks up. That makes perfect sense.
Your numbers tell you it wants a curve. It will be a slow curve but it wants a curve.
You may find out that it may want 32 at peak rpm but when you have more timing than you need before the engine wants it, you get the plug hotter than it would be with correct timing and it never cools off until the load goes away. That makes 30 look the best but it may want a skosh more if the curve is correct.
I forgot what ignition that is, but if you aren’t checking the timing at the other test rpm you don’t know what the timing actually is.
Im betting a correct curve would be at the very minimum, worse case scenario be 12/12 better. In a limited class like that engine live is that would be a significant gain. I wouldn’t be surprised if it was more than that because for some reason when you do the curve it makes more power than what a sweep shows with locked timing.
Interesting video. That is a whole different world. I haven't ever done a boosted motor on the dyno. The power numbers are crazy. 90% of what I do is less than 1/2 those power numbers. Only now since it's been pointed out to me that you can't develop a timing curve with a sweep on a dyno should I be skeptical of all the testing they did of being valid? I noticed they used sweeps to evaluate timing and fuel changes and no steady srate testing was done.
B3422w5
Well-Known Member
Here are a couple of comments Charlie Westcott ( who I doubt anybody here will doubt his knowledge) made to me
Newbomb Turk’s comments have some validity to them, and maybe should be given a bit of respect..lol
Charlie:
“if you have a crank trigger, you are firing off the front of the crank. If you are using a pickup in the distributor, and the gear is on the back of the cam, its gonna vary some, mosty from slack in the chain/belt. your guy that monitors it on the racepak needs to know that the racepak is just monitoring the signal from the box, not reading the actual position with a light. Its meaningless. I had a guy, Steve Yantus, that never checked the timing cause the "grid said" it was at 30. I said you are an idiot, hook up a timing light. Most cars have electronics on them that the user has no business using.”
Me:
So, is it a waste of time to look at timing with a light on the dyno at different operating rpm’s and setup a timing curve based on what the timing at those rpm’s tell you?
Or isn’t it worth chasing
Charlie:
No, thats a valid test. I am saying that if you have a crank trigger, it isnt going to move unless the pickup is odd. The holley pickup I used in PS retarded the timing and you had to comp for that.
Newbomb Turk’s comments have some validity to them, and maybe should be given a bit of respect..lol
Charlie:
“if you have a crank trigger, you are firing off the front of the crank. If you are using a pickup in the distributor, and the gear is on the back of the cam, its gonna vary some, mosty from slack in the chain/belt. your guy that monitors it on the racepak needs to know that the racepak is just monitoring the signal from the box, not reading the actual position with a light. Its meaningless. I had a guy, Steve Yantus, that never checked the timing cause the "grid said" it was at 30. I said you are an idiot, hook up a timing light. Most cars have electronics on them that the user has no business using.”
Me:
So, is it a waste of time to look at timing with a light on the dyno at different operating rpm’s and setup a timing curve based on what the timing at those rpm’s tell you?
Or isn’t it worth chasing
Charlie:
No, thats a valid test. I am saying that if you have a crank trigger, it isnt going to move unless the pickup is odd. The holley pickup I used in PS retarded the timing and you had to comp for that.
The ignition loses less than 2 degrees of timing through the entire curve. Consider for the sake of this example for now it loses zero timing and at the end you can adjust the numbers by adding 3/4 degree at the bottom and subtracting 3/4 degree at the top if you like.
Nowhere in the entire curve does 28 degrees or 34 degrees make more power than 30 degrees does.
That makes sense. I don't think anyone here is disputing that. I am using a timing light on the dyno when I check the timing curve. That does make me wonder if Turk is using a timing light triggered from the plug wire on his distributor machine?
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