Friend's '57 Chevy bracket car. 383", just pulled off a set of ported double humps and put a set of AFR 210's on it. We figured a tenth or so improvement but didn't pick up one bit. He has ignition timing set to 37 or 38 degrees total and all in by 800 RPM. Methanol carb. Runs 6.50's at 107 currently. I haven't seen the plugs yet so I can't tell you whether they're burnt or what. Do you think 37-38 deg is out of the norm? I ain't familiar with SBC stuff-not at all.

In theory, it should be faster. It may take some experimenting to get there.

My first suggestion is to change ignition timing to 30 - 32 degrees

I've been running sbc for quite some time on alcohol. When on gas i ran around 38 but alcohol more like 32. My other thoughts are if you change from steel to aluminum heads that alone should pick the car up unless something is different like maybe the old heads were milled and there was a loss of compression.

I would look at the plugs and then fuel system may need some changes. My combo is very close, timing is near to 33 drgress at idle as I remember ….

A 57' going 6.50's is pretty good, what does it weigh? Just taking about 40lbs off of it you would think that would give it a little. What carb? As someone said what CC are the chambers on the new heads compared to old?

Heat is power and the downside of aluminum heads is they tend to have less combustion chamber heat. But normally you do see a slight pickup gain a least with the weight difference. I am with the others, we have 4 race engines on methanol and none of them have timing beyond 30 degrees. We've tested higher but there's nothing to be gained. Methanol plugs are hard to read and the only time I feel like I'm doing the job right is to remove the thread section so that I can see the entire porcelain.

Just throwing this out there... You took off some high velocity heads and put on heads designed for higher rpm flow. What cam & converter are you running? I also run a 383 SBC, but I'm only running 195cc AFR heads. I'm on gas, and run high 6's in the eigth, weighing about 3100 lbs. When I tried a single plane manifold, I lost 3-tenths in the eighth mile. It's all about the combination, and trading 10 lbs ft of torque down low for 10 horsepower up high can slow down your ET.

If the heads aren't matched to the cam & converter, going bigger doesn't always pick up.

Just curious, several of you have said when you went from gas to alcohol you pulled the timing back what I consider is a lot. It does not make sense to me. Alcohol burns slower than gas. Normally it like more timing. What's going on....?

Take a good look at this THREAD .

My 388 sbc with mfi likes 36* +. I have Grid and set it up for 40* and then program the desired timing. Anything less than 36* is slower in my car.

This message has been edited. Last edited by: markemark,

quote:

Originally posted by markemark:
Take a good look at this THREAD .

My 388 sbc with mfi likes 36* +. I have Grid and set it up for 40* and then program the desired timing. Anything less than 36* is slower in my car.

......OK.... I read it.....??

Here is my two cents on it. On my car likes 28* timing but it does not slow much even at 38*. I am on alcohol, I think I would like to try it again with more timing. One thing if it is too fat you can get away with more timing.

quote:

Originally posted by Curly1:
Here is my two cents on it. On my car likes 28* timing but it does not slow much even at 38*. I am on alcohol, I think I would like to try it again with more timing. One thing if it is too fat you can get away with more timing.

.....if the motor is fat, it won't be real responsive to timing.

How do you know your comparing apples to apples?

Weather the same? You could have picked to .2 sec and weather could have washed it.

Not enough info to declare gains or not.

Weighs 2700 race ready to my knowledge. That's close. I haven't personally weighed it. PG 1.76 and best I can tell, stalls about 5600. Takes the stripe at around 6900-7000.

Pro Systems. Patrick was called; we had him on speaker, he says richen it up. But how does he know? He aint' seen the plugs and he ain't seen/heard the car run. It sounds too far advanced to me but again it's not my car, not my engine...I am just the guy who's trying to help him along. If he don't listen, I can't help that. I say it's got too much timing. Compression? I can't say. He bought the car with the "tall" double hump's on it. Arent they 64cc?

I know on my SBF stuff, at 30-32 it runs fine. At 34, it drops about a half tenth and a couple MPH. 36, falls off big time. You'd think methanol would be backwards being that it burns slower but I've tried from 26 to 42 and it falls off once I get more than about 32. Stays right around 31 and is very predictable. What's odd is that when I ran gas, the old iron heads liked around 35 degrees lead. Switched to aluminum heads later on and they were fine at 34-35. Went to methanol and had no idea what I was doing and burned a couple plugs at 35 degrees. Granted it was lean as well but richening it up picked up it big time, then another couple tenths by pulling the timing back to 30. AFR #1451 on mine.

You have a Ford head and he has a Chevy 23 degree head. Chambers and piston dome matter a lot on timing.....In general...23 degree heads usually if AFR is proper like around 38 on gas and about 2 degrees more on alcohol give or take 1 degree. If it's fat,.... timing can be all over the place.

This message has been edited. Last edited by: Ron C.,

Not to hijack the thread, but this has me thinking on my stuff. It seemed to be happiest at about 32-33* on gas in Denver. The one good pass I got here it seems that it's going to like about a degree less, but that's about it...

Once I do the alky conversion, I was going to make a pass with the timing as is...or should I back it down a bit first???

12* heads...

quote:

Originally posted by Coloradoracer:
Not to hijack the thread, but this has me thinking on my stuff. It seemed to be happiest at about 32-33* on gas in Denver. The one good pass I got here it seems that it's going to like about a degree less, but that's about it...

Once I do the alky conversion, I was going to make a pass with the timing as is...or should I back it down a bit first???

12* heads...

.....If your starting out a little fat which most do. Personally I would leave the timing alone and bring the fuel to the timing.

quote:

Originally posted by Ron C.:
If your starting out a little fat which most do. Personally I would leave the timing alone and bring the fuel to the timing.

That was the plan but wanted to check to make sure...I'm going to finish tuning it on gas here first before I make the switch. Want something to compare it to.......

The timing is too high for sure. The plug location in pretty much any modern head is better than double humps, so they need less timing. The combination of too much timing, and too much fuel will result in plugs that look good. It will also result in a car that's VERY humidity sensitive and hard on rod bearings. (detonation) Methanol burns "longer" than gas. The time from spark until pressure is quicker than gas, in most cases. I suspect, with no pick up from double humps the cam is too small too.

Reader beware,.....two threads going here, one 23 degree head and the other 12 degree head. Not good to mix these conversations.