'66 383 build, cam question

[dvw]

When it comes to ignition timing less is more. If an engine only wants say 33* advance, then 33*is the right number. Insisting that the engine needs 36-38 is just pushing against the piston in the wrong direction. Anything we can do to increase combustion chamber efficiency, start with a tight quench, then reducing total advance is a win -win situation. Tight quench is an aid to running what maybe a tighter than accepted compression ratio. Sure you can under cam a high compression engine and achieve high cylinder pressures that produce pinging. But why build such an engine and then hamstring it with a tiny cam?
For instance late Ford 302 gt heads. Most engines only wanted 28ish degrees advance. The more efficient the combustion chamber the less advance needed.

It could use more timing. I'm sure it coud use up towards 38 with this head. But it won't quite get there on pump gas. Yes I agree that proper timing could be a lower number with a different combo.. But that would require less compression, larger cam, or more effecient chamber and plug location. This car is a restored stock Coronet R/T convertible. So it has the inefficient 906 head. Did my best to make them as detonation resistant as possible. Pretty hard to get quench with a open chamber cast head. It was supposed to be 9.5-1. But the machinist made an slight error. The owner hates lumpy cams, thus the little cam. Comparing the timing required on big bore old open chamber iron heads with poor chamber design and plug location to modern aluminum small bore stuff is not even on the same page.
Doug

 

[1KoolBee]

If you plan on running HP exhaust manifolds, avoid too much cam overlap. The mopar .520 solid is a good choice. If you are going to run headers, size the cam for the realistic operating range you plan on. With 3:23’s I’d stay fairly conservative, maybe 220ish duration , 230 ish max for a cruiser. Look up David Vizard’s “128 rule” and calculate it for your combo. Might shed some interesting insights into your optimum lobe centerline. I really like my Hughes cam in my 383 BTW.

 

[68-500]

It could use more timing. I'm sure it coud use up towards 38 with this head. But it won't quite get there on pump gas. Yes I agree that proper timing could be a lower number with a different combo.. But that would require less compression, larger cam, or more effecient chamber and plug location. This car is a restored stock Coronet R/T convertible. So it has the inefficient 906 head. Did my best to make them as detonation resistant as possible. Pretty hard to get quench with a open chamber cast head. It was supposed to be 9.5-1. But the machinist made an slight error. The owner hates lumpy cams, thus the little cam. Comparing the timing required on big bore old open chamber iron heads with poor chamber design and plug location to modern aluminum small bore stuff is not even on the same page.
Doug

Big ole chambers on 906’s are a problem for quench for sure. I was referring to the 516 heads mentioned earlier in the thread.
1 thing is for sure engine building is an art not a science. Everyone has their own way to skin that cat!

 

[BSB67]

When it comes to ignition timing less is more. If an engine only wants say 33* advance, then 33*is the right number. Insisting that the engine needs 36-38 is just pushing against the piston in the wrong direction.

Sure. But how many people today actually do testing to determine what it wants? Few people, I suspect.

Me and some track friends tested a lot of big block factory head cars. With quench, without quench, 135 to 210 psi cranking cylinder pressure, headers, manifolds, mostly small cam street stuff. They all ran best with 37+ degrees. One of my cars slowed down a lot if it had less than 39 degrees. One guy was running 42.

I cannot tell anyone what their car wants, but suspect there are guys leaving meaningful et and mph on the table because what they believe to be true from the internet and magazines.

 

[dvw]

Sure. But how many people today actually do testing to determine what it wants? Few people, I suspect.

Me and some track friends tested a lot of big block factory head cars. With quench, without quench, 135 to 210 psi cranking cylinder pressure, headers, manifolds, mostly small cam street stuff. They all ran best with 37+ degrees. One of my cars slowed down a lot if it had less than 39 degrees. One guy was running 42.

I cannot tell anyone what their car wants, but suspect there are guys leaving meaningful et and mph on the table because what they believe to be true from the internet and magazines.

Years ago my son had a hopped up 340 Duster. First time to the track, 13.15. Second pass backed it up 13.16. I rthought I could hear a little rattle. Backed the timing to 33, 12.88. Backed it to 31, 12.68. Backed it again and it slowed up. So 31 it was. My 15-1 580 -1 Indy race motor doesnt care a whole lot. 34-37 might be .01-.02. Even turned back to 27 only slows it .10. My small block blower motor? 4 degrees was the difference between replacing pistons on a regular basis vs the current set that were installed in 1991.
Doug

 

[BSB67]

The small blocks we tested were always in the low 30s. If you’re in detonation it will always slow them down. It would be interesting to run yours at 33 with better fuel. Might not make any difference.

 

[BSB67]

My 500 motor with eddy heads does not seem to care from 32 to 36. Never tried 28 or 30. Probably should.

 

[Splush]

Thanks all! I am going to start tearing in down. I appreciate everyone's input and opinions.