'67 El Camino H/SA

[goinbroke2]

If everything is correct (balancer/marker/etc) I'm wondering if being a stocker cam on a less than ideal shortblock is producing low cyl pressure and the timing advanced that far is making up for it? As the rpm goes up, the better the cam breathes (less overlap losses of cyl pressure) and it gradually gets back to what is considered normal at 36*?

I'm thinking a tight ring package and decked block so the quench area is ideal and higher static compression would produce more cyl pressure and require less advance on the bottom?

What is the cranking pressure?

[HandOverFist]

Originally Posted by goinbroke2

If everything is correct (balancer/marker/etc) I'm wondering if being a stocker cam on a less than ideal shortblock is producing low cyl pressure and the timing advanced that far is making up for it? As the rpm goes up, the better the cam breathes (less overlap losses of cyl pressure) and it gradually gets back to what is considered normal at 36*?

I'm thinking a tight ring package and decked block so the quench area is ideal and higher static compression would produce more cyl pressure and require less advance on the bottom?

What is the cranking pressure?

Don't have those figures atm, but the same set-up is about to be tested on a fresh F/SA Corvette...that will answer some questions for sure. He will be using a maximum of 44 degrees on his runs.

[Dave Noll]

I don't know on the cranking pressure currently. Have been swapping cams. The heads are milled, the block is decked. Supposed to be 9 1/2:1, open chamber FFFord heads. I didn't pick up as much in the 60, but in the quarter it was better than .1 and almost 2 mph.

[goinbroke2]

Dave, you're running a Cleveland though and milled or not the open chambers have slow flame propagation and poor mix. I would think that would add a new dimension into the whole thing compared to a smaller chamber chev.
Compared to a Windsor, the bigger chamber Cleveland liked more timing all through the rpm from what I remember too.

For comparison sake, I built a 289 with 260 heads and it was quickest with 28*. Small efficient chamber required little advance (didn't breath worth squat even with the 1.78/1.48 valves put in) Would nose over around 6000 regardless of cam/carb/exh/etc but man it would go from idle to 5800 like a fuel motor!

[Dave Noll]

I had an 11:1 351 Windsor in my car before I decided to try Stock. With the timing at 36 it slowed .2 on 110 Sunoco. I raced it @ 40. It had 215lbs cranking compression.

[goinbroke2]

Wow Dave, that's abnormal for a sbf. I'm assuming you were using 69-70 351W heads? I had a 2 4bbl 302 I built which liked 38* which seemed a lot, when I pulled it apart the pistons were washed clean around the circumference of the piston and the centre was black. I chalked it up to something I did wrong while porting and chamber work and that was why I needed 38. 40 though, that to me seems pretty high.

Course they all ain't the same are they? Lol!

[Dave Noll]

Originally Posted by goinbroke2

Wow Dave, that's abnormal for a sbf. I'm assuming you were using 69-70 351W heads? I had a 2 4bbl 302 I built which liked 38* which seemed a lot, when I pulled it apart the pistons were washed clean around the circumference of the piston and the centre was black. I chalked it up to something I did wrong while porting and chamber work and that was why I needed 38. 40 though, that to me seems pretty high.

Course they all ain't the same are they? Lol!

Yes on the 69-70 351W heads.

Around the circumference? Can't say for sure but sounds like a Ring issue to me.

Can I ask what fuel you were running that your sbf liked just 28*?