I did the math.
On a 9.600 LA-deck, the 167s math to .0095 below deck. that is ~1.87cc
The pistons, as far as I can tell, have 5cc eyebrows.
the .028 gaskets are ~6.8cc
The 360 heads, by all accounts are usually ~72cc. I have none smaller.
Throw in 1cc for the crevice volume
That totals 86.7cc
at 3.91bore, the swept is 652.27
That makes an Scr of 8.52
The .028 gaskets need a rough deck, else the fire-rings like to migrate, and it doesn't take long.
With the .039 FelPros, the numbers work out to
(652.27 + 88.5)/88.5 = 8.37
Plugging that into the Wallace with a modest cam (Ica of 66*) at 500ft elevation (guessing OPs elevation); I get
Static compression ratio of
8.37:1.
Effective stroke is 2.52 inches.
Your dynamic compression ratio is 6.60:1 .
Your dynamic cranking pressure is 124.24 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 6.50 :1.
V/P (Volume to Pressure Index) is 90
V/P of 90 is just about 3% stronger than a factory 225 slanty.
The Effective DCR of 6.5, is about 1.5 points low and;
and Cylinder pressure of 124psi, is a good 30 psi low for open-chamber heads, and the Q is so huge as to be ineffective.
If OP had a stock convertor and hiway gears, this would be guaranteed to be sluggish to around 3000 to 3500 rpm.
Thankfully he has a manual-trans and 3.91s..
Op said
My advice still stands. but now with a low cylinder pressure design), I would add; Notta chance would I run this engine, in it's current iteration, with any other cam but the factory-sized one. With an Ica of 48*, the numbers improve to
Static compression ratio of 8.37:1.
Effective stroke is 2.89 inches.
Your dynamic compression ratio is 7.43:1 .
Your dynamic cranking pressure is 145.79 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 7.33 :1.
V/P (Volume to Pressure Index) is 121
VP of 121 is similar to a stock 5.2 Magnum. I could live with that..... if I had to.
But If it was mine;
I'd still run a compression test to see how bad it is. Then if it sux as bad as I suspect, then
I'd Zero deck it rough, to hold those .028s, then install 60cc closed-chamber iron, small-port heads. With an Scr now of 9.85, a Q of .028, and modest cam with an Ica of say 60* , the picture changes to
Static compression ratio of 9.85:1.
Effective stroke is 2.66 inches.
Your dynamic compression ratio is 8.10:1 .
Your dynamic cranking pressure is 163.55 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 8.00 :1.
V/P (Volume to Pressure Index) is 125
Now you got an engine!
Couple this with the 4-gear and 3.91s, and you are guaranteed to have fun in any A-body, and especially so in a light-weight Valiant.
To save a lil cash, I'd try it with the current decks and .028s, for a Q of .038ish; but the heads gotta be closed-chamber. and the intake I would use, would have ports matched to the head, and a Thermoquad.
But,
I have this Dual-Port, I got from a member here a few years ago, that I've always wanted to use on something.
Ima thinking Magnum heads and a port-match, to go with that lopey cam. Or, I'd really like to try the stock 360 sized cam, with this intake;
Static compression ratio of 9.6:1.
Effective stroke is 2.78 inches.
Your dynamic compression ratio is 8.21:1 .
Your dynamic cranking pressure is 166.49 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 8.11 :1.
V/P (Volume to Pressure Index) is 133
Oh yeah, this is starting to look like fun.........
Since the current cam already has a lopey idle, I'd screw the Magnums on, or any aftermarket closed chamber LA-heads and redo the compression test. If it ain't too bad, then, with the OPs 4-speed, and 3.91s, I'd try it.
So, at this point, my only cost is the closed-chamber heads and gaskets, cuz I already have a spreadbore intake, and matching 4-bbl.
If the heads I get have small-ports, I have this small-plenum Excelerator looking for a home.................
Like
@toolmanmike said;
I just narrowed it down some .....................
