I need to know what size chambers to run on my BBC. It's a .030 over 454, .040 Quench. TRW 2465 pistons, and 502A2LUN cam ground on 110 degree LSA. I have no idea how to get the calculations right for 8:1 DCR, and from all that I have read this is about right for a pump gas engine right? Thanks in advance!

I'd be glad to run the numbers for you but I have no idea what the specs are for the cam or pistons. You can go higher to around 8.25-8.3 DCR with pump gas. 8 is a nice round number that will work excellent.

Pistons, I believe have they a .226 height. The cam is a solid roller- 276, 284 adv. and 245, 253 at .050 .660 lift, 112 LSA, and 108 ICL. I'm thinking of having it ground on a 110 LSA, hoping that will make my 1/4 ET a little better, but don't know what that will do for DCR calculations. I have been asking about that cam and another similar but bigger(290, 300 adv. 255, 264 at .050 .630 lift) but nobody can tell me what one will work best. I have been all over your site, love the El Camino's. That's what this is going in.

We'll have to find out the "cc"s of the pistons to calculate the CR. Once we know that, we can figure the chamber size. Roughly about 10:1 will work well. But we need the piston cc to get the chamber size.

Generally, a tighter LSA will perform better on the strip than a wider one. This is because the torque peak is higher (but at a lower rpm) although it falls off faster than the wider LSA. This makes a narrower power band with a faster rise time. Gearing and stall are important to take advantage of this. Less power is wasted outside the desired rpm range.

Tighening up the LSA, given the same advance and dur, increases the DCR. Widening the LSA lowers the DCR. If the ICL is not changed the DCR remains the same.

I'm pretty partial to El Caminos. The 66 is a true daily driver. I don't have any other transportation. I had been putting some 20-25,000 miles a year on it, but gas prices have slowed me down, LOL. It's pretty rough but looks OK from a distance.

Mine is an '83. Heavy body modifications. Just got paint on it last fall. Now I have to make it as quick as it looks. They have a 27.5cc dome. I have been looking on this site and discovered that I may need to have the reliefs fly cut to fit the big valves and lift. Should I take as much out of the head volume as I cut out of the domes?

Originally posted by Pony Hunter:
They have a 27.5cc dome. Pony Hunter,

Looked up the specs for the TRW L2465F-30 and the dome volume is 25.7cc.

A 118cc chamber with the cam ground on a 112 lobe sep (advanced 4 deg) gets you around 10.3:1 SCR and 8.17 DCR. the cam ground on a 110 lobe sep (4 deg advanced) gets 8.29 DCR.

Thanks!

Cutting the pockets, and I'm just guessing, will probably not change the piston volume by more than a cc or 2. This could be advantageous with the 108º cam since it will lower the CR and DCR a tad. 8.29 is pretty much max for an easy to deal with pump gas motor (higher, to 8.5, is possible but extra care in building and running is required). The top ring land crevice lowers the DCR about .06 of a ratio. I didn't run the numbers but using Darrin's figures, the 118cc chamber looks good.

I wish you knew how much I appreciate your help, not even knowing if i'm just makin' stuff up. Kinda makes me wanna cry. ;) I was just reading on another post an article that has me worried, goes like this:


"Pat's DCR program is correct for SYMETRICAL cams.
I don't do symetrical cams, but only UNSYMETRICAL ones.
The 276 opens like it is a 272, and shuts like it is a 280. All cams in the same family work the same way, my 288 solid (UF1) thinks '284 open, 292 close'. My 288 ROLLER (UR10) thinks '282 open, 294 close'. Most of my cams are in these general ranges.

UDHarold "

Do you take this into account?
THANKS!

Harold's cam are quick opening and slower closing than most cams. I suppose you could try adding 4º to the closing side. The calculator is based on an industry standard formula for determining cam timing from LSA, dur, and ICL. The rest of the calculator should work fine since the intake closing is the determining factor. So enter the cam specs and run those number then on the DSL page add 4º to the closing angle then calculate the DSL and the DCR. I don't know how accurate this would be. Harold's cams should work with a higher CR than another cams with the same duration. This may be the reason his cams like 2º more advance than most others.

I got the same pistons TRW/Speed Pro Forged 2465 as a std bore size with 088 req port heads 2.19 and 1.88 valves and .041 head gasket thikness on a gen V 454 and was wondering if i am gonna have to cut the valve reliefs too, I am curently running a crower hyd roller with .563IN .587Ex.... 229in 237ex duration with no problems reving to 6300 and I want to change to a crower Hyd Roller with .585In and .612Ex with .236in and 245exh duration. Wondering if the exhaust valve is gonna hit the piston? Anyone know? :confused: