lxcoupe

iTrader: (8)

Hey all, I'm at a crossroads and need to let TEA know what to mill my 243 2.5's down to. I was hoping ya'll could help me figure out my ideal SCR, so my DCR will be liveable with CA 91 octane. I was originally going to bolt these heads onto an LS6 shortblock and mill them to 61cc, now I've changed direction and I will be bolting them on an LS2 shortblock.

TEA 243's unmilled have a cc volume of 67cc

I've calculated my SCR as 11.62:1 using this info:
CC: 61
Bore: 4.000"
Stroke: 3.622"
Headgasket bore: 4.020" (is this correct for a GM LS2 gasket?)
Headgasket thickness: .051"
Pistons out of the hole .007"
BTR Stage 2 cam: 44 degrees ABDC

Overall I'm unsure what to do here...

lxcoupe

iTrader: (8)

Any ideas guys?

redtan

iTrader: (5)

8.6-8.7 is the max you should shoot for with 91 octane. I have about 8.9 and it's pushing it on 93 octane.

Search on here for pianoprodigy's excel calculator and that will help you figure out your DCR given those inputs.

99Bluz28

iTrader: (35)

Here's what I came up with.

BTR stage 2, with .051" head gaskets:
61cc chambers should be about 11.25 SCR, and 8.6 DCR .
62cc chambers should be about 11.1 SCR, and 8.5 DCR .
63cc chambers should be about 11.0 SCR, and 8.4 DCR .

BTR stage 2, with .040" head gaskets:
64cc chambers should be about 11.15 SCR, and 8.53 DCR .
65cc chambers should be about 11.0 SCR, and 8.43 DCR .

lxcoupe

iTrader: (8)

Thanks for doing that, I appreciate it! I came up with similar numbers.

What do you guys typically like to see DCR wise for a street/ hdpe car? I understand some guys are running near 9:1 DCR on 91 octane, but it's all in the little stuff I would image at that point, head gasket thickness, cam, etc. I'm not really looking to push the envelope too much and win a dyno day... just looking to maximize this combo safely.

99Bluz28

iTrader: (35)

If you want a little added flexibility with head gasket thickness choice the you could go with a 63cc chambers and .040" head gaskets.
This will give you a slightly higher SCR(+.04 ?) and DCR(+.03 ?) than with 61cc chambers and .051" head gaskets, but if you have any issues because of the higher SCR and DCR you can easily swap to .051" head gaskets for the slightly lower 11.0 SCR, and 8.4 DCR .

You also have the option of a .045" head gaskets to put the SCR an DCR right between the two.

lxcoupe

iTrader: (8)

99Blu, thank you! Seriously helpful. I will mull it over for a day or so before letting TEA know what to do.

It's always better to run a bigger chamber and thinner gasket, to unshroud the valves, so I think I'll go 64cc and .040" Cometic and keep my DCR safe.

I'll update this thread when the motor is together.

lxcoupe

iTrader: (8)

99, which SCR calculator are you using? Because using this one:

http://www.csgnetwork.com/compcalc.html

I get 11.56 SCR with Cometic .040" thick, 4.060" bore gasket, and .009" out of the hole (worse case). Even with .003" out of the hole, it will be 11.37 SCR

99Bluz28

iTrader: (35)

I used the VE calculator available in the Advanced Engineering Tech section Sticky.
I had the " out of the hole" (deck height) set to .006".

I'd also ask TEA to calculate it for verification, just to be 110% sure.

lxcoupe

iTrader: (8)

Thanks. I'm taking the shortblock to RPM Motors to have them change out the cam bearings because I nicked one pulling the stock cam out, so I'm gonna have them measure the exact piston out of the hole height. I asked TEA to hold on the mill until I can figure it out 100% but I'm leaning towards 64cc to keep the chamber as large as possible to unshroud the valves, and a .040" Cometic...