Epra_Dzl728

Starting off the truck is a 04 2500hd that might tow a car 8-10 times a year. Current mods are long tubes, exhaust, 216/220 .550 112lsa with supporting valvetrain, stock converter.
Question is, I have a set of ported/milled .030 243’s with a complete tbss intake. I also have a complete set of 823’s also with a complete l92 intake.
Being that the 243’s are milled I’ve seen compression numbers in the high 10’s to low 11’s, is this to high for a pump gas truck that will occasionally pull hills with a car trailer?
Stock 823’s obviously make power, but up high where the truck doesn’t live very much, and possibly need a cam with a larger split to take full advantage of the square port heads.
What are your opinions on which route I should go?

madmann26

iTrader: (7)

The dick kicker is the compression you lose with the 823s.

Honestly, the 706s are a better choice but I’m a 706 dick swinger.

1redta

the cathedral ports would be better for a lower power band

1FastBrick

iTrader: (17)

With a standard pair of 243 you would be just over 10.1:1 compression ratio. Depending on what .030 took the combustion chamber down to you would be in the 10.5:1 ratio.

I am guessing 62=61cc range. But you would need to measure to be sure.

You can ran pump gas but you would need to run premium fuel. You would also want an in person tune and Should have it checked and modified based on being loaded and unloaded.

Epra_Dzl728

Thats seems to be an optimal compression ratio for pump gas, obviously each motor is different and at this moment I don’t know what my piston to deck height is until I pull the heads. I’ll have my machine shop cc the heads to be sure where I’m at, and go from there to get a definitive static and dynamic ratio. If it seems comes out to be in the high 10 to low 11 compression ratio I guess I could always have my 317’s milled

00pooterSS

iTrader: (40)

Testing has shown that the larger split doesn't do a whole lot, in other words it's not that big of a deal if you go to square ports to change the cam

But on that truck I would absolutely want the cathedral heads and tbss intake.

This test is an awesome read if you're considering cathedral or square port

Cathedral v.s. Rectangular Port Cylinders - Head To Head - GM High-Tech Performance Magazine

madmann26

iTrader: (7)

”In reality, the cathedral-port heads were within 1-2 hp at the peak, but offered as much as 20 additional lb-ft below 4,000 rpm.”

That extra 20 or so would make a truck feel so much better below 4K.

Epra_Dzl728

Definelty, it can use all the tq’s she can get. Seeing as the truck rarely lives above 4000, the cathedral port fits the vehicle much better. Sounds like I’ll slap the 243’s /tbss on, have the heads cc’d prior to get a better idea of what the static and dynamic compression is going to be like. Re tune and hope she doesn’t have to many detonation issues with 91/93 octane.

madmann26

iTrader: (7)

Tuning should not be an issue. I run 706s on my 370 at 12.5 CR and run pump gas just fine with no detonation.

I can only run 22 degrees of timing up top but it’s more then I need. Lol

Epra_Dzl728

Sweet that makes me feel better about the whole situation.