Tally TransAm

iTrader: (17)

i plan on getting PP 5.3L heads this week to go with my 224/581/112 cam

what would be a good compression to run. i was thinking something along the lines of 11:1, maybe a little higher.

i only run 93 octane and the car is a daily driver, what compression should i go with and how much should the 5.3L heads be milled to achieve this

thanks

ryan

z28man

.030" . this should put you at 10.5:1 compression. especially if high octane is not available to you this is all i would go. that should be good with the cam you have also.

Tally TransAm

iTrader: (17)

wont .030 on a 5.3L heads put me at 11-1

CrazyBosnian

iTrader: (1)

.030 sounds good and will be fine with ur cam, but if you decide to get a real cam :p, you might have clearance issues...

Tally TransAm

iTrader: (17)

ill get a "real cam" when i up the displacement

gomer

iTrader: (13)

Don't forget you'll need shorter pushrods when milling that much off your heads. I already had stock length hardened pushrods so I ordered my heads without any milling to keep from having to buy pushrods again.

CrazyBosnian

iTrader: (1)

*****

Ed Blown Vert

iTrader: (2)

I though 5.3l head already had a higher C/R?

94form2000z

iTrader: (10)

I was told by Jay @ Absolute that my CR was right at 11:1 without milling my 5.3's! Might want to talk to you head porter (miller).

gomer

iTrader: (13)

They are slightly higher, but most porters remove material from the combustion chamber on the 5.3 heads to "unshroud" the exhaust valve on the head.. the removal of the material equates to a larger cc of combustion chamber and lowers the static compression ratio over what it would be with an unmodified 5.3 head, therefore most people mill the modified 5.3 head to regain the lost compression.

Tally TransAm

iTrader: (17)

what length pushrod would i need with the heads milled .030

also how much could you mill and keep the 7.400" pushrods

i belive i was told by terry from patriot and jason at texas speed that i could mill about .015 to get 11-1 compression. does this sound right, i spoke with them i while ago and dont really remember. also could i use the same pushrods i have (comp 7.400")

basically im trying to figure out what a good compression ratio would be on an NA daily driver running 93 octane and how i would achieve this?

gomer

iTrader: (13)

I'm running my heads uncut, but I think your cam has a smaller base circle than a stock one ( know the TR cams do ) so you could probably get away with .015 on stock length push rods.

Tin Indian

gomer is right....

Case in point: Non- surface milled TEA 5.3L heads will have a chamber volume of approx 63cc after the CNC machine removes the needed chamber material in order to un-shroud the valves.

The 63cc chamber on a stock displacement 5.7L will get you a 10.8:1 CR when stock graphite head gaskets are used.

Ron,

Tally TransAm

iTrader: (17)

so unmilled 5.3's give you about 10.8:1, so i could mill them about .015 to achieve 11:1 and still run the 7.400" pushrods?

if that is correct,sounds good to me

would you go with a higher comp ratio on a street car, buying new pushrods would not be preferable, but if running a high comp ratio would benefit me i would do it

Tally TransAm

iTrader: (17)

ttt

Tin Indian

I don't know how much a givin amout of head milling changes what the chamber cc volume is, but if your head porter will actually CC the heads for you and give you the numbers, this is what it will equate to in compression ratio on a stock displacement 5.7L LS1:

72.27cc = 9.1 CR
71.71cc = 9.2 CR
71.05cc = 9.3 CR
70.59cc = 9.4 CR
70.03cc = 9.5 CR
69.74cc = 9.6 CR
68.91cc = 9.7 CR
68.35cc = 9.8 CR
67.79cc = 9.9 CR
67.23cc = 10.0 CR
66.67cc = 10.1 CR (stock LS1 head spec)
66.11cc = 10.2 CR
65.55cc = 10.3 CR
64.99cc = 10.4 CR
64.43cc = 10.5 CR (stock LS6 head spec)
63.87cc = 10.6 CR
63.31cc = 10.7 CR
62.75cc = 10.8 CR
62.19cc = 10.9 CR
61.63cc = 11.0 CR
61.07cc = 11.1 CR
60.51cc = 11.2 CR
59.95cc = 11.3 CR
59.39cc = 11.4 CR
58.83cc = 11.5 CR
58.27cc = 11.6 CR

MyLS1Hauls

iTrader: (2)

11:1 on pump gas in Florida heat is the absolute max I'd run personally. I've talked to a few sponsors and they think thats the cutoff point for pump gas. Jason 99T/A burned his pistons on 11.5 I believe. You'll just have to be sure to only use good gas and if you hear the motor detonating, take it easy on it. As for the exact compression ratio, I'd cc the combustion chambers and then decide how much to mill them since material is removed from there to deshroud the intake valve. I'm going to shoot for about 63cc on my 5.3 heads over the winter.

ONEBADWS6

iTrader: (22)

My 5.3 heads were milled .40 and I was told I had a 57cc chamber

Tin Indian

Jeeeze ... That thing must have the CR of a diesel!

I can't see how it runs on pump gas unless it's loosing all it's timing due to knock retard.

Tally TransAm

iTrader: (17)

damn thats a high comp ratio to run spray