maximum compression for pump gas aluminum head m

[428tom]

Just wondering on what is the maximum compression ratio for pump gas, you can run with aluminum heads?

[FINESPLINE]

Can only speak for myself----383 sbc with Dart 215 pro aluminum heads with 64cc chambers 6 inch rods port matched victor jr. comp cams small solid roller R 280 R. True compression at 11 to 1. Runs cool with no signs of detonation on any pump gas. Car is a stick and driven during the hot summers on cruise nights and to car shows. ALMOST left out the carb. A custom built 750 DP---money well spent here !

[BillK]

Tom,

I really dont think you can make a general assumsion about this. There are a lot of variables involved. I just read that some of the new direct injection engines are running almost 13 to 1 on 87 octane pump gas. A lot of it depends on how much time you are willing to spend optimizing the ignition and fuel curve to prevent detonation throughout all operating conditions. A fuel injected engine with knock sensors can get away with a lot more than one with a Holley and a distributor.

That all being said, I tell my customers 9 1/2 for iron heads and 10 1/2 for aluminum but I tend to be very conservative.

[Mike Croley]

That would depend on which pump gas ( 87 , 91 , 93 ) and on what day . Pump gas is not consistent batch to batch , day to day . It doesn't have to be . The computer and EFI in street cars can easily compensate for the differences in ethanol content and the different blends .
As a rule , aluminum heads allow a little more CR than steel heads , but on pump gas i'd stay below 11.1 and maybe even a little lower to be safe .

[X-TECH MAN]

My street rod with a bone stock ZZ4 crate engine with a GM rated 10 to one comp. (probably a true 9.5 to one unblueprinted) and alum. heads runs fine on todays 87 octane horse pizz.....oops. I mean todays junk pump gas. Car only weighs around 2700 lbs. Engine temp. plays a role also. Mine usually stays around 170 degrees and I run a 160 thermostat. Timing is set at 10 degrees and totals out at 36 degrees at 2500 RPM. I use a vacume advance on an HEI dist. and 3.55 gears with an over drive trans. Turns 2005 RPM at 65 MPH in overdrive. Not a lot of load on the drive train. Lots of things to consider when running pump gas and a med comp. ratio.
If its a race car around 3000 or under to 3400 lbs I would stay at no more than 10 to one with at least 4:11 gears unless its a late model with a computer, knock sensors, etc. then use 91 to 93 octain.

[FINESPLINE]

Originally Posted by X-TECH MAN

My street rod with a bone stock ZZ4 crate engine with a GM rated 10 to one comp. (probably a true 9.5 to one unblueprinted) and alum. heads runs fine on todays 87 octane horse pizz.....oops. I mean todays junk pump gas. Car only weighs around 2700 lbs. Engine temp. plays a role also. Mine usually stays around 170 degrees and I run a 160 thermostat. Timing is set at 10 degrees and totals out at 36 degrees at 2500 RPM. I use a vacume advance on an HEI dist. and 3.55 gears with an over drive trans. Turns 2005 RPM at 65 MPH in overdrive. Not a lot of load on the drive train. Lots of things to consider when running pump gas and a med comp. ratio.
If its a race car around 3000 or under to 3400 lbs I would stay at no more than 10 to one with at least 4:11 gears unless its a late model with a computer, knock sensors, etc. then use 91 to 93 octain.

I agree with you X- Tech Man. Although I run a lot more initial timing because of the cam , I have a Be Cool radiator with twin fans on a thermostat plugged into the heads set for 180 degrees and a mechanical stat at 160 on the manifold. You have to drive the car to build heat. I have to sit in stop and go traffic during the summer to set the fans off and they don't stay on long. I do use 93 octane all the time. My trans is a tremec tko600 with a .64 od with a 4:30 rear.