On a 400, how high of compression could you have and still run regular, not premium fuel?

 

. Depends on cam size/spec.s, combustion chamber and piston prep., ignition curve/advance, thermostat temp., cooling capacity, usual workload, and engine quench distance... etc...


. Usually 9:1 or slightly more... lots of variables... I'd aim for 9 for efficiency's sake and do what's necessary to make it work if sticking with 87 regular... avoid the actual 7's of '72 and later engines...

 

That's where I'm having trouble. This is going on a 79' 2wd that will be used as a daily driver and to occasionally pull a trailer (around 3-5 thousand pounds, 3-4 times per year) I want a strong motor that can run on the cheap gas. I'll be running an Edelbrock 2171 intake with a street demon 625 carb, just haven't decided exactly how I want to build the motor from here.

 

. Even Premium is cheap gas now... $1.79 here today for Regular...


. 400's came with 9:1 for the first year... 1971...

 

Another thing it depends on is the material of the heads. Aluminum will let you have another point or so of compression.

 

Agree with all the above......

Back in the day of when lower octane 1st hit, Crower had a series of grinds that would allow up to a 11:1 CR and not exceed 150 psi.....of course with all the right parts.......

 

. Geez... gas still dropping here in the new year... $1.59 now... gotta get that 400 built so I can put some serious amount of gas through it...

 

Amen, brother! My 400 is begging for life!

 

I'm running about 8.5 on my 2v cleveland. I've got a set of aussie heads that would bring me up to 10:1.