Mismatched Heads

[Michael Bell]

Gentlemen, I'm new on here so please bear with me, I'm building a 409 for my 58 Biscayne. I found that I have one 690 and one 583 head on this engine. I beleive them both basicly the same head. Will I run into a problem running one of each instead of a set of either number?? Also this motor has 11 to 1s in it, the block was decked and the heads were trued(enough to clean things up only), will this give me too much compression for todays fuels???? The car will be street driven only but I'm sure it will be screwed on occasionally Thanks for your help Mike

 

[dq409]

Don`t know about the heads but you might need to add a little octain booster. What I do is use a mix of 8 gals of super to 2 gals of racing fuel for the street. Friday i will run 50/50 for the drags,,,,dq

 

[Fathead Racing]

Drags, OOOOOOOH!

Post those times dq. I have yet to hit the drags. I still need to do a little tweaking! Glad to hear your getting the bugs out of the ride.

 

[bobs409]

Can't help on the heads either but can say that my 400hp is 11.0:1 compression and runs fine on pump premium. No pinging at all. Others here also. Supposedly the w-motors aren't too sensitive to octane like other big blocks.

 

[jim_ss409]

I also think the 583 & 690s are basicly the same. As far as I know the only real difference is that the area under the valve spring was cast thicker on the 583 to alow it to be milled deeper. This was to give room for a slightly taller spring used on the later model engines with the higher lift cam. You can get plenty of room for extra high lift on the 690s by using different retainers. If you are going to use a modern high lift cam you might want to check into this further. C.H. or Showcars can supply you with anything you'll need. They are both listed in the links section of this site.

 

[Michael Bell]

Guys- Thanks for the replys and help! Maybe an old dummy like me might accidently learn something. The motor will be togeather in about two weeks, so we'll see what happens then Thanks again Mike

 

[dq409]

Bob,,,your pretty much right thats why I said "maybe" , but when you come down to sea level you might become a little lean.,,,dq

 

[Bungy]

Just be sure to check your installed height on each head. You will need to add shims under the springs on the taller head to even them out with the other one. No biggie.