Heads, 675 vs 302

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cross_thread72

cross_thread72

Tattooed white trash
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***disclaimer : I know I "should just go buy a set of eddy heads or magnums" that's not an option right now***. I have a set of 302's ready to bolt on and go, my motor already has a set of 675's on it, I'm not looking to send the heads off and have port work done, or bigger valves installed. I'm basically looking for a budget head swap me and my boys can do over their winter holiday. The motor is a 72 318, mild cam of unknown pedigree weiand 8007, 1" ported spacer, and a spread bore holley 650 dp. I'll also be putting a set of Hedman 1-5/8" long tubes on it at the same time. I'd like a real world opinion and not speculation or a lecture on being dumb for not swapping out for magnums etc.
 
I'm not trying to be a jerk - but if they are what you have, what exactly are you asking an opinion on? 302 heads have a slightly better shape on intake port and roughly the same size chamber. Were the 302s rebuilt? Low milage" factory rebuilt" and all stock? Milled at all? My impression is you won't feel much of anything if the two sets of heads are in similar shape. IMO, unless there is work done on the 302s or a problem with the 675s you're looking at a wash in terms of the butt dyno.
 
The 302's are just factory rebuilt heads, but if there's not going to be a big bump in compression I might as well save them for a rainy day and the fresh roller short block. I was hoping to pick up a few hp.
 
X2,guy.Camshalf choice,goes with headflow numbers.What cam,stock?
 
Who knows what it is, it's fairly lopey. The old man I bought the car from had no idea about anything that was useful other than and I quote "one of them there 5/8 mopar cams"
 
Thanks.Next step.What is timing,initial,and 3000? Idle vacuum goes ,aong way.Give us that,would tell is how to help you quickly.
 
The Heads flow the same'ish, the intake ports are identical.
Any minor diff in numbers is due to the open chamber not shrouding like the 302's closed chamber does...so though it's not worth any real power cause its a couple cfm...it still comes down to the 675 on top...but like i said about a couple cfm, then vs the smaller chamber, i bet you will feel more gain from more compression than the 2 or so cfm...cause the 302 is 64cc as opposed to the 675 being around 68cc.

dont expect much power increase with the swap unless the old heads are worn out bad.
 
I've never put a vacuum gauge on it, but it really likes 32-34 degrees total timing, it came alive when I swapped the eddy 600 for the holley 650. Sounds like I might as well leave it alone and save the fresh heads for the fresh short block laying in the corner waiting for the green light from mamma to build up. Thanks guys.
 
that carb swap making it ''come alive'' might have something to do with the eddy. Smaller primaries...=air speed, which says a lot about the motor.
 
The holley I picked up is a spread bore thermoquad replacement carb, the primaries are tiny that helped low speed drivability, and fuel mileage, however it's no slouch when I kick it in the *** even with 2.76 gears. I guess instead of wasting time/money swapping the heads I need to get working on some carb tuning and gear.
 
Unbolting a set of 675 and bolting on a stock set of 302 might give 5hp at best, .20" off the 675 head would do the same thing. If your trying to go with 268 or larger cam, milled 302 heads would help a stock short block 318 to get CR needed for those cams but than stock ports would be limit the ability of those cams so some porting and maybe larger valves would be needed so EQ/RHS/eddy would start looking like a better idea.
 
If your just looking for a project, go ahead w/ the swap and a thin head gasket. 600 Holley & lose the carb spacer, its not gonna hurt you to do it. However I think more untapped potential lies in the tuning. The other goodies would make more power when used in a more complimentary package set up.
 
Hey dude! I think the 675 is what I just pulled off of mine (can't remember off the top of my head...). The 302 should give around 5-10cc difference I think, depending on what things have been done to them over the years, valve grinding you know all that. I'm pretty sure if the 675 are the regular 68+ 318 open chamber heads that I'm thinking of, you should get .5 - 1.0 bump in compression. I just CC'd one that I pulled off the other day (the 675 head?) and it came out to about 68-69cc, I think advertised it 62 or 64, something like that.
 
Saetun said:
If your just looking for a project, go ahead w/ the swap and a thin head gasket. 600 Holley & lose the carb spacer, its not gonna hurt you to do it. However I think more untapped potential lies in the tuning. The other goodies would make more power when used in a more complimentary package set up.
Click to expand...
getting pretty saavy there jeff...
 
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