I'm rebuilding my 305 and looking into aftermarket heads. I've found a lot of info on the S/R Torquer and L98 aluminum Corvette heads for the 305, but not on the Edelbrock Centerbolt heads. I emailed Edelbrock (technical support not sales dept) and they said that the heads will work for the 305 as long as the cam does not exceed a .450 valve lift. Everything else will bolt on.

I'm not comparing prices, cause I know the Edelbrock heads are hella expensive, but just wondering if anyone has any technical info why would you NOT go with these heads on a 305?

Also, they (Edelbrock) said NOT to use roller rockers and instead use stock rockers with a +.100" hardened steel pushrods. I do not mechanically understand why they said this. Anybody want to enlighten me? Thanks for your help.

 

Was there any discussion about chamber size? Those heads are intended for 350s, and use on a 305 should include some shaving to reduce the chambers by 6 cc or so.

Interesting what they said about roller lifters. No clue why they said that. Comp Magnums would be a good choice over stock stamped. The lift limitation probably has more to do with reduced effectiveness due to valve shrouding, rather than a mechanical limit. But, I don't know that for a fact.

I don't have those limitations with the Worlds. But, the porting should be considered a "must-do", at least the bowl work. I upgraded springs as well.

 

The Edelbrock heads have 60cc chambers. Stock 305 heads are 58cc. Stock compression ratio is 9.3:1. With the Edelbrock heads, compression drops down to about 9.0:1. Does anyone want to double check my calculation? What's the opinion on 9:1 CR for a 305 with a cam profile of (see next paragraph.)

I have a cam with 202/207 @.05" duration and .404/.415 lift with 1.5:1 ratio rockers. I want to change out the rockers with 1.6:1 full roller to get a lift of .431/.443 and stay under the Edelbrock .450 lift limit for the 305. Does anyone else (thanks for your input five7kid) think the heads might not flow well because of valve shrouding? Any other opinions/conductive criticism will be helpful. Thanks!

FYI: I received an email from Edelbrock that the +.100" pushrods are necessary because their head deck is +.100" over stock. I was thinking the valvetrain geometry would be altered because of the increase in pushrod size.

 

You need more compression with aluminum heads due to higher heat transfer/loss. For 350s, L98's went from 64cc to 58cc to make up that difference. Edelbrock went to 60cc - close. 9.0:1 with aluminum translates to about 8.3:1 with iron.

The .100" longer length corrects the geometry problems you would have with standard length & .100" thicker deck.

 

https://www.thirdgen.org/techbb2/sho...ds+compression

SSC
Senior Member states:


"Its not going to lower the compression because of the aluminum heads. The only advantage aluminum has over cast besides being easyer to port is the heat dissapation properties of the material. If you were to take a set of heads one aluminum one cast with the same exact size combustion chambers the CR is going to be the same but the aluminum heads will disapate heat better reducing the chance of detonation. Thats why high CR engines work better with aluminum heads, its like your droping compression due to the heat dissapation properties of the heads but your not touching the CR."


So, who's correct?

 

We're saying different things about the same thing.

You don't affect static compression ratio just because you have iron vs. aluminum. But, you need higher static compression with aluminum to produce the same power as iron would because of the heat loss. The higher static compression of aluminum won't detonate like the same static compression would with iron because of that same heat loss with aluminum.

Heat and power are units of energy. If heat is transferred (lost) through the combustion chamber metal, that is less energy to push down on the piston - which is what produces horsepower.