Does any one no this question also if 305 heads are not big enough for a 305 then why does the ZZ4 have 58cc heads?
Thanks

 

Intakes are 1.84" on 305 heads. ZZ4 heads use 1.94" and not the same head as the 305, they are similar to the L98 Aluminum Corvette head. They just share the same combustion chamber size.

 

Who says the 58cc heads aren't big enough for the 305? Or did you mean to say 350? The chamber size has nothing to do with the bore size. You just have to take that (head cc) into consideration when selecting your piston design to acheive your target CR. The valve sizes for the 305 head are, on 416 castings, 1.84" intake and 1.50" exhaust.

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George P. Lara
1994 Z28 LT1 T56
1984 Z28 High Output
Member: SCCA, SCFB, SC3GFB

 

Yup, that goes for any other 305 casting as well.

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So what does it mean when people say that a 58cc head will smother a 350? What stock GM head is the bes (pre fuel injection) to run a 10.1 or 10.5.1 compression. I have a set of 882 Gm heads but they are 76cc and I would think that it would be harder to get a higher compression ratio out of these but I dont really understand the combustion chamber size and how you pick the right one for your engine without getting to high to run on regular gas. I was thinking of the comp cam 270H.
Thanks for all the replies

 

#05 heads suck because of thier small port size and crappy ability to flow, which has NOTHING to do with the 58cc chamber size. There are both 64cc and 76cc heads that suck just as badly. 58cc vette L98 heads on the other hand flow reletivly well.

As far as compression, any compression can be gotten with any size heads depending on the engine, pistrons, deck height, gasket thickness, etc. Ie, you can have 58cc and dished pistons, and get the exact same CR as 76cc with domed pistons.

 

Jester speaks the truth. Depending on the combination of pistons and heads (assuming you are using the same gasket and deck height)... you can have the same compression ratio with 58cc/dished piston, 64cc/flat-tops or 76cc/domed pistons.

Given all three, the 58cc/dished pistons are preferable over the other 2 combinations because it will permit higher compression ratios and promotes better "swirl/tumble" in the combustion chamber. So don't get hung up on the cc's of the combustion chamber size...it is the FLOW CHARACTERISTICS of the head that matters far more.

The dilema faced by most of the 305 owners is that there is a limited availabilty of heads that flow well and will work on the 305. The 305's smaller bore prohibits running the majority of the larger valve heads that flow well. The smaller bore shrounds the valves and you often encounter clearance problems with the valves hitting the bores (either totally or at higher lifts that are not that high).

This is why the Corvette L98 Aluminum head is so popular on the 305s. It has good flow characteristics that can be further enchanced by porting, they do give you a large intake valve that clears the bores AND they retain the 58cc combustion chamber so you don't loose any compression ratio and don't have to change your pistons.

If you want to kill performance fast on a 305, put 64cc or 76cc heads on and DON'T change your pistons. You probably could drive your car in Guatamala where they get gas with the "octane of the day".

So small cc is good, but start thinking FLOW!

 

Yes you can bolt aluminum corvette Heads with the 58cc chamber. Even though you will retain the same compression on the 305 all of you guys are forgetting is that the aluminum head dissipate more heat. So to retain the same thermo efficiently with these heads you would need to mill the heads to get a full point in compression. If the heads are not milled it’s like running a 64 to 72 cc head.
Jim

 

I *had* a pair of 451 heads from a 78 305...they only had 1.70 and 1.50 valves in them; tossed them out a loooong time ago.

Pete

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Pete's Place
HiOutput Virtual Racing Team

 

Pete,

You're right. The older 305 heads had smaller valves, but they were actually 1.720". Not a major difference, since they were even MORE restrictive than the 1.840" valves on most later 305s. Personally, I feel that since you can squeeze standard 1.60" exhaust valves and 1.875" Olds valves in a 305 chamber without any trouble, and 1.94" standard valves with a little massaging, why throw out a perfectly good head that can be machined for larger ports?

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Later,
Vader
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"Make Me Bad"
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