I hate these riddles with more than one right ansewer so I thought I would give it to the group he he
this one has kept me up at nights
heads from 75-80 camaro 305 60cc chambers on a 350
the 350 was 8.5:1 with 305 heads the static compression will be 10.5:1 or so.
compression means power right... well thats how I was told as a kid. now we enter a grey area what about the runners should I increase valve size. will my power gains be diminished though smaller runners and valves what about valve shroud from the combustion chambers being to small for the valves. normally I would say the heck with it, dart heads but I wanna use as much oem type stuff on this as possable were talking total sleeper my hope is to foster a bit of a discussion on this because as I have learned everyone knows something that might help but no one can speak with authority on it. thanx so much

 

You really think heads are going to give away a sleeper?????

Factory 305 heads had 58cc chambers. Factory L98 iron heads had 64cc chambers, 4 valve relief pistons, steel shim gasket for 9.3:1 CR. Same L98 block with aluminum 58cc heads had 10:1 CR.

Composition head gaskets with .041" compressed height have around 9.1cc volume, the FelPro 1094 steel shim gaskets I used have 3.2cc compressed volume - gee, that difference is 5.9cc! Those numbers will vary a few tenths depending upon brand, compressed thickness, and bore diameter, but you're still talking the same neighborhood as the difference between 305 and 350 heads.

At most, you're going to have 10:1 CR with those heads on a 350. Put a composition gasket in the sandwich, it'll be closer to 9.5:1.

1.94" intake valves should be considered a must on a 350. Simple gasket matching, bowl cleanup, casting flash removal, and guide smoothing (okay, "porting") will increase port flow substantially. A little valve unshrouding will also improve flow without increasing chamber volume unacceptably.

 

https://www.thirdgen.org/techbb2/sho...n+head+project
Check out this thread, it's on porting the l98 iron heads, but similar kind of info. Part 4 upcomign. But I agree with the person above, do some porting on your current heads and use a thinner head gasket to boost compression, you could mill the heads a bit to.

 

oh sure that parts easy the question is weither it will hurt the proformance based on runner size or am I going the wrong way in my thinking also are you suggesting that I use the original heads I mean the motor was rated at 8.5:1 original out of the '75 'vette @165 hp I mean really can it be done without digging into the shot block I dont think so but I have been proven wrong before.
I'v got both sets of heads sitting on a shelf I am just trying to be educated about the install befor tossing parts together
and yes bright new heads would make them look new to anyone who looks I want the look of an old run out **** engine he he it'll be great

 

Heads are usually the first thing I look for when racing somebody. Not that I do a lot of street racing, but a lot of guys won't paint their new iron or aluminum heads, and it sticks out. Sometimes (like with Edelbrock) the manufacturers will stamp/grind their logos onto a visible part of the head. Heads seem to be the difference between a quick car, and a fast car. They can also help you decide if the car you're racing has a fairly matched system, and that the guy isn't dumb enough to run a monster Team G single plane on 76cc smog heads.
Next thing to look for would be a nitrous system, but that's a different story.

Not all 305/283/265 etc, etc, heads had 58cc chambers. There are quite a few that are 60cc, but these are usually crappy heads cast from the dark days of cylinder head technology.
I agree totally as far as 57kid's suggestion about the head gasket. Thinner is better. BUT, I've heard that the shims can blow out frequently. I'm actually about to do a head swap, 57kid (or anybody else that's used the Fel-Pro shims), can you give me your impressions on the durability? I've posted questions a few times, but never got any first-hand experience answers.

Pyro - Looks like you've got the right idea. Bigger valves, at least some heavy polishing, stock appearing heads, and higher compression.

 

Sure, you won't have to touch the short block, just soften the sharp edges of the combustion chamber a bit since the 305 bore is so much smaller than the 350. Also if it's a 75 350, it's probably got the 882 heads on them, with 76cc chambers, might these can be ported pretty well, though carefully cause they are thin walled, and if you're gonna run iron heads, 10.5 is pushing the compression ratio with a carburetor. Especially those 305 heads, which are known to be prone to detonation. If you convert to fuel injection it's ok, but better have a knock sensor. Also, by the time you get done rebuilding any set of heads, they're pretty much gonna be bright and shiny like a new set, if you do it right, so paint em black and smear some grease on em after you install. Also you'll want to convert to screw in studs, make sure the valve guides will clear the lift you'll be running on the cam, etc. Btw, the rated on your vette engine is probably optimistic, when I pulled my 77 apart it worked out to more like 8:1.

 

here is my .02.
The 305 heads can be made to work. Port and polish(if you know what to remove), bigger valves, etc. And thats if your heads arent cracked. Your smogger 882 heads on the 350 have huge chambers, so they arent as good a choice, as you cant mill them enough to get decent compression. Id stay under 10-1, unless you wanna run race gas when gettin "silly" with it. The best bang for the buck are the gm Vortec heads. you can get em complete for 450, and with a little modification(springs) etc, they run fast. Way better head than either the 305 heads, or the smog 350 heads, and not worn out old stuff either. just my .02

 

I'd stay with the 350 heads. mill them a little and use thinner gaskets. that'll get you SOME higher compression. and they won't be as flow restricted as the 305 heads are.

Hodge

 

I have heard both sides- that 305 heads will help out the 350 performance wise, and that it will hurt. There is a local stock car track by my house that doesn't allow you to run 305 heads on a 350, period. Makes me wonder why, if it would hurt performance. Then again, I ran into a guy once that tried putting stock 305 heads on a 350 and ran into cooling problems, not to mention a dramatic lack of power. I don't know what to tell you, but I would really like to hear from someone thats tried it and see how it works out.

 

well it seems like we may never know for sure cause now I will have to shell out the money for the vortec heads. I just finished my girlfriends honda civic (yeah I know but she likes it) the math
says that it sould run somewhere in the low 11's we will find out tonight at national trails raceway but I cant let her spank me in a honda so i guess its time to get a loan. unless one of you can tell me 100% for sure that either the 882 350 heads or these 305 heads are a good choice I was going for sleeper but now I just want to save my pride

 

How hot of an engine are you building? If it's just a mild small block, these heads with bigger valves will work great. Anything bigger than 160cc runners on a mild small block will actually hurt performance-just as you can over cam, over carb, you can overflow. I just bought a set a Aeroheads (267/305 casting originally with 60 cc chambers) for the mild 355 I'm doing they have 160cc runners, 2.02/1.60 valves, and 65cc chambers now, my compression for a flat top 355 should be around 9.3-9.5:1 which is what I want for a street/strip car till I get the 383 on it's way (first I gotta kick my buddies *** with a 350) So unless your doing a high rpm ripper these 305 heads with bigger valves will be perfect-even better with some minor porting and blending. But if your going Vortec that's better yet.

 

The vortec heads look like stock later gm heads on the outside, so the sleeper thing will still work. They are hard to tell apart. My .02 is they are the best heads in the price range for a mild/medium smallblock.

 

ok so here is the thing the guy at napa said that he cant put a bigger valve than 1.9 intake on these heads cause it just wont fit
these being the 305 heads as for how rad of an engine am I building you know how it is it never turns out the way you want from the get. but I would like to see 350 horse out of the original short block but I would like to use as I said before either genuine old parts to get it. or now it seems something that at least looks original enuff for a casual inspection before a road race.
nothing on the outside you wouldnt expect to see
i.e. headers, intake,carb

now the problem is as far as I can tell the short block with the dished pistons other than that I would have no trouble hitting the goal. not to mention I am still poor from building the '79
so it absolutly has to be cheap as it can be while maintaining streetability. thats the full scope of the project