Will 305 heads work on 350
Thread Starter
5th Gear
Joined: Nov 2006
Posts: 5
Likes: 0
Will 305 heads work on 350
First off ........Great Site
Would someone know if a set of 305 heads, casting No. 354434
60cc. would work on my stock 1977-350.
I have tryed to find more information on the heads but all
i could find was they have the small valves I believe.
If they would bolt up any idea about the difference they
would make in HP. over my stock 76cc. heads.
All reply's welcome.........Thanks
Would someone know if a set of 305 heads, casting No. 354434
60cc. would work on my stock 1977-350.
I have tryed to find more information on the heads but all
i could find was they have the small valves I believe.
If they would bolt up any idea about the difference they
would make in HP. over my stock 76cc. heads.
All reply's welcome.........Thanks
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
I hate to tell you the 305 heads are good for scrap metal and that is about all. Small valves and small ports make them a bad choice for a 350. Save your money for a decent set of heads.
Drifting
Joined: Apr 2002
Posts: 1,716
Likes: 4
From: New Baden Illinois
Abby Normal
Joined: Dec 2001
Posts: 53,463
Likes: 92
From: Press "2" for English
first off, 
. the 305HO heads will provide a decent CR bump over some stock open chamber heads and depending on the year of your car, outflow stock.
i ran a set of 305HO heads on my stock L81 bottom end and that with a cam change netted about 45hp.
i only found out later the stock L81 heads had the same 1.84" intake valves. only the chamber size in the 305 heads was less, hence the CR bump.
[EDIT]
just checked the mortec site (www.mortec.com) and it just lists them as 75-79 60cc chambers, but doesn't show valve size. if they're the "big" 1.84" intake valve heads, and the seals, guides, etc. are in good shape, they would probably be a good head.
if they're the smaller 1.76" intake valves, i would agree with everyone else.
. the 305HO heads will provide a decent CR bump over some stock open chamber heads and depending on the year of your car, outflow stock. i ran a set of 305HO heads on my stock L81 bottom end and that with a cam change netted about 45hp.
i only found out later the stock L81 heads had the same 1.84" intake valves. only the chamber size in the 305 heads was less, hence the CR bump.
[EDIT]
just checked the mortec site (www.mortec.com) and it just lists them as 75-79 60cc chambers, but doesn't show valve size. if they're the "big" 1.84" intake valve heads, and the seals, guides, etc. are in good shape, they would probably be a good head.
if they're the smaller 1.76" intake valves, i would agree with everyone else.
Last edited by IronJen; Apr 24, 2007 at 05:01 PM.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
millman -
I understand your logic in the 305 heads: Since they have smaller chambers, they will produce better compression, and better compression should equal more power.
Unfortunately, compression, in and of itself, does not neccessarily make more power. More compression is typically used in conjunction with more cam overlap & duration, and cam overlap & duration is used to improve volumetric efficiency and more flow through the engine. If the heads used will not support the additional flow, then the compression and cam overlap cannot work.
Unless they're the 305 H.O. heads, the 305 heads flow pretty bad. With the poor flow, the compression can't be used for any gain. In contrast, by combining a good flowing head with a compression ratio matched to the cam, a significant performance improvement can be gained. With the great prices on many aftermarket heads that really flow well (check out the Dart Iron Eagles for incredible prices on heads with amazing flow numbers), your best bet is to pick up a new set of ready-to-run heads. The cost of many of these new heads is about the same as you'd pay for a top-notch rebuild of a set of junk 305 heads, so it's tough to justify rebuilding junk....
I understand your logic in the 305 heads: Since they have smaller chambers, they will produce better compression, and better compression should equal more power.
Unfortunately, compression, in and of itself, does not neccessarily make more power. More compression is typically used in conjunction with more cam overlap & duration, and cam overlap & duration is used to improve volumetric efficiency and more flow through the engine. If the heads used will not support the additional flow, then the compression and cam overlap cannot work.
Unless they're the 305 H.O. heads, the 305 heads flow pretty bad. With the poor flow, the compression can't be used for any gain. In contrast, by combining a good flowing head with a compression ratio matched to the cam, a significant performance improvement can be gained. With the great prices on many aftermarket heads that really flow well (check out the Dart Iron Eagles for incredible prices on heads with amazing flow numbers), your best bet is to pick up a new set of ready-to-run heads. The cost of many of these new heads is about the same as you'd pay for a top-notch rebuild of a set of junk 305 heads, so it's tough to justify rebuilding junk....
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Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
If you're looking to bump compression and get a reasonable flowing head, you might check out a pair of ZZ4 take-offs. They have 58cc chambers and flow better than the older stuff. They're not a hotrod/performance head, but they'll do the trick. I just happen to know where there's a set for sale...
Safety Car
Joined: Aug 2000
Posts: 3,909
Likes: 26
From: Clymer PA
To increase the compression ratio only is a waste of time and money in my opinion. High compression is merely a tool to allow you to run a larger camshaft...that's where the power gains are at. IMO save your money for a good set of small block heads rather than slapping a pair of 305 heads on and restricting the motor. I think you would see a better gain in horsepower by purchasing a good flowing set of heads and staying at the same compression than adding a pair of 305 heads and increasing the compression. Just my opinion
