So, I just picked up a 350 out of a 78 Z28 and it has 77 305 small valve heads on it. I just got a set of free 350 heads with 1.94 intake valve, casting number 3998993 and was wondering if I should use the 350 heads instead. The engine is still out of the car on the stand getting new gaskets. From what I have been able to tell about the engine is that it has dished pistons, stock bore, weiand xcelarator intake manifold, 600 cfm edelbrock carb, and may or may not have a cam(have not dug that far in yet). I am planning on a set of headers in the future, but for now it will be a daily driver the 10 or so miles to and from work. Any suggestions?

 

For comparison, what are the casting numbers on the 305 heads?

I think the 993 heads have 76cc chambers. If the block you're going to put them on has dished pistons you might have a combo that has lower than desired compression.

 

354434.

 

You dont have a single decent head in the bunch. The 434 heads are..... okay-ish... but they're massively outclassed by anything made in the last 20 years. Since you've got dished pistons you might as well use them but you're hobbling yourself.

 

those are the heads that came on the engine when I bought it lol. I am kind of regretting getting rid of my old h.o. heads now.

 

If your car had a factory 305, it was the same heads regardless of whether or not it was actually an "HO". The LG4 and L69 got the same heads, they aren't uncommon. I saw something indicating that the 434 heads are basically early 416 heads. Not sure how true that is, but the 416 heads are what were stock on LG4's and L69's.

 

The 350 heads are going to better than the 305 heads. A 350 is a better than a 305 any day. Enjoy.

 

Nope......

Depends. There are some awful 350 heads, and some really good 305 heads. 350 heads usually have larger valves, but there were some 350s that got small valves too. There were some 350's that had heavily dished pistons, and there are some 305 heads that will bring their compression ratios up to something tolerable. You cant make blanket assumptions about "350" heads considering there's a zillion different variations from 1969 or whatever until 1998 with wildly varying performance levels.

 

yes I can. having access to test data on almost every factory 305 head available I know even old small valve 350 heads will out perform most 305 heads on a 4.00 bore. Yes 58cc 305 heads will boost compression but will run out of steam above 4500 RPM.

 

So...put the 350 heads on? or 305?

 

Perfect for a TPI car then, eh?

 

I would run the 350 heads. 58 cc 305 heads on a 350 tend to run hot.

 

You dont think a 58cc "350 head" would do the exact same thing? Im not really sure there's such a cut and defined difference between "350" and "305" head...... I'd be more interested in tangibles like port volume, valve size, and chamber size, among others.

 

The 305 head swap was the hot ticket backwoods trick that backfired when it was found they didn't flow worth diddly even ported.

 

These days Im starting to feel like any stock cylinder head is a waste of time.

 

3998993 307, 350, 76cc, 72-73,164/64cc ports, 73 had hard seats and 350 Crate motor, current, Hecho En Mexico, 159/64cc ports. 354434 1975-76 262,305 62cc, 1.72/1.30
305 bore is 3.736 and 350 is 4.000 inches. when 305 heads are used on a 350 there is a overlap in the cylinder causing poor combustion and hot spots around the ridge.
Vortec heads are a good choice. I made 462 HP with a flat top 350, Vortec heads on pump gas.