Guys, I know I wasting my breath but I still like to know. What kind of performance gain will get just by sawping the heads and add a good intake, carb, and cam. I try doing a search but everyone talks about 350 with 305 heads.

 

If you're lucky you should only lose about 20% of your power putting 350 heads on a 305.

 

Does that lower you compression? If so why not back it up with a supercharger?

 

Yes it lowers compression. Sure you could use a supercharger, but paying $2k to compensate for the wrong $50 junkyard heads doesn't make a lot of sense to me.

 

But there are some really good flowing 350 heads right?

 

its a 350 with 305 heads work the best

 

There are good-flowing 305 heads, too.

 

Yeah--but the valve spacing on 350 heads interferes with the cylinder walls on a 305: no can do.

 

not a good idea, as was stated you lose your compression ratio because of the smaller bore, and the valve spacing wont let you. literally any other 305 head that you can find is an upgrade so just look around a little bit

 

To me, the greatest tragedy of the 305 is that it's such a good, dependable motor but just doesn't have the power possibilities of the 350. They make stroker kits for people stuck in California that bump it up to a 331 but it's still just not a 350, won't take any really good heads. The best advice I got was from Crane Cams tech line: they said to leave my '82 computer controlled Quadrajet and HEI 305 alone, that it was so dependable and economical because the computer is not very bright, adjusts for efficiency constantly, and any monkeying around with that motor would ruin its mileage and give maybe 15 horsepower. I'm doing a stock-appearing 350 swap instead, cheap and easy, about $2000 and it will still get reasonable mileage.

 

Valve spacing is exactly the same.

Actually there aren't even really "305" and "350" heads... there are only SBC heads, with different chamber volumes.

 

That's what I was about to say. A head is a head is a head. Some have larger chambers, some smaller. Some have larger valves, some smaller.

I guess it's possible that someone might make custom heads designed with such large valves that they could use an issue with the smaller bore of the 305, but nothing stock off the shelf available. And if so, I'd think the flow wouldn't be very good given the proximity of the valve to even a 350's larger bore.

But again, you must remember the beauty of SBC - everything swaps from 283, 302, 305, 327, 350!

Yes, generally speaking, a head from a 350 motor will more than likely have larger chambers, thus you'll get way less compression on a 305.

 

Ok here is what my plans are?
305 4 bolt main Its free, its race block.
forged pistons
forged crank
A mild cam
Weiand supercharger 6-8 psi
flow tech short header
holley 660 dp carb
Just need some high flow heads without breaking the bank cheaper the better?

 

i know you dont want to hear it, but for the money your going to be spending just buy a 350, you can get a block for like 150$ if you know were to look. on top of that I highly doubt what you have is a 305 4 bolt main as they are very highly rare to come by and not a race block in any form, they were found in service vans and trucks