Opha

ok... i know i sound dumb, but i dont know that much about the engine block it self.
what is the difference between a 4 bolt main and a 2 bolt main. which is better?

and just for fun my friend wants to put a set of 305 heads on a stock 350.... the only thing i think might mess it up is that the 305 has a 3.75 bore compared to the 4.00 bore of the 350. meaning the cumbustion chamber is smaller, making higher compression. so i understand he reasoning, and he's kinda cheap. but would this work out good, or should he just spend his time on somthing more destructive???

thanks for helping someone thinking about building a new engine

IHI

iTrader: (1)

2 or 4 bolt is simply the number of bolts that hold the main bearing caps into place. There's been alot of argument over which is better, some say the 2 bolt because it has more material left in the block for strength, others say 4 bolt cause it's distributing the forces over a greater area, but most will agree that a splayed 4 bolt is the only way to go. The 305 on a 350 is a very old stock car racing trick that's good for a few extra ponies-works especially well on an otherwise stock small block.

ede

305 heads on a 350 would be more restrictive and cost power not make it. besides the smaller chambers, which would raise compression, maybe, they have smaller runners and smaller valves. even if they had the same size valves that would just be breaking even. if you're after more preformance use better (aftermarket or vortec) heads.

IHI

iTrader: (1)

Reread the post, it says his buddy is cheap and I know just what he's talking about cause my friend is the same way. As far as gains, the bump in compression will outweigh the loss of flow-remember this is a stock 350 short block and smogger heads-350's or 305's, besides unless you have a big cam that makes power at the higher r's bigger, better flowing runners will actually hurt performance. People would be stupid to think O, I have a all factory motor, let buy some Dart iron eagles, or some Brodix and think they're gonna make more power.

RB83L69

You don't say what 305 heads... these could be the 1.74" 267 heads, or TBI swirl-port heads, or if he's lucky, maybe "better" (less bad) ones such as 416 or 081.

The gain in compression will probably not outweigh the loss in flow. This is a very common misconception, about how much gain a small increase in compression by itself is actually worth. Less flow = less HP, less top end. What he'll probably end up with is a motor that runs like a tractor: big grunt off the line but no top end whatsoever; and will require that nice expensive premium gas to keep it from pinging all the time.

Not cheap or an upgrade IMHO, definitely a step backwards.

Other stock heads can be found that would be a whole lot better than any 305 heads. Or, he could port his existing ones, which is pretty cheap. All in all the 305 head idea isn't the best solution, and better solutions than that don't require buying a set of AFRs.

evil t/a

Wrong , the bump in compression ratrio does not make up for the loss of flow and I bet you that even aftermarket heads that are "too big" would make ALOT more power than 305 heads.

Opha

thanks alot everyone. i found a 4 bolt main block still complete at my uncles junkyard, only 150 and i dont mind stripping it down. and i'll let my friend know what everyone says, he wasnt going to keep it w/ 305 heads, he just wanted to do somthing different and see what would happen. thanks again

flyin89

iTrader: (7)

May be a little late on this one but if your buddy is as cheap as you say take a set of 993 or 882 casting heads and angle mill the weee out of them they will flow better than 305 heads and get a pretty good compression bump. But figure the cost of these options because Vortec heads are $450 a pr. If the heads you have need guides,angle-milled and a valve job(lord forbid valveseats) you may be kicking yourself for investing in a old head.