Ghettobird52

Hello there I am going to be rebuilding a 88-95 burban/silverado/caprice 350 block for my 88firebird 5.0 tbi. But I am thinking about using my 305 heads on it due to not enough money to buy 350 heads. Would this be bad or good?

Atilla the Fun

As long as you use dished pistons, and as long as you aren't considering the swirl-port LO3 heads that probably came on your car, it's a fine way to go. The best 305 heads have 081 as the last 3 digits of the 8-digit casting number.

Jim85IROC

iTrader: (2)

Certain castings may be adequate, but in most cases, 305 heads will choke the **** out of a 350. Back in the smog days people used to do this because ALL the heads flowed bad, so at least you could get some more compression by using 305 heads with the smaller combustion chambers.

Now that we have easy availability to heads that flow well, there's really no benefit to using 305 heads unless you either get one of the better flowing sets (of which there are very few), or spend big time/money working over a set of 305 heads with porting and bigger valves. By the time you do that, you're into them for more than good heads cost in the first place.

Atilla the Fun

true, but wrong. New Vortecs are nearly $600/pr. Used 416s are $75 or so. And with a little searching, you can find some that have recently been through a good machine shop.
Figure another $90 for good valves, delivered, and another $80 to get the intake seats cut.
Porting and polishing will get you close to stock Vortec results, for less than half the cost. Plus then the Vortecs need a specific intake manifold.
So if money is tight, salvage heads are a great value. Better than new Vortecs, and those have become the benchmark against which all others must be evaluated.

duckmanquacker

and another 480 to get the intake seats cut.

He meant $80.

Atilla the Fun

yes, thanks. Sometimes my shift key sticks and I don't notice. I just fixed my post.

aaronjohn20

I actually have a 350 4 bolt main bored 30 over with a set of 1985 305 TPI heads (416's) on it. Its got the 4 valve reliefs in the pistons, and I spark knock when its warmed up on cheap gas. Runs pretty good though. Havent had it to the drag strip yet but i realllllly want to.

duckmanquacker

If you need to run the cheap gas just drop your timing a few degrees.

aaronjohn20

nah, i'm thinking premium gas and 14 degrees base timing. Thats the highest i've went and thats where i get the best off the line throttle response. I tried putting pics up, but they are too big.

Atilla the Fun

That's what happens when you try nearly 11:1

aaronjohn20

yeah i figured it was up in the range of 10.5:1 or so. i was haveing a problem with off the line throttle response. Base timing was at 8, now it's at 14 n i cant turn the distributor any farther, But it's liking it alot better

toolegit86

i got about 150$ on my heads, my original 416's from my 83 l69, they have over 250k, now there ported polished and cleaned up, glass beaded, surface cleaned 194 valves, comp spings all new again. ill tell u how they perform when i get them on this weekend.

there just going on a stock 91 tbi 350 bottom end. only reason i used them, my swirls cracked, my buddy is a machinest so i get good deals, and i had them there.

mroth2008

you people realize the stroke on a 305 and 350 are the same so even if you do that the only reason it would bump is if the cimbustion chamber is smaller so I doubt it so you will most likely choke it since most 305 heads use smaller valves because of thje smaller bore that 305s have if you don't believe me look it up

aaronjohn20

yeah let me know toolegit. That'd be great!! Video would be cool too. MROTH, We know it'll bump the compression up because they DO have smaller combustion chambers, And like my buddy Tooliget has said, he's got bigger valves, with alittle bit of work done. Your car should like the heads man. I'm just wondering if it's gonna be like a night and day difference. Wish you woulda had them heads on there before all the work you've done to em

mroth2008

I stand corrected than dosn't matter to me I have a ollldddddeee ford a reallly old ford for me thies 272,292 heads, and 312 heads thats about it

Atilla the Fun

You're clueless. It's not just the stroke that affects static compression. The 350 has a much larger bore than the 305, increasing the swept volume. So even if both engines used true flat-top pistons at zero deck, 4.060" x 0.038" head gaskets and 58cc heads, the 350 will still have way more static compression. Put the same cam in both, the 350 will also have more dynamic compression, too.
When you type without knowing all the relevant facts, you just end up looking silly.

mroth2008

Well atilla I base my facts presented to me from my knowledge I still think it's idioticy to put 305 heads on a 350, even with all the work you do to them, the 305 heads are still going to choke them out even with the higher compression ration and yes I know that thiers more to it than stroke and combustion chamber cc's.

Doom86

Common misconception from people who haven't done it.

The only difference between "305 heads" and "350 heads" is the combustion chamber. 416's, 601's, 081's have better runners, intake, and exhaust, then a lot of SBC heads. And on top of that they are thicker so you can mold them to what you need for high velocity and flow.

Are they the best heads? Nope, not even close.

Atilla the Fun

I'd rather have 081 heads than ANY pre'87 327 or 350 head, stock or aftermarket. NONE of them can equal a set of 081s properly cut for good 1.94/1.60 valves, not even the old 2.02-valved heads. I've personally tested this on the SuperFlow 1020 bench.
Plus the 081 heads have more efficient chambers that are proven to be worth 10 HP just because they take less spark advance. More advance causes more negative torque, so that's why. It holds true even with deep-dished pistons and 8.0:1 static compression.
Max effort 081s can out-flow stock Vortecs, but the Vortecs have more potential.

toolegit86

so ive been running the 416 heads with 194's 150's mild port and polish and gasket match. even with my team g intake and cheap lunati Duration 270/280, Lift .420/.443 cam. it peformes way better. at first i did have a tuning issue, mostly timing/carb and valve adjusment. and my car actally has power from idle to 6500rpm, no problems, and it will blow the tires off going from 2nd to 3rd rolling..

i do have plans to change intake and cam now. if ur short on cash this is a good build to mess with and learn from. ill let u know how it like 100shot here soon... and i am running my timing right now at 12btdc, i want to try 14 but i need a better starter first. and a new carb...

with the right cam and intake combo i would say this is a night and day change.. even with my set up its fun to drive and a blast on the free way.

toolegit86

forgot... to have my heads cleaned, shaved and machined in new valves, full valve job. new valve stem seals. all free!!

my bottom end.. 1991 gm 350