ok so im swapping a 350 into my firebird. The firebird is an 87 with a 305 4bbl and the 350 is a TBI from and 89 pickup. I was told by another member that the 350 heads were bad (something about being swirls) and that the 305 heads would be better. I was wondering if anyone could provide me some information about the 305 heads. Me and my uncle cant seem to find any info on them and we want to know some stuff about them before using them on our car. We are doing a carbed engine with no computer, new intake, headers, cam, carb, and rebuild kit. We just want to make sure that the 305 heads arent very restrictive because we would just buy different ones if they were(however, i know that aftermarket heads would be better, but i want to use the 305 heads unless they suck to keep costs down) So if anyone could give me some info on the 305 heads and if they are good for my application that would be great.

 

The 305 heads wont work with a 350. My would be to buy an aftermarket set.

 

They're right, the 350 TBI heads have the swirl-port design. Not suitable for high-perf fuse.

The 305 heads will work somewhat OK in that setup.

Those are the same casting used in the TPI 305s from 87-up, which is the 081 casting. The valves in them are really too small for a 350, so they won't make much HP, and their chambers are small, so the compression will be rather high. They won't work near as well as "the right" heads will, but they'll bolt up and work. COUNT ON having to run premium gas, and not making a whole lot of power. Depending on what cam you use, you can somewhat lessen the high compression issue.

 

Thanks guys. I figured that they wouldnt make enough power. We are aiming for around 300hp, maybe more if i dont run out of money. Do you have any idea where i can get some good flowing heads for not a lot of money, used or aftermarket?
Also, what about vortecs? Are these good heads to use?

 

The 305 heads are actually fairly decent. They will have 58cc chambers, which with the dished pistons your LO5 350 most likely has, will up compression a little. They have 165cc intake ports, same as the TPI 350's head have. The valves are 1.84"/1.50" - the intakes are a little small, but not terribly. Having 1.94" intake valves installed will cost a little bit of machine shop and parts $'s, so you have to take that into account. If you do an aftermarket cam, figure on new valve springs and retainers. They do benefit from a little port clean-up, as do most heads. You can probably do all that for slightly less than a set of World S/R torquers would run you. The intake bolt pattern is the '87-up, which limits your intake choices a little - the center two intake mount bolts are at 72 degrees, vs. 90 degree used up through 1986.

Since you're doing work or replacing heads & intake anyway, consider this kit http://www.sdparts.com/product/SD806...RPMAirGap.aspx . Better flowing/performance heads than your 305 heads and most aftermarket (certainly for the price); already modified for more valve lift; includes the intake, gaskets, rocker arms, and bolts needed to install it all.

Since your 350 came out of a truck, it probably doesn't have roller lifters, and may or may not be machined to accept them. If it's machined for roller lifters, seriously consider using the lifters and associated hardware (cam retention plate and lifter retainers, pushrods) from your 305 with an aftermarket factory roller type cam. Slightly more expensive than a flat tappet cam/lifter kit, but worth it if you have all of the other stuff already.

 

Yeah i looked at that kit and i didnt really want to spend that much $. But you said the 305 heads are pretty decent? With a new cam, intake, carb, headers, and engine rebuild do you think those heads will enable me to produce around the 300 hp range? Or would i be maybe more than that or less than that? Also, how big of a cam can be used with those 305 heads? Basiclly, we are looking to be in the 300 hp range but we cant find any info as to whether or not those heads will enable us to do that.

And i am pretty sure the 350 can accept roller lifters, but i didnt know that the 305 already had them...

 

300 HP will be a day in the park with those Vortec heads.

Your 305 heads will be limited to about .480" lift after new valve springs. That can be easily increased if you have the heads worked for positive type stem seals (the valve guides are cut to give the seal a good clean surface to mount to, and in the process shortened so there's more valve travel available).

If you price out what it will take to rework the 305 heads, get a new intake, new valve springs and retainers, new rocker arms, gaskets, and certainly if you have the heads modified for 1.94" intake valves (like sofa indicated, a good idea for a 350), you're going to be within $100 or so of the Vortec kit. You may even end up spending more.

I'm running 305 heads on my 350, but they're not factory heads (depending upon who you ask, basically the same thing). Based on 1/4 mile performance, I'm well over 300 HP. I'm seriously considering the Vortec kit, though, as a simple upgrade to what I've got.

$'s/HP, the Vortec head kit is a much better investment than the 305 heads.

 

my uncle also suggested i look for some used vortec heads as a cheaper alternative. If i could find some, would they be potentially ready to go or would they need to be modified also? I already planned on buying new springs because of the new cam, but would the used ones need machining for a bigger lift and for 1.94 intake valves?

 

NAL-12558060 GM Performance Parts Vortec Cylinder Heads
Cylinder Head, Vortec, Cast Iron, Assembled, 64cc Chamber, 170cc Intake Runner, Chevy, Small Block, Each

1.94 in 1.5 out.

Summitracing.com

Today$289.95

 

Vortecs come with 1.94" intake valves standard. Stock Vortec travel has been reported to be as low as .440" - the only way to know is to check each and every valve on each head. Vortecs are weird with the size of the spring pocket, so be aware of that, also.

The linked Summit Vortecs are only the beginning - you still need gaskets, rocker arms, intake, and they are unmodified. By the time you're ready to use them, you might as well have gotten the SDparts head kit. This is the unmodified head kit http://www.sdparts.com/product/SD806...merIntake.aspx , which would cost you less to get installed than if you started with the Summit heads (assuming you bought everything new).

 

So the vortec lift is less than the 305 heads' lift? would the stock vortecs still allow for better hp even though the lift is less? And how much lift is really necessary out of your cam/heads for 300hp?

 

IMO, stock Vortec valve lift capability is moot - don't even factor it in. Either get heads modified for more lift, or modify the heads you get for more lift. The stock Vortec valve springs are junk to start with - so just do it right and don't worry about it.