RedAssassin

I have a question. I'm not a complete dumb *** when it comes to cars, but I've been in the import seen for a while. I have a 91 Z28 LB9 (305TPI) everyone talks about how the heads just dont flow and they suck. Well the 305 and the 350 are basically the same block. Am I correct? So will the L98 Heads fit on my LB9? I know it would probably be better to just get some good aftermarket heads but I dont have a grand or more to blow. I can probably pick some used L98 heads off someone who upgraded pretty cheap.

Thanks for the help.

Edit: Would it really be worth it? By the time I buy the heads/head gasket I might as well put new head bolts in. It would be a good idea to have them re-surfaced incase they are warped. I might not be getting out as cheap as I think.

91Z-28

The 305 differs only from the 350 in that it is a 3.76" bore, but they share the same 3.48" stroke. Due to the small bore a head built for a 350 may have valve shrouding issues, I do know people who run the L98 heads on 305s though. If you decide to do it get a pair of "real" L98 heads, the aluminum ones. Then at least you could raise compression up to around 11:1. The valve shrouding issue is well known, and just one of many reasons few people even bother with 305s.

RedAssassin

Thanks, yea I was looking on e-bay and found a few sets of real L98 Aluminum heads. They seem to be going for about 300-400 bucks. A lot of people talk about the 305. It kind of makes me wonder if I should just buy a 350 block and start to build it. If I do though its going to be old school. I'm registering in Indiana with no inspections so i'm only putting what I have to have on the motor to run. Although, like you stated not a lot of people want to mess with the 305. I like a good challenge =P Thanks for the info though.

91Z-28

My car is also a 91Z and used to be a 305 auto. Those are LONG gone, trust me if you do the same thing you'll be happy.

Kevin91Z

305 heads have 58cc combustion chambers, and so do the aluminum L98 heads. Swapping one for the other will not change the compression ratio. But putting iron L98 heads with 64cc chambers will lower the compression ratio a ton and cancel out any benefit of the slightly better flow.

Conclusion: Get a 350 roller block and mod the heck out of it.

blackztpi

I was one of those guys out to try and get that 305 making power. I had the lb9 tpi setup. i rebuild the bottom end stock. i added a ramjet 350 cam from the crate motor (scoggin dickey sells the cam) and the heads were stock lb9 castings with a 3 angle valve job and minor pocket porting. That cam gave the car awesome torque on the stock tpi intake. problem being there was no power above 4000 rpm with those stock runners. the torque was enormous though, even through 2.73's. i could smoke stock 6 speed lt1's all the way through 1st, but i'd get stomped through the 1-2 shifts since i had a stock torque converter. after that i was running equal to them through the top of 2nd and all of 3rd gear. i'd say my old car was a mid 14 second car with that setup and the complimenting bolt ons. If my budget would have allowed, i would have thrown on a stealth ram intake. i think that would have really awaken the car. with 3.42's and a good intake you'll be fine. not to mention a set of world torquer 305 heads. 305's can make power, but it's not as easy or as cheap as the 350. it's much easier to go the 350 route. my bolt on lt1 was soo much faster than that car, and i can now throw in a cam and make 400hp...unlike the good ole 305. lol

91Z-28

But he could mill the heads and use a smaller gasket, raising compression and not risking anything since they are aluminum.

Lynk

He could spend $400 on the heads and then mill them but at that point he might as well have bought a set of brand new heads out of jegs, for only a little more money and a lot less hassle. But personally I would just buy a 350 block get one of those performance rebuild kits that come with everything from cam to rings for $500 and wind up with a motor putting out just shy of 400hp. The parts might be cheaper and the motor might only last 30,000 miles but for $500 how can you beat it. After you do that save up and build a real motor, like a 377, 400 block with a 350 crank, lots of hp, lots of rpms, lots of cars in your rearview.

91Z-28

If you get a 400 block might as well bore it over and use the stock crank and have a 406, why build an engine with 30 less cubes? The 377 is a great combo, it doesn't make sense to throw away 30 cubic inches of displacement.

wbspoon

The real problem with what you are proposing is the bore of the 305 will not accept the 1.94 intake valve. It will not fit inside of the bore.

91Z-28

I guess I should have been more specific than saying "valve shrouding". Yes, to run a 1.94 valve you would have to notch the cylinders.

Kevin91Z

That ramjet cam is pretty small. Depending on what cam came in your 305, you probably replaced it with a smaller cam. It wasnt the stock runners limiting you as much as the small cam.

Kevin91Z

You cant mill the heads that much, or the intake and accessory system bolts wont line up any more.

Zepher

Are you sure the 1.94 valve won't clear the 305's bore? I thought that that wasn't an issue and the problem was with the 2.02 valves.

85_305

STOP! Before dropping that money on L98 heads, use that towards some aluminum Vortec heads. BETTER than L98's.

And I think you may be right, but I'm not positive.