fat_bastard711

i have z28 with a 305 tpi, and am going to upgrade with a set of corvette aluminum heads from an 89 model. will this be a good upgrade, and if so what size spark plugs do i go with? do i use what would go on the vette, or the camaro? thanks.

305sbc

iTrader: (3)

The plug style has to match the heads.

Vader

That "upgrade" should only cost you 15-20HP of the 190HP that your 305 already makes. The chambers on your 305 are 58cc. The chambers on the aluminum heads are likely 64cc. That should drop your compression from about 9.5:1 down to 8.8:1 or less.

The other consideration is that the valves may not clear the smaller bores of the 305. But if they do, at least you'll be able to use lower octane gasoline with the lower compression. If they don't clear, you'll bend a few valves and/or push rods as soon as you try to start it, so it will cost you the entire 190HP that the 305 WAS making.

Just because of the fact that it came on/in a Corvette, it isn't necessarily better. 1994 was another prime example. The aluminum heads on the LT1s were decent, but the iron heads on the LT1s in other cars actually flowed better. With an equal cam and programming, a Buick Roadmaster would have been more powerful than a Corvette - Not that the heavier car would have necessarily been faster, but the engine would have made more power.

Don't get caught in some unfounded stigma, like millions of Mopar drivers have.

Vader

Further research indicates I may be mistaken. It appears that by 1988, the aluminum heads had 58cc chambers. Now all you have to worry about is the valve interference.

SMURFN' Z28

iTrader: (2)

ya vader, I was shocked that you posted that. Another thing concerning vette heads that goes along with the valve issues you mentioned. Would the combustion chamber on the vette heads be more suited for the larger bore of a 350? seems to me if the opening for the chamber was wider than the small bore of the 305 that would have some bad effects on how the heads flow?

fat_bastard711

i did some reading up on this site and thought that aluminum heads off of a vette tpi would be a good upgrade. what would be a good upgrade? what would be a good head, cam combo? i am not looking for major mods here, just a good upgrade from stock. thanks.

1MeanZ

iTrader: (9)

They work great see the sig

Vader

I was probably remembering the earlier Y-Car heads - The pre-1988, perimeter bolt style. Working from memory is dangerous when there isn't that much memory to work with. 64cc heads would have sucked in that combo.

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1Mean,

Did you have any issues with valve interference or shrouding? Did you have to flycut the deck around the intake faces?

Just curious.

Guest

Starting in 1986, Chevrolet began producing Aluminum SBC heads for use on Corvettes. They came with 58cc chambers, centerbolt valve covers, the 'early' style intake bolt pattern (all holes perpendicular to the head), no EGR/heat riser, and from my experience are missing an accessory bolt hole. Over the years, these features didnt change. They didnt make these with perimeter bolts, or the 'late' style intake bolt pattern (4 center bolts vertical).

1MeanZ

iTrader: (9)

Madmax, my heads are as you say except that to my knowledge they have all the normal accessory bolt holes. I am using #113 casting heads off of a '90 Corvette.


Vader, I actually PM'd Willie a bunch of times about this, he was running them on his 305 some time ago. To be quite frank, Willie and I just bolted the things on and went. The only mods I did was I gasket matched and polished them before I had the valve job done and I installed push rods, guide plates, and roller rockers. (L98 heads come with guide plates but they are not hardened) I also used the .050" thick stock GM L98 head gaskets.

These heads as many may know feature 1.94 1.50 intake and exhaust valves respectively which clear the 305 bore just fine. I have experienced no clearance issues, and based on the numbers this car has put down with such a crummy driver, I dont feel that valve shrouding due to the small bore is much of an issue either. The midrange power these heads added was very noticeable. I feel that based in my rwhp#s and trap speed that these heads are helping me generate near 1hp/cid, which is not earth shattering by todays standards, but I dont think a near 300hp 305 that still gets 26mpg on the highway is anything to laugh at. heck with my new 5 speed I get 19-21mpg going back and fourth to work and around town if I keep my leg out of the throttle. I would recommend these heads to anyone running a 305.

RBob

iTrader: (1)

The spark plug is a 14mm thread, 3/4" reach, flat gasket seat, 5/8" hex. An Autolite 3924 works out nice on a modified engine. The 3926 is the stock heat range Corvette plug.

RBob.

Vader

Gee. And all this time, I've been playing around with porting the '416 heads and fitting 1.94 valves for nothing...

Guest

I've seen a few of these heads firsthand, and have read from quite a few posts and they have all said one of the 3 holes from the RH head or back of the LH head is missing. Yours would be the first that is different that I know of... but I'm sure its possible. GM is not known for being consistent. I know some people just omitted the bolt, but I drilled and tapped the head instead. I can take a look later and see which one I did, the heads right now are sitting on a block in a room in the house

1MeanZ

iTrader: (9)

Vader, the only reason I found out about the 'vette head swap, is because I dreaded the thought of porting a set of cast iron heads and I was seeking other alternatives. And through using the search button on this site I found out that others on here had done the same. So I started surfin the vette forums and for $600 got myself a good set of heads with roller rockers. (yah $600 is how bad I did not want to mess with iron heads)

madmax, I do not mean to dispute your claims in any way, I am confident that you know better than I. All I can tell you is that my stock '86 accessory drive setup all bolted right on. That was a concern of mine before I bought them, and I was assured that they would be ok, and they were. If they are missing a hole, then so be it, regardless, it did not affect how they fit my car. If I recall correctly these heads had 3 holes on one end and only one on the other, the 3 holed end faces front on the driver side.

Fastmax

I have a set of these same heads with extensive porting on my 89 IROC with a 350. All of my accessories bolted right up as well.
These heads rock in the power and torque dept. They are an excellent low dollar upgrade.
One noteable item is that there is no provision for EGR on them.
Roy

CrazyHawaiian

I also have a set and they are not on the car yet. I'll try to get some pics of the casting numbers and the bolt holes for the accessories.

fat_bastard711

i am a complete novice when it comes to working on cars. the heads that i have i bought used and i know they will need a valve job, but i don't really know what that is. What consists of a valve job? Also, what else should i have done before i have these bolted to my car? What is a good cam to go with these heads? thanks.

Grim Reaper

I had no missing accessory holes with mine BUT mine were from a ZZ3 engine. Also, there is a second casting, which is inferior. The 10088113 casting is the prefered casting.

Shagwell

valve job means taking them to a reputable machine shop, and having the valves and the seats ground, guide clearance check/fixed, new valve seals and springs (unless you don't like your motor to much...)and having them "bumped" on a surfacer(large belt-sander)

and if you're going to do a head swap, change out that crappy factory cam...

skifur555im666

iTrader: (5)

so who recommends the aluminum corvette heads? and for what years? i am looking for a cheap but decent set of heads to put on my 91 305 gta. i have a cam to throw in there once i have everything apart.

Kevin91Z

iTrader: (1)

My 113 L98 heads were missing an accessory bolt hole for my '91 serpentine system, too.

Here is the pic:
http://para.noid.org/~thresher/image...0/DCP_0033.JPG

I cant remember if that was before or after we drilled and tapped the hole.

The heads work fine on a 305. They're one of the only good heads for a 305. You should get an aftermarket intake (preferably) or a stock Corvette intake, as the middle two intake bolt holes will not line up with an 87+ f-body intake. Also you will need the external EGR hookup from your exhaust manifolds or headers to make the EGR continue to work, like this:
http://para.noid.org/~thresher/image...1/DCP_0162.JPG

If you want to know if this is a good upgrade, I would say no. My dad and I have put tons of time and effort and porting into these heads, as well as dealing with the differences outlined above. I wish I would have spent the money on a better set of heads like Trick Flows.
Are they good for a 305? The answer is always no, put the money towards a 350.