robz5150

I have a 91 Z28 305 (LB9) TPI 86,000 miles on it. It's been sitting in my garage for almost 14 years, I've been starting it and taking it for drives around the block through out the whole time. Recently decided to do some engine work to it to get more hp. I know what everyone is going to say.. drop a 350 in it. Well I don't want to go that route. I have ported, polished, siamesed the plenum and intake manifold. I purchased the LT4 (12551142) cam and 1.6 roller rockers for it. New timing chain (12371043). Was going to get the s/r heads 042750-1 but out of my price range right now. So I decided to work on my stock heads. I have the 14101081 heads that I was going to get a valve job on and new springs to accomadate the higher lift cam, do a bowl blend, porting and polishing on them. But just the other day I saw a machine shop selling the same heads for $400. They did a bowl hog on them, intake now is 2.02 and exhaust is 1.6 (stock is 1.85i & 1.50e) plus 3 angle valve job, new springs with lift now at .550. My question is what gains or losses would I get from going with these machined heads??? Would my compression change? Would I get more hp? And at what range? Low end high end? And if any one has a better option (other than dropping in a 350) all suggestions are appreciated. Thank you.

Rod Behring

The 2.02 intake valve is too large for the bore size of the 305.

The SR have 1.94 and that is about as big you should go for intake valve on your LB9.

Check ebay for deals on those SR's or the 113 corvette aluminum 58cc heads. The vette heads require an external EGR pipe if you need to run egr for emissions, otherwise they will work well with the LB9.

robz5150

Rod the vette heads you are talking about are they P/N 10088113? And will my manifold bolt right up to it? Thanks Rod.

giszo

As far as I know those vette heads use the pre-87 style intake bolt pattern, so your 91 manifold will not be a direct bolt-on piece.

robz5150

That's what I thought, I just saw some of these heads on ebay that came off of an 86 vette.

giszo

I am also in the planning phase of my 305 build and considered these Vette heads but decided to go with the same factory 081 heads as I already have them and don't have to pay for a new set.

I am using the original size valves with better springs, screw-in studs and porting, porting, porting.

Rod Behring

The heads I was referring to are the ones used on the ZZ4 crate engines. They also come stock on 87-91 vette. These are centerbolt 87-up style just like yours.

I'm not sure of the exact part number, but they are referred to as 113 casting so it must end with that.

Even if you got the older heads its easy to modify your intake to work with them. You just have to elongate the two center holes on both sides of the intake manifold.

Good luck.

robz5150

Rod once again thanks for the info. I found a GM head casting reference list and on the list the only heads that end in 113 are the 10088113 and the decription for that part number is 350, 88-up, Corvette, Alm., angle plug, 58cc, .100 raised D-port ex. 1.94-1.5 valve, 19 lbs. So now I'm confused, cause I saw a pair of 113's on ebay and it said they came off of an 86 vette???

robz5150

The ZZ4 cylinder heads are GM part number 12556463 and they are the 10088113 casting. Spoke to Jegs (they sell them for $620 a piece) and they told me they would bolt right up, even using my stock TPI intake manifold.

Rod Behring

$1240 is a lot for those, especially when. Trickflow TFS are $1100 and they (TFS) are better heads.

Some people take those 113's off the ZZ4 and sell them on ebay to put higher performance heads in place. The same goes for the zz4 cam. If you search you can find deals.

robz5150

Yeah those ZZ4 heads are out of my price range at over $1,200. If I could afford that I would save a couple hundred bucks and get the World Products s/r 042750-1 heads.