Mystery head 22551581

I found and bought a pair of new old stock bare heads. The casting number in them is 22551581 which I can't find any reference to.

Seller says they were Chevrolet Performance LT1 heads. Specs given are:

54.4cc Chamber, 2.000/1.550 Valves, 195cc/68cc Runners

Those specs seem identical to the stock LT4 head, not any LT1 head I can find info on. Anyone maybe have a lead on some info, or can tell me a good way to verify if they're LT1 or LT4?

Steel or Aluminum?

96 Aluminum heads are 12551561

12555690 is the casting number for the LT-4 cylinder head.

I cannot find the number you have on any of the casting number sites I use.

It's aluminum. Here's some pictures.

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Interesting. First picture the 8 looks like a 6. Neither one comes up. I did find a list that states this part number is for a Connecting Rod.

You know that could be a 6. It is hard to tell. There's also the A stamped next to the casting number too, which is weird. 22551561 doesn't work either.

If it really is a Chevy Performance part, do those have different part numbers from the regular GM stock? My guess would be yes, so maybe it'd be in an old catalog if someone out there has one.

That’s exactly what I’m thinking GM performance part or something similar.

chevy performance head. 96-98 C4 LT1

occ wrote:

chevy performance head. 96-98 C4 LT1

thanks- you have a source for that? There was no such thing as a LT1 or LT4 C4 so that's why I'm confused.

lamune wrote:

occ wrote:

chevy performance head. 96-98 C4 LT1

thanks- you have a source for that? There was no such thing as a LT1 or LT4 C4 so that's why I'm confused.

Sure there was. C4 was 83-96. The LT1 debuted in the 1992 Corvette. They were speed density and used an ECM.

94Woody wrote:

Sure there was. C4 was 83-96. The LT1 debuted in the 1992 Corvette. They were speed density and used an ECM.

Duh. Sorry. I meant "There was no LT1/LT4 C5 Corvette" - everything after 96 would be LS.

So booster had a crazy suggestion that I went with. Find a GM Performance catalog on ebay for a few bucks. I found one from 1996. No match on that casting number but what I did find was interesting.

On Page 26:

Code:

New! 12363287 - LT4 Design Aluminum Cylinder Head
This aluminum LT4 design head is the same as the 1996 production head except it has the LT1 rocker stud P/N 1255216 installed. This head has light weight 2.00" intake and 1.55" exhaust valves installed in this assembly. These heads can only be used on 1992 and later LT1 engines.

Note: This head assembly includes the following items, intake valve P/N 12553331, exhaust valve P/N 12555313, valve spring P/N 12551483, valve cap P/N 10212808. seal P/N 10212810, key P/N 23503856, stud P/N 12552126, and shim P/N 10212809

So far looking at pictures online of 12363287 doesn't show anything with the casting number of what I have, however so far I'd be inclined to think that these are LT4 heads.

I know the intake ports are raised a bit on LT4 vs LT1 intake. Is there any other difference that anyone knows of? I'd like to be able to measure something just to be sure.

lamune wrote:

So far looking at pictures online of 12363287 doesn't show anything with the casting number of what I have, however so far I'd be inclined to think that these are LT4 heads.

Don't think so at first glance. LT4 heads don't have the larger rocker arm boss rib reinforcements found on the LT1 heads. Have the intakes been measured @ 2.00"?

lamune wrote:

I know the intake ports are raised a bit on LT4 vs LT1 intake. Is there any other difference that anyone knows of? I'd like to be able to measure something just to be sure.

LT1 heads are supposed to measure 0.6" from intake port to rocker cover flange, LT4's are said to be 0.3"

These might help:

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Just a thought: If the '96 aluminum heads are casting number 12551561 as previously mentioned, and the 22551561 number can't be referenced.

How likely is is someone made a mistake with the core numbering and substituted a "2" for the intended "1".

- J

Jay thanks a ton for that info. Definitely these are LT1 heads now that you showed me what I need to measure. Also the other spotting items there match up with LT1... which is good because I don't want to buy a LT4 intake.

So your theory of the 2 vs 1 is plausible. I think it's probably more likely that they're a later run, maybe post-LT1 era, and they switched the 1 for 2. But that's just speculation.

If they're really 12551561 casting then 2.00/1.55 valves would be correct. I put a 2.00 valve in it, and it fits, but I must confess I don't feel confident I know how to measure the seat to see if 2.00 is correct.

Intake runner volume for that head is what I'm digging around for now.

Just wanted to add here that I figured out how you measure the valve seat and the valves in this head are 1.940/1.500 standard LT1 sized.

I also found a 1998 GM Performance catalog, and no mention of this head or any LT1 head for that matter in 98.

I did see though that even in 98 you could still order a crate LT4. Pretty cool!

Here's a fun find:

The rocker stud holes on this head are threaded 1/2"-13 and not 7/16"-14 like a normal LT1 head. I have no idea if that was done in the factory or afterwards, but I don't see evidence of secondary machine work.

Anyway since there's no such thing as a 3/8 threaded stud with 1/2 base, based on what I've been able to find so far there are two things I can do.

#1 take the head to a machine shop, wait a few months, and have them install a helicoil or time-sert to return the threads back to 7/16-14
#2 install a threaded insert (EZ-LOK 650- to turn the 1/2 hole into a M8-1.25 hole and use stock LS studs like ARP 134-7201.

Looks like the LS studs might have a .1" overall length increase over the LT1 stud- which shouldn't cause any problems.