I have done so many engine buildups over the past ten years to the point of becoming bored with hot-rodding (I know...I am sick...). Lately I have been doing projects with weird themes...like building a cheap, cast engine (pistons and crank) with iron heads and seeing how much nitrous I can lay on it (910 HP before the block split in the lifter valley) or, my latest project to see how much power I can make with only GM production small block parts.....now to the point of my post. I've got a forged crank, pistons and rods and I ordered a set of GMPP 12556463 L98 aluminum Vette heads from Pace. Got them today and promptly tore them down for a quick bowl cleanup and maybe backcuts on the stock valves. Imagine the surprise to see this work already done!!!! All of the intake and exhaust valves already had 30 degree back cuts on them as well as being bowl hogged. Also, the valve seats had three-angle cuts and the heads were fitted with LT4 springs and retainers and screw in studs!! They are good for .525 lift. The casting quality was as good as anything I've seen from the aftermarket, with the ports being smooth and clean. I called Pace to see if maybe they did this work. Nope...they ship them as received from GMPP. Its been a few years since I've had a set of these particular heads, but, these are definitely superior compared to the production Corvette versions. I am going to have them flowed tomorrow.....will post the results then........

What was the price?

Got them for $489.00 each.....

That is exactly what happened when I got my Vortec Iron heads. They were already backcut and with a 3 angle valve job and they had the bowls clean, with no sharp edges on them. I got mine from GMPP direct

Got the flow #'s today on the GMPP 12556463 L98 Aluminum heads....

Out of the box and with about $20 worth of hard rolls to finish the runners:

243 CFM at .500 lift Intake
192 CFM at .500 lift Exhaust

These are killer numbers considering the Intake port is only 163cc.
Even beats the Vortecs in the mid lift region.....

I think I'll put flat-tops in this motor for an 11:1 compression ratio and see if it runs on 94 premium.

You got enough retainer-to-guide (with seal) clearnace to get to .500? I had a set a few months back and did a similar tear-down on them just to get the lay of the land. The retainers were hitting the guide seals at only about .470-480". Also, I didn't have "LT-4" springs. Just old Z-28 "brown" springs that were all bound up around .510" lift at the factory installed height of ~1.70".

These heads are not the old Aluminum Vette heads that GMPP has had in the past. They are much improved over how I remember them from a few years ago.

to your point...... I forgot to mention earlier that the retainer to seal clearance is a whopping .575. The new version heads are now using the low profile, teflon LT-4 seals and retainer cap, so lots of clearance. Too bad the LT-4 springs bind at around .535.

Unless you really hogged these things out, I can't imagine any lift over .550 being beneficial on relatively stock sized ports.

Got some pics for us?

Those #'s seem a little to good to be true. How much "finishing" did you do to the runners? CHP only got about 200cfm @.5 when they tested those, they may have been casting #113 but why would gm redesign an OLD head?

Anyone else seen or flow tested these 463 heads?

good flow numbers.. how much porting is done?
do they have the stock size 1.94"-1.50" valves or were
they upgraded to LT-4/Fastburn style 2.00" x 1.56" valves?

Yea, any more info would be great. I would purchase a set depending on how worked yours were when flow tested.

TA-Wizard, I hate to keep calling you out, but........ I've got a short block that needs a set of heads.... and I've got a 305 in a vert that is starting to get better gas mileage than oil mileage. I can get a break on those heads and would like to know what all was done to yours at the time of flow testing.

Same here, if we can verify those #'s are legit, I'll be ordering a set from GM Parts Direct like right now!

What is the P/N for the driver AND passenger side heads? You only listed 1 P/N and I can't tell which side it is.

I was consdiering a set of AFR's but these are half the price!!!!

There is only one part number for any head. The passenger and driver's side use the same head (just turned around 180 degrees)...

92GTA, just incase you did not notice, the heads are $489.00 each....so $978.00. That's not far off a set of AFR 180's, just a little added info incase you missed it.

you feed NOS thru a stock cast pistons and crank to the tune of 910HP I Love it any idea what it made w/o.

I remember PHR did the same on a 318 with 150k,
pump 250HP before smashing ring lands. it was a great article
anyone still have the test???


OH with the GMPP heads will they work with SLP 1 5/8 headers, are they angle plugs heads?? Also I think the #113 are D port exhaust which wont work with the SLP headers. I wonder if anyone know if the #463 heads will work the smaller headers??

Not to hijack the thread but the new (June, 2004) Car Craft has a nitrous grenade article in it. Took a salvage yard high mileage '75 350 put felpro head gaskets, single plane, comp cams nitrous hp cam, valve springs, and slapped a dual stage kit on it.

turned out 310 hp 344 tq baseline
with 200 hp 521 hp 587 tq
with 300 hp 599 hp with 655 tq
ran baseline again found 325 hp (said due to cleaner ring seats)
with 400 hp ate acouple piston ring lands (after internally purging the system at idle)


Then they rebuilt it with TRW forged pistons and went at it again. Had a burp and melted some Speed Demon boosters.

Then went into talking about how gaining 100% hp increase on any size shot is hard to do on a "Stock" engine.

I also agree with the AFR price statement.
SBC 195cc Street Heads — $1275/pair (shipping included) (180s are the same price)

But it all comes back to what you want to use it's personal prefrence. Like this one was to use GM production parts, which GM doesn't use AFR on their motors even tho we wish they would.

These heads will work with SLP 1 3/4 headers, they have whats called a "L98 angle plug" (they're just at a different angle, but do work with SLP headers). I don't know about the 1 5/8 headers working with the D shaped exhaust ports, but I'm sure a lot of vette guys have run 1 5/8 headers before so I don't see why not? But I don't know guys, if these are the same castings as the old 113's they're nothing to lust after. I just get a price break through the dealer and thought if these were somthing different and flowed what TA-Wizard said they did out of the box (or close to out of the box) then they would be a bargain.

Interesting thread, wish I would have stumbled on this before now. Those heads come on ZZ4s and I'll be doing a heads/cam swap soon and selling my old heads so maybe I can get them flowed or whoever buys them can get them flowed and we can confirm those #s. That looks a lot better than the 208cfm or so that most sources list as Aluminum L98 head flow #s.

Why do you think I have been SCREAMING ZZ4 heads for 305 engines when everyone ask about L98 Aluminum heads. I have mentioned the fact that the ZZ4 heads are superior to L98 aluminum heads for quite some time. Especially since I have a streetable TBI 312 CID 10.3:1 compression 305 that made 423 FWHP @ 6,300 on an engine dyno.

I guess that does explain why ZZ4s make 300rwhp all day. Most people don't believe it, and even I used to wonder why the hell my car runs so hard because on paper 208cfm heads and the ZZ4 cam shouldn't amount to much. Now I know how the Hotcam version of the ZZ4 that Sallee Chevrolet and others sell makes 395hp as well. You're right, those would be killer for 305s and they even have 58cc chambers and the right size valves.

Same casting... 113

That maybe true, but the ports are better in the ZZ4 head as cast. It is a revision to the casting.

See above then for the reason that they would flow a little better. I think the castings may not be all that different, but it looks like GM cleans them up a bit. I remember hearing that the ZZ4 head was a slightly revised casting and flowed a bit better but I never took any stock in it. I always figured it was just leftover 80s castings that they put the LT4 valvetrain into. I can't find any info on a "463" casting as was mentioned above though. I thought everyone was discussing the 113s, and I don't think they ever did change the casting number.