Does anyone have the specs on stock L98 heads? Like intake runner size, combustion chamber size, valves etc...

Valves are 1.94 and 1.50 the chamber is a nominal 64cc's the intake runners are about 165cc's

actually the combustion chamber is 58cc. the runner volumes are 163/58 and flows 186/152cfm @ .400 lift

Not on iron L98 heads.

He said stock, and this a 3rd gen site so they would be cast iron L98 heads, with nominal 64cc chambers.

ahh, indeed. i know the accepted terminology for the iron heads is L98 but i believe B2L is what GM called them. L98 refers to aluminum heads. feel free to correct me if im wrong.

To add to what's already been posted, L98 heads are in (at least) two forms:

083 casting number, iron head, rounded rectangle exh port shape (as used on L98 Camaro/Firebird, Fcars).

113 casting number, aluminum head (1990+ version), raised D-port exh shape (as used on L98 Corvette, Ycar)

There may also be a 3rd head, also in aluminum because I think the aluminum L98 heads were available as early as 1986. EDIT: the first aluminum heads (1986) on the Vette had the same intake/exh ports as on the iron head. In mid-1988 GM altered the exhaust port on the aluminum by raising it (less abrupt turn to short side radius) and making the short-side into the D-shape to reducing backflow (flow reversion) into the head. Both helped the exhaust side to flow better. The data in Vizard's book is from the 88+ aluminum head. He further said that early and late versions can both be ported to the same flow, so the base casting remains the same --- but the stock flow numbers do not.

Here's the stock head flow data (peak values in cfm). All have 1.94"/1.50" valves int/exh, as listed with the casting number, head material, and peak flow values in cfm, and last is the source for the info (most are 3rdgen sources, plus CHP and Vizard):

083 iron L98 head: 185 intake; 106 exh (smithtc)
083 iron L98 head: 194 intake; 118 exh (rhuarc30)
083 iron L98 head: 202 intake; 141 exh (F-BIRD'88)

113 alum L98 head: 199 intake; 149 exh (Chevy High Performance)
113 alum L98 head: 182 intake; 145 exh (Vizard book, p124,127)
113 alum L98 head: 193 intake; 162 exh (GMHTP, 1.94/1.50)

The intake flows seem to be about the same, iron vs aluminum. The alum heads are better on the exh side.

F-BIRD'88 iron head data is substantially higher on both int and exh, be he pretty much said the same thing himself: "I get much higher numbers. Have so on numerous different sets of like heads". He was probably commenting on ported heads but his stock 083 numbers suggest a similar trend given that the same bench was used.

CHP's measurements also showed superior stock intake flow which makes me wonder if GM revised the 113 casting from the 1991 publishing date in Vizard's book, to 2002 (?) when CHP did their measurments. CHP's production L98 alum head specs and flow are here.

EDIT: according to the GMPP web pages, the 113 casting was retooled into a new 113 casting, so I wouldn't be surprised if GM altered it for better stock flow, which would explain why GMHTP and CHP's numbers were better than those measured by Vizard. That also means that you have to be careful in comparing the flow of the 193 castings (which were never updated) with those of the L98 aluminum heads because there are really 3 versions of the 113 casting: 1986-1988 (same as the 083 iron), 88+ (raised D-port exh), and sometime in the 1990s-2000+ in the re-tooled form having a better valve seat on the intake side. So that really means that there are three different flows possible on 4 sets of stock L98 heads: 083 iron, aluminum clone of 083 (used 86 to mid-88), late-88 alum 113 casting, to early 90s, and then the newest aluminum (113 casting). The 083 iron should equal the 86-88 aluminum; the other 113 castings show progressive improvement on the exhaust side (first 113 casting) and more recently to the intake (early 90s revision to the 113). At least that's how it looks based on what I've been able to find.

I think the only other detail is the combustion chamber on the 083s is 64 cc nominal, while the aluminum heads get 58 cc. IIRC the port volumes are very similar between iron and aluminum.

So the stock flow numbers on L98 head depend on whether they are iron, or early or late aluminum. The intake flow seems fairly consistent for either iron or aluminum and falls in the 180-190 cfm range for peak flow (at or above 0.500" lift). The exhaust flow looks like it will be around 120 cfm for all iron or early (86-88) aluminum heads, and 150 cfm for late aluminum heads.

HTH.

EDIT: per Swapmaster's post:

some thirdgens did come with aluminum heads including the firehawk

Not from the factory. A Firehawk is hardly a factory 3rd gen.

but it was advertised by gm and sold through gm dealerships. i have the original brochure right here. aluminum heads are also listed as an option in my 89 gm fbody manual. does that make it "stock"? the term L98 originally referred to an aluminum headed 350 and B2L was reserved for the iron head. later on, people just stared using the term for any tpi 350. its kind of like when slang makes it into the dictionary. but w/e its splitting hairs at this point and this thread is getting ridiculous. i'll just say youre right because if you're part of the thirdgen.org oligarchy youre right no matter what. i guess that makes me wrong.

Since GM, in its infinate wisdom, called two different engines (Vette or f-body) the same thing (L98), we just need to be specific which one we're talking about when we ask such questions.

cormyr,

I've been on this board for four years now and Tim (five7kid) has never used his position as moderator to legislate anything, other than an end to a bad thread. You can trust him

Sorry what? I was under the impression that the L98 in the corvettes and thirdgens where the same engines, except the 'vette had aluminum heads while the thirdgens had cast-iron ones, and then the drive-trains and whatnot too where different, but the engine itself...

Weird.