Anyone have an idea on what is the max horsepower the cast iron L98 heads are capably of producing? Not untouched, but ported, and flowed to their fullest ability? I know that there are many aftermarket heads, and vortecs that are the hot ticket, but just wondering, how good the L98's are, or can be.

not enough? Optimistically, i'd say the heads'll hit the ceiling at 400hp. Even ported, you'll still be choking that HSR of u'res.

I think they flow 198 cfm stock. Use the theoretical cfm/hp formula of: (cfm of 1 cylinder) * .2527 * # of cylinders= hp potential.

They can be ported to maybe 245-250, but after you put the bigger valves, screw-in studs, etc. you could have started with a vortec or aftermarket cast iron head. If you are porting them yourself it may be worth it.

As stated in the starter thread, I know there are other options, but I would like tho know the limit of the stock heads. Fully ported, stock valve sizes, etc....


1320 Right Ln. Thanks, that is the kind of resaponse i was looking for.


Anyone have a hp number, form personal expereince with these heads? Other than stock of course.

Head flow for factory unported and ported L98 iron heads appears here, approx 2/3rds of the way into the thread.

Stock L98 iron heads (083 casting suffix), by TGO members, flowed unported:

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, note that he says: "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 -- that he's approx 10% higher than the other two people listed here.)

Ported flow data for the same 083 iron heads was:

083 iron L98 head: 209 int; 137 exh (dj haf, stock valves) radiused int inlet, open no pipe exh
083 iron L98 head: 200 int; 139 exh (smithtc, stock valves)
083 iron L98 head: 206 int; 144 exh (smithtc, stock valves)
083 iron L98 head: 203 int; 171 exh (smithtc, 2.02/1.60 Manley)
083 iron L98 head: 229 int; 171 exh (rhuarc30, 2.02/1.60)
083 iron L98 head: 197 int; 160 exh (CHP)
083 iron L98 head: 248 int; 181 exh (Insomniac92z28, 2.02/1.60)

The links to each of these (the source for each of the flow numbers) is in the highlighted "here" above.

The rule-of-thumb provided by 89gta383 above basically means you multiply the cfm of the intake by 2 to get the theoretical fwhp (assuming an 8 cylinder engine). That also means a big cam, and everything else optimized, to allow the fullest power output. So the range would be 360 to 380 fwhp using stock heads and 400 to nearly 500 fwhp using the ported head values.

The rule-of-thumb method also ignores the exhaust flow (poor exh flow heads mean that the intake won't be fully utilized). The futher flaw in that rule-of-thumb is that it's not what you want for a street-driven car..... a cam that large would not be pleasant in ordinary driving. So don't take too much stock in what that approximation provides unless you are building an all-out race engine.

A better way is to look at the stock power output of the Fcar L98, at (?) 225-240 fwhp using the factory stock 773 L98 cam. From there, you can bracket the power range all the way up to 380 fwhp with stock heads or up to 500 fwhp with really good ported heads. That covers the range of what you could get, via porting and cam swap, assuming your parts match is reasonable and the tuning is covered. HTH.