Does anyone know the specs on L19 Heads casting 3998997? Thanks!

3998997 350, 400, 76cc, 72-73, hard seats in 73

Any idea about intake and exhaust sizes?

Valve sizes don't matter. Wrong question to ask. However, just FYI, they are most likely the same sizes as most other stock 350 heads; 1.94" / 1.5".

They are yerbasic early smogger trash. Totally NOT performance-oriented.

Throw them away and get something decent. Nothing you can do with, to, or about those, will turn them into anything worthwhile. Turds don't polish up very bright.

X2
Early hardened valve seats were total garbage, What do you want to do with the engine street performance, or drag car?

Street performance, the heads came on a 4 bolt main 400 I purchased for my vette. If the heads are junk I'm probably better off with the aluminum 113's that are on my L98? No funds right now to purchase new heads.

Yup, the 113s will win that battle by a mile.

Throw away the smoggers.

You're going to need some pistons with a helluva dish to get the compression down to a reasonable level if you want to use those 113 heads on a 400ci. Those 58cc chambers will make ALOT of compression on even a stock 400 shortblock.

That said... the 113 heads will flow about the same as the 997 heads (ie. mediocre for a factory head) but the 113 have a much more modern chamber design, and a slightly better exhaust port, so they will edge out the 997 heads, as long as you can get the compression ratio under control. 11:1 or lower should be good, depending on the cam you use.

A couple of comments:

The 113 heads will give you about 11.7:1 compression on that short block (4.155" bore, 3.75" stroke, .025" deck clearance, 6cc valve reliefs, .039" gasket). Clearly won't work.

If all else is equal, 67cc chambers will give about 10.6:1 CR. With aluminum heads, that's about perfect.

If all else is equal, 72cc chambers will give you right at 10:1. With iron heads, that's about where you want to be.

76cc or larger chambers will give you too low CR.

There aren't a whole lot of 72cc heads in the world. Most of the better heads have smaller chambers. The best possible MODERN combo is small-chamber heads with a heart shape to the chamber and an "inverse dome" piston; which is, a dish that approximately mirrors the chamber shape, not a uniform round dish. If you have a flat-top 400, then for the street, basically the pooch is already porked. If that hasn't already been built, I'd pick some other pistons, using the above criteria: the 113 heads, and a piston with about a 15cc dish that roughly mirrors the shape of the chamber.



That is THE WRONG cam for a 400. It's a single-pattern design from the late 70s-early 80s. Good cam in its day, for the way people built cars back then (VERY high-# gear ratios, stick shift, VERY close trans ratios); WRONG now. It gives a narrow peaky power band, which was great when the speed limit was 55 and there weren't even very many roads that had that, so you could gear a car using the above gear combo to force the engine to run between say 4000 and 5500 RPM at all times, including 4000 at 55 mph; not so good when city streets sometimes have 55 mph limits and the freeways are 70 mph and you get rear-ended if you're doing less than 80, meaning that same combo will be running 6500 RPM during your morning commute.

You need a cam that makes power over a MUCH broader RPM range than those old cams did. Furthermore, that cam was designed when 327s were still plentiful, and the 350 was a "big" small block. The bigger the motor, the more critical a restricted exhaust is. Therefore a big motor needs a bigger exhaust lobe, which that old Magnum cam doesn't have. Look at the Comp XE or the Lunati Voodoo series; that's more near where you need to be.

A 400 with the 113 heads with 2.02"/1.6" valves installed in them, the pistons in the pic, and a Comp XE274 cam with 1.6 rockers, in one of these cars with a 700 and about a 2800 RPM stall with about 3.42 gears, will humiliate ALOT of Mustangs yet still be useable as primary transportation.