arneoe

I am seeking technical information for GM iron cylinder heads, casting number 458642. I am looking for intake/exhaust runner sizes and flow. The heads came with my Five Star 383/360 HP crate engine.
regards
Arne

wfo76

Mortec doesn't say much about them,

458642.....75-84...350..........350

just look like generic passenger car heads and probably stock with 1.94/1.50 valves.

Did they go with bigger valves or do anything to them?

arneoe

Thanks for your reply... No I do not think they modified the heads.... the usual 1.94/1.5 valves and 76cc combustion camber.... They'll be quite ordinary smog heads I recond, hopefully close to the 333882?
rgds
Arne

arneoe

According to the engine builder the GM#4586642s on my 383 are 72cc not 76cc as I first mentioned. He also states that they are simular to the 882, 993 and 441. I am no sure if this is true... the 441 and 882 are 76cc and is different in flow. Any comments on this?
regards
Arne

gerry72

It is similar to any smog-era smallblock head. It was used on the 400 so there may be small holes for the steam channels. Certainly nothing remarkable except that it wasn't one of the "lightweight" scalloped castings so it's a bit more durable. Just a run of the mill head, really.

billla

FYI, any of the "smog" heads will make ~30 fewer HP @ 1 HP/CID just due to the combustion chamber shape.

arneoe

TNX OM! ... nice to hear that is not a "light weight one".... I plan do a porting job on the runners to just to get best possible alignment for headers and intake manifold. There is a lot to gain with such a rough casting...
best regards
Arne

arneoe

Sure mate!.... but I recond an extra 20 - 30 HP can be aceived using the existing "smogies" for us "amateurs"....Would'nt you think?.... I'll sure it's a matter of cylinder head casting and some skill.... This is this not the first time I've touched a cylinder head, so I know very well what to do, if there anough metal in the runners... lets hope this is true...

We'll see what brings..... Anyway, I'll follow E-Bay closely for a good bargin.... I might come across a pair of Dart Iron Eagle 180cc ... good for bolt on.... While waiting I'll stick to my "smogies"....

Arne

billla

The runners will be right around 165cc - and there's not enough "meat" there to significantly increase the cross-section, especially to feed a 383. Considering the inability to significantly increase the cross-section of the runner and poor combustion chamber configuration it's not really worth it IMHO. Flow is around 205/140 I/E @ .400 lift.

I also know my way around a head and a grinder - and there's little or no gain in matching the heads/intake at power levels of 1HP/CID or less.

Finally, if you must keep these heads and take a grinder to them, work on the short radius of the intake and exhaust and the bowl - you'll find a lot more power there than trying to hog out the runners or "flare" them to match the intake.

arneoe

Thank you very much for your reply OM! I appreciate your concern about possible wasted porting job on my GM 458642 cylinder heads. You assume a flow of 205/140 I/E @ .400 lift, which as I can see is very close to the GM 333882. If this is correct I’ll be very close to my goal for the time being. The 882 is, as I can judge, is one of the better smog heads and will serve my purpose. I am looking for cylinder heads, which give me highest possible flow speed, with less than 190cc intake runners, at 0.200 thru 0.400 lifts. I am not concerned about highest possible HP at WOT, I just want a descent torque in the range 2000 thru 4000 rpm. Just for your guidance here is my setup:

383CID (as per the engine builder: 360HP/410 ft. lbs @ 3800, ….blue print)

Static compression rate 9.6 : 1 (assuming with 72cc comp cambers)
GM 458642 cylinder heads, 1.94/1.5 valves, modified valve bowls and seats (I have not verified this yet by visual inspection), 72cc cambers (probably grid off from 76cc). Assuming similar specification as GM 333882……. information for the GM 458642s is very hard to find! ….So this is more and less qualified guesses.

Edelbrock 600 CFM (have also a 1411, 750 CFM to be tested out)
Power Plus Cyclone intake manifold (have also an Edelbrock Performer to be tested out)

Long tube headers (1 5/8” to 3”)
Dual 2.5” with H compensation close to headers (no Cats or smog devices) and low restricted mufflers

L82 Vette (4 speed M/T and 3.7:1)

I am looking forward to receive your comments,
Best regards
Arne

billla

The GMPP Vortec does exactly what you're looking for - plot out the flow numbers in a spreadsheet and look at the midrange flow; incredible, and for so cheap!

I just think you're really choking back 383 CID with those heads - they're marginal even for a 350.

arneoe

I have checked the flow for I/E and they seems OK for my purpose. However, the cambers are too small (need 70 - 76 cc) and the allowed lift won´t fit my XE268H cam. Any suggestions where I can get such pre-machined Vortec heads from to a resonable price?
regards
Arne