OK, you all have convinced me that my combo is flawed. http://www.nastyz28.com/forum/showthread.php?t=74419 To add insult to injury, when I calculated the DCR, I got over 9.1:1 with a SCR of 10.3:1 Yikes. That is probably bad with cast iron heads wanting to run pump gas. That was using a correted stroke of 3.485", .040" thick x 4.115" head gasket http://members.uia.net/pkelley2/DynamicCR.html (<---this method)...

So, I'm starting over. I'm only keeping the bottom end & intake/carb. Here is what I'm NOT changing:

383 - 3.75" stroke, 5.7" rods, 010 4 bolt block. 0.035" deck height.
RPM intake with 750 CFM carb.
Hydraulic Flat-tappet cam - MUST BE SMALL BASE CIRCLE to clear rods
Roller rockers (1.5 or 1.6)
3.73's with Tremec TKO 600 on this STREET car
HEI - MSD Street fire or the like... (for now)...
Long tube headers (1 5/8, 3") with 2.5" exhaust/x-pipe


I'm open to head suggestion ($1100 max - new) ... cast iron or AL...
I'm open to cam suggestions & rocker arm ratios...
I'm comfortable with 10:1 or so CR...


I know there are many combo's out there, but I'm looking for feedback on ones that you have actually tried & liked...End goal - 400 + hp with a nice torque curve over 400 ft*lbs across the board. Based on the carb & intake, i'm planning on staying lower than 6500 RPM's.

Thanks for being patient with me guys. I'm listening...

From your original post it looks like you were trying to build a mild combo, with the exception of the too-high compression ratio. Maybe stick with that idea but get compression down to a reasonable level.

Iron Eagles come in a 72cc chamber size which would put you just below 10:1 with flattops in a 383 and typical clearances/volumes. Their 200cc intake ports should be plenty to feed the combo with that mild cam- and actually even a considerably bigger one, too, if you want to go bigger with the cam.

Iron Eagles were my go-to heads for a few years. They work real well for the cheap money they used to sell them for (not so cheap any more).

Their more expensive aluminum cousins (the Pro 1s) are basically the same casting but in aluminum and with an exhaust crossover port.

I have a buddy right now using a set of box-stock Pro 1s (200cc intake, 72cc chamber) on a 383 with a Comp 282S flat tappet cam, flattop pistons. The motor originally came from the builder with 64cc versions of those same heads. Way too much compression. Pushed the head gasket, obvious signs of detonation. I directed him to exchange the heads with the builder for an identical set but with the larger 72cc chambers. That got compression down around 10:1 in his engine. Detonation problems went away completely on pump gas, tuning became much more predictable (no knife-edge behavior) and the thing went faster than it had with the small chamber heads. We could finally put some good spark advance to it and that more than overcame the reduction in compression.

Thanks Damon. Based on your advice (and PDQ, Rustbucket, & others from the last thread) I think I'll go with:

CompCams XE274H - 274/286 230/236 & 0.05" .487 / .49
Edelbrock Performer RPM heads - 70 cc
Harland Sharp 1.5 ratio roller rockers
Edelbrok Performer RPM intake

With my 0.035" deck height & a 0.028" x 4.130 head gasket I should have:
Quench: 0.063 (best I can do right now)
SCR: 10.02:1
DCR: 8.16:1

This is essentially the build from Chevy High Performance (August 2006). They don't say their CR, but their combo produced 490 ft*lbs/452 hp (peak) and 458 ft*lbs/405 hp (average 3300 to 6100 RPM's).

Did I miss anything?

Why are you pistons so far in the hole? 383s require aftermarket pistons and aftermarket pistons are typically no more than .025" even in an undecked block.

Other than that, I'd say you have it pretty well sorted out.

My buddy's motor has the pistons sitting .015 in the hole and we used a Fel Pro .040" head gasket, so he didn't end up with such great quench distance either. If I had ex[perience with the .028" GMPP gaskets at the time I would have used them, but I hadn't used them myself yet so we went with the "tried and true" Fel Pros. Didn't seem to cause much problem- motor still runs like a raped ape 3 years later.

Do you think I can run the GMPP gasket with a bored motor? IIRC, their gasket has a bore of 4.100"

Should I check the deck height at TDC (as degreed) or TDC of the stroke? The cam that is in there (at this moment) has 4* of advance built into it... I'm assuming that may be why the deck looks taller.

Get a set of Edelbrock RPM 60899 heads ($1000) a Crower 0211 cam ground a small base circle and you will have a very similar combo to mine (minus the machine work). Easy 430HP 450 ft/lbs of torque

Lowend - that looks similar to the combo listed a little over half-way down the page on this link (different heads though): http://www.geocities.com/MotorCity/7610/dyno.htm Nice torque curve!

I considered that one to get a better idle. I was a little nervous because my current 218* small base circle crower cam didn't have enough duration & my dynamic compression ratio was through the roof.

I went with the XE274 because the intake valve closed late enough to drop my DCR to around 8.2 (from the 9.7 that it was :eek: ).

Here is the CHP article: http://www.chevyhiperformance.com/tech/engines_drivetrain/cams_heads_valvetrain/0606ch_cylinder_head_performance_test/index.html

The XE274 is a decent cam choice for a 383/400 and will make decent power from 2500 to past 6000.
The cylinder heads dictate the head gasket required, not the block. The RPM heads will work with most 350 gaskets due to the older style combustion chamber. Go with a Pro Topline 200 cc head and even the 4.200 bore head gaskets get too close to the chamber edge or may even enter into the chamber. Also remember that certain gaskets will beat up the decks of aluminum heads worse than others that are designed to run with them, but nothing that a resurface job won't correct.

Yeah, you always check how far the piston is in the hole when it's at it's highest point. Don't go by the cam- it's not necessarily going to give you true TDC (especially not if you're using one of the +4/-4* offset keyways on the crank gear). And if your pistons have offset wrist pins that's another thing that will slightly alter the true highest point the piston will reach.

With AFR heads (74cc) and earlier Dart Iron Eagles (72cc) I didn't have problems with the GMPP gaskets overhanging the chambers. It's a 4.100" base gasket bore, but there are little "bubbles" in the gasket bore at the usual points where a true circle would overhang the chamber wall. They will also work with aluminum heads. I have used them with my AFRs twice now. Only the tinyest "witness mark" on the head where the fire ring presses into the aluminum ever so slightly.

Thanks Damon. You were right - 0.025" deck height.

EDIT: VVVVV
Edelbrock tech support says that I can run the GMPP 4.1 x 0.028" head gasket AS LONG AS it states that it is a composite gasket for both AL heads and Iron heads (which it does).

Thus, my new quench is 0.053, with a SCR of 10.3:1 and an DCR of 8.4:1. The DCR is a little high, but I think I'm OK.