383 heads: 64cc vs. 72cc [Archive] - Team Camaro Tech

: 383 heads: 64cc vs. 72cc

Mar 31st, 05, 05:24 PM
I've decided to have a 383 built for my 68 vert. The builder has given me two options at the same price.
Option #1
Dart Iron Eagles, 200cc runners, 72cc chambers, flat-top pistons.
Option #2
Pro Comp Aluminum Heads, 190 cc runners, 64cc chambers, dished pistons.

I'm looking for a streetable "pump gas" engine with compression around 9.5:1. What are the pros and cons of 64cc chambers with dished pistons versus 72cc chambers and flat tops?

67 Plum
Mar 31st, 05, 05:59 PM
My vote is for 72cc with flat tops.I think you get better combustion and the ability to make more power with flat tops.9.5:1 will work good with iron heads and 91 octane.With everything dialed in good 89 should be enough. My 327 is 9.42:1 and runs on 89.JMO

Mar 31st, 05, 10:57 PM
Get a dished piston that matches the shape of the chamber, that will make the best power.

Apr 1st, 05, 10:39 AM
Get a dished piston that matches the shape of the chamber, that will make the best power.

Ditto -- provided you get the right compression ratio for your cam and fuel.

Apr 2nd, 05, 06:08 AM
Ditto -- provided you get the right compression ratio for your cam and fuel.

I agree.......do your "squish" or as some call it "quench" here, and DCR homework too...it's as important for pump gas issues as anything else

Apr 2nd, 05, 08:00 AM
If I could add to the question asked here, I think what is being asked here is if the compression ratios are the same, what is the advantage of a larger or smaller chamber size.

In my plans for a 383, I was looking to keep my compression ratio down to 9 - 9.5 to 1. My thinking was to get the heads that will give me this ratio with the bottom end of the engine having flat top pistions that are zero decked and using normal .039 - .041 head gaaskets. My thought is you get a better burn across a flat surface of the piston.

Any other thoughts???


P.S. Don't hit the ESC key when typing your message, It goes away...

Apr 2nd, 05, 12:19 PM
go with flat tops
the domes will require higher octane and bump compression up to 12:1 or close to it.
sure its good to have high compression but will you be willing to pay the price for higher octane?
or even racing gas at around 7 bucks a gallon now.

Apr 2nd, 05, 05:16 PM
Assuming the compression ratio is the same my preference of combustion chamber design is as follows:

1. D-dish piston, small combustion chamber
2. Flat top piston, medium combustion chamber
3. Dome piston, large combustion chamber
4. old style dish piston (no quench pad) and small combustion chamber

There has been some tests and some debate about how much (if any) advantage there is to a D-dish piston over a flat top piston. I personally believe that if the compression ratio is the same the D-dish has a slight advantage due to combustion chamber shape -- being more compact in the center of the chamber will IMO burn a little faster and more efficiently than a larger, flatter chamber.

Pretty much everyone accepts the idea that the design of the combustion chamber makes a big difference in power production, but a lot of the time people forget that the cylinder head is only the "top half" of the combustion chamber -- the piston crown makes up the other half.

Apr 3rd, 05, 07:53 PM
I wonder how much difference there is between a modern fast burn style 64cc chamber vs. a 72cc chamber of the same design. I bet the difference isn't near as significant as the old 64cc gm iron heads vs. the 76cc iron heads.
Interesting too is the fact that the few dyno tests that I have seen of small vs large chamber heads always shows the larger chamber making more power on the top end due to less valve shrouding.

Apr 4th, 05, 07:01 AM
That's true Travis . . . larger chambers can flow better. Especially if the extra volume is in the right place.

Anyone ever seen a set of SB 2.2's up close -- like a used set that had been worked for a cup team? The chambers are a work of art themselves . . . the ones I saw had a shallow flat chamber -- only 44cc's if I remember correctly.

Apr 4th, 05, 09:59 AM
go with flat tops
the domes will require higher octane and bump compression up to 12:1 or close to it.Dish and dome are virtual opposites. Dome is convex, dish is concave. Dished pistons lower compression, not raise it.

Apr 4th, 05, 03:06 PM
Talked with my engine guy this afternoon, and he his now presenting OPTION #3.
>> Dart Iron Eagles, 180cc runners, 64cc chambers, dished pistons
Equipped with larger valves. 2.05 intake / 1.64 exhaust

Five sets in stock, and about $300 less expensive. But are 180cc runners sufficient for a 383 street engine? Would I feel any power loss at lower RPMs, or mostly just on the top end?

Apr 4th, 05, 06:08 PM
Sounds kind of strange -- larger valves with smaller runners . . .

It depends on the cam you pick and the RPM range you want to run. If you use smaller runners don't plan on making good power much over 5500, sure it will rev higher but you will be giving up power up top. I don't think you would loose power down low -- you might even pick up some low end grunt.

Apr 4th, 05, 06:37 PM

What cam are you going to run? How much are the heads setting you back?

I was thinking of going with that combo for a large flat torque curve. The cams I was looking at were the Comp XE268H or the Crane Z-268-2

Apr 4th, 05, 08:54 PM
What cam are you going to run? How much are the heads setting you back?

The builder is recommending a Wolverine Blue Racer (Crane) camshaft #WG1064 (Crane grind# 300-2H). .488/.510 lift, 234*/244* duration @ .05, and 112* lobe separation. I first thought it sounded too big for a street driven car. What do you think? I'm mostly looking for low end street power on pump gas.

I'm pricing a complete engine build, so it's hard to say what the heads really cost. But he said that an upgrade to 200cc heads would cost an additional $250 to $300. He has five sets of 180cc heads in stock and I guess he really wants to move them.

They just dropped one of these engines in the owners Chevy pickup. I'm going to arrange a test drive before I make my final decision.

Apr 5th, 05, 07:16 PM
I'm no expert by anymeans...but that cam seems way to large for a low end building small block. I'm looking in the 220* --.465 lift range to maximize torque and HP.

More input from the experts here would be great!

Apr 5th, 05, 07:36 PM
The cam your engie builder is wanting to use is the same as the edelbrock performer rpm cam...a cam not known for low end torque. That cam also needs about 10.5-1 compression to really run right anyway.
I don't see aproblem with using a 180cc head. If your looking for under 6000rpm power then a 180 will be just fine. A 200cc head with a moderate sized cam will go over 6K easily in a 383. The 180 should also offer superior low end torque and throttle response. With 9.5-1 compression, and a 180cc head, a cam somewhere around 222 to 228@.050 will provide a wide, torquey, and powerful powerband that would work nicely even with a 3.08 gear.

Apr 5th, 05, 08:23 PM
a cam somewhere around 222 to 228@.050 will provide a wide, torquey, and powerful powerband that would work nicely even with a 3.08 gear.

Thats what my work truck is sayin!

Busted Knuckles
Apr 6th, 05, 05:55 AM
A shop close to me ran several dyno tests a few years back, comparing flat top with bigger chambers to reverse dome (NOT the same as dish, but often called "D" shaped chambers) with smaller chambers. The small chamber/reverse dome made more power across the curve. It wasn't more than about 4% - 5%, but it was consisent with big blocks and small blocks. Smaller chambers are almost always better - look at the Big Duke/Big Chief heads. Their chambers are generally less than 90cc's!
When I was designing the 383 that I'll be assembling in a couple of weeks, my guys recommended a cam no larger than 230 @ .050 for streetability. After I had my heads flowed, the I/E ratio averaged 74%, so I ordered a custom hydraulic roller from Comp. $320 lets you spec it any way you want. I got a small base circle (don't care for grinding rod bolts) billet core (versus their hardened cast cores) with stock compatible distributor gear. I basically took their Magnum cam with 230/230 - 560/560 and had 'em grind it on a 112 LSA instead of their standard 110. This should give me an idle sound that I like, plenty of vacuum for power accessories and a broad, flat torque curve.

Apr 8th, 05, 04:07 AM
think i'll stick with the 274 xe and save a ton of $$$ over the higher lift needed with heads much over the vortecs!
hope you get 12.###'s!

Eric B

Apr 8th, 05, 08:02 PM
68 Driver,

Let us know what you go with and your satisfaction level. We know you are getting tight on time and the weather is breaking.


Apr 15th, 05, 05:49 PM
Strokers need slightly larger cam grinds. We have finished 3 tests in the past 2 months. All from the same short block with a 4340 steel crank (3.750), 5.700 H-beams, Ross L/W pistons, and a Comp Cams (custom-grind) retro-fit Hyd. Roller. The first with 9.75:1 C.R. using 72cc Dart/200 runner cast iron heads. The second with 10.6:1 C.R. using 64cc/195 runner Australian aluminum heads. And last, a 9.9:1:1 C.R. using Brodix 70cc/184 runner. All heads had 2.020/1.600 valves. The first combo made 457HP @ 5700 / 447 Ft.Lbs. @ 4700. The second combo made 441 HP @ 5700 / 447 Ft.Lbs. @ 5000. The third one made 476 HP @ 6100 / 453 Ft.Lbs. @ 5100. The last test was most impressive to us due to the fact the heads were cast up by Brodix back in 1988 and had only bowl work. Also they were straight-plug castings.
P.S. Everyone of these ran with no problem with straight 93 octane. You need about a full C.R. point higher for alloy heads. At the same time on the final "pulls" we took off the 25 year old Edelbrock "Tarantula" intake, bolted on some decent lookin' hi-rise (Professional Products #52036) and expected to see some 25/30 HP. It was only worth 5 HP. We didnt believe it! Thanks Gary @ The Performance Engine Shop

67 Prostreet
Apr 16th, 05, 09:00 PM
68driver, I'm in the restoration process with my Wife's ragtop. I built a 383 for it and finally got it running last weekend. It has been on an engine dyno and has better than 20 pulls on it. The recipe goes like this

.040 4 bolt main with ARP stud kit
3.750 stroke SCAT 9000 crank
Stock GM 5.70 rods
Speed Pro Hypertectic pistons with coated skirts .100 dome
Dart Pro1 215 cc Aluminum heads 72cc
Comp Pro Magnum roller rockers
Comp XE274 Cam
Edelbrock Performer
Holley Street Avenger 670 cfm

The motor is 11.2:1 and is currently showing no signs of detonation on 91 octane gas. Bear in mind that I'm at 6500 ft in elevation and we can run higher compressions here.

This motor makes 408 hp and 445 ft lbs of torque

Peak tq happens @2600 and falls off at 4600
Peak hp 5500
and is very streetable... Likes gas though. Used better than 5 gallons on the dyno
Hope this is of some help

Best of luck,

Apr 16th, 05, 09:42 PM
Tom, you should bring it by the shop someday, I'd like to see it.

Apr 16th, 05, 09:48 PM
You need 9.75:1 with the iron heads and 10.6:1/10.75:1 with the alloy heads.
The cam specs should come in around the 236/242 x .540 x 112LS. I only use Hydraulic Roller-Retros in my combinations so I have no dyno sheets with any flat-tappet cams. I tend to keep the cam a little short in order not to move the RPM range higher. The heads should flow about 260/270 cfm intake 190 cfm exhaust @ .600 lift. Don't use a hi-rise open plenum, stay with a lower open plenum, the 383's (low-compression) don't like long intake runners. It's not necessary due the long stroke (you need more amt. of air than velocity). The above combination (I have the dyno sheets) should put you in the neighborhood of an honest 475 HP / 460 Ft.Lbs. torque on 93 octane and it should all be in about 6000/6100 RPM. One more thing if possible, try to build it as an independently balanced unit and keep the bobweight around 1800 grams. This will mean a fairly light piston/pin combo and I would opt for a 5.700 rod to keep it as light as possible also (6.000" rods weigh more). Try not to use an external balanced ***'y. The smallest port (i.e. 190cc's) that passes the 260/270 cfm's will give a higher torque result on the dyno. In other words, if you use a 230 cc runner that passes 270 cfm, your H.P. numbers may be the same but your torque will be lower. I've had really good results using the Pro-Topline heads (both iron & alloy) on both SB's and BB's, but at the present time they're hard to find. They will be back on the market shortly (the foundry is in New Zealand), but I'm not sure how soon! Thanks, Gary @ The Performance Engine Shop in N.Y.

Apr 16th, 05, 09:54 PM
How do you delete a post here?