Chevy Nova Forum banner

1 - 20 of 28 Posts

·
Registered
Joined
·
68 Posts
Discussion Starter #1
Fellas, was looking for some thought and suggestions on head choice. I just pulled the motor and have it down to the block. I ran numbers on compression with my current set up and have 10.24:1. That is with 60cc combustion chambers that my current 388 heads have (1.72/1.5). I have a couple of options: 1) re-build my current heads and it is what it is, or 2) purchase a set of aftermarket heads (looking at trick flow's 62cc combustion chamber to keep compression right around 10:1. Can I get good flow/power out of the 388 heads after being rebuilt and polished and ported, or are the valves going to limit what I can do? Budget is a factor because there are a lot of other things I would like to do and it all adds up! Going with roller rockers and a hydraulic flat cam, haven't picked out the cam yet but def going with some lift thats why I want to keep my CR up.
 

·
Registered
Joined
·
1,034 Posts
An aftermarket head out of the box will easily outflow your stock heads. And for the cost of machine work on factory stuff its not worth it anymore. If you go aluminum, don't be afraid to raise the compression a little. The heat dissipation of the aluminum will easily handle a .2-.3 bump in compression.
 

·
Registered
Joined
·
125 Posts
I agree with braketchev if you have the funds aluminum heads are the way to go unless your trying to keep an original looking motor but for a little more cr and flow go aluminum.
 

·
Registered
Joined
·
68 Posts
Discussion Starter #4
I know the newer heads will be better performing I guess I was curious if I can make the heads I have now work or are they going to hinder my engine performance. If I go with newer heads I can only find a set of trick flows with 62cc combustion chambers. If I go with a bigger combustion chamber I loose CR. I know what CR I have with the stock heads with 60cc combustion chambers. If I go with a 62cc combustion chamber is getting them decked the only way I can increase my CR without changing pistons? I know the head gasket plays into the equation also. I would like to be 10.5:1-11:1 CR.
 

·
Registered
Joined
·
125 Posts
You can buy heads with 58cc chambers got to be carful cause that could bump your compression through the roof are they dished flat tops on your motor now? Like my 383 I have it’s got Keith black flat tops and 65 cc combustion chambers and I’m 11.1. But I’m assuming it’s stock pistons?
I know the newer heads will be better performing I guess I was curious if I can make the heads I have now work or are they going to hinder my engine performance. If I go with newer heads I can only find a set of trick flows with 62cc combustion chambers. If I go with a bigger combustion chamber I loose CR. I know what CR I have with the stock heads with 60cc combustion chambers. If I go with a 62cc combustion chamber is getting them decked the only way I can increase my CR without changing pistons? I know the head gasket plays into the equation also. I would like to be 10.5:1-11:1 CR.
 

·
Registered
Joined
·
68 Posts
Discussion Starter #7
I have flat tops right now, I assume they are a stock replacement. Who makes that 58 cc combustion chamber head? Does anyone know of any company that makes a 60 cc head?

Bracketchev70 I hear you there, just sounds like I shouldn't try and pinch penny's when it come to the top end, I have a edelbrock RPM air gap intake and a holley street demon carb I am putting on it.
 

·
Registered
Joined
·
9,964 Posts
Having built a few 331" motors, I'm curious as to how you arrive at 11.5:1 compression with 58cc chambers and flat top pistons.

The best I could do with -5cc flat tops, zero deck, a .025" shim gasket and 58cc chambers is 10.8:1.
 

·
Registered
Joined
·
1,596 Posts
I have flat tops right now, I assume they are a stock replacement. Who makes that 58 cc combustion chamber head? Does anyone know of any company that makes a 60 cc head?

Bracketchev70 I hear you there, just sounds like I shouldn't try and pinch penny's when it come to the top end, I have a edelbrock RPM air gap intake and a holley street demon carb I am putting on it.
Almost all the popular cylinder head company’s produce a 64cc chambered head. I’d get a set of 64cc heads and have them milled to get your desired 60cc chamber if that’s what you are after.
 

·
Registered
Joined
·
868 Posts
Head flow will always make more power than half a number of compression.
I agree. You will be a lot better off power wise to run the larger combustion chamber with say a 2.02 1.600 valve combination than the stock head with the smaller valves. The better head will also make sure you get more gains from a camshaft swap. I'd buy the best 64 cc head I could afford. I would not buy a new set of 64 cc heads and start milling them down. If you continue to run the engine you may see a day where you need to mill some off the heads but I wouldn't do it just to add a little compression. A good set of aftermarket heads is probably the best addition for making power on a sbc other than power adders such as turbos, nitrous or blowers especially when adding the correct camshaft and other components.
 

·
Registered
Joined
·
68 Posts
Discussion Starter #13
I plugged my numbers into a compression ratio calculator and got that number.

Bore: 4.060
Stroke: 3.25
Compressed gasket thickness: .042
Gasket diameter: 4.190
Deck Clearence: .030
Pistons Dome column: 0
Cylinder head volume: 60 cc

10.11:1 CR

If you run same number with 58cc head: 10.36:1

64cc= 9.65:1

So with out changing pistons you guys can see my CR numbers. That why I need to stay with a small combustion chamber. Unless you guys have some other ideas. I don’t have an unlimited budget being I am buying a new cam, rocker arms, push rods, timing chain, radiator etc, etc. I can swing some new heads but don’t want to buy new pistons also. Maybe look for 58 cc head to keep the compression up?
 

Attachments

·
Registered
Joined
·
68 Posts
Discussion Starter #14
If you look at those compression numbers I put 0 in for dome volume. I have flat top pistons and was told that number is 0. I spoke with trick flow and they told me that number should not be 0 even for flat tops. I haven’t 100 percent identified my pistons but I am quite certain they equivalent are 4 valve relief speed pro pistons. On the specs it said piston volume +5.40. Does that number go into the dome volume? If so that substantially raises my CR to 10.81:1 with 60 cc combustion chambers.
 

·
Registered
Joined
·
125 Posts
10.36.1 is pretty decent just remember that your main power is going to come from good flowing heads. You have specs on the cam your thinking about running ?
I plugged my numbers into a compression ratio calculator and got that number.

Bore: 4.060
Stroke: 3.25
Compressed gasket thickness: .042
Gasket diameter: 4.190
Deck Clearence: .030
Pistons Dome column: 0
Cylinder head volume: 60 cc

10.11:1 CR

If you run same number with 58cc head: 10.36:1

64cc= 9.65:1

So with out changing pistons you guys can see my CR numbers. That why I need to stay with a small combustion chamber. Unless you guys have some other ideas. I don’t have an unlimited budget being I am buying a new cam, rocker arms, push rods, timing chain, radiator etc, etc. I can swing some new heads but don’t want to buy new pistons also. Maybe look for 58 cc head to keep the compression up?
 

·
Registered
Joined
·
9,964 Posts
Are you sure -5.40? Spec sheet says piston volume +5.40. Piston are L2165. Not 100 percent who manufactured because that is all that is stamped on the piston. Closet I could find were speed pro’s that are spec’d for a 67 Chevy 327. Do you think I am right on my thinking here?
You need to read the part that says:

Enter Piston Dome Volume In CCs Negative For Dished Pistons (Use '-')

Flat top pistons with valve reliefs will be entered as a negative number.

4.06 bore
3.25 stroke
4.19 gasket bore diameter
.042 gasket thickness
60cc chamber
-5.4cc dome volume
.03" deck clearance

Calculates to 9.486:1 compression

Put some 58cc heads on there and you have 9.699:1 compression.
 

·
Registered
Joined
·
68 Posts
Discussion Starter #20
Mike,

Can you then explain why the piston specs list +5.40cc for Piston Head Volume for the pistons I more than likely have? If this is the case wouldn't I enter the measurement +5.40 and not -?
 
1 - 20 of 28 Posts
Top