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Old 06-15-2008, 06:42 AM
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SBC heads and CR advice needed

I'm in the middle of tearing-down the top-end of my engine to clean/inspect and ID the parts used. Unfortunately, the previous owner didn't have the spec sheet (the engine was professionally built elsewhere) and even though I've spoken with the builder, the engine was built 5 years ago, so he's a little hazy on some aspects of the build. So, having now taken-off the heads, this is what I know...


Edelbrock Performer RPM intake
Erelbrock 600cfm carb

462624 GM iron heads with 1.5" exhaust and 1.94" intake valves (76cc chambers)

TRW Hypereutectic domed pistons (H618P) +30

There is still a small question mark over the cam... the builder suspects it's an Edelbrock Performer RPM flat tappet. I've tried to measure lift at the exhaust and intake lobes using a cam checker tool (dial indicator that slips into a machined alloy body that slides into the lifter bore). However, I'm having trouble getting a dead-on accurate reading (due to slight play of the cam checker body in the lifter bore). My measurements, so far, put the exhaust cam lobe lift at 0.337" (0.505" valve lift) and intake lobe lift at 0.305" (0.457" valve lift). Edelbrock's figures are 0.510" and 0.488" respectively. So, it's possible (likely) the cam IS actually a Performer RPM, but I can't be 100% sure at the moment (gonna go recheck and see if I can get more accurate numbers).

My current static CR is 9.38:1, according to the TRW pistons site.

If I go with 64cc heads, my CR will be 10.72:1. I've measured my pistons and they're about 0.030" down the cylinder @ TDC (however, I suspect that's not quite accurate as I'm measuring with a digital vernier caliper, so let's assume the stock 0.025" down the bore). This puts my quench area at around 0.063" with a stock 0.039" compressed gasket. So, if I go for 64cc heads and 0.015" shim gaskets to get the quench up to 0.040", my new static CR will be over 11:1. So, if I decide to change my heads, should I go with 64cc chambers? What gasket compressed thickness would be the best compromise? Pulling the engine to deck the block, or change pistons isn't an option right now.

Cheers,
Ian.

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Old 06-15-2008, 08:54 AM
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If you decide to go with better heads, get some with a 70-76cc conventional chamber shape that will clear the piston domes. Or change the pistons.

Some of the modern heart shaped chamber heads like Dart Iron eagle/Pro I may or may not work with your piston domes or may need minor chamber clearancing grinding to work.
If you buy a Dart head make sure your get the new(er) "Platinum Series" redesigned heads. "P" at the end of the Dart part number. Many, like the "180 Iron Eagles" and early 200cc,215cc heads are the old design, often offered at attractive discounted prices. Pay a bit more and get the superior Platinum head. Make sure of what you are buying.
Anything with a combustion chamber shape like the vortec heads have, will not work (without modification) and radically changing the combustion chamber shape is not recommended on these heads. That leaves carving or milling off the piston dome.

A 70cc Edelbrock performer RPM head or a 72 cc chamber World Products Sportsman II head with a bit of hand porting will work and really wake that motor up.
A 70cc Brodix IK180 or custom ordered 70+cc chambered IK-200 heads will work well too.
Again minor chamber, piston dome clearance grinding may be required. It's up to you to check this.

The stock 624 heads are really limiting the power.

Last edited by F-BIRD'88; 06-15-2008 at 11:15 PM.
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Old 06-17-2008, 01:55 PM
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Quote:
Originally Posted by F-BIRD'88
If you decide to go with better heads, get some with a 70-76cc conventional chamber shape that will clear the piston domes. Or change the pistons.

Some of the modern heart shaped chamber heads like Dart Iron eagle/Pro I may or may not work with your piston domes or may need minor chamber clearancing grinding to work.
If you buy a Dart head make sure your get the new(er) "Platinum Series" redesigned heads. "P" at the end of the Dart part number. Many, like the "180 Iron Eagles" and early 200cc,215cc heads are the old design, often offered at attractive discounted prices. Pay a bit more and get the superior Platinum head. Make sure of what you are buying.
Anything with a combustion chamber shape like the vortec heads have, will not work (without modification) and radically changing the combustion chamber shape is not recommended on these heads. That leaves carving or milling off the piston dome.

A 70cc Edelbrock performer RPM head or a 72 cc chamber World Products Sportsman II head with a bit of hand porting will work and really wake that motor up.
A 70cc Brodix IK180 or custom ordered 70+cc chambered IK-200 heads will work well too.
Again minor chamber, piston dome clearance grinding may be required. It's up to you to check this.

The stock 624 heads are really limiting the power.
Thanks a lot for all of that info! Would these heads work (68cc chambers)...

http://cgi.ebay.com/ebaymotors/ws/eB...244038079&rd=1

I know this particular brand is very controversial right now but, that aside, would this chamber size and shape work with what I have? Just to reiterate, my deck clearance is 0.025" and my pistons are domed with 0.125" domes (TRW don't give the dome size in cc) and they have valve reliefs.

Thanks,
Ian.
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Old 06-17-2008, 02:33 PM
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v8hed these heads have the same kidney shape combustion chamber design as the Vortec heads. They will not work with your dome type piston. Your H618CP pistons have -3.5cc volume. You need the old style D shape combustion chamber heads for the style piston you have.
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Old 06-17-2008, 04:43 PM
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Quote:
Originally Posted by SSedan64
v8hed these heads have the same kidney shape combustion chamber design as the Vortec heads. They will not work with your dome type piston. Your H618CP pistons have -3.5cc volume. You need the old style D shape combustion chamber heads for the style piston you have.
Ok, thanks for the clarification.

Cheers,
Ian.
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Old 06-17-2008, 05:17 PM
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Actually, what is the reason I cannot use heart-shaped or kidney-shaped chambers with my domed pistons? Looks like the only 'decent' heads with old-school chambers are the Sportsman IIs? Could I go with 64cc chambers (10.7:1) if I run premium gas? I have a fairly large duration cam.
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Old 06-17-2008, 06:49 PM
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Quote:
Originally Posted by v8hed
Actually, what is the reason I cannot use heart-shaped or kidney-shaped chambers with my domed pistons? Looks like the only 'decent' heads with old-school chambers are the Sportsman IIs? Could I go with 64cc chambers (10.7:1) if I run premium gas? I have a fairly large duration cam.
If you look at the Kidney shaped chamber, the pointed part of the head that goes in between the valves will actually hit the piston dome. The chamber has to have pretty much the same shape as the dome or bang. LSA/The Lobe Seperation Angle on the cam and duration can help with high compression and lower octane. Narrow LSAs like 106-108 help. Wider 110-114 don't like high compression with low octane. PerformerRPM has 112 LSA. 10.7 may be pushing it with iron heads. With 4.03Bore X 3.48Stroke, 64cc Head, .041Gasket, .025Deck, 3.5ccDomes I get 10.79CR.
With 72ccHead, GM.028Gasket I get 10.14CR with a better Quench @.053, That's a better CR to try & deal with pump gas. Much of Europes octane is not rated like the US. 93-94 here is like 98 over there.
76ccHead + .028Gasket = 9.7Cr
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Old 06-18-2008, 07:21 AM
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Quote:
Originally Posted by SSedan64
If you look at the Kidney shaped chamber, the pointed part of the head that goes in between the valves will actually hit the piston dome. The chamber has to have pretty much the same shape as the dome or bang. LSA/The Lobe Seperation Angle on the cam and duration can help with high compression and lower octane. Narrow LSAs like 106-108 help. Wider 110-114 don't like high compression with low octane. PerformerRPM has 112 LSA. 10.7 may be pushing it with iron heads. With 4.03Bore X 3.48Stroke, 64cc Head, .041Gasket, .025Deck, 3.5ccDomes I get 10.79CR.
With 72ccHead, GM.028Gasket I get 10.14CR with a better Quench @.053, That's a better CR to try & deal with pump gas. Much of Europes octane is not rated like the US. 93-94 here is like 98 over there.
76ccHead + .028Gasket = 9.7Cr
Makes sense, thanks.

Yep, our octane is based on RON. Premium over here is called 'Super Unleaded' and is usually 97 RON, although Shell V-Power is IRO 98-99 RON. Regular unleaded is 95 RON.

Cheers,
Ian.
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Old 06-18-2008, 05:04 PM
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