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Discussion Starter · #1 ·
I have a chance to get my hands on a set of used 91Vette L98 113# heads. These are the same ones on todays ZZ4 motor. 58CC. It would put my at 10:1 Is this ratio too high for marine use? What do I have to look out for with running these aluminum heads. Fresh Water only. I was inititally going to run vortecs but they are getting getting out of hand in pricing. People want top dollar for these things. I priced a new set of springed and studded vortecs and it was about 900. Heck for 100 more I'll get a set of E-tecs.

Going back to initial post, this with the zz4 cam was 355HP and 405 TQ. I figure this could be pretty good marine motor. Probebly 310 at the crank.
 

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Mkos1980 said:
I have a chance to get my hands on a set of used 91Vette L98 113# heads. These are the same ones on todays ZZ4 motor. 58CC. It would put my at 10:1 Is this ratio too high for marine use? What do I have to look out for with running these aluminum heads. Fresh Water only. I was inititally going to run vortecs but they are getting getting out of hand in pricing. People want top dollar for these things. I priced a new set of springed and studded vortecs and it was about 900. Heck for 100 more I'll get a set of E-tecs.

Going back to initial post, this with the zz4 cam was 355HP and 405 TQ. I figure this could be pretty good marine motor. Probebly 310 at the crank.
I ran them for a season. I got them from a friend who upgraded on an 89 C4 Vette. While they are aluminum which is good they don't flow very well in stock form and I believe the Vortec's outflow them. They do respond well if you have them professionally ported.

I've ran 10-1 on my past 3 SBC's on 89 octane. 34-35 WOT timing with no problems if jetted right with the correct powervalve.

Some info....

SBC Corvette Aluminum Cylinder Head Assembly (This is also the ZZ4 350 HO Cylinder Head).
This aluminum cylinder head assembly for small-block Chevrolet V8s is ideal for street rods, fresh-water power boats, and high-performance applications. GM Performance Parts’ aluminum cylinder head assembly combines the benefits of light weight, advanced design, and an affordable price. This complete head assembly includes valves, chrome silicon heavy-duty valve springs, retainers, 3/8” screw-in rocker studs-everything an enthusiast wants in a high-performance cylinder head package!

GM Performance Parts aluminum cylinder head assemblies are based on brand new Corvette light alloy castings (P/N 10088113). The Corvette cylinder head’s advanced design features include D-shaped exhaust ports that enhance the flow of burned gases, high-velocity intake runners that provide crisp throttle response, and centrally located spark plugs that improve combustion efficiency. Valve seat inserts for 1.94” diameter intake valves and 1.50” exhausts are installed in the 58cc combustion chambers. Raised rocker cover rails with machined sealing surfaces virtually eliminate rocker cover gasket oil leaks.

This high-performance cylinder head assembly is used exclusively on High Output 5.7-liter small-block V8 engines. Unlike production Corvette cylinder heads, it is outfitted with special heavy-duty valve springs (see part number 12551483 for technical specifications(JIM: These are the same LT4 springs as the Hot Cam Kit). A pair of aluminum cylinder heads offers a weight savings of approximately 50 pounds over comparable cast iron cylinder heads. (A bare aluminum casting, less valves and springs, weighs 19 pounds, versus 44 pounds for a bare cast iron head). This reduction in total engine weight of 25 pounds each can improve handling, acceleration, and fuel economy.
Part Number ... Description.
12555269 ......... Stamped steel rocker cover.
10229162 ......... Corvette screw-in oil filter cap.
12342056 ......... Chrome screw-in oil cap with GM logo.
12338092 ........ .Valve cover hold-down bolts (8 required).
14094717 ......... Hold-down bolt washers (8 required).
14088793 ......... Hold-down bolt gaskets (8 required).
14088564 ......... Neoprene rocker cover gasket.
12557236 ......... Composition head gasket, .051” thick.
12495499 ......... Head Bolt Kit.
12495490 ......... Rocker Arm Kit.

Technical Notes: This casting does not have intake manifold heat riser or EGR passages. The exhaust port exits are approximately .100” higher than production cast iron heads; exhaust manifolds and aftermarket headers may require modification to maximize airflow. The spark plug holes are angled; check for adequate exhaust manifold or header clearance. Use 3/4” reach gasketed spark plugs with 5/8” hex heads (AC FR5LS), 904, or MR43LTS. In Rapid Fire use #8 plug. Both ends of the head are machined for alternator, power steering, and air conditioning compressor mounts. No pushrod guideplates; use rail type rocker arms P/N 10089648. This aluminum head assembly requires valve covers with central hold-down bolts and extra-long bolts with washers. A composition head gasket with stainless steel fire rings is recommended to prevent galvanic action between the head and a cast iron engine block. This head assembly is the same as P/N 10185087, except valve spring and retainer change.

These heads respond well to modest porting and a good valve job. The ZZ4 will get to an easy 378hp/412trq with just this mod. These heads do not like to ping at all, and they do not like over a 150 shot - that and the hypereutectic pistons. The intake port can get close to 180 in size after porting. The D-port exhaust means you have to check your headers and header gaskets to make sure everything lines up OK and that none of the exhaust ports are blocked in any way with everything attached and tight.
The Felpro Head Gasket with the pre-flattened steel fire ring works great and adds a little compression.

David Vizard talks this head extensively, as well as porting instructions and pictures, in his book "How to Build & Modify Chevrolet Small-Block V-8 Cylinder Heads (Powerpro Series)". Great book!
 

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How used is used? A rebuild along with porting would probably make the ETecs look a lot better (they are just a bolt-on).

I would pass on these heads.
 

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Discussion Starter · #4 ·
38K miles. 300 bucks. I would assume they should be good as GM still used them on their zz4 crate motors 355HP 405TQ with those heads and a GM 208/221 495/503 112 cam.
 
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