Thanks to all the previous threads on trying to get more HP out of the HP500EFI I am going forward with rebuild to original spec

main thing is cylinder heads, the ones removed look ok but I know I need new springs and full valve job etc -

any suggestions on just buying a ready togo head assembly with spec'd springs etc. that match the GM head - my casting is 12562934 w 2.25 and 1.88 valves, year is 2003 and 450hrs on ECM?

Thanks, Tom

If you want to keep it factory you have 2 options...

1. Buy from Mercury. Last time I called they would only sell loaded heads. They were $1800 each. Guessing it's all merc factory parts.

2. Summit racing offers loaded heads for the factory GM head but I don't know what they put on it in terms of springs, valves, etc. part number is NAL-12562920.

Have your heads pulled apart and checked, if the castings and valves are fine, rebuild them, surfacing, springs, seals, guids and a good valve job is going to be a lot less than less than new heads.

[QUOTE=Satisfaction;4527206]Thanks to all the previous threads on trying to get more HP out of the HP500EFI I am going forward with rebuild to original spec

main thing is cylinder heads, the ones removed look ok but I know I need new springs and full valve job etc

AKRacing/Promaxx heads will give you the best bang for your buck!!!

New complete heads should be torn down and checked anyways. May as well start with what you have.

assuming I pull and re install the heads, how much would this cost

You took the heads off running engines so no problems, right? Just have them gone over thoroughly by a good marine engine builders with new parts and you are on your way. JMO. Good luck

Agreed... I am a builder and that's what I do, hence the I'm the AK Racing in the AKRacing/Promaxx head... these are completely gone thru, spec'd and done with a marine friendly valve job and equipped with severe duty stainless steel intake and super alloy Inconel exhaust valves, hardened 10* retainers and locks and 1.50" pacalloy endurance valve springs, 4140 7/16" rocker studs, 3/8" hardened guideplates, fully assembled to the end users cam specs... these are drop on ready and on an order/spec to suit basis... NOT on the shelf production boxed parts...

that depends on the condition of the valves, seats and other components, IMPO it's usually not worth it when compared to My heads as you'd be almost 2/3rds of the way in rebuilding your heads and there's no performance advantage in it for you, so why not upgrade and get some bang for your buck!! that's my only thought... put your money into something that gives you something back...

There's no canned answer for that, but it wouldn't cost much for a head shop to give you an answer, then make your decision where best to spend the money