HP500efi Cylinder Heads
 

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

I had my 088s gone through. Same head as the 934. Cleaned. Surfaced. Valve job. New springs on all 4. I spent about a grand.

and that's about right.. and if you needed to add new valves you'd easily add almost another grand cause if you're changing them, you'll likely go bigger, and that's my point, almost $2k in and you're near into mine!!

Great feedback thanks! I will post the numbers i research and some more details as they unfold. Thanks Tom.

I'm here to help if you need it

You can easily exceed the price of new heads rebuilding old ones. I won't do it anymore because when you do just about everything and it cost a good amount, and 2 years later someone thinks they have an issue and freaks out over the guides not being replaced. Add guides and valves and new heads are cheaper, even if you take them apart and verify

do you think you'll have to rebuild the new ones at the same interval

I use the finest parts available, Ferrea Valves, severe duty stainless steel intake and Super alloy (Inconel)exhaust, Pacalloy endurance (300 hr) valve springs, and hardened 10* retainers and locks, 4140 7/16" rocker studs and hardened 3/8" guide plates, these are custom build to suit per customer not sitting on a shelf waiting... so "drop on ready" is what you get with "My" heads!!!

What does the community recommend for valve spring replacement part number for stock hp500efi?

PAC?

Thanks. Tom.

a Pac endurance spring is what we use.. and they have a service life of 300+ hrs

heads were in good shape so stayed with existing castings - was about $600 plus I provided the springs/locks and retainers

ran into one issue in that most of the recommended springs had a installed height of 1.875" but my 2003 HP's which still had engine seals on them had installed heights of 1.950-2.030" without shims -- not sure if others have seen that with the 934 casting heads -
my original plan was to go with isky spring 8005-a after talking to Isky about the height they suggested the 8205-SP spring which would be about 135# seat pressure if installed at 1.95"

I am not adverse to going to PAC or other spring either just trying to stay in bounds with what others have had success with

Curious of your thoughts - thanks! Tom

So castings were good and spent about $650- at marine machine shop with me providing springs / locks and retainers

did run into a glitch with springs - planned to go with isky 8005-a spring and 10degree locks and retainers per info in other posts but the installed height of those and most suggested HP500efi replacements are 1.875" w/ 135# seat pressure

My heads (casting..934) are set up at closer to 2" so shop said find a longer spring or machine in seat pockets -- and get to 1.875

I talked to Isky and they suggested ISKY 8205-SP which would have about 135# seat pressure at installed height of 1.950 and similar spring rate

Anyone else run into this? My engines are 2003 - both engines had same dimensions (one still had factory engine seals on it-so guessing it is original - at least no machining etc)

Not opposed to PAC or other spring either just looking to stay in bounds with what others have had success with!

Thanks, Tom

((glad I started early - need significant time to complete these projects!!!))

I have nextek endurance spring available... its a bit heavier duty comes in at 170# @ 2.050 these are the GO TO spring for upgrade