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HP500 buildup questions

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Old 04-29-2011, 12:39 AM
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Hey Dave,

Thanks for the info - you are way ahead of me!!!

We are presently stuck on the cam / exhaust situation with the stock GIL exhaust not liking any bigger cam than already installed. We were planning on cutting out the silencer baffles from the tips and using the existing GIL setup but when I emailed Hardin tech support (who bought out GIL) they said do NOT use the GIL manifolds with any bigger cam or HP than the stock ones that came in the HP 500s. They recommended a dry pipe exhaust. Since I can't (won't) spend 10 grand on 2 sets of CMI headers I'm looking for alternatives and someone said there might be a suitable manifold offering from Stainless Marine.

According the the specs I had Merc racing fax me last summer the original HP 500 cams were 339/352 lift and 284/292 duration.
I came across a August 2003 Merc service bulletin online stating revised duration numbers of 222/230. I wonder if they did this to fix the reversion issues??? Anyway, my motors were done once before, so I'm really not sure what was swapped out. I know they had roller top end but when my builder torn them down before sending to the machine shop he said they only had std BBC connecting rods which I though was odd. I thought they had Carillo or Manley rods - maybe the last builder pulled them or they didn't come with them?

Anyway, let me know what you think about cam / exhaust situation.

Thanks!
Joe
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Old 04-29-2011, 12:52 AM
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HP 500's came with stock Chevy rods. They are fine up to about 600hp. As for the Cam, listen to Merc, I tried the Gils on the dyno back in 2006 and it did show some signs of reversion plus they killed the hp. I have had NO problems with the CMI's, but I am in fresh water too.

You may want to rethink the blower option. You could easily get 650 with a small blower and low boost. You could also continue to run the Gil's!

BTW I run 89 pump gas!

Dave
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Old 04-29-2011, 07:31 AM
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My builder hates blowers and wants to keep me as maintenance free as possible. I thought of the options of blowers or headers but we're into these motors for 20k now and adding either of those will probably tack on another 10k.
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Old 05-02-2011, 12:33 PM
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Quote:
Originally Posted by Joe308 View Post
According the the specs I had Merc racing fax me last summer the original HP 500 cams were 339/352 lift and 284/292 duration.
I came across a August 2003 Merc service bulletin online stating revised duration numbers of 222/230. I wonder if they did this to fix the reversion issues???Joe
thats quite a difference, I'm guessing your numbers are advertised duration vs. duration @.050.
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Old 05-02-2011, 12:50 PM
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Great ideas guys, keep them coming....
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Old 05-02-2011, 08:18 PM
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Sounds like a nice project except the Merlin heads, did you buy them yet? If not maybe re-consider for soemtheing that will make more power. wags382/jeff wagoner built up his 382's hp 500's and made a honest 600 hp turning accesories BUT he used afr heads which flow considerable more than the merlins (easily 20%+). He has since turned motors into 540's and makes hp in the mid 650's and has his 382 formula in the high 80's, Smitty
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Old 05-02-2011, 08:26 PM
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Here is a similar thread on almost identical project
http://www.offshoreonly.com/forums/g...5cc-heads.html
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Old 05-02-2011, 09:03 PM
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Seeing how my HP500 blew the head gasket, I am now in the same boat.(pun) My builder in TX recommended a Cam he always uses on HP500's. Better than original and corrects for reversion, also more efficient and power. Here are the numbers, hope they make sense: Cam - LSA 112, 226/234 @ .050 duration, .600 lift for hyd roller. He said the Crane pt# is 168731, but Crane sold to someone he does not know. Hope this helps.
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Old 05-02-2011, 09:16 PM
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You might be right on the cam specs being at .50 duration - that is indeed quite a difference but I couldn't find original published specs to compare to the 2003 service bulletin. As for the heads my builder likes the Merlins - are the AFR's a lot more expensive?
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Old 05-02-2011, 09:28 PM
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I'm sticking with stock heads, new Comp cams springs P/N 929. I was told the HP500 motor is pretty much bullet proof left stock. He will zero deck the block, heads and intake for just a little more compression and HP, also to correct for burn in block.
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