gofastwannabe

Hey all you engine guru's, I have a question for you. I had my engine rebuilt year before last by a mercruiser master mechanic. It's was a Mark IV 330 HP 454and I upgrade to 461 CI with speedpro coated hyperutectic pistons, Isky flat tappet cam with 230 intake and 236 exhaust @.050 with 515 lift on 110 lobe separation angle. It is topped off with Edelbrock RPM oval port aluminum intake and edelbrock 750 cfm marine carb with GM large oval port heads, (230cc I think) with stock valves. It also has crane roller rocker arms and us still using the stock exhaust straight out the transom. I know it's not a race motor and I don't treat it like that but I was just courious about how much HP it may have if I go to sell it in a year or two.

picklenjim

400 hp.

jeffswav

Does not matter it will not last long with that cam and stock exhaust. You need aftermarket exhaust with long risers or you will be sucking water back in. You may even need dry exhaust with the 110 LSA.

I just saw you have run it a whole season with that setup. What did the oil look like when you changed it?

MILD THUNDER

iTrader: (3)

I'd be surprised if that cam didn't revert water with the stock exhaust. Even if it does not, the stock exhaust will choke down the better flowing intake manifold, cam, and heads you have. No point in putting that combo together then running stock exhaust. That cam is also a bit large for a 461CI with cast internals, like the 330HP has. You really want to keep the rpm 5000 or below, and that cam will probably not make any more power below 5000rpm than one with about 10* less duration. Less cam would probably make more usable power, idle better, and not revert.

I'm guessing here, but with your stock exhaust, and specs you have given, Im gonna say 350-370HP at 5000.

jeffswav

But it was a Mercruiser Master Mechanic that built it so it must be right.

MILD THUNDER

iTrader: (3)

Ya, that scares me almost as much as the drag racer car engine guys!

Not suggestion that a "Merc master mechanic" is a bad thing, but reminds me of the guys working at midas, being ASE certified techs. Doesn't necessarily make you a engine builder by being a mechanic.

I went to General Motors training school for 18 months when i was younger. I can still F-up a spark plug swap.

GPM

I ran a 233/241 Ultradyne cam for several years without a problem. 330 bottom end, rectangle heads, stock exhaust. Ran great for what it was.

MILD THUNDER

iTrader: (3)

And there are many guys who have run less cam and reverted water and milkshaked their motors and killed exhaust valves. It might work, but why risk it when you gain nothing. I'd bet a few bucks that a cam with less duration and a 112-114* would make as much if not more HP for his application throughout the powerband. HP500 cams were notorious for reverting water even with GIL exhaust, and they had less duration than his.

Dont get me wrong, nothing better than a great sounding cam idling, but nothing worse than a crankcase full of nestle quick!

GPM

I'm not saying reversion is impossible maybe I was just lucky. How does the reversion water turn the oil to Nestles Quick without hydro locking it.

Raylar

I don't think that cam size and duration is a high probability reversion candidate, the LSA is close to it but not quite. I do agree that the engine should make 400-425HP with this combination-EXCEPT FOR THE EXHAUST!-
As others said here, a good breathing power making engine needs to breathe on the exhaust side so invest in a good exhaust upgrade and get the power the engine is capable of making.

Best Regards,
Ray @ Raylar