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Mark IV 496 Build help

Old 01-12-2021, 10:01 AM
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Default Mark IV 496 Build help

Hello all, We recently picked up a '78 24 Pantera Sport, TRS 330, all original and in immaculate condition. Fresh water boat and climate controlled garage kept all of its life. The unfortunate part, 4 months after we got it, a bearing spun on crank journal 2.

Not being an engine guru and literally sitting in front of the computer the last 10 days trying to figure things out, I think I've come up with a parts list but would really appreciate your thoughts.


What I had:

Mark IV 454 bored 30 over, 5 and 7 were found to be 40 over

Pistons: number on top says 2377. Google showed them to be stock equivalent and forged

Cam: Cam dynamics cam, Enforcer 10307. Specs 533,533/ 226,226 108 LSA

Heads: gm oval port, didn't grab the casting number before they went to machine shop

Intake: Edlebrock TM2-0

Carb: Holley 4150 850cfm

Boat ran low/ mid 60s at 4400 rpm and came with a Mirage 25P prop


My thoughts on the "as bought" set up were, prop might be too large, and I was thinking carb might be too large?


Then outing number 6 or 7 with the boat, running about 4000 rpm at 50mph we lost oil pressure. Engine did not lock up or even knock loud for that matter

So, complete tear down and haul parts to machine shop. Upon tear down, oil pan and oil pump has A LOT of pieces in it

Heads... Bad

Block.. needs re-bore

Crank... Bad


So here is my build list, please let me know what you think, what could be better or what I may have figured wrong as this is all new to me.

Block is being bored 60 over

Eagle rotating assembly for 4.25 stroke B18020 which would put me somewhere near mid 8s for compression ratio OR the B18022 kit would put me at almost 10. Both are forged pistons and rods using cast cranks

Comp Cam K-11-451-8 Kit Hyd Roller

WP Merlin 030040M-2 Iron Oval port heads

Intake, I planned to use my existing Edlebrock TM2-O

Roller Rockers from Scorpion Racing Products 4014 (1.7 ratios)

No clue what HP this might make, my un-educated guess would be mid - upper 400s? I just do not want to be less than I was


Am I on the right track here? I don't need a high revving monster, mostly would be cruising, a couple fun runs a year it may get run a bit harder than normal. 40 to 50 cruising would be nice. Currently we cruised mostly around 40-45. 99% of the time will remain a fresh water boat and it is a raw water cooled engine. Thought about changing that but budget for now said no.


Thank you all for your input

Oh and I should mention. My go to local gas is 90 non eth and its got Glenwood manifolds w/ custom made stainless risers

Last edited by Scottski; 01-12-2021 at 11:25 AM.
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Old 01-12-2021, 02:25 PM
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I'll throw my 2cents in, look for a rotating assembly with a forged crank. I know there are plenty of stories about a guy who knows a guy that has a friend that made 800hp with a cast crank . If the crank goes s$&thouse its a big expensive mess that may leave you with a pair of used heads and an intake system.
for my build im going low on compression so I dont have to worry about finding gas at some strange dock .
Just my opinion
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Old 01-12-2021, 03:06 PM
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2 more cents, you may want to look at the Scat forged rotating assembly, 9:1 compression, your cam may be a little small in a 496 stroker
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Old 01-12-2021, 03:31 PM
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Originally Posted by carnutsx2 View Post
I'll throw my 2cents in, look for a rotating assembly with a forged crank. I know there are plenty of stories about a guy who knows a guy that has a friend that made 800hp with a cast crank . If the crank goes s$&thouse its a big expensive mess that may leave you with a pair of used heads and an intake system.
for my build im going low on compression so I dont have to worry about finding gas at some strange dock .
Just my opinion
Originally Posted by GPM View Post
2 more cents, you may want to look at the Scat forged rotating assembly, 9:1 compression, your cam may be a little small in a 496 stroker
Thank you for the replies. I was thinking about forged cranks but wondered if it was necessary for the HP id be making.

GPM, what cam might you suggest?

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Old 01-12-2021, 03:37 PM
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And that brings up another question. If an assembly comes internally balanced, am I looking at then getting an internally balanced flywheel and harmonic Balancer to go with it?
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Old 01-12-2021, 04:02 PM
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Originally Posted by Scottski View Post
And that brings up another question. If an assembly comes internally balanced, am I looking at then getting an internally balanced flywheel and harmonic Balancer to go with it?
Call Eagle to be certain but I think on their external balance assemblies a flex plate and damper are included in the price. I have never used one of their Big Block external balance assemblies but I have purchased two of their small block ones and they came with a flywheel and damper.

Personally in a marine engine I would spend the extra for the steel crank.
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Old 01-12-2021, 04:08 PM
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Itís not my old canary yellow one is it?
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Old 01-12-2021, 04:28 PM
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Originally Posted by BillK View Post
Call Eagle to be certain but I think on their external balance assemblies a flex plate and damper are included in the price. I have never used one of their Big Block external balance assemblies but I have purchased two of their small block ones and they came with a flywheel and damper.

Personally in a marine engine I would spend the extra for the steel crank.
Bill, I'm guessing you meant Forged crank?

Originally Posted by getrdunn View Post
Itís not my old canary yellow one is it?
Are you asking about the boat? No, it is still the original Blue Gelcoat, white deck, white bottom
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Old 01-12-2021, 05:23 PM
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Originally Posted by Scottski View Post
Bill, I'm guessing you meant Forged crank?
Yes
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Old 01-12-2021, 05:48 PM
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Scottski---maybe to get to the meat of your question. I had an old gas motorhome I used to haul my Rockcrawler around (7000# with trailer) and got tired of the gutless 454 TBI motor, so I built a similar engine (Gen V) with a 1/4" stroke and 9-ish compression (all forged internals--all balanced) on iron Big Oval stock heads that were massaged a bit by my machinist, big "RV" comp cam, aftermarket fuel injection, DUI ignition, and so on. 435hp and 510 ft/lbs. under 5500 rpm. Pulled like a friggin' tractor! About the same power to weight as my Diesel Pusher. I think you'll do much better than what you had, so don't worry. As mentioned, the right cam on a 496 is critical.
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