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

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

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?

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.

It’s not my old canary yellow one is it?

Bill, I'm guessing you meant Forged crank?

Are you asking about the boat? No, it is still the original Blue Gelcoat, white deck, white bottom

Yes

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.

Thank you for that info. So I'm leaning more towards the Scat Forged assembly, So, what Cam should I be looking for? I would like to go to a Roller Cam and like the idea of the Comp Cams kits that take some of the guess work out for me and hopefully help save a few pennies. Im getting really stretched on this budget wise as not only purchasing the boat, a week before it broke down I put a new aluminum trailer under it...

There is a possibility the weights can be removed from your existing flywheel and balancer, but they may not be in that good of condition to start with. Summit and Jeg's both sell those parts at a reasonable cost. The cam is personal preference, I'm not an engine builder, I like an 8 degree split with the BBC. I think your 4.250 stroke is going to want more cam than your 454. I would think something around 236 /244 at .050 on a 112 lsa in the motor at 106 intake center, but that's just my opinion. You would probably be better off calling Comp, Crane, Bullet, best of luck to you !!

Shameless plug. I have a new cam in the swap that would work great.
239°/245°-112
https://www.offshoreonly.com/forums/...ew-2-used.html

Scott,
Just one more thing to keep in mind. The 496 will make a ton more torque along with horsepower so you need to be certain that your drive can handle it.
I am not the one to answer that question but I am sure that there are others on here that can. I have built two pump gas 496's for cars and both of them were well into the 600 HP range and one was close to 680. Same with torque. All were what I would consider fairly mild engines. I would certainly expect yours to be in the high 500's.

Your cam kit choice is for a Gen5/6 Big block. It comes with roller lifters that require a D shaped retainer plate. The correct tie-bar lifters are required for a MkIV and are more expensive.

At the power levels you are shooting for, a hydraulic flat tappet should hit your target at a $400 discount.

A forged steel crank is money well spent.

But let's pause here.
You already have a MkIV block that's .030 over and blown up. It's not a factory roller cam motor, and has no particular "hotrod value" aside from you already own it.

If it were me, I would throw the brakes on hard.
Start with a tired Gen 6 502 block. It will come with hydraulic roller lifters, with Vortec large oval heads, a forged crank, steel 7/16 rods, and forged pistons. Zero deck it. Hone it with a torque plate. Put new rings in it. Polish the crank and put fresh bearings in it. Put an RPM Airgap intake on it and your existing Holley carb. Get a takeout 502 MPI cam for peanuts or step up to a Crane 731 or 741 (although you'll need to make sure your keepers don't crowd the valve seals).

Money-wise, I think you'll be cheaper in the long run. Motor-wise you'll never regret it.

As people have mentioned, your outdrive is reasonably durable at 350hp. At 450hp you better have a fairly light hull. At 550hp your outdrive has a very short fuse.

I went thru multiple Bravo 1 outdrives with 415hp 502s. The last pair had billet top caps, 6 rib clutches, and drive showers and they lasted nicely.

Another friend had Bravo XR drives on a boat with 575's. Boom. Pop. Crunch. Upgraded them with steel towers, billet caps, cryo gears. They lasted a season before the floor of a gear broke out. There are people here who swear their stock XR drives work great with their 700hp motors. I categorize these people in 2 categories. 1) Liars. 2) Lucky.

I'm not trying to scare you. I'm just emphasizing that with much hopping up you will need to spend money upgrading your drive. A freshly rebuilt/upgraded XR drive with some sort of warranty is pricey. The guy who proudly drops a 540+ hp big block in his boat without an outdrive budget is soon a sad boy.

That's more HP than I was planning for. I've been told by many about TRS that once I exceed 500 things can start to go wrong...

I appreciate that and actually thought about that as well. My fear was the Gen 6 into the old boat and what would need to go along with it to make it work, I feared Id do all that and still only have a stock Gen 6. Seems in all my searching I could not find a direct answer on what I would need to do to make it work.

As for power, I'm wanting to not exceed 500hp because of the TRS, Although many have told me Id be fine as long as I'm not hammering on it and chopping the throttles. I do know our Magnum has twin 500HP BBC on TRS and its been that way for a looong time without drive issue. Maybe thats on the luck side of things =/ As for the cam, interesting since Comp cams specked that for me and Summit confirmed it. It also shows on summit that it will go into the Mark IV, but Ill investigate both it AND look into a Gen 6

I saw that and was going to look it up.

In regards to swapping to a Gen 6, My concern was with the flywheel side. So Ill ask here and see what answer I get, again, searching led me to a few contradicting answers.

Will my Driveplate or dampner as Ive heard it called both, bolt onto a Gen 6 flywheel? Also, My current set up has a Magnaflo cam driven raw water pump. I'm assuming I could change the timing cover and bolt that up to a Gen 6 or do I need to go with a belt driven pump and all the brackets etc to make it happen, if a motor I got did not include any accessories.

There is an avail Gen 5 454 I can get, but am hesitant bc of power. It was a rebuild but roughly 20 years ago. All mechanicals were swapped into a new block bc of freezing and then it sat wrapped up in a shop. IM just afraid what I may be getting into with that, and the fact is a 330-360 hp motor from my searches.

I have built several 496 stroker engines. The transmission will bolt up to a Gen 6 flywheel. A Mark IV flywheel will not bolt up to a Gen 6 engine.Nobody asked what exhaust your a running, that will determine your cam choice. I myself would look for a new or old Gen 6 502. I didn't even think you could buy a cast stroker crank. Another big question is that block a 4 bolt main. And the weights can be machined off your existing flywheel. If you decide to go that route put in a roller cam, you will not regret it.

Having the TRS drive u have a transmission and from the year of the boat I’m assuming it has the mercury transmission and not the borg Warner c72. I’d be more concerned about having transmission issues than TRS drive issues. The weak link for the trans is the input shaft and front Gerotor pump. These trans are good if easy on them for 400-500hp.The key word is EASY.

I just caught that you have TRS drive. The TRS is a bit stouter than a Bravo because it doesn't contain any shifting mechanism.
For a Bravo, 450hp is where things get dicey.
TRS is happy thru 500hp if clearances and bearings are good. As stated, the trans will usually start slipping before the drive grenades. BW Velvet Drive upgrades are a lot more cost effective than Bravo upgrades.

As far as your raw water pump, I would probably set it up for pulley drive, although driving off the crank snout may be ok as long as the doubling of impeller rpm doesn't overtax the pump ratings.

A Gen 5 454 doesn't offer you anything of real benefit to you aside from factory roller lifters in a slightly weaker block casting. It's a sideways step, not a step forward.

As far as your cam kit, I never said the cam wouldn't work in your MkIV. I said the lifters in the kit wouldn't work. The cam will work in a MkIV block as long as you install a Gen 5/6 thrust keeper and use the Gen 6 timing chain set (which was already included in that kit). Lifters, nope.
M

First, thank you to everyone who has answered thus far. This has been my first post on here and the wealth of knowledge from all of you is greatly appreciated.


Actually I snuck it in at the very end of the OP. It has Glenwood Aluminum Manifolds and Stainless risers. Now, the set up is plumbed different than what I'm familiar with coming from inboard PCM powered ski boats. the manifold itself was plumbed with an in and out, as was the riser. Then there are block off plates between the two. So water cannot go from manifold to riser, they are separate And part 2, it is a 2 bolt main, however 3 marine engine builders have told me as long as I didnt make a beast of the engine that Id be okay on the 2 bolt. They all were told Id be 500 + or - HP. So I hope thats true because I got a call about 20 minutes ago my block has been bored cleaned up and ready....

I understand the flywheels not bolting from 4 to 6, but will the dampner bolt to the Gen 6 flywheel?.

You are correct, merctrans w/ the extra clutch disc mod and was told parts were... I cant recall the word terminology, but made stronger or hardened in some sense, foriegn language to me. Cryo something??

that was my thoughts exactly on the 454 which is why I hadn't pulled the trigger on it yet. I was thinking that in order for it to be what I wanted, Id be as much into it or more than doing my block or starting over completely.
And thank you for the clarification on the lifters. That makes sense

In all honesty I was pretty happy with the boat before with speed. And from other readings and finds from here on OSO, based on what was done to it, I think it should have had a cpl mph more. Maybe it was wrong prop, carb settings, combinations of several things. I'm not looking to make it an 80+ boat, I know there would be a ton more to do other than engine, but if I can knock on 70 Id be thrilled. And as mentioned, a solid 45-50 mph cruiser, without stressing it, is my main goal. 95% of it life will be on smaller lakes here in central FL and running up the Caloosahatchee. And even when out in intercoastal or ocean type running, Im not one to beat myself or my boats up so I don't plan to be hammering it through 4 footers, ever... that'll be the next step up boat, whatever that may be, HA!

Again thank you all for all the info so far. Such great knowledge here.

Bill K, please clear out your PM inbox so I can respond. Thanks

I'm goin to investigate soon where exactly my exhaust and water mix in my risers. i was just outside looking at it and cant visually figure it out.
I may have to call the previous owner that fabricated them to find out

I finally got to examine the risers today. Looks like the water is mixing basically at teh end of the tail at the transom. The risers are stainless, 6" rise and then they angle downward to exit the transom at about the level of the exhaust manifold.

I'm changing plans a bit and not going the 496 route. Ill keep the standard stroke, block was bored 60 over. Will be align honed. Scat crank, forged rods and Wiseco Forged pistons 10cc dome, .Hastings rings and King Si series bearings.
Comp Cam K-11-451-8 Kit Hyd Roller - (confirmed this is a retro kit and will work in my Mark IV according to Comp Cams help line. Need to get wear plate and button), WP Merlin 030040M-2 Iron Oval port heads 119cc.

I found a HP estimator and after figuring out all the numbers it needed, it looks like Id be in the 430hp range. My old set up, according to that same calc would have been about 405hp, both at about 4300rpm. Don't know how accurate that is but it was kinda fun figuring it out.

My opinion, you would be much happier with the 496 at basically the same cost.

Even w/ a 2 bolt? Most seem to think thats a bad idea. If I do that, My option would be forged crank and keep my current flatt tappet cam. Im about 1500 over what I can realistically afford and cant do it all the way Id like to, so Im trying to get the best bang for buck

You can have the machine shop add the 4 bolt caps if that's a worry. You don't seem to be going for max power, the 496 would be stronger across the RPM range and you wouldn't have to crank it up as far to get the top speed. My opinion, more cubes in a boat is always better, a mild 496 will do the job easier and better than a 468.

Thank you GPM, I read about the added bolts upgrade. Ill talk to my machinist about it and explore that route. And no, I'm not going for max power. Someday in a newer lighter boat, but not this one.