Scottski

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...

GPM

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 !!

Rookie

iTrader: (4)

Shameless plug. I have a new cam in the swap that would work great.
239°/245°-112
Comp Camshafts 2 New, 2 used

BillK

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.

mcollinstn

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.

Scottski

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.

Scottski

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.

1BIGJIM

iTrader: (1)

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.

cig28

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.

mcollinstn

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