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Mark IV 496 Build help

Old 01-13-2021, 01:43 PM
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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.


Originally Posted by 1BIGJIM View Post
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.
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?.

Originally Posted by cig28 View Post
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.
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??

Originally Posted by mcollinstn View Post
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
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.

Last edited by Scottski; 01-13-2021 at 01:47 PM.
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Old 01-13-2021, 04:24 PM
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Bill K, please clear out your PM inbox so I can respond. Thanks
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Old 01-13-2021, 05:43 PM
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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
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Old 01-17-2021, 02:11 PM
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Originally Posted by Scottski View Post
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.

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Old 01-17-2021, 02:53 PM
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My opinion, you would be much happier with the 496 at basically the same cost.
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Old 01-17-2021, 05:20 PM
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Originally Posted by GPM View Post
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

Last edited by Scottski; 01-17-2021 at 05:46 PM.
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Old 01-17-2021, 10:29 PM
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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.
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Old 01-18-2021, 06:54 AM
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Originally Posted by GPM View Post
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.
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