Glen-L.com

BBC is a Big Block Chevrolet engine....just what you have!

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Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

Like Pirate says, the Mercruiser 496 cu. in. is based on the big block Chevrolet of the same dimensions. But it has too little cam, too little fuel, and too low flowing heads compared to what you need to hit the 90s with a jet pump. Mercury tunes them for reliability, which is just the opposite of what is needed for speed.

When I was drag racing in a previous lifetime, I ran an American Turbine pump behind a 468 cu. in. BBC that was really a maxed-out 454. The pump was blueprinted with extremely close tolerances and a modified bowl and wear ring. I ran in the 70s in the quarter mile. I do not know what the top speed was (pre-GPS), but probably not much more than that. This was with an undocumented, approximate, 500 hp, maybe 550. I have no idea of the torque of the fresh motor. A jet needs lots of torque at upper RPM to make a jet pump go quickly. I did not own enough of either to be competitive.

With the same engine, a v-drive will be quicker and faster than a jet, again not accounting for water conditions.

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Paul Miller in Memphis, TN
"Yeah, I had lunch with him last week at the Cracker Barrel out on I-40."

Fuel wise the same motor in a Vdrive will also be more economical(use a little less fuel) then it would be in a jet.

Ah great thanx for the clarification guys!!

So i guess ill have to think about what setup i wanna go with before i start building the Rampage! But seems like the general choice would be a V drive... am i correct?

Cheers
Zane

You could try one of these.
http://www.arneson-industries.com/

Cool site. I gotta get one of these:



It's the ultimate "not-flatbottom"!

We have totally hijacked Zane's thread...

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Paul Miller in Memphis, TN
"Yeah, I had lunch with him last week at the Cracker Barrel out on I-40."

Correct - from my perspective, but I'm obviously biased.

Zane, the speed and performance you state as your target is on the edge for any boat except highly tuned, high horsepower applications. It takes the right equipment, rigging and preparation to hit those speeds - safely! Keep that last item in front of you at all times. Remember, too, that high performance generally means high relative cost.

My advice, if economy is a deciding factor, is to use the power and drive you already own. Pay close attention to the condition of the motor and all drive components because worn equipment may make a lot of speed, but it may not be the lowest total-cost (reliability) or the safest way to do it. The last thing you want with any high speed application is power loss or drive failure at speed - where it's most likely to occur and is the most damaging when it does.

With a jet, you lose steering when you lose power
With a v-drive, you have an instant brake when you lose power (unless a Whirl-a-way or similar is installed)

After you get the most you can out of that setup, start tweaking and improving to optimize it. If you use the outdrive, it will work best with some vee in the bottom. The v-drive is faster with a flatbottom (Tornado has only about 2* vee at the transom). The ride is smoother in any water conditions with a vee bottom compared to a flatty in the same conditions.

Safety! That came home to me at G5 after I gave a brief ride to Gayle Brantuk. She was heard to remark after that ride, "I realized that I could seriously die!" That sort of makes me rethink what I am doing. Wanna buy a flatbottom?

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Paul Miller in Memphis, TN
"Yeah, I had lunch with him last week at the Cracker Barrel out on I-40."

Yep,it's all fun & games till you get thrown out of a boat.....even at low speeds!!

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

Random suggestion - have you considered the renegade? https://www.boatdesigns.com/20-Renegade ... ducts/250/

The pic there doesn't make it look too sleek but remember, you get to choose how the top part looks! (just look through some different rampage pics!).

The reason I say this is because your power plant of choice is fully 50% over the suggested weight limit of the boat - the rampage, tornado, and especially thunderbolt aren't designed for that much engine weight (unmodified, at least) - they're meant for more crate engine type engines, that typically get much higher power and weigh much less (for instance, a BBC can produce over 600 hp "out of the box", weighing ~ half of the 496 HO, when it's not covered with mercruiser add ons. I'm not trashing mercruiser, but the drive and engine combo you have seems better suited to a slightly higher freeboard, bigger boat. There's nothing stopping you from lowering the freeboard 2", changing the deck to the layout of the rampage, and having ~ the same boat but bigger and safer

just my 0.02$...let us know what you decide!

Denon, that $0.02 suggestion should gain you a $0.05 return. It's the best idea I think I've heard in this thread. Since the Mercruiser is not the setup for hitting the 90s, why try, and then wind up broke or broken. That package should push any reasonable semi-vee into the 60s pretty easily. To do that in the high style of a good looking day cruiser is all the better.

Good thought, my friend.

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Paul Miller in Memphis, TN
"Yeah, I had lunch with him last week at the Cracker Barrel out on I-40."

Thanx again for all the info and thanx Denon for the suggestion!! I ended up going with the Rampage actually and might run a different motor on it.... probably a BBC with a jet sounds like fun to me!

Im don't with all the frames but putting it on hold till I'm done with some other projects.

Thanx again fellaz!!

Cheers

Hey, I can't take all the credit - I'm pretty sure two years ago I had this exact same debate, and someone else suggested the renegade to me ! But, like Z_wood, I ended up going with the rampage and a BBC crate engine/jet...I should be safely under the 800 lb limit, and my hull's a little bigger then stock. I probably would have gone for the renegade in the end if my parents didn't already have a nice safe mercruiser powered plastic tub to take guests around in ( ), but I'm happy I didn't!

Denon