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Twin aluminum Small Blocks good idea, or a bad idea?

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Old 08-11-2015, 12:56 PM
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You can build some potent packages with the LS platform. It's all about how much you want to invest. You can build a 450HP engine on a budget, or go off the deep end. I chose the ladder.

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Old 08-11-2015, 02:53 PM
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Precision, clean out your PM box
Done
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Old 08-11-2015, 05:18 PM
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GM did an article on crate engine comparisons. They had a chevelle, and installed these crate engines in it, ran it, and weighed it.

LS7 (alum block, heads)- 3420 lbs.
LS3 (alum block, heads)- 3334 lbs.
LS327 (iron block, alum heads)- 3386 lbs.
ZZ4 & ZZ383 (SBC, iron block, allum heads)- 3360 lbs.
ZZ427 (iron BBC, alum heads)- 3520 lbs.

Looks like the difference between a aluminum headed BBC, and an all aluminum LS3, was 186lbs. In your boat, thats times 2, so 372lbs off the stern. By ditching the iron heads off your MPI big blocks, the heavy cast iron manifolds for aluminum ones, you would probably knock off close to 300lbs of weight.

The question is, how fast do you want to go. There's a guy around here with some whippled 502's in his 32, that goes probably about as fast as you'll want to go in a 32 Fountain, and making a pair of 750hp big blocks is easier than can be these days. Right now, you pretty much have the heaviest, lowest power producing package available, the 454 MPI cruiser engine setup.

Play around with this calculator a bit.
http://www.go-fast.com/boat_speed_predictions.htm

Figure out weight vs hp vs mph. I'm pretty certain, that the 32 Fountain, is a hull, that you will find adding power, will easily exceed the gains from shedding weight. Pad bottom hulls, deal with stern weight differently than a straight vee. A simple change of blade style, rake, prop rotation, slight lifting strake modifications, etc, can be of 10x greater effect, than a few hundred pounds of stern weight. Gas tanks. Some of us hold 200+ gallons of fuel midship. Sometimes I have 1300lbs of fuel on board, sometimes I have 200 lbs of fuel on board. Does it change the attitude of the boat, sure. But its not like shedding 1000lbs of fuel from an area of the hull, far more important speed wise than the stern, raises my top speed ridiculously. With full tanks of fuel, its like a pair of small blocks sitting in my cockpit area. I see about 3mph difference top speed, when tanks are full, to near empty. Again, talking 1000lbs off the center of the hull. 300lbs, I'd be lucky to see 1mph difference. At least in my boat.
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Old 08-11-2015, 08:23 PM
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Hey that is some very interesting information.. That speed calculator is slick..

My target speed is 87 - 89 mph. This boat currently already has small blocks in it.. the other considerations
is easy swap out with another small, block and reducing the weight helps on the trailer. Well, I think I opened a can of worms - Weight, Power , and always, the cost of building small blocks.. There is a happy medium.

There is always the cool factor of such a build.. What would the sound be on this set up? hummmm.
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Old 08-11-2015, 09:51 PM
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LS motors sound NASTY!!!
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Old 08-11-2015, 11:00 PM
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Idk why i thought you had twin 454 mpi ...that changes things a bit lol sorry
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Old 08-12-2015, 05:42 AM
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LS motors sound NASTY!!!
That I have to disagree with. To me they sound kinda weak. All LS cams have a 113lsa so you don't have much overlap. Add to that the LS firing order and what you end up with is a motor that doesn't sound very nasty at all. Stick a couple in a boat and it sounds like to Corvettes running next to each other with some exhaust work.
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Old 08-12-2015, 07:28 AM
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That I have to disagree with. To me they sound kinda weak. All LS cams have a 113lsa so you don't have much overlap. Add to that the LS firing order and what you end up with is a motor that doesn't sound very nasty at all. Stick a couple in a boat and it sounds like to Corvettes running next to each other with some exhaust work.
To each their own there. In my 632 aluminum motor we just completed we did the 55mm 4/7 and 2/3 swap "LS" style big cube motor. Yes, its obvious its not the same as a conventional BBC... But it has its own sound, raspy mixed with choppy I guess?? Hard to explain, but I tell you something, if you heard it you know it means business.

The LS platform alone makes power in places a sbc never could. Just a mild build easily gives a 496 HO a run for its money... Mix in boost, the heavy hitter merc motors lose their appeal quickly. You will see more and more LS builds in the marine market. Power vs weight and part availability from mild to wild are all there.
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Old 08-12-2015, 07:34 AM
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I run the firing order swap cam in my 548 bbc and it still sounds healthy and makes people jump when it is fired up at the ramp. It doesn't have a "lope" at all with the EFI either. Just even bank-to-bank firing. Still sounds like a big block, just not a conventional HP500.
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Old 08-12-2015, 09:57 AM
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Another gain would be fuel savings... Not exactly sure how to calculate but there will no question be a positive gain with the efficiency of the LS and weight.
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