SC V6 or MPI V8?

About inboard or outboard motors.

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Denon Osterman
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SC V6 or MPI V8?

Post by Denon Osterman »

Debating between a supercharged 4.3 L v6 and a naturally aspirated 5.7 L V8 with MPI. either case, crate engine will be used and then built/tuned by someone else for around 350 hp (unless this seems too low/high for either engine).

here are my thoughts:
V8:
-MPI=more reliable, easier starts, etc
-uses less gas(?)
-cheaper(?)


V6:
-higher redline(?)(i figure the blower will make up the extra horsepower somewhat in terms of torque, but also somewhat in terms of RPM, leading to a higher redline...)
-lighter
-shorter
-looks way cooler

the V6 looks better in terms of a looks/performance/dimensions standpoint, but reliability and ease of use are paramount. so feel free to chime in with your choice but please give reasoning/explanations!!!

Thanks,
Dennon

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Bill Edmundson
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Post by Bill Edmundson »

Denon,

I forget which boat you're building. But, if you want all out speed I think max RPM will be what you want. If you want a ski boat, you want low end torque. Cruising you probably want reliability.

It is all a balancing act of torque/rpm/gear ratios/prop pitch/prop diameter.

I know that is not an answer. Just food for thought.

Bill
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J Patroni
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Post by J Patroni »

Denon,

I bought the 4.3L V6 for my crackerbox. The info from GM stated that
the WOT rating for the V6 is 4300 to 4500 RPM where the V8 is above
5000 RPM. Hope this helps.

Jim
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Denon Osterman
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Post by Denon Osterman »

It's a rampage with a jet.

Top end/performance overall, and reliability, are the two biggest issues.

rasorinc
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v 6 reliability

Post by rasorinc »

The GM V6 has been around for decades. I would say it equals
the 5.7 for trouble free operation.
Wood lasts generations.

Denon Osterman
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Post by Denon Osterman »

But aren't MPI engines far more reliable then naturally aspirated supercharged ones?

Dennon

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kens
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Post by kens »

Just get a MPI Big Block and be done.
http://www.michiganmotorz.com/Marine+En ... cations%29

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Mr Hot Rod
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Post by Mr Hot Rod »

Picking the perfect marine engine can be a daunting task since there are
many engine packages to choose from.

The following table was compiled from Simplicity Marine's website :
MarinePower Models and Pricing

Prices are for Bobtail Left Hand Rotation engines and are included for discussion purposes only.

Code: Select all

     CID     HP        RPM    Torque RPM  Engine model	   Cost
4.3  262	190  4300-4600  240	3000 Standard	   5355

5.7  350	260  4000-4400  325	3200  Standard	   5950
5.7  350	300  4600-5000  325	3700  Premium	
5.7  454	325  4600-5000  360	3600  Performance	

7.4  454	340  4000-4400  405	3200  Standard	  11305
7.4  454	390  4600-5000  405	3700  Premium	
7.4  454	440  4800-5200  450	4000  Performance	
Correct me if I'm wrong, but in previous posts you've stated that top end (70 MPH +)
and reliability are the two biggest issues. Your Jet supplier can provide recommendations
for power levels and estimates of anticipated performance. When you've got your
pump/engine specs, talk to local engine builders and machine shops that handle marine
rebuilds. They're an invaluable source of info and can save you a lot on freight !

As far as I know, Jets consume copious amounts of torque. If your budget can handle it, a
Big Block would be a good fit if you're not on a budget. When the need arises to go
a little faster, the big block is internally stout enough to handle future power upgrades.

I'm sure Caber will chime in soon !
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Denon Osterman
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Location: toronto, CAN

Post by Denon Osterman »

Yeah, i was surprised you and caber hadn't chimed in earlier, i would have thought you guys woulda been first!

are big blocks not much bigger/heavier? the issue is that i need to be able to squeeze the engine and two benches into a 19 foot boat...every little bit counts! and, i dont want it to sit too low.

either way, higher power/speeds will probably be out of the question...my dads having a hard enough time accepting 350 hp as is. someone wanna write an easy to follow explanation of how thats NOT overkill for a boat of this nature, at all?

ps, what do you think are reasonable HP expectations for a blown V6 or the V8 MPI? is 400-450 reasonable for either/both?

Thanks,
Denon

Nova SS
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Post by Nova SS »

the Rampage, Tornado, and I believe the Thunderbolt where Glen-l's answer to people putting high HP motors in his smaller vdrive boats such as the Missle and Hot Rod. Glen felt that the smaller boats (16') were too small for the high HP motors people were installing in them. So he designed these boats so that people could safely install Big Block motors in them. The Tbolt and Tornado designs have been driven at 100mph+

A Big block motor will likely be about 100 pounds heaver then a simularly setup small block. Overall the BB will be about 4 inches longer and about 5 inches wider.

http://www.team.net/sol/tech/engine.html

http://www.enginefactory.com/chevdimensions.htm

I could be out to lunch but I suspect you will need more then 350 HP to reach a true 70MPH

Denon Osterman
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Post by Denon Osterman »

Naw...still not keen on a big block, unless everyone thinks its necessary.

how much might i need to reach a true 70?

rasorinc
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Post by rasorinc »

check out the chevy 327, crusader makes all the necessary manifolds and I have seen 375 hp for this engine. It is a small block
Wood lasts generations.

Nova SS
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Post by Nova SS »

Just as an aside you can build some pretty stout SB and ones that have o ver 400 cubes are not uncomon today. You can sort of have your cake and eat it too. You get BB cubes with a SB package.

Just a thought

Denon Osterman
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Location: toronto, CAN

Post by Denon Osterman »

Yeah, i knew that...the new 7.0 liter vette engine is a small block. i think i"d rather super charge a 350 then increase its displacement, just for the looks/wow factor. but then again, superchargers might be a bad idea...i dont really know :?

Nova SS
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Post by Nova SS »

Denon Osterman wrote:Yeah, i knew that...the new 7.0 liter vette engine is a small block. i think i"d rather super charge a 350 then increase its displacement, just for the looks/wow factor. but then again, superchargers might be a bad idea...i dont really know :?
what kind of super charger are you thinking about 6-71 or something else? You will need to know what kind of boast you are thinking of running before you get a motor. The amount of boast will impact the compression ratio you will want the motor to have. Too much compression in the end will mean you will have to run expensive high octane fuel.

An off the shelve create motor may not be the best option if you are going to go supercharged. You might have to lower compresion (could need different pistons then the one they came from the factory with) Supercharging is a good way to add power but it has to be really thought out.

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