trans question???

[phegan]

Ok, here's what i'm thinking.... 300 hp detriot diesel with a low ratio cooled transmision( mount the trans backward , low rpm's in and high rpm's out ). That would give me about 4000 rpm's at the 12jc jet pump.
i have never heard of any one doing this.
my thinking is the high rpm's is killing the gas motors ,while a detroit running at 2.5 k is as bullet proof as you can get. I passed up a good running marine detroit 671 today. idea

[malcolm]

Ha-ha! That 6-71 would sink any boat you put it in. :D

[Wet Dream]

Can work, but here are the cons:
Very heavy engine and tranny.
For 300hp you're looking at over 1000#'s when you can have 500hp wrapped up in 650#'s
Try getting that diesel to spin up to 2500rpm. Won't be easy, most top out at 2250.
Why only 4k rmps on the pump? 5000 or better with gas
Try getting that diesel to spin an overdrive from 700rpm to 2500rpm in anything less than 20 seconds and waiting for the turbo to spool up, seems like a lifetime.
How big of a boat are you planning on? It can be done.
[ March 30, 2003, 02:31 PM: Message edited by: Wet Dream ]

[phegan]

oh yea, i forgot to mention this isnt for the sanger, it's for the aluminum "tug" I'm building. :p
the 6-71 had a side mounted gear driven blower,I think.
yea it would be heavy.
the idea is to create the ultimate in reliabily, but i'm afraid the trans would be the weak link. i have never heard of anyone increasing the output rpm's

[phegan]

MR. wet,well it's a all aluminum 28 ft fishing boat. I'm designing a transom box to house the jetpump i'm thinking of a stock berk with a "A" impeller,thats the 4k limit.
some guys around here wont take my boat seriously unless its got a diesel in it. wink
but really i'm open to all sugestions, I just want to do the right thing and it's gonna have a jet pump in it no matter what. :D

[Wet Dream]

Well then, if thats the case, you have the room and that pump is more than able to go 4000 revs. Don't let anyone stop you, it can be done. The diesel is reliable and strong, but I don't think you'll have the holeshot acceleration that you might encounter with a prop. You might look at the different drive ratios available to efficiently spin the pump.

[malcolm]

OK, I'm with ya now. 28 feet huh! That motor is still gonna be awfully heavy. I would be one of the first to say "go for it!" though. I work on diesels almost every day at work. A 6-71 would have to be jacked to the hilt to make 300 hp. It could be done, but it would shorten its life.

[phegan]

maybe a yanmar, then I could do away with the transmision due to the higher max rpms (3500)