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Bertram31.com General Bulletin Board
Re: Bertram 20 Repower
Posted By: bruce / Duke of URL In Response To: Re: Bertram 20 Repower (Doc)
Date: Thursday, 25 November 2004, at 3:56 p.m.
A few points you all may already know.
Over the road engines operate at different rpm's and loading than marine.
Typical over the road rpm at 70 mph is 1800.
Typical cruise for gas marine is 3600.
Cam design is the more important feature between the two.
Over the road engines tend to run lean in the marine environment and will cook themselves.
If you are going to use an over the road engine, most cam companies may have alternative cams already available or be able to grind one based on your needs.
Older engines were also designed to run with leaded gas as a lube for the valve guides.
Either use a lead substitute in the fuel or have the guides replaced.
Honda uses the basic car engines for their new upper hp outboards turned on end.
What would be neat would be to develope a 90 degree direct drive gear box that would bolt to a Merc transom assembly that you could plop a Honda power head on to.
4 stroke 225hp would run well on a 20.Another alternative is GM's Vortec 3500.
It is a new inline 5 this year. It produces 215hp with 225lb ft of torque. It has the power of a v6 with the efficency of a 4. It is based on the Vortec 4200 inline 6.
One thing about the new engines is the computer can be reprogramed or new chips bought to change the torque and performance curves to a point.Just about anything can be marinized.
I worked on the 300 Ford 6 for a couple of years in the 80's as a replacement for the GM.
I used 5 in repowers and they worked well.
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