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Bertram31.com General Bulletin Board
Re: Diesel Repower
Posted By: Vic Roy In Response To: Diesel Repower (Brian Burkard)
Date: Wednesday, 2 March 2005, at 5:47 p.m.
The 250's are 2600 rpm engines vs. the 300's at 2800. Other than that there is virutally no difference. A 300 run at the same rpm as a 250 will burn the same fuel and produce the same speed. The 300 will give you a few more knots of speed at high cruise - say 24.5 at 2400 on the 250 and 26 at 2600 on the 300's. Note of cuation tho - the older 300's, particularly the CPL 970's are pretty tender engines and most folks say they should be run most of the time like a 250, limit high cruise to 2400 rpm.
Inch and a half AQ 22 shafts are fine for both. I run 5" exhausts on my 250's with inch and a half raw water intakes, no problem. It would be better to use 6" exhausts and 2" raw water intakes on the 300's. I have 1.53:1 ZF IRM 220A gears turning 21x22 three blade nibral Michigan DynaJets and get 24.5 kts all day long at 2400 rpm (pretty heavy FBC with half tower and enclosure) and burn about 16 gph total at that speed. The 6BTA's do fine with 1.5 gears. Strut to turn at least a 21" dia. prop. Large dia. props are needed to get all that torque into the water.
I have had many engines over the years and the 6BTA 250's (I have the CPL 1247's) are far and away the simpliest, most reliable, and most economical I've ever owned. I have some 2700 hours and they run like the day they were built in November, 1989. Change the oil every 150 hours, use Shell Rotella-T 15w-40, premium Fleet gaurd oil filters, keep the fuel clean, use the S&B hi-capacity air filters, keep paint on them to kill rust, use a 50/50 Corrosion X/lacquer thinner spray a couple of times a year, change the Sherwood raw water impellers at least once a year (at least until Tony Athens has his new aftermarket super-dooper ones in a couple of months), and these engines will outlive you.
UV
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