Mercruiser 5.0 vs 5.7

moosehunter74 said:

Hi everyone, first time on here. I have a 21' Bayliner Trophy that had a 4.3 with a Alpha 1 in it when I bought it. Blew the engine on my way back from a fishing trip. I installed a 5.0 Mercruiser with a Bravo III. My question is how much would the RPS come down and would I get better fuel economy and speed if I go with a 5.7?
Here are my specs:

4.3 w/ alpha1 5.0 w/ Bravo III

rpm 4100 3700
cruise 27 29
fuel range
270 ltr tank 190 mi 198 mi

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Bond-o said:

Ayuh,... Welcome Aboard,... Yer What,..??

Rpms are limited by the Prop, or Props in the case of the BIII...
If yer only pullin' 3700 rpms at Wot now, yer luggin' the motor, 'n she's gonna detonate itself to a hole in a piston....

Puttin' a 350 in it, the bigger motor, Might possibly bring it's rpms Up to where they oughta be...

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Bond-o said:

Ayuh,... Which 5.0l,..?? Carbed, 4bbl., or Efi,..??

If you put more horsepower in it, you'll need to reprop to get the rpms back down...

Crusin' may, or may not be measureably better, or not...
That'll also depend on the induction system used...

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