correct prop for 74 mercruiser 140hp

Q

QBhoy

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jimmbo said:
In the early 70s the 140 MerCruiser had a WOT range of 3900 - 4300 rpm
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Excellent info there. Couldn’t remember what it was. So looks like he isn’t too badly set up at all then !
 
C

Chevyls6

Petty Officer 1st Class
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Oct 11, 2019
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yes very good to know. I thought 4400rpm was too low but i stand corrected.
 
jimmbo

jimmbo

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I wouldn't say 'corrected', informed is more appropriate. However, it is important to have the information of any engine you own. I really don't understand how New Boat Owners lose the Operator Manuals the boat/engine comes with. Engines should have something Permanently attached to them that states all the Specs.
I don't know what changes were made to the 181 in.(3 liter) engine since the 70s, maybe nothing, maybe several things affecting it's powerband and/or it's ability to reliably rev higher. Since the 70s, almost all the Inboard Engine rpm ranges have been raised about 1000 rpm, some in two steps, others in one
 
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C

Chevyls6

Petty Officer 1st Class
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Messages
242
I know for sure they went to a different cylinder head casting with smaller square ports in the early 90s and a 1 piece rear main seal. The parts catalogs also mention a dished and flat top piston depending on application.
 
Q

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,348
jimmbo said:
I wouldn't say 'corrected', informed is more appropriate. However, it is important to have the information of any engine you own. I really don't understand how New Boat Owners lose the Operator Manuals the boat/engine comes with. Engines should have something Permanently attached to them that states all the Specs.
I don't know what changes were made to the 181 in.(3 liter) engine since the 70s, maybe nothing, maybe several things affecting it's powerband and/or it's ability to reliably rev higher. Since the 70s, almost all the Inboard Engine rpm ranges have been raised about 1000 rpm, some in two steps, others in one
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You’re right there, for sure. About the rpms raising on these engine over the years. Slightly related to that…I’ve always wondered around the 350 mpi at 300hp and 4600-5000 rpm and the the 6.2 mpi at 320hp and 4800-6200 rpm. You’d think a stroked engine and 200 more rpm might do a little better than 20hp extra ? More confusing to me…is that I think there may be a 350 mpi variant that can range up to 5100/5200 and still remain 300hp. That’s weird. It’s one of the obscure models of it. Can’t remember which though.
 
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