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Swapped out 5.0 for 5.7, cobra gear ratio question-gctid343756
I'm currently running a 15x15 four blade stainless as the tired 5.0 was having a hard time getting near recoomended wot with a three blade 15x17. I also troll all the time and run heavy. I thought I'd have to increase pitch for wot purposes with the change but perhaps the 15 pitch will work out.
Am I right that the current 21/17 gear set will spin slower than the 21/16 which came with the 5.7 from the factory? I take it the 21/17 would be restrictive on the 5.7 for wot purposes and thus lowering prop pitch would compensate.
The difference in those ratios is not enough the worry about, if anything, you will be better off with the slightly lower ratio (more torque), if you hadn't seen the ratio tag on the housing you would never know the difference.
The ratios in the lower are the same for both apps. so there will be no issue there.
At the most you can play with prop pitch but depending on what hull you have, with that engine and overall ratio, you will able to tweak the prop. pitch and be good.
" WET EVER " 1989 2459 TROPHY OFFSHORE 5.8L COBRA / SX
mmsi 338108404
mmsi 338124956 "I started with nothing and still have most of it left"
I would test it as is before changing gears out. Test the boat as you run it most often.
Phil, Vicky, Ashleigh & Sydney
1998 3055 Ciera
(yes, a 1998)
Previous boat: 1993 3055
Dream boat: 70' Azimut or Astondoa 72
Sea Doo XP
Sea Doo GTI SE
Life is short. Boats are cool.
The family that plays together stays together.
Vice Commodore: Bellevue Yacht Club
Here's what I have in the 1988 OMC factory shop manual:
5.0 gear ratio overall: 1.50:1 upper ratio: 21:17
5.7 gear ratio overall: 1.41:1 lower ratio: 21:16
Lower ratios are the same at 14:26
I agree with the other posters, I'd try it out first and see what you get. The max rpm range given for both the 5.0 and 5.7 is 4200-4600. You may be closer to the upper end but even if your max rpms were 4800 I would not worry about that and you might well wind up with better out of the hole performance.
88 Four Winns 200 Horizon 4.3 OMC
98 Jeep Grand Cherokee 4.0/Selectrac
07 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II
Thanks gents I'll give it shot with the 21/17 and see what I can get out of the combo. i'll report back on the results. Gotta be better than the 23 year old 5.0 with health issues.
Reel Power wrote:
Thanks gents I'll give it shot with the 21/17 and see what I can get out of the combo. i'll report back on the results. Gotta be better than the 23 year old 5.0 with health issues.
Jarrett
Think of this as though your 5.0L started eating better, started working out at the local health club, and gained strength.
It's certainly worth trying.
.
Rick E. Gresham, Oregon
2850 Bounty Sedan Flybridge model
Twin 280 HP 5.7's w/ Closed Cooling
Volvo Penta DuoProp Drives
Kohler 4 CZ Gen Set
i have a 89 2755 with a 5.8 cobra drive. the drive has a tag that says 5.0/5.7/5.8. the three engines output are so similar you should have no problem with the swap. its not like your mixing a v6 or big block in it.
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