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502 rpm question

502 rpm question

Old 05-21-2020, 03:28 PM
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Default 502 rpm question

I have a new to me formula 400ss. I just got new props (bravo 3) running 4 blade 26p.
Motors are 502 mag mpi

Boat full of fuel (approx 200 gal) and only ran 4200rpm. Motors say 4600-5000.

One great thing is at 3000rpm Iím getting 30 mph, and even 3400 getting 34mph. A 1 to 1 all the way through really.

Now I love that Iím getting 30 at 3000 and most likely will just cruise and not hit 4000rpm and mostly 32-3500rpm. But will this ruin the motors?

I can drop to 24 and most likely be in the rpm range but most likely loose the mid. Any info is great.

Last edited by srdrago; 05-21-2020 at 03:32 PM.
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Old 05-21-2020, 03:42 PM
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I would research and find what boat was originally speced with. If 26 is correct prop you are low on power. If 26 is wrong prop you are lugging the engine all the time.
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Old 05-22-2020, 06:05 AM
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Originally Posted by liberator221 View Post
I would research and find what boat was originally speced with. If 26 is correct prop you are low on power. If 26 is wrong prop you are lugging the engine all the time.
It was originally 3 blade 26p
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Old 05-22-2020, 06:39 AM
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Just my opinion here: your max rpm is down from 4800 to 4200. Thatís significant to me and hard on the engine. This is all assuming engines are in good state of tune.
Sorry for confusion, but was boat manufactured with Bravo 1 drives running 3 blade 26, and now has Bravo3 drives with 26 pitch props?
Lots of Formula owners on here hopefully some has experience with same boat.
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Old 05-22-2020, 07:09 AM
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If memory serves the boat came with B3 26P. There are several on the Formula forum. I think your down on power, look at the plugs and see if there all the same color. If there is differences do compression test and fuel injector cleaning.

How many hours and does one motor achieve more rpm then the other?
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Old 05-24-2020, 07:00 AM
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Originally Posted by liberator221 View Post
Just my opinion here: your max rpm is down from 4800 to 4200. Thatís significant to me and hard on the engine. This is all assuming engines are in good state of tune.
Sorry for confusion, but was boat manufactured with Bravo 1 drives running 3 blade 26, and now has Bravo3 drives with 26 pitch props?
Lots of Formula owners on here hopefully some has experience with same boat.
came with B3 from factory and even with 3blade 26. Formula contacted me and confirmed thatís what came out of the factory.

curious if dropping to 24p 4blade will that be enough to bring the rpm back up to normal range and what will it do to my mid range.
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Old 05-24-2020, 07:02 AM
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Originally Posted by AllDodge View Post
If memory serves the boat came with B3 26P. There are several on the Formula forum. I think your down on power, look at the plugs and see if there all the same color. If there is differences do compression test and fuel injector cleaning.

How many hours and does one motor achieve more rpm then the other?
it was repoqered couple years back and so we donít have exact hours.
Both motors put out same rpm too.
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Old 05-24-2020, 07:06 AM
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If drive ratios have not been changed and your motors are healthy and fuel is right, you should have no issue getting rpm up. Need to do some testing
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Old 05-24-2020, 07:21 AM
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like humans boats gain weight over time something to consider
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Old 05-24-2020, 06:01 PM
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Are you reporting that your boat DID turn up correct rpm with 3B 26 props, and will only turn 4200 now with only the 4B prop change? Or are you saying you don't know what it was turning with the 3 blades? Just because two props are marked 26P, they don't necessarily present an identical load to the motors, especially on a boat with more than average prop slip.

Your bottom could be dirty, boat could be loaded more heavily than intended, motors could be down on power. Carbs could be not opening all the way up (cable adjustment), lots of things.
You really aren't giving us the bigger picture.

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