Has anyone ran the 4S SS impeller in a 2S

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redrum

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I have a new-to-me 95 Merc 45 Jet with the stock aluminum impeller. I sharpened up the impeller, which had been severely defiled :). It runs great but I wanted to get a stainless impeller for it. I didn't know the whole 4S cutback to the 2S impeller under the same part number. I ordered a new stainless impeller and I'm guessing it's the 4S style now. I don't want to run it if I may lose holeshot or over rev the engine with no added MPH. I'm very happy with the performance right now. I was thinking about returning the SS and just getting a new aluminum one from OBJ. I'll attach a picture of theimpeller if anyone can confirm that this is the 4S model, thanks.
 

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I haven't run the 4S impeller in a 2S motor so I don't know how it would perform, but I can identify your impeller for you. It's the 4S impeller. Below is the 2S & 4S side by side. 2S on the right.

Don't know if you would be interested, but I have a Wooldridge 4 blade SS impeller for sale in the Classified section.
 

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buy a cheap tachometer off ebay and try it if it revs to high sell it rotus on here might buy it I know he has a 4s and might want a SS impeller for it maybe. I'd be curious to know how it runs on a 2s
 
redrum said:
I have a new-to-me 95 Merc 45 Jet with the stock aluminum impeller. I sharpened up the impeller, which had been severely defiled :). It runs great but I wanted to get a stainless impeller for it. I didn't know the whole 4S cutback to the 2S impeller under the same part number. I ordered a new stainless impeller and I'm guessing it's the 4S style now. I don't want to run it if I may lose holeshot or over rev the engine with no added MPH. I'm very happy with the performance right now. I was thinking about returning the SS and just getting a new aluminum one from OBJ. I'll attach a picture of theimpeller if anyone can confirm that this is the 4S model, thanks.

Did you try running it yet?
 
The 4 stroke impeller will be fine in your 2 stroke. Might even be better considering you have the 52cube merc. I've got a friend with a 56cube omc and he's running a 4 stroke impeller and there's not much difference rpm wise maybe 200rpm nothing crazy that's going to over rev a stock motor. Plus the stainless will last way longer then the aluminum ever would.
 
The results are in:

Aluminum 3 blade Impeller - 29.7 MPH @ 5,400 RPM
Stainless 3 blade 4S Impeller - 30.0 MPH @ 5,300 RPM

Not the results I expected but now I know. :mrgreen:
 
I'm surprised that you got higher RPM with the aluminum 2S impeller than the SS 4S. When I first got my Mercury 4S 40 Jet, I tried both the 2S SS and the 2S aluminum impellers. I got around 4900 top end RPM with both. With the SS 4S impeller, I get around 5200 RPM. Guess the 4S just doesn't have enough power to turn the 2S impeller any faster.
 
I think my aluminum impeller is original. It has been ground on for sure. Here they are side by side. I bought the SS one new just last month. Im pretty sure it's the 4S model.

Hoping rotus will buy the SS one from me and I'll get that 4 blade from Larry then post the results.

IMG_9777.JPG

Gotta say I'm extremely happy with the upgrade from the 50/35. Just better overall performance and the 3 cylinder sounds good :D
 
redrum, if your new impeller is still out, could you post a photo of it laying on it's side with the same orientation that LarryMc used in his photo. Thanks
 
It's still in the pump now. It is in the first picture up top. Here are a few more pictures I have of it.
 

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No problem, LarryMc shows impellers from two different suppliers and it's easy to see how much material has been removed from Merc's new casting.
 
redrum, I enlarged your photo to show that the leading and trailing edge of each vane are almost directly across from each other, just like the 2s. On the 4s, the trailing edge has been cut way back to allow it to spin easier. I believe you have an original quicksilver 2s casting which is why your rpm did not increase on your test.
 

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mphelle said:
redrum, I enlarged your photo to show that the leading and trailing edge of each vane are almost directly across from each other, just like the 2s. On the 4s, the trailing edge has been cut way back to allow it to spin easier. I believe you have an original quicksilver 2s casting which is why your rpm did not increase on your test.
This impeller is a 4s. Trying to compare rpms between a worn aluminum and a new stainless is kind of a apple and orange comparison. The worn aluminum will turn more rpms then it would stock because it's not getting the same bite since the leading edge is has been file back from repeated sharpening. So stock for stock the 4s stainless might have turned as many rpm if not more then a new aluminum.
 
Lil' Blue Rude said:
mphelle said:
redrum, I enlarged your photo to show that the leading and trailing edge of each vane are almost directly across from each other, just like the 2s. On the 4s, the trailing edge has been cut way back to allow it to spin easier. I believe you have an original quicksilver 2s casting which is why your rpm did not increase on your test.
This impeller is a 4s. Trying to compare rpms between a worn aluminum and a new stainless is kind of a apple and orange comparison. The worn aluminum will turn more rpms then it would stock because it's not getting the same bite since the leading edge is has been file back from repeated sharpening. So stock for stock the 4s stainless might have turned as many rpm if not more then a new aluminum.

What information are you using to identify redrum's impeller as a 4s?
 
Another photo of the 4s & 2S impellers side by side, 2S on right. It's seems apparent to me that the impeller shown in the photo that redrum posted is a 4S impeller.
 

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Well, you can't have too many photos, (hopefully you aren't going by the finish that quicksilver uses), with your trailing edges fairly lined up, the respective leading edge of the 4s hasn't "rotated" into the picture. Gives you a feel for how much trailing edge was removed.

If you could get a photo of your 4s in the same orientation of his below, we could wrap up this post.
 

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