Impeller Question, Confused

[Burner71]

I picked up a 2007 Challenger 180 215hp this summer. I have never been able to get this thing over 7650rpm and 42mph. I found a good mechanic and he has changed the oil, the plugs, cleaned the IC and added a catch can. Still can't get over 7650. The prop appears to be original and was pretty banged up on the ends, he went ahead and smoothed it all out, same RPM results. So friday he says he can throw on his 14/19 Concord SRX just to see how it does.
The boat now runs at 8150RPM but never faster than 38mph.
What am I missing here? Shouldn't the rpms have gone down and speed up? Assuming the stock prop was a 13/18.
Any ideas why? Maybe the prop isn't fitting the way it needs or I used the wrong prop? Just curious.
Plan to add external cooler, injectors and bigger wheel this winter.

 

[Burner71]

also I thought the stock impeller was a 13/18. The parts pages show part#267000285. When I search this part I see 10/21 pitch. I don't know how that compares to 14/19 in rpm and speed.

 

[pug pug]

hello. Before I ask you more questions have you had a look at your ware ring what condition it is in first.

 

[Burner71]

Yes wear ring is new and perfect condition. I measured the stock prop and it was 10/21. So wondering what prop will give me better top end over the 14/19 since it lost speed?
maybe a 15/20?

 

[POPPS]

Have checked out the super charger?

 

[Burner71]

It’s not the supercharger it was rebuilt 10ths ago. I think y’all are missing what I’m saying.
The stock impeller runs the boat at 42mph but never gets over 7650rpm. I wanted more speed so I put in a Solaris 14/19 because it’s supposed to be better. The Solaris got my rpms to 8150 but the top end dropped to 37mph. What prop do I need to stay above 8k rpm and a better than 42mph speed?

 

[pug pug]

Yes 15/20 should sort it out. Am running 14/19. And she flys!!. He is that good I had to make the seadoo trim tabs to keep the Nose tight to the water.when I shoot out the hole. It am so glad I did because even when it’s really choppy he is a lot more stable. Let me know how you get on. Pug pug.

 

[Burner71]

thanks that what I was looking for. Oddly when I look up the stock impeller for the 215hp and the 255hp they are both 10/21. So the 15/20 you think would give better speed and RPMs up at the top where they need to be?

 

[pug pug]

Yes you will be flying!!.

 

[ski-d00]

...but you're going to lose low end acceleration!!

Your current impeller doesn't reach top speed because it is beat up and needs replaced. You can't just clean it up with a file and expect it to work like new. It will need replaced or rebuilt by a professional capable of welding it up and fixing the pitch. If the trailing edge has any slight ripples in them at all, you will lose top speed.

 

[Burner71]

Ok yeah makes sense. I had read that the wider the spread like 10/21 is better. So yeah i'm probably just a new one will run much better.