More power from My 7.4MPI´s
 

Hi. I just went from Mirage Plus 23´s to Bravo 24´s on my 29 OL. The top speed is exactly the same, 61 miles because it wont reach 4.600 rpm with the bravos.
I did gain around 5 miles at 3.500 rpm wich is great but it would be nice to get just a little more power out of them so they reach 4.600 rpm with the bravos in an easy and sheap way.

Is that possible somehow with other exhaust or something or should I just forget it?


Sorry about my english, I´m from Sweden.
/Teo

Those motors are RPM limited to 4850 I think. I would expect the same speed out of the two propellers as they are both very close in pitch.
The gain you saw at 3500 RPM is typical of a 4 blade propeller. They tend to increase cruise speed more than top end.
I think that the 24p Bravo 1 would get you a few more MPH by having it lab finished, but for the HP you are running I wouldn't expect much more than 62-64 mph out of that boat with that power.

Ok. I think mine are limited to 4.650 and with the bravo´s they only reach 4.300.

Do you think it will drink much more gas with the bravos?

The RPM range will be on the valve cover with all the other information on the engine.
It sounds like you're over propped.

Have the Bravo's labbed by Bblades or a propeller shop near you. This will gain you around 200-250 rpm's as well as possibly increase your current speed.

It's also possible altitude or elevation is effecting it. You should be able to spin 24's with 7.4L MPI's

I will do that. We have a propp-guru here i Sweden called "Propeller Björn". I will call hin right away.

Thanks.

I ran 62 MPH with 23" mirage on my old 29OL with 7.4s. It would flirt with 63 every once in a while. I also had 22" 4 blades and it was quicker, but would bump the rev limiters from time to time with a light load. I think labbed 24"s would be perfect on that setup. You only need to pick up about 200 RPM.

I think I tried every prop make on my 29ol with 7.4 MPI's including 22, & 24 Hydro 4 blades. The 25 Mirage Plus labbed is very fast if the engines are still strong, but my overall favorite is the labbed 24 Bravos.

Then it seems that I´m on the right track. How about the fuel consumption on Mirage 23P vs Bravo 24?

If your concerned about fuel keep it under 3500 rpm's any Big Block is going to burn fuel over that.

Hey we that live up here in scandinavia, should not think about fuelprices - too depressing. At least you swedish meatballs have cheap cars:lolhit:

Anyway. Your are not at the limiter at 4650 but 4850. Your fuel bill should be a tad better with the 24 b1 compared to the 23 M+'s in the mid range. To add a blade, gain mid range efficiency and not loose speed, is not a bad thing in itself by no means. Normally less is more when it comes to speed. So maybe the way around the speed increase would have been M+ 25"'s as someone else suggested.

Where in sweden do you boat?

First I will trye labbing with the bravo 24´s and see if I can get som more rpm out of my old MPI´s.
My plan was exactly that to get some more miles out at cruise. The engines don´t seem to work that hard with the bravos.

I´m running around in the Stockholm arkipelgo. Where are you located?

/Teo