Fuhgedaboudit

I have a 357 sr1 Formula, with 420hp 454s and TRS drives. I currently run a 3 blade 21" mirage prop 5200 rpm to speed of 61 mph. I am thinking of putting on 4 blade 24" bravo 1 props. What speed difference do you think I'll see? What do you all think of the set up? any input will be appreciated. I am hoping to see 66 mph at 5000 rpm...

MACDAD260

The 24" Bravo 1 four blade will compare closely to a 23" Mirage + in actual pitch so you will probably see a drop in your WOT RPM. You may or may not gain speed. 4 blades help you get on plane faster. You'll have to try one to see how it works on your boat. Some boats like them and some don't. Maybe someone with experience with your setup could tell you more. Good luck.

mopower

5 mph gain by changing props...maybe , but I kinda doubt it . Plus keep in ming 3 blades are generally faster than 4 , since there is less blade area and less drag.
My bet is 61 mph at 46/4700 rpm , but a major jump in your cruise speed , say at 3000.

cooltoys61

almost certain to lower your top end since you are dialed in at 5200 now,,less R's = less HP,,prob same take off since you are making a big change and going 4 blade,,small change,like 2 inch and you would have close or better but 3" and you would start to see as much influence from the pitch as the # of blades. Think about a 23" 4 blade??maybe 22. You are close to optimum on R's soooooo don't make any big changes unless you up HP or want to gaincruise speed at the cost of take off and top end.

Griff

If they are regular 21"Mirages, you will see a 400 or so rpm decrease going to 22" Bravo's.

If they are Mirage +'s, you will see about a 200rpm rpm decrease going to a 22" Bravo.

Take off another 400rpms if you go up to 24" Bravo's.

You will more than likely lose mph on the top end and increase cruise speed.

These are general rules and all boats respond differently. Best thing is to try B4 you buy.

powerguy

I will be trying a set of 22 Bravo 1 props this weekend. The boat is a Formula 336 and the previous owner said that he was getting about 4800 rpm with 23 mirage +'s .... 22 Bravo 1 should get me to at least 5000 rpm and hopefully no loss at top end and much better out of the hole and cruise. Motors are 454 mag's.

Fuhgedaboudit

I should also add to the equation I have a set of 25" 3 blade mirages that I also have not tried on the boat. I think that a pair of 420 hp motors should have enough guts to turn them...I know I'll lose a few rpms, but hoped to make a little more speed.. the boat does seem to be dialed in with 5200 WOT I just would like to see a little more speed

tomcat

Switching to four blade props will increase cruising speed and improve acceleration, but reduce top speed. The reason was given above; too much blade area in the water, more than is needed to absorb the engine's power.

You don't need four blades unless your propshafts are high enough that the Mirage props are blowing out in turns or rough water. That's why four blades, then five blades and now six blade props were invented. Racers and boat builders kept raising drives to reduce gearcase drag. It works, but then the prop slips, so you have to add another blade to keep enough blade area in the water to deliver the power available from the engine.

Unless you have spacers in your TRS drives right now, there's no easy way for you to raise propshaft height. I had 2" spacers in mine. When removed the boat went faster, but the Mirage props slipped and it was almost impossible to get on plane with any load. Went to four blades and the boat kept about half the speed gains and returned to proper handling. Overall speed gain - 2 mph.

The 25 Mirage is a great prop but you'll be lucky to spin them at 4400 RPM. Even if that gets you a little more speed you'd be lugging the engines too much.

IMHO the thing to do is bolt on a small blower and make 525 HP. That way you'll be able to spin the 25 Mirage props at 5200 RPM and go 72 mph!

HOUSTONPROP

23 ACCLERATORS WOULD be the fastest ALL AROUND prop.

22 stock four blds will run slower,lower rpm and good cruise speeds and planing time will be nice.

24 PITCH PROPS WILL TURN WAY TO SLOW,

TRY BEFORE YOU BUY.

last option work your props to a 23 pitch and convert them to the ACCLERATOR design.good luck,Darin