Formula 292 Fastech
 

Currently running box stock 26 bravo 1 with a 1.65 dr.

Top end is 68/69 in the fresh on the limiters-350 mag MPI MEFI 3. I think the limiter is set a 5250 or so.

I feel as if I need more bow lift, but this hull has 2 steps so maybe it should be ridding flatter than what I am used to, but at top speed I can trim out and keep gaining speed unit my props loose bite, and this is well within the safe trim range. So should I have my bravos worked to get more bow lift or try and find a different prop. I know the powertech oxf4 claims to have more bow lift than the box stock bravo but I do not know much about powertech. I wish rev 4 came in 27" pitch.

Any comments?

Thanks,

LC

I run 28P props. When they were stock, I ran 69-70. I had BBlades lab them and put some cup in the blades to help with coming on plane but gave up too much top end speed for what I gained in the "hole shot". I'm planning to have them redone to original specs this winter.

Dave

What are you seeing cruise wise. IIRC I get 45 @ 4000 rpm. And that is 25% slip.

I run 50 at 3800. Last time I checked it was around 12% slip. Your slip seems very high. Give Brett at BBlades a call, he is excellent.

Dave

Most stock 292's run 1.65 drives and 28 Pitch Bravo props

Some were special ordered with 26" box stock bravos to help with planing.

Went back and checked my notes. I am 3500rpm at 45mph GPS.

I do not seem to suffer speed wise from the 26" props, but I am a bit under propped.

Back to the original question. Do stepped hulls need as much bow lift as a striaght bottom. I wonder if the 28 labbed bravos on most stock 292 have more bow lift built in.

Perhaps will help you our experiences.

We test on our boat OXF5 and home labbed Maximus. We use MSA tunell surface drive.

OXF5 it is often blow out, cavitate at start and make strong torque which is want to turn boat on left.
At 45 mph we have 28% slip and minimum plane speed it was 28 mph. It is have bow lift, but nothing dramatic. At turns we must always trim drive down. If not, it is blow out emediatelly.
With this prop it is no away to made roster tail, it cavitate before of this.

Maximus we modified with smaller 15,25" diameter, tinner blades and cut tube on ST shape. I do not want to talk round of good or bad modification, but boat work much better with this prop. On start it pull boat easy on plane with out of lifting bow, just start to plane. It made almost zero torque and you must trimm it down only for sharpe turns. At 45 mph we have 22% slip and minimum plane speed it was under 20 mph. On this moment I do not know what will happen at expecting maximum speed over 70 mph, but I do not expect something bad. We made bigg (for surface drive classic) roster tail, but the best efficiency and stable ride we have with small only ca 1 m high roster tail. We are more than happy with this prop.
This prop we modified alone only becouse of bigg distance betwen us and BBlades. In future we will order labbing or complette props from this company.



oxf5
http://shrani.si/t/2W/iM/3OEZuKNk/20110729image0007.jpg

"Our" Maximus.
http://shrani.si/t/42/Jd/1BxqnFVn/fotografija0091.jpg

Here is what my 292 slip numbers look like running labbed 28" pitch Bravo's. The numbers are really a bit better than this since I have been told the actual pitch of Bravo props is slightly less than advertised (so maybe 27.5" for mine).

Your slip of 25% at that speed is a little high. I'm running 320 hp 6.2 liter engines and have no problem planing with the 28's. I did change the position of the trim-in limit spacer in the outdrives as received from Formula. Make sure the spacer is located in forward position. This allows the drives to tuck in slightly more and help with planing.

These props have worked out really well and have a best of 72.2 mph top speed in perfect conditions.

Apples to oranges when comparing my non stepped 25'7 boat with pad to the 29 Fastech but have the same engine/drive packages as some of you. 6.2L MX's [ 320 HP at the props ] with B1X drive with 1.65 ratio. B1 26P props turned 5150 @ WOT and holeshot was better, allowing the props spool up faster, before tuned the props to 26P+cup. The stock B1 props check out at 25P+1 with the cup. I'd leave it alone, especially for the 350 Mag with less HP.
With the re-pitch I now turn 5000 @ WOT, lost some top end and holeshot is slower.I doubt going to 28P is the answer for the 292 Fastech even with the steps helping.
I roll on for better takeoff using the flat section of the hull to plane my boat faster.
Used to run 74-75 with stock pitch, now run 70-71 at best. Only thing improved is fuel economy, turning slower rpm's on plane before falling off at around 3000rpm.
Boat carries the bow pretty good with props turning in.

http://www.youtube.com/watch?v=WD4mqNO0kNw
http://www.youtube.com/watch?v=l_axHfmDBw8

Figuring a 26P, 1.65 gear, 5150 rpm and 74-75 mph, this works out to 3% slip. Can that be right? 70-71 mph is 8-9% which is more realistic.

LC is on the limiters with the 26P. The 28P may be a little too much, but he could definitely use a little more pitch. The 28's would definitely help cruise economy. LC runs 45 mph at 4000 rpm and I'm at 53-54 mph at 4000 rpm.

A 27P would likely be perfect.