prop ideas needed
 

so my buddy grads2112 told me that I should present my prop questions here as this forum has some knowledgable folks. We've been testing a few props on my boat and I'm not quite at a top speed I'd like. I have a 2005 Ultra shadow with 1100hp and 1050 lbs of torque running on an Imco 4x4 drive and 1.34 gears. Here's what I've tested so far:

1.5 gears (now has 1.34)
6300 rpms on the rev limiter
34 pitch stock prop
actual speed = 111
prop slip = 17.92

then switched to 1.34 gears
5200 rpms
34 pitch stock prop
actual speed = 108
prop slip = 13.56

1.34 gears
5600 rpms
30 pitch stock
actual speed = 109 (full of gas and 3 fat guys on this run)
prop slip = 8.19



So, does anyone have a good suggestion for what to try next to get up over 115mph? Is this a pipe dream? any idea what a 32 pitch 5 blade would do? should I just lab the 30 and get up to 6000 rpms?

thanks for any help.

John

Tell us a little about your motor. Do you have a dyno sheet for the motor? This would tell us where it should run.

I'm not allowed to post attachments. just joined. is that why?

also not allowed to post a url to my photo bucket account.

I can email it to ya...

e mail it to [email protected]

If you go there you will only get one opinion. I think we achive the desired outcome right here.

You can type the engine rpm and hp curve from 5000 up if you desire.

It seems the gear ratio change definately caused the performance to fall on its face with the 34's and obviously this is telling us the mid to upper 5's will get this engine to perform. Also, if the engine builder has set the rev limiter at 6300, his desire would most likely be to run WOT at 6000ish.

Your slip % with the 30 BS is actually lower than you think since the true pitch of that propeller is lower than 30. For that reason, I believe it is a good propeller to work with. If you like the way the boat carries itself and the personallity the Bravo propeller creates, stick with it. If we Lab it to gain 300 rpm and the efficiancy stays the same, you will be at 114.8 mph. Most like the real world number will be in the 113 range.

I see no reason for 5-6 blades unless low speed cruising is your biggest desire. We do have 5 blade props for testing if you would like.

Thank you.

okay, I typed it out. here's my dyno from 4100 to 6200

RPM’s Trq HP
4100 998.8 779.7
4200 1004.1 803.0
4300 1001.5 819.9
4400 1007.4 844.0
4500 1016.8 871.2
4600 1021.3 984.5
4700 1019.8 912.6
4800 1020.7 932.9
4900 1011.4 943.6
5000 1011.1 962.6
5100 1022.4 992.8
5200 998.6 988.7
5300 1009.6 1018.8
5400 998.7 1026.8
5500 1000.4 1047.7
5600 992.3 1058.1
5700 980.3 1063.9
5800 977.4 1079.4
5900 957.7 1075.8
6000 954.4 1090.4
6100 939.6 1091.3
6200 926.1 1093.3

I'm a little worried about my slip being too efficient right now. I don't want to kill my drive...

here's another question...should I consider going back to the 1.5 gears and bumping up to a labbed 36 prop? am I better off to stick with the 1.34 setup I have now?

OK,

After looking at the dyno sheet. I believe working with the 30 is the appropriate move. I notice you have a steady trq. curve up to 5500 before it finally starts to drop. We also see the HP flatten at 6000. Labbing the 30 with a standard template will give you all of 300 rpm and maybe a little more putting you right where you need to be in the 6000 range.

This being said, the 400 rpm difference between the 36 and 30 with the same 1.34:1 ratio is a little weird. You should of seen a larger change in rpm. Also, the drop of 1100 going from 1.5:1 to a 1.34:1 is drastic. The drop should have been more in the 400 to 600 range.

Are you sure both propellers are stock and never reworked by anybody?

yeah, I'm pretty sure both the 34 and 30 are stock. both props have pretty thick blades and rounded edges...neither is sharp.

I'll give it a try with a labbed 30 and see how it runs. I think my mechanic has one that I can borrow to test...so I'll give that a try and report back. I'm just hoping to see 115.

Cool, keep us up to speed.