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Adam46BT
05-04-2004, 12:08 PM
I have twin 502 EFI's mated to Bravo 1's with 4 blade 26 pitch props. The best RPM I could get in 50 degree weather was 4700. Shouldn't I be able to turn 5200? What prop changes should be made?

33 DONZI
05-04-2004, 02:46 PM
are the lab finished? If not if you get them finished and thinned you should gain some rpm. But since you only got 4700 on 5o degrees I would consider moving down to 24 pitch 4 blade b/c when it get hot oout you wont be able to get that 4700 rpm your getting now

Adam46BT
05-04-2004, 04:10 PM
Thanks for the reply. They are not lab finished. Should I even consider three blade? I am also concerned about losing a lot of hole shot and mid range performance. Thanks for the help.

meyerwrench
05-04-2004, 04:40 PM
try calling Throttle Up or visit their website www.throttle-up.com :mrgreen: I'm sure they can help you. [smilie=twocents.gif]

Von Bongo
05-04-2004, 05:38 PM
I think the 502's have the limiters set at 5100. What you need to do is wait until you have some better baseline numbers. Get the boat and run it with the normal load and fuel that you will carry along with normal heat and humidity. My guess is that it was propped that way to get better cruse speed and efficency. Then you will have a much better where you want to be.

And then call Throttle up. I ran my cig a few times last fall and it isn't proped right but I want to wait, maybe through the summer. I want to know how it is going to run when it is 85 out and 70% humidity. I doubt very much that it would benifit from 3 blades and you also might call BT and see what they have to say about it.

Saleen367
05-04-2004, 09:49 PM
http://www.mercurymarine.com/prop_selector

Dr. Jeff
05-04-2004, 09:55 PM
Thanks for the reply. They are not lab finished. Should I even consider three blade? I am also concerned about losing a lot of hole shot and mid range performance. Thanks for the help.

You said "hole shot"! [smilie=071.gif] [smilie=071.gif] [smilie=071.gif]

Adam46BT
05-05-2004, 04:39 PM
Thanks for the input. I think I will wait until the summer temperatures arrive to do any experimenting with different props.

Northern Baja
05-06-2004, 06:49 AM
Check this link:
http://p201.ezboard.com/fteambajamarinefrm29

Houston Props moderates prop discussions. Over time I've gained a ton of respect for this guy. Seems to really know props, honest, and years of online feedback says that his work is excellent. [smilie=071.gif]

Maxx
05-27-2004, 08:52 PM
If that is on a 43' Black Thunder with 1.5 gears you are right you have too much wheel. I ran Merc 26 Bravo 4 blade wheels on a 96 flat deck with twin 560 hp engines. 76mph @ 5200 rpm.
Maxx

Throttle Up
06-09-2004, 07:46 AM
VonBongo is on the money!

The 502 EFI's should run at 4900-5000 RPM at WOT. We typically see our greatest RPM and speeds in the cooler months (H2O and Air Temps). With summer approaching you will notice your RPM decreasing. In your case Adam43BT this is not a good thing. You are already running low on RPM. In your case I would surmise that you are in to tall of a prop, assuming that your prop is in good condition. It might be a good idea to take her out for a good baseline run.

Record your WOT RPM and speed.
Note how much trim you are putting into it.
Fuel levels ( I would recommend testing with your normal load, fuel and gear)
Water temp
Air Temp
Note water conditions.

With this information we will be better equipted to dial you in.

Julie
Throttle Up Propellers
877-842-6855

eddie
06-10-2004, 06:37 AM
Adam - BSB is looking for a set of 26 B1's for his 36 Outlaw. He's at Stone Ledge at 20.5mm on LOTO. Might be able to work out a deal if they work on his boat. He's got 500's and is blowing out the 3 blades and would like to switch to 4's

Adam46BT
06-10-2004, 12:42 PM
Adam - BSB is looking for a set of 26 B1's for his 36 Outlaw. He's at Stone Ledge at 20.5mm on LOTO. Might be able to work out a deal if they work on his boat. He's got 500's and is blowing out the 3 blades and would like to switch to 4's

I would have to work something out with Black thunder. They have given me a set of Hydromotive 24's to try. If they work out, they will swap me for the 26's. We can talk about it this weekend at the Wilbus Run.

Adam46BT
06-16-2004, 01:03 PM
VonBongo is on the money!

The 502 EFI's should run at 4900-5000 RPM at WOT. We typically see our greatest RPM and speeds in the cooler months (H2O and Air Temps). With summer approaching you will notice your RPM decreasing. In your case Adam43BT this is not a good thing. You are already running low on RPM. In your case I would surmise that you are in to tall of a prop, assuming that your prop is in good condition. It might be a good idea to take her out for a good baseline run.

Record your WOT RPM and speed.
Note how much trim you are putting into it.
Fuel levels ( I would recommend testing with your normal load, fuel and gear)
Water temp
Air Temp
Note water conditions.

With this information we will be better equipted to dial you in.

Julie
Throttle Up Propellers
877-842-6855

Okay. I have switched to a set of 24 Hydromotive 4-blades. I can now get 4900-5000RPM. This is with a full load of fuel, trimmed out significantly in 85 degree air, 75 degree water. The top speed did not change over the 26 Bravos. I feel like I lost mid range performance. It now takes 4000RPM to cruise at 50 where it did only take 3700 with Bravos. Which set up is better for engine/drive wear and tear (With the 26 Bravos, it was pushing it to get 4600-4700 RPM)? How about fuel economy?

Thanks

Throttle Up
06-16-2004, 04:41 PM
With the 26P props being to tall or to low of an RPM you were experienceing the great cruise speeds. This occurs any time you are in to tall of a pitch that you can still turn. The 26P Bravo I's are lugging your motors. I would definately stay in the 24P range to keep the motors running in the apropriate RPM range. Fuel ecomomy is definately being effected by lugging. You are consuming more fuel with your 26P Bravo I's.

Julie

Adam46BT
06-17-2004, 07:45 AM
Julie,

Thanks for the response. This is a big help!

Adam

Throttle Up
06-17-2004, 11:26 AM
You are quite welcome!

Julie