Yes mine is 5.5" also.

Very interesting. I hit 84mph @5800 rpm as well but with a labbed Bravo1 28P. It had been further modified to gain an additional 200 rpm since at the time I was running less HP and 5300 rpm. Of course I did not do that at 5000 ft elevation and it was a winter run as well. Sounds like you are going to need a bigger prop when you get it all figured out.

What are you hearing as to the benefits of a nose cone on a Bravo X drive at these speeds?

Jon,

RBTNT provided very interesting insight on what speed the nose cone actually begins to improve things (on a particular installation) RE: "A friend had a twin engine cat with Bravos and nose cones. While he was getting one of the drives repaired he used a Bravo without a nose cone. Starting at ~85 mph the side without the nose cone started slipping more than the other side. At 90 mph there was a 300- 400 rpm difference between the two to keep the boat running straight."

WOW. Those headers look insane. What kind of power are you getting?

Thanks! I do like the way they turned out.

This motor has never seen a dyno, so my best guess is 650 to 675...

Hey Steve,

I found a willing soul with a -1 IMCO! The temps are dropping fast here in Utah, but I cant pass up the opprotunity to try it. Is there any special setup when installing a -1 IMCO on an XR upper? I have mated bravo lowers to bravo uppers and understand the orings and seals. I was just wondering if anything needed to be measured or if shimming was involved? Also, will I be able to run with out a bolt on cavitation plate?

Thanks for any advice you might have!
Jon

Hi Jon,
Congrats on finding a -1" to test. It's just like swapping a standard Bravo lower. You may lose a little holeshot without the cav plate, but I don't think it will affect your high speed handling. Your handling and speed should both improve.
The only oddball thing to watch out for is a dramatic increase in water pressure. Keep an eye on it. If it goes over 30/35PSI, I wouldn't run it any faster. The LWP on the IMCO rams a lot of water at high speed. I've seen it push head gaskets and/or break water pump housings. We get around it by additional water reliefs on the motor, and adding the Mercury blowoff valve, which is supposed to open at 30PSI, but I have seen them vary some.
Good luck with the testing!
Best Regards,
Steve

Thanks Steve!

I have a Merc blow off valve installed, so hopefully that will keep the pressure in check. Thanks for bringing it up though, I'll keep an eye on it.

The -1 turned out to be a -2 with a spacer. I wonder if it would be worth trying it both ways? I'm shooting for sometime next week or Sat at the latest. I will let you know what I find!

Jon

Are you going to test it with the labbed 28p B1?

Hi Jon,
This gives you a good opportunity to find the perfect propeller depth. I would try both -1 and -2. Then when you place your order with Imco, you'll know you nailed it :drink:.................
When you run shorter/shallower prop depth, you may be able to turn a larger pitch prop. Take some extra props for testing too. Since we don't have much data base on modified XD/PD Rages, this should be interesting information, particularly for our Rage owners.
Good luck, be careful testing (your boat may handle differently), and let us know how it goes.
Best Regards,
Steve

I would try it at both -1 and -2 in that order. I also agree with Steve about bringing along a bigger pitch prop to test with the shorter lowers. Try throwing the whole slip thing out the window, and concentrating on pure speed and boat handeling. The boat will definately handle differently with the shorter lowers.

What a great test opportunity,

Chris