swapping power 390s
 

Our next move with first 390 2003 year model, pull the IMCO'S SCX-4 back off, put the freshened XRs back on ,start looking for a 390 staggered set up. There is history on a staggered set up that worked, a few MERCURY 700 hp NXT drive 390's where built and the first one ran 114mph. So we talked about going that route, we needed to find a staggered 390 with smaller power and swap power. Can't make any of this up, having lunch with Kenny when talking about this idea his phone rang. It was a call, someone looking to sell 390 staggered boat. Kenny shows me who is on his phone ,I know the person . I think many of you know there was a 390 going through some up grades, being posted on Off Shore Only for us to watch to see how he made out. It is VERY unfortunate the up grades never made it to a completion. ( never received the drives he paid for ) I feel very bad for Chris ,this stuff should not happen to anyone. I sold the boat to Chris about a year ago , and Kenny ( Let's Talk Boats ) was helping Chris with his up grades. So I bought the boat back ( known as rocket man ) ,one motor was out ,the transom was filled ready for all new drives. It was just what we where looking for I knew the boat very well owned it for years. Rocket man boat was originally built 2007 with ILMOR 625 hp v 10 , had transmissions with Konrad drives ,one off a kind ,ran around 83 mph. At this time all motors are out. The 2003 390 side by side motor set up ,is the first boat to go back together ,putting the ILMOR 625hp V10, running XR drives. By dropping transmissions out of the driveline and going to XR drives, hoping to see low 90's mph for speed. I will keep posting need to get to 10 post to share any pic's.

The KE's dyno at a little over 850 hp . We are looking for the speed of the mercury 700 boat 114 mph, would like a little more then that. The side by side 390 did not like the SCX-4 drive at all. When we where testing to see how it ran could almost get 100mph ,which we where looking for more , the boat just didn't drive right ,when you pull back on the throttles, back of the boat was moving around. We think the drives needed to move up which is a lot of work and still not sure what we would have. I am hoping the XRs can hold up to the 625 ILMORS . The 625 tested close to the 600 Mercury set up, and I think most 600 ran XR drives. If we run low 90's with the ILMOR set up should be a fun boat.

As a little background, the main thing that contributed to the 114 MPH boat speed was the slippery NXT drive set-up (which according to Steve, had great laminar water flow loading the prop) and the ability to run large diameter Speedmaster props for a higher x. What drives are you looking to run on the staggered boat?

We are going to run IMCO SCX-4 with ITS . The lower part of this drive looks very similar to the NXT drive with a little longer skag. Can also run bigger props. We have a fresh transom, working with Steve to set the drives X, we may go a little higher then the NXT boats, can always come down if to high.

Well getting close to getting 2003 390 side by side 625 ILMORS in the water . Decided to make some more changes on the way , we put ITS on this boat set up going to test with standard XRs and also going to test XRs with -2'' lowers. We will let you know what props and drive configuration we run and what speeds came from them .

390 625 Ilmors made it to the water a few months ago. Did some testing right out of gate, started with standard XRs with ITS , 29 5 blade hydros boat ran 83-84 MPH. Pulled XRs off went to XRs with -2" lowers same props boat ran 90-91 MPH . Ran the boat some with standard XRs on, feels good still running 83-84 MPH then lost a blade. Now have on new -2" lowers going to run new 32 5 blade Maximus props. Hope to get some running in this weekend if weather allows.

Thanks for sharing results. You'll pick up speed with a 4 blade prop running at the STANDARD drive height and be easier on your drive. The 5 blades do handle better so that's the trade off at standard height. At -2" height 5 blades are required. The Maximus should plane off better than the Hydro's but likely be a little slower. Best of luck and please let us know how it goes this weekend.

Ran the 390 some more with the -2' lowers tried 32 5 blade Maximus , to big don't know what I was thinking on that. Then tried 27px-5 hydros it like that up to 85-86 MPH then it felt like it stop pulling tack read 5600 RPM , think there is a problem with the tack reading higher RPM motors sounded like they where turning the most RPMs I have run them. The boat comes up on plan with no prop slip, think that is the ITS system helping with that.

I'm getting ready, well a few months from now, to go through all this on my 41. I was going to start with a -2 lower as well. How deep is the propshaft from the bottom of the boat? With -2 I'll be just over 3". Is the boat the staggered setup you were looking for? The 29 hydros, were they px props? I have a bit more power but I also have a bit more boat than the 39 so I'll likely start with the 29s and take if from there.
Great thread, I can't wait to get out there and start testing!!!