Adding power. How do I prop?
 

I have a 2002 35' Lightening w/ 575SCI's. I'm spinning 32" Bravo's and 1.5 drives. I want to add intercoolers for an increase of 100HP per side. Here is my dilemma. As of right now I run right at 5200-5300 RPM. Last year I put a pair of 34" Bravo's on it just to see how it would run and get my rev's down because on cool days I am all over my rev-limiter. The boat would barely get on plain. It took 4 tries with an empty boat. It would begin to take off, then once the prop got some air it would just burn-out.

I look at a test Power Boat did on my boat in 2004 w/ intercoolers and they spun 37's. There's no possible way my boat would get on plain with 37's on it's best day. I have been told that you really shouldn't go any higher than 32".

Should I add drive spacers to lower my X-dimension or is the solution to go to 1:36 drives. I've been told that spacers would reduce slip but would also reduce speed.

There has to be a lot of people who have a similar set-up and added intercoolers. I don't want to open up a can of worms by making a not-so-costly upgrade turn into new drives, props, etc.

Re: Adding power. How do I prop?
 

I would go to a 5 blade prop. The 34 Bravos have talked about before and generally don't work well without being worked. I would think a 33-34 5 blade would be the best answer for you.

Re: Adding power. How do I prop?
 

I never really thought of that. This would give me more bite out of the hole?

Re: Adding power. How do I prop?
 

How will intercoolers give you 100 hp per side ?

Re: Adding power. How do I prop?
 

What is your speed at WOT?

Your speed will help with determining whether a spacer would help you.

Re: Adding power. How do I prop?
 

I just ran some numbers for my 35 Cafe - I am running 650 HP each - this is a help full site

http://www.rbbi.com/folders/prop/propcalc.htm -

it takes 100 HP for every 5 mph so fill in the blanks per the current RPM/prop size

Re: Adding power. How do I prop?
 

Whipple has a kit that replaces the entire intake with an integrated intercooler. You use a smaller pulley and reprogram the ECM. It makes 100 more HP and 125 more Ft Pds of torque.

I saw 91 MPH this year on a Garmin GPS on an average day. Temp & humidty makes a huge difference w/ my motors. It should see 93 or 94 with perfect weather & chop.

How much is the prop slip decreased by when you go from a 4 blade to a 5? I had a 3 blade on my last single engine Fountain and swapped it with a 4 blade. I had to drop from a 23" to a 21" because of the added bite the extra blade had.

Re: Adding power. How do I prop?
 

Based on your numbers it seems as if 5 blade props may be an answer to your problems.

Based on your information, assuming your current props are stock, and assuming the inter cooler adds an additional 100hp per side, you could run 33 pitch 5 blade props @5300 rpm and you should be running about 99 mph. These numbers work in theory and should be fairly close. With a tail wind and some cool air you should break 100.

Re: Adding power. How do I prop?
 

Now the question is, who's prop and what style? I am currently running a Bravo. Hydromotive has three 5 blade designs. Would you use a hydromotive?

Re: Adding power. How do I prop?
 

Our CNC props are ideally suited to your boat. They are available in 5 blade designs and whatever pitch you may need. Cost is about the same as a lab finished cast 5 blade prop from other manufacturers.

If you have any questions please visit our web site www.throttle-up.com or call.