mjb

I have a '97 straight hull top gun with modified 502's making about 525 crankshaft HP per engine at 5300-5400 rpm with rev limiter set at 5500. I can only spin my original Bravo 1-24's at 5100-5200 at about 68-70 mph. The props have never been labbed and they seem to be pretty straight. I thought that my new HP with my old props would hit the rev limiter but I can't get past 5200. I may need a little more timing on the top end (now it's 30* BTC at 5000) ??

I want to be around 5400 at WOT. I am thinking that labbed 24's would hit the limiter and stock 26's would be too much. Maybe labbed 26's with a little more timing on the top end would be the answer??? It seems that most boats my size with comparable HP are running 26's and 28's. Is there anyway to try a set before spending the money on the wrong pair of props? I would appreciate some feedback from those in the know. Thanks-

POOL WHORE

Don't know if this will help you out or not. I have a '91 Top Gun with 468's and baby blowers mated to TRS drives. Ocean running Bravo 26's and full tanks and 2 people hitting 4900 RPM. 5100 RPM when light on fuel. I just had Bronson Hill lab and balance a set of 26's. I tried them this weekend and hit 5100 RPM with full tanks and saw 5200 RPM after 50 miles of running. Should hit my 5400 RPM target. Picked up huge acceleration between 55-70 MPH and 1.5 MPH on top end speed.

Panther

Supercharged or Natrurally Aspirated??? I run 32 degrees of timing on my blower motors and ran 36 degrees timing on my old naturally aspirated motors.

If NA, sounds like you need some more timing but don't expect to gain as much RPMS as you think.

WildWarrior

Our 97 Kevlar Gun with 1.36 ratio Bravo drives Merc 600SCs spun 26s 4/b Bravos to 5400rpms 28s were way to big she couldn't turn em.
Now with 1.35ratios and 850 hp per side we now only spin 29 Bravo I props to 5500rpms.
The guy's swinging these larger props must have a 1.5 ratio, big difference!
I think you should be pretty close with labbed 24s blades.
Good Luck!

throttleup

Were is your Rev Limiter set? The rev limiter on a 502 is 5150 - 5200 usually.

Julie

mjb

Julie- my 502's (mpi's) have been modified...cam, heads etc... When AZ remapped my ecm, I upped the rev limiter to 5500 because my modified engines are making peak power at 5300-5400 rpm. Now I just need to prop the boat correctly to make peak power at WOT.
Do you have any type of exchange or demo program where I could try some labbed 26's ? If they are too much to spin 5400 then I will probably have my 24's labbed over the winter.
Thanks-

throttleup

Lab Finishing produces an increase of 250 RPM, approx. This will put you right were you need to be with your 24P Bravo I props, at 5350-5450 at WOT.

Julie

Panther

Sounds stupid but do Labbed props wear out? I've heard rumors that over time in higher HP boats with the blades being so thin, they tend to loose their trueness. Any fact to that?

CIG3

First Off If Your Running The Stock Compression Ratio, 8.75:1 Your Timing Is Down About 4 Degrees. You Can Comfortably Run 34 Degree On 87-89 Octane. I'd Try That First. If You See A Difference And Want Alittle More Try 36 Degree But Make Sure You Bump Up The Octane To 91-93. YOU SHOULD BE IN THE 74MPH RANGE BEFORE PROPS.

Get The Motors Dialed In First Then Worry About Prop Selection. Throtle Up Is A Good Source When Your Ready.

throttleup

Panther,

Yes, you are correct in that lab Finishing indeed weakens the propeller, as it is much thinnner. The degree of thinness varies, but this is the jist of it. Not everyone is a good candidate for Lab Finishing. For instance if you boat in waters that have a high debris count, then you definately are NOT a good candidate!

Julie