Boat.Buoy

Hi guys and gals, could you help me out with some Top Gun 38 setup questions?

1996 Top Gun 38
Cobra V8’s, on holley carbs (around 25 hours on them)
Bravo XR Drives (one marked as a Bravo 1 and the other as Bravo 3, but both model numbers show the same on the ID tag)
Matched props, 48-831915 28P & 48-831916 28P
Decent sized K-Planes
Clean bottom, old antifoul.

Boat runs at around 53 knots /60.1 MPH at around 4500 RPM, drives all the way down.

Main problem is once the boat is up on the plane, as soon as you raise the drive trim it begins to porpoise, which makes me think the X dimension is wrong. These Bravo drives are bolted straight to the transom. Please see attached photos, taken with drives all the way down. Engine RPM isn’t getting up as high as it should and before we start chasing faults with those we thought checking the setup would be the best place to start.

Anyone got a similar setup they could send me some images of?

Boat.Buoy

I have lots of pictures to send through but it won't let me until I hit 10 posts, is there anyway around this?

Unlimited jd

iTrader: (5)

It’s a straight bottom top gun, if it’s not choppy and the tabs are up it’s going to porpoise. The drives were pretty deep on most of these. Putting -2 lowers typically helps. You will need to measure the prop shaft depth below the hull to know for sure

Boat.Buoy

Thanks for the reply, I’ll measure the prop shaft depth tomorrow and post it here.

Smoke eater

A couple of quick posts to get your count up will help you get to 10 so you can post pictures

thisistank

There’s a sweet spot. Drives kicked out a little to loosen it up drop tabs a hair to settle the hop down. You’ll feel the back lift but settle the bow down. Straight bottom hulls do not like glassy water. I would avoid running at speed with drives tucked all the way in.

If I understand you right, all you’re seeing is 4500 RPM? something is wrong. And it isn’t the depth of your drives. Those cobras blower motors? How much HP? We were running warmed 525SC’s making about 650hp on our 95 gun with 3A’s and were seeing 75mph at 5800rpm.

Boat.Buoy

Thanks for the feedback, I'll forward pics and prop shaft measurements later

Griff

What HP are the engines supposed to be???

bigfarmer

Get in touch with Tres Martin and he will help you set the boat up to get rid of the Porpoise.

Boat.Buoy

The prop shaft is 5.5" below the hull, measured from the flat hull bottom not the notched transom.

Who makes the best mechanical trim drive mounts for the Bravo XR units?