[ampcarfan]

Hello to all!
A few months ago I picked up a 92' Diablo for a song. The boat was somewhat neglected but not abused. This is far from being my first boat so I knew what to look for and other than the drive being trashed from the previous owner dragging it up the launching ramp, and a ton of cosmetic needs, I saw a diamond in the rough.
I got the trailer work done, and all the mechanicals done and went to town sanding, compounding, polishing and waxing in the last few days (If I never hold that buffer again it will be too soon!)
After getting the new drive installed and doing a complete service on the engine (4.3), I took it out for a shakedown run. The first thing that struck me was that these boats are well built. It had a SS 19" prop on it, but during the initial run it planed and revved quickly to 47 mph but was turning 5400 and still climbing when I backed it down. I ordered a new 21" TP Hustler and installed it yesterday (Hopefully this will be a good choice as I can't imagine needing to jump to a 23"..lol)
Tomorrow will tell on speed and rpm.

[ColoradoDiablo]

Deja Vu
That thing looks awfully damn familiar.
Congrats and welcome to MOC amp!

[mikeyt]

Welcome and congratulations on reviving that Mariah! You said it reached 5400 rpms with room to keep climbing? First thing i would do is check that tach. With a 19" prop you shouldn't see anything more than 5000- 5100 and normally with a 21" pitch you wont have much in the way of hole shot on a 4.3 There's a small dial on the back of the tach marked 2-4-6-8. Give it a few spins and then re-set it to 6 cyl and see if that makes a difference.

[ampcarfan]

Thanks guys.. Will do on the tach check!

[gahooligan]

There is also a calibration screw but you need a reference tach to set it with

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[ampcarfan]

Well, with the 21" Turning Point Hustler installed.. the boat (trimmed and on smooth water) ran 50mph (gps matched the speedo almost exactly) and turned 5100rpm yesterday. It was just my son and I, half tank of fuel and no extra gear. After verifying those numbers on a prop calculator (Showed .13 prop slip) Those numbers seem to jive? Also with this prop, the boat was able to stay on plane down to 2900rpm and the "perfect" cruise seemed to be right around 3600... Smart tabs will be here Wed

[ColoradoDiablo]

Your gonna love em on the little "D"

Which ones did you get ,the SX or the ST series?
I put SX series on mine and love them.

[mikeyt]

The rpm's are still high, particularly for a 21" pitch prop but if its working and you're happy with the way it performs that's all that matters.

[ampcarfan]

CD, I ordered the SX, and I'll have to mount mine just about like you did. Mikey, I know that's still high, but I figure with the slight drag from the tabs, 4-5 people, gear and a full tank of fuel, that should put me right at the top of the recommended range (which should be perfect for tubing) .. don't you think? Btw, I spun the selector on the tach and then back to it's original slot. It's a Faria and seems in pretty good shape.

[ampcarfan]

Hey CD, I almost forgot... What setting on the tabs worked best for you? Nauticus recommended the 80s', but after reading all the posts, I ordered the 60s'.