guimond47

i have a thundercraft diablo 230 23ft boat. It had a modified mercruiser engine 350 - vortec heads and eldelbrock intake RPM. Then the intake gasket took a dive and let water in the oil and spun the bottom end. That being said. it was time for a 383 Stroker build. From what i can remember it was a 53mph On GPS boat with a 19p Mirage Prop at 4400 RPM WOT.

Now over the past year I built this stroker.
It has a sbc 400 crank in a 350 short block bored over .30.
Flat top two cut relief KB pistons.
.028" head gaskets.
Aluminum heads 64cc , 205CC intake runner.
1.60/2.02Valve sizes.
Comp cams 295-124188
Retro fit hydraulic roller lifters
1.6 ratio roller billet rockers.
push rod length is perfectly set up.
Eldelbrock Performer dual plane intake
STOCK quadraJet 800cfm carb i believe.
fuel pressure gauge 3-6 psi
holley marine intake filter
Stock mercruiser ignition system at 32 degree advance.
.030 quench deck to piston height.
Stainless marine headers

If im missing something please ask.

So I took it out for its first ride and was not impressed at all. Out of the hole the boat is impressive. but the top speed was only 54-55mph GPS reving at 5200 rpm with the 19p mirage prop. That prop is only 14 1/4" diameter.

I ordered a 23P x 14- 1/4" prop on ebay. Took it out. Out of the whole it sounded like i had a spun prop hub. It was slipping like a clutch. till the boat got up on plain then caught water and took off. i got 52mph at 4500-4600RPM. I am thinking prop diameter is not large enough for that pitch and weight of boat that its slipping.
The hubs in the props are plastic. no rubber.

Why havent i gained speed? do i need to retune my Carb? bigger jets for the stroker engine? cause thats the only thing i can think of. Also i am thinking of trying a Turning point Mach 3 prop that is 15.6" diameter 21P. hopefully prop slip will then be minimized.

ANY advice greatly appreciated as im about to buy a jet stage 2 quadra jet soon.

underpsi68

You must retune the carb for the new engine. You are probably lean. Hope you didn't cause any damage. Did you pull the plugs to check tune ?

guimond47

AllDodge

iTrader: (1)

Agree, motor needs tuning

SB

iTrader: (1)

What cam and what fuel psi at WOT at top rpm ?

guimond47

SB

iTrader: (1)

I've read the 1st post 10 times. I don't see it. So please flatter ,my old age. Thanks.

I tried.

guimond47

here is the cam part number 295-124188. it is comp cams.

compedgemarine

what gear ratio is your drive? based on a given ratio and the numbers you posted your slip went up 10%+. no amount of tuning is going to fix the slip numbers. if you have the ratio I can give you better before and after slip numbers.

guimond47

my ratio is 1.50... i've tried to use the mercury calculator but theres no prop diameter input...