Prop vs Performance

Jim,

My 289 in an old Mustang hull has the 12 x 14 and runs past 4400 RPM. Interceptor, rebuilt to 030 over, Performer Intake, Carter 4 BBL with 12 deg wedge plate, bigger valves in the head, 165 psi Compression. Still breaking her in so 4400 is Max for now, but it's no where near the limits.

I'm changing prop's to the one Keith recommended. I want low end torque, and quite frankly, the 4 BBL and HP Intake reduces the engines low end torque so I may have bought stuff I don;t need. I think your 2 BBL set up has the low end covered, but depending on your cam and valve size going to a 4BBL may not help you past 3500 RPM....if that's your question?

Exhaust hoses are tricky as well as the old manifolds and could be restricting your high end performance and or a restriction in the hose cold do the same.

The 289 should push the 12 x 13 higher IMO. How much compression is left in your '68 Stock engine?

Hope this helps.

Jim,
Your engine being a 2V is most likely the 165 HP version of the 289, although I believe they made a 190 HP 2V version during several years. 4000 rpm may be a little on the low side but not by much for that engine. If anyone else has a manual on that engine they can check it or I'll check mine this evening for the recommended max rpm. I would expect the boat to run 38-43 mph. The 4V Mustangs of that hull design normally ran 44-48 mph from what I've seen.

Also, the last couple of older boats I've been on that had original tachs were observed to be significantly off, so I'd verify that to make sure unless you have a newer one. And if you've got a boat that's been thru multiple hands and has a prop stamp dated somewhere back long ago, there's a good chance that it may not be exactly what it's shown to be. We wasted a lot of time once working on a perfectly good engine trying to find out why it was way down on power and it was the prop holding it back the whole time.