Next K/B 7.5 mods

[LC2nLS6]

I built a custom 1/8 ply tunnel hull back in college (late 90's). It was my first boat and I built it off the top of my head with some spare wood from my R/C plane hobby. See pics below.

I have a used, complete K/B 7.5 which I got off ebay in 2003 for its piston/sleeve/rod. However, I decided to just use the whole top end on my prather 32 racing tunnel. The bottom end has a tuned pipe, but I think it is too big though I'm used to stock K/B 7.5 engines. I've never run a pipe before.

This engine has a beefy polished rod, a head that is engraved with H.E.W., a lightened flywheel, a trimmed skeg and the tuned pipe. It ran fast without the pipe on the prather 32. So I was thinking of putting this engine on the custom wood tunnel and try the pipe out. I replaced the lower bearing with a barely used stock one, but the top one is making noise and I think it needs replacement asap. I saw the thread on KB bearings so that was helpful. This top housing doesn't have the oiling hole like my other two 7.5 K/B OB's.

What other mods would you all do to this engine? There are no shims on the heads and it loves 35-55% nitro.

I also have a stock 7.5 that broke a conrod which needs a new piston, sleeve and conrod to get going again. Is that a better engine to start modding since it has the oiling hole on the top housing?

I'm running a prather 235 prop right now. I also have a prather 230, octura 447/3, x452 and 1950/3 I can try out on this boat.

The wood blue boat is about pound heavier than my prather 32 fiberglass racing tunnel. It also can handle very rough seas with its crazy sharp sponsons and triangular leading tips. I've submarined it completely underwater (completely as in the entire boat, engine, antenna) dozens of times and it pops up and keeps going. I've run it flat out in 6 inch seas.

 

[aussieboater]

That has some serious flywheel machining done

 

[Geraghty]

That has some serious flywheel machining done

That was a "stock" K&B flywheel in the '80's.

 

[SayMikey]

That has some serious flywheel machining done

That was a "stock" K&B flywheel in the '80's.

GOOD PIPE LOOKS LIKE A EQUI FAT BELLY

 

[LC2nLS6]

GOOD PIPE LOOKS LIKE A EQUI FAT BELLY

So the pipe should work fine then?

 

[rmprecision]

That has some serious flywheel machining done

That was a "stock" K&B flywheel in the '80's.

GOOD PIPE LOOKS LIKE A EQUI FAT BELLY

Yep it is a Equi pipe.

I had one on my old K&B 45 and worked well.

I did have my modified a little thou.

Mine worked a 10 and 3/4 inches

with a modded head button and turbo crank mod

 

[Geraghty]

That has some serious flywheel machining done

That was a "stock" K&B flywheel in the '80's.

GOOD PIPE LOOKS LIKE A EQUI FAT BELLY

Yep it is a Equi pipe.

I had one on my old K&B 45 and worked well.

I did have my modified a little thou.

Mine worked a 10 and 3/4 inches

with a modded head button and turbo crank mod

Actually guys the Equi "Big Belly" 7.5 outboard pipe was a Equi 3.5 header section[diverging cone] with a larger header pipe and part of the Equi 3.5 converging cone with a larger stinger....with an Irwin 7.5 "Nitro" pipe center section weld in between them.

John probably made less than a dozen of them one at a time so the pipe you have is very rare.I haven't seen one of these for probably 15-20 years.

There are a bit better 7.5 pipes built now but the Equi Big Belly worked pretty dam good.

 

[LC2nLS6]

Actually guys the Equi "Big Belly" 7.5 outboard pipe was a Equi 3.5 header section[diverging cone] with a larger header pipe and part of the Equi 3.5 converging cone with a larger stinger....with an Irwin 7.5 "Nitro" pipe center section weld in between them.

John probably made less than a dozen of them one at a time so the pipe you have is very rare.I haven't seen one of these for probably 15-20 years.

There are a bit better 7.5 pipes built now but the Equi Big Belly worked pretty dam good.

I ran the boat today with the Equi pipe and it ran well! Definately sounded cool at WOT