Inboard ideas for outboard

Things have changed since my last visit ! I like the divide ! So once again I can't just be happy with what I have and I've been brainstorming . Buddy left his old impeller out of his Berkeley at my garage and I got curious and was looking it over and seen it was an "A". Got on the interwebz researching and found out they resize these by turning down the od therefore opening the window wider on the back end , giving the water less area to work against . This raises the rpm, about like changing gears in a rearend. They also clip the fins back some but I think that's to take it down another size. Has anyone ever taking this approach on there liner ? There cheap enough I might try it on a larger impeller and liner I have that's just a bit to large for my motor to pull.

I like the way you think. :mrgreen: Some more food for thought. Outboard jet offers a 6 5/8 and a 6 5/8CB (cut back trailing edge) for the 40hp-60hp 2 cylinder OMCs using the L series pump.(same pump as the 60-75hp 3 cylinders) Might be worth a shot to cut the liner down like your talking, be cheaper then cutting back the impeller. I'll take a look through my impeller and liner collection and see what I can come up with. I've got 6 1/8"s, 6 5/8"CB, and 6 7/8"s I'll see how they match up with the liners.

Well of course ya do , your about the only other person in here that wants to go fast with equipment that shouldn't ! I figure if it works its another step in between sizes . I replaced my liner earlier this year might take my old one down and see how it acts. Kind of surprised nobody has thought of this before , but then again rarely ever do outboard and inboard jet theories coincide , even more rare one person having performance knowledge about both

I think that ledge would be the perfect distance to go down , that's what sets outside of the top of the shoe

Here' 3 different impellers. 2 fit the large series pump and the 6 1/8" fits the medium series pump.

I'm interest to see what happens with it. My dad had talked about it back when I ran my 40/28 and I was going to try it but then I realized that the 6 1/8 is already flush with the top of the liner, I'd forgot about it since then but now I'm running the 60/40 I can try it out. It has to make some kind of difference. Looks like I got a project this week.

On your cb is it the fins or the liner or both that are cut back ?

The 6 5/8"CB just has the trailing edge of the blades cut down. You can see how much of a miss match it is from the top edge of the liner. That lip almost has to slow the water down some what as the blades are trying to sling the water off. I guess it depends on how the water is being directed weather the impeller is pulling water straight up and the waters just rolling out of the top of the liner or if its throwing water out to the sides once it gets above the liner. Or it might help direct water or kind of helps separated the incoming water from the water leaving the pump but if that was the case you'd think they'd built a lip on the 6 1/8" liner too. I don't know just brain storming all the possibilities.

Well I did this last night and let me tell ya I learned every way not to do it , if I cut down a good one ill take it to someone who can do it correctly . 1/3" thick alum don't sound like much but it ended up being quite a job. I ended up going a little more than I really wanted to and overall height is 2 1/4" . Try to slap it in and test it out in the next day or two

Is that the liner from your outboard jet you cut down? I haven't really tried any mods with the outboard jet other than straightening up the intake bars that were bent up by the previous owner. I don't run the outboard hard since I have the jet sprint boat to play with when I feel like blasting around.

Is that the liner for your 6 7/8 or the 7 3/16?

Yea it's my old liner out of my 6 7/8. Ima try to throw it in tonight and take it out to a local conservation lake to see what it does. Hate to haul it all the way to the river to find out it's worthless lol

Well that was uneventful lol . I broke my cheapie eBay tach thing so I didn't know what kind of rpm I was spinning , my phone died on the way down there so I can't say what speed I was goin so it was all seat of the pants. It really felt like normal except I loss alot of top end speed but didnt sound like I gained any rpm . So maybe my motor doesn't wanna breathe on the upper rpms. It did feel like it jumped on plain a bit easier and the boat carried a little higher up/ farther back . So ...... Thoughts ???

It's hard to say. Maybe it helped out the hole shot because it allows the water to get moving a little easier but once opened up not having the upper part of the liner the flows not controlled as much or not having the lip allows water in the pump to flow back on to the impeller some what. Don't know just brain storming. Did you shim your impeller back up to this liner when you swapped this one in?

After a little bit of time in the garage measuring the plot thickens. So what I've ended up doing by taking a inch off the top was turned my 6 7/8 into a 6 3/8. From what I gathered tonight with the two I have is for every 1/2" you take off of the top you lose roughly a 1/4 in diameter. The difference on the inlet size of my two is roughly 1/4 difference from each other. Next ill measure distance between the blades going up the impeller to see if theyre different . Not quite grasping what really affects what here but a trip to the river with a tach and a GPS is about the only way ill figure it out for sure. I didn't have enough room at the con. Lake to really run out and get a good feel for it. And it was close enough when I put it in it didnt need shimmed, maybe would have got one extra on top if I was lucky.

All of these are loose measurements but you kinda see the pattern