Johnson 90/65 Opinions?

rotus623 said:

P.S. That 90hp can be converted to a 115 if you are ever interested. Thats the same motor I have but Im going 115. Carburetors, exhaust plate and boom. 25hp........

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Is this the only difference and what years does this apply to?

Well,

They made these crossflows from 1978-1998. Two major things happened during this huge span.

1.) HP ratings went from rated at the crank, to rated at the prop. This happened in 1984-85. The 115hp was de-rated to a 90hp. The 140hp was de-rated to a 115hp. That being said, the pre-'85 exhaust manifold needs to be the 140hp, the post '85 needs to be the 115 manifold. These all have the same part number (as far as I can tell) from '78-'97.

If you have a pre- '85 motor, use the pre '85 140 carbs. Post '85, use the post '85 115's. I don't know if the pre '85 140s will work on a post '85 90 block of not. Never done it and the part numbers don't seem to match up.

2.) In 1992 the driveshaft became 7/16" longer. So the gearcases from '78-91 are the same, and '92-'97/8 are the same (for crossflow models.)

So, in short, yes, these are the only differences. You can find them on ebay, but be aware, they can be scarce and pricey. Everyone wants to step up to a 115, nobody wants to step down.

Another difference to consider is that the jet impeller changes a bit from the 65 to the 80. I am going to run the 65hp impeller and see where my rpms are. These motors like to rev up to 5500 so I am hoping that is the mark I am at. It will be fun to do some experimenting.

Also, I am going to put some carbon fiber reed valves in to help with hole shot and allow me to bring my idle down low. I may get my heads milled back to get the compression up and run '93 test. These 100 cubic inch blocks were rated low, hp wise. They are SCREAMERS!! Just never had one on a jet...........yet.

My engine is a 2000 so that leaves me out. Thanks for the info though.

I don't know the V4's as well as I do the 3cyl omc engines, but I think even that late the only major difference in the 90-115 was carbs, exhaust tuner, and maybe the heads were higher compression on the 115. I'm not for sure on that thought so don't quote me. Rotus if you go mod V look at the jet hulls built by the northwest/western boat builders they have a slight v but go to a straight flat pad ahead of the outboard jet intake, and then usually have a chine crimped in along the edges and maybe one other set of chines as well for grip. I've had a mod v boat where the front has a slight v of maybe 5-6 degrees that continued down the length of the boat, it wasn't any smoother riding or better handling than a flat bottom. My current is a mod v with a slight V pointed front but goes to an entirely flat bottom if I had bought it new I wouldn't have spent the extra for the mod v design. If your going to spend money on having a slight v design and your running a jet this is the sort of design that works best with jets in regards to making them handle and run better. There is a reason most of the reputable jet boat makers use this sort of general design to include woolrich, alumaweld, koeffler, etc cause it works best with jets. It helps clear away air before the intake, gives the boat some gripe in turns, it helps lift the hull for fast planning, and can stay on plane at lower speeds. This was just the best picture of general jet boat slight v, delta pad design with a lifting chine. Alumawelds site also explains the bottom design pretty well granted they have fancy names for each bottom. If I was buying a new hull and had the money I'd go with a design like what I'm referencing, but flat bottoms work pretty darn well with a jet, you get tough flat bottoms made pretty cheaply, and they really don't handle too bad when you know what your doing. Just my 2 cents worth. I think once I'm finally to a point a needing a new hull I'll probably go flat bottom due to cost. I've been pretty impressed with my friends 2060 for what he paid for it that he had made in Louisiana. Granted he got a pretty good deal cause we were willing to do all the finishing work he bought just a bare hull. We wired it, put it on the trailer, hung his motor on, put his trolling motor on, mounted the gas tank, and painted it was a lot of work, but he came out pretty well over all.

https://www.alumaweldboats.com/bottom-vee.htm

Eshaw, go to www.marineengine.com. Pull up the 2000 90hp and 115. Look through the parts diagrams. See if the block, crank, heads, carbs, exhaust, and ignition system differs. Takes a few minutes but will answer all your questions there.

Andy, I am looking to do the same with my hull. Most of the builders that I am interested in are far, far away.

The new rhinos are made way better than the one I had. They also include a 3 degree deadrise on all jet hulls. Something for me to consider.........

rotus623 said:

Yea I hear ya. I will have to see how much more the 18' is as opposed to the 17'. Id like to see other OBJ hull options but we just dont have a lot of boat builders around here. Id love to find some boat builders on the east coast that I could get some prices off of.

All in all, Id love to find what I am looking for used, but you know how that goes......

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Well if you want one that has it all here you go
2017 Rhino. 1860. 26" sides. 190 5086 bottom not his 5052
Five 2x4" structural grade Stringer system not architectural grade stringers.
31 gal fuel tank. Minnkota Ulterra .hummingbird helix 9si. Elect anchor. Center console. Rod boxes , larger gunnel rail. 5' front deck. Full carpet. And better yet full 1/2" UHMW. Tunnel. Good trailer
2001 Mercury 200/140 efi fresh complete build. New large power pump for outboard. Hydralic steering
Runs great! $22500. Have every bit of that in it plugs I did most of the labor build and uhmw.

Heck of a boat.

Out of my ball park though.

I run a 1760 xpress with a 115/80 omc. I started with a 90/65 and it turned 5200 rpm. Swapped powerheads, same impeller bumped up to 5450-5500 rpm and gained 2 mph. The proper liner and 80 hp impeller brought the rpm down to 5300.

speed with the 90/65 was 29 mph.
speed with the 115/80 and 65 impeller was 31 mph.
speed with the 115/80 and proper liner/impeller is 32 mph.

Hey Rotus thanks and as soon as the water warms and I finish my deck and patio we can take it out. I am plenty satisfied doing 32 on the water as the motor sits, but good to know it is only a small upgrade to 115. I do fish mostly east of Columbia though I have kayaked near Scottsville and definitely understand the perils in those waters... I am really impressed so far with my boat but need more time in it before challenging new waters like far west on the james and new river...

Samsdad, lookin forward to it.

Josh, thanks for the great info. Going up to 115 really doesnt seem to make much of a difference............ I guess I will run this girl with the 65 impeller and see how she does. I am picking up a 1752 riveted lowe, with max hp at 70hp, for free. I am going to slap her on there and see how she does. Gonna beat the tar out of that boat. :LOL2:

on a light riveted boat that thing will scoot I will be in virginia come sunday should have the weekend of the 10-11 free hit me up if your throwing that thing on then.

on a light riveted boat that thing will scoot I will be in virginia come sunday should have the weekend of the 10-11 free hit me up if your throwing that thing on then.

handyandy said:

on a light riveted boat that thing will scoot I will be in virginia come sunday should have the weekend of the 10-11 free hit me up if your throwing that thing on then.

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Hey thats cool man! You gonna be in VA for a while? Let me know if ya wanna stop by and check out my operation. Got quite a few boats/motors I am working on now.

Buddy backed out on the Lowe, so I am still on the hunt for a decent 17-18' hull. Lots of trackers around here but they are rated for 50hp and .80 gauge boats. Not sure I want to test them out on the rock shoals of the James............

Samsdad1 said:

pics of the boat after much work...

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Hey boss, what is the width at the bottom of your boat??

I will have to measure this evening...

So plans have changed. I am slapping the 80 jet (65) on the grizzly. Shes rated for 75HP so I think shell handle her. Got tired of looking for a decent hull.

I have decided to get a fiberglass CC with my 7 grand and just slap this motor on the Grizz and take my 50hp off there.

forgot to respond with measurements... Bottom is roughly 60"... Good luck with the new motor. just finished painting mine and putting numbers on... cannot wait until I get it out... Maybe Saturday.

Looks good man. You gonna UHMW the bottom or risk it?

UHMW is cost prohibitive for now... so I will risk it... that is why I have insurance on it...

Well fellas, after 5 months of using up much of my spare time and energy on this conversion, she is finally ready to roll!! Got her set up and installed this past Friday and took her to the water on Sunday. Had her weighed down at tournament weight and we were doing 32mph. 2 People, 3 batteries, 12 gallons of gas, full fishing gear, cooler, livewell and 2 people and we were doing 32mph. I just need to add a splash plate on her. Think I got the height set right 1st try, so that's awesome!!

This boat hops right up on plane, and man I'm telling you, I don't think any of this boat is even in the water when we are up and cooking!! The foot hangs down about 3" off the bottom of the boat and Id be totally comfortable running in 4-6" while on plane. I think the 5-6 degree deadrise is perfect for a jet boat. We didnt cavitate one time. I gotta say, Im not missing the tunnel hull one bit.

Here's a video of her:
https://www.youtube.com/watch?v=KGnusXUH7Ow