85hp johnson thinking about squeezing more hp out of it advice ? 1977

[Devonaaron]

I have a 85hp Johnson 1977 on my 16' glastron trihull I am going to be going far distances and I think I wanna get there faster like 30 miles round trip. I rebuild motors as a hobby and do it on the side off of craigslist for money time to time. The fact of the matter is I really work on the 2 and 3 cyls. So the v4 crossflow is not my specialty. At first the motor would only run at half choke and after going threw 2 sets of carbs and another fuel pump I realized it wasn't that. This motor was rebuilt painted and sat for 5 years and I bought them yes there were two I got them for 400 with a bunch of props and hydralic steering control box etc a great deal none the less im going to sell the other 85hp. Anyways I would like to know some opinions and FACTS =) as what I should do to get a good amount of hp. I changed all electronics and note it is rebuilt and can handle a load not that I want to stress the motor but I plan on converting to a 140. I already have a 115hp carb set, But I was thinking about ether shaving heads or getting the stock high compression heads as well as the bubble back exaust. I really have no interest in changing the reeds due to the fact I am not sure they will really do anything. I dont want to tear the block apart but if I could polish the intake up a bit or something around there. Not to crazy where I lose reliability or have to enrich oil mixture just enough to make me cruise at around 40 and top out at 60MPH. let me know Thank you very much also ill say again I have the 85hp Johnson 1977 (not TnT) also whats the big difference between the older ignition I have and TnT. I did just replace the melted stator and rectifier as well as the power pack, I believe thats where my idling problems started from for the most part and something backed up on the stator so a new power pack and known to be good rectifier. So were going from there. Thanks

 

[Faztbullet]

Re: 85hp johnson thinking about squeezing more hp out of it advice ? 1977

Best thing to do is get it running good ,sell it and get a 140hp with trim. You are starting with several disadvantages right off the bat: (1) No trim (2) Good used trims are hard to find for these years (3) Its a small bore motor (4) bubble back wont fit this block (5) you dont and cant shave head on a crossflow to increase compression as piston will hit top of head (6) 115 carbs may increase output about 5hp

 

[emdsapmgr]

Re: 85hp johnson thinking about squeezing more hp out of it advice ? 1977

Fastbullet pretty well summed it up. I had a 72 small bore V4 100 hp years ago. After a lot of fiddling with jets, I got a set of 125 carbs to run well on it. Also dismantled the engine and ported it and installed the rubber intake stuffers. In the end, after all that effort-the engine picked up about 400 rpm. About one prop size. I was really happy with the results, but looking back-not sure they were worth the time invested. Look for a big bore V4.

 

[F_R]

Re: 85hp johnson thinking about squeezing more hp out of it advice ? 1977

Along with all the work and expense to modify the motor, be sure to invest in a GPS. You will need it to detect any increase in speed.

 

[jay_merrill]

Re: 85hp johnson thinking about squeezing more hp out of it advice ? 1977

An 85 into a 140? That will very definately be a neat trick.

What I think you really need for this conversion, is a trinukularthingamachigamabob.

Seriously .... you can't do what you want to do. Just go find another motor and go fishing.



???

 

[Devonaaron]

Re: 85hp johnson thinking about squeezing more hp out of it advice ? 1977

Thanks guys, I was just trying to get some insight on what I could do to get some HP out of it. Also it dose have power trim its a very nice motor I just wish I could do more with it. The thing is im not trying to fish as much as I should I like island hopping and going to the clearwater beach in FL when it starts to warm up its defiantly the place to be. Also can someone tell me the difrence between the 85 and 115 I know the carbs are different but what else ? thanks again guys

 

[emdsapmgr]

Re: 85hp johnson thinking about squeezing more hp out of it advice ? 1977

It's pretty easy to determine what the parts differences are from the original OMC factory parts list. Check this web address and look up your two engines: epc.brp.com

 

[F_R]

Re: 85hp johnson thinking about squeezing more hp out of it advice ? 1977

The main difference is 1/8" larger bore on the 115. 3.375" vs 3.500". And that is why it has larger carburetors. Putting the larger carbs on the smaller powerhead may actually decrease performance. Sorry, there is no magic bullet.

 

[Chinewalker]

Re: 85hp johnson thinking about squeezing more hp out of it advice ? 1977

As said above - your motor is a 92-cube powerhead. If you want to go through the trouble of modifying a motor at LEAST start with a 99 cuber...

 

[iwombat]

Re: 85hp johnson thinking about squeezing more hp out of it advice ? 1977

Yep, that's about it. Keep looking for a '75-'77 115hp powerhead. Stay away from the XL shaft '77, it was an early introduced '78 powerhead.

 

[G DANE]

Re: 85hp johnson thinking about squeezing more hp out of it advice ? 1977

That being said, I start to wonder why you cant go 30 Mph with a 85 HP on a 16' Glastron, correct setup should give you a little more if the boat isnt waterlogged. That is if the motor is running, setup and propped right.