Johnson 112 vs 90 questions..

[bwilson2626]

For almost 15 years I ran a 1996 90spl on my boat, a double wide & deep all weld aluminum tunnel hull. Ended with a crack in the block. Bought a used 1994 112, had a remanufactured power head installed, am using the same prop from the 90, and see no noticeable difference in power or top end.. does that make sense?

 

[saltchuckmatt]

For almost 15 years I ran a 1996 90spl on my boat, a double wide & deep all weld aluminum tunnel hull. Ended with a crack in the block. Bought a used 1994 112, had a remanufactured power head installed, am using the same prop from the 90, and see no noticeable difference in power or top end.. does that make sense?

I'm going to vote yes on this.
90hp vrs 112hp.... Same prop.
Not sure if you have a tach but you could check to see if your engine is reaching peak horsepower and then adjust the propeller. You would need to go up to a 6 cylinder to see a big increase in performance.

 

[flyingscott]

No there should be a difference. The 112 Is just a rebadged 115 so you technically have 25 hp more. What is your compression? What are your Rpms at?

 

[bwilson2626]

I'm going to vote yes on this.
90hp vrs 112hp.... Same prop.
Not sure if you have a tach but you could check to see if your engine is reaching peak horsepower and then adjust the propeller. You would need to go up to a 6 cylinder to see a big increase in performance.

I do have a tach.. at 5500rpm I'm getting about 31mph, same as the 90hp got.
Should i change to a different prop? Pretty sure it's a 13.5 x 17 SST

 

[saltchuckmatt]

I do have a tach.. at 5500rpm I'm getting about 31mph, same as the 90hp got.
Should i change to a different prop? Pretty sure it's a 13.5 x 17 SST

That's about where you want to be rpm wise. I had a 90 for many years then switch to a 110 bubbleback. They were very close in performance.

 

[bwilson2626]

No there should be a difference. The 112 Is just a rebadged 115 so you technically have 25 hp more. What is your compression? What are your Rpms at?

I havent checked compression yet. I'll do that tomorrow.
It's got 13 hrs on it now, so I only got it up to 5500rpm's for maybe 5 seconds, just to check top end. Everything I've read tells me to run for a 20hr break in before really holding the rpm's up.
It just seems that 22 more hp would be noticeable, and it's not at all. Feels exactly like the 90 did on take off and cruising.

 

[saltchuckmatt]

I havent checked compression yet. I'll do that tomorrow.
It's got 13 hrs on it now, so I only got it up to 5500rpm's for maybe 5 seconds, just to check top end. Everything I've read tells me to run for a 20hr break in before really holding the rpm's up.
It just seems that 22 more hp would be noticeable, and it's not at all. Feels exactly like the 90 did on take off and cruising.

You are supposed to check max rpm at WOT with the motor trimmed up so you may be a little over propped. 30 seems slow but how big is the boat and what does it weight?

 

[bwilson2626]

You are supposed to check max rpm at WOT with the motor trimmed up so you may be a little over propped. 30 seems slow but how big is the boat and what does it weight?

I dont know exact weight, but its 18' x 80" and super deep. Was originally a coastguard vessel that I stumbled upon. Built like a tank.
When my 90 was in its prime, I'd see 31mph at 5500. I'm hesitant to run the 112 that high until the 20 hr break in is done... but like I'd said previously, I did get it up to 5500 for a few seconds today, just to see.

 

[flyingscott]

You are supposed to check max rpm at WOT with the motor trimmed up so you may be a little over propped. 30 seems slow but how big is the boat and what does it weight?

How is he over propped with a 90 hp prop on a 115?

 

[flyingscott]

Are you sure it has a 112 powerhead on it?

 

[saltchuckmatt]

How is he over propped with a 90 hp prop on a 115?

Well if he goes WOT and trims it out and he pulls 6000 rpm's out of it then he needs to take some inches out of it.

Sounds like a heavy boat with maybe some hull drag. Could be lots of things

 

[flyingscott]

Well if he goes WOT and trims it out and he pulls 6000 rpm's out of it then he needs to take some inches out of it.

Sounds like a heavy boat with maybe some hull drag. Could be lots of things

That's not over propped that's under propped. He would need to add inches.

 

[saltchuckmatt]

That's not over propped that's under propped. He would need to add inches.

Okay, well I'll have to recheck that...

Screw size might be to small. 13.5 hmmm I have, what I believe is, a 15 inch one on my 115 but it an Etec so hard to compare. So damn big that it just clears the cav plate! (1/4inch)

Props are tough....lots of things in trying to figure those things out.

 

[flyingscott]

Good luck with your motor. Buy a factory manual and do the tests.

 

[flyingscott]

Break your motor in then come back.

 

[saltchuckmatt]

That's not over propped that's under propped. He would need to add inches.

Yes, your correct. What was i thinking. Multi tasking in the kitchen and not thinking correctly. And your also correct, get that thing broke in and then see what the R's do and maybe put a 19 inch pitch on there. Should give you more top end speed.

One thing to note...the 48 and the 88 and the 112....in my humble opinion just scaled down motors so Brunswick could sell them cheaper.

 

[flyingscott]

Yes, your correct. What was i thinking. Multi tasking in the kitchen and not thinking correctly. And your also correct, get that thing broke in and then see what the R's do and maybe put a 19 inch pitch on there. Should give you more top end speed.

One thing to note...the 48 and the 88 and the 112....in my humble opinion just scaled down motors so Brunswick could sell them cheaper.

Let's start with Brunswick never owned OMC. The 48 and the 88 we're budget motors but mechanically they are identical to the 50 and the 90. The 110/112 we're full featured motors just cheaper than the loopers that were replacing them.

 

[saltchuckmatt]

Let's start with Brunswick never owned OMC.

I know that, but they contracted with them and put those on Bayliners all over the place. I never saw them on other boats but maybe they did. Are you saying they weren't scaled down motors?

 

[jimmbo]

I will assume that the 90spl is a Crossflow, as is the 112.
Both are 99.6 cubic inch Blocks, and there is supposed to be significant differences in the Porting between the two engines, The 90 makes its best power, around 4900 rpm, propping it to rev higher actually reduces its HP. Now the 112, does it have the Bubbleback/Turtleback Exhaust Cover, or is it Flat? Either way the 112 should be able to turn a prop with 2 more inches of pitch and keep close to the same rpm as the 90 did.
I doubt you have the History of the 112, so it might not have the original Powerhead either
So lets find out what condition the 112 is in. Compression test is the first thing

 

[flyingscott]

I will assume that the 90spl is a Crossflow, as is the 112.
Both are 99.6 cubic inch Blocks, and there is supposed to be significant differences in the Porting between the two engines, The 90 makes its best power, around 4900 rpm, propping it to rev higher actually reduces its HP. Now the 112, does it have the Bubbleback/Turtleback Exhaust Cover, or is it Flat? Either way the 112 should be able to turn a prop with 2 more inches of pitch and keep close to the same rpm as the 90 did.
I doubt you have the History of the 112, so it might not have the original Powerhead either
So lets find out what condition the 112 is in. Compression test is the first thing

He said the 112 power head is new and still being broken in.