Crossflow 110 1986 mods

**keefallan** · 09-27-2020, 04:17 PM

I had a 82 140 motor a few years back........I ended up scrapping it minus the lower. The carbs were 1-5/16 then. I think the 1-3/8 were only on the 70's 140 motors and I dont know the years. The bubble back 110's and 115's all had the 5/16 carbs

**slowracer** · 01-13-2021, 03:45 PM

Update to boats performance. I've gathered a set of 1 3/8" carbs and a set of '76 140 heads, still on the hunt for some 135 heads but will proceed with the 140's in the build if i haven't found them. Have sourced a limitless brain as well.

Here's why, before setting off on the engine build i thought best to set a baseline for the hull and set up. Ran through all the props i could get my hands on and learnt a bunch. Ran a 12 3/4" 21p and 23p SST to 5400 at 54mph (gps). then shifted and threw on a 13.5 22p raker and ran to 5k at 54mph. Learned that the little motor clearly wants to spin 12 3/4" to 13" diameter as the 13.5 is too much.

Here's where i start getting lost and presume my props can't be "as stamped", the 21p has a theoretical maximum speed of 54mph at zero slip which is what it ran. So the prop has to be pitched higher.
Ideally i had a goal in mind of reaching a boat speed of 65-70mph which i still feel is very realistic but prop selection at 13spline plus the 2:1 gear ratio do add challenge. I'm hoping for a conservative 6000rpm post rebuild (with limitless brain) which paired with a 26 or 27p should easily see me there. What size prop have you all managed to spin on the small v4 box and 2:1 ratio?

I say a conservative 6000rpm as everything i can see and read suggests i should be able to keep the motor alive easily enough at 6k as many of you are seeing numbers much higher post build.

**keefallan** · 01-14-2021, 05:39 PM

My stock 112spl would live at 6000-6100 completely unmodded.........trimmed out. The 140 heads are good heads. If you have them, why bother going after the 135 heads. Besides, the 135 heads dont have coil mounts on them.......you'd have to fab brackets for them.

**Motv18** · 01-14-2021, 05:57 PM

Stainless prop have cup. This cup can have them perform over rated pitch that’s derived from convoluted math and theory.

**racervboat** · 01-14-2021, 07:58 PM

Slowracer you never mention what boat you have , so that means all this don't matter until we know what you have?

**slowracer** · 01-14-2021, 09:56 PM

Thats fair. Small 15ft pad boat. Bullet 1500.
Restricted prop shaft height to 5" under pad so LWP not really beneficial.

**racervboat** · 01-15-2021, 10:33 AM

So what class are you racing in,and whats the powerhead mods you can do.I used to race formula-vee mod and built all my motors omc c/flows spun em at 72-7300 never blown one up and we beat the hell out of them on a 1 mi course back to back 10 lap heats.

**slowracer** · 01-15-2021, 02:56 PM

Its a mono class, can run up to 1800cc before going up a class. Or class lower is 1250cc.
Engine mods are restricted to no porting, but can run a class up and unlimited in what i can do as long as i keep prop shaft height at 125mm under pad. Races are long course and 60-70km events.
Looking at previous average speeds for the class the boat will be hard to beat in flat water if it can sit and be drivable at 70mph. Mathematically as i said even a conservative 6000rpm with a 27p should be able to run this easily as long as the motor can spin a 27p. Then its just a hunt to find one and start testing again.

**perfmarine1** · 01-15-2021, 05:27 PM

Don't waste your time with a 110hp,always start with the motor with the most hp in a powerhead class and mod up from there. Go find a 140hp and go up from there. Easy to find a 140 they are everwhere, people have been pulling them off for 4 strokes since they came out. Couple years back I had someone give me a 82 140 johnson,it now powers my duck boat with a jet on it after a quick rebuild and light mod.

**LakeFever** · 01-15-2021, 08:24 PM

6k is nothing. I spun a stock 115 to just over 6k for 25 years. No mercy I ran that thing wide open as long as I felt like and many many times every single time out. 6500+ is where I would aim if you can get it there. Props are more hull dependant than motor just keep buying and trying is really the best way to see what is best overall. Like most you will probably end up with a prop that’s much slower top speed than the fastest one you have because it’s the most fun to drive

**Revenge22** · 01-19-2021, 10:12 PM

the 110 is ported the same as a 140, had the same exhaust, carbs (accept for the 1978 & 79 motors which are the 1 3/8). Literally the only thing different would be to add tighter heads (I like the ones from the 85' 115hp or 81-84 140hp, as you can safely run 93 oct), and reed stuffers with CCMS reeds. Now you have an easy 130hp at the prop on a fresh motor.
Just rebuilt an strange one: the GT100. Has the 135/140 porting, but flat back exhaust and baby 1 3/16 carbs with 88/90hp heads. great low end though. probably last a heck of a long time!

**keefallan** · 01-20-2021, 04:39 PM

Originally Posted by Revenge22

the 110 is ported the same as a 140, had the same exhaust, carbs (accept for the 1978 & 79 motors which are the 1 3/8). Literally the only thing different would be to add tighter heads (I like the ones from the 85' 115hp or 81-84 140hp, as you can safely run 93 oct), and reed stuffers with CCMS reeds. Now you have an easy 130hp at the prop on a fresh motor.
Just rebuilt an strange one: the GT100. Has the 135/140 porting, but flat back exhaust and baby 1 3/16 carbs with 88/90hp heads. great low end though. probably last a heck of a long time!

I always wanted to peek into a gt100. I thought it was just a gimmick bubbleback 115. Now I know.

**Revenge22** · 01-20-2021, 10:02 PM

Originally Posted by keefallan

I always wanted to peek into a gt100. I thought it was just a gimmick bubbleback 115. Now I know.

I found it flopped over in a junkyard. got it with the controls and another 115hp 1983 for $150. all standard bore, so lucked out. really interesting one, for sure. I think it had stiffer mounts, too but will need to check. can't wait to fire it up in April. has the single pack ignition, too so more economical .

**keefallan** · 01-20-2021, 10:13 PM

It sounds like it was a 115 build from 1984........small carbs, flatback exhaust etc.........meaning that that is what they assembled back then to build a 115. If you check out that 83 motor, I bet its identical to the gt100, except for maybe the carbs..........1-1/4 maybe?

**Kevin715** · 04-28-2021, 11:46 AM

I saw a thread somewhere that said the V6 crossflow GT engines came with scalloped pistons from the factory , did you happen to notice if the GT100 had them ?
I just looked at a 1990 GT100 last week .