90hp v4 crossflow to 140hp build

[juanallen78]

Hi All. Just found and joined iboats.
I hoping to find some info from the guru's.

I am from sunny South Africa. Where anything boat related comes at the cost of a house.

That said I got a fiberglass bass boat and had to rebuild it from the hull up. Got a johnson v4 crossflow 90hp on it and life was great. Until it wasn't. Long story short I had 2 pistons that I have to replace. Bores cleaned up to with in spec. I have a 140 hp engine for parts. Block was junk.
I have read a fair bit on the mods some folks do to go from 90hp to 140 is spec, and man there's quite a bit that some guys do.

I want know since she is already open is it worth lifting the port timing to that of the 140. I have the bubble back exhaust, the 140 heads and carbs. Also plan to smooth out and polish/ match all the intake and exhaust passages. The boat is 17 foot and fully loaded with gear and kids she is around 1000kg or 2200pounds. She has a worked 17 pitch prop and was running at 58 to 60 kph. About 37 miles per hour at 5000rpm. Wouldn't mind get some more ponies out of her if it won't kill reliability. I also plan to do fiber reeds. Any advise would appreciated.

 

[jimmbo]

Welcome to iboats
To turn a 90 into a 140, the Porting will have to be modified, the Block will also need machining to install the Components for the Bubble Back. The Carbs on the 140 are different, as they have to flow more Air.
Some 140s also had Stuffing Blocks in the Crankcase side of the Reed Plate, to reduce Crankcase Volume.
I don't know what yr your 140 is, but there were some differences(besides the Bubble Back) in the Exhaust System over the yrs between the 90 and 140
You realize that 140 has a weaker Hole Shot than the 90, due to the Torque Curve moved to a higher Rpm Range, low Rpm will be weaker, add that you will likely need to go up to a 19in prop to keep the Rpm around 5400, which also slows Hole Shot.
Fiber Reeds, the Only advantage of them, is when they fail, they won't chew up the Engine. They will need to be replaced after a period of time. In over 50yrs, I have only seen one Stainless Steel Reed fail.
While all Crossflow V4 will eventually succumb to Piston Ring Issues/Failures, the 140 is likely to do so sooner, simply from the Higher Stresses imposed by the higher Hp

90hp ports


115-140 Ports

 

[juanallen78]

Welcome to iboats
To turn a 90 into a 140, the Porting will have to be modified, the Block will also need machining to install the Components for the Bubble Back. The Carbs on the 140 are different, as they have to flow more Air.
Some 140s also had Stuffing Blocks in the Crankcase side of the Reed Plate, to reduce Crankcase Volume.
I don't know what yr your 140 is, but there were some differences(besides the Bubble Back) in the Exhaust System over the yrs between the 90 and 140
You realize that 140 has a weaker Hole Shot than the 90, due to the Torque Curve moved to a higher Rpm Range, low Rpm will be weaker, add that you will likely need to go up to a 19in prop to keep the Rpm around 5400, which also slows Hole Shot.
Fiber Reeds, the Only advantage of them, is when they fail, they won't chew up the Engine. They will need to be replaced after a period of time. In over 50yrs, I have only seen one Stainless Steel Reed fail.
While all Crossflow V4 will eventually succumb to Piston Ring Issues/Failures, the 140 is likely to do so sooner, simply from the Higher Stresses imposed by the higher Hp

90hp ports
View attachment 416365

115-140 Ports
View attachment 416366

Thank you Jimmbo. I appreciate you're imput. Weirdly enough my 90 had the bigger carbs and intake stuffers in it. As for the year on the 140 I don't know either. I am aware of the ports needing to be modified to get to 140 spec. How ever since the hole shot will suffer I don't think this is the route for me. So I was thinking of just squaring the ports with a radius in the corners, so as not to hang up a ring. Also then adding the 140 heads ( they are tighter then the 90) and doing the bubble back. So now my question would be, will it give any noticeable gain. I know even standard will be better than she was before since she had two fried pistons. She probably closer to a 70hp.. Machining isn't a problem. I have access to machinery and the skills to do it. Just want to know if it's worth it. Got time to kill while the rings and gaskets are on there way. Oh side note I also had 1 Reed that wasn't closing , hence going to replace all.

 

[flyingscott]

Try to find a late 80s 115/110/112 motor. They are the prop rated versions of the 140

 

[jimmbo]

Reeds don't have to be locked against the Reed Block, to be considered fine. A gap of 0.005-0.010" is considered acceptable as Crank Case Pressure will close them.

While the post 84 115s are Prop Rated versions of the Crank 140(which BTW, really only put out about 128hp, but that was within the Tolerance Band), I'm not so sure about the 110 or 112, as I remember pulling off more than one Cowl, and not seeing the Bubble Back.

 

[juanallen78]

Welcome to iboats
To turn a 90 into a 140, the Porting will have to be modified, the Block will also need machining to install the Components for the Bubble Back. The Carbs on the 140 are different, as they have to flow more Air.
Some 140s also had Stuffing Blocks in the Crankcase side of the Reed Plate, to reduce Crankcase Volume.
I don't know what yr your 140 is, but there were some differences(besides the Bubble Back) in the Exhaust System over the yrs between the 90 and 140
You realize that 140 has a weaker Hole Shot than the 90, due to the Torque Curve moved to a higher Rpm Range, low Rpm will be weaker, add that you will likely need to go up to a 19in prop to keep the Rpm around 5400, which also slows Hole Shot.
Fiber Reeds, the Only advantage of them, is when they fail, they won't chew up the Engine. They will need to be replaced after a period of time. In over 50yrs, I have only seen one Stainless Steel Reed fail.
While all Crossflow V4 will eventually succumb to Piston Ring Issues/Failures, the 140 is likely to do so sooner, simply from the Higher Stresses imposed by the higher Hp

90hp ports

 

[juanallen78]

Thanks for the info. Finding these engines here in SA is a roll of an expensive dice. Most have been butchered and or beaten on. Part of why I am in my current state with my engine. Used parts are also crazy expensive if you can find them.

I will check my Reeds measurements this evening and if still in the specs you mentioned Jimmbo then I will call that a win. I will post back with my build once I get it together. Thanks again for the input.

 

[flyingscott]

Reeds don't have to be locked against the Reed Block, to be considered fine. A gap of 0.005-0.010" is considered acceptable as Crank Case Pressure will close them.

While the post 84 115s are Prop Rated versions of the Crank 140(which BTW, really only put out about 128hp, but that was within the Tolerance Band), I'm not so sure about the 110 or 112, as I remember pulling off more than one Cowl, and not seeing the Bubble Back.

The 110/112 blocks have bubblebacks on them.

 

[ct1762@gmail.com]

That green area is what you'd need to drill or mill out for the bubbleback. But has anyone ignored that? id think it wouldn't hurt much as it divides the bubble back exhaust better for more exit velocity vs. being open but I dunno. BTW this is an XP/GT 100 that has the 140 ports.