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