TOPIC: 90 or 115 bumped up to a 140??

ok since i have this 90HP spare motor for parts.. or what ever.. i was checking a few things.. and was wondering what i would need to do to get a little more HP out of one.. i noticed the cranks are the same from 90 to 140 hp.. what would be involved in bumping one of these up to a 140hp???? would i really notice a increase and would it be worth it??

Vintage runner ,, the 90 and the 1150 and the 1400 and 1500 share the same crank and accessories but the extra power is made with power ported pistons, finger ports in the block, different reed stop spacing,different carbs, different timing and so on. The 90 cannot be made into anything other than a nice motor with good low end torque.

Possible to bring a 115 (depends on year here) to a 135 with mods. Doc built me a 115 back to a 135. What he told me..

"The powerhead I am building for you was originally a '72 1150.

The '72 1150 is a choked down 1350 with a few flow restrictions to give the lower HP rating so Merc wouldn't have to come up with a different powerhead to fill that HP range for the consumer market.

Initially this 1150 needed a rebuild because the inner water jacket had cracked and let water into #3 which was trying to die when I rescued the beast. It still had 95 psi on #3, but the rings had started to seize and consequently had scored the bore.
I had #3 bored .015 and installed a new piston there.

I had all holes pro-honed while I was at it and mic'd for roundness, etc to insure the beast was still within factory tolerences.

The block surfaces were machined too to insure everything was flat in the water jacket areas for a correct sealing.

All other pistons were carefully inspected, mic'd, & cleaned. I replaced one standard size piston too, but (4) of the (6) original pistons went back into their original holes.

Everybody got brand new rings & needle bearings.

The crankshaft got new main bearings.

The end caps got new seals & so did the crankcase.

I installed 1500 reed blocks and reeds, which meausre out the same as the original 1350 reeds.

I am installing '72 1400 carburetors - which are virtually identical to the original 1350 carbs & I am installing the original .0785main jets required for the 1350 at sea level.

The exhaust tuner plate and inner water jacket are both NOS 1350 parts that I had machined to insure they too are flat so they will seal correctly.

These modifications: Main jets, reed blocks, tuner & inner wj complete the conversion of the 1150 to a true 1350.

The only difference between the 1350 and the 1400 blocks is the 1350 had an oval tuner to the mid-section and the 1400 had the dual square port tuner to the mid-section. And,...The inner wj & tuner plate configuration changed barely.
T"

By far the cheapest, easiest way to turn a 90 into a 140 is to sell it and buy the 140. I am not kidding here.

i just figured i'd ask.. since i had noticed a some things were the same...while i was working on mine... guess ill stick to my original plan of switching the stator and pick up with mine since these look new..using the mid section on mine for the trim and tilt. and either keep whats left of it as a spare or part it out and sell it off...

George is exactly right.
I've seen a couple guys try this, then forget the throttle arms are two different part numbers....I showed that to Doc Frankenmerc a couple years back too while we were discussing this subject
85441 left 90
88754 right 115

Here is an excellent reference website that gives you all the part numbers of components used in the various Mercury engines. By taking the time to do a little comparison study, you can learn a lot about similarities and differences between the in-line sixes over the years.

www.crowleymarine.com/mercury_mercruiser_hp/MERCURY.cfm

For example, it clearly shows that in 1978-1979, the 90's, 115's and 140's all had difference powerhead assemblies.

It also shows that from 1973-1979, all of the 115's used the same powerhead.

This one is even better, includes Mark series of engines and pre '66 Mercs.

www.seawaymarine.com/pages/OemParts?aribrand=MRC