1995 90 hp v4 to 115

[btomlins]

Would I gain any HP if I changed the exhaust manifold to the 115 bubble back?

 

[boobie]

Try it and see what happens.

 

[racerone]

You may find that there is more to this than bolting on the tuned exhaust manifold.----Look for information on intake port size.-----Carburetor throat size.

 

[Faztbullet]

Wont work as need the deflectors in block also...plus correct ports

 

[jimmbo]

Turning 90s into 115s is doable, Porting, carbs, Machining of the Block so the all the components of the Exhaust Tuner will fit. More cost effective is to just go find a Crank Rated 140 or a Prop Rated 115 to replace the 90

 

[racerone]

Or just let folks try it.-------Their neighbors have said that this will give them the boost in power they want.-------Remember those 200 mile / gallon carburetors for cars in the 1960's, they did exist too.----Oil companies bought them all or so the tall tale says.

 

[btomlins]

I'd like some constructive help and not browbeating. I am pretty handy with a wrench or two. I'm not figuring I'll get 115 hp, just want to see if it will bump up the HP. I have a 90 that runs fine. Is it possible to change to the 115 manifold or not. Are there other things I could change other than the exhaust?

 

[jimmbo]

You will likely end up with an Engine that no longer runs Fine.
The Carbs, Porting, and Exhaust Tuning are all part of the Equation to get more power out of a Specific Displacement, Changing one, without the rest will often result in a Poorer Running Engine. Changes to the Exhaust Tuning will certainly affect how the Engine Scavenging works, which can affect Fuel system Calibrations as well as Airflow Requirements

The 90 has small ports, Intake and Exhaust, Machining them to 115/140 specs will give you the biggest Increase in power, when combined with the larger carbs, and Cylinder Herds

It is not Browbeating, but this comes up every couple of months, and while it is possible to update the Engines, it is not just a Jet change or a screw adjustment

 

[Scott Danforth]

or to clarify...... it would be similar to the guy that takes a factory harley motorcycle and changes the carb and jets...... now he has to fiddle with it at every intersection to keep it running, fuel economy is in the tank, and overall drivability has suffered, however at that one throttle position while going down-hill behind a semi in Michigan along the lake superior coast in mid-June on an over-cast day...... he has a bit more power

simply changing the exhaust and not doing the other things needed results in a motor that runs like carp other than maybe a very very very fine window of throttle, temperature and load where you may gain a 1 or 2 percent of power.

 

[racerone]

You can bolt the bubble back onto your 90 hp block with one different gasket.-----There are also filler blocks that go along with the bubble back manifold.------There also may be a portion of the divider between cylinder banks that may need to be machined out.----Other posts have also given you information for YOU to look into.------And sorry ----Sometimes folks get upset when the answers are not what they were hoping to hear !

 

[btomlins]

Now that's what I was looking for. What s the point of a Public forum if you can't ask questions

 

[racerone]

There are a number of people on here with VAST experience.-----Some times it is hard to convince folks that they are dreaming !-----Posts #3 and #4 do indicate that there is more to it than bolting on 1 piece.----And you must realize folks on here are not getting paid either !

 

[interalian]

I went down the path of converting a 90 xflow to a 140. There is a huge difference between the blocks. Port sizes, heads, carb sizes, bubble exhaust cover and deflectors plus the notch in the bottom of the exhaust case. My conversion works flawlessly but I essentially put a 140 block into rebuild and bolted on a hybrid of parts from my 90.

There's a link to what I did in my signature line. Apologies if a bunch of pictures are missing, but you can thank Photobucket for that.

 

[jimmbo]

I went down the path of converting a 90 xflow to a 140. There is a huge difference between the blocks. Port sizes, heads, carb sizes, bubble exhaust cover and deflectors plus the notch in the bottom of the exhaust case.

I remember when you did that, 5 or 6 yrs ago

 

[interalian]

I remember when you did that, 5 or 6 yrs ago

It was fun. First fire May 31, 2016. Now I need to merge two lower units due to a corroded drive shaft. The torture never stops.

 

[Faztbullet]

Most of the time its " A buddy told me his friend did this to his motor and now it has 300hp"

 

[racerone]

Tall tales , just like the 200 mile per gallon carburetors will be around for a long time.

 

[interalian]

Tall tales , just like the 200 mile per gallon carburetors will be around for a long time.

There's no substitute for following the path OMC designed, at least as a basline. No "what about the carbs off this one, or the exhaust off that one". That's why I used the 140 (flywheel HP, equivalent to the later 115HP prop HP) block and all the required peripheral parts. I did part number comparisons between the 90 and 140 and only used common parts plus the specific 140 parts.

My little tin boat now goes fully 12mph faster with the rebuild than it did with the 90 (flywheel HP). And when towing kids on the tube it uses less fuel than before.

 

[jimmbo]

.

My little tin boat now goes fully 12mph faster with the rebuild than it did with the 90 (flywheel HP).

That sounds about right. When I went from a Crank Rated 90hp Merc, to a Prop Rated 115 Merc, I gained 11 mph.

 

[jimmbo]

Tall tales , just like the 200 mile per gallon carburetors will be around for a long time.

I'm sure it is possible for a Carb to meter the Fuel at a rate to get 200 miles per Gallon, only problem is that current engine Technology, and that for the Foreseeable Future, would not could not run on those mixtures
The past 40 years, Automotive engineers have made great Strides in increasing the IC engine's ability to convert a greater Percentage of a Fuels's BTU Value into usable Energy