90 to 115 crossflow hop up just a matter of carbs?

[MAW31]

(in the same year)

The part numbers are identical between the 90 and the 115 motors for the Piston, Rod, and Crank.

The carb and cylinder block numbers are different. (and only slightly)

How much might i get out of simply swapping in a set of 115 carbs then?

Could it simply be that the 90 is mostly a fuel starved 115 save for adjusted exhaust port timing?

What else is at work here?

thanks

 

[emdsapmgr]

Re: 90 to 115 crossflow hop up just a matter of carbs?

Depends on what year the 115 is. Are you talking about a 115 crossflow or 115 looper? Are you talking about a flatback 115 or a bubble back 115? The old crossflow 115's had flatback exhaust systems, like the 90. Those were primarily a carb difference. The 1985 and later 115's have the special bubble back exhaust as well as large carbs. In the 86 timeframe, the newer engines became propshaft rated, so they putout maybe 15% more hp than the same rated older engines. Many of the 115's also used four rubber intake filler blocks, which increased crankcase compression and hp-which the 90's did not have.

 

[Silvertip]

Re: 90 to 115 crossflow hop up just a matter of carbs?

Any time a part number differs for two parts -- be assured they are different and there is no such thing as "not much". Even one digit difference means the parts are indeed different. Whether you can use them interchangeably cannot be determined from the part number.

 

[kenmyfam]

Re: 90 to 115 crossflow hop up just a matter of carbs?

Completely agree. Different is different and that's all there is to it.

 

[MAW31]

Re: 90 to 115 crossflow hop up just a matter of carbs?

no argument on different = different.

the question was: being that we know the core components are identical, save for the carb and cylinder, and we know the block produces HP in the range of 88 through 115HP...

and lends merit to the idea that simply adding 115 bore carbs would likely generate measurable HP gains.

in this case, different = good.

we know that the cylinder block is identical in size (1632cc) to the 88HP block. (albeit a different id number)

so the relative (and only variable so far in the equation) would be how much of the power gains are the result of the exhaust port timing... (as opposed to the freer air-flow allowed by the larger bore carbs)...

 

[Dhadley]

Re: 90 to 115 crossflow hop up just a matter of carbs?

To answer your question specificaly we'd need to know what year motors we're talking about. There are different 90s and different 115s. Generally speaking - very generally - putting bigger carbs on some 90s will make it run worse and burn more fuel.

 

[MAW31]

Re: 90 to 115 crossflow hop up just a matter of carbs?

I agree Dhadley.

Purchased boat/motor used.

Motor: E88TSLEOC (Evinrude 88 w/trimtilt, special styling, 20" shaft, 1995)

Circle stamp on cylinder head: 03883276 Flatback

I've been on the evinrude parts site tracking down the numbers.

I dont believe that head can be a 1995 because only the 1987 schematic shows an 88HP with a flatback. The rest are bubble-backs.

 

[Dhadley]

Re: 90 to 115 crossflow hop up just a matter of carbs?

OK, in 1995 the 88 and 112 were the same as the 90 and 115 with some styling differences. The main difference between the 88/90 and the 112/115 is the exhaust. The porting is slightly different too.

Yes, you can turn a 88/90 into a 112/115 (or older 140) by opening the ports to match the porting, add the bubble back exhaust, heads and use the 112/115 carbs. Some 88/90 reeds had a closer stop, some didn't. Just something you'll have to look at.

Unless you have some sort of performance hull like a Hydrostream or Allison and turn a bunch of rpm you'll be disapointed with the final results. There's just not a lot of difference between the 2 motors torque-wise.

However, there is a lot of untapped power in the intake area.

 

[MAW31]

Re: 90 to 115 crossflow hop up just a matter of carbs?

thank you all for sharing your knowledge with me.

The summation of my thought was to buy a pair of used 112/115 carbs, clean em up, and bolt em on for some extra top-end.

I know I'll not not be going through any porting efforts, or any mod requiring tear downs for this purpose.

If Evinrude had left some HP on the plate that could be had with a bolt-on mod, I was interested.

 

[surrender]

Re: 90 to 115 crossflow hop up just a matter of carbs?

OK, in 1995 the 88 and 112 were the same as the 90 and 115 with some styling differences. The main difference between the 88/90 and the 112/115 is the exhaust. The porting is slightly different too.

Yes, you can turn a 88/90 into a 112/115 (or older 140) by opening the ports to match the porting, add the bubble back exhaust, heads and use the 112/115 carbs. Some 88/90 reeds had a closer stop, some didn't. Just something you'll have to look at.

Unless you have some sort of performance hull like a Hydrostream or Allison and turn a bunch of rpm you'll be disapointed with the final results. There's just not a lot of difference between the 2 motors torque-wise.

However, there is a lot of untapped power in the intake area.

Tell me more of the "untapped power in the intake area". Mine is an 88 hp

 

[Dhadley]

Re: 90 to 115 crossflow hop up just a matter of carbs?

thank you all for sharing your knowledge with me.

The summation of my thought was to buy a pair of used 112/115 carbs, clean em up, and bolt em on for some extra top-end.

I know I'll not not be going through any porting efforts, or any mod requiring tear downs for this purpose.

If Evinrude had left some HP on the plate that could be had with a bolt-on mod, I was interested.

What boat do you have? Tell us about your performance. In a lot of cases we are able to get more performance by adjusting the set up. If your set up isn't maxed out now you may actually hurt performance with bigger carbs.

 

[MAW31]

Re: 90 to 115 crossflow hop up just a matter of carbs?

In your asking the question, I realized I don' have enough information myself.

my tachometer, will work, then drop to zero, the pop back on, so i'm wary of the values it displays but I've not gotten the motor past 4400 rpm.
Far more consistantly is 4200 maxed, trimmed. (book says 4800 is target)

compression on the cylinders is 105 to 112 psi.

carbs were removed, and thoroughly cleaned 6 mos ago with about 20 hours of mostly open throttle operation.

I have not GPS'd the boat yet, hole shots are strong and quick, but rpms dont ever top out.

prop is a SS 3 blade, 15pitch.

boat is a aquasport 17.5 center console, bare bones.

no trim tabs, yes tilt/trim

CDI swapped out with another CDI, no operational diffs observed.

spark plug & wires replaced. (just housekeeping)

starts/idles fine.

looking for that top end.

 

[Dhadley]

Re: 90 to 115 crossflow hop up just a matter of carbs?

At 4800 rpm as your top rpm the motor is pretty stressed now and probably won't live very long. Your target rpm is 5800. If your tach is inconsistant you may have a problem on the motor. If you have a motor with the water cooled regulator / rectifier it may be starting to short out internally. It could be a tach issue too but it needs to be addressed.

The low rpm could be a boat related issue as well. we'll need to look at set up and boat condition. Normally with a V4 crossflow on a 17 AS we use a 17" prop and are well into the 5000 range.

In any case, putting bigger carbs on a motor set up at 4800 will, most likely, hurt.

 

[MAW31]

Re: 90 to 115 crossflow hop up just a matter of carbs?

rectifier is not watercooled. charge is above 12v when running.

tach drops out, its instantaneous, then big-wave, and voila, its back.
I gotta believe its a poor connection at the tach which i'm looking into today.

I swapped in a new foot last night, and will take it for a spin tomorrow morning. (I had lost some teeth on the existing lower unit when I ran aground recently )

checked plugs this morning, nothing out of the ordinary there. (decided to replace anyway). Had checked spark strength last week, good hot spark.