Magnum + ?

[Nubian]

I have a 20hp Kohler Magnum that I was thinking of reboring.How much more horsepower can I gain and is it worth the expense? Eddy

[PatRarick]

Don't think you would gain any noticeable horsepower. As to whether it is worth the expense, that depends on what you are comparing it to, and how much of the work you are going to do yourself. Compared to the price of a shortblock, it's generally not worth it if you are going to hire the entire job out. If you are going to purchase the parts, have the machining done, then reassemble it yourself, it IS worthwhile. Pat

[jkmustang1]

The other reason is originality in the tractor more of a concern as they get older.

[UCD]

Jon internal engine mods never hurt originalty or value as they can not be seen and do make for a better running machine. In most cases An internal engine mod. will add to the value.

[Nubian]

Ok, but if I were to do the job or pay to have it done, what would be the point if I would not notice any significant increase in hp? I only ask because I hear it is often done. Eddy

[thedaddycat]

I think most reboring is to correct a problem like a scored cylinder, where you have to take the scratch all the way out. Unless you're pulling or racing, the stock engines have enough power for most tasks and swapping out for a bigger one is no big deal either... Heck, some of these guys put motorcycle or car engines in these tractors!!

[Nubian]

I got the picture now;) Thanks again everyone^ Eddy

[Salthart]

You can figure the added power by the total amount of surface area gained. Its not rocket science, but its a close enough idea. Figure the HP into the standard displacement and you'll get a number of HP per cubic inches.. Now figure the added displacement at that same HP per CID. So, if your 20 hp engine is ( No idea what the M20 does displace) say 40 CID that would be .5 hp per CID. So if boring .30 over added half an inch ( Doubt it would ) your gain would be something close to one quarter of one horsepower.. If you want to make more power, You need to make more "Bang" . This means getting a harder push from the fuel you are burning. And I think you will find what you can do there to be pretty limited. Camshafts can be made so that the valves "Overlap" in timing and the leaving exhaust gases help draw in new fuel/air mix. But thats high RPM stuff. I don't think you'll find much room to play with lift hight on cams as there isn't much room for releaving the spring areas to allow more crush. Porting and smoothing the intake is another option but again, unless you plan to turn some RPM's you will see very little gain. As Flow only really matters at higher speeds. True and worthwhile gains can be had IMO in only a few ways. Changing center line on the rod bearings would add a small amount of CID and would also bump the compression. Shaving the heads would bump compression alone. There again, the gain would only really show up at mid and higher RPM's and like the cam work would make your engine weaker at low RPM's. What I am trying to say is this. You can make more housepower if you want to spend a good deal of labor and money. Question is why would you want to ? BTW, You want across the Board HP from go to blow ? Nitros, Alcohol, Nitrogen and blowers LOL.... I know all this is not what you asked so just ignore me..LOL Thinking with my fingers.. But in thinking about it, It does seem very limited. Anyone else see it otherwise ?

[ambler]

Fuel injection and turbocharger

[ambler]

Seriously, My 7119 has an M20 and I have never needed more power. She is quick and will mow all day flat out. I am boring two sixteen horse briggs right now to correct a compression problem.

[Nubian]

Salthart,seems like you like to play with numbers :D,the displacement on the M20 is 770. Thanks for the help. Eddy

[MikeES]

The displacement of the M20 is 47 cid (cubic inches) or 770 ccs (cubic centimeters). The best bang for the buck (and not much of a bang) is to shave the heads and get a little more compression. Maybe get you a few more horses.

[chivic]

I have an Onan 16.5hp and am told that the 19.5 hp is the same engine with a differant carb and intake. I wouldn't think you could get that much more hp by just changing the carb and intake. Does anyone know if that is true?