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increasing hp on Kohler?

Discussion in 'Lawn Mowing' started by jason2, Apr 10, 2001.

  1. jason2

    jason2 LawnSite Member
    Messages: 243

    I have a 18 hp Kohler Command. I noticed it has the same bore and stroke, and compression ratio as the Command 20 and 22 engines. This leads me to believe that they are the same engines. Where does Kohler get the extra ponies on the 20 and 22 models? Is it with the carb? I doubt it's in the cam.

    Somebody mentioned something about moving the trottle plate on a small engine to get more hp. Is this all that is involved in bumping the output on my 18?

    And when they say the throttle plate are they referring to the "butterfly valve"? If so, does the throttle plate have a limiting screw or something to limit it from opening all the way at full throttle?

    I know it's gotta be something simple. But I don't know what the differences are between the three engines. And I'd like to make my Command 18 into a Command 22. All three engines make their peak power at the same RPM. So it can't be govenor related. Displacement is the same, plus they all have similar idle characteristics so it's gotta be in the carb. Please help. I'm tempted to buy the new Honda 24 hp, but first I want to try bumping the power up on the engine I already have.
  2. Richard Martin

    Richard Martin LawnSite Fanatic
    Messages: 14,699

    To change hp without changing either the bore & stroke or the camshaft you can do these things. Change carb, change the intake gaskets, change intake manifold, make changes to the intake and exhaust passages in the cylinder head, change the valves, change the exhaust manifold and muffler and making changes to the ignition timing.

    Take your pick!

    BTW, the govenor on these engines does not limit rpm. The govenor senses when the engine is loosing rpm and opens the throttle in order to regain a set rpm. If you were to reach down and open the throttle plate (butterfly valve) by hand you would see that these engine will rpm well in excess of 3600.
  3. MikeGA

    MikeGA LawnSite Member
    Messages: 101

  4. jason2

    jason2 LawnSite Member
    Messages: 243

    Thanks guys,

    Richard, I could run thinner head gaskets, or mill the head for a bump in compression resulting in a increase in power. But then I have to run higher octane fuel. And I also could port match the intake and exhaust, clean up the head etc.. But I just am looking for the simple difference between the three motors. Maybe someday I'll build a killer Kohler. :) Hell maybe somebody builds a stroker crank for these babies. Add a stout cam, open up the exhaust and intakes and we'd have some fun.

    I didn't realize the governor worked the way it did, thanks for the info.

    Mike, thanks for bringing that thread up, that is the thread I was looking for. I'll be taking a look at my carb this weekend. I've never owned a vehicle that I haven't done a bit of tweaking to, and now this Kohler has bitten me and I need to make it give me more power. :)
  5. awm

    awm LawnSite Gold Member
    Messages: 3,354

    ive got a 96 command . if yours is the same as mine
    you really have a 20 with a stop or somthing built
    in .your dealer can make the change at almost no cost if he will. this is what i did.kohler did this to supply both hp requirements but only wanted to produce the one motor.
    as told me by my dealer.
  6. MikeGA

    MikeGA LawnSite Member
    Messages: 101

    I guess this was to make the poeple who don't want enough HP happy AWM??
  7. awm

    awm LawnSite Gold Member
    Messages: 3,354

    kinda sounded dumb to me to but pinckstons
    here in cabarras must know somethin.
    i know exmark owners 40 miles away that go there
  8. jrebeiro

    jrebeiro LawnSite Member
    Messages: 94

    Well this sorta thing seems common with Manufacturers in any speed enhanced industry. Intel used to do this with their pentium processors. They would make a base 200MHz chip and simply underclock it between 133 and 200. So hacker types simply changed a few settings and whalla they paid $200 less for the same chip. It is cheaper to make one product and disable a few things so it is easier to sell and they will have a higher stock of product.
  9. John DiMartino

    John DiMartino LawnSite Silver Member
    Messages: 2,555

    I noticed Onan did the same thing with the performer 18HP,and 20HP.They have same displacement,compression,cam #,and exhaust-so the only thing that can make the 2hp is the timing curve or carb size or settings.I bet its in the carburetor,not the timing.Be careful about bumping up compression on a Command Kohler,my 25Hp has 189 PSI already-that is very high,so if yours is anywhere near that ,you best leave it alone or you'll be runnning racing gas to keep from aerating the piston tops.According to my owners manual-the CV18-20 is 624CC,CV22 is 674CC,CV 25 is 725.Good luck cranking it up.
  10. jason2

    jason2 LawnSite Member
    Messages: 243

    I stopped by my new dealer today to ask about the differences in the three engines. The mechanic said he didn't know, but would find out.

    To his credit, he returned my phone call this afternoon. What he told me doesn't add up. He said the differences are in the flywheel and the ignition.

    First of all the flywheel has absolutely nothing to do with the power output of these engines. Sure a lighter flywheel will allow an engine to spin faster, and have less parasitic drag on the engine, allowing higher rpm's. But in all practicality a flywheel is not a performance adding part. Valvetrain limits rpm. Plus if the valvetrain can handle the higher rpm's (roller rockers, roller cam, etc..) the engine still needs to breathe. (Larger valves, additional fuel flow needs, etc..) These engines all make their peak power at the same RPM. Sure the flywheel may be different between a Command 18 and a Comand 22 but it isn't power related.

    Secondly, the ignition definitely has nothing to do with the increase in power between these three engines. The spark plug gap is the same on all three engines. For argument's sake let's say the 20 or the 22 had a hotter ignition than the 18. The plug gap would be wider, to take advantage of the higher voltage. Which would result in a fatter spark. But alas the gap is the same. Can you bump power with a jump in timing. You bet! But at what expense? Once again all three engines have the same compression ratio. You go and bump up the timing, you need to run a higher octane fuel. All three of these engines call for 87 octane fuel. And to make a horsepower jump from 18 to 22 with timing alone, you won't be doing it on 92 octane fuel. You'll have some severe detonation problems.

    So again I'm sick of being fed nonsense by a so called "mechanic". I've probably built more motors than he has, even if they are not small engines. And I believe as you all have told me it is in the carb. Big thumbs up to the lawnsite members! :) I'll be taking a peek at my carb this weekend.

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