Adding horsepower to a mower!

[thefly01]

I know this is waaay off topic but thought there might be a few gear heads out there. I just bought a John Deere LT115 riding mower. It has 19 HP and an automatic trans. It's gonna sound nuts but I'll be racing it soon against some other neighbors. Obviously I'd like to win if anyone out there has any ideas I'd greatly appreciate them

[tonydahose]

well like any engine make it breathe better. i dont know if they make intakes for that kind of engine but im sure the muffler is pretty restrictive. take that off. i dont think you need the back pressure that much and you can put it back on after the race. other than that and replacing gears in the rear end which i dont think you want to do, thats all i can think of. maybe a set of drag radials like my mustang has..lol

[cobrajoe]

Small engines are fun to work on

Quick question: Is it a single cyinder or a twin?

I'd reccomend putting some pipe where the muffler was, it will help scavenge the exhaust gasses out of the cylinder, just a short piece of pipe of the right diameter should screw in where the muffler was (if the engine could accept a screw in muffler). Approximately a foot of pipe should be the right length if you can fit it (and it will stop flames from shooting out near your feet).

Also, if you aren't going to be running in a very dirty or dusty area, take off your air cleaner, this will help the engine work less drawing air into the engine.

There is one more thing you could do without major engine work, but I wouldn't reccomend it because it could easily cause engine destruction.

Other than that, maybe clean your spark plug(s).

Good luck in the big race!

[cobrajoe]

Then again, you could always do something like this

http://videos.streetfire.net/search/...2401850f23.htm

Or...

http://videos.streetfire.net/search/...b81f4b75a1.htm

[Kn00b]

Removing an air cleaner on many engines will actually not pick up horsepower. In many cases the distubance of the airstream can cost a little power.

Muffler removal should help although I have to point out that 'backpressure' is essentially a myth. You always want less pressure but the whole 'bigger pipes doesn't always create that as exhause stream velocity comes into play.
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If you're feeling agressive you could:

1) Fit a small nitrous system. Adapt a 'cheater' system or over-restrict the jets of a plate style system.

2) Use a small supercharger or turbo (motorcycle) to the system.

Either of the above should really be used on a spare engine as most tinkerers will blow the motor up here.
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Best bet is going to be weight reduction. Remember, the whole point is power to weight ratio here. Check into removing the blade of your mower, bodywork, lights, etc. You can significantly change the power to weight ratio doing this.

Changing tire size will have the same effect as changing the rear end but much cheaper. Also, chances are you will not be traction impaired so you'll want to run the narrowest tire you can safely run without losing traction. Also run higher air pressure. (Less rolling resistance. Think bicycle racers).

[tonydahose]

Originally Posted by Kn00b

Muffler removal should help although I have to point out that 'backpressure' is essentially a myth. You always want less pressure but the whole 'bigger pipes doesn't always create that as exhause stream velocity comes into play.

on a big engine i thought you need a lil to make the cats work right and you dont pop up any codes. right??

[Kn00b]

Backpressure has become pretty muchthe layman's definition of 'adequate exhaust velocity at slow engine speed'.

With large diameter ports and piping but slow engine speeds exhaust gasses can essentially 'pool' in the piping. The fresher exhaust has to overcome the inertia of this slower moving exhaust 'pool'. This creates real backpressure.

The restriction of the muffler can keep the exhaust stream moving at a higher velocity at slow engine speeds and prevent this. Overall, proper pipe diameter choice for amount of exhaust produced (engine size and operating rpm chiefly) will be the best choice.

Remeber, a muffler is just a differently shaped piece of plumbing. No real magic to them. Either a multi-chambered box or a muffled tube really.

BTW, cats are normally premuffler and the code thrown is by the secondary O2 sensor located afer the cat. On most OBD2 (late model) engines, the code thrown is emissions only and does not effect actual performance of the vehicle in any way. Most pre - 1994 engines (OBD1) didn't even have a post catalytic converter O2 sensor though to throw a code

[cobrajoe]

Don't forget that we are dealing with a "small engine" here, and they do not quite opperate as the big vehicles do. The most notable difference is the govenor that limits the engine to a certain RPM. This means that no matter how efficient you are at getting the air and gas in and out of the engine, you will still have the same top speed.

In other words, your horsepower mods aren't going to help at all if you don't either bypass the govenor (which I highly reccomend against) or change your effective gearing.

On the mower I hot-rodded at home, the biggest gain I ever got was when I replaced the pulley on the transmission with a smaller one (I went from about a 6 inch diameter to a 3 inch), this increased the speed in every gear and gave me a top speed of around 25 mph.

I don't know if this would work on your Deere with the automatic trans, but if you can easily replace this pulley with a smaller one, be sure to get a shoter belt so your clutch (if you have one?) can still function.

[Kn00b]

Originally Posted by cobrajoe

Don't forget that we are dealing with a "small engine" here, and they do not quite opperate as the big vehicles do. The most notable difference is the govenor that limits the engine to a certain RPM. This means that no matter how efficient you are at getting the air and gas in and out of the engine, you will still have the same top speed.

Good points! It's important to note that I don't have experience with modding mower engines (only the small displacement automobile engines).

Although top speed will be RPM dependent, acceleration can still be changed by making more power within the given RPM limitations. E.G. a Cummins diesel motor is limited to under 3k RPM but there is a huge amount of torque that can still be made with the low rev limiter in place.

Personally, I'd look into upping the top speed through wheel/tire sizing and then lighten the vehicle up and remove the muffler to improve the power to weight ratio. Unless you've got the budget to blow up the motor.

[Darkfin]

Perhaps these links might help you:
http://www.letsmow.com/ (in particular: http://www.letsmow.com/FAQ.html )
http://www.mowerracer.com/
http://sportsvl.com/wheel/lawnmowerracing.htm
http://www.g-team.us/

If/when racing, wear a Shoei helmet--one saved my life in a serious motorcycle accident. www.shoei.com

Good luck!

Oh and check THIS out! (talk about lawnmower performance!)

[thefly01]

Thanks everyone! I forgot to mention the biggest point. It has to be stock I was already planning on removing the mower deck and adding higher octane fuel. The problem is as Cobra pointed out is the top end is still only 5.5 MPH. I've looked at all of the 100 series and all will only hit this speed. All have different HP but still only accomplish the same speed. The engine is a twin by the way. It's brand new so no sense in replacing or cleaning plugs. It's all in fun but I'd still like to take home the trophy I guess with the ideas I had maybe I'll get up to speed a little faster than the guy next to me in theory. I'm surprised I had this many replies to tell you the truth. I have a L82 manual vette that I've done some work to but obviously this is a different story. In any case I truly appreciate everyones replies. I'll let you know how it all goes soon.

[xdrewsiferx]

So Best things you can do to add HP to your mower is increase flow. I dont know much about the motors running in the deer your on but if you open things up a bit (Intake and better exhaust this will beef it up a bit. If you have a second motor around try polishing the block out with a dremel. But do that with caution and thats why I asked if you had a second motor around. And or you can just add a big turbo as posted by cobra.

[java]

Stock.....Schmock..

Go big. Trade up to Jesse James' 1990 Mustang 'Cutter and mow grass at 100 mph.




Or putt in style with this baby:











j

[cobrajoe]

Nice Java! I love the chopper chopper!

I don't know why, but you made me think of this...

http://videos.streetfire.net/video/b...1600cbec39.htm

[Stevie Ray]

With an engine like you describe your biggest (and cheapest) acceleration / speed gains will come from a couple of transmission or final drive gear changes. (For some mowers it may be as simple as a couple of pulley changes)

Back in the days of everybody and their brother modding a Mustang 5.0, the rear end gear was the first "wake-me-up' change that everybody went to for serious acceleration gains.

Remembering that an IC engine is nothing but a big air pump, big pipes, high flow filters, bigger carbs, etc do little without basic changes to the engine head / valves. Also remember that as you open up the exhaust on a small engine (thereby decreasing backpressure) that you will lose low end torque.

Do the gears first ... Assuming you can find the parts, it's cheap, relatively easy, and if you select the right setup, none of your buddies will have the slightest clue why your mower is faster.

[xdrewsiferx]

He will not loose low end if he throws a glass pack on it or puts a coffie can muffler on it. As long as he keeps the flow high but alows for presure to build in a light amount it will be a gain. I am not sure if he can do gears on a mower or not but pullys if the motor uses them would be a great idea. On my car I changed out a few pullys and I gained 8hp at the wheels.

Just a redneck idea but you could alwase get a leaf blower and connect it to the intake.
http://videos.streetfire.net/video/a...ad23ca9564.htm

[Kn00b]

Originally Posted by Stevie Ray

Do the gears first ... Assuming you can find the parts, it's cheap, relatively easy, and if you select the right setup, none of your buddies will have the slightest clue why your mower is faster.

As someone else alalluded to, on a rev limited mower, gears that make him quicker will actually make him 'not as fast'.

Quick = ability to get to speed
Fast = top speed.

Rear end gears for acceleration reduce top speed. Not an issue for a Mustang looking to improve quarter mile times as they come no where near their rev limited top speed. But on a mower alredy limited to 5.5mph, it would be a real issue.

[Civilian]

What kind of race? Straight line, circle-track, road course.

[cobrajoe]

Originally Posted by Kn00b

As someone else alalluded to, on a rev limited mower, gears that make him quicker will actually make him 'not as fast'.

Quick = ability to get to speed
Fast = top speed.

Rear end gears for acceleration reduce top speed. Not an issue for a Mustang looking to improve quarter mile times as they come no where near their rev limited top speed. But on a mower alredy limited to 5.5mph, it would be a real issue.

Yes, this would be the case, but since most mowers are geared so low, you will notice better acceleration when gearing for higher speed.

If you install taller gears, that will allow the engine to use the power that it's making for accelaration.

After I changed pullies on my hot-rod mower, I found that it would easily do wheelies in second gear when it didn't feel like it had the power to do so before (8 horse briggs on a Bonanza lawn tractor). It was fairly impressive, it would pull the front wheels to at least waist high even with the cast iron grill and heavy steel construction.

[java]

Originally Posted by cobrajoe

Nice Java! I love the chopper chopper!

I don't know why, but you made me think of this...

http://videos.streetfire.net/video/b...1600cbec39.htm

A 9-G aerobatic mower!!!!!!

That would beat any of my F15 flights.......if I could keep ahold of the handle...


Thanks CJ, that was awesome.









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