Anyone "soup up" their lawn mower engine?

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Have you ever milled the head,put in a bigger piston,a go-kart style header,bigger carb? Anything to not have a bone-stock engine? Let's hear it!!!
 
I put a Dyno cams 95-3 cam, .030 Wiseco piston and a Horstman I-beam rod in my Dad's Trac-Vac engine when I rebuilt it. I had the stuff laying around from my racing days.
 
Not exactly souped up, but I put a home made oil bath air-cleaner on mine--though the inner filtration element is made out of a soup can.
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Nice work on the air filter!
I've just tweaked the govenor on my lawnboy to gain some rpms when needed. Its a two stroke and the torque drops off pretty fast if the rpms dropped, so starting higher rpms helped quite a bit. It would cut 5-6" grass down to 3" as fast as I could walk, 4-5mph?, when I was in highschool.
I guess it would be possible to port it or open up the exhaust but it has sort of an expansion chamber muffler so it might be already "tuned". My lawn now doesn't have large unbroken areas where hp is important. I have all sorts of banks and trees and gardens to mow around so trimming weight for better "handling" would be nice but I suspect a two stroke aluminum deck mower with no bagger or drive is as light as they come...
 
Originally Posted By: greenaccord02
You need to draw up some plans for that filter, RiverRat.

I already did!
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(Choreboy copper scrubbers made a good inner element mesh)
I use about 3/8" deep pool of motor oil in the bottom half for the wetting agent.

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http://www.youtube.com/watch?v=Xu4AyTH_5zA

My stupidly designed snowblower used to blast exhaust at the operator. Put some pipe elbows on to make this vertical exhaust stack.

I got a toro 724 (7 hp 24" wide) off craigslist to replace my broken 824. Still had the 8 hp motor so there was an instant 15% gain by putting it on! I had to drill some holes in the mounting plate and grind off parts of the belt cover and get new longer belts. The 8 hp motor despite being one more pony is way bigger and it hovers over the rest of the deck like a V8 Vega.

For lawnmowers, just the governor spring tweak for me.
 
I tripled power output on my two stroke Echo mower by adjusting the governor. See video in another thread (Getting more Umph).

At 140 ccs, the two cycle engine is fairly big for a lawn mower. The carb and exhaust on it are quite large. I was surprised how easily it revved out to over 6500 rpm. It would rev higher but I wasn't too keen on pushing it much further.

After experimenting for a bit, I set the max rpm to 4000. I'd estimate that the power output went from 4.5 h.p @ 2800 rpm to an easy 6 h.p. at 4000.
 
the silencer (exhaust) is usually a ridiculuis piece of trash!
Open it up and let it breath, i once made a pipe and just let
it exhaust under the deck...didnt sound to bad.
also intakes are relly bad enginered, use your dremel!
Milling the head -ok but watch for valve clearance!
 
Originally Posted By: ac_tc
the silencer (exhaust) is usually a ridiculuis piece of trash!
Open it up and let it breath, i once made a pipe and just let
it exhaust under the deck...didnt sound to bad.
also intakes are relly bad enginered, use your dremel!
Milling the head -ok but watch for valve clearance!


Yeah, I used a 3.5hp Briggs mower with 3/4" straight pipes for a few years, the neighbors loved it.
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Cheap aluminum lawnmower engines usually have a lot of casting flash or other mismatch in the intake area, a dremel can really help. Just like working on a 350 chevy, but smaller...

I would also think if you wanted a less restrictive air filter, but not quite so much work as that cool oil bath filter, you could use a go kart filter that will let in more dirt, but mount it on the top of the recoil housing where there is less lawnmower dust.

Oh, and current production small lawnmower motors/carbs are GARBAGE for power (torque) thanks to our friends at the EPA. If your lawnmower has the newer non adjustable type carb, you might be able to find a bolt on replacement that is adjustable from an older mower. (ebay!) More power and easier to start.

I have a Horizontal Briggs Intek engine on a generator I built that started as a 5.5hp 190cc. I stroked it to 206cc, put in a go kart rod, replaced the plastic cam with an iron one, and found an older adjustable type carb, increased the CR a bit. It's putting out at least 8-10hp now. :)
 
" I stroked it to 206cc"

How would you go about stroking it to 206cc? Wouldn't you need to change the crank too?
 
Originally Posted By: boraticus
" I stroked it to 206cc"

How would you go about stroking it to 206cc? Wouldn't you need to change the crank too?

That's what I did. I got a forged crank (and cam) from the Briggs "Animal" racing engine, which is just a factory souped-up Intek. Now I notice they're offering a 250cc in the same size block, I need to check about boring/stroking mine again with factory parts.
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There's no replacement for displacement!

PS - you want lots of power, torque, and reliability for your push mower? Replace that plastic covered, EPA approved peice of carp you have with an old, rebuilt 8hp B&S flathead. It will last forever and give you tons of torque. Probably bolt right up too.
 
I use a 140cc two stroke Echo lawn mower with a governor adjustment. Power is not an issue. Stock power rating is 4.5 at 2800 rpm. I adjusted mine to throttle up to 4500 rpm if I want to run it that fast. I'd estimate that the engine is probably making a solid 7 h.p. if not more at 4500 rpm.
 
I know this is an old thread but.....

I took an adjustable carb off a gcv190 and put it on my Honda gcv160 mower, used a dremel to clean up the exhaust port, and tweaked the governor to run a little faster.

Yeah my wife thinks i'm nuts too.
 
I replaced the blown 3.5Hp B&S on my '80s Snapper with a '04 5.5Hp Honda engine, now that's a soup up...
 
I once took a 10 hp briggs and shaved the head on an industrial size belt sander and made an exhaust out of sink pipe and a half gallon tin tomatoe juice can. It gets better though. My buddy could weld pretty good so he welded a pulley that was about 1/3 the size of the original onto the motor. It was geared so high it would only take off in 1st and had to be shifted like a car. I will never forget the look on the neighbors faces when he hit a bump and fell off of the mower it was going so fast he couldnt catch it once he got up and i was too paralyzed with laughter to be of any help! We had alot more mowers that we toyed with but that one always sticks out to me
 
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