Engine Modding

[Justin]

I need more hp out of my 12.5hp briggs and stratton racing lawn mower. Only thing i have done to it is push button starter,new acme mowersports front axle, tether kill switch and new cast iron pulleys. Im looking for easy modifications like, exhaust,airfilter ect..
Also is removing the govenor on these pretty much the same as on the blue honda clones?

Thanks in advance

 

[freakboy]

Yeah exept the gov gear is on the bottom facing up its not that hard to find out which one you need to get rid of. and put a cone airfilter on it and if you want it loud straight pipes.

 

[Justin]

Yeah exept the gov gear is on the bottom facing up its not that hard to find out which one you need to get rid of. and put a cone airfilter on it and if you want it loud straight pipes.

thank you, do you know where i can get one of them filters? i have been thinking about a staged pipe, would it make a difference? i see a few people do it on there engines on here.
If i was to make a staged pipe, what sizes should i use?

 

[freakboy]

The filter you can get that at any auto store and just figure out the inlet of the carb and find a airfilter that will fit.

 

[Justin]

The filter you can get that at any auto store and just figure out the inlet of the carb and find a airfilter that will fit.

ok thanks, the carb on this engine is rather small, would i see more power if i got a bigger carb?

 

[Rotore]

not really

 

[theo]

I wouldn't go with a bigger carb but a better or newer carb.

theo

 

[Justin]

I wouldn't go with a bigger carb but a better or newer carb.

theo

mine at the moment is fairly new

 

[Justin]

What about a Uni Air filter? are they good filters?
Also i still need help with the exhaust and other ez performance enhancing modifications.
On the exhaust would it be best to just cut off muffler and use the pipe and weld another pipe onto it or buy a new one like that?

Any help is appreciated

thanks

 

[freakboy]

Yeah if your are going for a straight pipe make sure you have at least 6 inches of pipe cause i think you can burn out your valves if you dont. It would be easyer to cut the muffler and weld but if you ever need the muffler(people complaining) so if you can make a flange but if not dont worrie and hack it off.

For the air filter it looks like it should work.

 

[Kaptain Krunch]

Yeah if your are going for a straight pipe make sure you have at least 6 inches of pipe cause i think you can burn out your valves if you dont. It would be easyer to cut the muffler and weld but if you ever need the muffler(people complaining) so if you can make a flange but if not dont worrie and hack it off.

For the air filter it looks like it should work.

Its not that you burn out the valves exactly. Its that once you shut off the engine, cold air will go into the exhaust, and since the valves are burning hot, the quick rush of cold air going to hot valves will make them brittle.

Also upgrade the brakes, because the stock ones on a transaxle are useless if you blow the tranny since there not actually on the axle, wouldnt be fun to lose brakes at 30mph.

Also be careful how many rpms your tossing at that transaxle, depending on which one they will die pretty quick with anything above stock, and those bushing are pretty flimsy, you could try replacing them with needle bearings also.

 

[theo]

You want a pipe 14 or so inches long, it's suppose to be better for torque.

theo

 

[Rickracer]

For your application, I'd recommend at least 18" to 21" of pipe, if you want to run a straight through type muffler, you can include that in the total length. With a low restriction air filter and a header, you will likely need to open up the carburetor main jet a size or two, it WILL want more fuel,
Another thing that will increase power is to advance the timing. You can either buy an offset crankshaft key, or simply file one side of your stock one to give you a few degrees more advance. Another is to remove or reset the governor to allow more rpms. If you choose to remove it, beware, it may be able turn enough rpms to blow itself up, so YOU become the governor. One that's a bit more involved but yields great results is to increase the compression, either by shaving the head, decking the block, or both. With some motors, you can simply run a thinner head gasket to bump compression.

 

[Justin]

Ok thank you all for the help, now i just need some sources! does anyone know where i can get all this stuff you speak of?

 

[theo]

Try here, http://www.affordablegokarts.com/

 

[Tony]

k&n air filter the stock ones are always bigger than needed. port and polish it and higher flow exhaust.

 

[anderkart]

Hey Justin, there doesn't seem to be many guys on this forum that race big vertical shaft engines like yours. I searched around the net and found theres quite a few forums dedicated to lawn mower racers. Check out this search link: http://www.google.com/search?hl=en&...g+lawn+mower+forums&btnG=Search&aq=f&oq=&aqi=

I just briefly scanned through some of the sites and there seemed to be a lot of good info posted about speed parts used for mower racing engines. With a bit of searching, I'm thinking you'll probably find they have lots of race info posted about your model.

good luck with your project man...

 

[Kaptain Krunch]

Trust me, if your not serious about mower racing, and in an actual league, be careful at heymow and dont let them know your not racing in a class or at an event, they will flip **** and ban you. It is a great resource, though, they have tons of guides on all types of engine building, transmission prepping, and just other general info.

 

[Justin]

Ok thanks everyone for all your help i think i got it from here but if you have any suggestions feel free to let me know