i have an 11 hp B+S engine i took from a riding lawn mower...my question is simple..where will it top out RPM-wise?  

i have no idea.

thanks

you mean, "breaks & scrap'um"!

i run 5hp b&s "raptor II" on a roadracing kart. the class i run allows only limited mods, i.e. i have to use a stock brigg's conrod (the weak link in any briggs, imho). the motor is designed to turn 3600 continuous rpm on gas, no load.

after slight mods, and running on alcohol, i can crank a reliable 5750rpm out of it, under load.

i have a feeling that your 11hp, tuned and held on the governor, will run 4500rpm...for a while, at least. it's original application also called for 3600 no load running.

CampyBob is about right, if the engine is good and tight and you use a good oil (there is a synthetic 30 weight), she should last awhile. The secret to turning small engines fast is not only in the stregth of the parts but in how well the engine has been balanced at the factory. A Honda, Kawasaki, Kohler, will run these speeds longer because they are SOooo smoothe running.

My dad owns his own Lawn and garden equipmentstore and service center. He is currently sponsoring a garden tractor "pulling tractor", the owner has won like 10 or 11 trophies with a 12hp Iron Block (now discontinued) Kohler running almost 5k RPM on 89octane, tuned pipe and jetted carb.
BrenLover

what kind of minor mods did you do to increase the RPM under load?  what can i do that is relativly inexpensive to "better" my engine?  to make it more reliable?
i am building something just for fun...so there are no restrictions to what i can do to this engine.  only $$... any suggestions?
websites/stores for aftermarket parts?

thanks again

You realize, of course, that the guy that owns the mower is gonna be pissed when he discovers this.

damn right, and you wouldnt believe how hard it is to make mods to this mower in the middle of the night in someone elses backyard w/out waking them up...geez

BUT REALLY

what is the displacement (in cc's)of an engine like this?
is there any good place to find junk ATV's (bigger engines) (namely in SW Virginia)

thanks

As a youth of course on our coutry go-karts which usually meant pieces of welded junk with minimal breaks. We always had a string tied back to the govener. Yep they are supposed to top out at the 3600 range but when you top out just pull the string and they keep on winding.

There are springs/linkage located on or near the carb that runs to the gov rod that goes into the engine. You can experiment with differant springs to get the RPM you need. You will likely have to re-jett the carb to meet the new demand or she will go lean and eventually ping herself to death.
Depending on the age about 400cc in size, give or take a few. You can Bore it out .010, .020, .030 over as well as have the head shaved. over-sized valves are more hasle than it's worth.
Also, a correction my dad just said that guys pulling tractor is turning more like 6000RPM!

The Hondas, Kohlers, Kawi's are SO smooth you can use the usual Mechanical vibration sensing tach, it has to be electronic and driven of the ingnition or use a photoelectric light sensing tach.

Bryan

Also, you guys would not believe the new tech that is comming into lawn and garden engines. Catalitic converters, fuel injection, varitible valve timing. The days of shade tree mechanics and fly-by-night shops working on the new stuff are just about numbered. Think your car engine is pricey? Try a 22HP carburated V-twin Kohler with electric start...sitting down?...Try $2,800+$100 frieght. People into tuning their cars have it SO CHEAP yet they bitch so much about cost.

On a side note, we once built an extended frame go cart with big tires/wheels from a wheel hose and stuck a pull/electric start 17HP Tecumseh on her. NOT a good match for tight turns but man did she fly in a straight line, even made a homemade two speed tranny for it but you had to stop to switch gears.

BrenLover

ok, im a little new to this...never really gave it much thought till now...BUT
400cc?  and 11 HP?
ive seen a 440cc engine that put out 40HP - least that is what it advertised (it was on a 440cc dirtbike)
how much horsepower does a 350cc Warrior ATV have?

how does this work?

no direct correlation?

thanks

400ccB+S and 440cc dirt bike engine is apples to oranges. Two entirely differant applications of an engine. Dirtbikes requires a wide RPM range in order to obtain the HP needed to win races etc. In dirt bikes HP is king, in tractors, cars, heavy equipment torque is king. Also have to remember that were are talking about 2 cycle vs. 4 cycle (usually), two differant modes of operation as well as fuel and lubrication systems.

Bryan

SkaerE:

Have you considered fluting the barrel?

A girl that I work with has 2 kids that run Jr. dragsters with 5 hp B&S engines.  Her son routinely hits 80 mph in 1/8 mile track using alcohol.  Not sure how many rpm's.

skaer is correct. i have kawasaki's in two of my john deere garden tractors. the 14hp is a 380cc and the 17hp is 460cc (going by memory).

the best "cheap" trick to pull on a briggs is to increase the flow. bore the carb throat out a bit...and relieve and roughen the inside of the intake manifold. don't bother decking the head. the increase in compression is defeated by reduced flow volume (side valves suck!).

drill and tap the exhaust for a larger pipe/header.

install a good air filter (about $10)

if faster pick up on rpm's is what you are looking for, do lighten the flywheel.

just flowing a 5hp brigg can add hundreds of rpm's and increase the hp by about 1-1/2 to 2hp.

offset keys are available to advance your timing...a cheap and easy way to boost performance a little more.

find a local kart racer to teach you the in's and out's of alcohol. it burns cooler and will make your motor live longer.

buy a few extra carb jets and see where she like to run.

definetly get an aftermarket "dipper" on the bottom of that rod! the best $7 (max) you will spend towards brigg's reliability.

ok, but i still have some questions

why since my engine is 409cc (25cu in.) is it less HP than Bob's 380cc kawasaki?  just cause its a kawasaki?  ive noticed that many engines have the same displacement but vastly different HP ratings.

ALSO:  i know they generally dont get judged by this but...how many HP would a 400cc ATV engine have?  how is it different than my B+G?  assuming both are 4 stroke...(aparantly my engine has a no load RPM top of 3200RPM's...seems SOOO slow to me...)

the adjustments i can make...(just tell me if i am correct)

1.) ream out carb for more gas flow = more HP
2.) lighter flywheel = more RPM
3.) different air filter = more HP?

thanks again

                                              NOT EXACTLY a briggs$stratton!................try the string on the governor trick....it`l just keep winding till it flies apart........[:)]

well how much horsepower does a 400cc ATV engine have?  cant be more than about 20 i figure.  yamaha just came out w/a 650cc Vtwin that puts out 42.

can anybody answer the other questions i posted (2 posts up)

thanks

I currently work at a farm equip dealership we also sell lawn mowers landscaping stuff and the like. from kubota toro hustler dixon and shindaiwa and i think we deal a few others but dont stock them currently we are having probs with the smart boxes in the kohlers and they are not as well made as they used to be also a few probs with the larger kawias' if you have a qouestion about any of the above i may e able to help you