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  • How to make a racing lawn mower (Updated!)

    yeah, unless you use a turbo (or smog air pump I.e. "poor man's" supercharger), definitely want the intake turbulence, especially if you run methanol) not sure for high rpm If a tunnel ram style intake might work? never tried that but who knows. seems a dyno would be a great thing for these engines to really tune them. we had a 3hp Briggs on a minibike in high school that with centripetal clutch and no trans would do almost 40. had a Harley carb AND burned 60/40 125 gas / ethanol mix though, HAH! crazy days.

    really great Instructable and comments. Few things I'd add, anybody try sprint car gas? my father used to tractor pull with multiple big block engines and he used 125 octane gas(seriously it durometered as that) the performance jump from that in small engines(from Briggs to dirt bikes) was incredible. the engine has to be built for it (bottom end) so crank, rods, billet flywheel, etc, as in the Instructable but it's almost like a supercharger in terms of extra HP. another thing would like to agree with porting comment. I'd natural aspirated(carb or injection) you want the intake slightly rough to mix air fuel, exhaust as smooth and unobstructed as you can. we used die grinder with carbide cutter tip (cross section screw looking oval shape) same as big blocks. took flathead brigs ...see more »really great Instructable and comments. Few things I'd add, anybody try sprint car gas? my father used to tractor pull with multiple big block engines and he used 125 octane gas(seriously it durometered as that) the performance jump from that in small engines(from Briggs to dirt bikes) was incredible. the engine has to be built for it (bottom end) so crank, rods, billet flywheel, etc, as in the Instructable but it's almost like a supercharger in terms of extra HP. another thing would like to agree with porting comment. I'd natural aspirated(carb or injection) you want the intake slightly rough to mix air fuel, exhaust as smooth and unobstructed as you can. we used die grinder with carbide cutter tip (cross section screw looking oval shape) same as big blocks. took flathead brigs "L heads" and made "y heads" hah! also ground the cams on them (decreased duration by grinding g lobes thinner and increased lift by welding a bead on the top of the lobe and grinding down. seems we advanced the timing a bit too from the crank. with higher octane it tends to run drier so you have to fatten up the fuel mixture. again great Instructable thanks, very detailed and thorough. btw anybody use comet differentials or clutches? seems differential might give you better handling, also since it's circle track, do you stagger wheel size left to right like sprints do? seems some of the camber and steering issues might be addressed with that.

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