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 Briggs high rpm screamer

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biggasmowers
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CraftsmanQuad19
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PostSubject: Briggs high rpm screamer   Briggs high rpm screamer Icon_minitimeApril 5th 2018, 5:06 pm

Ok guys, little bit of an odd project but here goes. What do you guys think of a high rpm Briggs flathead single that uses all stock parts and holds up to 6k all day? I’m trying to make it happen.

I’m thinking of using a 25 cubic inch block. Then use the cam, piston, and rod from an OHV 28 cubic inch. The shorter deck height of the 25 poses a problem with the stock crank, so I’m thinking of using the crankshaft out of a 22 cubic inch Briggs.

Long rod + short crank generally = high rpm right?

Potential problems I can see. I know the 25 is a destroked 28 with shorter deck height, but is a 22 a destroked 25? (Prancstaman, you probably know this).

Now with the internals done, delete the governor, polish the con rod, and delete the synchro. Then some porting and polishing on the ports, and a mikuni clone carb for the best throttle response and powerband.

What do you guys think? Am I crazy or will this actually work?
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biggasmowers
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PostSubject: Re: Briggs high rpm screamer   Briggs high rpm screamer Icon_minitimeApril 5th 2018, 7:18 pm

Not sure about the synchro delete but the rest sounds feasible
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PostSubject: Re: Briggs high rpm screamer   Briggs high rpm screamer Icon_minitimeApril 5th 2018, 7:26 pm

I think the "dog bone" that ties the weights to the block can be upgraded. That's the part that usually goes first at higher RPMs. That way you can keep the engine balanced, but not have to worry about it failing.


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PostSubject: Re: Briggs high rpm screamer   Briggs high rpm screamer Icon_minitimeApril 5th 2018, 7:34 pm

Where would one obtain an upgraded dog bone? Which engine would have the strongest one?
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PostSubject: Re: Briggs high rpm screamer   Briggs high rpm screamer Icon_minitimeApril 5th 2018, 7:38 pm

ArcRacing sells a billet aluminum dog bone for $25. Here's the link: http://www.arcracing.com/6200-dogbone-counterweight/


"This'll either wake you up or put you to sleep forever!"- Red Green         "Whatever you do you should do right, even if it's something wrong." - Hank Hill
     
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PostSubject: Re: Briggs high rpm screamer   Briggs high rpm screamer Icon_minitimeApril 5th 2018, 8:50 pm

One interesting thing is, since this is a flat head there's no way you can drop a valve into the piston due to a broken valve spring.

I'm also wondering how an air cooled motor will hold up to these sustained high rpms.
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PostSubject: Re: Briggs high rpm screamer   Briggs high rpm screamer Icon_minitimeApril 5th 2018, 9:37 pm

Ok so o finally went out and started it up to take a video of how high it revs. I think the valves started to float and that's why it lugs a bit in the higher range.
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PostSubject: Re: Briggs high rpm screamer   Briggs high rpm screamer Icon_minitimeApril 7th 2018, 7:11 am

Interesting idea CQ! I like that you're using stock parts from different Briggs engines. As for the synchro balancing, I have an 8hp Briggs that is non-synchro and there is not much noticeable vibration. It may be different at higher rpms though.
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PostSubject: Re: Briggs high rpm screamer   Briggs high rpm screamer Icon_minitimeApril 7th 2018, 2:10 pm

My 17.5 OHV has a bypassed gov and a header. It hit over 6,000 RPM and the longest I held it there was 2 minutes and it never blew. The engine still runs today but it's not in anything lol.
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biggasmowers
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PostSubject: Re: Briggs high rpm screamer   Briggs high rpm screamer Icon_minitimeApril 7th 2018, 3:28 pm

i found out you can but a little digital tach on amazonfor 12 bucks. i need to get one to see how high the kohlers run.
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PostSubject: Re: Briggs high rpm screamer   Briggs high rpm screamer Icon_minitime

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