Does Milling the head on a flat head Briggs & Stratton motor increase power?

In this video we will try and see if Milling the head on a flat head 6HP Briggs & Stratton motor increase power or not.
Disclaimer attempt any of this at your own risk!
The riding lawn mower in this video originally had a opposed twin Briggs & Stratton 16 horsepower engine. I modified the mower to fit a 6 horsepower Briggs & Stratton Flathead pressure washer motor that I upcycled / recycled from a busted pressure washer with a bad pump. Before this video a friend of mine did a port and polish on this 6HP engine.
This video was just to see if I could get a little more oomph out of this little Powerhouse and more for fun than anything.

[@Alcorob]

I love the idea of using a wheelie as a dyno!! Making do with what you got. Awesome

[@davelowets]

Milling the head down WILL increase the compression, but you are also making the pathway to the valves, for the intake and exhaust airflow, smaller in the process. There's more power to be had by working this area of the head after milling it. Yes, you will make the chamber bigger, and lower the compression as you take material away from the head by the valves. So, keep this in mind when milling the head, and take a little more than you need, so when you work the valve area, you will end up with what you wanted for the compression ratio. Also, there can be work done to the block in the valve area. If you plan on doing this, it will affect the final compression ratio also, so keep this in mind before milling too..

[@akfo7691]

my grandpa used to race this on go karts and really knows how to build them so i went and asked him about shaving the heads and he said ur 100%right, and maybe take the gasket off also

[@evilbeetlekustomscreations4965]

Truth!!!

[@davelowets]

@@NubsWithGuns And not "going hog wild" is what I explained in my original post. It IS a fine balance between airflow and compression. If you coukdnt figure that out from what I had explained, then DON'T try it.. 🤷🏻🤦🏻

[@Omegadoomship]

This is correct. Grinding down the eyebrows from the edge of the valve seat to the cylinder will greatly increase flow. Just shaving down the heads alone will increase compression but also decrease flow.

[@960wattoffgridrv]

low compression is from the compression release mechanism on the exhaust lobe of the camshaft. if you really want full compression, carefully check the valve lash where the intake and exhaust valves are supposed to be closed for compression. I sometimes file about 1/2 a millimeter off the end of the valve stem to make the valves at BDC just before the compression stroke. don't get the compression release mechanism confused as an engine fault. on the pull start, compression is reduced mechanically by a spring loaded part that centrifuges out when the engine runs above 300rpm. unless you want that full compression, you can either file down the mechanism on the camshaft or shorten the valve stem 1/2mm to make it fully close at BDC. keep in mind that also increases the horsepower and torque and it can blow a stock muffler apart at high throttle

[@binkythecat457]

I'm an idiot, I was like "man he's having a hard time start that thing". Durp durp. Great video man.

[@dennistennyson4540]

Deck the block and file off the easy-spin lobe on the cam will bring up the compression too.

[@craigchiddo2794]

Put a bead of weld on the cam lobes

[@dylanphillips9745]

What did you mill it with

[@insanityworks3953]

the milling machine was a Harbor Freight manual milling machine I converted to cnc with a kit.

[@DrYosh2]

@@insanityworks3953what type of cutter did you use?

[@shawngoldsberry747]

A broken tap

[@FinalFront]

@@shawngoldsberry747 Is it actually possible to use a broken tap as a type of crude milling bit?

[@chuckhuff7123]

That to do for a mower😢