There's no way you're not an engineer, mechanic, or at the very least an engine nerd. Most people wouldn't even know where to start on this project. I'm glad somebody is making all these hypothetical lawnmower engine ideas into reality.
A flat plane crankshaft gives you more speed because the 2 banks of cylinders fire evenly back and fourth acting like two 4 cylinders 90 degrees out of phase but creates lots of vibration because of the way the pistons reciprocate inside the engine block
Id build a header that skips cylinders in the firing order, that jumps banks if needed , to get the most from the engine, the flat plane race headers often went up and over the rear of the engine and exit both on one side to allow this, to fit easily, say the firing order is 18436572, the right bank being odd, the right header would be 1467, or the left header would include the 1and 7 cylinder, but a 4 in to 1 header will work, a 4-2-1 would probably work ok also, the 4-1 is easy, I'd be tempted to just use a 1.75" pipe with 1" reducer cone in one end, and about 6" x 1" pipes going into the 1.75" pipe, connecting those pipes together into a turbo would be awesome, use a carb box, and use a single barrel carb from a car, maybe a carb from a 2.0L car engine, roughly,. Get it running decent without boost first, or one of the amr 500 roots supercharger from Amazon/ebay for about $200, and just mount the carb to it! And it to a intake made from 1" tubes reaching to the top of the engine, to a 1.5" x 4"-6" tube that reaches the length of the engine, cap the ends, and mount the inlet in the center, what ever width fits between the cylinders, it's difficult to describe, haha, this is Soo cool, I'd love to build one with motorcycle jugs and heads, connect the cams together, maybe use 150cc scooter parts, they can make near 15-20hp per cylinder,
The crankshaft is SS2541 and the camshafts are SS1672. Both are a kind of toughening steel. They are not treated in any way so this is not an engine that will last. And that was not my intension from the start. Just to see if I could make it run decent for a couple of minutes.
Now I in know this would take resources and machining. Would it be possible to do a camshaft with some custom aftermarket grinds and to upgrade to a stuffer valve spring to n increased the output. It doesn't have to be anything aggressive.
I don't think higher lifts is possible because the valves will hit the seeling in the cylinder head. Increased opening times possibly but it's a delicat engine so I don't think it will hold.
As far as I have found out the flat plane is easyer to balance. I'm a rookie. I thought two strait four side by side. Make a four cylinder crankshaft and make the crankpins a little longer to fit two pushrods. I found out a bit later that the crankpins should have been R,L,R,L. not R,L,L,R. But the crankshaft was made and the steel-piece was expensive so, what the hell. Mercedes AMG have one this way so, why not.
I'm sorry. At the time I made the cam and crankshafts I had no idea that I would end up on youtube. Nor did I know that I should have a working engine in the end. I just had some photos. I made the camshafts with the same lift and opening times as the B&S lawnmower. Same with the crankshaft. Same stroke, same diameter on crankpin to fit the conrods.
