Ya both wrong , 400 Wet /dry , rough it up on a piece of scrap steel to knock off the sharp edges and hi spots . Then use it to
make some scratches in the arbor parallel to abor and twist the chuck on till you can see cross lines in a 10 to 40 power microscope . The cheap China pocket types have a lens too small .
Make ur own , 16mm or larger diam' , flat one side , curved other side makes a focal length of about 10mm to 25mm , if it is low power , try 2 lens , flat side to ur eye . You will need to have a eye stand off so you can use all the lens to see , undistorted . Notice how : eye too close distorts , but same if too far .
BTW , i just read about engines , Atkison , Miller , Sterling , Scuderi ( Puch)
Sterling is too slow for the thermal resistance of the cylinder walls , Modern engines just dump the heat out the pipe , to speed up , they dont have to save the working gas . But its interesting to slow an engine and get efficiency . Atkison delays intake closing , reducing volumetric eff' but reduces pumping losses AND ! Improves the expansion for better power ! But since you're taking in far less air and fuel , you need to increase the engine displacement , but the "net" is better Now where is V-tec Honda ? Horse power over wider range ! If you could delay exhaust on V-tec you'd limit RPM , but econ would go up . 70 MPG ..... But as above , if the V-tec had 300 cubic inches , then you'd do 60 H.P. at better econ than a Honda HX !
Another idea doin only exhaust : you could simply restrict and expand exhaust after you sucked some heat from it by passing it thru the intake manifold ,by using a tiny turbo . I think Smokey did this . It produced very positve results , comparable to the big makers , like Honda , buthe did it for cheap and so can you . Just feed all the heat ya can into intake with a heat exchanger . You must reduce the compression ratio and of course the H.P. drops .
I have a carb that is so easy to make , only the control is complicated . But it nixes the stupid slow air past the venturri problem that every carb has ! It was so simply to solve , i can say it was genius ... The venturi is at the idle mixture hole ! It does not use a common throttle blade , it uses a simpler , easier to make and fit blade that simply pushes into carb body . The carb has a 2nd hole for air only , it opens when you take foot off , on the HWY , or when ya want to kill engine ...