Thread: port timing on my 371

There is a Sticky thread here in this forum on "Reading a degree wheel" where you can learn how,please read thru it.
For your stock intake port I would suggest you lower it 2mm,this is a safe amount to alter most stock intake ports for more duration resulting in better power without much real negative affects. Alternately you can also trim the intake skirt of the piston for the same result. When doing this try to keep the same shape/curve of the bottom edge of the port as stock,it must be slightly rounded,not straight and flat across. Also it is vital to chamfer the edge of the port after you alter it,it must have a bevel to prevent the piston from contacting a sharp edge and to help guide the piston skirt past it,again look at the factory chamfer job on all the top and bottom port edges as a guide. Failure to chamfer the port edges can result in the damage of the piston or rings,in many cases I will make a better chamfer job on the cyl. ports than stock for reliability and engine life. You can use a round file to do this,take your time and use care,you can chip off the Nikasil plating of the bore if you are not gentle.

..Have some rep Trappermike!!

Hi guys, I'm new here and loving reading all the posts. I've been porting and doing performance mods to engines since 1977.
And just recently had someone ask me to do some port work on a saw. So out of interest started looking and found this site.
I was Just reading some of the posts regarding the intake port timing. If you remove 2mm or whatever amount you want from the piston skirt or the same amount from the bottom of the intake port. The timing will be increase by the same amount.

But the area will not increase if you remove it from the piston. But if you remove it from the port floor both the timing and the area will be increased. This something to think about as you may or may not need more port area.

Same goes for the old trick of removing some material from the piston where the exhaust and or transfer ports open and close the ports
to see how the engine likes or dislikes the timing increase.

This can be a handy trick to play with if you are thinking of replacing piston anyway. But just remember the area does not increase just the timing.