could comeone explain the compression of pistons and about forged pistons, and about boes and strokes, i wanted to get my 350x motor bored to 430cc but am hearing diferent things about the reliabilty wiht a big piston, and compression, and hsould eihter just stroke it or bore it, I NEED HELP, I AM NOT UNDERSTANDINGz!

 

The compression ratio is the amount the air/fuel charge is compressed when it enters the cylinder. A stock 350x is probably around 10 or 10.5:1. This means that if, for example, 350cc of air is brought into the cylinder, it is compressed down to 33.3cc. At 12:1, which is what many performance pistons are, it is compressed down to 29cc. This makes the air/fuel charge denser and burns quicker and hotter. The added pressure is why built engines are hard to kick over. The hotter burning must be kept cool. Luckily the 350x has a stock oil cooler. I added a cooler on my 250x in order to keep my engine cool, and I had to run 105 octane or higher in order to keep my temps down. The bore and stroke question is kind of compicated. The bore is the distance across the piston, such as 74mm for a stock 250x. A big bore kit can increase the size to 78 or even 80mm. The stroke is the distance the piston travels vertically. To stroke an atv, the crank must be removed and the crank pin redrilled to a postion farther from the centerline. A 250x (this is what I own so I am familar with it) can be stroked an addition 12.7mm or 1/4 inch. You asked about reliability. Much extra heat is intoduced into you engine. Honda's are notorious for the oil thinning and burning up the cam. A high viscocity oil will need to be used. The additional cylinder pressure will be harder on crank case bearings. Starting a 430cc 12 or 13:1 compression motor will almost require it to be dragged behind a truck. Because of port size and other variables many engines are better to stroke. Two stroke always respond better to stroking instead of big boring. However, a big bore kit is around $300, and a stoker crank can run up to $500. To figure your final displacement after boring or stroking you can go back to high school geometry, Radius (half the bore) squared, times 3.14, times stroke, all in milimeters then divide by 100.