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Sorry this is so long winded and pretty basic to some of you...
Somebody correct me if I'm wrong in any of this. I don't know the specifics exactly. You can change performance many different ways, but one of them is by changing the timing and duration of your cams (When the open and close and how long they stay open) and the cam lobe height determines how far the valves get pushed open. Another way is to make higher compression. Third is more volume (As in boring the engine... bigger is better)
As the pistons go down and the intake valves open, they draw the air/fuel mix into the cylinder. The valves close and then the piston comes to the very top of it's compression stroke, near the very top of the cylinder. The compression ratio for say 10:1 means that if the cylinder on the very bottom of the piston's stroke held a total volume of 100 cubic centimeters for a round number, at the top of the stroke, this would all be compressed into an area of 10 Cubic Centimeters. This is all compressed into an area in the head that is cup shaped. This is refered to as the combustion chamber, which has your valves and spark plug in it. The '78 and '79 motors had smaller valves, which meant a smaller combustion chamber to accomadate these smaller valves. Since this area was smaller, the pistons were cramming this fuel/air into a smaller space... meaning higher compression ratios. As a general rule, more compression means more power. Also, even with these smaller valves, these bikes were the fastest of all the XSes due to higher compression and a higher performance cam. The California emmission controls hadn't been placed on these yet.
The later models recieved bigger valves, which needed bigger combustion chambers to accomodate them.. meaning reduced compression numbers. Bigger valves would let the motor breathe better, (and run cleaner for California rules) and should help it make more power, but the cams were toned down a bit. The later model pistons were also higher domed than the '78/'79's to make back up some of the compression lost when the combustion chamber was enlarged, but didn't make it all up.
So... short story REALLLLY long.... By adding the hotter 78/79 cams to the later model engines with the bigger valves is supposed to offset the compression lost power and run better. I can't prove anything as in a dyno or anything, but I know my motor has at least kept up with any of the stock XS's I have run against.... even with me having a much higher body weight than most. BUT... I have never installed the '82 cams to get a comparrison.
It has been said that running a '80 or newer motor with the higher domed pistons and using a smaller combustion chambered '78/'79 head and cams should make the best performance from stock parts.
As for the special order Wiseco pistons, I recently ordered and bored my motor for the 1179 kit. I compared the new Wiseco pistons to the stock '82 pistons, and the stock pistons were a little bit higher domed than the new ones. This would result in slightly lower compression ratio on a rebuild using Wiseco pistons in a later motor. The new pistons ARE higher domed than the 78/79 pistons though, which would mean an increase in compression for the early motors.
Tod
Somebody correct me if I'm wrong in any of this. I don't know the specifics exactly. You can change performance many different ways, but one of them is by changing the timing and duration of your cams (When the open and close and how long they stay open) and the cam lobe height determines how far the valves get pushed open. Another way is to make higher compression. Third is more volume (As in boring the engine... bigger is better)
As the pistons go down and the intake valves open, they draw the air/fuel mix into the cylinder. The valves close and then the piston comes to the very top of it's compression stroke, near the very top of the cylinder. The compression ratio for say 10:1 means that if the cylinder on the very bottom of the piston's stroke held a total volume of 100 cubic centimeters for a round number, at the top of the stroke, this would all be compressed into an area of 10 Cubic Centimeters. This is all compressed into an area in the head that is cup shaped. This is refered to as the combustion chamber, which has your valves and spark plug in it. The '78 and '79 motors had smaller valves, which meant a smaller combustion chamber to accomadate these smaller valves. Since this area was smaller, the pistons were cramming this fuel/air into a smaller space... meaning higher compression ratios. As a general rule, more compression means more power. Also, even with these smaller valves, these bikes were the fastest of all the XSes due to higher compression and a higher performance cam. The California emmission controls hadn't been placed on these yet.
The later models recieved bigger valves, which needed bigger combustion chambers to accomodate them.. meaning reduced compression numbers. Bigger valves would let the motor breathe better, (and run cleaner for California rules) and should help it make more power, but the cams were toned down a bit. The later model pistons were also higher domed than the '78/'79's to make back up some of the compression lost when the combustion chamber was enlarged, but didn't make it all up.
So... short story REALLLLY long.... By adding the hotter 78/79 cams to the later model engines with the bigger valves is supposed to offset the compression lost power and run better. I can't prove anything as in a dyno or anything, but I know my motor has at least kept up with any of the stock XS's I have run against.... even with me having a much higher body weight than most. BUT... I have never installed the '82 cams to get a comparrison.
It has been said that running a '80 or newer motor with the higher domed pistons and using a smaller combustion chambered '78/'79 head and cams should make the best performance from stock parts.
As for the special order Wiseco pistons, I recently ordered and bored my motor for the 1179 kit. I compared the new Wiseco pistons to the stock '82 pistons, and the stock pistons were a little bit higher domed than the new ones. This would result in slightly lower compression ratio on a rebuild using Wiseco pistons in a later motor. The new pistons ARE higher domed than the 78/79 pistons though, which would mean an increase in compression for the early motors.
Tod
lol. 
More power is better right!
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