old vs new

[inteva6184]

Hey guys I have a bit of a noob question but hey ill ask anyway sinse I havent seen this specific topic yet.
Why is their such a huge power difference between old and new bikes? I mean id expect a difference but my 80 supposedly peaks at 4.5 these new 80 bikesare almost 4 times that power. So why such a huge difference. Their isnt alot to these motors so I wonder ehat the big choke point is. Is it compression, reeds, tuning, exhaust or ignition? Anyway just curious why theirs such a huge difference.

 

[RM_guy]

The advent of power valves made a big difference and beside the items you already mentions, water cooling also made a huge difference. Bikes can operate closer to the "edge" without blowing up when the temp is better controlled.

The industry learns new techniques to sneak out more power every year and those things get built in the next model. Overt time it may seem like a huge difference but from year to year it was more modest and sometimes they even went backwards!

 

[helio lucas]

my 80 supposedly peaks at 4.5 these new 80 bikesare almost 4 times that power.

probably different type of engines... racing and street engines have different states of tune. modern simple two stroke road going 80cc engines may not have any more than 10 hp...
a racing mx 80cc from the '80s may have the same power as modern 85's.

even in road engines there is a huge variation. tzr 125 yamaha engine (yamaha, not minarelli) is power valved electronically with stepped motor with more or less modern technology and puts 20 hp (great smooth engine BTW with a big, large, flat torque curve). aprilia rs 125 engine (rotax) is mechanically power valved (although the solenoid is controlled electronically) but with a on-off actuation, puts almosy 30 hp...
they both are very similar on tech but the reeds of the yamaha goes on the crankcase and the aprilia goes on the cylinder.

small things does the most gain!

 

[dirt bike dave]

Ditto on the powervalves. That is huge.

Also, if your older bike is a modestly tuned trail bike, it is going to have much less power than a race bike from the same era. For example, a '78 YZ80 is going to have way more power than a '78 GT80.

The little race bikes have much more aggressive porting, higher compression, better tuned exhaust systems, bigger carbs, single ring piston vs. two rings, etc... It all works together, but the cylinder porting and power valves are the big difference maker, IMO.

 

[RM_guy]

Another thing worth mentioning is that the factory bikes back in the day were very, very powerful and there was a huge gap between what you could buy from a dealer and what the factory raced. Now, what you buy from a dealer is pretty close to what the pros race. They may have a few tweaks here and there but they are not nearly as far off as was in the 70's and 80's.

 

[inteva6184]

Great info guys. Dirt bike dave funny you mentioned the gt80 the bike I am talking about is a 73 gt80 or whatever they called it in 73. I think the name was changed in 1974 to gt80.