Can anyone tell me how a 1973 DT360 makes 30hp and the 1977 DT400 only makes 22hp,I guess I did not word my question correctly.
What did they do to the DT400 to detune it?

My quess is the US gov

That would be correct. The 77-78 models were detuned in order to meet the EPA standards for the last couple of years they were brought to the states. The 400 was not able to meet the EPA after 1978 and was discontinued here. There was also a move by Yamaha to push their XT/TT/IT bikes, so the two stroke enduros kind of petered out.

Though the motor is detuned from the 76-77 models, the better suspension makes those bikes more pleasant to ride. I can tell you that I have never run out of power with my 78, so the HP is not as big of an issue for recreational bike.

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Also, if I'm not mistaken . . . didn't the industry standardize or mandate the way horsepower was taken & reported sometime during the 1970's?
In other words ..... A previous years 30 hp engine would only equate to just 22 hp under the new rating system . . . . as in .... crank hp converted into rear wheel hp.

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This is getting interesting.

HP figures are pretty meaningless as everyone played with them for one reason or another not least of which was insurance costs.The better value is the torque figures.Remember there is no substitute for cubes.

Enduronut wrote: .

Also, if I'm not mistaken . . . didn't the industry standardize or mandate the way horsepower was taken & reported sometime during the 1970's?
In other words ..... A previous years 30 hp engine would only equate to just 22 hp under the new rating system . . . . as in .... crank hp converted into rear wheel hp.

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+1 on this.

bluntz465 wrote: HP figures are pretty meaningless as everyone played with them for one reason or another not least of which was insurance costs.The better value is the torque figures.Remember there is no substitute for cubes.

Yes, there is; technology. This is why Yamaha 250 and 350 road racers blew the doors of there competitors for ages with much smaller engines. The 250cc engine is only 15 cu. in., whereas the Harleys, Triumphs, etc. of the day were 750 cc (45 cu. in.). Don Vesco, Kel Carruthers and their folks were absolute magicians with the Yamaha twins! Could you imagine if a Harley 350 Sprint had to race against Yamaha 350s? From 1972 through 1984, if you didn't ride a Yamaha, why bother to show up?

Hammer

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Hammer wrote:

bluntz465 wrote: HP figures are pretty meaningless as everyone played with them for one reason or another not least of which was insurance costs.The better value is the torque figures.Remember there is no substitute for cubes.

Yes, there is; technology. This is why Yamaha 250 and 350 road racers blew the doors of there competitors for ages with much smaller engines. The 250cc engine is only 15 cu. in., whereas the Harleys, Triumphs, etc. of the day were 750 cc (45 cu. in.). Don Vesco, Kel Carruthers and their folks were absolute magicians with the Yamaha twins! Could you imagine if a Harley 350 Sprint had to race against Yamaha 350s? From 1972 through 1984, if you didn't ride a Yamaha, why bother to show up?
Hammer

Ah yes well there is that of course....even if it was made from rpm torque is still key.But I wonder do you think that 350 stands a chance of taking a VMAX?