390 hp

I found the 390 has 43 BHP. In the cycle world on Husqvarna 1977-1984 book. This special edition of Husqvarna cycle world published all the cycle world tests from that era. Braking horsepower would be on a dynamometer. It had the highest horsepower of the time in its class. Some food for thought.

looks to me like you got your #'s flip flopped Bill !

I think the 250 four stroke single race bikes are in that neighborhood low 40's.
Not sure when it started but if you get a new bike the certificate of origion has a sae hp rating spot to fill in. A 2004 wr250 (Hq) says 42. There is rear wheel horsepower and I suppose taken off the crank. It takes 12 horsepower to push a chevette 55mph so any of these things can get dangerous pretty fast.

I am not sure about what class a 390 is. There was a 450 not long before that.

thank you visiteur!!! i knew i remembered seeing that dyno chart in an old issue of cycle world.
so tired of hearing the 390 puts out over 40 horse.

It puts out 43BHP its not the 77 I believe it's a 79 I'll look it up again. The change is in the transfer ports.

you are saying its very close to the air cooled husky 500...i doubt thats happening. the 500 will tickle the spleen in ways the 390 cant touch..even the 400/430 is noticeably milder.

copied from everfree

I believe that husky did the 390 dynamometer test and got the 43BHP.

I built dynamometers using D.C. Motors that had the hp of 28 Chevy 427 engines. Now they said the 390 has 43BHP on the dyno. I assume they connected the load cell at the crankshaft. It's engine horsepower. Without going through the tranny or real wheel hp. It's going to be much higher going off the crankshaft.
Your 500 cc horse power could be from the rear wheel so it's lower. I put my drag car on a full body dyno. I had 299hp at the rear wheels. The dyne operator told me I'm losing 25% horse power going to the drive train. That 25% is 100hp. Now I wonder if the difference between horse power at the crank and the horse power at the rear wheel going through the tranny is a 25% loss.

It depends on where they connect the load cell. It's two different connections and two different readings.

I'd prefer the rear wheel horsepower then we know what power we're applying to the ground.

The 500cc and 390cc are two different beasts. The 500 is lower in rpm, but plenty of torque with a wider power band. The 390 has higher rpm, shorter envelope on the power band. The 500 should have more horse power.

I'm beside myself , 25 % of 299 is 74.75 not `100 . Just sayin...

He said I had 400+hp at the engine. I lost 100hp going through the drive train. That's 299hp at the rear wheels.

Sweet, Are you on track for any Super Bowl break ins this year ?

Here's the husky test.

Been getting knee injections but ready to check and fit the rings on my 250cr.

Don't forget the larger transfer ports since the moved the cylinder studs apart more plus the 36mm bing was replaced by a 38mm mikuni.

I had a '81 250cr husky that I ported that was a screamer. This was a year before the lower case was changed. The transfer ports in the older case were the largest the smaller case could handle. I think the case number was 2079. For a 250 with a good rider she really flew.

Btw, my orginal cycle world '77-'84 Husqvarna book is MIA. I purchased another from HVA very fast shipping from across the pond. I look forward to doing more business soon he has a lot of goodies I want.

The 43 hp on a stock 390 is at the crankshaft. Old school marketing to push to show more hp than a competitor. We deal with the output after losing a significant number of those calculated hp numbers going through the clutch and transmission I have seen rear wheel hp results in the 35 to 38hp range.

The old crankshaft / rear wheel HP comparison discusion again.

you just dont get it man....the revised-port 390 puts out more and better power than any other husky engine made. the later engines actually made less power...less than the 390

It depends on where they take the horsepower from the crankshaft or the rear wheel. Even the old man who owned the Husqvarna dealership from back them till now even said he liked the 390cc the best too. Now the guy in Stratford,ct if he's still there is an older husky dealer too. He races a flat track 390 auto. There's something special about the 83mm x 71mm stroke. Do you think that big flywheel could add turning mass to the crankshaft?

I think the bigger engines are under rated they have to be more horsepower. But the 390 has a shorter stroke so it revs higher. The bigger we go stroke and piston wise we lose some rpm. But the longer rod increases the torque at a lower rpm.

Not too sure hp numbers but I have an 83 500xc that is hand down the fastest husky I've ever ridden. I've got a 79 390 or with quite a bit done to it, an 85 500xc, 87 500 and 430 both Xc, and the 83 side by side has beat em all. I don't understand it as I bought the bike for 300 bones with a stuck kill button (po said ignition probs) and it is bone stock and the thing is scary as hell. The 390 has the most linear powerband by far and torque for ever but i can't see it being the most powerful. Definitely an incredible engine though and probably the best sounding too

I liked my 390 Auto engine. I felt there was no shortage of power and had a very broad powerband. Just didn't like the freewheeling after getting the brakes wet at a water crossing