A forum for owners of Yamaha TTR250 trail and enduro bikes!

Lin · Senior Member

BHP

TT-R250M · Super Guru

No, but I am very interested myself as there is a lot of bad info floating around about the HP. I would also like to Dyno mine to see what sort of increase the ''mod's'' has done. My bet is that it has raised it HEAPS!

I think that top of the list of rubbish mod's is the ''cutting the snorkel'' mod. It did nothing for performance and only made it run rich. So rich that it did not even rev past 1/2 throttle.

Of course, others may see this differently.

Jarrah

brindabella · Senior Member

doesn't seem to be any ttr250 dyno charts floating around on the internet.

but Brian was recently advertising silencers from Motad that were developed using his loaned bike.
the exhaust people claimed 4% power increase, so maybe they still have the dyno results to back their claim?

Lin · Senior Member

Yes I remember that. Any figures Brian?

TTRfan · Super Guru

OE silencer and standard header topped out at 22.6hp at 7,002 revs so that's about the figure for a dead standard TTR at the rear wheel.

The Motad silencer and shorty front pipe topped out at 25.1hp at 7,471 revs

brindabella · Senior Member

Brian I'm guessing it was the shorty pipe that pushed the power peak up the rev range.

It is pretty weird that Yamaha specs give the standard maximum power point at a much higher 8500rpm.
I am wondering was the loan bike they used in good condition and did they do any other tuning?

It sure would be interesting to see the full chart, if available - to see what effect it had on the bottom end,
and at what RPM the torque dropped right off (and where the rev limiter cut in).
That would be handy when considering gearing options.

Lin · Senior Member

The MCS website claims 28hp at 8500rpm. I'd assume thats an at the sprocket figure. Allowing minus 3% for chain losses leaves 27.16 at the wheel, a long way from 22.6 at 7000rpm (23.8 at the sprocket)

http://www.motorcyclespecs.co.za/model/yamaha/yamaha_tt250r%2000.htm

I'd have thought that despite it's skinny carb and asthmatic exhaust the TTR engine, having a narrow angle four valve pent-roof combustion chamber, 10.2:1 compression ratio, and a bore/stroke ratio of 1.22:1 would at least make 110hp/L = 27.5hp at the sprocket. Brian's dyno test says otherwise.

TTRfan · Super Guru

It was a "well used" TTR on trials tyres so that may have lost some power but the comparisons are probably still fair.

I am still planning to get the 325 on a dyno to tune it up and check some airbox and exhaust combos but my upcoming Stateside trip has put that on hold!

Brian

petenz · Super Guru

Lin wrote:

The MCS website claims 28hp at 8500rpm. I'd assume thats an at the sprocket figure. Allowing minus 3% for chain losses leaves 27.16 at the wheel, a long way from 22.6 at 7000rpm (23.8 at the sprocket)
http://www.motorcyclespecs.co.za/model/yamaha/yamaha_tt250r%2000.htm
I'd have thought that despite it's skinny carb and asthmatic exhaust the TTR engine, having a narrow angle four valve pent-roof combustion chamber, 10.2:1 compression ratio, and a bore/stroke ratio of 1.22:1 would at least make 110hp/L = 27.5hp at the sprocket. Brian's dyno test says otherwise.

You will most lightly find the 28hp figger is crank shaft HP... So the 22hp rear wheel works out about right

as on avarage you lose about 20% from crank to rear wheel..

primary reduction / clutch / gearbox / final reduction / mechanical drag ........ it all adds up...

oil alone sucks a increadible amount of power...

Lin · Senior Member

Yes petenz that would make sense. At 28bhp and allowing and 20% for mechanical losses we would see 22.4bhp at the wheel which lines up with what Brian reports. At 3% chain loss we would see a shade over 23bhp at the sprocket. Agree oil churning soaks up hp and contributes to heat generation.

I guess Yamaha have used an engine dyno rig that allows direct power measurement off the crankshaft.

JDM_stig · Veteran Member

Did they take a before run?
the max bhp isnt the bee all when it comes to tuning,
I remap cars and the drive-ability is what surprises people, not just the higher bhp that their mates talk about,
So the tuning may bring more mid range or allow the bike to pull from lower down.