Anyone ever dyno a bike on a Dynojet 248

[xchief1320]

If so then you know it's a unique experience and I doubt i'll ever do again.
I've seen a few shops online that use them and since we have one at the shop I figured I would give it a try tonight. It felt like I was pulling a car trailer behind the bike. So bad that I was worried to do any full pulls in any higher then 3rd gear. (which I know is the wrong gear)
I did 3 pulls to adjust the A/F since it felt real rich up top. Only pulled them to 10K or so, and that was past my comfort zone bigtime

The final SAE #'s were 174 rwhp and 100 rwtq after slight A/F corrections to get it to 13 to 1.
I did do a 4th gear partial pull and the Tq was higher but I let out at 7K and it made 159 rwhp or so ( I'll have to look at the dyno computer again to be sure)

I know the #'s are pretty low. I am curious to see what it would do on a bike dyno and in the correct gear. I'm thinking the DJ 248 with the huge drums has to be a major drivetrain % loss.

It's a 08 with only a R77 4-1 exhaust.

[Johnnycheese]

it has no idea what is on the dyno all the dyno is measuring is the torque that is turning the drum
4th is the correct gear 3rd would be about 2-3 hp less as long as the weather station was reading correctly those are real numbers

[xchief1320]

Yeah I agree it doesn't know or care what's on the rollers, But the drum weight of the 248does seem to effect the hp/tq on lighter cars a good bit. Due to the fact that most lighter 4 cyl vehicles don't have the TQ needed to turn the drums. And most won't even accelerate the drums in 1 to 1 gear at higher rpm's. They just fall flat and stop pulling.
I've dyno'd lighter 4 cylinder cars (Hondas,ect) on our dyno then put them on a DJ 224 next door and they made more hp on the 224. Some as high as 10-15 rwhp difference. As to where we've compared them on 3000+# cars (mustangs,camaros,ect)and the RWHP/RWTQ numbers between the two dyno's are almost spot on the same. We did a few different tests just to see the differences between the roller size/weight.


Where do stock/piped 08's stop making power? This one seemed to still be pulling when I stopped the run.
I'm heading back to the shop to pick up my laptop and the dyno sheets in a bit and i'll post the graphs..

[Dozerdriver]

My 08 stops making power around 10,500 on the dyno...I think with the ram air in the real world it might go higher.

[Johnnycheese]

anything over 10k will fall flat ram has nothing to due with it
head and cams does

[Dozerdriver]

anything over 10k will fall flat ram has nothing to due with it
head and cams does

Thanks for the info Cheese...

[xchief1320]

Yeah thanks alot for the info..
I'll post up when I get it on a bike dyno. Even though it won't be super accurate since it's a different dyno/day/ect it will give some info..

[crawler]

I've been on them a bunch. Not my choice for the bikes just due to setup. Easier to strap on a bike specific.

But, never had an issue tuning on one.

For me I'd rather tune on something a bit heavy than on something too light and no way to provide load.

[servion]

Wow, I'm surprised, it must have been tough to engage the clutch fully and get it started, that's a big heavy roller for a little bike to turn. Load bearing light-weight rollers are wonderful! I use a Dyno Dynamics car dyno with zero issues.

[xchief1320]

Wow, I'm surprised, it must have been tough to engage the clutch fully and get it started, that's a big heavy roller for a little bike to turn. Load bearing light-weight rollers are wonderful! I use a Dyno Dynamics car dyno with zero issues.

I'm sure my clutch didn't like me too much. I'm pretty sure the drum weight is 900# each so 1800# total drum weight since they are linked together.

Run 1 was in 4th and i let out at 8600
Run 3 is a 3rd gear pull to get the A/F decent. Let out at 9800

[Johnnycheese]

standard drum on a DJ250 is 1000# then add the eddie current brake 750# (frame and all)it is close to the same

[xchief1320]

Wow, I didn't realize the DJ250 drums weighed that much.. Thanks for the info Johnnycheese.

I was wrong after doing some research. It seems the drums weigh 3000# each. The drums simulate a 2400# cars rolling resistance.
The shipping weight of a DJ248 is 8000#

[Johnnycheese]

that sounds better