I noticed by accident yesterday on the HD website that, even for models that all have the same (except for balanced and unbalanced) 103 cubic inch engine, the peak torque varies by model. A fair bit.

I THOUGHT all the 103 engines are identical except for the 103B "balanced" engine used on the Softails. But, apparently there ARE differences.

Here are the peak torque values for all 5 of the Dyna models on the site:
98.8 at 3000 Street Bob
98.8 at 3000 Low Rider
98.8 at 3000 Wide Glide
98.8 at 3000 Fat Bob
98.8 at 3000 Switchback
ALL are 98.8, so the peak "average" is 98.8. All peak at 3000 rpm. So far so good.

Here are the peak values for the Softail models with the Softail "balanced" engine that has the internal balancing weights and chain:
97.4 at 3000 Fat Boy
97.4 at 3000 Fat Boy Lo
98.7 at 3250 Softail Deluxe
95.2 at 3000 eritage Softail Classic
97.4 at 3000 Softail Slim
95.2 at 3000 Breakout
Note that the peak average is 96.9, or 98% of the Dyna models, and only 92.4% of the touring models below. Note that one of the models, the Softail Deluxe, peaks at 3250 versus 3000 for all the rest. Why? Note also that the Breakout, the model that poses as a "dragbike", has the LOWEST peak torque. Why?

Here are the peak values for the touring models. All of these are at 3250, versus 3000 for all but one of the Dynas and Softails:
104.7 at 3250 Road King
104.7 at 3250 Street Glide
104.7 at 3250 Street Glide Special
104.7 at 3250 Electra Glide Ultra Classic
105.5 at 3750 (3750!) Ultra Limited
So, the peak average is 104.9, which is 6.2% better than the Dyna models, and 8.3% better than the Softail models.

Note that the rpm for peak torque on the touring models is 3250 for most, and an incredible 3750 for the Ultra Limited - that's "hot rod" rpm for a peak torque reading.

I can certainly understand HD wanting to put more torque into the touring models, since they are notably heavier than the Dyna models or Softail models, but having the torque curve peak at a HIGHER rpm is not where you would expect it for a heavy touring bike.

And, it make sense that the Softail "balanced" version of the 103 engine should show less power and torque than the unbalanced A version of the 103 engine, since it takes torque (and power) to accelerate the balancing weights, sprockets, and chain in the balanced engine.

But what creates the extra 6.2 to 8.3% more torque on the touring bikes? Is it a less restrictive intake? Is it a less restrictive exhaust than on the Dyna and Softail models, because the exhausts on the touring models are in general far physically larger than on the Dyna and Softail models?

Any why do some models peak at higher rpm (3250 or 3750) even though supposedly all the 103 engines have the same cam?

Can any of the forum members who actually work on and dyno these bikes explain what is going on?

Jim G

 

The touring exhaust accounts for the the higher torque in the touring models. I can't answer the question about the variance in peak torque but expect that there are multiple contributing factors.

 

Could it have to do with gearing differences?

 

I am not positive on this, but I think all the 2014 big twins have the same gearing, don't they? In any case, HD is quoting CRANKSHAFT HP in these website ratings, not rear wheel HP, so gearing wouldn't be a factor.

But, good question to have asked, JohnnyC, as gearing differences do very much affect dyno readings taken on a DynoJet dyno, where the torque and power being measured are rear wheel, and where the accelerating nature of the test makes gearing a big factor.

Jim G

 

what aspect of the touring exhaust makes it that much better than the softail or dyna exhaust?

 

Volume! Bigger mufflers can muffle more sound with less back pressure.

Don't know what the deal is with the Heritage and Breakout??? But it looks like they have "true duals" without a crossover?

 

This. The bigger mufflers on the dresser. On the Softails there is a slight parasitic loss with the balancer.

 

Great observation on the "true duals" versus having a crossover tube between the two pipes. Not having a crossover definitely hurts mid range torque.

HD probably did that on the Breakout specifically to "look" right, since they wanted us to think "drag bike".

Jim G

 

Yes, and that loss is accentuated by a further, fairly large "diversion" of power to accelerating the balancer mechanism (sprockets, chain, and balancers) under acceleration conditions on a Dynojet type dyno. That extra diversion does not show in the HD website numbers because they get those numbers from an ENGINE dyno (no acceleration of the engine) versus from a Dynojet (engine is forced to accelerate from minimum rpm to maximum rpm inside of 8 seconds or so).

Jim G

 

Interesting. I have always been a fan of the cross over. Harley seems to go for form over function a fair amount of the time.