I’ve been thinking. Dangerous, if allowed to get out of control, I must admit, but these things sometimes happen!

A few days ago I enjoyed one of those near perfect rides, on my Dyna, which was truly flying at the time. The weather was beautiful and the traffic was kind, so when it slowed me down, I was soon able to accelerate by, on a wonderful surge of torque. There, I’ve used the T word.

But first a bit of background. My TC88 Dyna is set up with a solo seat and has basic stage 1 mods, of a SE air filter, carb jet kit and Supertrapp mufflers. However my major improvement is to its gearing. I have replaced the stock 25T crankshaft sprocket with an SE 21T, reducing gearing significantly and increasing rear wheel torque by a healthy 19%. To put that change into perspective, the increase corresponds to the equivalent torque levels of a 103 conversion kit on stock gearing, or indeed the S&S 107 in my Evo.

The significance of this is that my Dyna will comfortably ride in top gear down to below 40mph, then accelerate without hesitation up to 100 or beyond. Fast! No messing or changing gear, just roll the throttle and grin! The bonus is that above 3,000rpm, in other words around 60mph, the engine is wonderfully smooth (not so nice below!) and riding along at say between 3,000 and 4,000rpm, from 60 to 80mph, is an utter joy.

Which finally brings me to that thought! And the connection with Evos. Just what is required to make my 1990 ‘Evo’ Glide accelerate as fast as my Dyna? When we are two up and fully loaded, of course!

Well I’ve done the maths and played with the numbers, taking into account overall weight and gearing. I could reduce the gearing, as I have with my Dyna, but that won't get the improvements I would like and the parts are not available. Alternatively I could throw cubic inches at it, which it seems is just about do-able.

I have concluded that what it needs is a truly serious increase in torque, of almost 40%. In summary, I need around 131 cubic inches. Which is about the biggest motor we can get into an unmodified frame.

Makes you think.....

 

Always here to encourage you to spend your money, GR !
Just ask NGH.

So your Dyna cruises at between 3k-4k rpm at 60 mph? A 6 speed would sure be a nice addition, no?
Same on the FL, dropping your gearing for torque off the line, but keeping reasonable rpm at highway speeds. Probably other suggestions out there.
Keep us posted.

 

Yes, me too! Man, if I needed big power from an Evo I would get the S&S 124" stroker kit and do some head work while the heads are off the motor.

 

Thanks Dale, any help is greatly appreciated!

The revised gearing on the Dyna gives about 19mph per 1,000rpm, so 60mph is a tad over 3,000rpm. Stock gearing is around 23mph per 1,000rpm, so 60mph was around 2,600rpm and it didn't get into the smooth range until almost 70mph. Frankly the engine is not very Harley-like below 3,000rpm and vibrates/shakes quite a lot, but from there on it is wonderfully smooth. 80mph is just over 4,000rpm.

Fitting a 6-speed would defeat the purpose of changing the stock gearing and reduce rear wheel torque substantially.

 

Just taking this discussion on a step further, in my distant youth the bikes I rode were geared to reach maximum engine speed just as they reached their maximum road speed. The classic example is a Velocette Venom, a 500cc single, which with only 34HP could just about reach 100mph.

Going back to my Dyna, the stock gearing gives a theoretical top speed of 145mph, but with the power it has available has no hope of achieving that. My reduced gearing gives a theoretical top speed of about 120mph, which is much more feasible. So I have achieved a more traditional degree of gearing and gained a serious improvement in performance, at very low cost. Travelling at the normal road speeds I use, the engine is running at up to 75% of peak rpm, which is a healthy margin below peak engine speed.

 

I realise this is persisting with TC rather than Evo, but I just happen to have this graph, to show the affect of gearing on rear wheel torque.

The bottom green graph shows typical torque for a stock TC88 at engine speed. The three upper graphs show torque at the rear wheel, taking into account overall gearing. The centre green graph is stock gearing, the upper blue one is my revised gearing and the lower red one shows a 6-speed over-drive gearbox in sixth gear (but otherwise stock gearing).

 

Graham, are you talking about having changed a sprocket in your primary or a pulley on your final drive? on the subject of 6 speeds, isn't 6th gear essentially just an overdrive (1:1)? So that 1 through 5 ratios are the same as a normal 5 speed? Please correct my ignorance on this.

 

makes sense to me, Graham.
What I was saying involved keeping the setup and ratios you have now and adding the 6th gear for highway cruising. I believe Harley makes a 6 that has all the stock gears + .86:1 OD. So on your FL if you reduced the crank sprocket to raise the RPM range across the board, you would have one more gear on top for relaxed cruisng.
Some of riding a Harley is mindset too, for me anyway. I hear the revs climbing and shift down, chugging away with the torque. My cam gets into the sweet spot higher than I 'usually' run it, but that is my own lazy habits. When I ride her like I mean it, you can feel the difference.

Your FXDX sounds like on heck of a curve-riding bike!

 

Hi Jeff, I replaced the primary crankshaft sprocket, originally 25T, with an SE kit of a 21T plus shorter chain. The rest of the drive-train is stock.

There are two types of 6-speed, either with direct 1:1 sixth, or more commonly with an overdrive sixth, where fifth is direct 1:1. Harley tend to use an overdrive sixth of around 0.86:1.

 

Hi Dale, I think you must have posted while I was writing my last post.

Gearing is a funny thing! We Harley owners have been persuaded largely by the noise police to like low rpms. Harley have steadily raised overall gearing to reduce engine revs at the road speeds the noise tests are done at. We International owners suffered before our North American cousins, because of the Swiss, who have tighter noise limits! So I have already reduced the gearing on my old Evo, by replacing the stock 61T rear pulley with your stock size 70T.

Yet while I had my first Harley back in the mid-70s I read about noise from a rider's perspective (in a US bike magazine) and have used ear plugs ever since. So any bike trip other than local I wear them, indeed we also wear them in the car, such as while on our 450 mile trip to Scotland last week.

So whizzing along at say 4k rpm on the Dyna is not a problem!