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Getting More out of my Dyna: Things to know

By July 14, 2015Articles

The DYNA Transformation

2013 FXDBA From this .............

2013 FXDBA From this ………….


….. to this. Transformed to 114 bhp, sub 12 sec 1/4 mile

I bought a new Street Bob FXBDA, first of the 103 motors, four years ago. Since then I have incrementally upgraded the bike so that I could judge improvements and have done 95,000 kms. The Bob now has 114 bhp at the wheel and does sub-12 second quarter miles. If you want more from your bike then this is my story.

When I bought the bike I had a Stage 3 kit installed with the Screaming Eagle race tuner, Screaming Eagle air cooler, and Bisani two into one pipes. The Bisani pipes worked well with this engine and produced a nice note. I also installed an external oil filter since the engine had been upgraded, to help with the extra heat generated.

Although I had already upgraded the performance of the bike it’s important to make sure both you and the bike can control the bike with more power at the throttle. The initial problem was the handling. It was hard to hold a set line and either wallowed or bounced through corners depending on the spring setting. The shocks were just that, shocking. They had to go. I replaced them with a set of KAZI shocks from GAZI suspension with adjustable dampening and spring preload; a quality shock but at local pricing. That made a huge difference straight up. I haven’t had to touch them since and they’re still working perfectly.


PM brakes, GAZI shocks, Bisani 2-1 exaust

The next issue was the front end. It tended to get flex, right when you didn’t want it. So, I put on a H-D fork brace with a noticeable improvement. The next issue was braking. The brakes were either on or off, with little tactile feel in between. So, I upgrade them to a set of PM brakes, 6 piston front and 4 piston rear. What a difference good brakes make. You had that tactile feel going into corners and could feather the brakes whilst dropping into it. But, the front end was still tending to walk out on rough roads, so I upgraded the suspension with a set of Race Tech suspension using their Gold Valve emulators with internally adjustable dampening. They cost about $300 plus fitting. This made a further noticeable improvement.

Now that I had a bike that could handle improvements in power it was time to look at the rest of the bike. If you are going to have a motor that produces more power than the standard bike you’ve got to expect to have problems with the drive-train because of all the extra stress. Well, at 20,000 kms the clutch started showing signs of stress with it completely collapsing when doing a burn-out; the clutch was out, the motor was revving but the rear wheel was not having a bar of it. That was at 30,000 kms. Good bye clutch. When I pulled it down I wasn’t surprised; engineered to minimal specs. I replaced it with a JIMS racing clutch. The difference was chalk and cheese. Not only in appearance but feel. A much smoother clutch with various spring settings supplied.

Well, talking about minimal specs, and while we are on the discussion about clutches, the next thing to go was the clutch basket. It cracked up. There was a rattling sound coming from the primary case. The clutch basket had fractures all around the basket with a section about 2″ long missing. So we replaced it with another standard basket. This didn’t last long. The next time it broke up I was flying down the drag strip at Willowbank on my first run when it went. I didn’t realise until someone noticed all the oil pooling under the primary case when I was lining up for a second run. It had thrown a section of the basket and cracked open the primary case from top to bottom. You could see the drive chain through the gap. Lesson number two, minimal spec, if your going to upgrade your engine performance you need to look at everything in your drive chain. I replaced this with a billeted clutch basket from Rollies and upgraded everything in the primary case area including the harmonic balancer (H-D came out with an upgrade).

I had done only 50,00 kms and was noticing a decrease in performance. I had a compression check done to find that the front pot, yes, the front pot not the back pot, was only 110 psi compression. After pulling it down to do a top end upgrade we found that the front pot had glazed over. This was most probably due to a poor finish on the cylinder walls. Since this was problem to address, and while the top end had to be pulled down I decided to do all the engine mods to improve performance and reliability of the motor. These included a high flow oil pump, geared cam drive, adjustable push rods for ease of adjustment, roller rockers and lifter kit, as well as a new set of barrels, pistons and 110 cylinder head that has all been diamond honed (cylinders), ported and polish heads with upgraded springs, and 10.5:1 compression pistons that had been matched to the barrels. The bike was then dyno-tuned through Procycle Dyno to produce 114 bhp.

When is enough, enough? Never, if there is an improvement that still produces an everyday rider. In order to help put the power to the road the next mods would shave one second off the quarter mile. The bike was due for some maintenance like steering head bearings, swing arm bushes, etc, so I decided to replace the drive belt and put a smaller drive pulley on, from a 32 tooth to a 30 tooth pulley which I got off J&P Cycles in the States who can supply a hardened steel pulley in this size. This gave the bike more grunt at lower revs making the bike quicker off the mark without any significant loss at the top end; the bike still does the 210 kms from corner to corner. I also replaced the gear box which was showing signs of wear with fine steel grit in the transmission oil, with a 7-Speed Bake box. This was the last link in the drive train, and while I can’t complain about the standard H-D box, the Baker box is a stronger, smoother unit. This gave a much smoother feel through the gears with the 30-tooth pulley upgrade. The top end gear revs at 3,000 rpm at 130 km/h.

Well, if you were asking yourself how much did all this cost, then all up about $15,000 for the upgrades. I paid $31,000 for the bike new with the Stage 3 kit and accessories. So the bike owes me $46,000. If I were to do this all again would I do things differently. Probably. I might start with the new Street Bob in the 110 motor. But if I could find one second hand I would opt for that. I had to throw half the new bike away, and then rebuild the engine within 30,000 (which is not uncommon), so I could save a good chunk of change buying second hand. The savings I could then throw into upgrades.

The only thing that remains is a bottom end re-build and upgrade. That is happening right now. The later Dyna aren’t fitted with tincan bearings as standard like they used to be; ouch, HD’s cost cutting again. So, a kit will be put in to give it more strength and longer life. The engine is also getting some attention while it’s all pulled down. It’s being bored out to a 106 cubic inch with S&S Forged pistons 10.5:1 and the crank refurbished and balanced. The Harley barrels have enough wall thickness to accommodate this without the risk of the barrel warping due to heat. Of course, it’ll have to get dyno tuned. So it’ll be interesting to see how these modifications have improved the outputs by comparing this dyno record with the previous – can’t fragrantly elaborate of how great the bike is now without proof – even though it’s tempting.

I’m considering an upgrade to fuel management system for the next improvement, maybe a Thunder Max. I’m running the Screaming Eagle module right now. It’s been alright, can’t complain. If I do switch it’ll be after these upgrades have been done and the bike dyno tuned. Then I’ll be better able to gauge the true value of such an upgrade by comparing the dyno tune output and performance records.

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