Hi All, I'm new to this forum but have been in and out of the Harley universe for many years. I'm starting this thread to share my thoughts, some technical analysis, and answer any questions about my 2018 Fat Bob which was stock for ~500 miles before receiving Slip-Ons with a Stage 1 tune, and shortly thereafter receiving a Stage IV 117 kit with dyno tune around 650 miles.

Here is the beast chilling in my garage

Some quick background on me: I work in industrial communications as a sales/product engineer and am a partner at Performance Dyno, which specializes in dyno tuning late model American V8 gas cars and trucks www.performance-dyno.com. My first "real job" was washing bikes at Heritage Harley Davidson in Concord, NH when I was 15 years old. I spent four years there, ending my dealer tour as a service writer. My first street bike was a 1995 Buell S2 Thunderbolt, which I still own. In fact, through the last 18 years no street bike really caught my eye until I saw the release of the 2018 Fat Bob. I knew I'd own one after reading the first review..... Well lucky me, my wife worked with my friends from Heritage Harley to purchase the bike as a total surprise for my birthday in September. I am one lucky guy!

I must have hit the lottery... my wife got me this 2018 Fat Bob for my birthday in September!

Overall, I am very impressed with the 2018 Fat Bob. The ergonomics are perfect and the handling is everything I expected from the reviews. I find the chassis to be extremely predictable. There is no noticeable wiggle when cursing the back-roads of NH. The bike maintains composure and stability, whether hitting rough patches of pavement or making line corrections midway through a sweeping corner.We all know beauty is in the eye of the beholder and as such I must admit, I love the looks of the Fat Bob. Besides the black Screamin' Eagle slip-ons, I can't think of any necessary aesthetic changes. I did add a small swingarm bag for a minimal amount of storage, but this was simply adding function without ruining form.

Though the 114 M8 does not have the full audible character of a classic Harley, it does hit enough of the right notes to keep me happy. The fueling control and torque around 2500rpm were really impressive for a stock Harley. However, the throttle feels a bit artificial an the power delivery really flattens after 4500 rpm. I found myself running against the rev limiter much more than I would like. With all that said, the bike simply needed more revs and of course more power!

There are always multiple paths to get from A to B, and adding power to a late model Harley is no different. I'd like to give a shout out to Heritage Harley's Service Manager Tim Alexander and Technician/Tuner Alex Moorehead. After extensive conversations with these guys, it was decided that we would have some tuning fun with the Fat Bob. First we would spend some time on the dyno working through a typical Stage 1 setup. I would then get some seat time on this combo while we waited for the Screamin' Eagle 117 Stage IV kit to arrive. Once the parts arrived, Alex got busy stripping the bike down and building it back up the way it should have arrived from Milwaukee!

Here is the Fat Bob, ready to get Stage 1 dialed in

Stage 1 included install and dyno testing of the Screamin' Eagle slips-ons, the canned Screamin' Eagle Stage 1 tune, and then dialing in the tune on Heritage Harley's Land & Sea load control dyno. I am well aware that third party tuners, cat removal, and head pipe upgrades would offer additional benefits, however I decided that this project must be accomplished with the emissions compliant Screamin' Eagle Pro Street Tuner within the 60 day window to maintain full factory warranty.

I have compiled some dyno sheets below to show the testing results through the setup of Stage 1. The long and short of it is: the slip-ons are not worth any noticeable power, but they do add some nice exhaust volume once the small baffles are removed from the tips. The canned tune from the Pro Street Tuner is an improvement, but a dyno tune is necessary to properly optimize fueling and ignition timing. The resulting dyno chart for the fully tuned Stage 1 kit shows a strong increase in power in the upper RPM regions: peak horespower increased just 2hp, but there are 10% power gains at 5500rpm and the motor pulls cleanly to 6,000rpm.

We all know extra power is good, but my favorite result from Stage 1 is the increased snappiness from throttle tuning. These throttle table changes removed the artificial feeling from the drive-by-wire system. The bike now snaps to attention when a fistful of throttle is grabbed from low RPM, rather than having the ECU feed the power through a nanny whose sole intent is to prevent the bike from testing the limits of traction.

The Stage 1 work was completed in mid October and we had a couple unusually warm weeks to get some seat time in. I was very happy with the achievements of Stage 1, but enough is never enough. Tim, Alex, and I anxiously awaited the arrival of the Stage IV kit... Well I can confirm that it was well worth the wait. As you can see in the charts below, the Screamin' Eagle Stage IV 117 kit produced 123hp and 120tq at the tires on Heritage Harley's dyno. This is nearly 50% gain in power at 5500rpm, and the bike pulls hard all the way to 6500rpm.

114 cubic inches was good... but 117 cubic inches, ported heads, more cam, and higher compression is better!

Here it is strapped down for the final Screamin' Eagle Stage IV tuning session

Though the bike lost a bit of power below 2500rpm, I don't notice this on the street. However, I do notice the massive onslaught of torque once the revs hit 4,000rpm. First gear roll-on burnouts happen with little thought, but the most fun is blowing the tire loose with a 4,000rpm clutch drop in second gear. I don't think I will ever get tired of laying rubber from a 30mph roll, but I am curious what the clutch will have to say about this as the miles pile on.

I am very happy to report that the bike behaves as if it was designed for this much power. The chassis is more than happy to keep up with the hot-rodded 117 motor, and Alex's tuning with the Pro Street Tuner yielded factory drivability. This really is a turn-key, easy-to-ride muscle bike with arm stretching power just a short twist away.

The charts below will outline the steps taken with the bike. I will provide dyno results and some comparisons along the way. As many know, dyno results are not always apples-to-apples. Since all testing was done on the same dyno with the same loading parameters, I calculated percentages gained to provide dyno-independent insight into the power gained. I also did some run time calculations to see how much quicker the bike accelerated from 35mp to 80mph on the dyno.... this is not a real world test, but I like data and this calculation verifies the enormous seat of the pants gain that Stage IV provides over stock.


stock dyno results, not too bad
slip-on dyno run with no tune
the slip-ons yield negligible gains, but they do sound better!
canned Stage 1 tune with slip-ons
the canned Stage 1 tune with slip-ons
final results after Alex dialed in the Stage 1 tune
Alex's tune gained the same amount over the canned tune, as the canned tune gained over stock tune
the final Stage 1 results show a much stronger top-end pull, the snappy throttle is not seen on dyno
the final Stage IV tuned dyno pull
this really shows the enormous gains seen in the top half of the power band compared to stock
it took 5.17 seconds to accelerate form 35mph to 80mph on the dyno in stock form
the Stage IV combo cut 1.17 seconds from the 35mph to 80mph dyno pull... this is ~23% improvement

 

helluva 1 st Post! welcome, congrats and nice work!

 

Welcome ,does well.

 

Works for this bike but shows why this kit is a poor choice for a bagger. All that dough and work and it’s no better than a stage 1 below 3300 rpm. Bet it’s fun to rip on tho!

 

Great Post - I'm staying tuned.
I just converted my brand new Sport Glide with a 107 to 114 with the SE Stage IV factory upgrade which yielded 111.86 hp at the rear wheel.
I posted dyno chart already.
I am gonna be pretty cautious because I don't want to run into the sumping / oil transfer problems I read about on this forum for M8*'s running in the higher rpm's for extended time periods rather than just short blips.

 

Thanks for all the attention to detail and documenting the changes along the way. I figured Stage I wouldn't do much, seeing as the bike already has the Ventilator A/C on it, but even so, having Heritage eke out 10% more HP is a pretty impressive gain, not to mention the additional power opened up from the RPM limit being moved from 5500 up to 6100 RPM.

I went with Stage II, but now you've got me thinking about Stage IV someday (once they sort the sumping issue). I was originally turned off Stage IV by the charts in the Harley book, since they show you lose torque below 3500 RPMs. Your chart shows that (with a proper tune at least) the loss is only under 2700 RPM, and even then, the worst loss is really only down 5%. That makes it much more interesting. I spend most of my riding time in the range of 2000-2800 so I thought Stage II was enough, but if you only lose a little down low but gain a TON up top, well... I can see it may very well be in my future.

The only chart I didn't see was for the 117ci Stage IV with the canned Harley map, vs. the Heritage-tuned map. Beggars can't be choosers, so I'm already grateful for what you've shared, but if you had that comparison it'd just be nice to see how much a knowledgeable tuner was able to squeeze out of the Stage IV canned map using the SEPST. I've got a 4-year extended warranty on top of my 2-year factory, so I'm pretty much locked into the SEPST for the next six years, so the improvements possible are very interesting to me.

Thanks for doing this and for sharing it!

 

I agree with Dave, the M8 is all about tq, especially on heavy baggers. I'm sure your bike is a blast to ride, but you're used to riding high revving bikes. Most people complain about the M8 running out of steam when revving it when all you have to do is shift earlier & let the tq take over, just shift between 4-4.5K & you're good. Thanks for the post & all the info though, it also shows the advantage of a good dyno tune, even with the limited PS tuner. It would be interesting to see the 35 to 80 time with a power shift at 4400 RPM.

 

Your tuner evidently had the vss unhooked for the stock runs at least, the tq management really kills the the stock motors.

 

Welcome to the M8 and that was a great post! How many rear tires so far?

Happy New Year!

 

Thanks for the write up. The new fatbob is on my list of bikes to have. I have a stage IV on my street glide and it's a ton of fun. I could only imagine how it feels on a bike as light as a fatbob and I don't think I'll have another Harley with at least this stage kit installed.