Get On, Twist and Hang On
Part two of our Milwaukee-Eight Power Build series features a spectacular 162-horsepower Fat Bob from Alpha Performance Engines.
The invitation came from Alpha CEO Mark Harris, “We’re running our 2019 Fat Bob build at Willowbank Dragway this weekend, Dave. Why don’t you come up and take it for a test ride between runs.”
Naturally I was there at bang on time and watched Mark tear up the strip with several runs around the 10.1 to 10.2 second times before he gave it a splash racing fuel and said “Off you shoot”.
First Hit
I rumbled slowly out of the track compound, cruised leisurely down the Champions Way until I turned right onto the Cunningham Highway where I did give it a handful. That’s when I heard myself exclaim “J-i-i-i-m-m-m-iny!!!” (or words to that effect), right out loud, as those 162 ponies and 154.55 ft-lb came into play.
It pulls.
It keeps on revving well beyond the point that you would normally reach for the clutch and upshift, with no diminishing of its surge – long, long, long and strong. Linear power until well after you run out of daring on the open road.
The way the bike has been set up with FXDR triple trees and wide off-road style tapered handlebars makes the surge even more exhilarating.
After a good session winding on and off the throttle over some of the Scenic Rim’s quieter back roads I returned to the strip with a huge grin across my dial and set about finding out how this high-performance machine was built.
Built for Speed
It started life as a 2019 Fat Bob and the first modification was the FXDR triple trees and headlight assembly to change up the looks and to make the wheelbase longer for added high-speed stability.
From there XR1200X wheels were added to make it lighter and to offer a better range of drag-racing-size tyre options. The rear is a 180-55-17 and the front is a 120-70-19 running Dunlop Q4 qualifier rubber.
Inside the 128
The engine was originally a 107 cube but is fitted with a 114-cube stroked crank for starters.
Initially the build was done with the balancers removed in an effort to extract more horsepower in conjunction with the lighter crank but it vibrated badly over 5,000rpm so the balancers were lightened slightly and then re-fitted. There was no noticeable difference in measured horsepower with the balancers removed or fitted.
Capacity has been increased to 128 cubic inches using a proprietary APE Kit which includes 4” 250-thou bore CP Pistons, Stage Two Warflow cylinder heads that were milled to lift the compression to slightly over 12:1, 64mm Screamin’ Eagle throttle body with Warflow ported manifold, APE 530" cam, APE 6.2gps injectors, Screamin’ Eagle High-capacity lifters, Screamin’ Eagle extreme flow air filter kit and a good quality D&D 2 into 1 pipe. There are a choice of tuners available to suit the kit while the Powervision PV2 unit was chosen for this setup.
It’s running stock M8 Valves with the Screamin’ Eagle spring upgrade and a ported inlet manifold that has been modified for consistent flow to both cylinders.
Finding the Flow
In the early stages of development, the motor was producing 155 horsepower with the APE 530 cam fitted but some inconsistency and cross-port contamination was evident in the intake manifold.
Different cams can have varying effect on manifold flow on the M8 engine so the manifold was split, rebuilt and reshaped using metal putty to achieve optimum flow. This manifold has been scanned and digitised so future builds will be made from CNC-machined billet aluminium – as well as being offered for sale as a stand-alone part.
Interestingly the bike produced one less horsepower with the Extreme Ventilator pod filter removed.
The Winning Combination
Mark summed up the process by saying “The reasons we have been able to extract such impressive power and torque from this bike are all around the cylinder heads, the intake valves and the right camshaft for the job. Also having the right exhaust system is crucial. The D&D we have fitted does the job really well.”
The clutch and gearbox are stock apart from Screamin’ Eagle 1275 Springs and they are handling the increased load without issue. The stock oil pump is also proving adequate for the job.
What APE have achieved is a bike that will run close to 10-second quarters and wheelstand past balance point in second gear if encouraged appropriately.
Back at the Strip
Back at Willowbank I watched the bike do a few more very impressive runs as it qualified in top spot for the final.
Unfortunately, Mark ‘Picked a Cherry’ and red-lighted in the final so they didn’t come away with the win on the day, but as a high-performance Harley that is still very rideable in real-world conditions and on the open road, this build is a winner every day.
APE Milwaukee-Eight Power Kits
Stage One
Capacity124 / 128 cu in
Core parts4.250-inch bolt-on cylinders and pistons; bolt-in cam; high-capacity tappets
FuelSE 55 mm manifold; 5.5 gps injectors
Output125–130 hp; 140+ ft-lb
Price at test$3199 parts / $4799 ride-in, ride-out
Stage Two
Capacity124 / 128 cu in
Core partsWarflow Performer heads; .470-inch cam; high-capacity tappets
FuelSE 55 mm manifold; APE 6.2 gps injectors
Output135–140 hp; 145–150+ ft-lb
Price at test$4499 parts / $5900 ride-in, ride-out
Stage Three
Capacity124 / 128 cu in
Core partsWarflow Stage Two heads; .530-inch cam; SE lifters and pushrods
FuelSE 64 mm throttle body; ported manifold; APE 6.2 gps injectors
Output145–150 hp; 150+ ft-lb
Price at test$5799 parts / $6999 ride-in, ride-out
Requirements
Stage TwoQuality 2-into-1 exhaust and adequate air cleaner
Stage ThreeStepped-header 2-into-1 exhaust and large-volume air cleaner
SupplierAlpha Performance Engines
NotePrices reproduced from the original article
Guts & Bolts — APE 128-Cube Fat Bob
Build
Bike2019 Harley-Davidson Fat Bob
OwnerAPE
BuilderSam Fry
EngineMilwaukee-Eight; 107 base / 128 cu in
Power162.52 hp
Torque154.55 ft-lb
Maximum revs6500 rpm
Engine
CrankSE 4.5-inch
Cylinders / Pistons4.250-inch bolt-on / CP X-Forged
Compression12.4:1
CamAPE .530-inch lift
HeadsWarflow Stage Two
InductionSE 64 mm throttle body; Warflow manifold; APE 6.2 gps injectors
ExhaustD&D Fat Cat 2-into-1
Drivetrain & Chassis
ClutchStock 114 pack; SE 1275 N springs
WheelsXR1200X
Front tyreMichelin Scorcher
Rear tyreDunlop Sportmax Q4
Brakes / SuspensionStock
Triple treesFXDR
HeadlightNight Rod
Finish
Front guardModified Sport Glide
Rear guard / TankStock
ControlsStock; Arlen Ness grips
PaintCustom APE theme
PainterMark at QMPP
Quarter mile10.1–10.2 seconds during test session
