Since the riding season is winding down for some of us, it’s a good time to consider performance upgrades for next year.

I thought I would take Mogollon’s advice and start a thread asking for feedback from anyone with a 124-128 using the 408 or 22x cams in a heavy touring bike. If you are interested in this topic and haven’t read his posts over on the S&S 124 Kit thread, I recommend you check it out.

I would like to expand this thread to include all things related to Big Bore 124-128 performance upgrades collecting thoughts, advice and results on everything from kits to cams, intake to exhaust.

For openers, I am approaching 5K miles on my 2017 RGS with the FM 124 build and a 408 cam, I did the FM Level A porting with the 64mm Throttle Body, 5.5 G/Sec Injectors, and Ported Manifold. I chose the S&S Oil Pump and Cam Plate with the SE High Capacity clutch (10 Plates) with the AIM/SDR. I also went with the FM / K&N intake and the Jackpot 2-1-2 xxx Head Pipe with the High Roller Slip Ons. The shop that did the work for me said I got the whole kit and caboodle.

I was realistically expecting HP and TQ in the 140s and I was not disappointed with the Dyno results: flat arcing torque curve over 120 at 2500 rpm peaking at 135 and staying above 120 to 6500 rpm where the motor is making 148 horse power. We have to remember dyno results will vary, but I can tell you my butt dyno was not disappointed. My wife (who questioned the funding) is even happy with it and told me if we get another bike, it needs to run like this one does.

The bike is a real treat to ride from the clutch engagement to the low rpm torque to the high rpm power and fuel consumption runs between 37 mpg and 31 mpg depending on how it’s loaded and how I’m riding.

I hope this thread will collect some good information for those who are considering a Big Bore upgrade.

 

In!
Thank you for starting this, I will be checking in regularly. I have my sights set on the FM 128 kit, and am specifically looking for input on the SE CNC heads, vs the FM Level B exchange heads.
My plan is to run the Zippers 468 cam I already have, but am open to suggestions.

A recent post from Jamie @ FM suggests a different exhaust system than I am currently running, and I need to call him to discuss. I will post that suggestion after we talk.

I look forward to reading the input from those that have been through it!

 

I don't have a 124 with a M8 but have one with a twin cam and 648 cam ( I think, been drinking and cant see clearly at the time) any way I would go 128. More is better LOL. got 50k on the 124 I still like riding it, but damn my dads 124 with the skinny rear breaks loose faster then my fat 09 tire. blind sum itch got on it next to a deputy in Sturgis, didn't get stopped though LMAO. a a128 in my bike should get er done.. congrats on your motor OP.

 

I have a 2018 Road Glide Special and went with:

• S&S 124 cylinders and pistons;
• S&S 550 Cam;
• S&S High lift valve springs
• 11.1: Compression Ratio
• S&S Oil Pump & Cam Plate
• S&S Premium Lifters
• S&S Premium Tappets Tappet Cuffs
• SE CNC-Ported heads;
• SE 64mm Throttle Body;
• SE 5.5 g/s injectors
• Harley High Capacity Clutch Springs and Disks;
• Arlen Ness Method air cleaner
• RCX Tormentor Headers and Torx mufflers;
• ThunderMax Tuner
• ThunderMax Oil Cooler

I’ve just finished the break-in miles and will be taking it to get dyno’d in the next couple of weeks but the “butt dyno” has me grinning so far.

For those interested in how I arrived at this combination of parts, it was quite simple... I had the SE 114 Stage IV kit already that included the SE parts listed, and swapped out the components that came in the S&S 124 kit. I relied on the experts at S&S to do the engineering and leveraged the larger capacity components I already had.

 

Signed up

 

I have a 2017 Street Glide Special with the following components in my 124" build:

Cycle-Rama 480 cam
S&S 124" Big Bore Kit
S&S Stealth Air Cleaner
S&S tappets
S&S quickee pushrods
S&S premium lifters
S&S valve springs
S&S head bolts
Stock heads
Stock throttle body
AIM light force slave cylinder
AIM VP SDR clutch with heavy duty springs
SE Extreme-flow 55mm intake manifold
Feuling 6.1 fuel injectors
Feuling oil pump and cam plate
Fuel Moto Jackpot Street Outlaws
De-catted OEM headpipe
Dynojet PowerVision

 

In less than 2 weeks, I'll be taking a little trip up to Appleton, WI to have some wrenches turned on my 2019 FLHXS. She will be getting:

128" piston & cylinder kit, with 10.75:1 compression
Wood WM8-22X cam
64mm throttle body, with 5.5 fuel injectors
S&S oil pump and cam plate kit
AIM variable pressure SDR clutch
FM AC/DC air cleaner kit with S&S stage II air filter element
FM typhoon clear cover for the air cleaner
FM Jackpot 2-1-2 stainless head pipe
Jackpot Hi Roller mufflers
Dynojet Power Vision

I'm very excited about this build, and am expecting a bike with excellent street manners, that has a nasty side to her. I'll post up the numbers when I get back, but I'm expecting mid to high 120s HP, and torque at 140+ Ft Lbs. Whatever the numbers are, I'm sure I'll be very satisfied with the outcome.

 

What bike? Did you consider doing headwork or are you sticking with the stock heads?

 

It says right at the top 2019 FLHXS

 

Good luck with your build, make sure to report back....

I'll be in Appleton on the 28th for "some work".... I made the appointment over a month ago, and I'm like a kid waiting for Christmas...!!!