Low Compression 128 Upgrade

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Apr 4, 2026 | 11:22 PM

UrbanRunner

Thread Starter

Road Master

Joined: Aug 2014

Posts: 881

Likes: 378

From: Texas Hill Country

Low Compression 128 Upgrade

My 2020 FLHTP is currently at Stage II, and I'm considering upgrading.

My current build includes:
Wood 22XE cam
D&D Billet Cat (Quiet Baffle)
Vance & Hines - VO2 Naked Air Intake
Dynojet - Power Vision
Evolution Industries XR2 Clutch Assembly
Baker Compensator

I've had a Fuel Moto 128" Big Bore kit on my shopping list for several years.

I use the bike for weekend rides with friends to spend the day seeing the scenery and get lunch somewhere (currently ride 2-up about 30% of the time). I ride around 3k RPM and shift around 4k RPM. We average about 300 miles/ride and have also done some Iron Butt rides.

I'm generally very happy with my current build and performance. But...

What are the pros and cons of upgrading, and what specific recommendations do you have? I don't really want to change any of my existing choices listed above.

Here's how things stand now:

Last edited by UrbanRunner; Apr 4, 2026 at 11:32 PM.

Apr 5, 2026 | 07:18 AM

Rains2much

Grand HDF Member

Joined: Sep 2022

Posts: 4,476

Likes: 3,861

From: Florida

Quote:

Originally Posted by UrbanRunner

Youre happy now? Than leave it be. If you have a small dog and feed it a half cup per meal you can’t expect to get a big dog and feed it the same amount.

The performance level you have now with that cam won’t yield the same % gain using it to feed more inches. The inches will still give you more power… but % wise you’ll make less unless you feed those inches more. Your Exhaust may or may not be the right one for more cubes. The tune will be different. The clutch may or may not be enough.

if your goal is more power and keep it as reliable and affordable as possible than the 128 might be great. But it might not be the “big” night and day it would be if you feed the big dog what a big dog needs to eat to be a big dog.. as in compression and cam.

That said.. this is a blanket statement. Maybe that cam and pipe are well known to work well with a 128.. but my statement still isn’t wrong. Whatever % gain you have now can’t be the same % gain on more cubes with the same cam and pipe.

Last edited by Rains2much; Apr 5, 2026 at 07:21 AM.

Apr 5, 2026 | 03:31 PM

Beartooth Rider

Supporter

Joined: Jun 2014

Posts: 439

Likes: 483

From: Montana

If you are going into the engine for that kind of work and spending that kind of money, do it all and enjoy it or leave it alone!

I did the FM 124 Stage IV eight years ago and have nearly 40K miles on it now and I have never had an issue with reliability.

I have ridden it hard, frequently into 4.5-5.5K RPM range.

Just have the work done by a well-qualified Technician.

Apr 6, 2026 | 11:16 AM

Steve Cole

HD EFI Guru

Joined: Jan 2008

Posts: 4,494

Likes: 4,784

Quote:

Originally Posted by UrbanRunner

My 2020 FLHTP is currently at Stage II, and I'm considering upgrading.

My current build includes:
Wood 22XE cam
D&D Billet Cat (Quiet Baffle)
Vance & Hines - VO2 Naked Air Intake
Dynojet - Power Vision
Evolution Industries XR2 Clutch Assembly
Baker Compensator

I've had a Fuel Moto 128" Big Bore kit on my shopping list for several years.

I use the bike for weekend rides with friends to spend the day seeing the scenery and get lunch somewhere (currently ride 2-up about 30% of the time). I ride around 3k RPM and shift around 4k RPM. We average about 300 miles/ride and have also done some Iron Butt rides.

I'm generally very happy with my current build and performance. But...

What are the pros and cons of upgrading, and what specific recommendations do you have? I don't really want to change any of my existing choices listed above.

Doing a bigger build is going to produce more heat, it has too, its the way it works! Now whether or not you feel the addition heat is debatable but it is there, none the less. The HD engine (Evo, TC, M8) has a tolerance of +/- 0.5 on the compression ratio due to the tolerances of all the parts. So unless you tear an engine apart and measure all the parts during assemble you have no idea what you really have. Most shops just assemble the parts when doing builds as doing it and measuring each and every part and then re-machining as necessary will add an additional 10 or so hours of work to the job. This is typically called blue printing the engine. This typically gives a better performing engine as an end result, and cost more too. So one needs to compare Apples to Apples when looking at an engine build, Not Apples to Oranges.

So how much more are you willing to spend and is it worth it to you to do?

If your happy with what you have would you rather wait until a rebuild is necessary?

Apr 7, 2026 | 06:54 PM

thereal142

Road Captain

Joined: Sep 2007

Posts: 602

Likes: 51

From: central MN

I used the FM 10.75:1 kit. 22XD, 64mm SE, 5.5gm injectors, FM headpipe, SE Street Cannons, PV3-B. You will like the difference!

Apr 7, 2026 | 07:19 PM

NorthWestern

Club Member

Joined: Apr 2016

Posts: 11,605

Likes: 8,439

From: Inland NW

I have a FM 128 torque build. There is no down side, other than NOW I am looking for a broader RPM range, so I have it scattered but I got 6 years and 30K happy, happy miles out of it before I decided to change to something different. No leaks, no issues, and after looking at the cylinders...a tinge of regret. Damn, that thing was solid!

Get a great dyno tune, and the felt heat is no more than OE, and the mileage is even better!