Perhaps we need to hear from those that have done upgrades to 1250 or 1275 and with high compression what battery they have to get the engine cranking.

This is where compression releases and hi-torque starters come into play. Allballs starters are supposed to be hi-torque with no additional load on the battery.

Although I guess that doesn't help the OP.

Stuff like this is why I seldom do internal engine mods. At least in my case it always seems to take me down an expensive rabbit hole of upgrades.

So true. The engine rebuild I just completed ran about $5k in parts and machine work and I didn't even split the cases. And I got a crazy good deal on the head work and rocker boxes which saved me a couple grand. I think S&S stands for spend&spend. It adds up. I wouldn't even want to know what a shop would have charged me to do the build.

Hammer Performance 1250 conversion done in 2016 using the 30degree reverse dome pistons,
Crush ported XL1200 heads @10:1CR and Hammer's Jackhammer 570 cams.
I asked about needing compression releases added and Aaron insured me that
it would not be necessary. I use an EarthX ETX36C LiFePO4 battery.

https://earthxbatteries.com/product/etx36c/

hth,

T.

I have a 1250 w/ high compression.

Used an Antigravity LiFePO4 battery for over 9 years before it wore out. Below is a video of me installing the even smaller Shorai LiFePO4 battery. Both of them are 210 cranking amps. When it is cold, it will hesitate some. But if I turn on the ignition switch for about a minute before I go to start it up, the load of the lights will warm the battery a bit and it starts easier.

As you can see in the video below, it was not cold, and it had just the smallest hesitation before starting up.

New battery
 

Fit a new battery in the 48 & picked up a new Sportster S to keep it company.

https://cimg0.ibsrv.net/gimg/www.hdf...28b2739b34.jpg
2017 sportster 48
https://cimg1.ibsrv.net/gimg/www.hdf...50f4d5bc39.jpg
Sportster 48 & Sportster S 2022

Nice! Both good lookin bikes. You'll have to do a review on the new Sporster.

Around 250 miles on the new 1275 build. Definitely puts a smile on my face.

https://cimg4.ibsrv.net/gimg/www.hdf...d58120bafa.jpg
https://cimg5.ibsrv.net/gimg/www.hdf...37e2665fec.jpg

Removed turn signals and installed the fork wrap sequential LED strips.. the damn thing is wven brighter than the headlight..

installing is straight forward red wire is drl which connects to blue, yellow is turn and connects to purple and black is ground…

only issue i had was probably the small wires assuming theyre 22 gauge wires..
https://cimg0.ibsrv.net/gimg/www.hdf...0840e34cc.jpeg