I have a 75 Shovelhead FXS, 74 CI. I'd like to change out the rear sprocket to run faster speeds while minimizing excessive vibration. I'll be running 23/48 after the conversion rather than a 23/51. My question is will I need to shorten my drive chain?

 

Probably...Note ; You are going to be putting strain on that engine... but, who says the MoCo knew what they was Doing??

 

I run 23/46, it ran 24/48 for years before that (same ratio, just more room under the starter housing) I cruise at 75mph and use 3rd a lot in the twisties, I have a close-ratio gearset.

 

But, We are talking stock '74- 74" I won't..

 

I ran 24/51 for years on my shovel. The bike is still that way today.
Buddy with a panhead was running 24 /48 and when we took off side by side we shifted at the same time.. He had a different gearset in his trans.

 

Too Tall... I won't.. If I wanna accelerate...I bust out a Drag Bike...
Edit...if ya Hate yer Starter Housing that bad...go on and Lower yer bike along with that 24!!!

 

Different strokes for different folks, I have always run tall gearing, even on my first Yamaha moped, it's a thing with me I guess lol!

 

^ Same here

 

My very first incarnation of a Harley was a 74” with 24/51. It had a cobra 440 cam, short straight pipes with mufflers, a B carb and a Dyna S ignition. OP… I loved to ride and I could cruise 75.. that part was good… but oh god was it slow. All my riding buddies just left me behind. It wasn’t fun being last everywhere, everytime.

I bought that motor and title together and had no idea what I was doing. It was my first Harley. The very first winter I tore that 74 down not knowing a thing. I had nobody to help me. I had to guess. I had to read magazines and Clymer lies to figure things out. In the spring came a 93”, lots of set backs and unknowns because it was all on me. I had built dozens of Ford 460’s & 429’s, that mechanical side was solid. And I had good practices established such as neat orderly environment. I knew how and why to use a torque wrench, and I could borrow tools. When that 93” fired up and got through its break in… all hell was unleashed on my buddies. It was their turn to Nash their teeth at night and toss and turn not understanding how an old shovel was spanking them silly..

‘’From that first spring onward it was a race. Everybody got tight lipped and every winter everyone was sneaking behind everyone else’s bakes updated their bikes. For example: An 883 got traded in for a 1200 with 10.5:1 pistons, Buell ported heads and fancy cams, a softail got heads, pistons pipes…

It didn’t matter the Shovel spanked them all. They spent a fortune with dealers and professional dyno tuners only to be embarrassed by the Red Hornet (as they nick named my bike) I think when they finally gave up is when I smoked the new V-rod while two up. They couldn’t wrap their mind around how I could carry a extra 115 lbs and still beat the v-Rod.

That 93 went from 10:1 cast with V-Thunder 4030 to 11:1 with Redshift 580S to 12.4:1 with Redshift 550 to 11.7:1 with Andrew’s M Grind. By that time I was participating in Hot Street and had ran 11 second quarter times. By that time I was building other peoples motors.

All this to say, you may not like the 48 tooth out back off the line. You may not like it when passing a semi. Racepres is right.. 74” isn’t enough to pull that gear. But what it will do is cruise nice and bring your rpm down.

 

Think of it this way...There is just about "that Much" power available...Less on an old 74"er.. If you want to go Fast...you have two choices..DragStrip Fast...otherwise known as Quick, (get there Now)!! Or Bonnieville Fast... get dragged to whatever speed you May have enough power to continue to gain speed.. reason salt runs are 3 miles long and only register the "Flying Mile".. I have No need nor Desire to hold wide Open for Miles...waiting to accelerate... if I can achieve 55-60 in a Short burst...I happily ride along at that speed..Someone goes Faster...Oh Well ...Good on em..hope they have a Beer on the Bar for me when I catch up.. Not unbearably long...maybe a **** Break!!!
Edit; Oh Yea...like Fast??? I provide a Place to Prove what ya Gots...the Dragstrip... at least once a Year..