I've recently upgraded to V&H Big Radius 2:2 with their stock baffles, V&H Fuelpak and an Arlen Ness Big Sucker Stage 1 cleaner on my 2012 Fat Boy Lo. I've started started paying closer attention to the bike's response and it seems that the low end torque is, well, low.

The bike's performance overall isn't poor, but it feels like it's expending more fuel getting going in first than what it's putting out in torque; as if the bike is trying to get out of it's own way to *really* get going. Second, third an even fourth feel far more responsive than first does off the line.

As a comparison, I rode a friends stock 2011 Fat Bob and it simply flies out of first (though I admit my Fat Boy looks and sounds way better )

Any suggestions on what I should look at? I suspect (and fear) this can quickly degrade into a "get that Fuelpak off of there and go with X," but I'm hoping that some technical merits as to why the low end torque feels the way it does could be offered up. I'm not familiar enough with what can actually be tuned on the bike for given results, so input and insight into the hows and whys is greatly appreciated.

 

Put in some Low-Mid tq cams in her.. That will put a smile on Ur face and Ur motor will thank You...

Fuel pac for sure ain't the best it only changes Ur A/F. Doesn't tune the motor at all.





.

 

255se cams. Lot of punch off the line.

 

I can't help you with the torque, but you need to know, friends don't let friends drive stock Harleys!

So save your money and give it your buddy so he can do some upgrades.

 

One of the factors that will reduce low end torque is your exhaust system.
The stock exhaust while restrictive has a good amount of back pressure (a good thing) and more importantly a crossover system (a pipe that connects both exhaust pipes together). The V&H Big Radius 2 into 2 is NOT a crossover system and definitely lowers torque. Vance and Hines does make exhaust with crossover technology (i.e. Big Shots and what I have on my bike, Side Shots)which are designed similar to the factory exhaust which maintains torque. A 2 into 2 system while reducing torque actually increases horse power which is probably what you are feeling at higher speeds.
(torque=pickup/acceleration hp=top end speed)

Did you have the bike dyno tuned or just have a generic map loaded in the tuner.A dyno will definitively improve performance over the generic map.

I have just recently switched out my factory head pipes (with crossover) and Rush slip on mufflers for a V&H Side Shots with "Power Chamber" design (V&H's name for a crossover pipe) and I lost some bottom end too.

Lastly the V&H Fuelpak, while a good unit is somewhat limited. I bought a Power Vision http://www.dynojet.com/powervision/ that can actually tune your bike based on YOUR driving conditions. I don't believe that the Fuelpak can do this.

If you don't plan on gettting cam's etc. I would just get it dyno tuned and you will get the best performance out of the bike possible with the setup (pipes,a/c etc.) possible.

I have no experience with dyno tuning so someone more familiar with it might give better advice as to how much an improvement over your Fuelpaks map it will be.

 

Had the same issue with my 2012 Fat Boy & V&H Mufflers a little diffrent set up but I think the problem was caused by the same thing. What I did to solve the problem cost me about $60.00

I just took out the factory 2" V&H baflles & installed the V&H quiet baffles there about 2 decimals quieter and have a more mid throaty sound still pretty loud. The problem was solved way better low & mid torque now & the bike still sounds great.

I have the V&H twin slash mufflers but the baffles work just like the kind you have in your pipes. I also have the stage 1 A/C unit & the HD stage 1 download & my bike runs great plus has good milage averages 42mpg.

I did have the V&H fuel pack but it shorted out so I sent it back but the bike ran so good I did not put it back on. V&H does have a map for the fuel pack & the quiet baffles and your application no problems there.

The quiet baffles may be a cost effective way to solve your issue while still making your pipes sound nice and give you that low & mid torque back. That's what the quiet baffles did for my set up and I bet money they will do the same for your set up.

Best Of Luck & Ride Safe,
Bill G

 

I agree that the quiet baffles will add some back pressure but you can't get a 2 into 2 system to perform as well as a crossover system.

 

You have a good point, but the quiet baffles if available for his system may help him out a little...My system has a crossover between the two headpipes so the quiet baffles worked well.

Ride Safe,
Bill G

 

In what I've learned from this thread and further research, the value of back pressure isn't to be underestimated and makes more sense to me now.

Is that tiny connecting tube between the pipes on the stock exhaust what's contributing to the crossover? I thought it was there purely for support and spacing.

Have not had the bike dyno tuned and am trying to determine the all up value of static vs. dynamic fuel management.

Today, I simply have the V&H recommended map loaded into the Fuelpak. I'm still in research mode on this one with the contenders being the Fuelpak (easy installation, easy removal, decent results thus far), a PowerVision (easy installation, huge amount of custom control and endless tinkering) or a Terminal Velocity (moderately more difficult installation than the Fuelpak, dynamically alter TPS information based upon O2 sensor readings to provide a constant A/F ratio throughout.)

The cam option intrigues me. Thanks for the discussion and insight, bulldog

 

Thanks for the insight, Bill. I'll do a little more research and see if I can get some additional feedback on the performance of the quite baffles without any crossover. I have to admit, I enjoy the way the bike sounds right now, and there's a notable difference in things like reduction of decel popping with the Fuelpak. And while I know that the low end torque isn't there, it's not so bad as to force my hand for a solution. Then again, I don't know what I'm missing!