The pic below shows the mod....you bend the tabs out to "add backpressure and therefore torque" I've read all over the internet about it. However, anyone who actually understands exhaust knows that adding backpressure never increases torque. You get more torque by increasing exhaust gas velocity, which in turn increases scavenging, which is where the torque increase comes from. Any added backpressure means the engine has to work harder to expel the exhaust gasses.

So i'm trying to wrap my head around how bending the tabs on the TH baffles, which would indeed increase backpressure, would increase torque. I know people swear by it and supposedly there are dyno sheets to prove it, but I just don't believe it. And I just don't want to start ****ing with bending the baffle just to experiment. Anybody have actual numbers to show?

 

I've heard of this and am curious as well.

 

Cam only 96" bending 3 tabs.


Mild 103" bending 2 tabs. Bottom end is from the baffle mod, top end was a timing fix. The chop is clutch slip.


Same 103 2 tabs vs 3.


I just retuned my 145hp 114" with a Thunderheader muffler on a boarzilla headpipe and picked up low end by bending 2 tabs. 3 didn't pick up anymore and lost 1 ft lb. in the middle. I don't have that dyno sheet on my phone.

 

on my bike I had a dip in the tq at 2500-3500 dan thayer said to me lets bend all four tabs to see if it makes a difference. some due some don't. he made another pull on dyno and my tq came up. he made some changes in the fuel cells and changed some timing and made another run. the dip was all most gone, made some more adjustments and gained 12 lbs more tq in the bottom end. and said you will defiantly feel this when you go for a test ride. I cant find the sheet right now but you can see it in my earlier post for my 107 build.

 

I knew you would have that thunder header back on there sooner or later!!

 

I appreciate the dyno data. I just wish someone could explain how increasing backpressure in these cases seems to increase torque, when that is counterintuitive.

 

Lol. A zilla on a bagger sounds nasty, dyna zilla sounds like **** imo. Put a vrod th muffler (larger diameter) on the zilla headpipe. A little deeper and quieter than a normal small tube th but still way better than the zilla. It lost a couple hp switching the muffle but I made some changes to the heads over the winter and it made 145/131 Monday @ 91 degrees and humid with the thunderheader muffler and a hair more bottom than the zilla.

 

Vdrop I like the look!!! did the guy from N.H.that you tuned his bike ever make that stepped thunder header pipe??

 

I get your point but results are more important than theory to me. We could talk about it all day and the dyno sheets are the same. The only bike I've ever seen no or negative results on was a sportster. Pretty much every twin cam benefits, and tuners who say otherwise don't know or are too lazy to try. If my 145hp 7000rpm screamer can benefit from this on the bottom without losing a c-hair on top I think it's the best free mod out there. It picks up at every throttle position too, not just wide open, throttle response improves.

Also can add that my old 95" picked up 7ft lbs on the bottom from 3 tabs but I can't seem to find those sheets. I have over 300 dyno pulls on my bike, you could say I've experimented a little.

Nope, not yet. I think he's been enjoying how well it runs with a tune vs thundercrap. That bike was fun to ride. I think I'm putting an od6 and 3.37 in it this winter so hopefully he builds the pipe before then to see what it does.

 

Fair enough, can't argue with that. I'll probably start with 2 and retune with the PV. Wish I had a dyno. You bend them to about 1/4" from the outside, right? Any decrease in sound?