I was trying to find out which was best. One person would say the factory headers and the next would say the tru-duals. I had my 2006 Ultra Classic with the Stage 1 download, Screamin Eagle II mufflers and Vance & Hines tru-duals checked on the dyno and then put my factory headers on and had them dyno it again. The results kind of shocked the guys at the Harley shop. The factory headers put out 80.67 hp and 80.43 lbs of torque. The tru-duals put out 76.76 hp and 77.08 lbs of torque. I tried to include a copy of the dyno sheet, but I don't know if I did it right or not.


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I don't dout that at all, a good set of slip ons with factory headers will out perform true duals most of the time. The 2/1 will give you better performance than either, if you take a set of Hooker tuneables with stock head pipes, set the left to tq and the right to hp that's as close to a 2/1 as you can get, you loose that option with true duals

I had Hooker tunables on a 2001 RoadKing and changed to Rinehart true duals, I lost 5hp and 6ft/lbs tq

 

That is pretty solid proof. I could mainly tell I lost some low end tq when I installed my true duals. . .it is interesting to see how much though.

 

If you really want true duals on an FL bike and you are interested primarily in power, Rhinehart Stepped Duals are the only choice.
All other true duals will rob power like you just found out.
For the price, you can't beat the stock headpipes and good slip-ons. Vance&Hines or Samson are the best I have found and used, even Screaming Eagle Slip-ons are quite good.
True duals are for looks or telling stories - not for performace unless you spend the money on Rhineharts.
Mike

 

FYI they printed them uncorrrected. Look at the temp and the humidity. That could easily make the difference right there. Have them reprint both charts on SAE and smoothing of 3. Also make sure both runs were in the same gear.

 

There must be a breaking point on this theory. I have no doubt that the factory Y pipe w/ slip ons will make better numbers on stock and mild performance builds. I don't think they can flow enough air to out perform a true dual on higher performance builds. That rear pipe creates too much turbulence and will eventually impede the flow of the exhaust. High lift, short duration cams (something similar to a Woods TW6HG) with ported heads will most likely be the difference where true duals will out perform the factory header.

As you said, a 2-1 should outperform all on most engines. However, I'm sure there are exceptions to the rule.

 

Your correct, there's always a point you step up, but mild performance builds as Magna stated in his post most always do better with a good slipon over true duals. The 01 Roadking I had was 95", stock heads, stock TB, SE 211 cams, Power commander, nothing I consider over mild build, I'll try to find the dyno charts to post. (Besides that was my wife's bike and I didn't want her outrunning me)

 

Magna,

Thank you very much for posting your results. I have been preaching what your results proved for years. Some guys bolt on True Duals and let the placebo effect of spending money on something new make them believe they are making more power.

 

One S.E. is right, I noticed this also. You have 3 things in the second run working to your advantage:

1) Air pressure. The "elevation" differance is almost 500 feet. Much higher pressure on the second run thus like being at a lower altitude.

2) Temperature The temp is almost 15 degrees cooler on the higher horsepower day, big differance.

3) Humidity Although this is minor it is much less humid on the high hp day making more room for o2 thus more power

You went from a lower than standard day (29.92 hg and 59 degrees F) to a higher than standard dry day. this is the reason you made more hp, not just the pipes.

Paul

 

With stock headers and V and H slip ons I was at 75HP and 83TQ. Installed V and H true duals and used same slip ons and turned out 79HP and 90TQ. Not great gains but I didn't lose and I gained the sound, look, and a cooler right leg!