S.T. closed cap dyno mod...?

[tireater]

Has anyone made a mod. to the end cap so you don't have to take the discs off twice to use an A/F sniffer...
What would happen if you left a 1/4" hole in the middle of the disc...? Thanks....

[maineultraclassic]

If you call Supertrapp, they will send you another end cap for free if you tell them you need a hole in it for dyno tuning.

Or, some dyno shops have the endcap with a hole in it already.

Steve

[tireater]

My problem is that I have to pay the dyno guy to put the disc in and then to take it out after the dyno run...and after it cools...
I also have to remove the safety wire I use on the end cap...I lost the guts on the freeway awhile back...
The dyno guy already jokes about me being a frequent dyno flyer...Just trying to save time and money...

[RevFastEddy]

So drill a 5/16" hole in the end cap and leave it that way when you are going to a dyno tune or just leave it. If it bothers you make sure you drill the hole in the center and put in a stainless cap screw with a nut on the inside aftet the tune so it looks like normal. That is all it takes, either $0 or 25 cents for a bolt.

[FLTRI]

The 1/4"-5/16" hole in the middle does absolutely nothing to the tune or the sound.

[tireater]

Perfect...i'll just drill a 5/16" hole and leave it there...

[TQer]

Yep,

What they said. Mine has the hole there, no change in sound or performance. Wouldn't notice unless you look for it. TQ

[Faast Ed]

Almost on topic here,......

Tireater, if you are going to be on the dyno anyway, I think it would be interesting to make one pass with the endcap off.

The reason behind this suggestion is the fact that my bike (which is also grooved similar to yours) reacted positively to taking away exhaust restriction.
This may confirm or disprove my theory about the grooves hating restriction.

[tireater]

I went from 21 to 24 discs...closed end cap...I thought they people at S.T. said that was the same as 14 and an open pipe...

[hdpegscraper]

If you dont like the hole in the end cap, just weld a nut on the inside to the end cap before you reasemble the discs. I used a bolt that has an Acorn head, kinda gives a nice "finnished" look. Or you could alwys get an open end cap?

[Faast Ed]

I went from 21 to 24 discs...closed end cap...I thought they people at S.T. said that was the same as 14 and an open pipe...

While I am not full of knowledge on the ST pipes, I have some experience watching my tuner mess with my grooved bike. I was fortunate enough to have him all to myself on a winter Saturday, and we played with my bike on the Dyno, all friggin' day (it was fun, to say the least).

If you looked down the pipe on my 1 3/4 Rush, the hole looked huge. No kind of end cap.
Yet adding the bigger baffle (2 inch) brought the numbers up more that you'd expect.  A 2 inch diameter hole with no obstruction, no end cap.

Keep in mind that the grooves get you running much leaner.  The "lean" thing I believe is what causes the slightest bit of restriction to take away power.
Keep in mind too that this was only one bike and yours could react altogether different.  That's why I suggested the "one pass without endcap".  So we could both learn if this theory is correct.  Who knows, you might gain a few ponies from it.  If not, you'll still gain a bit of knowledge, as will a few readers here.

[FLTRI]

"The reason behind this suggestion is the fact that my bike (which is also grooved similar to yours) reacted positively to taking away exhaust restriction.
This may confirm or disprove my theory about the grooves hating restriction."

Interesting, I know that pulling the restriction from any HD exhausts cause a reduction in low end torque and usually an increase in upper end hp.

The only way to prove or disprove your theory that grooves hate restriction is to do back-to-back testing with the same engine with/without grooves on the same day, same tuner/dyno, unless, of course you believe there is a huge difference, in which case it will be in the 5-10+hp/tq gains. I don't think so.....but?

Bob

[maineultraclassic]

The open endcap is equal to 9 discs, that is according to a chart I have from Supertrapp about tuning their exhausts.

Steve

[Faast Ed]

prove or disprove your theory that grooves hate restriction is to do back-to-back testing with the same engine with/without grooves on the same day, same tuner/dyno,

I don't dispute that one!  LOL
We have talked about that for a few years now, but nobody wants to fork out the money, time and effort.
Think about it, you take your bike apart putting time and effort into that. Plenty of it too.  It's pretty friggin' hard to reassemble it without doing other mods.  The incentive to reassemble it without a thinner gasket, better valve, or something else to better you motor is pretty low. 

Need a shop guy with lots of time on his hands to experiment like that. Last winter we were begging for a back to back groove/no groove test.

We have to settle for what we are getting for now.  That's why when I read that he's gonna be on the dyno anyway, won't take much time to pop an endcap off,.......  Get it?

[tireater]

We do have noise issues with the popo here. I can't run an open end cap...
I know this bike barely runs w no baffle, discs or end cap......

[Tattoo]

The open endcap is equal to 9 discs, that is according to a chart I have from Supertrapp about tuning their exhausts.

Steve

Steve, what are you running for a pipe now? I have not seen you in awhile.

[maineultraclassic]

Still have the Fatcat 2-1 with quiet baffle.........just about a year and a half now.

Took me 9 tries, but I finally found the keeper.

Steve