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Old 04-15-2012, 09:54 PM   #1
Tuff Tunica OP
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Question Exhaust crossover pipe?

So I've ordered some new pipes for my new to me air head cafe. Bike came with race pipes that are painfully loud. The race pipes have had the crossover cut and welded so there is no link on exhaust left to right. New pipes will allow foe the exhaust crossover. My question is...is there an advantage in performance to eliminating the front crossover on the exhaust?
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Old 04-16-2012, 03:51 AM   #2
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balance pipes

i think balance pipes are better for performance, i was originally going to do away with mine but changed my mind after reading up a bit

i'm having short silencers so i went with twin balance keihans

i could be wrong though, i'm sure some of the more experienced members will let me know if i am!
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Old 04-16-2012, 03:59 AM   #3
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It's my belief (without dyno data to back it up) That the crossover is about sound reduction, and has little to do with torque, or horsepower.
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Old 04-16-2012, 04:06 AM   #4
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Old 04-16-2012, 05:22 AM   #5
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I removed mine from a /6 that I cafe'd years ago(before it was hip!), didn't notice any change in power, but it sounded different. I could hear each side more distinctly.
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Old 04-16-2012, 09:09 AM   #6
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No, there's no horsepower advantage.

The opposite in fact.

Removal of the crossover reduces the size (volume) of the exhaust system ... as does a 2->1 system, both reducing performance.

BMW's middle name is "motor" and they get it right.

Taking things off not understood is common and contrary to popular fantasy "mechanics" and shadetree modifiers can't come close to real engineering ... despite the fact the advertising tells you you can.
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Old 04-16-2012, 10:00 AM   #7
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Quote:
Originally Posted by lkchris View Post
Removal of the crossover reduces the size (volume) of the exhaust system ... as does a 2->1 system, both reducing performance.


This bike uses a 2-2 with no crossover and is not known for it's low performance at bonneville. I'd say your statement is an oversimplification and far too sweeping of a generalization. There are many different measures of performance. Large exhaust volume is not ALWAYS better. It depends on what the bike needs to do. Many airhead race bikes use 2-1 systems and it's not just because of marketing hype as you claim.
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Old 04-16-2012, 10:19 AM   #8
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I thought the addition of the second crossover served the primary purpose of moving the power band toward lower RPMs... So removing one or both would effectively move peak power/torque up into the high RPM range?

Obviously you lose (useable) power if you never rev to the higher RPM range.
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Old 04-16-2012, 10:42 AM   #9
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I have a Luftmeister aka "Goofmiester" 2 into 1 on Das Beast. I recently re-wrapped the baffle to make it a little quieter and a little more "neighborhood" friendly.

It'll fly. But then again, I live in a 70-75mph world and only need a little performance.
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Old 04-16-2012, 11:16 AM   #10
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Quote:
Originally Posted by ignatz72 View Post
I thought the addition of the second crossover served the primary purpose of moving the power band toward lower RPMs... So removing one or both would effectively move peak power/torque up into the high RPM range?

Obviously you lose (useable) power if you never rev to the higher RPM range.
+1 I have done back to back tests and I think the crossovers most noticeably reduce noise. They also increase just off idle and decrease top end although I never really could tell the difference on top but you never get anything for free so I suppose it is true. I suspect the secondary crossover is primarily for noise reduction since the inventors of the crossover (British motorcycle industry) reported that their effectiveness is reduced tremendously the further away from the exhaust valve they get. The trouble with dyno proof is that is next to impossible to reliably record real low rpm differences with wheel dynos. Too many variables. Most all such tiny incremental develops are better recorded on engine dynos.

Nowadays lots of four cylinder racing exhausts have crossovers either right after the port and/or further down mixed in with the collectors. Lots of four cylinder exhaust are now running four into two and then two into one.

Different tuners favor different setups and some tuners prefer one over the other depending on the bike. Displacement makes a huge difference with your options! Chris from San Jose for instance has used both over the years although I know he use to favor two into ones usually and that includes I believe even one of his LSR holding bikes. This notion that two into ones cost hp is not right any more than exclaiming that two into twos gain hp. They both have gains AND losses. It all depends on what the tuner AND rider feels is the best compromise. It often changes from track to track let alone other variables.
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Old 04-16-2012, 11:33 AM   #11
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Quote:
Originally Posted by lkchris View Post
No, there's no horsepower advantage.

The opposite in fact.

Removal of the crossover reduces the size (volume) of the exhaust system ... as does a 2->1 system, both reducing performance.

BMW's middle name is "motor" and they get it right.

Taking things off not understood is common and contrary to popular fantasy "mechanics" and shadetree modifiers can't come close to real engineering ... despite the fact the advertising tells you you can.
...............

"BMW's middle name is "motor" and they get it right."
The list of things that BMW didn't get right is long. The idea that BMW engineers can do no wrong is "fantasy".
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Old 04-16-2012, 01:26 PM   #12
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Quote:
Originally Posted by robtg View Post
...............

"bmw's middle name is "motor" and they get it right."
the list of things that bmw didn't get right is long. The idea that bmw engineers can do no wrong is "fantasy".


+1
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Old 04-17-2012, 12:09 PM   #13
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race versus street

Race versus street is apple and oranges, I mean they are both fruit and all, but still not really the same. Very few are running anything remotely built like Chris's R75. Have you seen the pistons and vavles in that thing? I have . BTW the R75 is running 130s MPH. SJs R100 "wrecking ball" had a two into one on it last time I saw it.

What works at Bonneville may not translate well elsewhere. You have a three mile straight, all high RPM, with no need for fat torque lower down to accelerate out of a corner, etc, etc.

I don't have as much dyno time as some here, but my experience is that the crossover helps flatten the tourque curve and improve midrange at the expense of a bit of top end power. My next exhaust experiement will be two into twos with no taper, no megaphone. Just a straight pipe tuned for one RPM. If I can keep in up "on the pipe" and not loose too many RPMs in the 3rd to 4th gear shift I think it will work. If not I will be stuck in a torque trough trying to claw my way out.

My vote is to keep the crossover.

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Old 04-17-2012, 01:11 PM   #14
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I am with you ericrat to a certain degree but I don't think there is much difference between race and street. Pistons and valves? If it runs on pump gas and it very well could, there is nothing in that engine that wouldn't last at least 50,000 miles if not more.

I have never been to Bonneville but I have talked with a number of record holders and worked with one. Bonneville is a long drag race. Weight and acceleration are critical as is controlling wheel spin. No one shoots you out a cannon at high rpm speeds. You have to get there from low rpms and the way your geared it's a race to get to high rpm before the speed traps.

It seems that so many have this misconception that racing is just about high rpm and it very much is not especially if you want to win. It's like my dad use to advise me while I was helping tune WINNING short track and MX bikes: High rpm? First you have to GET to high rpm! That's a big chunk of a lot of racing if you are looking to win!

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Old 04-17-2012, 02:15 PM   #15
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The front cross over pipe should help with a smoother idle and off idle response. The rear cross over is far enough back to help with better exhaust scavenging which would help with mid range power. I would think performance wise a rear cross over is better than the front. If you look at the large per-silencer on the post 85 models you don't see a huge drop in performance however with out it the bike seems to come alive- Supershaft should have some good info on this since he rides a modified post 85.
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