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Old 04-17-2012, 01:52 PM   #16
supershaft
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I have never done any back to back testing with the exhaust plenum. I hope to soon. I am willing to give up a bit of low end for removing that boat anchor. It weighs a ton!
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Old 04-17-2012, 03:38 PM   #17
Tuff Tunica OP
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Quote:
Originally Posted by ericrat View Post
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.

Eric
Thus far seems to be good advice. It would require some cutting and welding to eliminate the crossover. Seems to be arguments both way so the crossover stays. If for nothing else it reduces the complexity of swapping exhausts.
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Old 04-17-2012, 03:42 PM   #18
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Here's a link to the bike

http://www.bonnevillevintagegp.com/raffle.html
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Old 04-17-2012, 05:28 PM   #19
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Originally Posted by Tuff Tunica View Post
Thus far seems to be good advice. It would require some cutting and welding to eliminate the crossover. Seems to be arguments both way so the crossover stays. If for nothing else it reduces the complexity of swapping exhausts.
That is another big diff. The ease of taking off the exhaust. I just got some thin wall 4130 tubing from the scrap box at work and cut two two inch or so pieces, welded some sheet metal circles on the ends, welded some bushing stock to run a pinch bolt through on the other, and then cut a slice through that for room for the pinch bolt to pinch down on the crossover sticking out of the headers. On and off in seconds. I still have those caps. I made them about 25 years ago. Time flies!

supershaft screwed with this post 04-17-2012 at 05:48 PM
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Old 04-17-2012, 09:33 PM   #20
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Following up

Quote:
Originally Posted by supershaft View Post
I am with you ericrat to a certain degree but I don't think there is much difference between race and street.
We usually, mostly, agree. And there may not be much difference the way you ride.And I mean that in the nicest possible way.

Quote:
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 wouldn't trust the 6mm valve stems in that particular engine for 50k without pretty close scrutiny, espececially considering the very custom CP slipper pistons under them.

Quote:
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.
You should go. I have been twice, which is not nearly enough. It is... different. It is its own thing. Weight doesn't matter much at all, really it doesn't, (please don't ask to see the maths unless sincere) many add weight to counter the wheelspin. At the 108-112MPH we were running, the 130s the R75 went, even the 150MPH the Vincents were running wheelspin wasn't a problem at all. Even the Vincents aren't big HP, we have to get there on smoothness. The truly big HP bikes fight wheelspin the whole time.

Quote:
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!
Well put.

BTW, I lost my record at Bonneville (BUBB meet)... to my wife. It was a long ride home.

Keep the crossover. Noise reduction is an advantage. Performance, by consensus is either the same or slightly better low to midrange with some trade-off on top. No point chopping up new pipes on thin reasoning. As we agree, you have to get to the high RPM end first and that is generally a bigger problem. If nothing else, if you tune for midrange and pass them into and on the corner exits and then get passed on the straight it looks way cooler than just being in the back of the pack. Or at least that is what I tell myself.

I have a couple of dyno sessions planned this season, maybe I will try a few things...

Eric
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Old 04-18-2012, 12:08 AM   #21
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Quote:
Originally Posted by supershaft View Post
I have never done any back to back testing with the exhaust plenum.
I had loose baffles in mine, the noise at idle was terrible, so opened it up and removed the baffles. Admittedly running short megaphones, there was no difference in noise or power. I have since made an equal length 2 into 1, and using a Supertrapp have lowered my needles back down and have the power pretty close to stock....whatever that was. I am going to remove my headers soon to paint them, and am tossing up whether to cut out the balance pipe or not....not sure what advantage they are to a 2 into 1. I'd rather experiment than take the typical BMW owner fuddy duddy safe line.
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Old 04-18-2012, 11:50 AM   #22
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Thanks ericrat. I know you mean well and I know we often agree on stuff. We are just discussing the finer points and half of discussing that is in the wording. It's great and fun when everyone involves actually has some real world experience around the matter versus just repeating what they have googled which is very often not right from the get go.

Except for RIGHT off idle, a good race setup has just as much torque and more than stock IMO.

6mm? I highly suspect he meant to type 7mm.

I was mostly thinking of the faster classes talking about weight and wheel spin. I knew a lot of people add weight for traction and angle of attack in the slip stream. Depending on the condition of the salt, I hope everyone is comparing wheel speed. From what I have heard, loss of traction is more common there than many think. Plus, building light lets you choose where to add weight. There are some car guys that fill there old bomb frames with lead!

I can take crossovers or leave them. What they do to top end is doable on a wheel dyno but just off idle? I think your better off reading the seat of your pants.
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Old 04-18-2012, 12:46 PM   #23
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Eric & SS have you guys got links to pics of your bikes or could you post some please? cheers
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Old 04-18-2012, 01:17 PM   #24
supershaft
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Thanks for asking Padmei. I am thinking I might learn how to do it soon. That and find a scanner to use. I was just wishing I had a photo of my crank breather setup. It is so easy to do and it really is about the cleanest setup I have seen for a stock square airbox.
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Old 04-18-2012, 01:18 PM   #25
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Originally Posted by supershaft View Post
Thanks for asking Padmei. I am thinking I might learn how to do it soon. That and find a scanner to use. I was just wishing I had a photo of my crank breather setup. It is so easy to do and it really is about the cleanest setup I have seen for a stock square airbox.
Would love to see photos from you SS. Hit me up if you need assistance.
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Old 04-18-2012, 01:29 PM   #26
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Thanks! I think what I am going to do is have mykill over for a beer and have him show me how it's done on my own computer. (He has offered to do that kind deed before!) That will save me at least a whole afternoon fiddling with something I really have no desire to fiddle with. A lot of my friends warned me that when I went on line I would get addicted to all that stuff and somehow I still just don't care. A good friend of mine that is a complete luddite got on line just last year and he is already posting picks and links and music and whatnot. For some reason I just don't care but I have gotten the twinge a bit lately! At least about posting pics.
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Old 04-18-2012, 08:45 PM   #27
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Crazy?

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Originally Posted by supershaft View Post
6mm? I highly suspect he meant to type 7mm.
I did not. 6mm.

This is the Bonneville bike. Sadly, there was a seperation of the team and, well, you know how these things go. I doubt that bike will run again anytime soon.



Pipe lenght was calculated using Pipemax.



I will put some picture of my street R100S up. It is pretty, but is nothing special performance wise.

Eric
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Old 04-18-2012, 11:03 PM   #28
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I've run sans cross over and noticed no difference except for a more defined exhaust note. Not particularly louder, just undiluted. Sure makes it easier installing and removing the exhaust.

It's true that BMW is good at designing engines, but they also have contorted to environmental concerns and conformed to DEQ regulations. One of the tests they had to pass was noise, and the second crossover could very well have been due to that one.

Frankly, I like ditching the crossover.
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Old 04-19-2012, 01:53 AM   #29
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The impression that I had was that in the late 70s and 80s was that BMW was really concerned at getting airheads through increasingly restrictive noise and environmental regulations both in the US and coming down the track in Europe. This did result in bikes that were generally less powerful than the late 70s bikes. Also much of the R&D effort was concentrated of the forthcoming K range of bikes.
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Old 04-19-2012, 02:05 AM   #30
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Quote:
Originally Posted by ericrat View Post
I did not. 6mm.

This is the Bonneville bike. Sadly, there was a seperation of the team and, well, you know how these things go. I doubt that bike will run again anytime soon.



Pipe lenght was calculated using Pipemax.



I will put some picture of my street R100S up. It is pretty, but is nothing special performance wise.

Eric

Ok that there is a major thread in itself. Do you have one about the build up mods, speed runs etc etc? if not could you please start one up.
No offense to the owners of ordinary airjeads but i'd love to read & hear about something truly different.

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