New member/k75 Supertrapp question

[snowcat]

Hello everyone,
Owned my '88 K75C for a few years now but just now joined the club(I'm kinda cheap).
Anyhow I'm interested in a Supertrapp for my K75.
E-mailed a company spokeswoman who kept saying they don't make a muffler for my bike and couldn't/wouldn't help me find a universal that would work.
I've seen pictures of K75's with supertrapps but haven't found anyone that could give me a part number or info on how well they work.
I've seen the dyno tests Don posted with the Staintune and was wondering if a Supertrapp would work better because of the tunable disks
thanks
Happy to have found this forum
Dave Norris
88K75Cafe' project

[deilenberger]

Originally posted by K75'd
Hello everyone,
Owned my '88 K75C for a few years now but just now joined the club(I'm kinda cheap).
Anyhow I'm interested in a Supertrapp for my K75.
E-mailed a company spokeswoman who kept saying they don't make a muffler for my bike and couldn't/wouldn't help me find a universal that would work.
I've seen pictures of K75's with supertrapps but haven't found anyone that could give me a part number or info on how well they work.
I've seen the dyno tests Don posted with the Staintune and was wondering if a Supertrapp would work better because of the tunable disks
thanks
Happy to have found this forum
Dave Norris
88K75Cafe' project

Dave - I have seen (and vaguely remember doing a dyno run or two on) a Supertrapp on a K bike - which was likely a K75. I don't have the dyno run to refer to, but I will say - I've never seen an exhaust that improves power over the stock exhaust (if I did - I'd have it on my K75S..) I've seen exhausts that look prettier (StainTune) are lots louder (Luftmeister) - and are likely ligher than stock - but more power? Haven't seen that (and that includes with other "hot" mods to the engine.)

I think you can find the Supertrapp that will fit by looking at the size of the input hole - it has to mate up with the K75 header. Once you find that - your challenge will be to figure out a way to support it - and to make something for it that will function as the sidestand/centerstand stop (which is part of the stock exhaust and every aftermarket one I've seen for the K75.. but wouldn't be on a SuperTrapp.)

Sounds like an interesting project.. and be interesting to do some dyno work on it. It's possible with the tuneable disks it could be tuned to be at least as good as a stock system, or at least close to it. The disks primarily are used to tune the backpressure (and noise level) - so you can probably get it close to the stock system.

Keep us up to date on the project!

Best,

[Ridealot]

K75'd,
Back in '91 I bought a K100RT that had a Supertrapp exhaust that was made for it. It had the side and center stand mount that used the stock BMW rubber bumper. To say that I didn't care for the exhaust at all is an understatement. With the disc system the exhaust is allowed to exit in a 360* pattern. Whenever I leaned over into a left hand turn the noise would suddenly increase by about 3 fold. The sound would bounce back up from the road towards me. After a short time it was very annoying to have the sound level reaching the rider go way up everytime you turned left. I couldn't wait to tear that thing off and go back to the stock pipe. I sold it to a guy I worked with and he also absolutely hated it.

[AntonLargiader]

In my opinion, there is nothing that says "I don't give a s**t about this bike" more than a cheap aftermarket exhaust, and this one tops the list.

If you really want to mess with the exhaust, find a Staintune Touring (not Sport) or maybe some Remus thing.

[deilenberger]

Originally posted by AntonLargiader
In my opinion, there is nothing that says "I don't give a s**t about this bike" more than a cheap aftermarket exhaust, and this one tops the list.

If you really want to mess with the exhaust, find a Staintune Touring (not Sport) or maybe some Remus thing.

And only consider the StainTune if you don't want the power BMW built into the engine, and AFAIK - Remus never made one for the K75..

IMHO - stock actually works quite well.

[paulsibek]

I recently put on a Staintune and a K&N air filter.

The bike seemed more powerful, especially in the 4500+ range, passing on the freeway.

Recently I took it to the Ford/Shelby Design Shop, a client of mine, where they designed the new Cobra and Mustang among others.

The dyno, setup by engineers, said I had a gain of almost 8hp in the mid-to high rpm range. Torque was about the same.

I'm very happy with the perfomance gain but the gas mileage seems to have fallen a couple of mpg.

Keep you eye on the IBMWR site and you'll find a deal on a muffler sooner or later if you want to save the money.

[paulsibek]

I agree with the poster who says not to get a cheap aftermarket, afterall it is a BMW and we have an image to maintain.

EPCO makes one that is reasonably priced and looks pretty good, there are usually a couple of Staintunes and such at the IBMWR site.

The thing about Staintune is they don't need repacking and seem to hold up very well. Mine is (I was told) a 1992 (hardly used...) but looked nearly new.

I was patient and got a beauty with SS headers for...

$100

This was a good upgrade.

[deilenberger]

Originally posted by Paul Sibek
I agree with the poster who says not to get a cheap aftermarket, afterall it is a BMW and we have an image to maintain.

EPCO makes one that is reasonably priced and looks pretty good, there are usually a couple of Staintunes and such at the IBMWR site.

The thing about Staintune is they don't need repacking and seem to hold up very well. Mine is (I was told) a 1992 (hardly used...) but looked nearly new.

I was patient and got a beauty with SS headers for...

$100

This was a good upgrade.

Paul - unfortunately - the facts don't agree.

See: http://www.eilenberger.net/k75exhaust/index.html

And since that page was written - there have been two more dyno runs done on K75 Staintune equipped bikes. The results are identical.

If a good upgrade is nicer looks, then you've got it (BTW - the factory headers are stainless steel, assuming that's what you mean). If you're looking to even keep the limited power a K75 produces - it's not IMHO a good upgrade.

Different folks, different strokes, and as usual YMMV (especially if you have a StainTune exhaust on your K75)

[deilenberger]

Originally posted by Paul Sibek
I recently put on a Staintune and a K&N air filter.

The bike seemed more powerful, especially in the 4500+ range, passing on the freeway.

Recently I took it to the Ford/Shelby Design Shop, a client of mine, where they designed the new Cobra and Mustang among others.

The dyno, setup by engineers, said I had a gain of almost 8hp in the mid-to high rpm range. Torque was about the same.

I'm very happy with the perfomance gain but the gas mileage seems to have fallen a couple of mpg.

Keep you eye on the IBMWR site and you'll find a deal on a muffler sooner or later if you want to save the money.

Paul - can you pass along those results to me?

I'd be REALLY interested in seeing them.

Some questions:

1. Were the runs done on the same day?

2. Were these A/B tests - ie, done without the modifications and then with the modifications?

3. Any info on the exact type and model of the dyno?

4. Could you possibly email me the dyno results? Doesn't have to be a screen prinout (although that's how most are presented) - it could be an Excel or CVS (Comma-delimited) file.. I can move the data files into a plotting program.

Best,

[paulsibek]

It was a Mustang MD250 with a motorcycle conversion with software made by a Ford engineer for his Hyabussa (sp?).

We didn't have a baseline for comparison as I sold the stock muffler, so we went with what the service manager from Seavers told us was the stock hp. 75. The dyno reading was 82-83hp.

I can't share this hard copy without a release from the client, but I will say this is a good upgrade and well worhwhile. It added some needed punch to my K75.

[deilenberger]

Originally posted by Paul Sibek
It was a Mustang MD250 with a motorcycle conversion with software made by a Ford engineer for his Hyabussa (sp?).

We didn't have a baseline for comparison as I sold the stock muffler, so we went with what the service manager from Seavers told us was the stock hp. 75. The dyno reading was 82-83hp.

I can't share this hard copy without a release from the client, but I will say this is a good upgrade and well worhwhile. It added some needed punch to my K75.

Paul - sorry.

IMHO those are bogus numbers. NO K75 ever measured 75HP at the rear wheel. The 75HP number is crankshaft HP, gross. There are "transmission losses" (power spent to spin things) in getting the claimed 75HP to the rear wheel. EVERY K75 I've dyno'd has measured 55-60HP rear wheel. So that casts suspicion on the motorcycle conversion software.

The other problem I have is without an A vs B comparison the nunbers are valueless. HP is directly effected by temperature and humidity, plus there are variations from engine to engine and variations in accuracy dyno to dyno..

So unless the numbers are done on the same bike, on the same day, on the same dyno, with and without the modifications (A vs B), they really don't hold up to scruitiny.

All my dyno runs are back to back A vs B, same day, same bike, same dyno.

The StainTune does make more noise, which seems to make butt-dynos think it's giving more power. Unfortunately - that's not true. K&N is pretty much snakeoil on a K bike.. it not only doesn't give more HP, but it also allows more dirt into the engine.

The other point I think you overlooked is shown rather clearly on my plots of the Staintune. It does sometimes make 1-1.5 more HP at max RPM. No argument there.

The problem is - it does this at the expense of 10-15HP right out of the range of the engine you most often use it at (4,500-7,000 RPM). Overall - the result is a loss of HP, and even worse - a loss of USEABLE HP (I don't know anyone who runs a K75 at red-line all the time.)

I'm sure the StainTune looks nice. They usually do. They sound nice (a bit loud for my taste when touring.) They are a bit lighter than stock. But even Staintune will not claim any power increase from them.

Best,

[davel]

Originally posted by Paul Sibek
I recently put on a Staintune and a K&N air filter.

The bike seemed more powerful, especially in the 4500+ range, passing on the freeway.


Not sure if there is a clear answer here (Don has a more technical approach since he has been dynoing the K bikes), but I did the above plus the highoutput fuel regulator, (didn't dyno) and the seat-of-the-pants feeling was great! I noticed a nice rush around 4500 and beyond, throttle response improved, and I noticed that I loss about 2 or 3 miles per gallon. If anything, the K75s may have lost a little below 3K, but other than starting from a stop you want to keep the RPMs around 5K anyway. If you do all 3 I think you will be happy with the results. I also found the Staintune "sport" version a little to loud after about 5K miles. Good Luck!

:bliss

[deilenberger]

Originally posted by davel
Not sure if there is a clear answer here (Don has a more technical approach since he has been dynoing the K bikes), but I did the above plus the highoutput fuel regulator, (didn't dyno) and the seat-of-the-pants feeling was great! I noticed a nice rush around 4500 and beyond, throttle response improved, and I noticed that I loss about 2 or 3 miles per gallon. If anything, the K75s may have lost a little below 3K, but other than starting from a stop you want to keep the RPMs around 5K anyway. If you do all 3 I think you will be happy with the results. I also found the Staintune "sport" version a little to loud after about 5K miles. Good Luck!

:bliss

Dave - the first set of dyno plots I referred to - are on a K75 with Staintune, K&N and the high-pressure regulator (it seems like a package Bob's BMW liked to sell.) Unfortunately - this package didn't work any better (or worse) than a stock bike with just the exhaust changed to the StainTune.

You can see it at:

http://www.eilenberger.net/k75exhaust/index.html

Slightly different curves for the bike with the K&N and HP-FPR vs the one with JUST a Staintune swap, but no significant change in the loss of power from 5,000 to 7,000 RPM.

There is a small boost in power between 4,000-5,000 RPM which is probably what you felt. Dunno about you - but I really rarely ride in that RPM range at sustained speeds.. I'm usually up in the 5,000-7,500 RPM range (which is 60-85 MPH on my S.)

Best,

[k12allen]

Responding to Paul Sibek's post on dyno results with a K75 and Staintune:

Paul, while I have nowhere near the expertise that Don E. has, I have a comment anyway. You note an increase in hp with the mods although you say the torque stayed about the same. This is impossible since hp at any speed is directly related to torque. If you double the torque at 5k, you double the hp. OTOH, if the torque remains the same, the hp remains the same at that rpm.

Add this to what Don said and you should realize that the data you got is beyond suspect. I have a particular feeling about this issue since it was me that Don refers to regarding use of Bob's suggested combo of Staintune, K&N air filter and high pressure fuel regulator. I wuz burned. I still remember the feel after I went back to stock and got on the highway - really felt that hp restoration.

It seems that the K12RS does respond to an aftermarket pipe (have seen dyno results run the way Don sez they need to be run), but having been burned once, I'm not going there again. Plus the 12 is in less need of more umph :p :p

[Argus 21]

I am no dyno expert but wish to offer my .02 cents worth. We are all fortunate in owning bikes that have no great need for a different exhaust. Both the BMW's I have owned were and are stinky fast with no exhaust mods. These machines are well thought out unlike the famous American brand (I have owned 4 of those) that is in need of many modifications to make them have acceptable power levels. If you settle for stock with bar and shield logo, you get an anemic machine that wheezes out the dealer's door with paltry performance. If you mod them, they can be made to run but you pay for it by putting up with ear splitting noise and very reduced reliability. We should count our blessings......:)