XR400 Arrow exhaust system - high expectations??

[adamxr]

Hi all,
Has anyone else out there tried an Arrow exhuast system on an XR400?
I bought one for my bike, and mine seems to have lost a bit of torque after I installed this system. :(
I've tried going richer on the jets (#62 to #65 pilot, and then also #155 to #158 main) - with pretty much no impact - hasn't improved, or gotten worse either.

I'm just hoping there might be a remedy for this - as the grunt of the XR is one of its shining points. And doesn't it seems strange that you would buy an aftermarket exhaust system to get less power from your bike?!?

Any tips on this problem would be really great.

 

[snaggleXR4]

Hey,
I've got a '96 XR400. I put on an XR's Only Competition exhaust, UNI airfilter, and of course the snorkel is removed. XR's Only recommended the jetting 160/60 down from the 162/62 stock jetting. I thought it was odd at first because they recommended leaner jets and not richer as I would have expected with the pipe. It turns out that the 162/62 jets are just too rich for me in NW Florida (sea level). The 160/60 jets really crispened the throttle response up.

It seems that almost all high air flow pipes tend to do more for mid-top end, at the expense of bottom end. Large diameter headers do the same I'm told.
I can't imagine that you are below sea level, so you might try a 160 main, and either keep the 62 pilot or maybe try the 60 pilot. It looks like you are rich on the bottom, and lean on the main.

I'm not familiar with your pipe. However, if it is a Supertrapp design with the discs, you might try to remove a couple discs. Straight from Supertrapp's web site says fewer discs means richer, and more bottom end. More discs means leaner and more top end. Furthermore, there is a 4 page article on JustXR.com about a guy's experience modding out his 400. After trying different pipes and carbs etc., he decided that the stock pipe with a Vortip insert was the quietest, most torquiest combo out there.

Again, try the 160/60 jetting or some combo with the 162/62 jets and see what you have. Mine rips straight from idle to a screaming mid and top end. Even with the relatively tall stock gearing, 15/45, I can still chug and lug along very slowly with plenty of torque. If the jetting doesn't help your situation, see if Arrow has a slightly more restictive end cap or something, maybe that will salvage some torque. Or, if you have 15/45 gearing on your bike, and don't need the top end speed, try to gear down a bit. A 46 or 47 on the rear should do you well, or even a 14 tooth front sprocket that you can swap out with the 15. Good luck. Let me know what you find out with experimentations.

 

[DualSportr]

It seems that almost all high air flow pipes tend to do more for mid-top end, at the expense of bottom end. Large diameter headers do the same I'm told.

Yup. Increased airflow will reduce low end torque.

Most 4 stroke engines need a certain amount of backpressure to perform effectively. This is why some of the aftermarket systems actually reduce low end hp on stock engines.

You might look into installing a bushing in the first 1 1/2" to 2" of the new headpipe - this may return your torque to stock numbers without reducing the increased top end. Then again, it may not change the power at all! It just depends on the engine characteristics, and that specific exhaust systems original dimensions.

I've heard good things about the Arrow system when used on a Yamie 400 (independent dyno results), but some manufacturers can produce basically the same pipe for many different models, creating sort of a hit-and-miss product line.

I agree with Snaggle - try a smaller pilot and see if it helps.

 

[SFO]

Who did you get the pipe from?
The distributor or your dealer?
What kind of customer service did you get?
Did the pipe have a spark arrestor?
Were there any fitment issues?
What does it sound like?
Is it the stainless silencer?
How much was it?
Thanks, Bill

 

[adamxr]

Hey, thanks for the tips guys.
In the back of my mind I was thinking the next thing I'd try would be the leaner/richer combination that snaggleXR4 suggested.
I'll go try that today.
As far as the pipe goes, the design seems very similar to the Big Gun exhausts - with a big alloy muffler. The stainless headers do have a larger OD than stock, but are a different shape - tuned length I presume.
Don't think the pipe came with a spark arrestor, but I must say it does sound pretty damn good :) - Slightly quieter than the stocker with the restrictor removed - with more of a deeper boomy sound & less tinny - kinda like a yzf.
It was pretty fiddly to fit, the headers wrap in very tight around the frame. And the slip-joint between the muffler and the header/collector was really tight, so tight that it probably doesn't even need a clamp to seal the joint!
Price here was (in AUD$!) $600 for the muffler $400 for the headers - so for US dollars you could pretty much halve that amount - considering our crappy Australian dollar buys about 50 US cents!! Cheaper than an FMF or WB system over here anyway - with similar build quality.
Customer service? Whats that?!?
I bought it from a parts dealer - who had no idea of any necessary jetting changes, I might try hunting down the distributor though!
After a bit of looking around, I found that this would have been the case no matter which system I bought - that I would be pretty much on my own when it comes down to getting the jetting cleaned up.
Anyways, I'll press on with the experimenting. And I'll post in here how I go.
Thanks again guys

 

[SFO]

Even though I like the fit and finish of the pipe, neither the distibutor or Arrow has been able to answer any of my questions. My dealer is a very large Aprilia dealer and they say Arrow is the only pipe that really works on their big twins. Kind of a bummer when you run into a cool product with piss poor support.
Watch your slip joints...
The connection from the header to the midsection became one piece(almost) after one ride. It was painfull to try and twist it apart so I could remove it.
Upon reassembly I polished the mating id/od with scotchbrite and removed all burrs, then I slathered nickel based anti-seize on the junction.
I hope it works...

 

[adamxr]

Well, after a week or so of messing around, the 60/160 jets seem to be the cleanest combination. The plug confirmed this with more of a tan colour than before.
Torque is still slightly lower than stock, but it does seem to rev more freely.
I guess the lower torque must be a characteristic of the new exhaust system - as it seems more related to rev range than throttle position.

Most of my testing so far has been on bitumen, so I'll have to hit the dirt in earnest to see whether the new exhaust is actually an improvement over stock... Who knows, maybe the Euros are on to something, and it'll actually hook up better than before!!

I have had an improvement in customer service - finally. I went to a different branch of the same dealer, and they were a lot more helpful -- go figure!

DualSportr:

You might look into installing a bushing in the first 1 1/2" to 2" of the new headpipe -

Just out of curiosity, what did you have in mind here --
It'd be pretty cool if there was something that you could easily add and remove to this kind of pipe to do this... (I'm starting to regret not going for the WB E-Series muffler with the diffuser discs actually!!)

Cheers guys

 

[DualSportr]

Basically, reducing the first 1 1/2" to 2" of a headpipe by 1/4" will allow the engine to have lots of great backpressure at lower rpms (keeps airspeed up at relatively low cam/valve speeds) without backing everything up at higher rpm. This is the thought behind the stepped headers.

Unfortunately, the modern stepped header design is more for looks than performance in most cases - since the optimum point for the restriction is just after the exhaust leaves the head (this really depends on the length of the exhaust tract too!), and up to the first pipe bend.

Everything after that is normally better off with the same diameter, until the end of the tuned length. Then if a pipe then needs to be longer (to reach a good mounting point, etc.), a megaphone or cone can be added to increase volume, then a muffler can be mounted onto the end of this.

There's more to four stroke pipe building than most companies realize. Even though the designs are simplistic, and the gains are minimal compared to two stroke exhausts, if it's not done correctly, lots of power can be lost!

You can easily build a removable bushing. Just give it a flange (so it doesn't slide back and forth in the pipe), go with something 1/4" smaller than the pipe you're using. Start as long as possible, try it, then cut 1/4" off the far end, until the power feels good down low, and isn't losing anything off the top.

BTW, White Brothers used to sell a torque stuffer for some of their pipes. Don't know if they still carry this little jem, but you might check to see if they have something that will fit - it'll save you lots of work!

 

[Boozer]

i have a WR250f with YZ cam timing and so on. I bought a R4 White Bros. pipe and i have the option of running it with or without the spark arrestor. The manual says that i will gain some top end power and lose some midrange when i use the spark arrestor. If i remove the arrestor, they say top end will be down a bit, but mid range will be better. They have a dyno sheet proving this. Just interesting how some back pressure can actually assist top end power.
When you run the bike at idle and stand back 4 metres from the pipe, you can feel the gas hitting you in the face, then in the leg, then it might miss you and then it might find your shoulder. Strange how the gas doesn't leave the pipe at the same spot all the time. It must come out while rotating, or something. Any one know?

 

[DualSportr]

My belief is that it works in waves - like sound waves. Rich???

 

[theMotoMan]

Does Arrow have a web site?

 

[Rich Rohrich]

Originally posted by DualSportr
My belief is that it works in waves - like sound waves. Rich???

The shock waves you feel are definitely a function of unsteady wave dynamics, which is also the reason that things like the WB Torque valve have an effect. The velocity change at the port exit and the expansion wave produced due to the sudden step in the pipe changes the scavenging effect when these things are inserted in the pipe. Backpressure really doesn't enter into it in this case.

 

[SFO]

Try this link

http://www.speed-sports.com/Home/index.html

This is the U.S. distributor I believe.

 

[adamxr]

sudden step in the pipe changes the scavenging effect when these things are inserted in the pipe. Backpressure really doesn't enter into it in this case

Hmmm, so a restrictor at the beginning of the pipe would change the pipe's scavenging characteristics, but not necessarily affect the the flow/back pressure of the pipe?
If there were very few adverse effects of this - wouldn't this mod be included in most aftermarket pipes? (Arrow for one!!)
I checked out Arrows website www.arrow.it , but most of it seems to be in 'Italiano'... not much info on specific exhausts for specific models. Hopefully they're still working on the site, & there'll be more useful stuff on there soon.

 

[Rich Rohrich]

Originally posted by adamxr

Hmmm, so a restrictor at the beginning of the pipe would change the pipe's scavenging characteristics, but not necessarily affect the the flow/back pressure of the pipe?

In the specific case of inserting a tapered convergent cone in the pipe inlet that DualSportr is referencing the tradeoffs can be minimal, but a generic restriction at the exhaust pipe inlet or outlet would tend to decrease flow and increase back pressure. The effects of inserting a tapered cone at the exhaust pipe inlet and generating a sudden expansion wave three inches from the valve face are difficult to predict or model. The simple fact is two fairly similar engines can (and will) tend to respond to it completely different. It's an interesting concept and worth playing with but in most cases it's a bandaid fix for poor pipe design/selection or incorrect cam timing. The idea of using a cone at the pipe inlet is far from new. I talked to Russ Collins of RC Engineering about this in the early 80s and according to him they had already done testing and abandoned the idea. He felt proper pipe design would mitigate the need for it. Many respected cam designers feel the same way about stepped headers. They feel if you get the cam timing correct the value of a stepped header tends to be diminished.

 

[DualSportr]

<<If there were very few adverse effects of this - wouldn't this mod be included in most aftermarket pipes?>>

Like Rich says, each engine responds differently. Which is why I recommended trying it - but didn't go into saying "this is the absolute answer to your problem!".

Rich, actually, the idea for stepped headers is from the early 'teens. I've seen the design used on a Pope - the thought behind it was to do exactly as you mentioned - fix a bad cam design!

I think maybe the Arrow design was perfected on the YZF 400 or 426. They did a bunch of testing on this model, then basically took that design and made it fit other models. I don't know this for certain, it's just a guess.

Other companies do the same thing. I know of one very popular company who tells their pipe manufacturer - 'here's the bike, bend a pipe to fit the chassis'. They don't test - they just count on their original design to do the trick for every bike. So - some of their pipes work very well, others are okay, and still others are worse than the stock system.

Because of advertising, this company sells more exhast systems that don't work well than anyone else I know of. The owners of these pipes swear by them, and say they gained a ton of power with the new exhaust. Go figure.

When we first began testing on the XR400, we found the stock headpipes performed exceptionally well with a stock engine. Even after installing a 440cc bore kit, the stock pipes were the best choice (with a White Brothers muffler). After changing the camshaft and going to a 440cc bore and stroke combo, then larger diameter headpipes did offer a good increase.

Anyway - that's what we found, back when the XR first came out, and we were racing the beast.

If you do decide to try an insert - tell us how it worked (or didn't)!

 

[Rich Rohrich]

Originally posted by DualSportr
Rich, actually, the idea for stepped headers is from the early 'teens. I've seen the design used on a Pope - the thought behind it was to do exactly as you mentioned - fix a bad cam design!

It seems like that is true of MOST things we perceive as "new" technology :)

 

[SFO]

I was wondering if the stepped header controversy would ever be addressed...:o

But oh my god, we are also going to take on the best selling pipe manufacturers too?

Get ready to lose subscriptions...
Oh, DRN isn't selling subscriptions!:confused:

 

[DualSportr]

But oh my god, we are also going to take on the best selling pipe manufacturers too?

Let me at em!!! grrrrrr!!!


Oh, um, sorry - what were we talking about???

Silly me - saying that advertising dollars equal sales! What a radical I am!

Rich - I know we've talked about it before - but it really is amazing to study the old bikes and see the things we think of as 'new' showing up on a 50+ year old machine.

No wonder the old guys in this industry are so grumpy - they've all 'been there done that' a few times over.

 

[adamxr]

we found the stock headpipes performed exceptionally well with a stock engine

It's a shame the OEM headers are so damned expensive... It's even more of a shame that my original ones are now quite bent!!:ugg:
I think what I'll try next is going back to the original headers (albeit a little bent) with the new muffler, then the old muffler etc... Then we'll know exactly where the culprit lies.
I don't think the system was badly designed (not yet anyway!). It looks very different to the yzf system anyway - the muffler is more oval shaped, and really big too!
Perhaps, as you were saying DualSportr, the new headers were intended to complement a big-bore kit in the XR... (Although the dealer didn't mention this! Ahhh, the hidden costs! I wonder if I have grounds for a refund, if this turns out to be the case!!)

 

[BigBore]

I don't know about the XR400, but on my XR600 I seemed to have the best luck with the stock head pipe, and the White Bros. E-Series silencer with 12 discs. In the case of the two people I know who put Big Gun systems on their 400's, they were pretty impressive.

 

[DualSportr]

In the case of the two people I know who put Big Gun systems on their 400's, they were pretty impressive.

Is this data from dyno testing, or seat-of-the-pants?

 

[BigBore]

Sorry to say its not dyno testing, just riding the bikes. My brother has a '98 XR400. At first when he got it he put on a Super Trapp race series muffler, and used the stock head pipe. This was quite an improvement over the choked off stocker. He rode it like that for several years, and then decided to go with a full Big Gun system. WOW!! What a difference. Flat out gained power everywhere.

My brother-in-law has a '98, too. Ever since he first got it, he was using a Yoshimura slip on. After a couple years, he put a 10:1 440cc kit and a hotter cam in his motor. He rode it for a while like that, then he bought a Big Gun system. Again, big improvement over what he was using. Said it really made the bike come alive. I just have to take his word for it, because I never rode the bike before he put the 440 kit in.

I wasn't all that impressed with the Big Gun on my 600, but it seems to be a good choice for the 400.

 

[DualSportr]

It's interesting how a jaggedy power curve - one that drops below stock hp, then bumps up above, then maybe drops down again a few times - will make a seat-of-the-pants evaluation feel like the bike has gobs more power.

The drop in power, then subsequent hit, makes most riders feel the bike creates more power - even when tested against systems which deliver a smooth overall power increase (of a much greater percentage).

I'm sure your friends with the 400 and the Big Gun would be amazed if they were shown a dyno chart comparing the Big Gun system to the stock headers with the White Brothers muffler.

Anyway - as long as the owner is happy - that's all that matters!

 

[SFO]

Thats one thing Dale always says as well....
A properly tuned and jetted bike will feel slower but give you faster lap times...
I am wondering if this particular Arrow pipe can also be run the stock head pipe?
My yz pipe had the stepped header as an option. I can run either set up...