Exhaust Link Pipes?

[collinsda]

Hi, just wondering if anyone has any opinion or info on this... I am currently building a race bike and due to limited budget I am going to be using the stock exhaust system. Firing order is 1-2-4-3 and the downpipes are linked 1 to 4, and 2 to 3. The collector is a 4-2-1. The cam profiles (stock) are quite short and so I am going to tune the bike for maximum power in quite a narrow rev range.

My question is this - can I gain any power by removing the link pipes?? Are the link pipes there to help power throughout the whole range?? If this is the case then surely removing the link pipes will help the top end...

Ideally speaking I would like to make power over a wider range but unfortunately I can't invest much more money into the bike and my only option is to modify what's there to suit.

Thanks in advance,

D.

 

[thundair]

Try this

http://www.eng-tips.com/threadminder.cfm?pid=668

I t will be great to get more motorcyclist there...

 

[MikeHalloran]

Peaky engines win dynamometer pulls, not races.



Mike Halloran
Pembroke Pines, FL, USA

 

[collinsda]

Thundair, thanks, I've been keeping an eye on that forum. Cheers.

Mike, if you had read by post properly you would see that I am financially restricted to the amount of development I can do on the engine. My question was about link pipes, not whether the bike will be competitive...

 

[Tmoose]

I don't know where or what you'll be racing, but on 230 lb off road bikes it was once proposed that a 7 lb bike/(rider) weight reduction was about as useful as 1 extra HP. If the surgical removal of my "link pipes" saves several pounds there might be an advantage right there. I can think of only one way to determine whether defeating the acoustical and/or flow function of the "link pipes" produces a result I would find useful. That is to try it. For experiments I try to concoct temporary modifications so I can find my way back home. I'm picturing stuffing the link pipe with something, or for more reliable A-B-A testing, even sawing a slot half way through a round section so a thin disk could be inserted to close off the pipe.

For reference, on any given day, starting around the middle of the previous century, and continuing through today, there have almost always been some proponents of ADDING a crossover or link pipe between the branches of a hIgH PeRfOrMaNcE exhaust system. A few have even had their names beside a drag racing or Bonneville record or two. "Scientific" explanations of what crossovers do, and why, vary a bit. The one I find easiest to believe is basically 2 mufflers flow more than 1. Methods of determining "the" location and size of the crossover have been "interesting," too. For a while it was popular to paint the (single wall) pipe and look for a transition between charred and non-charred paint. Allegedly just as useful for setting collector length or installing a crossover.

For sure my biggest tuning successes and failures have involved carburetor jets and needles. The butt dyno reports HP and torque improvements (and crushing losses) of over 100%.

 

[mburgess]

More than likely you will lose power by removing the cross overs. The engineers that designed the exhaust system have alot more equipment/time/knowledge to design the exhaust for its specific engine operation. I have seen many aftermarket exhausts for motorcycles a direct copy of the standard system mad from thin wall tube. Often gains can be made by repacing the collectors with a higher quality merge style ones. A slip-on straight through muffler will help. Often in mass production these are pressed out & can be rough internally to the gas flow. By the way which bike it is?
Regards,
MB

 

[collinsda]

Cheers Tmoose, yeah, that's pretty much the gist I got from some lit. I found on the web. i was thinking of splitting the pipe and blocking it to see if I found any difference.

MB, I think you're right, they're best left alone - the documentation I found was pretty basic but explained the difference between H and X link (or balance) pipes and the effects each had on performance. It seems the X type is fair better but it's actually more like a collector than anything else. I used to ride a VTR1000 and that had the same set up, both exhaust pipes coming together and then splitting again to seperate cans. The bike in this case is a ZXR400.

I'll leave it as is anyway, but I still want to get a more meaty breakdown of why it works better and how to determine where the X 'join' is. It would be interesting to do a Matlab (or similar) simulation of an exhaust system...

 

[mburgess]

Are, I have been racing a ZXR400 for about 5 years. In this case they do better withouth the link pipes. The whole ZXR400 standard system is double skinned (heavy). It is a 4-2-1 system with a verticle plate in the tail pipe to extend the secondry collector. I have found a good result in copying the standard primary header in 1 1/4" stainless tube (1/8" larger than standard) into 1 1/2" secondaries at 6" long into a 1 3/4 tailpipe tapering to 2". Total system length same as standard.
Regards,
Michael

 

[collinsda]

Hi Michael, so should I get rid of the link pipes then? Could you give me the exact dimensions for the primaries & seconadries? Sounds interesting! Are you using the same secondary collector then?

Cheers,

Dave

 

[mburgess]

Use same lenght as standard for primaries (660mm from memory, you may have to measure). Even though the standard headers measure 1 1/4" they are double skinned so effectivly are 1 1/8". Use 1 1/4" for primaries & 1 1/2" for secondaries (shorten the secondaries to 120mm). There is a race kit exhaust from kawasaki that has tapered headers at 1 1/2" but have not been able to find a set to measure yet. There is also a BEET 4-1 system with 1 1/4" headers. The 4-2-1 configuration works alot better the 4-1 leaves a hole at about the 10k rpm mark.
Regards,
Michael

 

[Rob45]

MB writes:
"The engineers that designed the exhaust system have alot more equipment/time/knowledge to design the exhaust for its specific engine operation."

which is true as far as it goes, BUT the "specific engine operation" that the original engineers intend is likely very far removed from the specific engine operation "collinsda" intends.

Now regarding those pipes, Collins:
It is also quite likely that those crossover pipes are present to improve noise rather than performance. Even if intended to improve performance, it's unlikely they would improve performance in the peak rpm range that you intend to operate in, so I wouldn't hesitate to remove them.

But here's something you can do: cut the pipes and block them with e.g. a flat plate, and test the bike with the pipes blocked. If performance is worse, remove the plate and repair the cut. If better...

 

[collinsda]

Thanks a lot guys - I'm still rebuilding the bike at the minute but I'll try that and see how it goes. I'll let you know how I get on. Like you said Rob, I can also remove the 'plug'.

Cheers,

Dave.

PS: thanks for the pipe dimensions Michael!