Exhaust Termination Box on a motorcycle?

[sc2dave]

Is this also possible? I was thinking of a 4 cyl 4-stroke engine 750c.c.

[Devious]

The problem with trying to fit a termination box on a bike is that many bikes are already limited in collector length, and locating the box will take up even more and add weight.

IMHO, it is easier to simply get the lengths right in the first place.

[84Dave]

With the relatively small engine, and DV's 'rule' of termination box volume 8x the volume of a single cylinder, that would put the box volume required @ 100 cubic inches. If I performed the math correctly, a 4" diameter section of tubing, 8" long, would satisfy the 100 cubic inch volume requirement. If the engine rpm operating band versus induction lengths would allow operation on/between/near the 1st and 2nd ramming peaks, for best delivery-ratio (DR) into the cylinders, the exhaust lengths would be correspondingly short and 'packaging' might be doable. BTW.... I'm far from being any kind of 'expert' on bikes! Dave

[sc2dave]

What does this come out in in.? 750c.c.?

[84Dave]

750cc = 45.77 cubic inches (4 cylinders) = 11.44 cubic inches/cylinder x 8 = 91.5 cubic inches (minimum required volume for the termination box). Dave

[seattle smitty]

Now maybe I don't get it at all, but I thought the whole reason for the box was that on a car the desired tuned length of the exhaust system is only three to four feet long, and to avoid having the exhaust come out behind the front wheels (or beneath the driver's feet), the termination box lets you have a tuned exhaust that comes out at the back of the car. I don't see how this applies to a bike, which doesn't have the problem.

[sc2dave]

I asked about a bike because i've never heard of this.

[84Dave]

Smitty...... again, I'm not a bike expert. But if the bike was being raced in a class that required a 'muffler', then a termination box might be considered a muffler, if Tech agreed. If a 'muffler' was not required in a race class, then it would be just as effective to run the exhaust/tail-pipe, properly dimensioned, to the open atmosphere. On the street, you might get tagged by law enforcement for not running a muffler, if too much noise was being generated. On my paved-oval track Pro-4, tube chassis, 4-cylinder cars, we're required to run a 'muffler'. But instead of a true muffler, we run a termination box. Or, as I call them, an 'expansion chamber'. But still, in my simple mind, one would have to have a bike engine operating in a high rpm range, so pipe dimensions would/could be relatively short, in order to be able to 'package' the whole affair with 'tuned' dimensions.
sc2Dave...... have you used Larry Meaux's 'Pipe Max' software and attempted to dimension your exhaust system as a function of your desired operating rpm range for max power? It's some powerful software if one measures everything carefully. I also authored an extensive thread on 'induction/exhaust tuning' at the '4M.net' 4-cylinder Technical forum, using Dr. Gordon Blair's empirical data derived formuli for induction/exhaust tuning. To include calculations for Induction Ramming Peaks, Ramming Troughs, Header Primary-Pipe Length, Collector/Exhaust-Tailpipe Length, and Collector-Area-Ratio. I've used the good Dr's formuli, quite successfully, for a few years. And DV, the main man right here, got me started with the 'expansion chamber' thought/idea and implementation for 180-degree firing 4-cylinder's. Even Dr. Blair in his book, has 2-3 paragraphs on the definite advantage/effectiveness of a termination box/expansion chamber on 4-cylinder's. Dave

[seattle smitty]

Dave, probably not a good idea to call a termination box an expansion chamber since that term is used for a very specific device used on 2-stroke engines (in outboard racing, forty-five years ago, we called the first expansion chambers "bounce-pipes", which is actually a better descriptive name than expansion chambers). Finding agreed-upon terminology is an ongoing problem in this game!!!

[Brian P]

Having been forced to design and build my own exhaust system for a bike that has lost much of its aftermarket support, I'll give this a shot.

On most high revving 4-banger bikes, the proper length of the primary header pipe usually works out to have the pipe end somewhere near the middle of the bottom of the crankcase. What happens beyond that point mostly affects how the engine runs below the RPM at which the primary header pipes are designed for.

Traditionally either the 4 pipes join into one collector at that point, or the left and right pairs join and then a short distance further back, those two join (4 into 2 into 1) and then there's a tailpipe that ends where the muffler starts. The 4 into 1 setup is known for giving a bit better top end power but is notorious for "holes" in the mid-range. The 4-2-1 gives a better spread of torque.

Measured from the exhaust valve, every place where pipes join together is tuned for a certain RPM range: The first junction of the primary pipes for top end power, the junction of the secondary pipes for upper mid-range, the end of the tailpipe where it goes into the muffler for lower mid-range.

The header that I made was for a Yamaha FZR400, an engine known for making nothing below 10,000 rpm. I built a 4-2-1 (nothing "back in the day" was that advanced - the stock header was 4 into 1) and I selected a tailpipe size more appropriate for the engine (all others that I have seen are too big). Guess what ... it now pulls from 4000 rpm, and if you work out the tuned RPM for the full length from exhaust valve to the pipe expansion where the connection to the muffler is made, that's about right. It's rough below 4000 rpm, but on a 400cc engine, that rpm is only used for getting from the paddock to pre-grid ...

If you take a look at a 2006 or later Yamaha R6 or the previous-generation Suzuki GSXR600/750 (the ones with the stubby exhaust) they have a big collector box underneath the engine, which is a combined catalytic converter and muffler. I don't know what shenanigans happen inside that collector box as far as pulse tuning is concerned, but there are a few aftermarket pipes for those bikes that have a convoluted spiral pipe in that area, not just a collector box, which would seem to suggest that the traditional pipe arrangement is the best for tuning, if perhaps not best for catalytic converter placement.