How different are exhausts on the inside?

[photomike666]

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I won't get into any discussions about 'back-pressure' and 4-stroke motors..... unless of course you want to discuss 2-stroke exhausts - this is where back-pressure discussions actually belong....

All I can say is EXUP valve

[IsleofNinja]

The muffler does exactly that - it muffles the noise produced by the motor. Some of them (ie the 'absorption' muffler - straight-through design with packing) are the noisiest, but also flow the best. These need to have the jetting/FI tuned to suit the better flow. The other style with multiple chambers (generally OEM style) are made to keep the bike really quiet and under dB limits for ADR compliance. Every manufacturer has their own 'design' of muffler, but they all do much the same job.

I won't get into any discussions about 'back-pressure' and 4-stroke motors..... unless of course you want to discuss 2-stroke exhausts - this is where back-pressure discussions actually belong....

thank you Gos .

All I can say is EXUP valve

Hmmm what you mean you still have yours fitted Mike?? what about the secondary flies .. .. they still there too??

I would strongly suggest a really good close look at a number of bikes running same brand/style cans on your next ride / event. Think you might be suprised at just how similar they turn out to be when you take a good hard look at them.

[photomike666]

All I can say is EXUP valve

Hmmm what you mean you still have yours fitted Mike?? what about the secondary flies .. .. they still there too??

I would strongly suggest a really good close look at a number of bikes running same brand/style cans on your next ride / event. Think you might be suprised at just how similar they turn out to be when you take a good hard look at them.

Exup value was a Yamaha design in the old FZR exhaust, aimed at giving a 4 into 1 system more mid range while being tuned for top end power.

Yes my 10 still has the secondary valves and the flapper thing. I see little point in modding it to make it more powerful when I don't use all that is on tap already, and I don't see the need to make it any louder. I can already set the wife's car alarm off just idling down the drive

[Gosling1]

.......All I can say is EXUP valve ......

all I can say is - Marketing gimmick.

Its right up there with YEIS, YICS, ATAC, KIPS etc etc. and there were *shitloads* of these during the 80's and into the 90's.....although most of them seem to have gone the way of the dodo ??

The only acronym's worth their weight were TSCC from Suzuki (Twin Swirl Combustion Chamber) and YPVS from Yamaha (Yamaha Power Valve System.) - In the case of YPVS, this is only applicable to 2-strokes, and actually does have a logical basis for working in *that* application. Both the Honda version of this system (ATAC) and the Kawasaki version (KIPS) were abject failures, and dropped from the relevant model range very quietly.....

You could rip an EXUP valve off *any* five-valve Yamaha (and heaps of punters do), then re-tune the motor to suit the removal of this exhaust restriction - and *bingo* you would instantly release anywhere from 5-8hp at the back wheel. The EXUP phenomenon meant of course, that the other manufacturers had to have their own version, to keep up with the Joneses.....except Suzuki afaik ?? They haven't fitted any type of exhaust 'flaps' to their bikes have they ??

If that exhaust flap had any real engineering significance and benefit, it would be fitted to every 4-stroke motor built. The fact that its *not*, is just proof that it is nothing more than an exercise in marketing and nothing more. The design of the head, the size and number of the valves, the lift/duration/overlap of the cams, the compression ratio of the motor.....all of these things dictate how well a motor flows. Not some poxy flap located *somewhere* in the bowels of the 'zorst !! But the stickers look good on the side of the fairing !!

- I will agree though, that putting a restriction in the exhaust down in that area, will improve the perception of mid-range response, due to the restriction in flow (although this is not 'back-pressure' at all - its actually a function of the increased richness in the air/fuel mixture at that point in the rev range..........)

Putting a free-flowing exhaust system on a bike - WITHOUT - tuning it to suit - will always result in reduced performance. And in most cases, the average punter will say - Ohh its because you don't have any back-pressure.....or ' Your back-pressure is all gone'.......or ' you need back-pressure to make it work..."

Its the greatest urban myth in the history of motorcycling.

If you put a free-flowing exhaust on a motorcycle, THEN tune it properly - what happens ? Does it go like a dog shot up the arse ?? Of course it does ! - its now flowing the correct air-fuel mix, so it has a corresponding performance Increase !! Where is the *back-pressure* argument now ??? Its dissapeared up its own exhaust outlet, thats where its gone ! Or do you increase the back-pressure, by bunging in bigger main-jets ??

If you need more convincing - ask yourself the question.....if some concept called 'back-pressure' is required to make a 4-stroke motor work......how is the 'pressure' formed ?? Where is it formed ?? Where does it go *back* to ??? Why would it go back there in the first place ?? and exactly *How* could it go back there ?? Where does it go from there ??? ( its important to note at this point, that the concept of an exhaust 'slug' of gas, creating a 'low' pressure point in a collector box - the correct design of which, according to firing order, will actually 'assist' or 'extract' the exhaust slug form another cylinder - is NOT the same concept as some esoteric thing called......back-pressure.)

Sorry about the sermon......

[photomike666]

So why does a 4-2 system give more mid range, and a 4-1 top end power? If one system was significantly 'better' at allowing the gas flow, surely all bikes would have that system.

[IsleofNinja]

So why does a 4-2 system give more mid range, and a 4-1 top end power? If one system was significantly 'better' at allowing the gas flow, surely all bikes would have that system.

VERY good question Mike

As you know the average inline 4 4stroke motorcycle can run ; 4 into 4 (ie early CB400) , 4 into 2 (ie CBR1100XX) , 4 ito 1 (CRIM,BUG etc), 4 into 2 into 1 into 2 (like yours n my Gumby Mike) and so on and so forth....

To say a 4 into 1 will give you performance 'X' and a 4 into 2 will give you performance 'Y' on any given bike would be somewhat of a vague generalisation at best.
There are soooo many more factors involved with the actual header / midpipe design. The manufacturers of exhaust systems must consider all the above mentioned factors ie valve timing/camshaft profiles , engine capacity , firing order (Take the early R1 "screamer" compared to the 'big bang" engine for example) , operating rpm , engine swept volume , number / config' of valves ...... yada , yada ,,,,

There is far more involved in the design process than simply 4 pipes into one collecter will make the bike a top end weapon vs 4 into 2 into one or two makes for a nice broad powerband..

A great example of how manufacturers can sometimes compromise cost vs efficiency and / or not quite get it spot on is the ZX9r... The stock headers are a mild steel 4 into 2 into 1 with a balance pipe approx 4" from the header flanges .... works OK and most riders would be happy as pigs in poo with the stock 9 zorst with maybe the addition of an aftermarket can (for the sound more than outright performance) not knowing any better nor feeling any need for improved performance.... fair nuff.
As MANY members here could testify , the addition of a full Yoshi system for example GREATLY improves the bikes mid range / roll on power / torque as well as enhancing the bikes top end.
Point being , header design on any engine is a FAR more complicated science than actual MUFFLER design as such.

Generally an aftermarket muffler designer aims to acheive a few very basic objectives:
1. To reduce exhaust noise - (re 2 mufflers vs 1... ie How loud is a Crim vs Gumby??)
2. Muffler must match or exceed the engines exhaust flow capability to allow maximum POTENTIAL power output. (ref Gos's tuning notes)
3. The muffler design / flow characteristics must compliment the header design / mid pipe.
4. The muffler must conform to the design constraints of the bike intended ie undertail single / twin / side pipe etc..

An OEM muffler designer must;
1. Comply with ADR noise restrictions(a special note here re Gumbies/ R1's etc - twin mufflers are more for maximum flow and MINIMUM noise via double the damping area)
2. Comply with ADR emmisions constraints.
3. Find a compromise between the above 2 listed vs performance.
4. Conform to the bike designer's aesthetic blueprint.
5. Last beyond the bike manufacturer's warranty period.
6. Comply with the manufacturer's budget constraints.

FINALLY - A straight through / 'absorbtion' style muffler relies on the packing material being in good condition in order to work efficiently (also affects power/torque potential) Almost EVERY aftermarket bike muffler [espescially dirt squirters] require re packing to maintain their peak effectiveness and efficiency. Some such as Tingate are less prone as they use a stainless mesh matrix rather than glass packing (wool or matting type) which does not break down as easily from heat but makes for a VERY heavy muffler.

Conclusion - If you can find a muffler with a straight through core about 50-57mm ID approx 600mm long would be absolutely fine on your Sprint Dave. The KEY as mentioned on several occasions is tuning the bike to suit.

Sorry for the rant but hope it helps clarify a little.

[Gosling1]

Its a great subject, there has been a lot of misconception about 'back-pressure' ever since Herr Otto made his first million, and I could talk about it all day if we were talking stinkwheels !! Where back-pressure in an exhaust system is *absolutely crucial* to obtaining the best power.

The point about the balance-pipes in the headers is a good one - this is all about balancing the 'flow' of the exhausts - which achieves maximum 'velocity' of the exhaust slug.....giving the best power output for *that* particular motor ....

A 4-1 achieves a better top-end, because the exhaust gases flow faster in this style of exhaust (assuming the design of the collector box is correct) - and there are less restrictions for the gases. A 4-2 will generally have a bit less top-end, because the flow of the exhaust gases ( ie the velocity) is lessened - the exhaust gasses have restrictions. Manufacturers like having the power restricted a bit, because it makes the bikes easier to ride and therefore sell. Its also about making exhausts cheaply - stamped and presses sections welded together by robots are far cheaper to produce, than say an Arrow 4-1 for a Z1000, with its 18 seperate pieces.

[DaveGPz]

Holy crap! I am grateful for the overwhelming response, based on a huge amount of experience out there. Thanks all and sundry. The idea of tuned header pipes rings a bell in the deep, dark recesses of my brain. I remember spectacularly convoluted headers on V6 and V8 race engines, and comparing them to the stock manifolds which looked like a piece of rough cast pipe with holes in the side. And fitting a set of Pacemaker headers to my old diesel LandCruiser, which let it over-rev to 4200 rpm! Heady numbers! Weighed 1.5 tonnes and had the same power as the Sprint, which explains why I used to put it in first gear at the bottom of the Adelaide Hills at Devil's Elbow, and stay in first until the Eagle on the Hill (a South Australian reference).

So, to summarise the discussion so far, the real black art is in the header design (hence the full system); in all likelihood there are some basic similarities between muffler internals such that a muffler for one bike will probably suit another of similar capacity, providing the tuning/fueling is appropriate. There are differences based on engine size (exhaust flow) and possibly engine configuration.

Or for 6 grand I could turbo the sucker, get 160 bhp+ and screw the muffler

Only 5200 problems with that solution

[IsleofNinja]

Maybe not quite so much hocus pocus as you might think considering a Yoshi tri oval to suit a 99ZX6r for example is the EXACT muffler configuration as sold to suit say a 04 ZX12r - only difference is the mounting nipple/flange.
ie generally street bike muffler manufacturers keep the design from bike to bike as generic as possible to keep costs down.

Don't take my word for it .... look for yourselves




........................On these forums there are many opinions and everyone is entitled to one , remember when reacting to opinions that some are based on rumour , some articles written in magazines by journalists and then others based on hands on experience/facts.

[DaveGPz]

An OEM muffler designer must;
1. Comply with ADR noise restrictions(a special note here re Gumbies/ R1's etc - twin mufflers are more for maximum flow and MINIMUM noise via double the damping area)
2. Comply with ADR emmisions constraints.
3. Find a compromise between the above 2 listed vs performance.
4. Conform to the bike designer's aesthetic blueprint.
5. Last beyond the bike manufacturer's warranty period.
6. Comply with the manufacturer's budget constraints.

Conform to the aesthetic blueprint! Have you not seen the muffler on a 955 Sprint? They make a 44 gallon drum look sleek!

[Nelso]

Sorry for the rant but hope it helps clarify a little.

I didn't think it was a rant, just good solid tech. Thanks to Gos and IlseofN for their contribution to this thread as I enjoyed reading your posts and have learnt from them. Great stuff.

[DaveGPz]

Sorry for the rant but hope it helps clarify a little.

I didn't think it was a rant, just good solid tech. Thanks to Gos and IlseofN for their contribution to this thread as I enjoyed reading your posts and have learnt from them. Great stuff.

Seriously, couldn't agree more. Thanks guys!

[IsleofNinja]

Conform to the aesthetic blueprint! Have you not seen the muffler on a 955 Sprint? They make a 44 gallon drum look sleek!

Had a peek a boo at a 955 today dave ,,, see what you mean!? looks a tad ZX12ish ,,, This one had the side pipe and his mates had the tri outlet undertail jobbie.

-If yours runs the conventional style side pipe , I reckon a replacement 304 stainless midpipe with the provision for slip-on (57mm nipple) muffler.
-Obviously look for a new or good second hand can ie fleabay etc or local bike wreckers first then have midpipe made to suit. (pref' rebuildable ie rivited /cap screwed end caps)
-If you strike up a good relationship with a zorst shop proprietor of your choice (via favoured liquid motivation or similar) , A replacement midpipe should be pretty reasonably priced.
*** Considerations ;
-mounted pipe angle should follow the rear cowling lines or maybe kick up a bit (do a dummy up and see which you prefer)
-Ensure you have enough pillion peg clearance (if you need to move can a few inches rearward ask Hoffy etc re stubby can conversion - would look/sound HAAWWWTTT!!)
-Ensure you have enough room to attach the muffler bracket ** you may need the Zorst shop to make/modify mounting strap for you to support the can correctly.
-The midpipe WILL get hot enough to cook your boots without a heatshield [original in dual walled] -- tip ; make one out of sectioned 64mm stainless zorst pipe with tabs to be welded to midpipe just aft of the rearset...a bit of time with some Autosol will work wonders here also

****Most good zorst guys/gals take a lot of pride in the end result so ensure you give em a fly by when the job is done *******

Patience and homework are key here for a top job / minimum cost

copy and paste item # re micron can ex USA on ebay 390081098698

should point you in the right direction

[DaveGPz]

This is going to be fun! I'll see about the fender eliminator at the same time, and new mirrors. Thanks for your help!

[Saki]

i enjoyed reading that information too! I found it quite informative and answered a few questions i never knew before.

Also very interesting poin on the stock zx9 headers. My mate said after i got him a set of D&D headers for a 99 zx9, he chucked them on with the D&D muffler and he reckons the 9 went "off" he said it felt like it had heaps more power.... I sort of fobbed it off as if he was just going over the top about it, but sounds like there could be some merit in what he is saying!