An exhausting question

[GMC]

18.3.0.4 'Exhausts may be modified but must generally follow the original lines'

This is what the rule says & as we debated on Doc's question, we came up with many opinions, however the debate would be futile if we don't get MA to try to change this.
I doubt MA officials read this site & then change things to what we come up with so if you think the original rule isn't workable then take the time to fill in the sheet & send to MA.



Print off & fill out this form & send to MA. Address on the form.

Don't be whinging about the rules if your not prepared to try to fix them.

[Lozza]

The problem with narrow definitions is if someone produces evidence that contradicts or makes a mockery of the rule then it forces even more rules, changes and definitions.Also IMO make pretty complaints easier to uphold.A more open and less defined rule like; Rule 1.1"Exhaust specification is free" 1.2 Exhausts must generaly follow original lines.Copies or iterations of aftermarket exhausts and designs available/published in the period are considered acceptable. 1.3 The use of materials in the exhaust(excluding silencer) such as Titanium and Inconel are banned.
The worst case scenario I see (dunno about you Geoff)is a overly wordy complex rule will stifle developement of exhaust designs which was never the case in the day.

[DJRacing]

GMC, I like number 3 -  (Exhausts may be modifed but must generally follow the lines of pipes available in the era.)

But I would like it better if the word "diameter" was added.

Exhausts may be modifed but must generally follow the lines and diamaters of pipes available in the era.

Just my thoughts to keep extreme fat-pipes from creeping in where they dont belong, but still leaving enough room for the keen chamber makers and experimenters to play with their pipes.

[Nathan S]

The current Option #3 is really no different to option #1 - there are a limited number of ways that pipes can run:
1. Up pipe.
2. Down pipe.
3. Snail pipe.

Everything else is a variation of that, surely?

When did snail pipes first appear - pre-70 or pre-75?
What about up-pipes? Pre-60 or pre-65?

Maybe the solution is to just prohibit snail pipes on pre-70 bikes (if appropriate)?

DJ, I kinda agree with the direction you're heading in, but all that does is advantage the smaller capacity bikes - I'm sure I can prove that there's a pre-75 open classer with a 120mm belly, which means that any 125 can have a modern style pipe, while limiting the open class bikes.

To my eyes, there's no problem with anything to do with diameters or tapered headers or the path the pipe takes along the bike.
The only pipe-related thing that offends me on VMX bikes is the pipes that are bunched up at the front of the bike (modern/low-boy style) - writing a rule that effectively prohibits that is damn near impossible (well, its elluded me anyhow...).

Something like "The belly must be in the same general location as the original" or "The most upstream part of the exhaust stinger must be located rearward of the carburetor slide" both sound OK, but are so full of loop holes that I would never support them.

So my conclusion is that we should simply ditch the existing rule, and let the fashion police sort out anyone who turns up with a low-boy pipe.

[DJRacing]

Just for you Nathan   

Exhausts may be modifed but must generally follow the lines and diameters for it's CC rating that were available in the era.


Is that better Nathan ??   

[Nathan S]

Definitely better.
But I still reckon its fixing something that doesn't need fixing, while leaving the (possible) problem area untouched.

Kinda like "Ron Jeremy is going to have sex with you - but his back will be freshly waxed" - sure its an improvement, but it doesn't really solve the problem.

[gorby]

the exhaust rule has the ability to affect the four strokes too,
my 74 XL 350 originally has an under type crossing from the right of the motor under the frame and up the left side.
I run a copy of the peter allen type and others which runs down the middle of the bike



so the wording has to be careful so as not to cause more problems.

[holeshot buddy]

too bad for the fourstroke boys
they would have to run peashooter exhausts
i think the follow the same line rule is ok
i dont think size comes into it
you are limeted  with room for a start
and diameters are not a lot bigger than standard anyway
depending on size of motor
this rule only applies to current aftermarket pipes anyway
dg procircuit fmf etc if they were made for the era bike they are ok even
if they have large diameters
most current pipes seem ok to me
gmc pipes may be infinatley coned but the ones i have seen still follow same line
i think leave it alone been no problems to date

[090]

i dont think size comes into it/quote]
Only guys with small pipes say that 

I think the fashion police keep a handle on things. Shit i get a hard time for my taste in riding gear

[GMC]

I like option 3 best myself, remember this whole debate started out by the fact that some after market options of the day may be outlawed by the current rule.
I originally thought the current rule was fine but I now believe this needs rectifying to stop any unjust protests.
Any overly complex rule will not only make it hard for me as a manufacturer but also for scrutineers & the riders themselves.
I don't believe the rule needs changing in an attempt to stop something that we may deem to be ugly.
One man's trash is anothers treasure.

I was thinking of making a Ti pipe just for the hell of it but I have now seen too many moderen Ti pipes fatigue too quickly & have canned the idea. I don't know that it would be any real advantage to worry about banning such stuff, remembering BSA made some frames out of it in the day.

I think this debate has also developed a bit of tunnel vision. Does this hatred of "fat" pipes extend into the Evo class as well as pre 75. Gorby reminds us of four strokes that  often used FAT pipes as well so consider these if trying to write an anti fat pipe rule.

Exhausts may be modifed but must generally follow the lines and diamaters of pipes available in the era.

Well I would be against this as it would outlaw a lot of my pipes, & as sizes changed between manufacturers who is going to decide what the max dia. should be for any given bike. We will then have protests because someones pipe was 1mm too big.
I believe in the KISS principle.

Do fat pipes really look that out of place or am I used to seeing them?





Personally I think Fatbars look more out of place

[Freakshow]

I think its too hard to worry about, just make pipes open.  I mean how fat is fat ? at some point the angles and ratio just dont work anyway so the pipe sets its own perfermance limits.

This Fatter pipe was on my boss yza in 75, you could say that fats, but hey its on it and they ran it, so not only is it legal by age cut off but by under design of the frame also, but could you then argue the motor was sold with an up and over ? so where does that rule cross over. 

Meh... delete it, its not worth trying to rejumble it to work, you will always find another example of something that someone tried back in the day and we should embrace it.     Most things have been tried before so other than metal materials the concept of expansion chamber design should be open to personal choice and fitment, it dont need a rule

[LWC82PE]

I tend to think to have no specific rule. If people want to put modern design low boy fat pipes or whatever on their 1970’s bike and make them look silly and crap and out of place with these sort of pipes then let them go for it, it really doesnt bother me. Also the same goes for adapting a pipe off a modern bike, its probably not going to suit or match the engine porting and it may even go worser than if the stock pipe was fitted. I know back then computer programs were not around to tell you what shape/length to make the cones etc but I do have old 2 stroke pipe building books and there are all the calculations in there to be able to make a fat looking pipe so in theory people could of made these sort of pipes back then anyway.
But if there HAD to be a rule I would only say no pre built pipes off modern eg 1990’s 2000’s. bikes allowed, but if custom built then open slather and let the people who want these fat low looking pipes have them on their bikes. I personally think they look a little out of place but as long as the owner is happy then that’s the main thing. You have to use common sense here though. I know not many people would race an early 80s TS 185 but  for example a pipe off a 2000 model TS 185 should be allowed (although its off a modern bike) as it’s the same as a 1980’s model. What I mean is no fancy pipes off a 2000 model YZ 250  to be used on a 84 model or what ever. But when I think about this how do to you truly clarify what pipes have stayed the same for 20 or so years, so It may just be easier to say no pipes off bikes modern 1990’s/2000’s bikes full stop to save confusion.