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Author Topic: Exhaust opinions
Andy Bettencourt Verified Driver
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We just finished up the latest version of our exhaust and we have found a repeatable 1.5hp and 2ft/lb gain over a current popular design on our DynaPak for the 1999 cars. My issue is now with design legality.

Our muffler has an integrated exhaust tip that is 2.5" in OD. When I look at other exhausts (like the Sprigfield Dyno version in the attached picture, the inlet and outlets are much larger than the allowed piping - as we know. Even the flaired piece that mates to the outlet is larger. My question is, if there was no piping further downstream than the integrated outlet, would people still consider it legal?

Not sure I am getting my point across but if that muffler shot straight out the back without choking down to 2 1/4", would people consider it an illegal piece?

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Andy Bettencourt
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tony senese Verified Driver
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Something must be wrong Andy, apparently nobody around here has any opinions......

I personally and trying to imagine what that muffler would look like.

I think if the hole is in the body of the muffler you prolly could get it ruled either way depending on the mood of tech that day.

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David Dewhurst
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Andy, I could care less about your exhaust or anyone else that is spending their way through the class. [Smile] What I will say is that Spec Miata is a spec class & IMHJ this past change of no taping/coating/whatever with the exhaust rule didn't go far enough. Spec the O.D. with a reasonable manufacturing tolerance, spec a wall thickness with a tolerance & were done with it. I want to add a connector flange to the output of my exhaust pipe for doing Dyno work except if I weld the piece to the exhaust it will be larger than 2 1/4 inch & make the whole deal illegal.

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9.1.8.C.1.m.4.a "....and the tubing is a maximum of 2.25 inches outside diameter."

1.m.4.c. "No expansion chambers. A single muffler may be added."

No size is given for the muffler, so it can have 2-5/8" inputs, but the pipe can't have the 2.5" O.D. section, and be compliant. You would have to run the 2.25" pipe up to the muffler and attach it without the expanded (too wide) section of pipe.

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Andy, my take on it would be that the tubing (or pipe) cannot be over 2.25" od. You are aloud a muffler and it doesn't say where or what OD it has to be. The muffler inlet and outlet are not the tubing. Having said that, you have opened up a can of worms. Even you called it an integrated OUTLET. I consider that not part of the muffler even if it is welded to it. If I put the muffler way up front and build it with a 2.5 x 4' straight pipe integrated to it would that be ok?
I'm sure smarter heads will have a better answer but I would say no.

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are the springfield dyno exhausts built that way?

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The SD muffler has a 2.5 inch input and output( about 3 inches before and after), the pipe coming into and out of the muffler is 2.25. Legal to the rule IMO.
Jim

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If the muffler is manufactures with an outlet of any size and no tubing is added/system ends at muffler outlet, I see it as legal as the rules are written.

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Jerry

Andy Bettencourt Verified Driver
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Good discussion guys (except DD LOL). The picture I posted is the SD exhaust. It runs from right (engine) to left (bumper).

The inlet and outlet of the supplied muffler is 2 5/8" OD.

Our tubing all the way up to the muffler inlet is 2 1/4". As with the SD exhaust, the inlet and outlet of the actual muffler is more than the allowed 'system size'. The issue is that we don't have any more pipe past the 'muffler outlet'.

I agree Jerry...

Soup: I am not sure you can say that the inlet and outlet aren't tubing and then say in the same breath that it's not part of the muffler?

Look at the picture again. If the system terminated at the end of the 2 5/8" piece (muffler outlet), would you consider that a legal piece? I do because there is no spec on muffler size. Right?

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Andy Bettencourt
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Looking at the photo, the non-compliant part would be the short section of pipe that has been expanded to 2.5". Other than that, the pipe and muffler are compliant. Would somebody bust you for that couple of inches of oversized pipe? Only if it meant you were the National Champion...... Or, ......

Andy Bettencourt Verified Driver
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quote:
Originally posted by wheel:
Looking at the photo, the non-compliant part would be the short section of pipe that has been expanded to 2.5". Other than that, the pipe and muffler are compliant. Would somebody bust you for that couple of inches of oversized pipe? Only if it meant you were the National Champion...... Or, ......

I agree 100%. Ours does not do this.

The issue in my mind with our design is that the 2 1/2" muffler outlet is effectivly a 2" long tailpipe and LOOKS like part of the system which would require it to be 2 1/4", when in reality it shouldn't. [Frown]

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Andy Bettencourt
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Rich Verified Driver
Oh, that's where that is.

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I've never been 100% comfortable with the way the SD goes together. We all had it so I never gave it a thought as to getting protested. It seems to me that if somebody got himself out of the glass house while making the same or better power, and wanted to start throwing stones, that person would probably win the protest.

IMO the rule should read "muffler must have 2.25" ID inlet/outlet with 2.25" ID internal perforated muffler pipe, additional muffler may be added for low sound pollution tracks." Or something. Too easy (well, not easy, but possible) to simply make an expansion chamber in a muffler housing and call it soup. Some of the DDG exhausts have looked like this, and IMO are legal to the letter of the rule.

I agree with Wheel's interpretation, mating to the 2.25" pipe should be accomplished with lots of welding wire.

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Rich Wiese

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Andy Bettencourt Verified Driver
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Also, our system does not use any of the SD componentry, including the muffler. Just trying to make a legal, quiet(er), light and powerful system for our internal customer base which we may market outside out little fifedom.

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Andy Bettencourt
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If that 2.25" tube was expanded within the entry to the muffling device, and then welded in, it would be very hard to find it non-compliant.

Rich Verified Driver
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Yup.

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Rich Wiese

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Can I ask "what picture?"

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Andy Bettencourt Verified Driver
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The one in the original post.

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Andy Bettencourt
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Andy Bettencourt Verified Driver
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quote:
Originally posted by wheel:
If that 2.25" tube was expanded within the entry to the muffling device, and then welded in, it would be very hard to find it non-compliant.

And not saying or not saying it's legal or illegal. Just using the unit as an example of what is being used and how the inlet-outlet is interpreted.

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Andy Bettencourt
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Drago Verified Driver Made Donation to Website Series Champ
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I dont see the picture either?
Jim

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Blake Clements Verified Driver Series Champ
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quote:
Originally posted by Andy Bettencourt:
quote:
Originally posted by wheel:
If that 2.25" tube was expanded within the entry to the muffling device, and then welded in, it would be very hard to find it non-compliant.

And not saying or not saying it's legal or illegal. Just using the unit as an example of what is being used and how the inlet-outlet is interpreted.
Andy,
Did you try putting a "restrictor" on the end to take it back to 2 1/4? What about a conical taper on the end back to 2"? Could be argued all are part of the "muffler", but still meet the intent of the rules?

Blake

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Andy Bettencourt Verified Driver
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Ya Blake. It makes the same power put takes away the cool sound. [Frown]

Link to pic of SD exhaust:

http://www.roadraceautox.com/picture.php?albumid=6&pictureid=632

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Andy Bettencourt
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still no picture.

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Paul McLester

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The link 2 posts above works for me.

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Andy Bettencourt
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I see nothing in your first post and the 2nd link goes to a blank page.

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Jerry

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Friggen technology! lol

 -

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Andy Bettencourt
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Here is how we did my last SM. We took pieces of 2-1/4 and taper swedged to meet the major diameter of the muffler inlet / outlet. Thus no part of the straight tubing is larger than 2-1/4. Why 2 mufflers ? I like quiet and the chassis dyno said the engine did not care.

http://forum.specmiata.com/files/00005545/SMExhaustComboEM.jpg

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I would say the 2-1/2" flared section is not legal.
Why? How long can the flared section be? 1 inch or 36? The way I read the rules is not at all.

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Jerry

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Andy, the picture in my head the your's weren't the same. I would think that would be legal. Nowhere do the rules say what OD or length the muffler outlet has to be. At best maybe you could have shortened the 2.5 od pipe by 1" just leaving enough sticking out of the flange to weld.

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Charlie,

The pic Andy is showing is the SD exhaust.

It is, in my opinion, nowhere near (not) legal.

John

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Guys, I am not trying to say that the SD exhaust isn't legal. I am just asking if it ended at the muffler outlet (which has a 2 5/8" OD), would people agree it's legal or illegal. Simple question.

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Andy Bettencourt
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I've had the same thought, but not the inclination to pursue it.
I would say it's legal for the same reason you do. Same parts, just different placement.

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Andy I've been down this road already. This is not legal because (I was told) the rules require the pipe to be 2.25 and I had increased / changed the diameter of the pipe. I lost the protest and fixed it. Rap the exhaust so they can't see it.....no wait, you cant do that.

Go bang your head against the side of your trailer.

David

   

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