H. Dan Smith's Muffler, Trunk, and Graphics

Originally Posted Sunday, July 9, 1995

Rd TriClick HERE for hypertext link to lots of e-mail and other memoranda regarding the muffler modification. A big "thank you" to all those who have contributed . . .


Spare tire mounted under the car. Fits like it was made for this spot!
The muffler is from a Camaro Z/28. (the muffler guy told me that it
is a "Walker Dyna Max Mini-Turbo"). The tail pipe is the original.
This is an easy pipe-bending and welding job for the
average muffler shop. This job cost about $150.00.


Another view. Nothing is seen from the street.

Thanks to Patrick at Discount Tire in Fresno (Blackstone/Herndon) for the "lift."
(He sold me those nice Dunlop D60 A2's -- I like 'em)


University professor's 2nd office.
(this old Mac SE/30 is NOT Internet connected!)
Lots more space; very good for traveling.

E-mail and stuff regarding the muffler setup

Lots of contributors!

Originally posted Thursday, July 13, 1995

Original post from ME to Miata.Net on Muffler Setup.

From: dans@zimmer.csufresno.edu (H. Dan Smith)
Subject: Exhaust Notes
Date: 14 Jan 95

Several San Joaquin Valley Miata Club (Central California) members, under the able leadership and guidance of club member and Miata Maven Larry Galat, tackled what I think is the biggest problem for Miata owners in this neighborhood. No trunk. We are a million miles from nowhere, so traveling up to SF, down to LA, or over to the coast is part of living here. Trunk space is a must if you have a friend or use a toothbrush.

The obvious answer to the dilemma was to just take out the spare tire, and for a while some of us did just that. A certain level of angst goes with such a decision. Blowouts, etc., and I am not known for my luck. A few Miata Magazine issues ago a company in the PacNW called "CanDoo" came out with a kit that moves the spare under the car, replaces the muffler with a different shape, and voila, a real trunk and a spare tire. A few of our members purchased this kit. Although it is made amazingly well, there were problems. The one that bothered me the most was that the exhaust came out about the center of the rear deck via a turned-down pipe (that does not show), and the stock chrome outlet tip is replaced with a fake one. It looks fake, too. No one's motor burns quite as clean as these jobs make it appear. It just looks "funny" on those cold mornings with the exhaust vapor coming from the rear center and nothing coming from the tailpipe. Also,there was a problem with the conversion melting the lip of the rear bumper cap on some cars (ugh). Therefore, I stayed away from this system.

Then, the aforementioned Larry Galat found a wizard at a small, private muffler shop with one of those Huth Bend-o-Graph machines. With a bit of experimenting, this young craftsman found a way to move the spare under the car, and make a super-clean conversion. He cut the existing pipe just ahead of the rear axle, constructed a new (and more direct) pipe to a nice oval muffler from a Z-28 Camaro, and then reattached the outlet pipe from the old muffler (with the chrome tip) to exit the stock location. Very sanitary. He also moved one of the three stock muffler hangers to a new location, which was easy to accomplish and provided added stability for the exhaust system. It all welded-up very nicely.

Benefits. A trunk. Surprisingly large. You can get real suit cases in there. You won't believe it. Also, the car looks much cleaner. I was beginning to loathe the appearance of that ugly Coors-Silver-Bullet- beer-can-looking stock muffler with the big bluish-purplish scorched spot in the middle. This new setup causes the rear of the car to be absolutely clean. Nothing is visible underneath but the differential. The spare tire and the muffler tuck completely under the rear bumper cap. Also, there are NO heat problems, NO rattles, AND a noticeable increase in power and gas mileage (two things that weren't even expected).

Drawbacks. Noisier, but a very nice sound. Frankly, it was a bit much for me at first. Some of us purchased a $4.95 Harley-Davidson exhaust pipe baffle and installed inside the chrome exhaust tip. It fastens with one screw, is completely adjustable, and best of all, it is removable for more noise when you want it. I eventaully took mine out. I like the sound.

Cost. The guy has been hitting us for $150. Worth it to me. Particularly since the CanDoo system is $200+ not counting freight (and paint and body work if it cooks your rear end). Actually, I think they have this problem fixed and I am not knocking their system--it is just not as clean as this other set-up.

Cautions. I was warned by Miata Mavens that this modification would goof-up my handling geometry, violate Mazda's carefully engineered weight distribution, make the handling squirrelly, etc., etc. None of this is apparent to me. But then, I might not notice these subtle changes. All I can say is that the conversion probably accounts for less handling change than a passenger vs. no passenger. I did this in May, have had no regrets, and last week finally put my stock setup in the dumpster. Oh, the aforementioned Miata Mavens have subsequently followed suit and made the conversion. Go figure.

Warranty. I'm still under warranty, and I did wonder some about this. I've had my Miata in the shop a time or two (oil changes, brake pads), and there was no trouble. My dealership, however, is so bad that they may not have noticed the change. I'm not convinced they really work on my car anyway.

If anyone wants more info, give me a holler. I'm neither selling anything nor recommending who might do this for you if you are interested. I did, however, learn that there are some pretty talented pipe benders and welders in some small, private shops out there. I'd stay away from the chains. I don't have a photo of the setup, but might make one available should there be any interest.

Take care. Enjoy your Miata. :-) Dan

Letter from Jack M. (& Kansei).

From: a.mccombs3@genie.geis.com
Subject: What can Candoo do?
Date: 1 May 95

I'm sure others who have installed this thing will reply also, but here's my $.02. I like the concept of providing room under the trunk floor for the spare tire, and I like the freer breathing (available with all kinds of other aftermarket systems also). I don't like the dufus routing of the pipe out the center of the car, and the installation of a fake tailpipe in the old rear valence cutout to fill it in. In fact, my don't likes of the Candoo system have taken precedence so far, even though I really want to relocate the spare.

In a few weeks, I'll be checking with some exhaust shops about this. Tentatively, I'll use the H. Dan Smith system, with a Camaro muffler. (He put out word of this on the net a couple months ago, but I haven't seen his name for a while - you still out there, Dan?) However, I dunno how this will work out with the Racing Beat rear subframe brace which will be installed in a couple weeks or so. (So many aftermarket goodies, so little time.) Anyone tried any of the baloney-shaped glass packs? They're very compact and are generally relatively free flowing and would probably sound OK, and are also relatively inexpensive. One could afford to replace them every year or so, which is probably about how long they'd last. Any other thoughts out there?

Jack M. & KANSEI

Letter from Jack M. (& Kansei) after he made the modification.
This letter speaks to the change in exhaust sound/volume.

From: a.mccombs3@genie.geis.com
Subject: Exhaust
Date: 22 May 95

Hi, Dan, and thanks for the reply, and my apologies for failing to recall your name when I posted to the list about this mod. Yes, I think it sounds GREAT, no buzzing or resonances, just a nice, throaty somewhat more bass sound to it. My wife is not crazy about loud exhausts, but she agrees that it is in keeping with the nature of the car.

Before getting the exhaust done, I found on the few occasions when I put my foot in the turbo (say, 50 - 70 passing uphill) that the exhaust note had more of a "whoosh" sound to it - the whole thing sounded to me as though there was too much back pressure, and that the engine was having trouble overcoming that pressure. I've had little chance to experiment since the new system was installed, but I don't sense that any more. The above is quite subjective, but it "feels" as though that's what has occurred.

Still have to mount the tire under the car. You might note my earlier message RE: bending the heat shield around the muffler, and securing one end to a muffler clamp. this should keep the heat down in the trunk (as opposed to removing the heat shield entirely) and also protect the spare somewhat. Next weekend I'll accumulate the appropriate hardware and install the tire, but all the hard stuff is done now!

Thanks again -- Jack M. & KANSEI--

Great letter form Jack M. & KANSEI on how he mounted his spare.

From: a.mccombs3@genie.geis.com
Subject: Re: Spare under trunk
Date: 29 May 95

Kansei is now perfect. I relocated the spare under the trunk this afternoon (Sat., May 27), and have all that room in the trunk now. (One benefit is that the boot cover fits very nicely in the "tunnel" area which was forward of the original location for the spare, and doesn't take up any otherwise useable room in the trunk.)

Parts needed:

  1. One: Six inch long by 1/2 inch dia. bolt (cross drill for safety pin);
  2. One: 1/2 inch plastic insert lock nut (or equiv.)
  3. Four: large dia. (approx. two inch) fender washers, 1/2 inch holes; one: hitch pin

I found I had to cut away one of the original muffler hangers under the car (no longer used after relocating the exhaust, in accordance with the Dan Smith system) in order to have room for the spare between the bumper and the rear sway bar. Also trimmed and bent the heat shield around the new and smaller muffler. Positioned the tire where I wanted it, marked the center under the trunk in the bottom of the trunk floor, took a deep breath, and drilled a hole. This comes out pretty close (just forward, on our car) to the left hand drain hole rubber plug in the trunk floor.

Enlarged hole (and the one in the retaining washer for the spare) to 1/2 inch, and installed a six inch long, 1/2 inch bolt through the trunk floor, with a couple of large fender washers on each side of the floor, and a Nylon insert lock nut run up against the bottom of the floor.

Essentially this leaves a 5-1/2 inch long stud sticking down from the trunk floor. I checked for length before installing, and cross drilled a 1/16th inch hole through the end of the bolt, about 1/2 inch up from the tip (for safetying). After installing the bolt as described above, place the spare up against the bottom of the trunk floor, slip the original retainer over the end of the bolt, and install the wing nut on the bolt. In my case, I had a couple threads to spare between the wing nut and the safety hole, but installing the hitch pin through the safety hole causes it to grip one of the wings on the wing nut, and thus safetys the wing nut to keep it from turning.

The above is for installing the spare with the outside of the wheel facing downward. One could get by with a much shorter bolt (about two inches) if one were to turn the spare over. I felt that having the outside of the wheel facing downward provided a couple of advantages: (1) the spare contacted the bottom of the trunk floor at points on its periphery (the wheel rim and/or the tire side wall) rather than the center of the wheel, thus making a more stable installation with less likelihood to rock around and rattle; and (2) it's easier to get at the tire valve to check pressure this way, as it faces downward (and when one installs the spare, one should place it so the valve is toward the back of the car - very easy to access this way). BTW, I also now carry a large plastic trash bag in the tool compartment with the jack and all, to serve as a mat if and when I ever have to get at that spare.

No rattles or problems so far on the drive home, and the car handles much better now due to the lower center of gravity, since the spare is about six inches lower now. (Yeah, sure.) I'm actually looking forward to my father in law's annual visit this fall, and sliding that huge suitcase of his into the trunk.

--Jack M. & KANSEI--
Team Empty Trunk

Letter from Cindy Paloma after her modification.

From: Cynthia Paloma - paloma@cs.ucsd.edu
Subject: Re: Howdy
Date: 22 Mar 95

Hi Dan,

It was nice to be able to put a face to an email address! I should have left San Diego earlier - I didn't get out till 10am, and the roads were busy. The run was great fun, although we apparently missed the main (but ephermeral) blossom time.

I really enjoy my new muffler (and all the trunk space!), however I noticed when I finally returned to San Diego on Sunday that my trunk was relatively warm - and luckily the old heat shield was on the bottom, soaking up some of that warmth! Now this was after 8+ hours of driving, and won't be a problem in my normal commute (12 miles one way) but I was wondering if you or any other people who've had this conversion had noticed any similar problems, and have some solutions. Should another heat shield be welded on?

I am thinking of painting the inside of my trunk with white ceramic thermal paint - the kind used on the space shuttle tiles to keep it from burning up on re-entry! But I worry about cooking other stuff on the underside of the car.

Cindy Paloma

Subsequent letter from Cindy Paloma regarding heating problems.

From: Cynthia Paloma - paloma@cs.ucsd.edu
Subject: Re: More on Spare Under Car setup
Date: 13 Jul 95


I have a thermostat problem too, especially climbing hills. Last weekend at Angeles Crest I had to turn on my heater to keep the engine temperature down. But I've bought some RedLine Water Wetter and need to check on where to get a different thermostat.

Cindy Paloma

Letter from Ken Retzler who DID THE MODIFICATION and found a better price!

From: "Retzler Ken" - retzler_ken@space.honeywell.com
Subject: Exhaust Mods
Date: 14 Jul 95

I want to thank you for all your info and advice. The local Meineke muffler shop did the installation for less than $150! Looks good, sounds good, and only took about 2 hours. Now I'll ponder what audio stuff (amp, CD, etc.) to put in the extra room. Vroom!

Ken Retzler
Clearwater, FL

Followup letter from Ken Retzler with particulars on the setup

From: "Retzler Ken" - retzler_ken@space.honeywell.com
Subject: Exhaust/Spare Conversion
Date: 20 Jul 95


Sorry for taking so long to get back to you, but I was hoping for further info from Meineke in order to be as complete as possible.

The muffler used is described as an "aftermarket Camaro/turbo type". Judging from the pictures of your installation, more than one type can be used, as mine has both pipes offset and yours is offset only at the rear. Another suggested difference is to have the tailpipe (mine used an aftermarket rather than the original) extend somewhat further than the stock one, to lessen blackening of the bumper from the heat & exhaust. Two options were offered regarding size, those being described as 10" and 13". I chose the 13" in hopes of minimizing neighbor offending noise, and in my opionion, was successful. Exhaust note is louder than stock, but plesantly so, and deeper.

Bottom line for anyone considering this modification is to use any trustworthy shop in your area who guarantees their work. My installers have been in this area for some time and give 1 year parts & labor.

Thanks again for all your advice.

Ken Retzler
Clearwater, FL

A new muffler setup! I think Jay Andriot is pleased!

From: Jay Andriot -- pp000596@interramp.com
Subject: Muffler Job
Date: 26 Jul 95


I want to thank you for your great Web page. I just got home from my local muffler shop where they did a very nice rendition of your muffler set up. I just took the pictures from you web page in and 6 hours later drove home a Miata with a trunk. Its cool and sounds great too. I got charged $50 more than you all are paying on the left coast, but I dont care. I think the car looks a lot better now too. See you on the highways,

Jay Andriot

Perhaps the definitive letter. From Drake Daum of Ohio:

From: "Drake A. Daum" -- daumda@asc-en.wpafb.af.mil
Subject: Install a Basement in Your Miata
Date: 14 Sep 95

At the recent Rock 'n' Roll National Miata Rally in Cleveland, hosted by the great folks of the Northcoast Chapter, I saw Andy Cork's Miata with the CanDoo exhaust system. I was flat amazed at the increase in trunk space as a result of relocating the spare tire. He just kept stuffing more and more things in his trunk that would never have fit in my Miata. I'm thinkin', "Man, I gotta do this to my car as soon as I get home!" But since I already had an free-flowing aftermarket exhaust system on my car, I didn't want to trash it and start all over again.

As luck would have it, the commercial CanDoo system is NOT the only way to relocate your spare tire under the car. I did the mod myself for a total of about $85. Of course, I did it with the help of Dan Smith of Fresno, CA. Dan and some Miata nuts on the left coast figured out how to do this and posted a lot of details and pictures on the Miata.net.

I just downloaded all the info and printed it out, pictures and all. I picked up all the necessary tire remounting pieces at a local hardware store (6" x 1/2" bolt, matching nyloc nut and wingnut, two 3/16" thick 2" diameter washers, one thin 2" diameter SST washer, and a hitch pin/spring clip). Per a good suggestion from Jack McCombs, I drilled thru the diameter of the bolt about 1/2" from the end to slip the spring clip thru the bolt to ensure the wing nut didn't accidentally come off. Hardware costs: $5.

I used the left hand drain plug hole in the floor of the trunk to attach the tire hardware (no drilling). Remove the rubber plug, slide a thick aluminum washer over the bolt and insert it thru the hole from inside the trunk. From underneath the car, slide on the second aluminum washer and secure the bolt with the nyloc nut (takes two people, one in the trunk and one under the car). Seal the junction of the trunk floor and the bolt with Silicone RTV on both sides.

The tire attaches thru one of its lug holes (NOT the large center hole). The tire will be offset towards the front of the care. Another good idea from Jack McCombs is to invert the tire/wheel assembly and position it so that the inflation stem is pointing downward for easy access without having to remove the tire from the car. Secure the tire with the SST washer, wing nut, and safety clip. You may have to bend one of the stock exhaust hangers up out of the way for the forward part of the tire to lay flat up against the floor of the trunk. I even cut/bent the stock heat shield to retain its use in deflecting some muffler heat.

The muffler you need is a Walker DynaMax Mini-Turbo Flow, Part Number 17704. It has a center inlet and an offset outlet. I purchased mine for $18.75. I next took the car to a local muffler shop that was willing to do REAL custom work. I checked out about 6 local shops and some wouldn't touch this kind of work.

I showed the technician all of Dan Smith's pictures and directions and the guy went to work. He cut off the intermediate pipe at the differential, bent up a connector pipe to the muffler and another one from the muffler to the tip. All pipes from the cat back are 2"D. All joints are welded, no clamps. He also custom welded new hangers in the exact locations needed. Pipes and labor: $43. I also purchased a SST exhaust tip from him for an extra $17.

Everything clears well, tip exactly centered in the bumper cutout, no heat problems with the spare tire or trunk contents. Since I already had a Walker aftermarket TurboFlow DynaMax system, my intermediate pipe has a welded-in resonator. This in combination with the new Mini-Turbo muffler sounds just as good as the system before -- deep and throaty, not raspy.

I finished off the installation with a few strategically placed sprays of Hi-Temp flat black engine paint on parts of the muffler and pipes to visually hide any shiny spots. From the rear of the car, you cannot see any of the spare tire, and only about an inch of the lower part of the muffler. The inlet pipe to the muffler comes up across the rear of the diff at an angle. The flat black hi-temp paint makes it virtually invisible now.

The trunk now is CAVERNOUS by comparison. It's like adding a BASEMENT to your Miata. Of course, now I've had to order the custom carpet kit from Brain-Storm to cover all the exposed trunk sheet metal where the spare tire used to be. I've also lost my "spare tire catch-all bin", so Andy Cork has also sold me the Brain-Storm trunk pouch to hold all kinds of loose articles. Good 'ol Andy -- always thinking of the customer !!

Now that the trunk is so beautiful, I've also added a hidden switch in the trunk to turn off my trunk light to save the battery when I have the trunk deck open at car shows. If you attended the R 'n' R national rally, you may have seen my engine compartment, which is the real reason I enter car shows.

Final cost of muffler mod:

To see all the details of this great innovative mod, go to the Miata.net section marked Photo Gallery. Then click on the hypertext marked Dan Smith's Muffler Installation. Print or download the info and pictures and head for your nearest muffler shop. YMMV.

Good luck !!!

DRAKE A. DAUM, President
Miami Valley Miata Club
PO Box 33503
Dayton, Ohio 45433-0503