12 replies to this topic

[DES4]

I have a 1.6 Spec Miata with a Springfield Dyno exhaust that exits from under the car in the stock location (pretty much all intact and unaltered). I'd like to quiet it down for occasional street use (running to the workshop and back, getting the car up to temperature, bedding pads, etc...). It's got tags, but I don't care to draw attention to myself when doing so; is there a relatively simply way to drop it a few decibels?

I'm inclined to add a flange so I can unbolt the tailpipe to bolt on some sort of street muffler (Supertrapp, perhaps?), but I'd prefer the simplest method practical. Added back-pressure/lost horsepower is not an issue; I'm just looking to run in parts or take it to the shop to piddle with it... if there's a simple drop in/clamp on baffle or exhaust tip, I'd be interested. Anything like that exist?

[Duncan]

Do you have a welder or access to one?

[Jim Boemler]

I welded up a bent section that ran from the SD end out to the stock exhaust location, with a small muffler in line. It attaches with a band clamp to the SD pipe, and also uses two of the stock rubber supports. I drive the car to the track, and the SD is just WAY too loud pulling a tire trailer uphill. The system works well, and only takes a few minutes to install or remove.

[DES4]

Yeah, I have a friend that is a pretty decent welder/fabricator who's looked at the back of the car; we can pretty much build on any good ideas.

Jim, it sounds as if your exhaust doesn't exit out from under the car (I've seen a few that end under the left axle)... I guess eliminating the s-bend tailpipe is an option; not too sure how that'll affect the system overall. I've considered flanging it at the rear axle and bolting the tailpipe back up when I'm done with whatever mess I'm using as a silencer. Definitely something to consider, but I'm wondering if a simpler/quicker solution might be available.

Which brings up another question: Having noticed that some Springfield Dyno exhausts do not exit out from under the car, what are the inherent advantages/disadvantages of it exiting out the stock bumper location (as mine does)?

Thanks!

[Jim Boemler]

Not sure what you mean about "not exiting out from under the car". The SD exhaust (at least all that I've seen) ends just aft of the rear sub-frame -- basically as far forward as the rules allow. Everything after that was stuff I custom-made -- I didn't modify the SD parts at all.

Sounds like you've got an exhaust that exits under the rear bumper on the passenger side, right? Did you buy it used, perhaps? Sounds like it may have already been modified.

[DES4]

Not sure what you mean about "not exiting out from under the car". The SD exhaust (at least all that I've seen) ends just aft of the rear sub-frame -- basically as far forward as the rules allow. Everything after that was stuff I custom-made -- I didn't modify the SD parts at all.

Sounds like you've got an exhaust that exits under the rear bumper on the passenger side, right? Did you buy it used, perhaps? Sounds like it may have already been modified.

The car was bought used with the exhaust in place; the tailpipe seems to be made of the same pipe that the rest of the system uses, but I imagine it could be, as you suggest, an add-on. I probably need to consider that. All else looks like any other Springfield Dyno exhaust I've seen, right down to the muffler (which, as I understand, is a Magnaflow 10415 glasspack). Nonetheless, it sounds every bit as loud as any SM I've been around (or driven), even with a tailpipe.

[Jim Drago]

As Jim says...
You either have an altered SD exhaust or it is not an SD exhaust, they ALL end at the rear sub frame, not the rear bumper
Jim

[SaulSpeedwell]

I have a 1.6 Spec Miata with a Springfield Dyno exhaust that exits from under the car in the stock location (pretty much all intact and unaltered). I'd like to quiet it down for occasional street use (running to the workshop and back, getting the car up to temperature, bedding pads, etc...). It's got tags, but I don't care to draw attention to myself when doing so; is there a relatively simply way to drop it a few decibels?

I'm inclined to add a flange so I can unbolt the tailpipe to bolt on some sort of street muffler (Supertrapp, perhaps?), but I'd prefer the simplest method practical. Added back-pressure/lost horsepower is not an issue; I'm just looking to run in parts or take it to the shop to piddle with it... if there's a simple drop in/clamp on baffle or exhaust tip, I'd be interested. Anything like that exist?

I

I have your answer. I did this on my first car.

1. Weld a diaomond-shaped two-bolt flange near the exit of your Springfield tailpipe ... maybe 3-6" before the exit depending on how well your particular Springfield is routed.
2. Get a cheap "Turbo" muffler, or anything you have laying around for free (or any muffler of approximate size and shape of the stock one), lay put an elbow on the inlet and weld a flange to that. On the outlet of the muffler, weld a tailpipe that follows the OEM path and uses the OEM hanger locations. You can lay the muffler sideways like an OEM muffler, or just draw a straight line from the SPringfield tailpipe to the camel hump in the RR of the bumper cover.
3. In race mode your Springfield is just exiting out the open flange.
4. In street mode you have an extra muffler and tailpipe bolted to that flange.

I ended up using a Flowmaster I had laying around, it sounded very "blatty" and had some weird resonances, but it WAS quiet enough for the street and for Waterford HIlls which had a sound requirement well less than the GCR specifies.

If you are an ultra-cheapskate and won't use it often, graft on a big diameter tailpipe packed with some steel wool with some hardware cloth hose clamped over the end to keep the steel wool from blowing out. When guys get desperate to pass sound requirements, you see these types of solutions emerge.

[Alberto]

Most of us SFR peeps have a "Laguna Seca" muffler that adds a second muffler in the stock location mating a flange after the normal SD exhaust w/ tail pipe exiting on the stock, passenger side. This makes the car very drive-able on the street. Works well on track too. I had my car on the dyno and we didn't notice a repeatable difference with or without the 2nd muffler.

It's just a generic muffler back there. TC Design fabbed mine.

[LarryKing]

Just short-shift and coast.

[Jim Boemler]

Just short-shift and coast.

Doesn't work uphill. That's the only time I've attracted unwanted cop attention -- there's just no way to drive quietly there.

[Dave Lewis]

I made my exhaust years ago from the JD write up. My local track (Waterfordhills) has a 75db limit 100 feet from the track. A 12 plate Supertrapp got me legal and dyno runs showed only 1/2 HP loss.

[plane]

My car actually increased HP and torque a little with a good "Laguna" exhaust and dyno tuning. I think you need to do them together and not just put the "Laguna" exhaust on with the straight through tuning. This may also be a 1.6l thing where you can open the AFM and may be just a way to help even out on the 1.8l. It was my dyno guys call and says he sees it a lot if you have a good system like the SD. Made my life a lot easier than changing things out.