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so basically ISR(formally ISIS) fucked up cuz they didn't really take into account for 1.6's. Hmmm guess that makes sense.
 

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~Foo's Best Friend~
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yep

i figure there are three ways to make it work.

you can buy a 1.8 downpipe and fit it to a stock 1.6 header, and then get the 1.8 resonator from isis.

or

you can notch the bolt holes on your 1.6 header, and notch the bolt holes on a stock gasket to mate them together and hopefully have no leaks.

the last option (which i dont think would work because any bolt you would use would contact the resonator piping and distort the bolt alignment) would be to notch the isis resonator enough to account for the margin of bolt spacing between the 1.6 and 1.8 downpipe.

so yeah they dropped the ball.

edit: tomorrow im going to notch my header bolt holes and notch my stock gasket to try and make this work. if worse comes to worse ill either return the exhaust, or get them to send me a 1.8 version resonator and attempt to sell at a loss and pick up the garagestar exhaust like i shouldve done in the first place.
 

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fuckin ****.... i mean i'm not gonna be using the resonated cat anyway so i should be fine with just the midpipe and muffler but still....

fuckin ****.

I just cursed out both Enjuku and ISR on FB. Well not really but i told them how i felt. Too late now.
 

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the midpipe and muffler aligned great and look awesome.
ran it with my enthuza test pipe but it was ridiculously raspy and drony which is why ill try and make this work with their resonator.
with this being said this isnt what one would expect from a reputable company to be honest.
they pumped it out too fast and didnt correct the flange diameter issue.

HOWEVER there should be a discounted price for those that want to run the midpipe and muffler but not the resonated section, alas we still pay full price and may not be able to use a 1/3 of the product we bought.
 

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Update, Update:

Upon further examination of the test pipe portion I saw that the oval bolt holes on the flange of the test pipe are spaced too far apart in accordance with Christoper's findings. So I spent some quality time at work today with the power tools and was able to widen the bolt holes plenty wide enough to make it so that it would bolt up to the stock header.

However! I would not under any circumstance as a manufacturer expect my end user to have and use $100+ worth of carbide burs, professional level air tools and shop air to make my product fit. That is a serious oversight on the part of ISR/ISIS. But often one that is found in masses. I'm willing to give them the benefit of the doubt in saying that maybe all of their (one?) test vehicles had an aftermarket header and so they didn't know there was a problem at all.

I dont know! It is certainly a failure on their part but hopefully someone more intimate with them, (Handball?) can explain the issue to them in a rational way and they can rectify it for current and future owners.
 

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forget them and this exhaust. Had it installed this morning and didn't like it at all. Threw back on my Cobalt which sounds even better to me now compared to the ISIS. The ISIS exhaust note is meant for like a Subie or M3 with a nasty ass Corsa exhaust.

Anyway, not so great fitment and too annoyingly loud. The mid-pipe was hitting my axle, the muffler tip was hitting my rear bumper support and I was definitely not gonna try to mess with the resonated cat. This is Top Speed Pro, OBX, Yonaka caca. Mine is up for sale. **** that.
 

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Miatas and Roadsters in general should never sound like this. To me, the best exhaust notes are from Racing Beat, Cobalt and the RoadsterSport. Oh wellz.
 

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Got mine on, and im pleasantly surprised after all the recent dislike. It does sound like a Subaru which I'm not too terribly excited about... But its fun and amusing in its own right.

It fit well, minus the test pipe which needed to have the holes widened to bolt up. Doesn't seem to make contact with anything. I probably have a bit more tolerance for obnoxiously loud exhausts on their Miata than most, but it was much quieter and less droney than what it is replacing.

Definitely not as bitchin' as my old sound but easily livable for a younger driver.

Would I recommend it?

"Meh :dunno: " For $300 or used and if you already have a good header so that you don't have to widen the flange bolt holes, sure. But if I wasn't planning to put a supercharger on soon, I'd go RacingBeat, RoadsterSport or Enthuza.

I wouldn't pick this over other options, but it fit pretty well other than the issue I have mentioned and sounds pretty good if thats the sound youre looking for.
 

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Hello!

First of all we want to thank all the customers who have purchased the different versions of our Circuit Spec exhaust, we spent a lot of time trying to perfect the look and sound to fit the Miata's as best as we could while maintaining an affordable price point. We think when this is fitted on a stock header Miata and utilizes our resonated front-pipe its aggressive but not overly loud note makes these cars sound awesome!

With the 1.6L Miata's we enlisted the help of two individuals who had, from what we could tell and what they described, 100% stock NA 1.6 Miatas so we could get an accurate base for our R&D team to work off of.

We noted a flange orientation difference that was addressed and corrected within the new 1.6L variant of the exhaust, and also re-designed the mid pipe to provide the best ground clearance possibly while still allowing good tolerances to clear factory suspension and axle components.

With that being said, the cars used for R&D are around 25 years old at this point so some components could have been replaced years ago yet still seem original, or perhaps there is some variation in the original OEM equipment, throwing off our measurements in the development process or making the piece only compatible with a certain style header.

If one of the customers who was experiencing issues with the front pipe fitment could be so kind as to take a measurement of their OEM header 2 bolt flange spacing from centerline to centerline of the bolt holes and let us know we will forward that information to our R&D and Fabrication team to try to get a revised flange designed if necessary to accommodate any and all 1.6L headers.

Please let us know so we can look into this immediately, and also remedy this issue with any current customer that may have encountered the same problem.

Thank you,
ISR Performance
 

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Center to center of the bolt holes looks to be about 3 3/8th inches

With a piping I.D. of 1 7/8th inch.
Awesome, thank you, we truly appreciate that info!!
We have that information over to our R&D and fabrication team to look into. If it appears our flange dimensions are a bit out we will most likely have the R&D team draw a new flange up that will accommodate all style headers and also draw up a new gasket for that unit!

We will try to research this and work to get any issue that may be present corrected immediately, as we are committed to making the best quality and fitment pieces we can for the Miata market :)
 

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1.8 owner with non-factory header

I personally think the exhaust is great. Install was quick and easy. I've heard multiple other exhausts from various companies such as Racing Beat, Top Speed, Roadstersport, 5Zigen, etc and personally think the ISR exhaust sounds the best.

Most exhausts made for miatas are A. too quiet (Racing Beat) or B. too raspy (Top Speed)

Their price was extremely competitive.... so I don't see how people can complain about that?? This exhaust was made to resemble RS*R Exmag and have a deeper sound. Yet you all sound like you hate that it is a deeper tone. Most Miata exhausts sounds just as quiet as OEM so why are you even "upgrading" lolololol

An perhaps the 1.6 problem was that they used aftermarket headers for testing... but the real question is why do you guys still run your stock header after it is at least 20 years old. Maintenance your car with cooler stuff than OEM :fab:
 

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Hey! I like mine. I wont be changing it out anytime soon!

I've heard lots of miata exhausts as well, excluding this one at the time of my purchase. I wanted to give a full and thorough explanation of my thoughts. For $300, I'd buy it again. And if someone asks me what exhaust I have, at this point I wouldn't tell them not to buy it if they like the sound.


(And a header is not a maintenance part. :fab: )
 

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whether it was an aftermarket header or OEM shouldn't matter. I have an OBX header btw. Not everyone likes to drive around with an obnoxious exhaust like you but I'm glad you're happy with it.
 

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whether it was an aftermarket header or OEM shouldn't matter. I have an OBX header btw. Not everyone likes to drive around with an obnoxious exhaust like you but I'm glad you're happy with it.
maybe more research wouldn't have put you into this situation. sucks for you lololol

true, I like my exhaust. sorry it hurts your ears grandpa.
 

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maybe more research wouldn't have put you into this situation. sucks for you lololol

true, I like my exhaust. sorry it hurts your ears grandpa.
maybe you're right but how does it suck for me? I already sold it and made a few bucks actually. Lololol

but seriously, it doesn't "hurts" my ears youngster. As you get older you will begin to realize less is more. You're not too far.
 

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First off we want to thank all the forum users for their input, it has been INCREDIBLY helpful for working through this small issue!

Our R&D team has found a solution for the current lot of exhausts we have in stock, new hardware has been ordered for the front flange which is a slightly smaller diameter, allowing you to orient them tighter to the inside of the flange and bolt on to the flange of the OEM header that a few users here had noted. This should be in stock in a few days and all exhausts on-shelf will be updated accordingly :)

By moving to the slightly smaller hardware it allows the 3 3/8" centerline to centerline noted on the smaller OEM header, as well as any aftermarket header.

We are also looking into having a slightly different 2 bolt gasket included in order to provide a better seal.

We will also be re-visiting the front flange design to see if there is room to revise it and improve it further with our current tooling and equipment.

Thanks again for all your help and support! Hopefully we will continue to develop new parts for the Miata community to help improve and customize these already great cars :)
 

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I got my ISR exhaust w/ resonated cat delete pipe installed for my 1.8 a few days ago and this thing is loud! I really don't mind it and I actually think it sounds amazing when driving on side streets but when I'm on the freeway holding high revs, my ears are ringing! and dat drone....anyone else having this issue? I'm thinking I'd just throw on a cat but then I'd lose that nice gurgling sound haha

oh btw, for those with a 2nd O2 sensor, it costed me $20 to get a bung drilled/welded. No biggie and no CEL
 

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Discussion Starter #240
I really don't mind it and I actually think it sounds amazing when driving on side streets but when I'm on the freeway holding high revs, my ears are ringing! and dat drone....anyone else having this issue?
Ive found that at certain speeds the sound hits a harmonic that isnt so bad. For me it's usually around 62mph or around 75mph
 
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