Now that competitors are releasing downpipes, folks asking why we have not done it. We had our first highflow cat prototype over a year ago in testing on our Fiat 124, made several more, and was just not happy with results of any 3 or 4 inch diameter core. Below is one hand made 4 inch core example from last year with heat shield attached, spec is much like competitors are releasing as a 'finished' item except we were adding a heat shield we feel is really necessary in the tight space. We could sell same as the other guys are selling...except I want our product to exceed expectations, not just sell something that works 'okay.' A year of testing has taught us a lot with the downpipe....including that we really want to stuff a 5 inch diameter core in the space if we can for best flow, longevity, less chance of codes, reasonable sound control....much like we have done with our new ND Miata MaxMidpipe 5 inch 200 CPI converter....which took over a year to get right and now is acknowledged as best engineered midpipe available for ND.
We have also learned that a real heat shield is required....ceramic coating is just not enough in the tight space. Those other guys selling a ceramic coated 3 or 4 inch converter will have unhappy customers when lifespan for nearby water lines is cut short....eventually they will bake hard and crack, leak, etc. I give the coating 2 years max effective life in that space, we killed one of the better known brand of coatings in that tight space in a single track weekend...just baked it too much.
Challenges to getting a 5 inch diameter downpipe core to fit include that you cannot fit ANY off-the-self 5 inch converter in the space. So ...we went direct to a converter core maker, put our Fiat 124 on their lift, laser scanned the space, and designed in CAD software a CUSTOM fabricated 5 inch diameter 200 CPI core from scratch to fit the space. Nobody else will bother to put in this much effort.... but it is the right way to get it done for MAX flow, the right fit, and max longevity.
Perhaps we call it MaxDownPipe? Our custom designed and fabricated 5 inch diameter downpipe will easily outflow any 3 or 4 inch diameter core the other guys are releasing and yet have much higher chance of not tossing codes, and will last much longer, particularly in motorsports use....and be THE CHOICE for anyone going with stuffed turbo or bigger turbo upgrades.
Ultimately....I might do like the Abarth Rally 124 and move the converter further down the system. Having the turbo blowing direct into the converter is good for emissions of a mildly driven street car but terrible for every other performance metric. The further down the system we push the converter the more life it will have, and the less back pressure (faster spool). Watch the night starts of the Fiat 124 rally and notice the tailpipe glows the moment they rev the motor to start the stage...because the 'green' rules of the series now require a converter be retained so they literally run it as the muffler at the back of the car where it will run cooler and have the least impact on turbo spool. That's not practical for street cars but what could be easily accomplished is putting the converter under the car in the midpipe location where the ND Miata normally has a converter and the Fiat version of same chassis still has the big space that is lined with thermal reflecting material for placement of the cat in the Miata version of this car. We would need to make an extension cord for the second O2 sensor...but that's easily done. The only thing holding me back from doing that now is many customers are SCCA racing, we want to use this car for SCCA events, and the SCCA rules require the converter move no more than a few inches from stock location.