I simply pointed out that you are repeating something incorrect, that I have direct experience with it, and that the materials in question do not need to be replaced. You do not have any actual knowledge or experience with the subject. Why would I be interested in addressing any challenge you make about this?

 

For anyone who is interested, I took a look at the sounds logs from last Sunday's autocross. At 60ish degrees, with no wind and light cloud cover, the car registered at 82.xx, 83.xx, and a highest of 84.3x dB at 75 feet. Our region's limit is 90 dB at 75 ft or 94 dB at 50 ft.

 

you'll find that it will vary all over the board. Sometimes I'm in the 70s @ 50 ft, other times in the 90s @ 50 ft. BTW, I was referring to loud in the car earlier.

What rear exhaust do you have?

 

Yes, I've seen that as well from working the sound meter on occasion. I'm just glad to be well below the limit. Based on how loud it is inside the car (yes, it is very loud), I was a little concerned.

The cat-back is just the standard off-the-shelf Borla street model with the input flange cut off.

 

I had the mid-pipe off today, so I took the opportunity to weigh it. These measurements were on a bathroom scale, so take the results with a grain of salt...

Including the first six inches of the cat-back (with the heavy input flange, gasket, and hardware), the parts removed totaled 26.8 lbs:


The new midpipe (with all clamps and heat shield installed) came in at 16.4 lbs:


That does not include the extra hanger that was added, but that added weight should be relatively trivial. I was hoping for about 10 lbs of weight loss, and it looks like I got it. That should put me around 2765 lbs with 1/4 tank of gas. I still have stock seats, stock header, stock pulleys, and a few other spots to lose some weight. I think 2725 should be within reach without too much trouble.

 

Sound clip (please ignore the crap driving):
http://www.youtube.com/watch?feature...&v=GIBh97grqio

 

Sound comparison against my own exhaust as well, which reads from 82db at 75 ft away up to 85db. Also ignore my crap driving on the same course.

http://www.youtube.com/user/Zelse?fe.../1/U3NR1bpUG0k

Dave's exhaust setup does sound nice in person though I feel like it emphasizes the rotary rasp a little more than I would like personally. All in all it's a hell of a lot better than a lot of the other exhausts I've heard out there though, so I can't complain. :D

 

lol.. Thanks Marc Zelse's exhaust and my exhaust are complete opposites in terms of muffler philosophy. He has two baffled mufflers with no packing, while I have three straight-through mufflers, each with a different packing material.

Surprisingly, they don't sound that dissimilar. His has a bit more buzz, while he complains mine has a bit more rasp. Both are nearly identical in volume (confirmed by a sound meter). I believe we are both using 16 gauge 304 stainless. He is single outlet, while I am dual outlet. Anyway, I think they both sound good.

 

My entire header, cat, and three muffler exhaust system is under 40 lbs, keep digging ...

you'll get a whole 1/4 lb out of those OE pulleys, w00t

 

lol.. showoff. It's loud enough inside the car without going to thin-wall tubing. And the extra weight from the dual exit muffler is as low and far-back in the car as it can get. I'm not terribly worried about it. There is weight to be lost in the header, but it's not a high priority for me at the moment. Maybe if I win the lotto.

 

Isn't 1/4 lb the same weight loss you got from the lengthened Miata shock mounts?

 

Or not eatting that subway footlong at lunch?

 

It was 3 or 4 lbs as I recall, two large steel towers replaced with aluminum. The pulleys are steel, but thin stamped sheet while the aluminum ones are solid stock so the weight is less of a feature than the drive speed change. Two of my three mufflers are for a dual rear exhaust too

And who are you calling show off, show off?

 

I didn't realize posting a 175 hp dyno was considered showing off

Thanks for the info on the pulleys, though. I didn't really mean to imply that pulleys were one of my primary targets for weight savings. I was wondering if anyone would call me out on that.

I need new shocks before I worry about finding that last 1/4 lb anyway. New shocks, or maybe a BMod car.....

 

meh, dynos are only good for judging your own gains or comparing to someone else at the same time

All that matters is time vs distance. What is your datalog time in seconds going from 30 - 60 mph WOT in 2nd gear on a level road (uphill/downhill grades will skew the results)?

 

AccessPort is on my wish-list, but it's not at the top of the list. Maybe next year...

 

Well we can datalog tonight when I get over there. While you're datalogging I can chase you in my Miata. :P

 

UPDATE: With some help from Zelse (thanks buddy!), I was able to locate and repair a small exhaust leak over the weekend. What a HUGE difference! The car is much, much quieter now. I can talk on the phone, listen to the radio, have conversations with passengers, etc. The difference in sound volume is night and day. It is still louder than with the stock mid-pipe, and with a different tone, but I will no longer feel guilty driving it through my neighborhood at 6 AM.

I had suspected an exhaust leak for a while, but it was difficult to locate. It turns out that one of the take-apart Coast Fab mufflers was not pushed all the way together. I'm assuming it happened during test-fitting/fabrication and was not delivered like that. Anyway, all I had to do was loosen three screws, push the muffler firmly together, and tighten the screws again. Easy peasy. Also, I'll mention that Gary from Coast Fab was very helpful when I contacted him for advice.

 

Bump from 7 years ago... I'm looking at cat options for a dedicated track car. Any feedback on how the HJS cat held up? I'm assuming it was for Auto-X. Any track use (20+ min sessions)?

 

Hey man, this subject is well covered if you go to more recent posts. I was the first person to ever use one, maybe even first in my the USA for rotary back in 2006 when I imported on from Germany. The answer is yes. I recommend the 100cpis Motorsport cat rated for 300 hp with 3” OD tube in/out as the minimum size. I ran a second larger 3” OD tube 400 hp size starting in 2009. They now have an even larger 3.5” OD Tube 500 hp size, but that be better suited for a turbo setup.

 

Looks very well made!