I was in the market for a queiter catback exhaust. The Fujitsubo RM01A was recommend to me due to its very quiet exhaust sound (it has 2 resonators). I sent some PM's and responded to some sales threads asking if the exhaust was 3" through out including the resonators and mufflers. Both vendors stated they were 3" through out including the resonators and mufflers. I decided to try it out and purchase the exhaust.

The exhaust came in a huge 7' box, since it is a one piece design. I pull it out and it is really nicely made except that it is missing the rear 02 bung. I then look inside and notice that the pipe has a wicked taper inside at the resonator. I measure it up and its 2 1/4" . I then measure the inside of the muffler and it 2 1/4" too . Do vendors not look at what they sell? I waited 3 weeks for this exhaust and this is what I get?

 

How much actual turbulence do you think the resonators would cause? I realize you have some larger that stock snails so I would imagine that it would reduce spool time significantly, but quantatively exactly how much?

I think that with turbo upgrades the loud factor really can't be reduced a great amount, without significantly hurting performance unless you can a series of 3 inch resonators (do those even exist?)

off topic:

I was thinking about the exhausts and tapers/neckdowns and realized there really hasn't been any actual scientific quantifable data on the subject, except for butt dynos, if you have any ideas on how to setup an experiment shoot me a PM.

 

Yikes that sucks.... maybe that's why the exhaust is so quiet???? It is a nice looking system though.

 

Gives you the impressiom is a 3" cat-back. But in reallity is a 1" cat-back.

 

Sorry to see that you had to learn this the hard (i.e. expensive) way.

I was close to purchasing the Fujitsubo as well until I learned about the resonator neck-down. I posted about this, but I guess it didn't come up in your searching before you placed the order. It's still a nice system, so perhaps someone who doesn't mind the neck-down will take it off your hands.

https://www.evolutionm.net/forums/sh...ight=fujitsubo

 

Its not much of a big deal.. A very close friend of mine customed an exhaust with 3 (yes 3) resonators and still made 500+whp with a GT35R kit w/ meth+93 pump... and yes dont read my words wrong.. you will still get robbed of hp and spool... but not by much... tuning dependant

 

How in the hell did I miss that thread. I do lots of research before I buy performance parts and I never found anything that confirmed the neck down besides that thread.

 

2 1/4" is a huge deal. Putting 3 properly sized resonators in a 3" pipe is a lot different then necking it down to 2 1/4". I am more disappointed w/ the vendors that market it as a full 3" catback system.

 

I could do some road dyno's and show before and after results. But this is a very expensive science experiment. It's definitely going to increase spool up and decrease power.How much, is the question.

 

damn taht sucks ****...i just realized my ti/carbon also necks down in the muffler =/

 

Most of the catbacks on the market that connect to the stock cat have to neck down in size to the stock piping diameter. I own the RM01A and am very happy with it, it is by far the quietest catback out there and a real quality piece. I've compared it sided to side with the RS-R ex-mag (quiet) and a lot of other exhausts and the RM01A is a lot quieter.

The resonators are going to shrink the inside diameter a little more as it seems to be part of their design. Otherwise most of the exhaust piping is pretty much a straight shot, meaning the exhaust gas doesn't have to go through a convoluted path to come out as I have seen in some other mufflers. And the ones that do provide a straight shot are super loud. That is the beauty of the RM01A ...

If you don't like the neck down and want to connect it to a 3' cat (which you either have or will have in the future) you can just cut the portion that neck down and weld some 3' piping with a flange at a local muffler shop for cheap as the rest of the piping on the RM01A is 3' ...

About the missing O2 bung, you purchased the JDM version and just need a shop to drill and weld an O2 bung ... its a pretty easy fix, just make sure you measure everything properly befor you drill and weld.

As far as power, you will definately feel an increase in power once the turbo spools up as this exhaust is much more free flowing that the stocker. I think you made a good purchase

 

The RM01A I have does not taper down at the cat. It's a full 3" there. It's the resonators and muffler that neck down to 2 1/4".

 

when I swapped out the HKS Hipower exhaust to a custom 3 inch exhaust there was definately a power gain as well as better spool up. With the HKS exhaust during idle you could actually hear and feel how restrictive it is when you put your hands near the muffler tip...it was sputtering like it was out of breathe

 

We found this out back in the Type R days when a few guys purchased this exhaust. I know somewhere I've made mention of this also...

 

There are a lot of variants of Fujitsubo Exhaust Systems. I think the particular one you bought is the "street legal" version that has JASMA stamp on it. JDM exhaust systemw/ JASMA stamped on the muffler usually means low emission, low dB level system for street use. It is a very quality piece. But if you are not happy with it, I am willing to take that off your hands. PM me if you decide to sell. I am in CA..