Quietening single turbo for street
 

Hi guys, looking for some guidance from experienced FD owners on this topic. Apologies for the long post but I feel laying everything out helps me better understand and learn what I'm doing, and will hopefully help other noobs also. This way I can also get opinions based on my specific set-up and find updated links/parts availability as some threads on this topic are pretty old.

So firstly, my current set-up is:

Streetport, Precision Billet 67/68 single turbo
Upgraded TB & charge piping
No-name intercooler (future upgrade)

Adaptronic PnP ECU
2200cc injectors
OMP removed (running premix)

Air pump delete / Idler pulley kit (anyone needing more info on this, check this thread)
Tial Wastegate, open dump
Unknown manifold + downpipe (TBC)
Invidia N1 3" cat-back, unsure brand of mid-pipe (TBC)


Some diagrams and pics below as it helps me visualize


https://cimg8.ibsrv.net/gimg/www.rx7...e993cdd62c.jpg
https://cimg9.ibsrv.net/gimg/www.rx7...edfb400ed7.jpg
https://cimg0.ibsrv.net/gimg/www.rx7...6940023e90.jpg

Per the title, my car is loud past the point of obnoxious. At startup it shakes the house, moving the car sends rattles through the cabin (imminent project to reduce horrendous rear hatch vibration), and the highway drone is deafening. I don't mind so much the open dump wastegate as the car can be loud when I'm hammering it out in the open - when I want it to be loud. Also, I usually don't mind the smell of petrol but stinking of 2-stroke after a drive gets old fast.

Some points:
- Car is currently on a run-in tune, and I will soon be getting a full tune (+ possibly dyno), I would obviously like to address this issue beforehand.
- I'm more than happy with where the power output will end up (anything north of 350bhp is bueno), so not worried about restricting peak HP as I don't have crazy power goals. I want as "streetable" a car as I can get with this set-up.
- Though the ability to shoot flames is pretty "special"...I'm getting too old for this ****
- I don't need to meet any emissions requirements in my state so don't need a CAT for that reason, only the above
- Over summer I'll look at stripping the interior and making a plan for extensive sound deadening, which will also help
- I'd like to keep my Invidia exhaust as I'm trying to stick to a budget. Open to all cost-effective options though.


Doing some research, this thread was very useful, though lacking in detail for my specific set-up/requirements. Also there was some confusion with mid-pipes and cat-backs etc so I wanted to clarify this.

Options for reducing sound/improving smell:
Resonater and/or a high-flow CAT

1 - would one or the other be sufficient? Or would installing both become too restrictive given my set-up?

2 - looking at the second under-car picture, it looks like some kind of resonator is already installed (section A/B). If it is a resonator, it does jack****. I’ve tried to research the Invidia N1 exhaust for the FD and can’t find any info on it. I don’t know if I have a full N1 system, or if it’s the back section only with some other brand mid-section.

3 - per Q1) where along the exhaust system are these typically installed. The stock CAT is mounted on the mid-pipe (part C on the diagram), would the resonator be after this (part A/B)? FYI for anyone researching, there is also a pre-CAT on the stock system (part D).

4 – The simplest solution may be to ignore the resonator, buy a new high-flow catted mid-pipe, saving on fab cost of cutting/welding existing piping. What parts would you guys recommend? (e.g.something like this )


Thank you!

No wonder its loud, all youve got there is basically two hot-dog resonators. If you can get an exhaust shop to incorporate a large resonator, and a large muffler and maybe even a hi-flo cat up front you will be golden.
On my car (its an FB with street port and efr8374ewg) all ive got is a 6x4 x18 SMB resonator roughly alongside the gearbox, and a big SMB 7x10 x18 muffler. As far as 450hp rotaries go its quiet as a mouse. Dont get me wrong the neighbours all know when Im coming or going but its not offencive, and its still loud when its "on the pipe" so to speak. I reckon if i put a cat in as well it would be approaching being as quiet as any high performance OEM car.

Very well laid out post. Honestly getting the car quieter is going to be a combination of midpipe and catback. The magnaflow midpipe on rx7store.com is going to be a big help in bringing the noise and the drone down. I have one on both of my rx7s and I wouldn't use anything else ever. Everything about it is perfect. I suggest starting with that and seeing what it does for you.


If the volume still isn't where you want then a different cat back should be the next step. Something with a large canister on it. Resale values for cat backs is pretty low so finding a new one shouldn't hurt the wallet a great deal. The hks hi power is pretty popular and the blitz nur spec that came on my car is pretty quiet too. I made the drive from Florida to north Carolina on it comfortably.

Thanks for that - seems to be what I'm looking for! I'm assuming you mean this one? I can't see any info there on what power/torque that's rated for, or the pipe diameter (3inch straight through on my car). Would I have issues with fitment?

Probably this one, https://www.rx7store.net/product_p/resmidpipefd3s.htm 3" and you can faintly see the magnaflow logo on the resonator/muffler

Yes, the one that ae racer linked is the one. It will bolt direct into your car. There's no reason you will have fitment issues unless your downpipe is super long, which it doesn't appear to be. I agree with wankfactor though, you are basically straight piped lol. Those little resonators you have really only work in conjunction with a high flow cat or something and they will change the tone slightly. Definitely get that magnaflow from rx7store and go from there. It may be all you need.

:lol:

Thanks guys - that seems like a good option and there are couple for sale in the classifieds too. What would you say are the benefits of this resonated midpipe vs a Cat? Also, If I got the resonated midpipe, could I then add a Cat later? Where would that be installed?

I had a catless 3" Turbo back with RB 3" universal resonator and RB 3" universal muffler on my GT35 TII. Very quiet and no drone.

I'm pretty sure there is honeycomb material in the magnaflow unit. This is where terminology can get fishy. Midpipe, cat, hiflow cat, resonated midpipe.... to a degree it's all the same thing. It's really all about the context. I like to refer to the magnaflow unit as a high flow cat. Meaning it has honeycomb material in it but to a less restrictive degree than factory. It is also resonated because of the design of the actual magnaflow center section. It's a little slippery here but they're mostly all interchangeable terms.

Thank you - that's really helpful!

I think the plan I'll go with then is to grab the RX7Store resonated midpipe and see how we go. If I want to quieten even further, I can look to swapping out the smaller hot-dog resonator with a more restrictive resonator/Cat in the future

Reviving.

Can you share any insight if this helped quiet it down? I've got a Semi-PP with a BorgWarner S400 straight piped all the way through and it's unbelievably loud.

My plan is to start with the RB Presilencer but i can't really find much about it. This video, albiet not rotary, has a before/after when using RB presilencers: