exhaust where's the restriction?
 

Ultimately, I know that I'm going to be getting the Stillen or Borla exhaust for my sedan. However, I'm curious as to where in the stock exhaust is the restriction that keeps horsepower down. Our stock pipes are 2.5 inches - isn't that the same as the Stillen/Borla systems? Both these systems are cat-back, so it can't be the cat. I'm guessing all the gains are to be had in the muffler? If I understand things correctly, the G35 sedan muffler is variable capacity and both pipes are only active at high RPM. Would it be possible to modify this operation so they both were always open? Would this release some horsepower without sacrificing the necessary back pressure?

-townsley-
2003 Brilliant Silver Premium Sedan
Z Inlet, K&N Filter, Tinted, Grounded

Re: exhaust where's the restriction?
 

From what I understand the Stillen or Borla will be true dual back all the way to the muffler for the sedan instead of a single 2.5" pipe back. The pipe will be mandrel bend since the stock is not. Also the flat pre muffler not sure how the air is going through it.

-PratG35

Re: exhaust where's the restriction?
 

OK - I see. The problem is that there's a single 2.5 inch pipe stock and Stillen/Borla will use dual 2.5 inch pipes. That makes sense. Thanks very much for clearing that up!


-townsley-
2003 Brilliant Silver Premium Sedan
Z Inlet, K&N Filter, Tinted, Grounded

Re: exhaust where's the restriction?
 

Mandrel Bending also makes a big difference. I am not sure if they still do it this way, but they used to pack sand in the pipes during the bending process to reduce kinks and narrowing of the pipes. Allows for quicker flow and less back pressure.

'03.5 Brilliant Silver Sedan
Premium, Aero Kit/Package, Sport, Winter
Stillen Air Box, Z pipe, Clear Corners, Alum Pedals

Re: exhaust where's the restriction?
 

Borla uses 2.25" pipes.

Lou

Re: exhaust where's the restriction?
 

townsley,

You might try a search. The Sedan's exhaust system has been kicked around almost as much as the air inlet systems.

I'll try to address some of your questions from my perspective.

"I'm guessing all the gains are to be had in the muffler?" -
IMO the Sedan's huge resonator is more restrictive than the muffler. Many guys have replaced it with a 22" Magnaflow glass pack or installed a Coupe's midpipe/resonator assembly.

"If I understand things correctly, the G35 sedan muffler is variable capacity and both pipes are only active at high RPM." - True. There's an internal valve inside the muffler that opens with increased exhaust gas pressure/velocity.

"Would it be possible to modify this operation so they both were always open? - Probably if you wanted to cut a hole in the muffler's housing.

"Would this release some horsepower without sacrificing the necessary back pressure?" - You would probably lose torque. Any Hp gains are unproven at this time. Even with the valve removed, the muffler's abilty to flow exhaust gases (CFM) would most likely remain unchanged.

In doing your search you should find several good threads. One that comes to mind is mbarrad's OMG... Speachless Thread. It's very informative and details how well the HKS Muffler worked on his Sedan.

Hope this helps.

DaveO

Re: exhaust where's the restriction?
 

borla is a true dual indeed, meaning no Y pipe (to join pipes after cats, prior to the first muffler)
Also, borla uses an H pipe and possibly less restrictive main and rear mufflers (it sounds a bit less restrictive)

<font color=green>-Rambo</font color=green>
G35c 6MT DG/Willow/HyperGround/BorlaExhaust

Re: exhaust where's the restriction?
 

Well, when I look at the sedan exhaust system up close while the cars on a lift I see allot I don't like when using a critical flow eye. I don't like the small cats, the sharp bends in the Y-pipe, the Y collector itself, the premuffler and I think it's a shame that the coupe got a performance muffler that flow's better and the sedan get's the variable capacity muffler.

Here's some pics of the sedan's entire exhaust system, the Y-pipe and the stock Y-pipe next to my Acosta Racing Y-pipe with Magnaflow high flow cat pipes. In the first pic, you can see how I replaced the stock premuffler with a Magnaflow 22" 4" round muffler acting as a resonator.

http://www.montypics.com/pic.php?url...7892_R1_23.jpg

http://www.montypics.com/pic.php?url...7892_R1_21.jpg

This pic shows the stock cat's and the stock Y-pipe.
http://www.montypics.com/pic.php?url...7892_R1_20.jpg


http://pics.montypics.com/Gcoupe35/2...05_17_full.jpg

Ivry 6mt sed
Crawford Pleneum
Injen CAI
22" resonator
Cusco sway bars
350Z springs&struts
Enkei RPM2

Re: exhaust where's the restriction?
 

Here's a picture of the stock Sedan resonator to round out Gsedan35's exhaust system pictures.



111082-Exhaust G35S Resonator.jpg

Re: exhaust where's the restriction?
 

You wouldn't gain anything by forcing the stock variable-capacity muffler open all the time. At higher rpms, where the engine makes it's peak torque/power, it's already open. At lower rpm's, you need the increased backpressure. Aftermarket exhausts actually reduce your low-end torque, and forcing the stock muffler open all the time would do the same.

2003.5 G35 Sedan Desert Platinum/Graphite Premium/Sport/Aero/Nav/Winter

Re: exhaust where's the restriction?
 

Don't forget the coupe get's a high performance muffler that is not a variable capacity design and the coupe's torque power curves don't really look any different than the sedans. And pooring over the various exhaust system dyno test's I don't see a trend in lessoned low end torque. Only time I have is with test pipes and with 2.5" test pipe(s) into a 3" mid pipe combo.

Ivry 6mt sed
Crawford Pleneum
Injen CAI
22" resonator
Cusco sway bars
350Z springs&struts
Enkei RPM2