Efinity

iTrader: (6)

hey guys, i recently swapped in a 13bre into my FC3s im not sure if the old school 2.5 HKS exhaust does the car justice anymore. i have a set of dual 3 inch PROF with extra resonators right after the Y pipe that ive been coveting for when and if i go turbo. as a race car, though, im always concerned about weight. slapping on the prof may be too much diameter and weight combined. it sounds good, but may lower performance if the 13b re doesnt push enough air.

hense my third option, the single apexi or hks single exhaust. that would reduce weight and probably give flow a little more like the dual 2.5. im concerned about scavenging lost from this option. i also dislike the blank exhaust port look. usually you gain some high end power but give up low end torque going from dual to single on NA.

the 2.5 dual on the car streams exhaust out from the back of the car for about 3 feet with good pressure/force with brap brap brap. this could mean its doing its job great, or that theres not enough diameter, i dont know.

the prof is anywhere from 15-20 pounds more weight
the single is anywhere from 15-20 pounds less weight
sounds/looks count, but so does performance!!

jorx7

iTrader: (11)

2.5 is perfect. dont go biger unless your turbo. you running n/a rotors?

Efinity

iTrader: (6)

NA rotors. switched it wasnt dual 3, it was dual 70mm or 2.75. im going 2.5 test pipe into the 70mm y pipe!

GREAZERLOU

iTrader: (2)

Whats up... nice FC man! Im jealous!!! Im hunting for a clean white S5 NA FC myself.

Before I go any further, I just wanna understand your combo... you have a twin turbo FD motor that you stripped the turbos off of, swapped to high comp NA rotors and put a header on it. So, a high compression NA FD motor using the FD intake manifold right? And this is a track car that mainly sees 5000rpm and up. I gotta think your using this car in a track day/road race scenario on bigger/longer tracks (as opposed to smaller auto x tracks with tight slaloms that are set up in a parking lot or something).

When setting up your exhaust system, you have to address 2 things... volume & velocity. Just as an example, back in the glory days of IMSA wide-body RX7s and unlimited ARGO class/GTP racers, race teams were running pretty small diameter 1-7/8 headers & piping into collectors ranging from 2-1/8 to 2-3/8 in full on race "D-Bridge" (the mega huge ones!) and P-Port motors.

Keep in mind that these were open, unmuffled exhaust systems. If you need to add a muffler (aka restriction), you gotta compensate with bigger piping diameters, but be careful! It doesnt take much to kill your bottom/midrage to gain what might "feel" like a lot up top.

The R&D that guys like Takayuki Oku & Jim Mederer from Racing Beat, Dave Lemon and his guys at Mazdatrix, Jim Downing & the Atlanta Race Team (among others) did back in the early days set the foundation for what is known to work and not work and why.

(and I say why not make good use of all their hard work since theyre willing to share the info!!! lol)

Fact of the matter is, peak hp numbers on a dyno sheet dont win races. The highest amount of torque and hp across the rpm range the motor sees in an actual race is what gives you a truly optimized powerplant.

Its easy to make a monster sized exhaust system that flows huge numbers and makes good peak horsepower but thats not the point. Your intake port size & shape, exhaust sys & intake all gotta have the same operating range to get the most out of your motor (plus a way of tuning your fuel/timing of course).

Now, that being said, you want useable power starting at 5000rpm so I gotta imagine you either have stock intake ports or a mild streetport, with a stock intake manifold which should top out somewhere around 7500rpm or so.

For a combo like that, I have 3 suggestions depending on how quiet your car needs to be.

1. Loudest
Chop the collector off your Header
Run dual 2" piping all the way to the back
Finish it off w/a single 2.5" straight-through muffler

2. Louder
Chop the collector off your header
Attach 2) 2.5" Racing Beat "Universal Presilencers" to the header
Run dual 2.5" piping to a single 2.5" straight-through muffler

3. Quietest
Chop the collector off your header
Attach a Racing Beat Road Race Presilencer (2" inlets/outlets)
Run dual 2.25" piping to a single straight-through 2.5" muffler

The moral of the story is if you want a broad power band a) run the smallest diameter exhaust (high velocity) that wil flow enough volume in the rpm range your intake ports are sized/shaped for and b) with stock ports or a street port, run separated piping all the way to the back with a single muffler. If you want more high rpm power (within the limits of your intake port configuration), just run a true dual exhaust with 2 separate mufflers. The higher peak hp/narrower you want the power band, keep stepping up the piping & muffler diameter until you get what your looking for.

Anywho, thats my $.02, good luck with your ride man!!!

DairokutenMaoh

iTrader: (4)

October seem to be the thread resurrection month. But, 13B-RE is not a FD engine. It's for JDM Eunos Cosmo.

I was just thinking about the same thing. Since the intake port on 13b-re is the largest of all 13b however the exhaust port is smaller than 13B-REW. Wouldn't that make a pretty good NA engine if I use a high compression rotors from s5NA or renesis?

Not sure if the RX-8 rotors will work with this setup. If yes

Then this concept would be some nice NA engine

1. 13B-RE Block large street port or PP
2. RX-8 rotors and e-shaft
3. 2.5 headers
4. 2.25 cat-back single
5. other mod to make this setup reliable (too much to list)

pros : a lot of weight reduction, responsive engine, decent horsepower and torque
cons : probably won't go higher than 250 hp