paposwing14

Well I got my exhaust finally put on my GSL 12A I went with RB header and a high flow CAT from summit racing and with 2 1/4 in pipe back to a DTM muffler the dual outlets are 3in big , well my only problem now would be the cops it has that buzzzz to it and it sound nice till you open the secondaries it's gets louder , well I seem to get better responce on the throttle but I might have to upgrade the ports to like a street port cuase I seem to loose more low end , Im open for suggestions , Im thinking of also porting the intake or maybe up grading to RB intake with a holley 600cfm how about that!

ioTus

iTrader: (5)

Sounds like you got it all figured out.

On my old GS i had the racing beat header, dual center section piece (of the street port exhaust) into a 2.5" over axle into DTM dual 3" tips. those muffler perfectly suit the Rex's.

Yeah i think you should get a large street or bridgeport, then get an upgraded intake/carb setup. You will be very pleased.

paposwing14

yeah i was talking to Eddierotary and he was saying the same thing the engine only has about 50,60,000miles and it was always stock with everthing on it , I took off all the junk and added this exhaust and it just feels like it emtied out the engine now I will put on the msd box with the direct fire to see if that makes a difference, i hope!

85RX7GS

iTrader: (1)

Cool I'm running the Bonez presilencer/cat with the stock header and RB muffler. It's not loud like a chainsaw, although it's louder than the stock setup.

diabolical1

iTrader: (3)

it's the pipe diameter. bigger is NOT ALWAYS better ...

eddierotary

iTrader: (7)

is 2.25 inch and yes that true but i use to have that same setup but with a dinomax muffler in my old gsl and it added more power, that why i told him to do some thing like i had.

RotorMotorDriver

iTrader: (1)

That and a street port, from my understanding, will actually take away some more of the bottom end...Right guys?

~T.J.

eddierotary

iTrader: (7)

street port is for more top end not bottom end. i think there something wrong.

Wankelguy

Street porting doesn't necessarily TAKE AWAY from the low-end power, it just generally affects the top end power MORE. Remember than in a street-ported motor, both primariy and secondary ports are opened up. And pipe diameter can definitely affect a stock motor's power characteristics. Some back pressure is necessary for proper exhaust velocity, which is needed for proper scavenging. It's easy to get too big on a stock port motor. Plus, the bigger the pipe, the louder it is.

diabolical1

iTrader: (3)

no, i'm not saying that it doesn't yield more power. it certainly does. i'm just saying that it moves the torque up in the power band, so you have a weaker low end.

and yes, streetporting usually yields more midrange to top end HP than it does low-end torque, but it does not "take away" torque. depending on how large you make the ports, it might be to the point where the low end does feel a bit rubbery. but that's when you have to decide to either adjust your idle mixture (which may cause a faster idle that normal) or just live with having to slip the clutch a bit more.

diabolical1

iTrader: (3)

hehe
i guess wankelguy and i posted at the same time, but yeah, that's pretty much what i was saying. it's about maintaining intake port velocity and exhaust pulse momentum.

eddierotary

iTrader: (7)

anyway i gonna test his car tomorow and see if it need timming or something else. because he told me that is now more slower that before.

Hyper4mance2k

iTrader: (40)

compleatly false. think about the exack word usage you used. BACK PRESURE!?!?!?! absolutly no back presure is needed to create power. ture a little back pressure can help scavaging effects and increase exhaust velocity, but for the ideal situation would be NO back presure and the properly tuned port and exhaust that would cause alot of velocity and absolutely no back pressure

Stripgear

iTrader: (2)

We have been discussing this in the general rotary tech section...https://www.rx7club.com/forum/showth...hreadid=130867

onepointone

wrong.. when i got my exhaust, i rode around with the racing beat header and a glasspack (i would call that no backpressure) just to see what it was like because ive never heard/felt a rotary opened up like that. it was quicker, but not as quick when i got my exhaust put on that same day. (racing beat header, generic high flow cat, 2.25"pipe, and a dtm style muffler) i like it alot, minus the fact that its WAY too loud. i feel like a honda or some kind of rice, like i blend into the ricer crowd. i have to do something about it. ill probably pick up the power pulse muffler at a later date becasue i think the muffler is whast doing it.

fatboy7

Velocity and backpressure are completely two different things. Of course, when considering pipe diameter the two are inversely related. Small pipe = more backpressure & more velocity. Big pipe = less backpressure & less velocity.
Headers use the acoustic principle that more or less says, any change in the area of the pipe causes a reflected wave back in the direction of propagation.

A traveling sound wave in a pipe moving toward an end, open to the atmosphere creates a reflected wave that travels back toward the engine. The same thing happens (although slightly differently) at the collector of headers. In a properly tuned headers the rarefacted part of the wave (the part with negitive relative pressure) hits the exhaust ports as the ports are closing. The negitive pressure draws the left over exhaust out, lowering or eliminating reversion, and decreasing pumping losses In your example, the glass pack or whatever was attached to the headers was probably out of phase with the wave traveling back from the headers collector, effectively canceling a portion of the gains that the header was making. This is nothing to do with backpressure, but with mistuning the headers for the given situation. Headers work better with no backpressure. But RB headers are NOT a stand-alone exhaust component, they are still very dependent on what is downstream (they would be different length if meant to vent directly to atmosphere, or through a very short exhaust).

diabolical1

iTrader: (3)

guys ... listen!
i don't have any dyno numbers to prove this, but i do have 15 years of driving and working on Rx-7s that say my ***-o-meter is pretty sensitive to real power changes in the SAME car. i owned my third Rx-7 for 8 years before i got rid of it, and it therefore pretty much became an extension of me.

i think we can all agree that an open header (the road race type) will be a good representation of NO backpressure, right? in addition to driving my car with open headers a few times, i went through about 5 different exhaust systems (Rotary Engineering, RB collected system, a custom 2.5 inch system, a custom 2.0 inch system and an RB streetport system)

without any doubts ... the collected RB system and the RE system were the best for low end torque. the open header and 2.5 inch system COULD NOT compare!!!! the streetport system was great, but it was noticeably a little softer on the low end, and finally, the 2.0 inch consisted of the RE presilencers and a muffler that i bought off the shelf ... not much testing went on with that system because it was killed by my 13B - literally! (the 13B tore the muffler into 2 pieces! )

so trust me ... backpressure does help low end torque. another thing that seems to need clarification is that exhaust systems do not ADD HP ... they only free up HP that would otherwise be used to expel exhaust gases.

that is why anytime someone brings up this "exhaust system" i always try to find out the application. because these large diameter or uncollected systems may be great on tracks, but they are NOT ideal for daily street use. they will extract the most topend power and flow, but they will move your torque to much higher RPM than a real street system.

it's okay ... take what i say with a grain of salt. it's only MY input ... i am far from being an authority, but i'm not just spewing what i read in a magazine, which is what it sounds like some of you are doing. that's not meant to be as harsh as it sounds, but i'm just being real.

peace.

RotorMotorDriver

iTrader: (1)

Yeah. Thanks for the correction guys. But thats more or less what I meant, I just didnt verbalize it correctly. It just doesnt help the bottom end, which is what he was making it sound like he wanted it to do.

~T.J.

eddierotary

iTrader: (7)

well i test the car today and it look like the car is alot slower that before, i can understand why because he did the same setup that i use to have in my old gsl, and his car has less mileage that my gsl i use to have (52,000 his Vs 125,000 my old gsl) i cound check nothing today because is raining out. i talk to him to install a direct igntion like v8klr had to see if that cures the problem and now is hard to start the engine even hot. any ideas anyone? thanks

Wankelguy

Hmmm, do I need to justify my position to someone who can't even spell?

I think not.

Besides, Fatboy7 did a pretty good job of it. -Mike