Lodrix

hey guys! i have no back pressure, how could i increase it? or do i not want to increase it?
this car has VERY LITTLE low end power, how could i increase that?
when i bought my car it had some aftermarket exaust, and you could smell gas out of the back like you were about to start a bond fire! (88' vert) its almost like fuel is going straight out the back. and when i am driving, lets say 45 miles per hour, and i go to 5th gear, my car will putt along, i have to put my petal 3/4 of the way just to go a little faster. i had a buddy of mine who has never worked on a rotary but many other cars say that it has no back pressure, he said something about putting something in my exaust, kinda like a ring to build more presssure??? sry if it seems like too much, just need some help. and i know that 7's dont get great mpgs... but im getting like 8-12... wtf is up with that? anyone? thanks!

Icemark

Back pressure is always a bad thing.

The mistake is when people put bigger exhaust ora mufflers on (like a 3 inch dia. exhaust on a non turbo), and the aux ports stop working on that S3 or S4 non turbo. It is not from reduced back pressure, but rather reduced exhaust velocity. But people think that they reduced back pressure from the larger piping. They of course think wrong. The larger pipe actually slows down the speed of the exhaust leaving.

And if you don't have enough exhaust pressure/velocity, you loose high end power... not low end power.

So your buddy is clueless.

You probably more likely are out of tune (check timing, spark plug condition, filters condition, and TPS) or have a major exhaust clog from a failed cat converter.

rotarybeat1287

iTrader: (16)

what is it with all of these upstate SC people?!?!?! i see none of you... ever!!!! except dregg100 and a few others. lol.
-allen

Lodrix

but im losing low end power! well have none, if im in 3rd gear under 2500 rpms, the only way i can increase more than 1 mile per second is to downshift. maybe i expect to much performance out of this car, but it just seems like such a drag. I think it has something to do with my fuel maybe? because when i start my car i can smell GASOLINE from the back. serious, ya and i got flames too! my friend says they look cool as ****, but kinda scary when all i ever smell back there is gas and i hear popping all the time.

btw im in downtown greenville, where are you in easley?

iceblue

As posted your car is probably out of tune. Something is not setup correctly or broken.

Exhaust BP will NEVER under any circumstances create power. The whole aspect is to increase proper scavenging with optimal velocity with as close to zero bp as possible.

rotarybeat1287

iTrader: (16)

so your in downtown... i live near the movie theatre here in easley. you said its an 88 vert? if so, my friend justin has one and my 91 automatic coupe dusted it by almost two cars from a roll. and my car is SLOW. but i hate drag racing. i like teh curvz!!!

toplessFC3Sman

iTrader: (1)

well, you shouldnt expect too much acceleration from a 'vert; the S4's had the weakest engine in an FC and were the second heaviest body style, beat only by the S5 'vert. However, it still sounds like you have a big tuning issue, follow Icemark's advice and see if it helps at all.

drago86

Any stock NA isn't going to accelerate more then 1 mph/sec at 2500 rpm,..... thats why there is a shifter,..

rb240z71

If your car is popping when you step on the gas, you need major tuning.

Check your spark plugs and wires, adjust TPS, fuel filter , and check if there's airleak.

Those are the 4 common problems with these engine. As far as back pressure, yes it does affect the low end performance and driveablity (not WOT). I had the same problem with my TII with an aftermarket exhaust (single outlet) and the smell is really bad for daily driving. So I put in a cat and it did made some improvement on the low end but lost some at the high end.

If I were you I would fix the bogging/popping problem first before you drive it around because your engine can be at risk.

turboefini88

iTrader: (1)

IF your smelling gas, read this thread. https://www.rx7club.com/2nd-generation-specific-1986-1992-17/fire-612506/ Might be your problem, and its a dangerous one.

anewconvert

iTrader: (1)

Back pressure is a bad thing.

There is this idea out in the car world that backpressure creates low end torque. It doesnt. All it does is reduce power through out by increasing the amount of work the engine has to do. Opening up the exhaust is good, to a point. Once you cross that point the exhuast cant properly move through the exhaust piping and it starts slowing down. this increases back pressure and means the engine has to push against it to get the exhaust in the engine out.

Your buddy is probably talking about an anti-reversion piece. Its like a cone that is placed in the exhaust. The small end is placed facing down stream and once the gas passes through it prevents the exhaust from reverting back into the engine. Its a bandaid. Your best option is to get an appropriately sized catback and high flow cat, or no cat, and to get the car tuned. Further, its an S4 vert, its going to be slow. It sounds like you are going slower than you should, but its going to be a pig. Look into an S5 mani swap (search button is your friend) and get a good cat back with either a high flow cat or no cat.

BC

RotaMan99

Read this. Tells you about the exhaust pulses and explains why bigger or smaller is not always better. Pretty interesting

http://www.nsxprime.com/FAQ/Miscella...austtheory.htm

Also this. The so called "truth" about exhaust systems.

http://www.uucmotorwerks.com/html_pr...torquemyth.htm

95celgt

dam, guess i wont take my fc to school in the morning, it has been smelling like gas horribly in the front area and even in the cabin, ill check out the PD tommorow, can I use a S5 one?

RotaMan99

You will have to use a S5 fuel rail. the PD is permanently fixed to the rail on S5s

SukMy7

you are running mad rich if your seeing flames tune the car to spec per the FSm and then tell us how it does