JimB

Removing the mufflers and cats from my 996 3.6L added hp and torque up top but predictably made the car worthless below 5500 rpms. I really don't want to put the heavy cats back on. Does anyone know of an exhaust tip that can be used to add some backpressure? I've seen cars with the "capped off" tips but I'm not certain of their function. Any ideas?
Thanks,
Jim

Larry Herman

You could probably neck down the bypass pipes to add some back pressure, but you would have to live with that in the upper rev ranges. My son had a cool device on his EVO 8. It was a spring loaded flapper valve in the exhaust. Ostensibley it is there to increase back pressure at the lower rpms, and then blow open at the higher rpms. Then he just ripped it all out for a 3" exhaust anyway. Something like that would be perfect for you though. A restrictor plate (maybe with a hole in it) in the exhaust that funnels all the exhaust throught it, creating more restriction at low rpms, that blows open when the back pressure builds so that you can have your torque and hp too!

RedlineMan

Hmmm...

A potato is generally a cost effective way to add back pressure, and can easily be tuned with a pearing knife.

It is my gut feeling that a restriction closer to the cylinder might give you more backpressure without dramatically effecting high speed flow. It's only a hunch.

A rig like Larry mentions would be intriguing.

earlyapex

Jim, have you considered SuperTrapp mufflers?

penguinking

interesting...on turbo cars like the EVO you generally gain more throughout with less backpressure. i found the same when i installed essentially a straight pipe in my WRX. however many who had straight exhausts or removed their cats on NA cars lost low end torque. i dont think theres a compromise

RedlineMan

Hmmm...

Backpressure keeps NA cylinders from scavenging too much. Low charge density = low power. Turbos are not that "concerned" with charge density, it being high quite by default. Backpressure limits how fast a turbo will spool. Faster spool = faster accel.

JimB

Thanks for the help. It looks like Supertrapps may do the trick.
Jim

KRA993tt

Is this what you are looking for? www.awe-tuning.com They may be able to help. These are for a 993TT.

JCP911S

IMHO Supertrapps are junk. They are not well made and if they can actually be "tuned" at all, you probably need a dyno. I can tell you taking all the disks off will make your midrange torque disappear, but not sure that is evidence that addind disks will make things "better."

I messed with them all over the place and could not get any seat of the pants feel for what different set-ups do. IF they do work they are also a PIA.

IF you do buy them take the following advice.

First, repace the bolts that hold the glasspacks in with a grade 8 steel bolt. The factory bolts on both mine broke from head expansion and I blew the cartriges out on the track several times.... V embarrasing and dangerous.

Second, only use 3 screws to hold the disks in. In my experience it was impossible to get all 6 screws torques equally, and they kept breaking off. With 3 they held together.

Third, take them right off the car and throw them in the trashcan.

If you follow this advice you will have a good experience.

TT Gasman

What about x style cross over cat bypass pipes. I think Fabspeed makes them. This should add some backpressure.

MJR911

is Fabspeed still in business? Haven't heard from joe fab in awhile.

JCP911S

Check back on threads a couple weeks ago Steve Weiner did an good explaination of what is really going on here. Bottom line "backpressure" has nothing to do with it. It is tuning the pulses from the various cylinders to create proper scavenging of the cylinder (or something...).... but look at what the experts said.

JimB

Well I ordered some Supertrapp disk only tips before reading the negative comments. They are pretty cheap so I guess I'm ok with trying them out. I think I have a pretty good grip on how backpressue slows down the evacuation of exhaust from the system and how that effects your power curve and I fully intend to do my homework on a dyno. My plan is to do a base run with open exhaust and then runs with full restriction, 2/3 restriction and 1/3 restriction and see how the charts come out. It should be interesting.

Thanks for the help.
Jim

JCP911S

JimB.... let us know how it comes out. Also, I think Harry Hall is a big Supertrapp fan... he may be willing to share some tips. My opinions are my opinions... I give them out free because I know what they are worth.

Lothar

RE Supertrapps: Anti-seize on the bolts is a must. I use no more that fourlong bolts to secure disks because there are only four holes that don't have broken bolts in them.

If you run them without the arrestor and disks they will spew glass from the glass pack.