TR6

Now that I've had a chance to spend some time under my recently acquired RSA, I've been trying to figure out what I've got in terms of exhaust. It looks like I've got stock exhaust headers (because it still has the heat exchangers) and it has what appears to be a stock primary muffler (not sure how to tell if it is stock or aftermarket) in the center between the engine and the rear bumper. However, the secondary muffler on the right side has been replaced with a U shaped pipe (I guess this is what is called a G pipe or J pipe?) that leads to a single outlet. The exhaust sound is very nice right now. Not what I would consider too loud but it has a very aggressive rumble.

I'm looking to gain that extra 10 to 15 HP over stock and the car is for street use. Has the removal of the secondary muffler already yielded any additional power increase over stock? If so, how much? What would the next change be that you would recommend? A cat bypass or a primary muffler bypass? Which would yield more increase in power? Would a cat-bypass or a primary-bypass combined with the already missing secondary muffler be too loud for street use? (I like an aggressive sounding exhaust, but don't want the neighbors calling the police). From reading previous Rennlist threads, I'm guessing perhaps the cat bypass is the way to go and keep the primary muffler since the secondary is already removed?

I need to stay on a budget, so please keep that in mind with your suggestions. I've seen some very expensive exhaust systems advertised that I cannot afford!

KirkF

The three parts of the exhaust that are commonly changed out are the
1. catalytic converter
2. primary muffler
3. secondary muffler

The primary muffler if it is stock will look like an ordinary muffler. The secondary muffler is a squarish box on the right side, positioned before the exhaust tip. The catalytic converter I am sure you can identify.

It is common to replace 2 out of 3 of these pieces, but not usually all three because the car is too loud for most people.

If you replace the primary muffler with a straight pipe, its called a 'cup pipe'

I think that replacing the catalytic with a cat bypass and the primary muffler with a cup pipe is supposed to be a nice way to open up the breathing, without too much noise. But of course it would depend on if you live in an area with smog laws or not.

Below is a picture of a fabspeed cat bypass next to the regular cat, and a picture of the exhaust, showing a cup pipe at the bottom.

Any of this help?

Kirk

TR6

Yes, the pictures help a lot. Thanks. Question: Are those the heat exchangers in the photos and the pipes for the heating system?

Would it be exceptionally loud if I replace the primary muffler with a cup bypass pipe in addition to my secondary muffler already being removed? That seems like the cheapest and simplest route to go. I'm a little concerned that if I go with a cat bypass, I may run into emissions inspection problems (Texas). Depends on how thorough the inspector decides to be.

KirkF

On the second picture, the two pipe outlets facing the top are from the heat exchangers. The middle silver pipe would be from the blower. (so the blower goes in from the left, blows across the heat exchanger and then out the top towards the heater ducts in the car)

I have heard that having the primary & secondary removed is kinda loud. If you go to the fabspeed site they have some video files that let you hear the sound with different setups.


www.fabspeed.com

Kirk

Chris M.

Bypassing all three is very LOUD and I don't think you'd want it for anything but a pure track car. I believe Tom W. has done the dyno work and says that a cat bypass and g pipe is the way to go.

c

BostonU

Cat-bypass and Monty exhaust. Great power and great sound.

Cupcar#12

Cat By-pass and open up your primary muffler and remove everything inside, run a single pipe (drilled liberally) from end to end. any competent welder will be able to do this realitively inexpensively.
you will have some muffling but it is largely a straight through design based on the 964 European Cup muffler design (required even then for some tracks)

TR6

With the secondary muffler already missing (replaced with a J pipe), would this be too loud for street use? (I realize that "too loud" is subjective) Or would this be considered a track-only suggested setup?

Tom W

While a cat bypass and secondary bypass is great for a track car and I found it gave the best performance, there is the issue of legality for a street driven car. Yes, you can remove the cat or get rid of both the primary and secondary mufflers (or all 3), but not legally in any state that I know of.

To answer the original question: yes, for a street driven car I think you've got the best you can expect for a cheap price. The only other legal thing that might help is to get a sport cat. I'm just not sure if they pass emissions in all states.

I'd also add to save your money and not try to get that 5-8 extra hp that might be possible. Spend the money on track dates or autox and learn to use the hp you have before worrying about the need for more. You'll need the money for tires.

[edit] A cat bypass and secondary bypass is close to the legal limit for sound. Whiloe mine measuerd 89 db at Laguna Seca, that's with a sound station about 20 feet away. I'm not sure how the legal limit of 92 db is established (how close it is measured). If right at the tailpipe, mine would not pass.

kgorman

Also to add a tidbit, on the PCA site, there are a bunch of Q&A tech questions. You might want to read through them. There is a ton of info about this topic.

http://www.pca.org/tech/tech_qa_area.asp?id=8

From reading them, and here on RL, I went with secondary delete, and cat bypass (just put the cat bypass on today!). I think you get more torque with the secondary bypass, but more HP by bypassing the primary. If you bypass both you get a loud and less powerful car. The secondary bypass also yields a grumbly throaty sound, the primary delete a more high raspy sound.

The fabspeed cat bypass is not just a straight through pipe. It is tuned to keep backpressure. If you just put a pipe in the place of the cat, I believe you will loose power. It appears from reading the 3.6 does require some amount of backpressure to achieve max power.

Some companies make headers that replace much of the exhaust plumbing. Some say there is a power gain in doing this. Others no.

Replacing the primary muffler with a BB or GHL or Fabspeed, etc generally does not add any HP but does lighten up the back a bit. In addition, it also generally bypasses the secondary muffler in one swoop. They sound great though.

In terms of weight savings, removing the secondary is about 30lbs the primary is about 40lbs (if I remember correctly). Of course add back in whatever you replace it with. I have not weighed my cat and it's heat shielding I took off today, but it's substantial (est 40lbs) and replacing it with a maybe 8lb cat bypass. Removing weight is another motivator for replacing exhaust parts, not just (mild) power increases or (very nice) sound. Removing the weight from the farthest point in the rear of the car is a good thing.

There is my entire sum of knowledge regarding 964 exhaust hehe. Hope this helps some. People correct me where I have it wrong.. ;-).

boze_man

quick questiion...sorry to hijack...so it is my understanding after reading the above that if i am looking for a little more growl i should replace the primary muffler, correct?? can i get into anyuthing that sounds good (not too loud were i wake the neighbors) for less than say 500$...i see fabspeed is about 1k...thanks

garrett376

There is a ton of info, but just about all of that information is not substantiated. Bob (a.k.a. fstockcarrera) is one of the few that has done dyno testing with all bypass variations. He's posted his findings before on here somewhere...

With a fully open exhaust (no cat, no primary, no secondary) the car runs great on the track, but you need earplugs for sure.

forklift

See post #21: https://rennlist.com/forums/showthre...0&page=2&pp=15

garrett376

YES! It was Bob who posted that... not JW in Texas... thanks Jim