"the head" can you comment on how the bypass pipes sound on the CTT with stock muffler? Thanks

 

I like it in that it does not drone at any speed. It gives more sound under throttle. I just don't like the sound of the aftermarket muffler combos - too noisy for me on this particular vehicle. Do some Youtube searches and you'll see what I mean.

 

Thanks, thats what I was looking to hear. I had looked at you tube, but most of the vids where NA motors. They sounded a little raspy from what I can tell. Was planning on keeping stock muffler. Thanks for the feedback.

 

I have the bypass pipes and will be getting the plenum sometime down the road, my question is, does an a\m intake really make a significant difference? My experience from previous turbo 4cylinders was that they only add to the sound gain not actual hp.

 

Arerrac911,

Personally, I think that Porsches air boxes are all designed better than most folks give them credit for. They will suck in all the air you need without un-necessarily exposing your intake system to water, etc. Therefore, IMO a set of BMC filters is all you need.

 

Moto,

Porsche does not care about the Plenum because they handle the resonance and timing of the air AFTER the plenum. I don't know exactly what system they are using on the CTT, but do a google search for "Porsche intake resonance system" and you will learn the "how and why".

Also read the fine print on each individual IPD Plenum, as some require sport cats, and free flow exhausts to get the full gains.

As far as intake, IMO, all you need is BMC filters. The v-flow looks cool, but is not needed.

Lastly, anytime you open up the exhaust system you will rob power from one part of the power band and gain power in another. That's a simple law of physics. I haven't researched the parameters of the CTT intake/exhaust, but it could be that the bypass pipes and free flow exhausts are robbing power from the lower part of the power band and gaining power towards the top end (where you rarely go). The intake/exhaust has to be "balanced" to put the power where the driver wants/needs it most. It is both an art and a science that manufacturers like Porsche are constantly trying to perfect. And, not unlike marriage, it is always a "compromise".

Bryan at RSS and Alex at Sharky are both excellent resources.

A

 

Late to the game here, but I'll add my experience.

I have a 955 CTT with BMC filters, IPD Plenum, and Fabspeed Cat Bypass pipes, everything else is stock.

I can honestly say, if you dyno your car, you'll get about 58 to 62 HP to the wheels with this combo. That means a 450 HP CTT will be about 520 HP at the crank, just like the CTT S for a fraction of the cost.

The reason it seams unbelievable to some is because you just don't feel horsepower in AWD cars like you do RWD/FWD cars. Also, 60 wheel HP only makes you about 6 tenths of a second quicker in the 1/4 mile. It's enough to feel, but it's not going to blow your mind, just your wallet.

There are so many factors that effect HP from day to day. IMHO, the best way to look at it is no matter what the variables are, the following will always be true:

1. You will make more HP than you do without the bolt-ons.
2. You will definitely get better gas milage.
3. You car will perform better than it did given it was healthy to start.

The boost response is really good with the plenum, definitely noticable. You will also feel more power as the charge air is definitely cooler (more dense). I opened the hood of my car after driving from the shop and the engine was still pretty hot, I touched the plenum and it was ice cold. I know what the secret is to the IPD plenum but like a good magician, I'll keep my mouth shut

The Fabspeed pipes are great, you save like 25 pounds off the car and they make the car sound like it should have from the dealer (they sound great with stock mufflers). Seriously, I'm seeing huge gains in gas milage when my foot is out of it.

Oh, and I smoke E46 M3s with just the mods above all day long

I'm going for the 700 HP club, so I'll post more mods as I add them. I need Forge diverter valves next.

 

Not trying to argue with you but those mods will not net you 50-60 wheel HP without a tune...and the tune is responsible for most of those gains.

 

E46 M3 runs low 13's at about 106mph. If you're beating them routinely with just those mods then I'm guessing you're beating the driver, not the car.

 

Actually, they will and you're wrong. What's responsible for most of the gains from an ECU flash is the raising of boost pressure. Also, boost pressure alone doesn't make horsepower, air flow does.

With BMC filters and Fabspeed Cat Delete, you're talking about 28 HP to the wheels on a bone stock 955 CTT.

The IPD plenum makes about 30+ HP to the wheels on a bone stock car.

You do the math. I'll do some dyno runs hopefully and get specific numbers for my car, but I guarantee you that you don't need a tune to acheive those numbers.

The IPD plenum and Cat Bypass pipes are the two biggest single mods you can do to the car before ECU FLASH (which I'm doing last).

 

That's all on paper.

The E46 0-60 MPH is supposed to be 4.8 stock and I have never seen one that fast. 5.3 is more like it.

I'm beating stock M3s, that's nothing unsual for lightly modded CTTs.

Porsche tends to be conservative with their numbers and BMW tends to be fanciful with theirs.

 

Do the Cat Bypass pipes give an emissions problem?

I'm already planning to (if I opt to keep my 955 CTT) add the BMC filters and the IPD plenum but being from the UK I'm concerned about the emissions with the bypass pipes and don't know enough about them not to have to ask.


I will have to have my car tested (MOT check here in the UK) annually and dont want to risk problems?

If not doing the bypass with the other two mods be good on their own or a bit pointless without the bypass pipes?

Thanks

Carl

 

Mods are not additive. Mod A may be advertised to net 10hp. Mod B mets 20hp. Add both and you'll get 25hp, not 30hp.

Again, since all you have to do is press the accelerator in the CTT you are probably beating the driver in the E46 M3 since they have to launch and shift a manual.

I'm faster than an E55 AMG in my EVT700 997TT from a roll any day of the week. But from a stoplight I struggle to launch and shift while the E55 driver just floors it and claims to his buddies that he beats 997 Turbos all day long.

 

Eh....not always.

Sometimes Mod "A" only nets 10hp on a stock vehicle and Mod "B" only nets 20hp on a stock vehicle but add them together and they have a greater effect and = 40+hp

Just pointing out that it really depends on the mods, the car, etc. Sometimes mods even take away from each other. Not as simple as saying "mods are not additive"

 

This can definitely be true, but not in the case for the mods we're talking about. This is often true when cars are moderately to highly modified as the test baseline configuration is far too varied to calculate HP by addition alone. Technically this can start from the very first HP altering mod done to a car, but not here.

Let's take a look at the Fabspeed Cat Bypass dyno sheet (since I don't have mine yet) and make some assumptions.



Based on Porsche's SAE net corrected flywheel horsepower (HP) number for a 955 CTT at 450 HP in stock configuration. Here are some calculations based on the Dynapack runs they (Fabspeed) did:

For the run above, stock wheel horsepower for the example car (and obviously this number would vary from car to car, but usually not too much) was 363.5 HP. We can deduce fairly easily that the car was most likely stock as advertised by factoring in a 23.97% AWD drivetrain loss. So HP measured at the flywheel would be 363.5 HP + 23.97% which is 450 HP right on the nose.

The run included filters + Fabspeed Cat Bypass pipes (if you read closely) and bumped HP at the wheels (really the only number that counts) from 363.5 HP to 390.3 HP, a 26.8 wheel HP gain over stock. Using the 23.97% AWD drivetrain formula above, the car would now be 483.5 HP at the flywheel. So a 33.5 HP gain as seen at the flywheel.

I can tell you that these numbers are definitely on par with my car based on the "butt dyno" alone. The Fabspeed Cat Bypass pipes are an absolute must and they work.

I don't have any IPD example dyno runs to extrapolate from, however, let's make some assumptions again. I have spoken to IPD and can tell you that the 30+ HP claims for the IPD plenum were tested on a totally stock 955 CTT and as measured at the wheels.

So let's say we put the IPD plenum on the test car above without the Fabspeed Cat Bypass pipes. While it's a completely different car and would quite likely render a different wheel HP number than 30 HP (though likely not too much); adding the Fabspeed Cat Bypass pipes would be mostly additive in the literal sense.

This is because the main HP gains from the IPD plenum aren't from exhaust flow but from charge air cooling (almost like a 3rd Intercooler) and air channeling. As an interesting example of this, go run your car really hard once the plenum is installed. Then pull over and pop the hood. You will see that the plenum is pretty much ice cold compared to other engine components!

When you add the Fabspeed Cat Bypass pipes, you're greatly improving engine breathability so these two mods (three with some BMC filters) really can be looked at additively.

So for example, let's take 390.3 HP + 30.0 HP is 420.3 HP to the wheels. So flywheel corrected HP is 420.3 + 23.97% (AWD drivetrain loss) making 521.04 HP at the flywheel.

Now, given that dynos, dyno runs, and cars vary and this is very theoretical, it's safe to assume about a 15 HP variance from the top of the 521.04 number and down (506.4 HP). The point I'm making and will hopefully be able to demonstrate conclusively soon with my own dyno runs is that a stock 450 HP 955 CTT in good mechanical condition should be bumped to well over 500 HP with these mods alone.