[Kunz]

Hi Friends

 

It's a long time since I have posted or even read here.

Some of you might remember my and my blue CS. Back then I was one of the first ones that converted to SC, based on the SFR-System.

 

Actually everything run well as I tuned the car to run @ 0.55Bar of max boost. There were still some issues that would have had to be solved such as belt slip and the O-rings sealing the injectors that didn't seal proper on higher boosts...

In the end it was a much more banal, but nevertheless an extremly anoying problem that made me go back to NA... the authority really made it a hard time when taking the car to the periodical exam... grmpf.

 

Well yes, so I am back on NA as said.

Sure I couldn't let things be the way they are, so I modded the following things:

- Airfilter box, homemade design and welding

- RS-Barn-Header (Stahl / ceramic coated)

- 100-Cell cat in the original housing

- straight through 2 1/2'' Catback with 2 mufflers (pics)

 

... ahh, yes, and conversion to E85 by installing bigger injectors and using a fuel-computer ;-)

 

As I ran out of time last autumn, I couldn't finish the tuing for fueling; the car needs a bit more fuel above 4500rpm. Still the package seems to work fine, indeed, the car never made more power than with this one. The curves are messured by a G-Tech RR (As said before it's not the absolute values that have interest me, but more the relative data, the change / improofment... so I cut of the scale ;-) ) The curve you see here is messured with still too little fuel up the revs. By altering the fuel pressure quickly, the car made even some 5% more power... I will tune that this spring.

 

Now you know, where about I stand.

 

My next project no is to upgrade the exaust again. I am planing to weld a 3'' Catback with 2 mufflers again. Basicly the same design as the one I use now.

Why should I do that, when the car is just running fine? Well for two reasons:

- I hope to get a deeper tone (this is how the car sounds like with the upper setup and recorded with a smartphon, but just on normal fuel and not E85... so it is a bit faster now btw ;-) https://www.youtube.com/watch?v=2Wo1pTwUsJw )

- And yes, somehow I feel like it also could be an advantage for the performance ;-)

 

Now:

Has anybody here own experiances with 3'' Exhaust?

I have seen RSBARN has some new things in stock like a bigger header and a 3'' CB. Is anybody here using one of these?

 

Thanks for the replies!

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[ds968]

When I spoke to the folks at BB about their products ( they offer only a 2.5 " catback system for the 968 ) they advised me that a 3 " catback option was tested on a N/A 968 , but resulted in a significant loss of torque in the low to mid-range. They suggested that loss could only be mitigated if you have a heavily modified engine ( supercharged or turbo ) with at least 30% more power than the N/A .

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[flash]

don't do it if this is a street car!  you'll lose power right where you don't want to.

 

i wrestled with this one already when i was working out the exhaust for my supercharged car.  while there was some power to be gained up over 5krpm, there was a significant loss down low, and it did not respond well at the throttle.

 

if this is a track toy, then opening it up will help quite a bit.  you will probably need to go with larger injectors though.  there is a limit to how much pressure the pump can put out, and it ends up dropping volume, which makes it go lean.  at 7lbs boost, you'll need <b>at least</b> 42# injectors.

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[Kunz]

Thanks, lads!

well yes, i remember back in the last century when i decatted, used a straight through desing... on mine it always made huge torque down low, a big dip in midrange and a loss in high revs.

this is why i am so suprised this setup works great... i think it is just the combination and the design...

i am sure, only now using header-100 cell-straight through cb makes the advantage of the header and the low backpressure visibel, resp brings them out.

still i will think about building a 3'' cb... and will keep you informed if i do.


As for the injectors: i use 48er right now...


As for the fuel pressure and pump: yes, i agree... altering the pressure was just a quick fix to see, what the car does with more fuel and as i didnt have the tool to program working. Tuning will be the thing to do...


Btw... the car is no longer sc


Something that could help the car is the conversion to e85. Not only do you have more cooling of the combustion chamber and the possebility to run more ignition advance, but also - and this could be important - makes more exhaust... which means higher flow... etc etc

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[flash]

there is no back pressure.  common misnomer.  if there were back pressure, things would be popping all over the place.  

 

the issue is going to be the combination of pulse timing, gas velocity, and cam overlap.  when you go that much larger on this, it adversely affects the flow, and starts to mess with the scavenging.  been there done that.  i lost 25lb/ft at 2k when i tried 3".

 

if you could find 2.75" you might really nail it.  good luck on that though.

 

the other issue is going to be the collector on that header.  it's way too small, but there is no room for a bigger one.  i actually went back to the stock manifolds and got better flow by modifying them.

 

as for the cat, the 100 cell cat allows a bit of a reversionary pulse, which in turn causes boost to go back upstream.  i took some readings and saw some significant fluctuations in mixture on and off throttle as a result of that.   that's bad.   from my tests, the OEM cat works better.  i suppose you could install an anti-reversionary cone.  the stock header has one for that reason.

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[Kunz]

Yes, Flash, I agree!

This is... let's say the 8th to 10th combination I am on... Made some misssteps and experiances as well :-)) Probably similar to some that you have seen...

The actual setup is the result of this ongoing search / pain / work / fun etc...

 

To make it short: it's complex!... Due to many factors, which - to make it even more interesting - influence each other.

 

The CB I welded was an over-all-advantage for itself, but changing from stock header and cat to the above setup really gave it a push all over the revs...

 

Most probably I will first tune and then see ;-)

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[Kunz]

BTW, Flash:

Very interesting the thing of modifing the stock header. I would love to know more about that ;-)

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[flash]

i had planned to do some very specific dyno testing as a part of the cat-back i developed.  however, now that i am getting out of the 968 business, i am shelving that.  there is someone who has expressed interest in developing it, and i may work with them to produce it, so there is a chance that will still happen.

 

basically,  after spending nearly $15k trying to work this out,  and after 14 systems, i went back to the drawing board and started looking at what porsche had done and why, and then started doing some math.  i'll put all of that together in a very detailed thread when i have charts to show how and why it works.

 

suffice it to say that i tried messing with that header, and found it to be crippled with a couple of design issues that could not be overcome to my satisfaction.  keep in mind though that i was also focused on low end and up through the midrange to 5k, and did not really care about anything above that at all.  i was also focused on maintaining  the daily driver characteristics of stock, which meant maintaining a 14.7:1 mixture when not on boost.  it could not do that, and was far worse when i tried 3".  essentially the same issues it showed normally aspirated were still there.  that's why i yanked it off and went back to the tri-y. as it turned out, all of those exhaust experts were right.  4 to 1 for top end.  tri-y for bottom and mid.

 

have at it though.  maybe you'll find something that i didn't.

 

one thing that is key, is to make sure you test on a dyno that can produce and adjust a load.  a regular dynojet can't do that, so your results will not be at all accurate.  a dynojet will show falsely high low end numbers, misleading you into thinking that it's working.  then, when you actually take the car out on the road, the bottom falls out.

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[Kunz]

Hey, it's a real pitty, you will leave somewhen, Flash!!!

I was also almost at the point to sell the car. But then i really came back to the point where I said to myself I hould keep it. My daily driver is en EVO X MR with SST which makes some 450hp and a good 600Nm... but with all the differnt computers, all the connections between them... grmpf...

the 968 is so simpel, anachronic... there is only one ecu, one switch close to the steering wheel and the shift logic is programmed in my spine... i am sure, you know what i want to say ;-))


From what you say, you were very systematic. I was by far not as scientific, but tryed to count together what I experianced over the years... maybe a good mixture between thinking and having some luck ;-)


As for the dyno: this is the reason why i usually messure on the road (g-tech). Done properly it gives very consistent results and especially times... this is what matters in the end... performance on the road, pic up and so on...


Maybe i will take the car to a dyno to see some numbers... even though they do not really interest me. If so it will be a dynapack. A great solution with defenetly no tyre slipping or cars racing of the dyno during the runs... but the possebilty to load as much and as long as you whant...

a friend of mine uses one in his shop

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[flash]

i use a dyno to tune, because it is a lot easier to get consistent and repeatable results.  i tuned about 2 dozen maps when i did the kit. yup -  the dyno i use is a dynapak, and has the ability to add load, and adjust it, so i can create a reasonable facsimile of road conditions.  i could never have done that using a g-tech.  i have one, as well as dynolicious, and i do use them, but only to verifiy the tuning ("yes, that worked" or "no, that didn't").  it's just too hard to get identical launches and such, but i do like those tools, and do use them.

 

good luck with your project.  it will be interesting to see where you end up.  i'm hovering at just a tick over 340hp and a bit over 300 lb/ft right now.  i have to find the time to see if i can fix an off-throttle rich thing, which made me de-tune it to 340, so i can bump it back up to 375hp.  i don't really "need" to do it, but since i was there, i am pretty sure i can make it happen, and that unturned stone bugs me.

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[Kunz]

Thanks for your good wishes!

Hmpf... yes, if you have been there once... i remeber the cs running @ 0.55bar... great fun. Im am sure so is yours!

but as said above, it does not run bad now at all... and for the first time there is real good torque at low revs, no significant dip im midrange and still a nice kicking in from 3500rpm up the revs to redline. For the first time the car has a real "pointe" as we say in switzerland... some kind of a joke, a suprise, something fascenating...

This is said for the different NA setups i tried... sure the power and the smooth but always growing torque with no dip at all as and sc was great and really fast as well.

what i like about the actual setup beside the performance and characteristics is the wide modulation of the exhaust note depending on trottle position, revs and load... it is never really silent... that's for sure, but it is warm and defined when rolling and hard and aggressiv when it's stepped on... you can hear what the engine is doing. Not every exhaust alows this, even when they are loud. this together with the power and characteristic makes it fun to drive... aLso as a NA only

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[flash]

another thing to think about when building a system, is that mufflers and resonators that are fiberglass filled change in resistance over time.   the fiberglass burns out.  for that reason, many manufacturers are changing to steel mesh or ceramic.   the fiberglass filled ones may well carry a lifetime warranty, but that doesn't mean the unit will last a lifetime.  they figure that most people will just buy a new one, because the return procedure is such a pain, and they would have to wait weeks for a replacement, meanwhile the car is dead.

 

after burning out 2 resonators like the one pictured above (magnaflow) in less than 25k miles, and the power curves changing quite a bit as a result, i finally changed to something else.  i have a magnaflow with minimal miles on it if anybody wants it.

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[Kunz]

Yeah...

I already thought about if this could be one of the reasons, why the exhaust works so fine... now... as said also a bit of luck?!?

Difficult to say, as I changed many other things since I have it.

I have also thought about making mufflers on my own... without any filler... but never found the time as this is everything but my profession :-))

 

I welded the system some years ago in a real hurry, but never used it together with the header and 100-cell up to now. Still it has been blown trough and heated up a bit as it was in use while the car was SC... I think, the burning out is more ore less trough in this case

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[Kunz]

Ah, yeah, a short update about lifetime warrenty ;-)

After the fast ride through the swiss alps some weeks ago the car got louder and shattered... A quick view made obvious why: the rear resonator has "exploded"... well a little bit at least ;-)) 

The laser-weld on the side has been opened over half of the lenght of the mufflers body while the sheet of the outer skin started to open to the point where the laser-weld cracked. So I quickly took the exhaust down and welded everything togehter as it should be. You can also see the weld 90° to the longitudinal weld; that's where the sheet started to open up...

Well obviously there are some vibrations, resp pulses with quite some energy, even if it is a straight through...

 

For those who are interested who the car sounds right now (this was today in the morning @ some 30°C, recorded with my handy).

The setup is like: RS-Barn-header, 100-Cell-cat, 2 1/2 CB with resonator and straight through-muffler like shown above. I realised, the sound you can hear strongly depends on where you watch the video. On my computer it is very poor, on my handy it is best... not really... sorry, in the car it's best ;-))

 

https://www.youtube.com/watch?v=0SZHzvWDvOE

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[ds968]

Maybe you can license your system to Formula 1 and help them change that ( new 6 cyl ) pathetic, wimpy tune to a more imposing 968 note....and they don't even have a muffler, lol :-)

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[Kunz]

???

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[Kunz]

Got some parts today :-)

Beside the parts on the pic I got a 100-cell-cat, 130mm in diameter...

As I got for a holiday now, I will weld in some weeks time...

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[Kunz]

Hi friends

Just quickly from my mobile...

I finally did it. Today i fitted and welded everything together. 100 cell cat, 2.5 in and 3" out. From there 3" straight to the tip. I welded in a resonator and the biggest muffler i could. Everything fits just fine ?

Any results yet?

Just a quick testdrive and only one gtech-run...

Sound is significantly softer than with the 2.5", but not really lauder. By far not as raspy as before. Drivability is perfect (in my eyes) pick-up is very spontanious, the curve is smooth without any dip. A significant kick-in at around 4000 (a bit earlier than before), full power to redline. Torque and power is a bit higher as my gtech reads some maybe 2% higher... Some more testing has to be done sure...

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[Bulti]

Nice work!

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[Kunz]

Thanks ?

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