[mdss]

Hi Guys



Gutted my cat today although the throttle response is a little sharper i am now getting a little more vibration through the gear lever which is almost directly above the cat, is this because the cat is almost 5" and now it is empty. should i just bite the bullet and buy a custom system and have them cut the 5" dead cat! off? and weld a nice join on with the custom system starting there?



would love to know all your thoughts the car has promax chip and flash' aorbox trumpet mod



thanks in advance

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[JWahlsten]

You're probably losing power somewhere in the rev range now with the cat missing, and creating the resonance and vibrations. I know Pete and Bob have done lots of research to find the combo that works the best for power through the entire range.



Our engine is sensitive to the amount of back-pressure and the scavenging that occurs with each pulse. There's really no free lunch with this engine, intake, exhaust combo.

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[Scott Collins]

+1 on that - the system is "finicky", like my 16 year old tom cat who only eats "Max Cat" food, and nothing else. He won't even touch the really expensive stuff my sister the vet can get.



The individuals mentioned above have the experience and knowledge. The Pete mentioned above is Pete Fitzpatrick, who owns and operates RS Barn. A number of other vendors also offer exhaust packages designed for our car and a little bit of searching will turn up quite a bit.



Best of luck.



-Scott

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[mdss]

are you guys saying that i should not have cut the cat out trying to buy an rs barn exhaust here in the uk is very difficult. The exhaust builder i use build exhausts for many race cars i think i will explain to him that back pressure is required.

How much back pressure is required, oh dear i wish i had not bothered now!!

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[flash]

this one is a problem. pete and i each spent over $10k working this stuff out.



it's not technically back pressure that people really mean. back pressure is never a good thing. what it is is gas velocity and pulse timing. if you let things flow too freely, bad things happen on this car.



the dual resonant intake manifold creates a problem in what you would normally do for exhaust. porsche went to great lengths to design the shape of the system, and locate things where they did to perfectly match the pulse timing to the mergers, and not have too fast or too slow a gas velocity. there are small things in the system that are specifically designed to tune the flow. removing those messes things up.



the factory cat works extremely well, and is not restrictive.



opening things up may give some throttle response, and maybe even a couple of upper end horsepower, but it invariably results in a midrange torque drop, sometimes as much as 20ft/lbs.



to date, no aftermarket cat-back exhaust system has been proven to make gains without losses. so far, the only one not to lose anything is the rs barn system. there is no magic there though. the dynomax muffler and 2.5" tubing just plain work. other mufflers have been shown to gain a bit up top, but lose in the middle. i also have a system that has no losses, but it is a custom install, and is a bit heavier (though still lighter than stock). it works better with the supercharger though.

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[ds968]

The need for back pressure in these cars because of their so-called unique resonance pulse is a highly questionable theory, and the alleged loss of torque at certain midrange levels has never been proven by any truly INDEPENDENT tests..so go ahead and believe what you will, but I think as long as you stay within a 2.5" pipe size catback free flow exhaust system, you won't be disappointed with the performance increase.

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[flash]

yes it has been proven. plenty of charts out there to show. i did quite a few tests myself. you just don't feel the loss in your car because you're a lunatic and you never let the revs drop to where it is, but it's there, i assure you. i can see it clear as day on the dyno chart you sent me of your own car. it's almost 20 ft/lbs on your car, and exactly where all "free flow" systems lose it.

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[ds968]

My dyno chart is only the "after" , no way to tell what was the " before" since I did not do that test.. It could have had had twice the drop in that spot prior to the catback addition..

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[flash]

the OEM chart is posted here, and is extremely consistent from one car to the next. the only variation from car to car is a very small one and is pretty much across the board and even. the drop is not there with the OEM system. it only comes in when you add a "free-flow exhaust" and is very consistent with all systems like that.



sorry. you've got the loss. it's as clear as day. i know you want to think that the B&B is perfect, and you love the sound, as do many, and that's fine, but it isn't a free lunch. remember, i had one for a week or so. i pulled it because of the loss. it was noticeable to me while driving, as that is where i spend most of my time, and it definitely showed up on the dyno.



but, as i said, you probably don't notice it because you never let the car down below 4k rpm, and at that point you are already past it.

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[ds968]

Not sure about " perfect " but aside from the sound it clearly adds significant torque and hp over the entire rpm range, with the possible exception of that single 200 or 400 rpm span which , just as you said, I'm never at for more than 1/10 of a second at any given time. But I also don't think anyone else would sense that loss unless they have a habit of driving in 6th gear at 35 mph and step on it - 20 ft/lbs of extra torque in that situation might make a difference.. for a fraction of a second. Also when it comes to charts and graphs or even oem stats I remain a huge skeptic..I've learned that in "real life" cars rarely act consistently with what the readings would suggest, and you've been witness to some of that; I know you feel that many other factors could play a role so it can't possibly just be the BB, but so far no one has proven that to me in head to head contests .I'm sure that day may come and I'll gladly ( or grumpily ) stand corrected when ( and if ) that happens ;-)

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[94SilverCab]

Does B & B claim significant Torque and Horsepower improvements? I was under the impression that no system made any claims (including RS Barn) of more than a modest 1-2 BHP and some faster revving. Not taking any pokes at B & B, just want to know.



Jay

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[lbpesq]

Having just adopted two kittens, I was horrified by the title of this thread! lol



Bill

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[mdss]

Hi guy very interesting reading indeed, i have to say that i can clearly feel more power without the cat and having spoke to a few 968 specialists that race the car in the porsche series here in the UK they all seem to run the car with no cat. They simply weld in a pipe which i am going to have done on friday as i think the resonance i can hear is the second skin(internal) rattling.

I will report back. I do trust what flash says though as yes when between 2000-4000rpm range the car feels a little slower but definately better at the top end.

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[JWahlsten]

Were I to go catless, I would remove the factory cat and have a test pipe built in its place. With a straight through muffler, you have a race system. You won't have the same resonance you do now, and the car will sound more like a tractor...Just my opinion, but I have had open exhausts on 4-cyl Porsches in the past and don't think they really sound all that appealing.

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[mdss]

I will have a pipe welded in place as you said 2.5" the rest o the exhaust is fine and will be left alone to be honest. The car sounds great now still very similar to before just a lttle louder on full chat.No tractor thankfully here. haha



thanks guys.

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[flash]

NO cat-back system sized similarly to the OEM system (B&B, cargraphic, rs barn, whatever) makes a significant power increase anywhere in the band.



what you feel is throttle response. the engine revs more freely. that is commonly mistaken for a power increase. however, it is NOT actually producing more power (more than at most a couple of horsepower up top). the trade-off with any of them that do make more power at all, is a very noticeable drop in torque over a 400rpm band centered at about 3400rpm. this is exactly where you are in 6th gear on the freeway, and an rpm that is very commonly driven around town by most people.



it is there. it is documented. it is so far without exception.

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[ds968]

BB's claim based on before and after dyno charts tested on the 944s , showed hp and torque increase over the entire band, from a low of +4 to a high of +17 hp and related / proportional torque but I do not recall exactly what that one was.. I think + 11ft/lbs or so at the high end ..and no loss of either anywhere in the band. In talking to them they stated unequivocally that with a more powerful engine in the 968 ( vs the 944s )those increases would without a doubt be slightly more . Sorry, but I tend to give a lot of credibility to a mlti-million dollar enterprise as reputable for their engineering and produtcs as successful as BB is , and the resources at their disposal over almost any other testing performed elsewhere, except at comparable companies ( Magnaflow, Cargraphic, Borla, etc.. ) If they dispute the BB claims with proven testing, fine, until then I'll stick to what I know.

BTW, I have not seen a single before and after BB testing result chart from RS Barn or anyone else, but even if one exists see above comment re resources and engineering credibility. I guess we'll just agree to disagree on this, no point opening up a Pandora box , there are many other threads addressing this matter.

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[flash]

well, they don't know what they are talking about. they are wrong and we have proof. what they are saying is typical of those companies. they develop something for one car, and incorrectly make assumptions about the next. a 944 engine, even an S2, does not in any way behave like a 968 engine when it comes to intake or exhaust. i see this kind of thing all the time.



by the way, those companies aren't that big either. you would be surprised at how little real testing any of those companies do. they rely heavily on independent users for a lot of their data. i've worked closely with a couple of them over the years. it's not nearly as high-falootin' as you might think. but the media hype sure makes it seem so.



by the way, we do have before and after charts. they just haven't been published because we would get into the inevitable "yeah, but blah blah blah on my car, yada yada" conversations with the psuedo-expert who read something or heard something and makes post hoc ergo proctor hoc assumptions that are totally erroneous. it's like thinking that a chip gives "x" and an intake gives "y", so therefore i should have the sum of those 2. WRONG! while not set in stone, you can pretty much figure that the second mod will get half of what it did by itself, and the next one will get 1/4, and the next one 1/8.



as for the B&B, even your chart clearly shows the typical torque loss. it's not like it's even close to not losing. i've driven your car too. it's definitely there. that doesn't mean it doesn't run well or anything like that. it just means that, in that area, it's exactly like every other car that has the same kind of system.



i have no vested interest in any system either, so my commentary has no basis in bias. there isn't one system on the market that i like or prefer. none of them are without things that i don't like about them, and i've tried and tested them all but the cargraphic (and pete has tests on that one)



if you still have your OEM system, i am more than willing to make you a bet. we go to the dyno, and if i am right, you pay for it, and buy me dinner. if you are right, i'll pay for it, and your trip down here, and buy you dinner.

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[Rap]

So where is dinner and are there any restrictions? I mean like really lets make it worth the while!

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[flash]

lol - i'm game for just about anything. i'm that sure of what the results will be.

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