hally

jy951 how do you explain the before / after dyno charts posted by Karl2bdc showing more torque at all RPMs?
It directly contradicts what you're saying

jy951

hmmm...did u notice the date stamps on his dyno sheets? For FAIR comparisons, DYNO runs should be done BACK to BACK, because performance (especially on TURBO cars) is DIRECTLY affected by atmospeheric pressure, ambient temperatue, etc.

The only way one can get a TRUE comparison of changes in performance (especially turbo cars) is to run the tests on the SAME DATE at roughly the SAME time of day. Otherwise, your numbers will be skewed. So, be careful when ppl throw out dyno sheets as the ultimate proof.

I'm sure that this is enough to satisfy Karl2bdc, but when running experiments, it must be done under the SAME conditions for the results to be considered accurate for comparison purposes.

I stick to my point, my mid-range performance SUFFERED when I ran my 951 with a straight-pipe. I replaced the straight pipe with a high flow cat and the mid range improved significantly. Keep in mind, that NO TWO cars OPERATE exactly the same - even with the same set-up. Atmospheric conditions have a significant impact on turbo car performance - even on the SAME car - from day to day.

If you troll the AudiWorld B5- S4 (biturbo - I also own a MY2000 S4) forum, you will see posts from S4 guys making this observation frequently (same mod set-up, different results, even with atmospheric conditions being similar).

So, dyno nbrs are nice - but they aren't the - "BE ALL" - "END ALL" - for ALL cars of this type (951s, turbo cars, etc.). It's the "BE ALL, END ALL" for Karl2bdc's car on those PARTICULAR dates. Like I said, in the future comparison dyno runs should be done on the SAME DAY, (relatively) SAME TIME, under the SAME atmospehric conditions - to eliminate variables.

ehall

You're right. We're all wrong. I give up AGAIN!

jy951

The best way I can describe YOU - READING COMPREHENSION IS LACKING!

In YOUR NEVER ENDING quests for TOP END horsepower, you and SOME other listers, were (are) LOST the main point of my original and follow up posts. Fortunately, there were listers who had a CLUE about my point (loss of mid-range torque with a CAT DELETE and ithe nstallation of straight pipe on MY 951), and their posts reflect such (just re-read the thread). NOT EVERY CAR (951) BEHAVES THE SAME WAY WHEN YOU ELIMINATE THE CAT!!!!.

That what cracks me up, people like you say in an internet forum, do this and do that and your 951 will make 800+ HP, not necessarily true, every turbo car (ditto for normally aspirated) behaves DIFFERENTLY when modded, even when the mods are EXACTLY THE SAME on each car. Any qualified tech who wrenches a forced induction car will tell you that.

Did I include CLUE-LESS in my description of you?

951_RS

dude you are so BLINDED by lack of LOGIC and no COMMON SENSE lol....

Seriously, are you telling me that because he did the DYNO another day he gained 50 some odd hp to the wheels? You are delusional
It doesn't take a genius to realize that the turbo ITSELF does not need backpressure to create torque, the engine itself does. Have you ever seen a turbo's exhaust size FOR yourself? You go ahead and look at one and tell me how small the port into the hot side is. Now THAT is restriction, oh did I fail to mention so is the fact you have to spin blades along THEIR rotational weight now also? That is called backpressure and trying to say that some "porsche" tech said not to delete it (you probably talked to some guy whos been in the business of porsche oil changes for 30 years ) because IT'S a "complete system" is absolutely -mike tyson voice- ludicrous. I've been to NUMEROUS porsche mechanics who just want to keep every car OEM no matter what the circumstance. The one nearest me has worked on 944's since they came out but he refuses to do any aftermarket work. Why? Because he's never done anything other then what the book said. You theory about the magical exhaust system porsche somehow made into a complete working unit to increase midrange torque doesn't hold up a semblance of reason or scientifically backed up FACTS.

I really HOPE you take the time to go read some good tech books about turbos, or perhaps look up on the internet how a turbo works and STOP capitalizing certain WORDS to try and make your POINT seem more TRUE. All it does annoy people, trust me I am ONE of THEM. Here go to www.howstuffworks.com maybe you can start the learning process instead of spewing forth false information to other people. The cycle of ignorance must end.
/thread

951_RS

So what you're saying is that the exact same mod to one car, might make another car lose power? You really are worse off then I thought
the only way thats going to happen, is if by removing a cat your a/f goes all screwy or something similiar. But to me, thats not properly doing a mod.
If you like the audi forums so much, by all means go back there, I'm sure they'd be glad to have their forum idiot back

Here you go, reading
http://www.cobbtuning.com/tech/exhaustdesign/
Don't feel like reading it? I'll post for you.

Post Turbo Exhaust
"The main performance goal of a post turbo exhaust is to create the least amount of backpressure possible."

Oh and what's this?
"Pipe diameter does have an effect on flow rates as well, but again it is not the major factor in most cases. 2.5" may flow enough for 300-350 h.p. without being a restriction. 3" is usually capable of flowing 500-600 h.p. before becoming a restriction. This is assuming that you have designed the rest of the system up to par. There are also full 3.5" systems and those that start out at 4" and taper down. Unless you are making over 500-600 h.p. anything over 3" is a case of diminishing returns and in most cases has no advantage. There is more to gain going from 2.5" up to 3" than there is going from 3" to 3.5". A 3" system will not loose torque compared to a 2.5" system if designed properly. In fact if designed properly 3" may be capable of making better low end torque than 2.5". Again, since the way to make the most torque with a turbo exhaust is to get the turbo to spool-up as quickly as possible, it should be the main goal of the entire exhaust system and good flow after the turbo is one way to achieve it. We use 3" as we want our system to flow enough to be capable of coping with a customer's changing goals. Properly designed we can offer it to the big power crowd while still appeasing the low end torque club."

The only reason to reduce the size towards the end of the pipe is for packaging, cost, and noise reasons. Tapering the diameter does not make more power, torque, or bring on boost faster. However having smaller pipe towards the end has less effect that having smaller piping at the beginning. In other words a system that has 3" pipe for the majority, and necks down to 2.5" at the end will flow enough for more power than a complete 2.5" system. The further downstream you neck down the exhaust the better……..if you decide to neck it down.
Like I said /thread

hally

RPM TORQUE DELTA
2400 0
3100 20
3800 35
4500 50
5200 50

Maybe these results came from that dyno shop on the grassy knoll
As Llyeton Hewitt might say, "come on" u can't just dismiss these numbers.

jy951

Oh God, another HP junkie (thinks that performance equals mo' powah period)!!!

Any REPUTABLE dyno/performance shop will TELL YOU - You should do dyno comparisons (before / after mod) on the SAME DAY, under (relatively) the SAME ATMOSPHERIC CONDITIONS, if possible!!

The fact that you don't GET THIS POINT - means I don't take YOU SERIOUSLY - that's Perfromance Car / DYNO 101 stuff!!!!!

Especially when capturing turbo car performance - you MUST take atmospheric conditions into account (that's why it's ON THE DYNO SHEETS) - and when doing comparisons - make sure that the conditions are as CLOSE as possible - thus the SAME DAY, SAME TIME approach - jeeeeez!!!!!

As far as your point about techs trying to keep cars stock - who the HELL cares - that's an irrelevant rant - that means NOTHING!

You better stop believing your OWN rants and talk to people who WORK on Porsches and Audis for a living (and also OWN them) , that's what I do!!!!!

In fact, I use one of the SPONSORS (AWE Tuning) on RENNLIST for mods on my Audi B5-S4 biturbo - and have had many a turbo perofrmance conversation with the 20 and 30 yr old techs in their shop which is LOCAL to me (shot your ' a tech doing oil changes for 30 yrs' rant - down the hole - where it belongs).

I also use an independent shop to wrench my 951 and S4 that specializes in forced induction cars - I'll take the opinion of the tech there over YOURS any day. He also OWNS an Audi 2.7T biturbo and has done MANY mods to it. I've seen it with my own eyes.

When I need a backyard oil change - I'll call you - make sure you have a lift in your driveway.

jy951

U give me a quote from Llyeton Hewitt - ha!!!!!
What has he won lately????
I'd say the Roger Federer has HIS NUMBER - mate !

951_RS

Wow, yet another completely ignorant blockhead... Did you even read my post? Are you so blinded by the truth you can't understand simple as pie facts?
You seriously need to not be allowed another car ever again.
Ok, so your mechanic isn't knowledgable awesome, you should be glad to have someone like that work on your car...
Horsepower junkie? When did I ever even say anything about that?

So, your friend OWNS an audi 2.7bi turbo, that makes you god of turbo knowledge now? My rant about your tech? You mean the guy you claim to know =/ Psh, how about I shoot all your responses down the hole where they belong as noone is retarded enough to beleive you?
You do not know who I am or how much automotive college I've taken now do you? Before you open your mouth again you should realize how dumb you make yourself look when you blatantly are going off someone ELSE'S information instead of things you've learned yourself, don't you think?

Because you obviously know nothing about turbo cars whatsoever. I don't go by some "tech" because I'm better then you and can learn for myself without having to rely on false information fed to me by illegitimate means.

Seriously you should read what I posted, an expert from cobb racing posted that, and if you want I will scour the internet and prove you wrong, time and time again with more experts in the field of tuning that have forgotten more about turbos then you'll ever know.

So who at AWE tuning do you know? Please let me know who they are so I can send them an email and see if you are for real? Don't be scared of being called out now...

When did I ever say you shouldn't do a dyno run on the same day anyways? Simple, I didn't.
Go ask one of your "friends" if dynoing on a different day is going to make 50 hp magically appear on your next dyno run? Same exact dyno? It won't happen... It's sad people like you even know how to operate a keyboard because it makes the rest of us look so bad.

You have not provided one single fact yet, all you have is BS talk and benign comments that do not prove your point AT ALL.

Ryan in SD

Im not a know it all but just keep in mind that cats are for emissions...not performance. + you still get back pressure from the muffler.

Ok now Im ducking for some cover

Glider

JY 951, I believe that porsche and audi did "tune" the exhausts to work with cats. But I think it was only because they had to use cats, not because they help in a system.

SD Porsche Fan

FYI, Karl2bdc is a professional Porsche tech.

My original post that started this whole mess was a statement of MY experience. It is possibly the experience of many others on this board.

I'll also consider my particular driving application when determining if the cat delete improves performance for ME. Although not a track car I live in rural state with long wide open highways. Our Interstate system here has a 75mph speed limit. Our local car club does a lot of highway crusing. If you are in the right gear for acceleration at highway speeds you are probably living in the upper end of the power curve. If that is where I will recieve more performance than I can say... "Cat delete completed! - WOW! Big differece!" because for me it was a noticable night and day difference.

Well, I'm off to the Omaha Zoo with my kids and then on to Kansas City to turn some wrenches with the KCWS!

Evan70

Well, the opinion of Tom Charlesworth (you may have heard of him, arguably THE BEST 944/951 mechanic in North America), is that the cat bypass is one of the best mods you can do on a 951. I did it on both the 951 and 951S I've had and it made a very noticeable difference in how fast the turbo spools up on both cars, and did not noticeably impact low end TQ.

As for dyno differences, it's always been my experience that dynojets give very consistant corrected results across different days. As long as you are using the same dyno, I've found my typical variance from different days after correction to be less than 5HP. However, if you change dynos, then the variance may be more (I've seen as much as 10HP between dynos with the same weather conditions).

User 41221

jy951, were you suggesting that the shop that Karl works for is not reputable? I'd suggest you tread very lightly there, or clarify your comments. The circumstances of the dyno pulls that Karl did were not the result of a scientific experiment designed to ratify the results of a cat delete, it was comparitive data that was done around Karls available time on his own vehicle that happens to show before and after results of a cat delete, with no other mods done in between. And while the best methodology would be to do back to back pulls on the same day, it is still legitimate data that Karl presented, and its certainly better than ANY data you have presented in this argument.

Karl and the shop he works for, Imagine Auto, are not only EXTREMELY reputable, but they are also Rennlist sponsors.

Regards,