Stephen,

This has gotten a little off topic. Again I commend you for the effort and information you are about to provide.

Please answer me one simple question. One car has two exhausts installed. Car A produces 500 rwhp at 6700 rpms with a afr of 12.6 with X exhaust. Car A produces 500 rwhp at 6700 rpm's with a afr of 12.2 with Y exhaust . If car A is tuned to an afr of 12.6 @ 6700 rpm's with Y exhaust will it produce more power than with the X exhaust? Everything else presumed to be equal.

 

Chad,
Surly you have to know that the deviance from 12.2-12-5 is about a 5-7HP difference? You continue to make reference to tuning in such a short range. Once the AFR is set the car looks for maximum advance at target AFR. I have seen some circumstance where the car did not make better HP because of other controlling factors. The Motronic is never a constant, ever. It is active and adaptive. The 40HP change we have seen is simple proof of that. This is why we ran runs until they were overlaid on one another. So your question is not easily answered because its situation almost never exist. In our situation I felt that it would have made little difference. Why would I say that? well the mufflers all would move around looking for target AFR, so I had an opportunity to witness what each muffler would do in its range. The short answer to your question is no, not based on what I know and have seen with these cars.

 

That book is awesome, my friend Sil (the guy you met with the Supra) bought that for me for my birthday...

 

sharkster,

A. Graham Bell actually has three books out on the subject. He is beyond a doubt the formost authority I have ever come across. There may be better, I just have not met them yet. His sharing of past experiences has saved me a lot of money and aggravation.

Stephen,

I may stand corrected, however this has been my experiences over approximately seventy dyno runs involving the 996tt. I am sure you have performed more. For the most part we use a load bearing dyno with the big drums. If you can't load up the dyno then I agree you should not be using the more efficient afr's. People who tune on the other type of dyno's run the risk of detonation when they place their cars under loads on the road or track.

I have also discovered if I make a change and I don't go out and make four or five hot runs my ECU won't adjust to the new part. Another way I have found that does the same thing is to just drive it for 200-250 miles. Even with this the car will change if you do some hot runs before I dyno it if the milage was put on in a lazy driving manner.

What I don't understand is with the dyno I use, I get a read out at every ten rpm's from start of run to the end of the run. At every ten rpm increament it gives actual hp, torque, afr and exhaust temperature. We can hold the dyno at a certain rpm. The afr is not in a range, it is an exact reading at that rpm. This is the only information I know. I can only conclude you are using a dyno which provides information in a different format or doesn't provide the same type of information. I am not trying to be argumentative. It has just occurred to me that I may be asking for something that is not available. If so, I apologize for the misunderstanding and will leave it at that.

 

We are on the same Dyno. RPM uses the same as the unit we are on and yes I have all the same readings that you want. Yes, I will post them when the article is out. I think you are misunderstanding the point. The AFR holds steady on each muffler. The range is all the mufflers combined. The 12.2-12.5 is what the range was at 8 different test. The Europipe was 12.5. Some of the others were 12.3. I will post these numbers later. My dyno runs are printed every 10 to 1000 depends on how we set it. I have them every 100 to read easier attached with all the necessary data. As we have also talked it has always been my recommendation that 50miles should be put on ECU when a change is needed. Also don't forget it will shut its self down in a 1/4 of the time and take 5 times longer to readjust on the up swing. Depending on the circumstance the car will not make the same power even given a target AFR.

It is not my goal to seem argumentative on this subject either. I have over 100 dynos on my personal car since Nov. That seems like a fair amount just on my own personal car. Not to mention the amount of work I have done with other 996TTs and certainly the 993TT and before. Unless you are running a locked VE table out of loop then the car will always be active and confirm that a target AFR will not always yield the identical number. Keep in mind I am not talking about a 50 HP difference, however I am talking 10HP and with x muffler running 12.2 and then 12.5 the difference was less than 7HP at its peak and more like 5HP.

 

Stephen -

Back to the main topic. Did you also register any observations about sound characteristics. I don't care too much whether an exhaust is loud or queit at WOT. But, I'd like to find, if possible, an exhaust system with a low level of resonance at 2000-2800 RPMs.

Thanks in advance,

 

You know resonance and level of it is a little hard to describe. It is some what subjective. The quietest was the Europipe hands down, but only in the resonance department. The actual db level was higher than some of the other units. Once you have spent some time with a huge resonance muffler a little resonance is ok. I actually started judging if I could hold a conversion with my 5 year old in the back.

 

That criterion works for me too as I have a two and a half year old that I'm sure will want to ride with me in the not to distant future. But, seriously, I think that's a sensible way to describe. I guess my ideal exhaust, holding HP constant, would have little or no resonance at cruise (like the stock system) but would be louder at WOT. A little louder inside, and even a little louder still outside the car at WOT.

Thanks Stephen.