Validation, the missing link
nota4re said:
No reason at all for me to doubt the strong recommendations of Bob himself as well as his products. For me, the weight savings alone of this exhaust makes it a contender. A louder, potentially better sounding exhaust note is icing on the cake. I am, however, very skeptical about the claimed HP gains for at least a couple of reasons;
1. The shape of the before and after curves are too similar and non-typical of what you might expect to see from an exhaust change. It is rare that you would see such a linear improvement across the entire RPM range. Additionally, you would tend to see this "shifted curve" phenomenon with grossly different IAT's, as an example. I must stress that this is NOT an attack on Bob or the great work he has done. I'd just like to see a couple of additional tests to see if the results are repeatable.
2. At least one other well-known tuner (Kenne Bell) saw NO improvement with their experimentations with exhaust mods.
3. You'd think the Ford engineers are smart enough not to leave 60HP on the table.
nota4re,
It's after 2 AM and I will not be able to sleep tonight unless I reply to your always-excellent comments.
In my business (I am a half-ass electronic engineer), whenever I design or "invent" something which I perceive new or novel, such as an electronic circuit, I must always scrutinize my work, especially if I get achieve much better than calculated results. I have designed and licensed products that most of us have either seen or heard about, on television or radio. Part of my job as a good engineer or "scientist" is to check and recheck any change or update for consistency
and repeatability. Person's that design new products or gadgets will usually get caught up with "Inventor's Syndrome." When they notice a
favorable change in their data, they refuse to look back and examine cause and effect. If a person makes a claim that is either extraordinary or "to good to be true," it needs to be closely examined. So, I would like to add to your comments above, in order;
1. I agree with the linear improvement that you talk about. Could this possibly be due to the effect of a positive displacement supercharger, or, was it bad science? So, I would need to ask, what were the ambient air temperatures when the
before and
after runs were performed? Was the stock system measured on a hot day and/or with a hot engine compartment? Was the new exhaust system tested during a cold ambient temperature condition with a cold engine compartment? This will influence intake air temperature. One thing that could be somewhat representative of the engine compartment temperature is simply measuring something which has a reasonable amount of thermal mass, such as the case of the supercharger. You are correct about repeatability, just as I had also stated above. Put the stock muffler back on and remeasure everything! Of course, NOBODY wants to do this... In my line of work, I just have to do it, even if it takes days of work.
2. This is another good point. If it worked that well, Kenne Bell and other's would have done this.
3. I agree, as no one passes up a free lunch. Consider how much cheaper it would have been for Ford to use some bent tubing instead of that huge, double-walled, internally insulated, huge box... However, one known thing is the 50 pounds of weight loss!
In closing, I feel that all of you in the performance business would greatly benefit from performing carefully controlled experiments.
It's so easy to take bad data, and only one way to take it correctly...
