You might be able to eek out 1-3% more HP with intake and exhaust mods made to the stock engine at red line.
Really? Dunstall published numbers that were much higher than 1-3% at many different rpms with only an exhaust system change and 115 main jets (everything else stock):
How do you account for these increases?
Advertising bravado, at least at some level.
Are those exhausts still available for testing? That IS and interesting advert! Do you have an any independent party testing data of the product?
Things I notice:
They carefully said they compared their exhaust to the stock exhaust system on
A CB750, rather than specifying an otherwise stock
motor on which the comparison was made? Hard to tell if it was intentionally word-smithed that way, or not. But, I never underestimate advertising "slickness".
Certainly that last picture with the CB750 red head, leads me to suspect they changed something other than the exhaust, as well.
I'm sure you are aware that there are variances among dyno machine readouts, too. If I was in marketing, I'd have it tested where the results came back as favorably as possible. I've experienced that practice before, as well. In the shady world, have the base model tested where the dynos numbers are low, and have your added product tested at a different facility that returns generally higher numbers.
I've encounter this sort of thing many times where confirmation testing fell far short of manufacturer claims, or they did the test in such a way as show more emphasis than is actually realized.
But, I will admit that some exhaust systems do perform better than others, if they were indeed engineered for that specific task. Take a poll and see how many posters actually have a true performance exhaust vs, a MAC replacement that has had no performance engineering. This was what I was typically addressing.
Still, Dunstall has a good reputation in track matters, and clearly had skills. But, were all those engines really in stock configuration?
The "Gilding the Lilly" practice is particularly rampant in the performance parts arena where buyers are more interested in the bottom line goal than how it was tested or if the offering can really gain them what the advertiser promised on their particular machine.
The manufacturer nowadays has the disclaimer the equivalent of, "Your Mileage May Vary".
Certainly you know that among 10 identical production models, they will not all perform identically. Some will be faster and some will respond to certain changes better than others. If you applied you product to 10 samples, with varying results, would you publish the least favorable data, the average of the data samples or just the best of the data?
I have one Cb550 that is faster than all the rest of them. I wish I knew why. They are all stock. Were I to showcase a performance enhancing product, I'd pick that bike to install it on, for public observation, were I a slick marketeer.
I'd have to be pretty hungry to do such a thing in real life, though.
Also, you can "trick" the numbers by using a combination of the above techniques.
As usual, it's just my opinion, your mileage will vary. If you can really bolt on 11 HP for not much money, go for it! I remain skeptical.
But, I'd much prefer to see the raw test data, than just the advertising carrot offered for scrutiny. I can be swayed with the proper data.
Cheers,
