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Old 02-15-2011, 02:51 AM   #101
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Originally Posted by cmiller219 View Post
ok so that answers the question of power. does it mess with your back pressure? and the midpipe was the section that i was referring to but it seems you already knew that and possibly have something in the works for that. I just found it unclear as to why you where going from one size to another back down. And as i stated in a previous post that the product looks very nice and well engineered and built. The welds are very nice i just couldn't convince myself to eliminate mufflers to a 3in pipe but still run the stock piping to it.
I'm going to try to answer this as clearly as possible and I'm working a little to understand what you're asking me here. Some of your questions are quite contradictory (doesn't it mess with backpressure? vs. 'still run stock piping to it.') First, it does decrease backpressure. On a turbocharged engine, that is beneficial, both in the spool characteristic - as backpressure is equivalent to drag on the turbine wheel and also at the top end while the car is in boost, which is where you're going to get the majority of your power. The factory rear mufflers, while large, are restrictive due to their multi chamber baffled design. The factory pipes going into the factory rear mufflers are 2". So are ours. This section of the exhaust does flow slightly higher than the 2.65" midpipe. The dual 2" exhaust pipes that we produce are the equivalent of a 2.83" single pipe. Not really sure where your knowledge comes from that indicates a .35 or .17" difference in diameter would make any difference. So if you think the axleback pipes are too small, it's the difference in the effective diameter of the size of a bb. Seriously. .17" Smaller than the diameter of a BB.

Now I'll tell you a little of my emperical knowledge. Eight dyno tests on eight different four cylinder vehicles, turbocharged and naturally aspirated. Each of these vehicles, in terms of catback gains, we found 90 percent of the gains came from the elimination of final muffler backpressure. 90%! And that is over a stock vehicle test.

Now lets talk about exhaust backpressure performance gains. Downpipes, catbacks, in some instances midpipes for vehicles with a two piece factory downpipe each of which have catalysts onboard. In 100% of the dyno runs I have done on exhaust designs across multiple platforms and engine configurations, exhaust gains on boosted vehicles are asymptotic. Meaning that as you pull restrictions out of the system, you reach a point of diminishing returns. If you do a stock vehicle baseline, then throw a downpipe on and do dyno pull tests, you'll see x amount of hp gain (for explanatory purposes we'll say 18hp). If you put the catback on after that, you might see
8hp out of the catback. But if you do the same test the other way around, you might see 13 out of the catback and 13 out of the downpipe. Because these deletions of restriction reach a point of diminishing returns, it is beneficial for any enthusiast to find the most restrictive points in their exhaust system and replace them with less restrictive performance alternatives. If I can sell you a downpipe and an axleback exhaust for a reasonable cost, fit it into a reasonably sized box and get you a good deal on shipping, and the last piece that I do not make is bulky and only makes 3hp gain after you've swapped the downpipe and mufflers out, then I'm doing you a favor. I'm selling you the best bang for the buck. I have a $1100 catback design on the wall at my shop that we tested for almost a MONTH thinking it was going to be our go-to design.

Afterward we decided to make a budget alternative which was this AxleBack. When it was finished we couldn't think of a single reason to sell the big catback when the simpler, cheaper and easier to install AxleBack achieved everything that the catback did. Explain what my ulterior motive would be in not selling a product that has a higher price point and thereby a higher overall profit margin?

Originally Posted by xluben View Post
Any more word on the 2011 hatch? Haven't gotten any e-mails in a while
Yes! We have been gathering up parts to finish out our design and we're hoping to get that done by Friday of this week and start testing it on a local 2010 STi Hatch this weekend. We are evaluating three options for muffler and muffler delete configurations.

Originally Posted by xabre1200 View Post
Uh btw is a muffler delete illegal in California?
No. Catback exhausts are not regulated by the California Air Resources Board. Most noise ordinances are local and you can call your local highway patrol office to ask them what the standard that you need to adhere to locally is in advance. There is usually a decibel rating that they will refer to, just make sure to ask them specifically what the local ordinance numbers are that refer to this. If need be, call your local court house or law library, these are public facilities that you can access as a citizen. The law librarian will be able to point you right to local statutes. Arm yourself with these standards and be polite, but be ready to defend your choice to modify your vehicle in a legal way.
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Last edited by GriffithBuilt; 02-15-2011 at 06:01 AM.
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