But its not backpressure at all...backpressure would cause less exhaust velocity, not more.

Velocity is determined, in its simplest form, by the pipe layout, the pipe diameter, the pipe material and the rpm under which the power band is being operated at

 

Something we can agree on..Backpressure will reduce the Delta P accross the system and result in lower exhaust flow..which should result in less O2 flowing thru the engine and lower tq output..

 

I think "backpressure" gets mislabled a lot. People seem to use the term a lot when they really mean having a point where the velocity increases which creates a siphon/suction effect

real backpressure is bad. No one wants something pushing back directly against the flow of the exhaust. No one wants sharp bends or sudden bottlenecks

I agree that the layout, diameter etc needs to be carefully planned out and experimented with to find the best overall efficient design. I think when people say "backpressure" they're referring to leaving key portions of the total exhaust to serve as "choke points" where the air velocity can build up which then helps to create a suction to pull the exhaust out of the engine. It's the same reasons Vtek, variable valve timing, variable vane turbos, and butterfly valve exhausts work well instead of just being as big and high flowing as possible.

I've never subscribed to the "bigger is better" approach with exhausts, because I think that's really oversimplifying it and ignores what the siphon effect can do between high and low pressure zones towards helping total area under the curve. If bigger is better, why are there so many people and dynos of people losing so much power at low rpms when they went with the largest exhaust available? IMO it's pointless to lose 20 lbs of tq up to 5500 rpms just to gain 5 hp at 7500 rpms, but there's some people want that. Especially in the case of centrifugal SC's where tq is already hard to come by at low rpms

 

misunderstood is more like it I think


I think anyone who is talking about an exhaust needing backpressure isn't really understanding what they are even saying, and should probably spend more time researching the how's and why's of how that type of stuff works. I know a small fraction of what there is to know about fluid dynamics as a whole, but either way, it all starts with understanding that backpressure is never, ever, ever a good thing in an exhaust. The idea, as anyone can guess, is to balance velocity and flow capability.

 

A excellent article on backpressure and exhausts.

http://www.aaxel.com/tech_back_pressure.php.

 

http://www.aaxel.com/tech_back_pressure.php

 

you listed the same link twice and I agree with everything in that link.

I pretty much agree with their general rule of thumb, but one place it doesn't work is if it's a rear engine car and the exhaust is shorter than normal. Then it doesn't need to be as wide of a diameter


...still have that data if you want it

 

Would X02 with headers be good or am I better off just getting headers, y-pipe, and test pipes and keeping the rest stock? I actually like the idea of keeping the stock muffler and mid pipe and just upgrading headers, test pipes, and y-pipe.

 

what pulley are you running or how much boost/power?

Aside from the cats, the Y-pipe is probably the primary bottleneck in the exhaust with those sharp bends, then large volume area before going into the long single exit pipe. Next in line would be the stock manifolds since they collect together so early on.

IMO if you wanted to keep the stock exhaust and change the Y-pipe, headers and cats, that'd probably work perfectly well. It'd probably be cheaper to just change the whole exhaust and cats than headers, cats, and Y-pipe and it'd probably yield pretty much the same gains.

Headers by themselves don't always make a huge difference to make them really worth the money, especially if you get some of the cheaper ones. If you changed your cams or did some elaborate headwork/larger valves, then you'd start seeing more benefit from headers.

 

3.12 pulley. I really like the sound of the stock exhaust and thats mainly why I was asking if just changing the headers, y-pipe, and cats would be good enough. I was kind of thinking that just doing that would free up the "exhaust" power and anything else would be overkill.

 

well doing anything will change the stock sound. I can tell you though that test pipes will drastically change the sound unless you maybe get resonated test pipes. Test pipes are known for raspy buzz normally unless you're turboed - which acts as an additional muffler

IMO if you get an exhaust with either a Y-pipe or X-pipe, it'll have the characteristic of the stock sound, but with a little more bark.

normal test pipes or a true dual exhaust will absolutely change the sound a lot beyond 5500 rpms.

IMO, I'd go with either the nismo, Fast Intentions 2.5, or stillen exhaust if you want an exhaust that still has the characteristics of the stock sound. There's probably a couple others too, but I haven't kept up with all the exhausts out now. Resonated test pipes are cheaper than high flow cats, but will be much louder. So if you don't want things too loud, then consider HF cats.

I've met a local G35 guy with a 3.12 pulley vortech with resonated test pipes, and an HKS dual exhaust. His car sounds great though it does deviate a little from the stock sound characteristics. It sounds great though. Him and I used to use the same dyno and from comparing his and my charts, I can say his combo works well

 

Yeah, I was definitely going to get resonated tp's. I've heard both and I don't think I would be happy with non resonated tp's. I think i'll keep the stock mid pipe and muffler and just change everything else out.