Arguing on the internet is like playing in the special olympics, you may win but you are still retarded!

 

i have an 8 month old #15609 ss magnaflow catback for sale- 3" in /out- 3 inch intermediate pipe is tapered in thew first 3 inches to 2/12" to mate to the oem y- pipe!

 

...that's funny as heck!

 

Now that none of the over 425 members that read this thread have come forward to support MedVader, I would like to add what ACTUALLY takes place at the typical cat-back connection. For those who are interested, the intersection where the 3" cat-back connects to the 2.5" factory Y-intersection is simply an ADAPTER. It is against Federal law to tamper with any part of a properly functioning factory cat setup within certain limitations. Since the cats are welded in, this means the entire front section of the exhaust system from behind the exhaust manifolds to the clamp behind the factory Y-intersection. Technically, the Y-pipe mod is against Federal law outlined in the Clean Air Act for most. All but one of the F-150 cat-back designers address this issue. Since this ADAPTER doesn't function as a divergent cone, as is being improperly suggested, the topic was only addressed as a reference. It is impossible for the negative wave created by a divergent cone to scavenge exhaust gases unless it's properly placed. Any VERIFIABLE explanation includes this caveat of proper timing, even MedVaders example (paragraph 1): http://e30m3performance.com/installs...haust/exh4.htm That paragraph also explains what happens to flow and pressure. The F-150 head pipes are 2 different lengths and the ADAPTER is placed almost 10 feet from the driver's side head. This makes the entire topic moot and separates Nascar engineers from those who spectate.

 

Great the resident moron cannot leave well enough alone. He obfuscates and puts up strawmen because NOTHING I have said has been proven wrong and everything posted in this thread backs up what I've postulated. Nothing MuddledMitchell has posted is remotely correct.

PROVEN WRONG. The Darcy-Weisbach equation shows that a 3" catback is much less restrictive at 600cfm than a 2.5" and that the the few inches of 2.5" is a NEGLIGIBLE restriction. Not 0 or behave like a merge collector. I actually read the link to the gas flow equations MuddledMitchell posted. Given decently made gradual transitions, the rectrictive effects due to turbulence are NEGLIGIBLE compared to the static diameters and lengths of pipe in the system. But Mr. Mitchell is too disingenuous or TOO STUPID to actually see that. I belive it's stupidity.

PROVEN WRONG. Because MuddleMitchell doesn't know that this experiment is entirely dependent on cfm. IOW if I blow lightly enough, pinching it in the middle forms negligible restriction.

PROVEN WRONG. Merge collectors have NOTHING to do with adjusting backpressure and EVERYTHING to do with pressure wave magnification. Otherwise you could just put a restrictor plate in the collector to "tune" backpressure. And a single merge works just as well on an inline 4 motor.

I brought up merge collectors to refute MuddledMitchell's belief that you cannot have a larger pipe behind a smaller pipe and expect to gain anything from it. Merge collectors do and IT IS A RESTRICTION but a NEGLIGIBLE ONE.

This doesn't even begin to explain the idiocy Mr. Mitchell keeps displaying by claiming a few inches of straight 2.5" pipe is "poorly engineered". Where's the poor engineering in a straight pipe? Now if the inside of the Y-pipe is crap, then by all means clean it up or replace it. BUT IT WILL STILL MAKE LITTLE OR NO DIFFERENCE WHETHER THE MERGE PIPE IS 2.5" or 3". This is what happens when a backyard mechanic turns wanna be design engineer. He causes people a lot of useless trouble, wasted time and money by giving bad advice.

Oh and the aftermarket catbacks are 3" IN and 3" OUT.

Here's another well designed header/Y-pipe system. With smooth merge. Notice the outlet size. 2.5"

http://www.secureperformanceorder.co...ProductID=6165

 

MedVader wins the Gold medal.

I stand corrected on the 15609. Yes it has a 2.5" to 3" transition but not all cat backs are this way. As I said some are 2.5" all the way to the muffler. I plan on putting the 15749 on my truck. It has both 2.5 and 3 inch pipes and 3.5 inch tips according to Magnaflows own specs on their site.

 

"PROVEN WRONG. The Darcy-Weisbach equation shows that a 3" catback is much less restrictive at 600cfm than a 2.5" and that the the few inches of 2.5" is a NEGLIGIBLE restriction. Not 0 or behave like a merge collector. I actually read the link to the gas flow equations MuddledMitchell posted. Given decently made gradual transitions, the rectrictive effects due to turbulence are NEGLIGIBLE compared to the static diameters and lengths of pipe in the system. But Mr. Mitchell is too disingenuous or TOO STUPID to actually see that. I belive it's stupidity"


Not to add to a hot subject but I'm a mechanical engineer and wel versed in fluid mechanics. A 2.5" section of pipe in any 3" system IS NOT NEGLIGIBLE....Plain and simple. The Darcy_weisbach equation a component of the Bernoilli equation and is not the whole story.

Also, these are Trucks, not corvettes. Everyone please grow up and deal with.

 

Well I'm an electrical engineer.

And I can tell you that the Darcy-Weisbach equation is the MAJOR LOSS in smooth walled pipe.

Furthermore I can tell you that transitional losses from 2.5" to 3" are small compared to the head losses of the total system.

hL= K(V1-V2)^2/2g = K(Q/A1-Q/A2)^2/2g

K= .07 for a 70 degree transition
Q=10cfs
A1 = (2.5/12/2)^2 * pi = .034sqft
A2 = (3/12/2)^2 * pi = .049sqft
g = 32ft/sec^2


Thus our infamous 2.5-3" step up takes a grand total of 8.86ft of head loss! WOW.


So the headloss of a full 10.5ft 3" ideal pipe is 546ft at 600cfm

And the headloss of our 6in 2.5"pipe TRANSITIONING to 10ft of 3" pipe is 594ft

And the headloss of a full 10.5ft of 2.5" ideal pipe is 1365ft !

So it is NEGLIGIBLE. If you can clean up the Y-transition, the few inches of 2.5 collector makes almost NO DIFFERENCE (at 600cfm)

And it is worthwhile to put a 3" catback behind the stock Y-pipe.

 

Well I am an electronics engineer and I can tell that MedVader just likes to try to impress people with his textbook knowledge but does not have any practical or real world experience in the field he is spouting off about. He probably just graduated from college and doesn't have real world experience in anything yet.
I know the type, we have hired and fired a few of them.
He is right that flow is an important variable in the equation but it is only part of the picture.
He should leave the exhaust engineering to the companies that specialize in that field. If he truly believes everything he is saying he should apply for a job at Magnaflow or flowmaster. I am sure they could use an expert at flow dynamics. I think that he should start at Midas or Meineke first though.

 

Well Norm considering you've been nothing more than a cheerleader, I suggest you put your opinion and that "electronics" degree back where they belong, in the drawer.

Another dope without enough grey matter to even try to show what I've said is wrong. Go ahead bro. Give it a shot.

 

You sure are a combative a$$hole aren't you. Even when people try to remain civil you go on the attack. I am an EE and I do not come here spouting physics formulas, Thevenin, Norton, Kirchoff and all the crap I learned in college 20 years ago etc. I could open a text book or do a Google search and fill my posts with mathematical crap but that is not the point. The point is that several companies have already engineered very good exhausts for our trucks. Let them do the engineering and we can enjoy the benefits. When you grow up you will see my point and realize what is truly important. Pretending you are always right is not one of those things. I already admitted I was wrong when someone pointed out that the 15609 is 3" in and 3" out at the muffler. I did not fall out of my chair at the fact that I was wrong. It is no big deal.
If you have some useful info or factual data rather than Physics book formulas by all means share it with us. That is the reason we have this forum, to help each other with info we can actually use. If I were fabricating a race exhaust myself then your formulas may help me but I am just going to buy a system that someone that knows more than me engineered to do the job I need it to do.
Dyno tests have been done that show the results from the available catbacks. They work even when they change from 2.5 to 3. We can agree on that right? They have also shown that pipes that are too big cause a loss of tourque especially down low where you want it. Agreed?
See I did not need some textbook formula to say that. These are practical real world examples. All of these catbacks do start with 2.5" tubing. Some jump right to 3'" after a few inches and some are 2.5" all the way to the muffler. You could have answered Scott's question like that instead of coming off as an arrogant jerk. This thread would have been more useful that way instead of deteriorating into a **** measuring contest.

 

Since this has degraded into childish namecalling, it's time to close it. For those that want to continue a mature, civil, adult conversations without resorting to namecalling, then feel free to start another thread.