I wanna make a custom exhaust system for my 2002 silverado 5.3 vortec (all stock). I wanna go from the manifolds till the end custom. I was thinking to use my metallic catalyc-converter (200cells) it got around 7" diameter means a lot of flow! I wanna get from the manifolds to a Y, and then to the converter. from then straight 3" to the flowmaster 40-series and then to dual exhaust-tips under the rearbumper. All in stainless steel.

But i heard that not enought backpressure in the exhaust-system can make a that i need more fuel and that i have less power in the bottom of rpm-range...

I dont wanna use a piggypack-computer or somthing else. I just wanna get nice sound. Not to loud.... and maybe a bit mor hp on the dyno (maybe i also get a k&n filter).

Best regards frim switzerland.

I hope for your help..............

 

I wouldn't say that it would be bad for daily driving; it would be overkill though. I still have yet to 100% conclusive evidence of loss of low end torque with less backpressure.

Unless you are planning on adding a supercharger down the line, I would go smaller than dual 3". Dual 2.5" will get you the sound and performance increase. Are flowmasters offered in stainless? Unless you are completely sold on the sound of flowmasters, the magnaflow product line might be a good alternative for sound and performance. You might also look into some headers, as the stock mainfolds will be choking you off at that point.

 

So i dont wanna go dual 3" only after the muffler. from the cat till the muffler is one 3" tube....
Yes the flowmaster is available in stainless....
I dont wanna get headers. In switzerland a performance exhaust isnt legal. So i have to put the stock oine every 2 years (for technical inspection) so only the exhaust is not that much work to change, but inklusive the headers.....??!?! That is to much work for me.

 

go magnaflow, just my opinion

 

Slap on a set of headers with 2" primaries to your everyday 4.8/5.3/6.0 and you'll understand the detrimental effects of a lack of exhaust gas velocity in the lower (relatively speaking) rpm range.

Proper exhaust gas velocity in the desired rpm range is what you're after when sizing exhaust components. Discussing "backpressure" is for bench racing junkies.

 

Fair enough, but like I said, I have never seen 100% conclusive evidence.

Breth, I made an assumption about the duals. I just noticed you mentioned a Y in your post.
As long as you have a flowmaster in there, you should have plenty of backpressure; if that is your worry.

 

I ran 3" all the way to a 22" single in, duel out hooker areochamber then ran duel 2.5" piping to the roll pan. Sounded like a beast!

 

What more evidence do you need other than physics? If you would like to see for yourself, go to Home Depot and conduct an exaggerated experiment. Grab a 1" pipe and a 3" pipe. Your breath is the same temp in both tests and the temp of the pipe will remain the same, thus negating the effects of a change in temperature between the tests skewing the results.

Blow through the smaller pipe with a constant (or as close as you can) force. Now, remembering how hard your blew, do the same for the 3" pipe. Notice how much easier the 3" pipe was? The larger pipe is super easy to blow through but the air velocity (the speed of your breath) is really lazy inside the pipe. Don't believe me? Put your hand near the end of the pipes and repeat the test. You'll see that the smaller pipe moves air with a lot more velocity but the volume of air is less. Vice versa for the larger pipe: less velocity but a larger amount of air.

In an engine, at lower rpm levels, the exhaust gas isn't moving as fast so we try to promote the effective evacuation of exhaust gas from the cylinder by fitting a suitably sized pipe to the port to help keep the gas velocity up so we can get a clean incoming charge of air/gas into the cylinder. Now at higher rpm levels, the piston speed is much higher so as to help "push" the gas out, along with being "pulled" in a sense from exhaust pulses but that is another discussion, so we don't need the aid of the smaller pipe as much. Hence where a larger pipe is handy to help move the larger volume of air in this circumstance.

An engine is just a big air pump. We try to size the exhaust according to the rpm level we want the engine to thrive. Smaller pipes are going to help lower rpm cylinder filling but might (keyword might) hinder upper rpm performance. It all depends on other things as well. The same goes for upper rpm performance: a larger pipe helps move the larger volume of exhaust gas but the gas velocity suffers at low rpm as a result. It's a trade-off in a sense, but again, a lot more can effect proper exhaust performance too.

 

Pathfinder got it right. An optimum exhaust setup has NO backpressure while still maintaining the correct velocity and flow. The best way to acheive this is a very slight reduction from the engine to the end of the exhaust. That's why so many people (me included) have had excellent results from dual 3" Y'd into single 4".

 

Pathfinder got it right. An optimum exhaust setup has NO backpressure while still maintaining the correct velocity and flow. The best way to acheive this is a very slight reduction from the engine to the end of the exhaust. That's why so many people (me included) have had excellent results from dual 3" Y'd into single 4".