this is probably still directed twords eugene, but does anyone think that a
4in. turbo back with a single 5 in. stack would flow more than a 4in. turbo back dumped behing the rear wheel. Im uncertain there is any gain one over the other at 310 hp.

 

I think the majority of what is going to determine the flow rate between those two is how many bends and what type of bends they are. If you are shooting straight up through the bed with only a singe 90 bend then going to a 5 inch stack, I would think it would flow more, course this is dependent on the amount of turbulance created at the transistion to 5in.

 

Trust me, it DOESNT matter.

 

I still haven't received my book, but here's a few things that I think relate to your question based on general principles. First, flow rate isn't the issue. If a given mass of air and fuel flows into the engine, an equal mass of waste exhaust gas has to flow out. The issue is how much Exhaust Back Pressure, EBP, is required to push this mass of waste exhaust gas along the tailpipe and out the end? More EBP reduces your HP, that's for sure, but the exact amount of reduction is TBD.

In general, a shorter pipe with fewer bends will generate less EBP than a longer pipe with sharp right angle bends like are required for stacks. Pushing exhaust gas up the stacks against the force of gravity also increases EBP, but the amount of increase is TBD.

Yes hot air rises, but my 15 years of messing with my smoky Vermont Castings wood stove convinced me that hot air rising has trouble overcoming the force of gravity. I don't know if there's an optimum diameter for a tailpipe to minimize the EBP, but I do know from personal experience that there's something like an optimum diameter for a flue pipe to help cure a smoky stove. In the case of the stove, a smaller diameter pipe maintains the flow velocity and gas temp all the way to the top, and this increases the draft to the stove. A pipe with too large a diameter will slow the gas velocity, and allow the gas to cool and get heavy before it gets to the top, and this increases the back pressure in the stove and makes it smoke.

 

i don't think that it matters which one you use, either way you don't have to worry about losing any power, if you do it most likely won't be enough to be seen even on a dyno. if you can dyno prove that a pipe exiting before the rear tire give more power than stacks, then i will believe it. i like the look of stacks better and trust me, my foot has no problem expelling the gases from the pipes. LOL

 

I just went from 4" dumping in the of the rear wheel to dual 5" stacks. It drives differently but you'll get used to it in about 2 minutes. Don't worry about it. Do what looks cool to you!

 

well, i like the idea, but if its not helping egts or adding power, its not worth the money to me, i can put the money in parts that will.
the reason i ask, seems all the trucks at the track, to include the fastest duramax has a single stack through the bed, but snow white has a turn out infront of the back tire, and the pulling circut truck and tractors run 18 to 36 in. of pipe through the hood, so I wonder, i know the shortest route would be best, and a stack is approx. the same length as a turn out behind the tire, the difference would now be turning into a 5 in. pipe instead of a constant 4in. out the rear. Now, i understand eugenes theory of heat smoke vs. gravity to include the intake= exhaust, so I have a 4in. AFE being sucked through a 3in. turbo inlet, and exhausted by a 4in outlet. I would think that at this point the intake and exhaust is
equal, but, once your putting 25 lbs. of preassure into the intake, seems that the exhaust may not meet the input flow. now, heres a thought, when you turn of the motor, the exhaust pulse takes a sec. to push the last exhaust note out the tail pipe, so, in essence, you could test the time difference between different systems
to see the idle flow difference or even run steady too 2000 rpm and turn off the ignition to see the time flow difference. i wonder if this test could show a semi-accurate exhaust flow rate between systems running similar engine mods being the lesser time would have a higher flow rate. hummmmm or does this not make sence at all.

 

That's what I was thinking after reading the first post. Out the side or out the top it isn't going to make a lot of difference.

A 5" exhaust is heading your way!
http://home.comcast.net/~kwikkordead/UPLOAD/Excellent_return.mp3

.

 

I'm going to see if I can do this test at Smokin, by testing my side exit tailpipe in front of the rear wheel, and then taping a piece of vertical 6" stove pipe with a right angle bend to the end of my tailpipe, and doing a second run.

 

That wouldn't be a fair comparison for what I would think to be obvious reasons Gene.

 

Keep in mind that they're two different types of flow. The MAF, lb/min, that goes into the turbo inlet plus the lb/min of fuel flow, are exactly the same MAF, lb/min, that comes out the tailpipe. Otherwise your engine would fill up with the lbs of stuff that didn't flow all the way through.

Since MAF=(AD)(VAF), and AD~P/T, and the exhaust T is higher than the turbo inlet T, the exhaust VAF, cfm, is much larger than the inlet VAF,cfm.

I plan on measuring VAF and T for various exhaust systems at Smokin. This will allow me to calculate MAF. I'm also looking into ways to make acoustic measurements using a microphone and digital recorder.

No one who's posted answers to your question here can possibility know if the answers they gave a correct or not unless they've made some measurements that they're not telling us about! The way science and engineering work, is something becomes a known fact only after many independent and repeatable measurements prove it to be so. Until that time it's only an educated guess at best, and usually just an opinion.

 

Ok, what obvious thing did I overlook this time? Maybe that most stacks have 3 right angle bends instead on the single bend I proposed?

 

Actually they have 4 if you think about it for duals. What I was getting at was the size of your pipe and the length at which you would turn it up. Not to say that wouldn't be useful info but not exactly a apples to apples comparison.

 

The way my tailpipe exists in front of the tire will allow me to attach the stack and tape it in place to the side of the truck, pretty much like an actual stack, but with only one bend. I'd use 5" dia pipe, but I don't think stove pipe comes but in 6", 8", and 10" size, besides are you suggesting that 6" will give more HP loss than 5"?

I'm open to suggestions here, and I'll need some help doing a quick install so I don't hold up operations. I figured I'd do the simulated stack as the middle out of the 3 runs you get?

 

I say do it. That ought to prove that there is a negligible difference right there on the dyno. I don't think you will see a big difference. Small enough, nobody will care.