You Do Need 4" Exhaust

[Todd T]

your methodology is wrong

to perform a test like this you need to control the variables. you did not do that.



First. you changed the exhaust AND air filter in the same test. no-no



Second. a Dyno (which is where Joe D. and Lawrence performed their tests) should have been used. a slow shift or short shift could throw the whole test in the can. or a biased foot on the pedal.



I would also ask that you post this type thing in one place. jeez

 

[Ted Jannetty]

CONTROL THE VARIABLES

We do control variables, Engine temps, oil temps, trans, temps, weight, fuel, tire pressures, etc, and computer controled transmissions shift exactly the same every time.



You read more into it, we did all testing of components seperately.



Dynojet chassis dyno can not put enough load to properly test these items.



You will see very low boost and EGT on dyno compared to road.



Not everyone visits all sections of this message board.

 

[Joseph Donnelly]

The heavy roller NASCAR version of the Dynojet has more slugs (inertia) and does a better job than the standard one. DD has the heavy roller.



Expansion of hot gases drives the turbo, not backpressure. Try this: run along at 2000 rpm and read the boost gauge. Run 2000 rpm going up a steep hill and read the boost gauge again. Same rpm, same airflow, backpressure, and pumping capacity were present (because the rpm was the same) before boost is built. So where did all that boost come from--it didn't create itself! The gases are hotter from using more fuel to make more power. The expansion of the hotter exhaust gas causes spoolup. Sure the backpressure has increased because of the boost pressure, but that is an effect, not the cause.



I posted other stuff in the 12 valve forum under this thread. Overvalved cousins may visit that forum, but be prepared for some rough humor



Why not post this thread on all the forums? I'm sure the Sept. 11 forum really needs it too geez, put stuff where it belongs, please.

 

[MikeR]

I think this was an unfair comparison. And it is the same thing I keep sticking to when the 3" to 4" arguement comes up... FLOW,FLOW,FLOW. The stock junk muffler and resonator flow very poorly, so it is only obvious someone is going to see a drastic change in performance when going from the restrictive stock mufflers to a straight-through type muffler. With either a straight through 3" muffler or straight pipe 3", I still say you'll see the same turbo performance and egt drop as a 4" under a certain hp level.



To properly compare, the following exhaust setups should have been done:

-3" with stock muffler

-3" with straight through muffler

-3" with straight pipe

-4" with straight through muffler

I also agree about the truck and conditions used for the test. A stick shift truck can skewer results with a slow or bad shift. An automatic truck should be used, and preferrebly on a dyno because the load would be the same every time, and changes in wind resistance won't exist.



Case in point, a certain truck with a 3" straight pipe, dynoed 300hp/650tq. On the road it's egt's max out at 875deg (preturbo) and it has very fast turbo spool up (just as fast as any 4" setup).



So my arguement remains that under a certain hp level it doesen't matter which size pipe you have, it matters on the exhausts ability to flow.



-Mike

 

[Diesel Freak]

I think we need to define some terms



Backpressure: pressure in the exhaust system created by the restrictions in the exhaust system measured at the turbine outlet



Drive pressure: pressure in the exhaust manifold created buy the restriction of exhaust gas flow by the turbine housing.



Atmosphere: 14. 7 PSIA



Boost Pressure: intake plenum pressure



The turbo turbine in an impulse turbine not a reaction turbine as Joe Donnelly is suggesting. There are no fixed blades in the housing for the expanding gases to act on, and the turbine area between the blades does not axialy decrease to form a venturi jet .

And one more thing



BACKPRESSURE IS NOT CONSTANT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!







2000 rpm unloaded and loaded are two completely different things. Yes the same "pumping" ability is there, but this is not a static condition. Remember that all the O2 is not being used for combustion... . and that air is roughly 80% N2. Where did the "boost" come from?



Let's look at what happens when rpm is kept constant but load is raised.



Fuel is added, so more fuel gets burned, but no boost pressure yet. Exhaust mass flow rate rises. (intake air+combustion products) yes I am deliberately omitting temperature.





Exhaust mass flow rate out of the engine continues to rise as more fuel is added (more fuel and more O2 being used to burn it). Mass flow rate through the turbine housing MUST be the same as the mass flow rate out of the engine. Exhaust gas velocity rises through the turbine housing to compensate (smaller flow area) this restriction is why drive pressure rises.



The High velocity gas impinges on the turbine blades and cause them to turn..... the turbo begines to accelerate. Boost pressure rises, and mass flow rate through the entire engine rises untill steady state is reached.



oh, and for testing use a Mustang Dyno..... then you can load an engine as much as you want!



I almost toasted the one here in Hillsboro on my 3000 to 1500 full load run YEE HAA

38 psi of boost and 1150 for egt (the funny thing is that EGT is higher with the 4" than the straight 3") looks like I need MORE exhaust volume to fill that big pipe!

 

[QRTRHRS]

Humor

This subject appears to be heading in the same direction as a discussion on oil.



The reaction to that big ol' 4" pipe with a 5" megaphone on it is worth the purchase price. Especially, when you have a 12 valve blowing excess smoke in someone's face.

 

[SpeedBump]

It's all Greek to me...

Personally, I'm into the awesome sound and looks of the 4" exhaust. My truck's gonna be in here(fingers crossed) next week and my first plans have been to rip out the factory exhaust and install the 4". Then, I'm gonna drive over to my brothers house who owns a PSD and show him what a real truck sounds like.

On the other hand, if the 4" is going to rob performance from my stock truck, then should I hold off on that 'til more goodies are added.



Yea or Nay on the 4" in a stock truck?



Thanks!

Eric

 

[Diesel Freak]

Re: It's all Greek to me...

Originally posted by Red Baron

Yea or Nay on the 4" in a stock truck?

That decision is completely up to you. Your truck does not need it like this thread's title would have you believe.



if you do put it on, you will like the sound... and it will get even better as you bomb the engine.

 

[Boldt's Wagon]

Ted:



With your next before and after testing, get the following data.



Hit your 9% grade with the cruise control set at 60 mph. Then give us the computer reported mpg and the exhaust temperatures at your 4 points. This should be about 120 HP to the ground and about the value used when pulling a big trailer on the flats.



These are a constant output HP runs and will show the other side of the increased efficiency coin, increased HP or increased mpg.



There are more of us out here interested in increasing mpg than are interested in increasing noise or maximum HP.

 

[pcorssmit]

Originally posted by Diesel Freak

... oh, and for testing use a Mustang Dyno..... then you can load an engine as much as you want! ...

What kind of test do you do on the Mustang, ie how is it setup. A local shop here has a Mustang, but during a dyno event recently there were some doubts as to whether or not the trucks were getting enough load to build full power. The first runs done were acceleration runs, then a couple of constant speed runs were done (on the same trucks) which yielded higher numbers. Seems to me there is a better way...



Pete

 

[Diesel Freak]

We did a full load torque test. I brought the engine up to 3000 rpm in 5th gear, and had the operator of the dyno pull the engine down to 1500 rpm while I was feeding fuel to it to try and keep it at 3000 rpm. Talk about fun... I have never heard a turbo scream like that in my life. We were at 83% of the dyno's capacity

 

[Stefan Kondolay]

I had my truck around the 500hp range with no problems. When I changed my exhaust to a 3' performance muffler and eliminated the resonator my egt's drop by approx. 150 degrees. I have talked with several people with 4' exhausts and they lost about the same. I will go for 600hp with the 3' as I feel that the 4' is to big for my cubic inches and that it will be a waste of my money. We had a conversation with Mopar Muscle about the spool up times with the 4' system on his truck and he said that the 4' made a difference in spool up, but when we pointed out his time slips from the race track had said otherwise. Maybe the seat of the pants might feel a little different than whats actually going on. He also went from a factory 3' to your 4', so what would have happened if he had a performance 3' system? I know that I don't have any spool up problems other than I can't keep traction.

 

[Bigsaint]

Nice R+D, Ted, but I think I'll stick with this, courtesy Auto Wurks Diesel... .

 

[DieselB59]

Right on Scott!!!! Must be all that New Jersey Diesel fuel we're running... . even the four inch system's too small!!! Or maybe, just maybe, it's the guy who's turning wrenches for ya!!!!! Remember, we don't work on no stinking gas engines here Hats off to Ted for coming up with the time to put this one together for us. I personally am sick of hearing that these trucks run just fine on the stock system.

 

[Mopar-muscle]

scott , you need a better pic , thats to dark , at least on my puter , and can't see it , maybe one with a flame shooting out of it would help



chris , you may be sick of hearing it , but if its true and can be backed up then whats wrong with it ? other than its not helping someone sell a product that may not be needed for an individuals application ???

 

[Mopar-muscle]

scott , you need a better pic , thats to dark , at least on my puter , and can't see it , maybe one with a flame shooting out of it would help



chris , you may be sick of hearing it , but if its true and can be backed up then whats wrong with it other than its not helping someone sell a product that may not be needed for their application ???

 

[SpeedBump]

Diesel Freak

That decision is completely up to you. Your truck does not need it like this thread's title would have you believe.

Diesel Freak,



Hey, thanks for the reply. I really like the sound of that 4" and that 5" stainless tip just screams for attention



Thanks!



Eric

 

[DieselB59]

John,

Make some sense here. The only truth is that a 200-250 hp truck works with the stock exhaust. I agree with that and don't think that I said otherwise above. But... . how many of these trucks, INCLUDING YOURS, is using a stock exhaust and making that stock level power? I don't profit by selling exhausts. Frankly, I don't profit by selling anything. I'm there to make my customers happy. What they want I provide. If someone came in and wanted four, six inch stacks, I'd figure a way to make it happen. Doesn't matter what I think. What I think doesn't make the world go round or keep the lights burning late at night. It matters that the customer likes the way his truck sounds and feels after I get covered in rust, soot, and metal shavings working on his exhaust. That satisfaction is enough. And I still stand behind the facts that Ted Jannetty took the time to figure out. In this economy he actually took time out from business and did some old fashioned research, and backed it up with true measurements. He proved something we've been saying for years. Diesels like to breathe, both intake and exhaust.

 

[Ted Jannetty]

Big Saint; WAAAAAAAY COOOOOOL.



I love stacks, If I didn't need the cap on my truck I would have two like that.



Nice Job Autowurks!!

Thanks for the support.

 

[Bigsaint]

Mopar, just for you . . This is a pick of 'Ignition on-all systems go' .



edit... DOH !!! see below



Scott W.