Isn't 3" piping better than 2.5" piping on these trucks????

[Skyydiver]

Curious Question….

Now that I have this "money pit", it is time to start working on the exhaust system. If I am correct, the factory exhaust system is 2.5" piping. So my question is this, to me it would seem with the amount of displacement of this motors (8.3L) that the truck would be better served with 3" piping all the way back. Obviously back pressure and scavenging of the cylinders is crucial, so much like carburetors, bigger is not always better when it comes to exhaust work.

I did a search before asking this question and I found one post where a gentleman said he lost power changing his mid pipes to 3" and doing the Magnaflow exhaust (which is also 3" piping). The loss was so noticeable, that he went back to the stock 2.5" system. But it seems like everyone else is up for the 3" mid pipe conversion and no mention of having lost power.

These trucks no doubt are very expensive to modify and I have learned over the years to do my homework thoroughly before investing in after-market "go fast goodies". So before I sink $700 into a set of JMB high flow cats (Austin has yearly state and emission testing) and 3" mid pipes, I want to make sure that I am doing the right thing. My truck is going to stay N/A and I will only be doing very minor upgrades (i.e.…Exhaust, some form of intake…still researching the 100's of post on this one, and DC Performance's Tuning Programmer once it is ready).

What are your thoughts, experiences, comments, suggestions on 3" piping vs. 2.5" piping? Any dyno testing or track times to show gains/losses?

Justin, Boomer, Dan…any input on this???? What has your testing shown?

Thank You,
Joe

(This elephant cracks me up... :elefant: )

 

[BigRed460]

#1 - You can go catless, get O2 sims. and it will pass, all they do is plug into your trucks obd2 port and read what the computer thinks, all you have to do is "trick the computer into thinkere that you cat are still there...

#2 - 2.5 will be fine, as long as you have a cat back, to get the full gain all you have to do is make sure the rest of you exaust(past the mids) is free flowing to...

#3 Your in austin, so you might talk to The Mopar Connection, he just moved to austin...

 

[hunter_angler]

There are a lot of factors to consider. For one thing, the factory exhaust manifolds have 2 1/2" collectors/outlets, so going to 3" plumbing behind them may not do much good and may even slow flow velocity to some extent, possibly effecting low-end torque negatively. Also, I understand that while the inlets/outlets on the Magnaflow exhaust are 3", the tubing narrows to 2 1/2" inside at the crossover, so it's not a true 3" muffler.

My exhaust is 3" from the collectors back, but lots of guys have had great results with the Mopar headers and midpipes, which I believe are 2 1/2", when they pair them with the Magnaflow or Mopar/Borla cat-backs. The bottom line may be that 2 1/2" is plenty big unless you have an engine with serious mods making serious horsepower and exhaust flow.

Aftermarket exhaust systems offer more advantages than just the diameter of the tubing. The midpipes are straighter than the factory setup, the cats are high-flow or nonexistant and the straight-through designs of the mufflers are less restrictive.

More extensive dyno and track testing of various combinations would be interesting. It seems that most folks gain peak HP going to aftermarket 3" exhausts, but I know of at least one guy who claims to have lost E.T. with B&B midpipes and high-flow cats behind his stock manifolds. Again, there could always be other factors involved.

Just my $.02.

 

[mmmmtorque]

I gained 18rwhp and 30ft lbs by replacing the stock mids with B&B mids w/HF's.

99% of the feedback on replacing the mids have been positive...its the best bang for the buck mod for these trucks

 

[hunter_angler]

I gained 18rwhp and 30ft lbs by replacing the stock mids with B&B mids w/HF's.

99% of the feedback on replacing the mids have been positive...its the best bang for the buck mod for these trucks

B&B claims a gain of 20 FWHP from the mids and another 19 from their catback so your independent results are almost spot on. My SOTP meter liked them as well. Just curious if they do much if anything to the lower end of the torque curve.

 

[rottenronnie]

I had been struggling with low(er) m.p.h. for several months, ever since I installed the 3" B&B Hi Flows. Trap speeds dropped at least 2 m.p.h. (20 horsepower) on the 3 tracks I tried it on. For the money I spent and looking at the differences in the B&B and the factory system, I had been trying to convince myself it was something else.

In my case, at our altitude, the 3" did have a negative effect on power. It was regained as soon as I reinstalled the 4 cat, 2.5" factory system. The lost torque returned when the velocity returned to "normal" and the m.p.h. is now back where it should be.

I have seen this before with headers, especially guys that go to even a slightly bigger primary, say from 1-5/8" to 1-3/4"- torque/h.p. in many cases drops but sometimes many other changes were also done at the same time, so it is hard to realize there was a loss. When header size was the ONLY change however, torque drops if they are outside of the range (too big) to correctly scavenge (rarefaction and all that other good stuff).

I would like to say primary size is critical on ANY engine. And apparently, so is exhaust pipe diameter coming off of the factory manifolds.
It is hoot to see 2" primaries on some of the n.a. Honda cars running around.

I would think that running closer to sea level or especially in forced induction apps; the 3" would likely be a better choice.

Ron

 

[Annu Kumar]

Ted May (viper tech) Is going to delete my rear cats And do 2.5 Inch piping along with the borla catback. He said he dose a lot of viper Cars the same way :dontknow:

 

[nycstev]

I upgraded to 3" HF and Catback on SC RC with stock manifolds. Did this on the advice of
manufactures. However I don't really have any documentation to substantiate any gain/loss :dontknow: :dontknow:

 

[Nowwhat]

big picture.................:rock:

mods work WITH each other....figure out your end game and build toward that....

 

[05viper qb]

just stright piping for me no cat no muffler

 

[Skyydiver]

Gentlemen, I appreciate all the candid responses...please keep them coming.

Robert, Justin, Gary, Dan....where are you guys????

My ultimate plan is to do a nice set of long tubes with some mid-pipe set up WITH HF cats and of course into a cat-back system...Magnaflow.

There is no discussion about the cats...I want them and I have to use them. I really want to keep the focus on the topic at hand and that is the advantages / disadvantages to using a 3" pipe over 2.5" pipe.

I am just having a hard time comprehending that an 8.3L motor (or 4.15L per bank feeding a single exhaust tube) making this kind of power, is suffeciently exhaling through dual 2.5" pipes.

I will use this as an example because I have dyno numbers to back it up...

Prior to owning this beautiful piece of American Bad Ass Muscle...I owned a 2006 Nissan 350z... These cars have a 3.5L motor. The factory set up is 2 x 2.25" piping that merge together just past the cats into a "Y" (2.75") configuration which fed into a single muffler and came out as dual tips. Just changing that set up to "true" dual 2.5" piping all the way back into dual mufflers netted a peak HP gain of 13rwhp and 11ft-lbs of torque. The bottom end of the RPM range also showed gains with no deficits.

This 350z motor redlined at 7,000 with peak power dropping off around 6600rpm. From what I have seen/read, our motors are about 1,000rpm less with respect to both of those of numbers. I mention this, because obviously with higher rpms, the more the motor is breathing and of couse, the more exhaust that needs to be expelled...but obviously, we are only talking about 1000rpm difference between the two motors.

So...with that said, our motors are approx 2.37 times bigger then the 350z motor, and yet, we are expelling spent gases through basically the same size piping.

I know that dyno testing and more importantly, track testing are the real determining factors here as to what works best for these trucks, that is why I am hoping some of our sponsors / testers / tuners will jump in here with their experience as well.

Thanks again guys for all the input. Looking forward to more in depth discussion on this topic.

Joe

 

[hunter_angler]

If you're going to go with any 1 3/4" longtubes you definitely won't need to worry about velocity and low-end torque because of the long primaries. I think you will see an increase with a well-designed 3" setup. RR is most likely an exception due to altitude as he mentions. The stock 2 1/2" 4 cat setup is dyno proven to be very restrictive.

It is interesting that you bring up the powerband issue. VT 2933 made the point the other day that even with a heads/cam buildup like his our engines really don't make good power past 5800 RPM. Intake limited most likely. This may mitigate somewhat the benefits of a bigger exhaust. None the less, 500 plus HP needs adequate airflow...

 

[Prof]

big picture.................:rock:

mods work WITH each other....figure out your end game and build toward that....

Stephen Covey says: "Begin with an end in mind."

Plan your work and work your plan...what is your goal?

Some have been very happy with no mods at all...and then there are the rest of us hp psychopaths...

 

[ViperTruck2933]

If you're going to go with any 1 3/4" longtubes you definitely won't need to worry about velocity and low-end torque because of the long primaries. I think you will see an increase with a well-designed 3" setup. RR is most likely an exception due to altitude as he mentions. The stock 2 1/2" 4 cat setup is dyno proven to be very restrictive.

It is interesting that you bring up the powerband issue. VT 2933 made the point the other day that even with a heads/cam buildup like his our engines really don't make good power past 5800 RPM. Intake limited most likely. This may mitigate somewhat the benefits of a bigger exhaust. None the less, 500 plus HP needs adequate airflow...

I'm not sure what the limiting factor is regarding the rpm drop off. PBJ ported my heads, larger valves, ported intake runners, ported the throttle body and installed the larger cam. Looking at the dynographs, the hp and trq both still fall off at 5800 rpms. :dontknow:

As far as the exhaust goes, I have Belanger long tubes and Belanger mids with high flow cats and Magnaflow catback. Belanger mids DO have a neck down to 2 1/2" to create the slip joint into the catback. Justin cut the neckdown off for me and welded in a 3" section to create a true 3 inch exhaust. This was done after my dyno tuning, so I don't know how much of a difference it made.

The Belanger high flow cats have almost no restriction. My truck is just as loud as a catless truck.

 

[nycstev]

The engineers designed the system to work with 2.5" pipe. Exhaust is more than an open door. Fluids flowing through a pipe will not flow correctly if the pipe is not sized right.
Ex; Waste leaving your house flows through a 3-4" pipe; Lets say you in crease the pipe to6-8-10? Eventually the waste would just sit there.

Cost is also a factor !!

Adding a SC to this motor is another story.It is the equivalent of adding another 150 Cubic inches. So in that instance yes a 3" pipe would be justified. Im sure a 650 CI engine from the factory would have came with 3" exhaust More air in= more air out

 

[nycstev]

What I dont get is this little ricer cars with 4" exhaust.. Im sure its just for looks?

 

[HOT RAM]

If the MagnaFlow is only 2 1/2" inside,would that restriction be enough to negate the effect of the 3" piping ? My theory would be that if it goes to 2 1/2" inside the muffler,then you shouldn't need anything larger feeding into it.:dontknow: I would think that the flow could only be as great as the smallest restriction in the system (which is 2 1/2" in the MagnaFlow) and anything larger couldn't help upstream from the restriction.:dontknow:

Just thinking out loud .Maybe an engineer should chime in ?

 

[ViperTruck2933]

If the MagnaFlow is only 2 1/2" inside,would that restriction be enough to negate the effect of the 3" piping ? My theory would be that if it goes to 2 1/2" inside the muffler,then you shouldn't need anything larger feeding into it.:dontknow: I would think that the flow could only be as great as the smallest restriction in the system (which is 2 1/2" in the MagnaFlow) and anything larger couldn't help upstream from the restriction.:dontknow:

Just thinking out loud .Maybe an engineer should chime in ?

I think the Magnaflow is 3" all the way thru. :dontknow:

 

[HOT RAM]

I think the Magnaflow is 3" all the way thru. :dontknow:

I don't know for sure,but I have read several posts stating that it is only 2 1/2" inside.I THINK Jack said this,but again,I am NOT sure.:dontknow:

 

[Prof]

I don't know for sure,but I have read several posts stating that it is only 2 1/2" inside.I THINK Jack said this,but again,I am NOT sure.:dontknow:

If I recall correctly, FstJack tore one apart and measured and found a 2.5 inch restriction in it...