Any Real Advantage To 4 Inch Exhaust?
 

My exhaust system is original, as is the rest of the truck, and I now need to replace my tail pipe and muffler. I have heard that going to a 4 inch system will improve my fuel economy, and increase my horse power. I just want to know if this is true. Since I have to replace half of the system anyway, this may be an option. I have talked to a couple of shops who say that this is really a waste of time and money. The other issue for me is, the noise level. My truck is a Ram 2001 with the 235 hp, and is normally quite loud, even without exhaust problems. ( No sneaking home late at night. You know what I mean ). A lot of the 4 inch systems I see driving around are very loud. Don't know if I really want my truck any louder than it already is. Any advice?

2001 Dodge Ram 3500 4x4 Dually. Unaltered Factory Stock. No Chip. 165,000 miles.

I never documented any increase in either HP or MPG.

I love the sound though.........

It increases flow to eliminate back pressure and heat. The stock system necks down to about 2.5 inches over the rear axle....

Cummins spec'd a 4 inch exhaust in the design, Chrysler put a non mandrel bent 3 incher in with a 4" tip.

You can add a resonator and muffler to a 4 incher to quiet it down...

Only real gain at stock HP ratings is a possible drop in EGT's...

easier breathing always helps. Not enough to make it worth scrapping a good system but if you have to replace most of it anyway and have the extra bucks, going 4" all the way through will make the turbo spin faster and overall exhaust temps go down.
Depending on how sensitive your butt is you may not notice a difference in performance but if you dyno before and after there will be an improvement.

Pulling my camper, seen an average 75 degree temp drop with the 4 inch. I upgraded due to road salt.

Aside from increased noise,I didn't net any change from the stock system when I went 4" on the '98.5.
What made a difference was an Edge EZ and boost elbow for more air.
I had a BHAF on it for awhile. Ditto on that. Cleaned the air and simulated an engine with COPD but I couldn't feel a seat of the pants increase in performance.

Hmmm. Interesting. I'm starting to think that going to 4 inch may not be the best route, especially with my wallet in mind. Thanks to all of you who replied so far. Any other comments are still welcome.

I was an advocate of the stock exhaust system being adequate until I installed my 4" system. Just to point out too.....the VP is crazy loud and the engine noise will dominate. A loud exhaust is generally not "loud" unless you're on the throttle but the engine will make quite a racket all the time. A good 4" system with a muffler will not be overbearing to most.

In saying that, the stock 3" system will flow fine without the muffler and leaving the resonator if the power is at or close to stock. I've had a straight piped exhaust on my truck for years with no issues. Its kinda "rappy" sounding but thats simply because of the smaller diameter. But after purchasing a large 5th wheel, I was dealing with overly sensitive EGT's while towing the behemoth size trailer. So I decided to invest in an exhaust system since it was really the only easy sensible thing left to do in trying to help those EGT's.

This is what I found out..... Its nothing outrageous by any means but the engine now feels more "comfortable". Sounds amazing and the EGT's are far more stable too, and I'm able to power into the hills harder and longer on the throttle. Again not a huge difference but definitely something noticeable for me. Did it up the power?.....I'm not sure but the turbo spools quicker and holds the boost more rock solid. That said, boost is a byproduct of the heat being generated from fuel making power so there has to be something going on as a result of gained hp. Again.....just to make it clear..... its not a huge difference but something noticeable for me. Matter of fact, one reason I know it added a little power was because within days of adding the exhaust before a camping trip my clutch started to slip. Without going into the details and explaining everything when and how, I'm positive and completely contribute the clutch slippage to the new exhaust, especially since my ability to hold more power in the hills.

So do I think a 4" exhaust is worth it?.....Absolutely. But is it necessary?.....no, not really and it depends on your power and situation.

Lastly, in the pictures below you'll see that even though the stock exhaust is 3", its not a real 3" system since the crimp bending of the pipe and smashing of the clamps narrowed it down to at least 2.5" in many locations. That was surprising to me..... :thumbsup:

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Just to add a little to the discussion.....There a e a couple must haves for these 24V VP trucks in my opinion.

Order of importance:
Fuel Pressure gauge
Lift pump R&R
Chargers decal on rear
Mandrel bent full diameter 4 " exhaust
Thuren trac bar (if 4x4)
Then the fun stuff ie injectors, Smarty/Edge/Diablo/BullyDog etc.
re-route puke bottle

Any reason why "Chargers decal on rear" is 4th on your list? [laugh]

My friend picked up mileage with new RV275 injectors along with his Van Aaken box back when he bought his 24v. Those injectors and the ancient box still work great.
I sprung for Mach 1.6's and an EZ on mine. Gobs of power but pretty smokey at high elevations.

I know, I know....that should have been at the top![duhhh]

I was skeptical until my stock exhaust system bit the dust from doing the Mojave Road twice. It was the 2 trips across Soda Dry (some of the time) Lake. The soda attacked my pipes big time. yes, I thoroughly pressure washed the underparts after the trips. The soda also attacked my shocks, bare brackets and leaf springs.
I had the 4" pipe and muffler installed and this what I noticed:
Engine runs cooler when you are not on it.
Turbo spools up quicker giving slightly more boost at lower rpms feeling like more acceleration power.
Very, very slight improvement in mpg. Almost none.
Exhaust sound is more throaty mostly because of the removing of the resonator.
But, as mentioned above, the NOISE of the engine trumps the noise of the exhaust system any day.