I have a stock truck except for an exhaust brake.

My local performance shop swears i will get a 15% - 20% power boost by going to 4" exhaust from the turbo back and removing the catalytic convertor. Lots of guys say otherwise. What's your experience?

If you use a lower restriction air filter like K&N, then shouldn't there be a bit more power available?

BTW I read somewhere that Cummins does not recommend the K&N air filter with this truck - anybody had any problems with it?

 

More air (in or out) doesn't make more power in a stock diesel - a stock diesel operates with excess air by design. More fuel makes more power. When you do add more fuel, then more air helps to burn it efficiently and cleanly with lower EGTs.

Rusty

 

I think that is probably inacurate info. A 15-20% increase means around 36-50HP. If that was true then EVERYONE would be running 4" exhaust! The reason guys change the exhaust is to lower EGT's and or make more noise. By lowering EGT's you can add more power and keep the EGT's more in the safe zone. Same for changing the air box system and for getting a larger turbo. The more air that can get in and out of the motor the better. You get power by adding fuel and changing timing. But huge is not the solution either. Going to big on the size of the exhaust will cause the exhaust to cool to fast and become more dense, slowing the flow and causing a restriction, possibly lower performance. You have to match the exhaust size with the power output of the engine. Lots of guys just remove the muffler cause its cheaper and does the same thing, plus you really dont need a 4" system untill you get around (I think) 400hp. I'm pretty sure you can run a 4" and still run a muffler while getting the same results as a straight 3". Also you dont have a catalytic convertor. It called a resonator and all it does is stop any resonating, and muffle a little. As for K&N, guys use them with great results and no Cummins does not specify K&N as no good. I hear the real problem is the stock air box is prone to leaking unfiltered air. Sounds like your perfomance shop isnt smart to the Cummins or any diesel. This is the place to ask opinions.

 

After I installed 4" on mine I noticed the following:
- just normal driving no towing slight decrease in MPG
- towing, seemed little better power, quicker spool up, significant lowering of engine temperature (aircraft propeller ran less) and slightly better MPG.

I have not figured out why this is yet. But, I suspect with the 4" it reduces backpressure in the exhaust and at low load reduces efficiency of the turbo until there is enough exhaust gas volume to raise backpressure pre turbo. Probably would not be as noticeable on an HY as an HX.

 

yannick,

As much as I would like to be able to say that's for real ( we sell exhaust so it would reallyhelp sales) it isn't! You will get 20-25 HP and 30-35 lbs of torque but unless you have a way weak truck a 20% increase is optomistic at best.

What you will get is a quicker spooling turbo, lower egt's, better sound and the ability to add other HP mods safely because the exhaust will keep EGT's lower and safer.

Call us if you need any questions answered, by the way install it yourself and save yourself some green stuff, our Dodge kit uses 100% welded factory location hangers and is way easy to do in the driveway.

Mark @ DPPI

 

Tell them you want it in writing that you will get a complete refund and you get to keep the exhaust if you don't get what they claim. From my experience, there is no difference in power by going to a 4" system.

 

For what its worth, my truck was Dyno'd before and after the installation of a 4" muffler back exhaust and K&N filter in the stock box. HP went up 6.4%, torque increased by 11.8%. No pump tweaks.

 

hey yannick,,,for about 30 bucks,,just remove the muffler and replace it with a straight pipe.leave the resonator on though ,it gives a really good sound thats not loud at all.it gives the feeling of loosening up the top end,,makes the truck not so tight running in higher rpms.its a good cheap mod for trucks that arent modified much..................bama

 

Removing the cat is worth it, by about 60k they are plugging and begin to restrict.
Only problem is your '02 doesn't have a cat. That someone told you it did would make me suspect anything they say when trying to sell you on a product.

 

other than needing earplugs, are there any serious drawbacks to just pulling resonator and muffler off----no pipe? or would the resonator make much diff as far as restriction?

 

I left the resonator and put a 4"piece where the muffler used to be. Not much in a resonator, basically straight through. Not as loud as a straight pipe and no drone.

 

I bought a 4" duel exhaust (from MBRP) and had it put on a few days ago. The only seat of the pants I can feel is in the mornings. Before the installation, the turbo spool at the first few intersections was slow, now it is much improved. I have not run an entire tank of gas yet to check mileage but I think it's going to be less. Maybe because my lead foot is looking for the extra hp and tq claims?

Cheers,
Ron

 

phox

 

Well I filled the tank up today and my mileage dropped to 16.5. I'm sure it's from the lead foot and not the exhaust.

I will be more civil on the next tank and report back. I usually get 19/20/21 mpg, just depends on how much hiway driving I have per tank.

Cheers,
Ron

 

Could someone chime in with noise variance between system.
I want the benefits of flow without the loud.