Can too small (2") exhaust pipe / muffler cause poor performance?

[MechaNuts]

When I purchased my 06 it had a few kinks to iron out. One of those kinks is a previously installed muffler/cat delete done by someone willing to put a small pipe where a big one goes...kinda like Toyota guys,LOL. Anyway it sounds like a frikken honda over 4k rpm and pops and bangs like a ricer so this is enough to install new exhaust pronto. Which leads me to the question " is this why my Rubicon feels like a 4banger on accel"....
Ya see heres the deal...I had an 04 Sahara 4.0 4spd auto 3.55 gears and it would smoke this 6spd Rubicon hands down
Yes I know tire size and gear ratio make all the difference but I have experienced a 4.0 pull with 3.08,3.55,3.73, and now 4.10..all on 33x12.50 tires. Granted this is my first manual but I expected more umph with a 6spd vs 4spd auto and furthermore I have lower gearing and less drop between each gear so Yeah...whats the deal

To clarify I have no codes,all sensors are Mopar OE, plugs look great so injectors and coils appear to be fine. Throttle body has been cleaned thoroughly and IAC as well. Seafoamed it twice now and coolant flush as well. Holds temp at 210 sometimes 215ish with ac blasting when its 95deg outside

It just sounds like $#!t and pops and bangs out of that weird ass muffler and I cant help but think its a restriction to an already weak exhaust flow
I inserted a pic of just how big a jump it is. Looks like at least from 2.5 to 2 maybe even 1 7/8

 

[LONGJP2]

Looks like at least from 2.5 to 2 maybe even 1 7/8

2" ID wouldn't be too small. Especially if it's straight.
Maybe you should measure it.

 

[Jerry Bransford]

Exactly what size tires are on your 2006 and what axle ratio does it have? By the way 1997 was the only year that had 3.55, your 04 either had 3.73 or 3.07.

 

[ColoJeep]

2" ID wouldn't be too small. Especially if it's straight.
Maybe you should measure it.

If you had a 484 cubic inch V-8 , would you run 2" dual exhaust ?

 

[reddvltj]

Ya see heres the deal...I had an 04 Sahara 4.0 4spd auto 3.55 gears and it would smoke this 6spd Rubicon hands down
Yes I know tire size and gear ratio make all the difference but I have experienced a 4.0 pull with 3.08,3.55,3.73, and now 4.10..all on 33x12.50 tires. Granted this is my first manual but I expected more umph with a 6spd vs 4spd auto and furthermore I have lower gearing and less drop between each gear so Yeah...whats the deal

Yes the 6 speed manual has closer gear ratios between gears,.... but!!! that can be a drawback when you're talking about the torque multiplication gained in an automatic. with a lock up torque converter.. My 2000 Sahara with a 5 speed, 3.73s, and 30" tires wouldn't keep up with my 2003 Rubicon with the 42rle, 4,10s and 31s.. until it hits overdrive.. 5th gear in the Sahara can pull a steeper hill than the Rubi in OD with the 42RLE.

 

[ColoJeep]

Yes the 6 speed manual has closer gear ratios between gears,.... but!!! that can be a drawback when you're talking about the torque multiplication gained in an automatic. with a lock up torque converter.. My 2000 Sahara with a 5 speed, 3.73s, and 30" tires wouldn't keep up with my 2003 Rubicon with the 42rle, 4,10s and 31s.. until it hits overdrive.. 5th gear in the Sahara can pull a steeper hill than the Rubi in OD with the 42RLE.

I want to see a 4.0 drag race with a 5 spd. vs. a 42RLE both with 4.10's and 30" tires. I think I can guess the winner.

 

[reddvltj]

I want to see a 4.0 drag race with a 5 spd. vs. a 42RLE both with 4.10's and 30" tires. I think I can guess the winner.

Depends on who's driving the stick and how willing they are to tach it up to 4800+RPM before they shift...
First time I pinned the go stick to the floor in the Rubicon I kept thinking to myself... shift... Shift..... SHIFT DAMNIT!!!
At first I thought I had accidently put the shifter in 2nd not drive...

 

[reddvltj]

I want to see a 4.0 drag race with a 5 spd. vs. a 42RLE both with 4.10's and 30" tires. I think I can guess the winner.

Do you have a 4.0 with 4.10 and 30s? If so I'll be your huckle bearer... I have some 30's I can bolt on... Until it's new owner comes to get the Jeep they're on, that is!!!

 

[LONGJP2]

If you had a 484 cubic inch V-8 , would you run 2" dual exhaust ?

Not sure what your point is.
IIRC, the stock size is 2.25 and that's with non-mandrel bends.

 

[ColoJeep]

Depends on who's driving the stick and how willing they are to tach it up to 4800+RPM before they shift...
First time I pinned the go stick to the floor in the Rubicon I kept thinking to myself... shift... Shift..... SHIFT DAMNIT!!!
At first I thought I had accidently put the shifter in 2nd not drive...

RPM's are your friend in a Drag race! And even a Fuelie Rambler based six banger has a Rev limiter. 5000 rpm shifts drop you back into the sweet spot of the torque band.

 

[ColoJeep]

Do you have a 4.0 with 4.10 and 30s? If so I'll be your huckle bearer... I have some 30's I can bolt on... Until it's new owner comes to get the Jeep that is!!!

Damn it , now I know why I like you ! If you lived here I would swap my wifes 30" summer tires on my Jeep. Win or lose this would be fun!!!

 

[ColoJeep]

Not sure what your point is.
IIRC, the stock size is 2.25 and that's with non-mandrel bends.

The OP's likely non-madrel bent , 2" exhaust is a step in the wrong direction. A 4.0 doesn't need negative performance mods.

 

[reddvltj]

Damn it , now I know why I like you ! If you lived here I would swap my wifes 30" summer tires on my Jeep. Win or lose this would be fun!!!

Might have to plan a trip towards the end of summer... I need to get my a$$ in gear and get my DOT physical done so I can get sent out on some fires this summer and make some mad money!!

 

[Duck Doctor]

I have an 06 LJ rubicon with 6 speed and 94 YJ with the 4.0 and AX15. Both rigs are geared for 35s. The YJ will smoke the LJ Rubicon no problem. The 06 is a gutless pig and slowest of the eight Jeeps I’ve owned.

 

[MechaNuts]

Ok guys ill try and answer all of you...ill try.

Found out the last time I was under the hood doing maintenance I managed to booger up the intake pipe where it clamps to the throttle body. It was tucked and rolled under itself so air was sucking in there. Im not sure if that was really the problem though because I cant see that being "un-metered air" unless we are talking in terms of iat. it is pre throttle body and should not have been a real issue unless im missing something.
Regardless im starting to think I was just not using the skinny pedal enough and "afraid" to rev it out.

I measure the exhaust with calipers and found the following out... 2.5"od pipe welded in where secondary cat was before..then drops down to 2"od and into a walker quiet flow ss meant for a small passenger car that is definitely NOT the correct Walker qf-ss for a jeep.
I have a run of 2.5"i.d. and a couple of 9" resonators im gonna replace it with as soon as I feel like it.

I could totally be wrong about having "felt" a 3.55 ratio pull but I have driven a 97 wrangler on 33s..but I cannot confirm it had 3.55. I suppose then the 04 must have had 3.73 as it did pull out pretty good and was an auto.

 

[tr21triton]

I'm really trying to figure out this cat delete part. so is it still using 02 sensors without the cats ?

 

[MaximusLJR06]

Based on my experience between the 2004 Rubicon I had with 33's and my 06 LJR I have now on 33's, the 04 would smoke my 06 on acceleration. Main difference is my 04 was the NV3550 5 speed and the 06 is the NSG370 6 speed. My 06 is a dog and by no means is as fun to drive on the street as my 04 was.

 

[JustDandee]

Regardless im starting to think I was just not using the skinny pedal enough and "afraid" to rev it out.

Probably already know, but if you don’t, it has hard cut out on the rev limiter. Computer will keep it safe from over revving.

I will also share that this is my first 6 speed, I found when cruising about and you Want to GO! That extra gear, close ratio, I need drop down two gears. Meaning if I am in 5th gear at 2000 ish rpm ….skip 4th, go directly to third for some zip.

Aside from that slight tweak, on 33’s myself, this 4.0 scoots.

 

[bluescapegoat]

If you want your Jeep to go fast the biggest issue with the 6 speed is you can't shift them fast. Synchros no likey. You spend half your time between gears. I love the 6 speed but that's the truth. And I think people trying to drive them like civics is why so many of the 6 speeds grind between gears.

As for this popping and banging... Makes me wonder how they did a cat delete. My 05 is catless at the moment, there's more than one way to go about it. But if your Jeep is stuck in open loop then I believe that will defeat the fuel cut on over run and you're also running too rich. That minus the cats in place equals pops and probably a slight lack of power.

When I was messing with the timing retard on over run I was able to get my TJ to shoot flames for shits and giggles. Just like those ricers lol

 

[tr21triton]

If you want your Jeep to go fast the biggest issue with the 6 speed is you can't shift them fast. Synchros no likey. You spend half your time between gears. I love the 6 speed but that's the truth. And I think people trying to drive them like civics is why so many of the 6 speeds grind between gears.

As for this popping and banging... Makes me wonder how they did a cat delete. My 05 is catless at the moment, there's more than one way to go about it. But if your Jeep is stuck in open loop then I believe that will defeat the fuel cut on over run and you're also running too rich. That minus the cats in place equals pops and probably a slight lack of power.

When I was messing with the timing retard on over run I was able to get my TJ to shoot flames for shits and giggles. Just like those ricers lol

kinda what I was thinking about the cats. if removed I dont see how there's not a code being thrown. but I dont know a lot about deleting cats thats why I was asking !