Another update for the PT mod... Since I opened up the Dak airbox & found performance with the 2nd PT mod installed, I went over to the wifes Jeep Wrangler 3.8L & opened up her box as well. (Hers will never see deep water so no worries, plus the mounting pins on the bottom of the box are a design that drains any water in the box).

Performance wise on her jeep, It liked to downshift into 2nd at times where you would not expect it, that did not occur on the test drive. There is a grade near home that is pretty steep and IIRC the jeep struggled to keep 60 in 3rd. To my surprise, it held 67 in 3rd going up this hill. The pic below shows how the fenders are cut & act as a huge parachute. Additionally the concrete blocks she calls tires are way to heavy for the tiny 3.8L motor. But, she loves it and it will stay as is until she wants to change it.

 

Another update for the PL mod... took the wifes jeep out over the weekend for a follow up test drive heading into town... there is another steep hill on the route that the jeep likes to drop into 2nd... yeah 2nd... to maintain 60ish. This trip it easily held 3rd doing mid 60's. She reported a 13.6xx mpg (hand calc'd) on her last fillup last week, she is typically in the mid 12's. She had a whopping 27 miles on the odo since the fill-up so no idea yet how this tank will pan out. I am pretty sure we doubled her miles on the tank with the drive lol.

 

Another update... for the longest time now, (not sure when this started) there has been a very low amplitude thumping that only shows up at light load, part throttle. I assumed this was in the air box because of the 2.5" exhaust dump I'd been using to throttle airflow into the box. When I pulled the exhaust dump off the air box the noise I'd been hearing remained. So the next step was to smooth out the airflow into the box. Yesterday I did just that... and found more power. Nothing like what the PL mod did for the bottom end but noticeable. So I opened & closed valve on the 2nd PL for comparison & 100% stronger with the 2nd PL open & in play. That leads me to wanting to change the 2nd PL to a longer version to further experiment with.

What I'm still stumped on is the part throttle thump. I have always assumed this is turbulence in the air box and am now wondering if this is in the intake tube. So the next step is to create & experiment with a Helmholtz resonator off the intake tube port that is currently plugged and originally earmarked for the IAT sensor by design. While I am at it I will check on the turning vane that is in the intake tube elbow to see if that might be a contributor to the thump. Last time I had the intake tube off it appeared to be just like I installed it (no changes in location or bends under airflow). I once saw a video on a jeep intake tube design that indicated a performance bump with a Helmholtz resi on the intake. I am going to see if I can find it and will link it here.

MPG's last tank came in at 16.4 mpg, 100% DGAS tank with zero mpg considerations.


Video mentioned earlier was not a video... here is the link

Breathing Fresh Air - Intake R&D, Part 8: Final Design | Mishimoto

and after re-reading that article, it appears the resonator affects part throttle performance. I say that as the 1st dyno with no resi shows similar numbers to stock, yet the test driver complains of a loss of part throttle bottom end power.




and the final version restores the full output power but must make the part throttle driving experience better.





So next I will learn what I dont know about Helmholtz resi's in the intake tube.... and I still have not messed with the y-pipe & remaining exhaust.

 

Another update... did the research on the Helmholtz resonators on the intake tube and have concluded my potato launcher mod is actually a crude Helmholtz resonator. By adding a 2nd, shorter one onto the IM the pressure waves from the valves closing are being handled by the 2nd 12" PL tube. So the new plan is to make (or borrow off the wifes jeep) a 9" PL tube and test it out along with the 2 existing PL tubes installed. I now believe the thump is the pressure waves making noise in the IM & the 2 PL's installed are reducing the pressure waves for the higher rpms. Knowing what I now know, the plan is to install the 9" PL tube (total of 3, 1 ea 9", 12" 15") and see how the thump is handled and what performance does. If there is success there, then the plan is to add a 4th 6" tube and repeat the eval. The thinking is the low rpms would benefit the most with the shorter PL tube.

On another note, I am attempting to find out how the current setup is affecting mpg's... typically 110 miles at 3/4 tank gauge gets me mid 16's for mpgs. Currently I'm at 130 miles at 3/4 tank gauge so its an extra 20 miles. Gauge has been calibrated to match fuel pumped across the 24 gal tank size via HPT. Will be filling up at EOD Friday.

 

got 18.0xx mpg out of that tank.

Installed what I had for another PL mod, a 3/4" 22" pvc pipe capped on both ends & tapped into the vacuum line to one of the other ones. And again... performance changes. Unclear if its better or worse... its just different.

 

Took it out for a drive yesterday and played with the ball valve feeding 2 of the PLs. Did some freeway on ramp hard accellerations & a back road to the starting point. The difference in ball valve positions is noticeable (full open, half open & closed) and half was the clear winner.

Next up, a new engine to try this on... Sons 2014 hemi

 

Y-pioe install today...

not done... found the cat is on its last legs so might as well do the whole exhaust.

 

Magaflow makes a 4wd ypipe, ordered it today & will he here on 6/10, install possibly the following saturday. This pipe however has a 2.5" outlet from the cat, planned on 3" but like the mandral bent tubing and 2 piece install. Holding off on cat back exhaust for now.

 

I thougt the Y-pipe was a cat back exhaust Steven ?

I went from 2,5 to 3 inch after the cat, going too a Simons Free Flow Stainless muffler, over the axle to a 2.5 inch Free Flow muffler,
still have to make the last part duall, because i have 2 exhaust on the back, one isn't connected yet.

Reason why i made the dual exhaust with mufflers is i got them for free, and wanted to go back to 2.5 inch for better torque.

Don't know, or can't tell for sure the difference, before or after, but it's a little quiter when idling, so my neighbours stay friendly...

Greetz Ludo

 

The y-pipe comes off the headers... it is the center section between the headers & muffler

MagnaFlow 2000-2003 Dodge Dakota HM Grade Federal / EPA Compliant Direct-Fit Catalytic Converter

I measured the output of the OEM manifold & it was 2", the assumption is the JBA output is also 2". This pipe has 2" inlets off the headers & a 2.5" outlet out of the cat. The goal here is to see how much of a change, if any, there is with just the y-pipe. Research on the forums tells me there should be a change to a stock/slightly modded truck but... mine, with the efficiency updates, has gone well past what a typical CAI & tuner setup would do. I saw a video a guy posted on a thread where he filmed a high speed run from 0 mph. It was impressive to watch. IIRC he stated he had the HO cams & all the bolt ons, not sure of what his gearing was. So the other day I decided to beat on mine to see how it compared to his, to my surprise it is very similar & a tad bit slower in mph climb but yet still impressive... and this is with the restrictive y-pipe & stock exhaust. Recall this truck has 3.55 gearing with 265-75/16 E rated tires... aka boat anchors.

I may go find a spot to do a 0-60 run & log it with the Torque app before I do the y-pipe install... curious. One concern is the lack of a wide band O2 sensor to know what the AFRs are at WOT. That may hold me back. Needless to say, I dont go around flooring it everyday because of this, my limit is the STFT indicator on the Torque app & it not going to zero (assuming it is using the WOT settings at that point)

One other thing to comment on, the PL mod... the current setup has 2 1.5" pieces installed with a ball valve on the 2nd one (this one has a 3/8" vacuum line vs the 1st one attached to the brake booster) and a 3rd one I tossed in there for the heck of it to see if it would allow me to tweek the performance any (it did, which led me to install the ball valve on the 2nd PL), I played with the valve closed, 50%, 75% and 100% open & in every case there is a noticeable performance change in how the engine shifts & where the bottom end torque is. I settled on 50%, I get a good balance of bottom end torque & shift performance with this setup. Anxious to see how it will change with the y-pipe install.

I am not sure if I mentioned this but I also added a diverter plate in the air box to reduce turbulence from both sides of the air box, all this is is a piece of sheet metal cut to fit side to side reach up from the bottom of the air box to the filter. Recall I pulled off the 2.5" vacuum controlled exhaust dump off the air box & it is just an open hole atm (preferred with the bump it gave in performance). The goal there was to divide the airbox in to 2 sections, one where the oem inlet airflow comes from & the 2nd where the valve used to be. I've found all this adds up little by little to give me a ride that is fun to drive... even with the crappy gearing & boat anchor tires.