Join Date: Jan 2011
Location: Tacoma Washington
Thanked 51 Times in 33 Posts
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I don't think you will see ANY gains with a BHAF. You stock air filter & box are not a choking point with a stock engine, turbo & exhaust. I'm willing to bet the filter minder thing on top of the air filter box is still all the way at the top. Until you see your turbo sucking hard enough to start pulling that down (with a clean air filter inside), save your money to spend elsewhere.
A bigger exhaust and loosing the Cat will let your turbo spool a little quicker and let the EGTs drop faster after pulling a hill which will help.
I agree with the idea of the governor spring kit making it more driveable (or at least more fun to drive) especially when accelerating up to speed on freeway on ramps.
Moving the stock fuel plate forward will also give you some more power if/when you want it. this will not change mpg either way unless you start putting your foot into it far enough to use the extra fuel that would now become available.
I think a slightly bigger set of injectors would help too. With these diesels, makeing them more efficient makes for better economy (and more power if you put your foot into it). I don't have any first hand experiance with them, but I like the idea of having 7 holes in the injector nozzel instead of 5(which is stock), this idea keeps all the holes small for good atomization and spreads out the spray pattern better for a more complete burn. AND also allows more fuel to get into the cylinder when you stand on it!
The spendy item that I've heard local guys praise, is an aftermarket torque converter with a lower stall speed. which basically lowers your RPM's across the board. If you currently cruise 70mph @ 2100RPMs, that same 70mph will then be down around 1800RPMs, which is more in the peak economy band of the engine. Torque converters start around $700 and can go to over $1000 and that is just the part. If you are not going to put it in yourself add labor to that too. then since you have all the fluid out of your transmission you may as well change the filter in there and add new fluid.
Beyond that you have to start messing with the air-o-dynamics. Your miles per gallon will be higher at 55mph than the 75mph you mentioned due to the amount of air pressure working against the front of your truck.
If you search you will find other threads on here that talk about improving mileage.
a tapered top over the bed, as high as the cab in front and tapering down to the tailgate.
smoothing out the air turbulance in the front at the grille helps.
I've read that the lack of the factory, little rubber strip under the front bumper can cost you 1 mile per gallon. lowering the front skirt and adding side skirts reduce turbulance under the truck. Lowering the whole truck will have a similar effect.
smooth style wheels, like a pizza pan let the air slip by easier.
highway tread radials instead of off-road mud & snow tread cause less friction on the road (as does a good front end alignment) and disturbs the passing air less.
You have a nearly 7,000 pound truck that you are propelling around and it has a certain size that are conteding with. It is NOT a Prius!
have fun with your mods. please report back what your miles per gallon is now and what it becomes after each mod so others can see what mod had the most/best effect.
My trk gets me about 18mpg to and from work (non highway) and in the 14-15mpg towing a 28 foot travel trailer that weighs about 7,000lbs.
1997 ext cab 2500, 2WD, SLT, 5 gauges, #10 fuel plate, afc tuned, head studs, 60# valve springs, 5in exhaust. DDP 75HP injectors. timing 18*, 4k GSK, HE351VGT, 13spd road ranger trany, Home made twin ram style intake, sump drain with FASS fuel system
Last edited by drooling piston; 10-29-2011 at 02:10 PM.