Intake / Exhaust mods for better MPGs

HI All,

Been looking for easy hardware changes / mods to increase fuel economy and I have been thinking of the following:

On truck diesel forums it seems like increasing intake air flow helps (maybe EGTs rather than more power / or economy) but I have read numerous posts here that say our intakes are pretty much optimal as is (of course assuming clean filters (stock not Oil and gauze filters) and snow screen). However, I was a little intrigued by the "Old Man Intake" pipe.

Is this pipe worthwhile in terms of actual MPG gains NOT for better sound or looks?

Secondly, I know reducing exhaust back pressure can help get better mileage so I was thinking of gutting the cat (I say gut rather than straight pipe since we have inspections in VA and a missing cat would be a no go).

I also saw a video where a man gutted a cat and put a straight pipe inside the now hollow cat....Supposedly this has better air flow since air runs in a tube rather than getting turbulance in a big chamber.

Anybody have real world results by doing these mods? How much gain was there?

I was thinking of a muffler delete but I really do NOT want drone since I mainly drive highway for hours at a time so quiet is a plus.

Most people do exhaust mods for the sound....I would prefer quiet but free flowing (or more free flowing than stock) to help with fuel mileage.

Any other suggestions would be helpful too.....

Thanks in advance for any and all help.

Andrew

Tune and nozzles, set timing at the green line using VCDS, run the pipe thru the kitty otherwise you create a huge resonance chamber. I run an Aeroturbine muffler, no drone and basically a straight thru muffler-has a nice tone. Also might have to play with the IQ to get optimal power and fuel economy.

Change trans oil, run synthetic engine oil.

Make sure tires are inflated, brakes aren't dragging, no roof racks, all the shields are in place etc.

Change thermostat and coolant sensor if heater output sucks.

Andyinchville1 said:

Secondly, I know reducing exhaust back pressure can help get better mileage so I was thinking of gutting the cat (I say gut rather than straight pipe since we have inspections in VA and a missing cat would be a no go).

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There are no visual inspections for our diesels in this regard in VA. I've had mine inspected the past six years with just a straight pipe from turbo all the way back to a magnaflow muffler. This setup does have a tiny bit of drone, so if you're looking for quiet just keep the stock muffler.

Everything turbovan+tdi said is great advice. I had an old thermostat hit me for several MPGs as the car doesn't warm up as fast or stay hotter (my needle would come off of 190 during the winter when sitting at a light or in traffic with the heat on). I have recently been averaging consistent 50+ with my new commute, no complaints at all.

adjat84th said:

There are no visual inspections for our diesels in this regard in VA. I've had mine inspected the past six years with just a straight pipe from turbo all the way back to a magnaflow muffler. This setup does have a tiny bit of drone, so if you're looking for quiet just keep the stock muffler.

Everything turbovan+tdi said is great advice. I had an old thermostat hit me for several MPGs as the car doesn't warm up as fast or stay hotter (my needle would come off of 190 during the winter when sitting at a light or in traffic with the heat on). I have recently been averaging consistent 50+ with my new commute, no complaints at all.

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I guess it depends on where you get it inspected...Tuffys service center here in town failed my truck for not having a cat since it was original to the truck (at the time I had no idea my old 97 Dodge with 5.9 Diesel had a cat but apparently it must have since I called the auto parts place and they listed a cat for it....I got it and hollowed it out before putting it in the exhaust...shame to do that with a new piece but I wanted every bit of performance I could get...plus they would be looking for a cat when I went back to get my rejection sticker replaced by a valid sticker.

On the flip side my other dodge has a 4" straight pipe and it passed inspection (I did use another shop for it in light of what happeed at Tuffy...they passed it no problem....they even commented how nice it sounded with no muffler....this truck was older than my 97 so maybe it never had a cat to start with (it is a 93 model).

Question tho for my Jetta....Im running the stock ectaust....If I gut the cat and NOT put a pipe inside the case (to make it into a resonator) can I then remove the muffler and NOT have drone since the empty cat case would act as a resonator?....I have read in other posts if you remove the muffler and basically straight pipe it otherwise you have drone but that drone can be eliminated by a resonator...in this case an empty cat...

I was basically trying to low buck mod what I have currently to save $$ since my exhaust is in really good shape still and I already popped $$ for LED lights and a Tune.

I WANT to hit 50+mpg ;-).....I drive alot of highway but typically get only about 48.5 MPGs....I got 51 once on a trip to NYC but that was basically ALL highway so I guess I can do it ...I just want to hit it more often.

Thanks

A hollow cat isn't a resonator, without a muffler, it will be loud. If you to, just remove the cat and leave the stock muffler, that works perfectly fine.

The exhaust helps but the other things listed are better towards mpg gains.

Thanks for the input...

I'll take a closer look at the exhaust this weekend if it doesn't rain (I have no garage or cover).

My guess is Ill sawzall the cat out (unless it is bolted in but I guess that is wishful thinking) to make hollowing out easier and undetectable (hollow out from the ends or cut access panel on the topside and hollow out and seal back up)... then put the empty cat case back in.

Then I'll try a muffler delete (and use a pipe to carry the exhaust out from under the car to prevent another chance for droning to form.....

Which is the best way to have the exhaust pipe exit the car....Factory way?...Straight out the back past the bumper (or flush with the end of the bumper)...Out the side?....Other options?

I'll leave the cat internally pipe less at the point to see if it helps to prevent drone with the muffler gone and the cat hollowed out.

If I get drone at that point I guess the dilemma is whether to put an internal pipe inside the empty cat case or simply put the muffler back on....I guess I could cut a section of pipe to see what a straight through pipe would do so as not to have to weld a pipe inside the cat case then maybe have to try to take it back off if it dose help with droning...

I guess it'll be some interesting experimenting....A lift would be very helpful but I guess we'll have to do it the hard way!

Andyinchville1 - If MPG's is what you're aiming for, don't bother with intake/exhaust modifications in my opinion. At the engine operating conditions that you're looking to get MPG's, there's relatively little air flow so the intake/exhaust don't pose any tangible restriction. Unless your air filter is clogged or your cat is plugged, doing any of this won't help at all.

Run a higher temp thermostat (200-205F), low viscosity engine oil (0w40), low viscosity transmission fluid (Redline D4, VW G070, etc), low rolling resistance tires, block off all frontal areas of the upper, middle and lower grilles, insure your cam timing is straight up to a little advanced, run a tune with advanced injection timing, will all provide more MPG benefit than intake or exhaust modifications.

If you decide to do this anyway, run the exhaust pipe out the back flush with the valance or put a turn down on it pointed out 45 degrees tucked up under the car.

Listen to FUB.

You'd see a bigger gain in mpg by increasing tire pressures and slowing 3mph everywhere versus exhaust mods. Exhaust/intake mods for fuel economy are a total waste of time/money, IMO and would likely never pay off. Driving style is the single most influential factor for great fuel economy, followed by FUB's list and others.

Look into Snow Performance's water menthol injection also

FXDL said:

Look into Snow Performance's water menthol injection also

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Thanks for that....I almost (well did) forget about that possibility.

Is anybody here using this?

I even saw where Snow's makes on custom for our TDI's

http://www.snowperformance.net/product-p/45005.htm

I may make a separate link to see if anybody on this forum is doing methanol injection .....

Click on the link in nicklockard's signature for all you'll ever want to know about W/M injection.

Fix_Until_Broke said:

Click on the link in nicklockard's signature for all you'll ever want to know about W/M injection.

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Well its full of mostly theoretical discussion, so might not be the best place to start for practical. But I have noticed the 335D guys are bonkers for w/m, and many have sworn they see fuel economy improvements. I suspect compound turbodiesels benefit more from w/m. If you want to know too much, read my thread and all the links, lol.

nicklockard said:

Well its full of mostly theoretical discussion, so might not be the best place to start for practical. But I have noticed the 335D guys are bonkers for w/m, and many have sworn they see fuel economy improvements. I suspect compound turbodiesels benefit more from w/m. If you want to know too much, read my thread and all the links, lol.

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Actually I did read through lots of posts dealing with water / Meth injection and was hoping to find a user who was not necessarily performance oriented but more MPG oriented to see if water injection helps with cruising fuel economy....I'd ask the sellers of the systems themselves but somehow I think they'd be a little biased....

Anybody out there have real world MPG results after adding water / meth injection....from the standpoint of trying to get MORE mpgs NOT trying to hold down EGTs because of serious fueling as in racing or towing?