# Which TDi mods increase mpg?



## 76 Golf GTi (Aug 24, 2001)

I am a newbie to diesels. It seems chips increase both hp/tq and fuel economy. I assume bigger injectors used properly







decrease fuel economy. What other typical mods increase or decrease fuel economy? If you get bigger injector and a chip is your mileage better while normal driving and worse while spirited driving compared to stock? Thanks in advance. Hope this made sense.


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## GoFaster (Jun 18, 1999)

*Re: Which TDi mods increase mpg? (76 Golf GTi)*

Very little can be done to improve fuel consumption by much beyond the stock arrangement. *BUT* your thinking concerning big injectors isn't correct.
The closer you can get all the fuel injected all in one shot just before TDC, the better off you are in terms of efficiency, and that setup requires BIG injectors and SHORT duration. If you put in the big injectors, the shorter duration (under cruising conditions - not at full load) will come by itself.
Chips don't change the way the engine operates at part-load conditions. Usually there is no change in fuel consumption. It's a little optimistic to expect an improvement from this ...


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## Gern_Blanston (Dec 12, 2002)

*Re: Which TDi mods increase mpg? (GoFaster)*

The best mileage (stock) came from the euro 110 rotary pump engine, which is very similar to our US 90 hp except for bigger nozzles, so bigger injectors don't necessarily cost you efficiency if you can keep your foot out of it. A biggy with these cars is tire pressure. I picked up a solid 3 mpg when I bumped the pressure up to 42f/40r. Other than that, it's all technique. It's a fun game to play, so have a good time.


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## oldmanTDI (Feb 27, 2002)

*Re: Which TDi mods increase mpg? (Gern_Blanston)*

right Gern, MPG mods are:
tire pressure
alignment
Energy tires or even better conti touring tires which have low rolling resistance and very good grip unlike the Energy.
for sure the stock tire size is the best and you lose a little by going bigger, I have 225 45 on 17 inch rims contitorung and they are -1.5 to -2.5 MPG
bigger injectors I like the 190 bar setup .205
shift below 2000 rpm, keep you foot out of it, coast a lot.
Then the iffy mods:
clean intke track and filter
no muffler
downpipe
no ccv,
disconect the EGR or be like me and run the eruo non cooled EGR
11mm
Amsoil 3000
chip or bump you injecton 2 degrees via vag com
now really iffy:
propane
water injection
water methonal injection



_Modified by oldmanTDI at 9:55 PM 2-23-2004_


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## Gern_Blanston (Dec 12, 2002)

*Re: Which TDi mods increase mpg? (oldmanTDI)*

Oooooh... Mod I hadn't thought of... Non-cooled EGR...
Not too expensive? Not too difficult?


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## 76 Golf GTi (Aug 24, 2001)

*Re: Which TDi mods increase mpg? (Gern_Blanston)*

A mod you didn't list for me, but I think (hopefully correctly) that would aid to better mpg would be lowering the car e.g. Eibach etc. That should decrease that aero drag, right? Maybe right? Anybody?


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## Gern_Blanston (Dec 12, 2002)

*Re: Which TDi mods increase mpg? (76 Golf GTi)*

I don't think lowering'll help. These things already have some underbody aerodynamic equipment.


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## oldmanTDI (Feb 27, 2002)

*Re: Which TDi mods increase mpg? (Gern_Blanston)*

rigth and the car is too low, you might look into aero mods like I have:
chin spoiler (not on cause it gets wiped out)
Zender trunk spoiler
rear window spoiler
These are spoilers not wings etc they are made to even the flow, you can check out a Civic Hybrid to get an idea of the aero mods, do they work? dunno every little bit helps plus it looks good not bling bling at all, and if they think it is all bling, I carry some backup under the hood.


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## mgwerks (Jan 5, 2004)

*Re: Which TDi mods increase mpg? (oldmanTDI)*

First of all, LOL at Oldman's (something extra under the hood)! I'd love to drive 400 ft/lb of torque!
My 17's are with 1/3" of stock dia. I am sure it is an MPG hit, but not much. I run 42psi rear and 40 psi front. Why? because as an old VW/Porsche driver, these things understeer way too much, and until I get a rear bar, this will have to do.
As far as lowering to improve mileage, my New Beetle is actually *raised* 2"! And it has a 30 lb steel skid plate under the engine/transaxle. My mileage did not change after these mods.
The rest is all spot on. My EGR was garotted via a VAG-COM setting. CCV mods will soon have cured the other ill. Still haven't heard a comparison between the .205 injectors and the .216 (actually .203) injectors. Smaller but has supposedly smoother flow.
Beware more than one power-type mod (injectors, chip, etc) or you will also be buying a new clutch soon. Remember, diesels do not work like gassers. Their entire power is controlled by fuel quantity, so all the mods like injectors increase the capability to deliver fuel, not the necessity of it. Keep your foot out of it, and mileage will still be fine.


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## 76 Golf GTi (Aug 24, 2001)

*Re: Which TDi mods increase mpg? (mgwerks)*

Let me see if I understand. Even though Oldman's car has awesome hp and tq comparatively, he can still get roughly the same mileage as an unmodded car if both are driven very efficiently e.g not much throttle, low rpm upshifts, coasting etc. Am I now starting to see the light or am I still off? Thanks in advance.


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## jck667 (Aug 3, 2001)

*Re: Which TDi mods increase mpg? (76 Golf GTi)*


_Quote, originally posted by *76 Golf GTi* »_Let me see if I understand. Even though Oldman's car has awesome hp and tq comparatively, he can still get roughly the same mileage as an unmodded car if both are driven very efficiently e.g not much throttle, low rpm upshifts, coasting etc. Am I now starting to see the light or am I still off? Thanks in advance.

I think you're getting there. IMO the best mod for mileage is the "driver mod" where you adjust your behavior behind the wheel.








WRT your other statements, some will argue that accelerating to cruising speed as fast as possible will help your mpg despite the common wisdom of "brick under the accelerator pedal".


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## mgwerks (Jan 5, 2004)

*Re: Which TDi mods increase mpg? (76 Golf GTi)*

Sure, he probably would get near stock MPG if his ride were driven sedately. You want the best mileage, learn to drive very _smooooothly_. Also known as the driver mod.
Using more *fuel* is what lowers MPG - this is directly connected to the right foot/throttle pedal interface. The nozzles won't give more fuel than the ECU is demanding, and all things being equal, (x)fuel = (x)MPH. I don't think most chips have fuel maps that alter delivery at the lower ranges, so essentially - you are the variable.
If you want mileage, mod and plod.
If you want fun, buy and fly!
Let me end this post by blatantly plugging http://www.tdiclub.com. This will be your single BEST resource for TDI anything.


_Modified by mgwerks at 1:45 PM 2-24-2004_


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## dmodderman (Feb 2, 2004)

*Re: Which TDi mods increase mpg? (oldmanTDI)*

>>shift below 2000 rpm, keep you foot out of it, coast a lot.
Do you mean upshift before 2000rpm when accelerating?? Doesn't that bog the engine and cause harmful stresses in the engine?


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## Gern_Blanston (Dec 12, 2002)

*Re: Which TDi mods increase mpg? (dmodderman)*

Just don't floor it below 2,000 or so. If you shift at 2,000-ish and give it just a little throttle, you'll increase your mileage greatly, particularly around town. It's just that a lot of folks don't like to be so slow and smooth.
As for Oldman getting great mileage AND 400 ft/lbs of torque: That's the neat thing about the diesels. No matter how much you mod 'em, they'll still get great mileage if you take it easy.


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## 76 Golf GTi (Aug 24, 2001)

*Re: Which TDi mods increase mpg? (Gern_Blanston)*

Which companies make wind tunnel tested spoilers we can use to decrease our drag and thus help mpg as well? I am guessing most TUV approved German shops, but at the same time kits like Rieger will worsen your drag. Any ideas?


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