Improving mpg in Vw TDI
 

I have an 06 jetta tdi. I have increased the tire pressure in my car. The car is out of warranty now and I'm trying to understand a few things.

I was trying to find out if I went to larger intercooler if that would help mpg and the pep the car has? The other thing is changing out the muffler to something that's more high flow. I read elsewhere that adding a fogger (water methanol solution has worked well with the older diesel vws. I read some place that he was able to get 3-4 mpg with the fogger on his 98.

I haven't heard that intake or exhaust modifications as you describe will improve mileage. I suggest taking care of the easy things first, like a good thermostat and a clean air filter. You could find out if you can get a chip tune oriented towards economy, but the TDI engine is hard to improve.

You could focus more on the car itself, and work on blocking the grille, using a coolant heater, possibly adding a lower air dam....that's where I am currently focused.

As a diesel owner. may I suggest a some suitable easies.

I am UK based and therefore suffer the sub zero damp morning starts that kill fuel economy.

Therefore I can reccomend a grille block, it does three things for diesels.. it helps improve aerodynamic drag, it helps reduce the airflow over the engine which means improved warmup time, and a curious bonus I've discovered is that if you seal it in, it helps reduce heat loss when the car is parked. Thus the engine is a couple of C warmer in the morning. I strongly suggest blocking the UPPER part of the grille, not the lower part. It helps push air over the top of the car and helps in the parked insulation there... I've tried blocking upper and lower.. I've only had gains with the upper blocked. Do make sure you're not blocking off cooling to other components such as the gearbox

Tyre pressures you've done.

Mud flap removal bought me a couple of percent.

Weight reduction of course.

Adjust the nut behind the wheel.. let's assume you've done that.

Clean out the pipes.. diesels have dramatically higher air throughput that petrols.. if you've clogged pipes then that will hurt.. check your Mass Air Flow sensor and your Exhaust Gas Recirculation... which often get horribly coked up.

The exhaust will have diesel particulate filter (DPF) and/or catalytic converter, you MIGHT be able to delete these depending on local annual legal testing and what sort of control signals if any they chuck back... you might be able to chip the engine not to worry about the DPF.

Also take further a look around this site.. there are some excellent posts by someone else with a jetta.

Derek

Having a larger IC would be good, but the gains from replacing an existing intercooler with a larger one are much smaller than from adding one to a non-IC engine. IF you are going to do it anyway, then instead of replacing, plumb it parallel to the first - this will give you the best cooling and the biggest drop in pumping resistance, but still not worth it, neither price-wise, nor space-wise, nor weight-wise.

Improving your exhaust may give you better FE (Our Peugeot Diesel - Part 1 - The Exhaust), but then again it may not (New Muffler = Lost MPG's). A free flowing intake is good, as long as it's cheap and easy (1.9L VW/Audi/Skoda/SEAT Diesel Mod alert! :))

And an upper grille block is a must if you are going to be driving a turbodiesel efficiently. In my case, the engine never really got up to temp, even with a lower grille block, until I covered the upper grille and put some thermal insulation on the engine.

The intercooler is a big restriction on the TDIs, some people have measured a boost drop across it as much as 3 psi. An after market intercooler could help reduce this a lot. I doubt there is room to plumb a new one in parallel. There was a nice place selling an upgrade that had a nice write up showing pressure and temperature drop before and after the upgrade.( Found it http://www.tyrolsport.com/product_in...ynotesting.pdf )

I would go to talk to the people on some TDI forum about reducing exhaust restriction and maybe see if they have figured out how to improve the intake too. (Don't use a K&N style filter)

I would forget about a radiator block as I wouldn't want to risk engine damage. (I've encountered times when I needed as much cooling as I could get)

Diesels like it warm.
Mine loves the 195deg thermostat I put in it.
A warm air intake is good too, I've heard of people putting shrouds around the exhaust even.
Mine just pulls warm underhood air.
Opening the exhaust is good if it doesn't lower your boost.
Bigger injectors will give better FE. Tdiclub.com lists the combinations that will work for your model on their FAQ page.

All that aside, as UFO said, the VW TDI is hard to improve upon.
The cars aerodynamics however are like a brick.
Anything is better than factory, airdam, grillblock (upper not lower), skirts and a kamm or boat tail.

Actually diesels like cold air better. It results in a cooler combustion which looses less heat to the cooling system and puts the energy saved into moving the piston. It also allows you to pack more air in the cylinder which further keeps the combustion cooler. More air also allows for a more complete combustion.

The only thing a warm air intake helps on a diesel is warm up time. Other than that it just makes more NOx and reduces power and fuel economy.

Opening up the exhaust never hurts boost as it reduces back pressure allowing a bigger pressure drop across the turbine of the turbo. Of course on the newer TDIs the boost is limited by the computer, but this is still a win because the back pressure on the engine is less.

Bigger injectors usually give more fuel and more power not better economy.

If diesels like it cold, why do some big diesels have intake warmers ? I'll agree it depends on the engine and outside temp. Typically intake manifold temps below 50deg F are less than optimal.


Try unhooking your exhaut after the down pipe and let me know how the free running exhaust works for you. Everything has limits. That said, it won't be an issue if he stays with practial pipe size. I have seen trucks that run like dogs with dual 8" straight stacks.

The larger injectors alow the same amount of fuel to be injected in a shorter time. This causes more to be burnt while the piston is closer to TDC. These engines are individual solenoid operated injectors, not distribution pumps like ours. Totally different animal. They vary pulse width like a fuel injected gasser not stroke length like a dist pump system.

Big rigs have them to aid in starting and engine warm up. In figure 14 of this report http://aerade.cranfield.ac.uk/ara/1937/naca-tn-619.pdf you can see that fuel economy and power increase as intake air temperature go down. All the way down to 26 Degrees F. At -3 Degrees F there is some power loss at lighter fuel settings. The engine in this test was only 14.5 to one compression ratio so with higher compression ratios the peak power for the intake air might be at a lower temperature.
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Try unhooking your exhaut after the down pipe and let me know how the free running exhaust works for you. Everything has limits. That said, it won't be an issue if he stays with practial pipe size. I have seen trucks that run like dogs with dual 8" straight stacks.
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Actually I know people with engines just like mine who have run a straight pipe right out the side after the down pipe. It works great other than the fact its loud and against the law in most states.
I can't speak for the pickup trucks. They probably went with a turbo that is tuned for towing and max power that takes longer to spool.
Actually the whole idea behind the Diesel cycle is to keep the combustion stroke at a constant pressure. The closer you approximate this the more power you get per unit of fuel. Trying to get all the fuel to burn near TDC is like the Otto cycle which is less efficient.

[QUOTE=ConnClark;218634]Big rigs have them to aid in starting and engine warm up. In figure 14 of this report http://aerade.cranfield.ac.uk/ara/1937/naca-tn-619.pdf you can see that fuel economy and power increase as intake air temperature go down. All the way down to 26 Degrees F. At -3 Degrees F there is some power loss at lighter fuel settings. The engine in this test was only 14.5 to one compression ratio so with higher compression ratios the peak power for the intake air might be at a lower temperature.


It is still not an Otto cycle engine. The HP/FE gains are well documented. It is the same principles used in VWs 150hp race version and in Mercedees new Bluemotion (well they upped the injector PSI, but same result)