Author Topic: Fuel Economy mods (Read 7169 times)

92Wolfsburg · « **on:** October 26, 2007, 06:34:37 pm »

Hi all, I just bought a 96 AAZ Jetta and plan to put some serious miles on it. It has 240,000kms on it, is in really nice shape and seems to be well maintained. On my drive from Toronto to Thunder bay, I averaged 5.6L/100km or 42mpg (US) - thirstier than the 92 Wolfie. Understandable seeing as its a bigger engine and has air conditioning and power steering. The car is probably heavier too.

90% of my driving will be on the hills and twisties of the north shore of lake superior.

Other than the usual wheel bearings and tire pressures and not driving like I stole it and stuff, what can be done to improve the fuel economy? Most of the threads I've read dealing with turbo/inj. pump mods are focused on increasing power not increasing fuel economy, although I'm sure some of the mods will accomplish both.

I do not have to worry about sniff tests where I live, but I dont want to do any mods that will effect reliability/durability of the engine.

Fuel: I currently run Huskey DieselMax with 1-2oz of Power Service fuel conditioner per tank. Anything else I can do with the fuel to improve economy?

Tires: Will be purchasing new winter tires soon and plan to go with the narrower 185/60/14 instead of 195/60/14. Narrower tires = less resistance = better fuel mileage right? For summer tires I plan to get hard compound touring tires.

Turbo: I can't even hear it spool up on this thing! On the MKII you can tell when the turbo is performing. Will increasing boost increase fuel economy or will it just suck more fuel in?

Intercooler: Has anybody noticed a difference in mileage after installing one?

RPMs: 105km/h in fifth is roughly 2700rpm. If i put taller tires on the front, say...185/70/14 the rpms should drop a bit. This may work in my favour on the straights but will it work against me when going uphill? Too much load on the engine?

Fuel Pump: I probably wont touch the pump for a while but I'm sure theres many things than can be done here.

Again, I'm not looking for any more power out of this thing, I'd just like for it to be as efficient as it can be.

Oh, and I run Castrol Syntec 5W40 for VW Diesels, with a fresh air filter every two oil changes and a fresh fuel filter yearly.

What have you done to improve your fuel economy?

Thanks for any input!

spencebm · « **Reply #1 on:** October 26, 2007, 07:23:53 pm »

lots of air in the tires, make sure your car is as light as possible, no dead bodies in the trunk haha, clean injectors, lots of air flow in and big straight pipe out the back! the intercooler helps a little too. just keep your foot out of it. good luck!

spencebm · « **Reply #2 on:** October 26, 2007, 07:28:39 pm »

big bumper mk2's for life!

92Wolfsburg · « **Reply #3 on:** October 26, 2007, 07:36:59 pm »

Yeah I guess I could pull the cat out eh...
Will MKII downpipe/exhaust components work on a MKIII?

Oh, and can the injectors be shimmed for economy or is the best economy reached with clean stock ones?

andy2 · « **Reply #4 on:** October 26, 2007, 07:40:02 pm »

In short the answer is no :wink:

subsonic · « **Reply #5 on:** October 26, 2007, 07:52:30 pm »

I remember reading here that a lower breaking pressure- somewhere in the mid to upper 140's had a benificial effect on performance and economy. Timing would have to be adjusted . It's in here somewhere. Perhaps someone else can chime in who read it.

Jim

92Wolfsburg · « **Reply #6 on:** October 27, 2007, 09:26:37 am »

How 'bout the tires? Anyone notice a difference after going to taller tires?

Black Smokin' Diesel · « **Reply #7 on:** October 27, 2007, 12:06:41 pm »

Get some rebuilt injectors with a breaking pressure of 130bar and set timing to 1.05. That should increase mileage a bit without any loss of power. The lower breaking pressure makes for less pumping losses and there is no hard evidence that the lower breaking pressure means less vaporisation when injecting.

You could also add some undercarriage cladding to decrease drag. I read an article about a guy who added plastic sheets under the car where the engine is and got something like a 10% increase in mileage. I think it's worth trying.

Edit: Found some interesting articles.
Part 1
http://autospeed.com/cms/A_2455/article.html
Part 2
http://autospeed.com/cms/A_2456/article.html

spencebm · « **Reply #8 on:** October 27, 2007, 03:37:10 pm »

the bigger the tires and wheels the better, i run some 14" teardrops and thin and tall tires like you said. It would probably be better to have bigger, lighter wheels and shorter sidewall tires to look cool and make the engine turn slower...

clbanman · « **Reply #9 on:** October 27, 2007, 05:26:09 pm »

Well, bigger is not always better. Say you put a set of 22" rims on, your rotational inertia and mass would be so high that you couldn't accelerate. This is one big reason that some of the ricers that sound so fast and have huge rims can't actually pass anyone. I remember one test in a magazine (I believe Sport Compact Car) where they dropped quarter mile times substantially by removing their aftermarket "dubs" and installing the stock rims. Unsprung weight is a problem as well for handling. You need to look at the type of driving you do. If you do long steady state runs, you can get away with a larger set of tires/wheels. The flywheel effect won't really hurt you all that much. If you are constantly accelerating and decelerating, get the lightest tire/rim combination you can find. The closer to the hub the weight is, the more you can get away with. If you're going to extremes, weigh the tires you are considering before you mount them. The less weight you have to the outside of the tire diameter, the better your acceleration will be. (Your brakes will also spend less effort slowing the wheels and more slowing your car.) For optimum fuel mileage, you want your engine to be in it's most efficient range for as long as possible.

I tried a set of 195/70-13's on the front of my 1.6 NA Golf instead of the 175/70-13's, and there seemed to be a slight increase in fuel mileage, but nothing I could quantify with complete certainty. The difference (about 1-1.5 mpg IMP) was small enough that it could have been due to other factors.

spencebm · « **Reply #10 on:** October 27, 2007, 06:16:37 pm »

i was assuming of course that no one puts dubs on their dub! i personally wouldnt go any bigger than 15's or 16's because of acceleration loss like you said.

92Wolfsburg · « **Reply #11 on:** October 28, 2007, 07:44:39 am »

Nice posts, I'll try the 130 injectors for sure.

This car (96 AAZ) actually has a big plastic shroud that covers the engine from underneath. It keeps everything nice and clean, but its a PITA when it comes time do do the oil filter!

In the summer I think I'll try a set of 195/70/14...so another 10% taller. I'm sure the narrower 185 tires would be better on fuel but if I'm increasing the diameter I should also increase the width to keep handling somewhat normal.

madmedix · « **Reply #12 on:** October 28, 2007, 08:24:49 am »

Actually, the skinnier tire will help you in the snow. But stay away from the steel wheel to reduce the unsprung weight. Find some aluminum or aluminum/magnesium "dingers" that still balance well and seal the tire normally at a garage sale or some such. Added up over 4 wheels and you can save pounds depending on what you get. That also translates into longer lasting brakes...

Andy

Ziptar · « **Reply #13 on:** October 28, 2007, 10:50:54 am »

You can get 4x100 15" Steelies from Impex http://worldimpex.com/parts/genuine-part-wheel-disc_54110.html Corrado Steelies $70 each.
Details and pics Here, http://forums.tdiclub.com/showthread.php?t=151192[/url]

92Wolfsburg · « **Reply #14 on:** October 28, 2007, 05:02:21 pm »

Just looked at my car, dont think the 195/70/14s will go. I'm planning on buying my snows from here http://www.discounttiredirect.com/direct/findTireDetail.do?c=2&sw=true&cs=185&pc=11206&rd=14&ar=70 but I wanna make sure they'll fit without rubbing first.

Anybody running 185/70/14's on a MKIII? Hows the clearence?

Anybody running any larger than normal tires? If so what size? I'll do the math to see what the diameter is.

I wish they made these tires in a 185/65/14!

Thanks for the input.

Author Topic: Fuel Economy mods (Read 7169 times)

92Wolfsburg

92Wolfsburg

andy2

92Wolfsburg

92Wolfsburg

92Wolfsburg