'97 Passat TDI Build

[Arctic Fox]

I haven't read through this entire post (this site is not mobile friendly), but have you taped up the main and lower grills? Tape up all the seams (ex: between hood & fenders)? Folded back the mirrors? Antennae delete? Tire pressure to ≈45psi?

I did a similar test with fuel fillup versus milage driven, no scan guage, and got 75.9 or 79.5 on one drive from Albuquerque, Nm to Flagstaff to Prescott, Az (I-40 to I-17 to Hwy69). A lot of coasting and drafting the big rigs when they let me.

Still... Hate that car! Will never go to Germany for vacation!

[Caddylackn]

Following Summary Mods done already, see start of thread for build:

Roof rack delete
antennae delete
passenger mirror delete
passenger wiper delete
Driver wiper deflector
tires to 41 psi
Full lower grill block except intercooler opening. upper grill stock, upper grill doesn't have many grill slots anyway to plug
Full undertray with supports. Undertray smooths into the rear diffuser, except 15" by 30" section of undertray is cut away from the exhaust tunnel until past the cat to allow air flow out of engine and radiator
Full rear skirts but no hub caps
Factree aero hubcaps up front.
195/60r14 tires front
185/60r14 tires rear
New front wheel bearings and rotors. Front Bearings tightened less than spec.
Parking brake adjusted loose and not used so it doesn't self tighten
2" cat back exhaust, with exhaust tip that exits flush to the diffuser
0.681 5th gear
Hammer mod advanced timing, chip tune by a TDI Forum vendor
0.205 nozzles (110 hp)
Scan Gauge II and GPS Speedometer.

I haven't reduced any weight and have not put on the rear spoiler I built, yet.

[Caddylackn]

Originally Posted by Caddylackn

Some A B A B A B A B A Testing results with the full undertray and no air dam.
compared to A B A B A B A B A B results with the air dam and diffuser only.

-Using Scan Gauge II trip, no fill up yet.

To work (trip mpg)..............Home (trip mpg)
67.9 .................................64.3
71.7..................................67.7 3 mile shortened trip
66.9..................................62.2 3 mile shortened trip
68.2..................................64.2
68.3..................................69.4

With Full Undertray tied to diffuser
78.2....................................77.4 To work from gas station to work only
81.7....................................76.1
83.7....................................78.6
82.5....................................79.4
81.8....................................79.5
85.3...................................... -

Well throw out these A B A B A B A testing results. I refilled my tank and my Scan Gauge II was off by 2 gallons. This is about 30% low, so it was reading mpg about 25-30% high. IDK why that the gauge would be that far off from factory settings. It was not reading fuel (gpm) correctly. I double checked my initial settings and they are correct. I am reading about 3% error in my speedometer based on GPS speedometer. My gas mileage after fill up (7 gallons) was 57 mpg, which is more reasonable than above, but still lower than I hoped. The SGII was thinking fillup would be 5.0 gallons, but it was 7 gallons & change.

I adjusted the fill settings so now the SGII increased my fuel usage settings up about 30% after first calibration after fill up. I will check and recalibrate after another fill up. I think some of the "missing 2 gallons of diesel" may have actually been some spillage from driving around with the tank full up to the neck of the filler tube. I have the wrong gas cap and I may be getting some spillage. From now on, I will just have the pump shutoff on its own twice, then stop. That is about 21 gallons. I don't need the full 26 gallons in, driving around to work and back.

so today, 8/22/22
I measured To work:
63.5 mpg ;

I did have some rear wheel brake drag on part of the trip, from adjusting my rear wheel bearings. I took off rear rotor to replace the rear wheel bearings then noticed that Rock Auto didn't ship my outer wheel bearing So, I just repacked them with fresh grease and retorqued them. This left an overtight brake setting, as rehooking up my emergency brake cable tightened the rear caliper piston, so it needs to burn the pad in. I could smell the burning brake pad at a stop light after 5 miles, but not when I arrived at work so it stopped sometime on the way.

So I have a bunch of A B A B A testing done on my mods with the uncalibrated SGII, but the values are too high, but the % improvement between the mods should be the same.

[Caddylackn]

My typical coroplast and metal corner design:



Gorilla taped and 4 screws secure it to the hatch. I can open my hatch all the way without interference. I have about 10 degree deflection on the spoiler from roof and sides. It is very stiff and secure.




I also took a few 2" strips of lexan and made clear trailing edges to my taillights. No photo yet.

[oil pan 4]

You had a roof rack this whole time?
Have you tried brake pad anti drag clips?
I found they are good for saving about 100 watts per wheel at 65mph.

[Caddylackn]

Originally Posted by oil pan 4

You had a roof rack this whole time?
Have you tried brake pad anti drag clips?
I found they are good for saving about 100 watts per wheel at 65mph.

Tell me about these anti drag clips? Do they work for 4 wheel disc? Where do you get them?

The roof rack delete was one of my first mods. There is still a flush strip of plastic from the factory that fills the void between panels in the metal roof. I have gorilla tape covering the holes in the plastic where the roof rack mounts were.

My rear wheel drag is gone. This model uses the parking brake to turn the caliper piston to adjust for brake wear. So, putting on the parking brake on full rotates the piston out, which causes some brake drag at first. This tightening happened while removing the emergency brake cable from the bracket on the caliper to remove the rotor. I don't have the tool that will push the piston back while rotating it.

I have no brake drag now, the wheel turns freely. I don't use my parking brakes very often, if I do I only use one or two clicks. Not enough to move the piston and tighten the brakes.

This morning I got 69.6 mpg on the way to work, so about 9% more than yesterday when I had some residual brake drag.

I did pick up some terminal velocity coasting on my normal hills after the spoiler install. I hit over 70 mph on one hill.

[Caddylackn]

I have noticed my intake manifold pressure (boost) has been creeping up on normal driving cruise and I am seeing some black tailpipe smoke on even gentle acceleration (black smoke is fuel).

I decided today's drive would be spirited to clean out the built up carbon from the turbocharger and wastegate mechanism. TDIs are known for fouling wastegates from long durations of low or no boost driving.

So I drove to work at 70mph and did some aggressive acceleration on onramps. Not floored but up to 8 - 9 psi of boost. I was expecting to see a huge mpg drop on the one way commute, but I got 57.4 mpg trip commute to work (only a 10% drop from yesterday)

That was unexpected. I only got 65 mpg yesterday driving very conservative with max coasting and a max speed of 60 mph.

So, either my Scan Gauge II is still not reading fuel usage accurately, or my granny driving, and super slow acceleration, and general lugging the motor in 5th at 51-55 mph on the big hills is not conducive to getting the best mileage. I may be over fueling the motor running it at too low of rpm. I try to not cruise below 1,500 rpms or it shudders.

I am happy with achieving 57 mpg with normal driving. Can't complain about that. I will try some normal acceleration and keep it at 60 mph max and see if that increases my daily mileage.

The good news is that none of my cheesy coroplast aero mods fell off at 72 mph. and I am getting real close to my goal of achieving 60 mpg at 70 mph steady driving.

[Arctic Fox]

I have read [somewhere] that slow acceleration uses more fuel - that, it's better to accelerate to speed quickly, then ease off as you continue on your way.

[freebeard]

It gets you to a sweet spot in BSFC chart. ecomodder.com/wiki/Brake_Specific_Fuel_Consumption_(BSFC)_Maps

Any benefit 'shrinks' with the length of the journey.

Introducing the turbo complicates things.

[oil pan 4]

I got my brake pad return springs off eBay.