Here From TDIClub - looking to increase highway mpg

[dremd]

Originally Posted by roflwaffle

Turbos on diesels are generally designed to help out efficiency and power, so staying on boost isn't a bad thing per say. Some, such as variable vane turbos, can make boost at with very little exhaust flow. I think a pressure wave supercharger is similar, but I'm not sure which one has better overall efficiency.

For the unfamiliar the TDI in my car (ALH) uses a variable vane design and no wastegate. It spools very easily/ quickly, if you lug it you can have 12 psi by 1300 rpm.

[bestmapman]

Here is something interesting that happened to me in the TDI.

I went on a trip from Cincinnati, OH to Nashville, TN and back. After starting out I noticed that everytime a stepped on the gas the engine would start to miss. I thought something was wrong with the turbo. For the whole trip, I had to keep my foot off the accelerator. I was able to maintain 70 MPH with no problem, but when I put my foot into it it would miss bad.

When I was done with the trip and filled up, and the TDI got 51 MPG. The best ever. I took the car into the shop and all it needed was a new fuel filter.

Basicaly, I stayed away from the turbo the whole trip. How do you think this figures into the above graphs.

[roflwaffle]

Originally Posted by dremd

The only "real world" load to fuel consumption data I have is that my mpg's stay virtually the same @55mph when climbing a slight hill. Maybe an indication that I can put more load on it at the lower rpm and not increase fuel usage?

If engine speed stays the same and load goes up with no change in mileage then engine efficiency must have gone up. If there's a steep enough downhill grade it may be worthwhile, depending on fuel trim during acceleration, to give it a little gas/pop into neutral/rinse and repeat since there still is some difference between load and efficiency on a TDI, it's just not as large as on most gassers.

[newtonsfirstlaw]

I'd say it's easier to do a boattail on a hatch than a sedan. You won't have the issues with boot/trunk opening into the boattail.

[dremd]

I'm certainly not opposed to a boat tail, and it MAY happen, someday, but right now I'm going to focus on under carridge and wheel covers (rear first).

I've read metrompg's thread about making wheel covers out of plastic snow sleds (magic carpet??) I'm considering making a set out of 20ga and flaring the outer edge to match the inside of the fender so I can screw them in place (hopefully with factory holes).

I have a fairly large metalworking tool shop (2 plasma cutters (large Procut 60 and a 110 unit that is easy to carry but falls in to the hobby category), 2 wire welders (one with inverter and one DC), Crappie Tig welder, Oxy Acetylene, 40" Brake, Slip Roller, Beader (wrong name but used to put beads on sheet metal), 2 presses (50 ton manual and 12 ton pneumatic) 550lb Anvil, Swede block, slotted, cone, along with the accompanying hand + power tools, however I don't have an english wheel ( http://www.harborfreight.com/cpi/cta...emnumber=95359) which would be the perfect tool for some nice compound curves, but I can pound some out and see how they work.

[dremd]

Looks like my post about LRR Tires didn't make it up last night; Essentially.

I don't see much info on LRR tires here, are they not worthwhile on cars as light as a metro? Or have they just not been covered yet? Should I start a thread someplace else to discuss?

[MetroMPG]

Originally Posted by dremd

I've read metrompg's thread about making wheel covers out of plastic snow sleds (magic carpet??) I'm considering making a set out of 20ga

Yeah - Krazy Karpet

The plastic turned out to be too thin - in the heat of summer, they got almost soft - to the point that I think they started oil-canning in certain conditions.

I've since stiffened them with a coroplast backing, contact cemented in place.

I have a fairly large metalworking tool shop

Envy... You're set to go, man. This just got much more interesting.

As for the LRR thread - go ahead and start one. It's unquestionably worth pursuing, even on a light car. I know there's a link out there to a listing/rating of LRR tires. Hopefully someone will dig it up.

[DifferentPointofView]

If he's would like to, he could either turn up or down the boost on the turbo. Also, I'd try and get the final gear ratio where it sets at around the most torque (probably low, under 2000 rpm) at 70, but this escalates to the problem of gearing. you'd probably have the best bet of gearing it to a 6 speed, the first 5 where you get the most torque in fifth gear at around 60, and 6th most torque at 70. If you wanna know about boost, SCC has lots of info on tuning your turbo's for the correct PSI.

[dremd]

Cruise boost is essentially not adjustable; it is around 2psi (regardless of actuator position).

The VGT on the VNT 15 is pretty darn awesome though. If you run, say 75% throttle to accelerate you will get around 6~8 psi of boost almost instantly. 90% throttle gets you 10~11 psi. Not like driving a wastegated turbo at all. For reference the exhaust wheel is just slightly lager in diameter than a US Quarter.

On that note, I am beginning to doubt my SGII readings. I drove 150 miles today (at highway speeds approaching 75) and am still reading full. Normally I see the gauge move off of full around 3 gallons consumed. So I'll go re-fuel in the morning and we can get an idea if my highway readings are just wacko.

[RH77]

Welcome by the way

I've always been an advocate of the Diesel -- I too would like more members here with those.

I came within a fraction of an inch in purchasing a new '05 Golf TDI. Test drive and everything. It came down to the running costs -- timing belt and synthetic oil, so I kept my current car.

Just curious, are these something that you do yourself? I know the TDI forum has a great how-to section for such items.

I look forward to your input -- enjoy the site!

RH77