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Old 04-21-2009, 09:05 PM   #1
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SpeedKnight's "experiments"

I'm putting this here as opposed to the Experiments section mainly because I'm not being strictly technical and scientific in my "experiments."

I've been doing two different things, as of late. I'm trying to get my FE as high as I can, mainly to save money as opposed to reducing my carbon footprint. Reducing my carbon footprint is a nice side effect, though.

1) I have an 80 mile round trip commute to/from work. It's predominately 60+MPH highway driving. I can see definate changes in fuel level over the coarse of a day. Based solely on the needle's position, I can grossly judge if my FE is better or worse. As a "standard," I use up 1/4 tank per round trip during my commute. From day to day, I will change my average speed, use coasting more or less often, use the brakes more or less often, etc. By habit, I get into the highest gear possible as soon as possible.

2) After ~205 miles driving, I top off the gas tank. I then record my trip odometer and how much gas I put in. I started doing this 3 fill ups ago.

I understand neither of these is super accurate, but it's better than nothing.

The latest "experiment," which starts in the morning, is to test closing up some of the grill. I've taped over about 1/2 of the openings in my grill. I'll make a very gross judgement on the effect based on how much the fuel needle moves. Then, when I hit ~205miles for my current trip, I'll fill up again and roughly calculate the "new" FE.

Again, I know my "experiments" leave a lot to be desired, but at least I'm doing something. Regardless, I'm interested in any ideas that can be offered up here. I'm also happy to be sharing my attempts to improve my FE.
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Old 04-21-2009, 09:13 PM   #2
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Duct tape is great to test whether or not a grille block will work on your car. Keep us posted...

-Jay
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Old 04-22-2009, 03:39 AM   #3
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Duct tape is great to test whether or not a grille block will work on your car. Keep us posted...

-Jay
The neat thing about the duct tape I used is that it's black. My car is black, too... so it's not brutally obvious that the tape is there. When I get home tonight, I'll snap some photos of the taping. I need pics of the car anyway.
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Old 04-22-2009, 04:40 AM   #4
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Welcome.

Addressing content in your "Welcome Thread" post as well as this thread...
That's a lot of family for a guy driving a GTI.

Worn tires are actually good for FE (fuel economy). They have significantly less RR (rolling resistance), according to theory and measurements reported in most RR documentation I've read. I have no way to confirm that for myself.

Good job, getting down to 60mph as a spirited driver. I've managed to calm my driving a lot but I can't cruise at 60mph on the highway.

For reasonable accuracy, fill at the same pump facing the same direction and don't top off. Also, it can be difficult to trust results from a single tank, so you might not want to declare success or failure until you've had a few tanks (while conditions/driving seemed to be the same before and after).

Your GTI VR6 has a normally aspirated V6 engine, right? I wouldn't be surprised if it has the same transmission as the 1.8T, which is probably geared low even for that engine, let alone yours. How many RPM at 70mph in your car?
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Old 04-22-2009, 12:29 PM   #5
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Welcome.
Thanks.

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Addressing content in your "Welcome Thread" post as well as this thread...
That's a lot of family for a guy driving a GTI.
lol
The GTI is my car. One of my gazillion hobbies is working on cars (making them go faster, handle better, get better FE, etc.). The GTI is my latest "patient."
The family vehicle is a slightly less fuel efficient, but much more accomodating Chevy TrailBlazer EXT. Yes, it's big, and yes the I6 under it's hood gets horrible mileage, but the truck offers up plenty of room for the family and our Ren Faire hobby.

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Worn tires are actually good for FE (fuel economy). They have significantly less RR (rolling resistance), according to theory and measurements reported in most RR documentation I've read. I have no way to confirm that for myself.
The worn out tires might be good for FE, but they're horrible for my nerves. I know how to handle a car pretty well, but I'm not too fond of the car going sideways when I don't want it to. The tires on it now are Wynstar Exocet 205/55-15 tires. I can't pass any judgement on them when new, but they are TERRIBLE at the end of life. They hydroplane easier than a boat does, and they are horribly noisy. Their dry traction is horrendous also.
Where I like the idea of having a low RR, and thus better mileage, I cannot have tires that won't let me hug a cloverleaf at 60MPH or so (especially in a car that has the ability).
The tires I plan on getting are Falken Ziex ZE-912 225/50-15 tires. They rank #1 on Consumer Reports "Ultra High Performance All Season" guide. Many an internet form also gives them high marks, at least for performance. I can't seem to find anything that tells me how they fair as far as RR goes.

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Good job, getting down to 60mph as a spirited driver. I've managed to calm my driving a lot but I can't cruise at 60mph on the highway.
Trust me... keeping the car at 60 is TOUGH. I usually end up lagging traffic, and I normally hate that. In the end, though, the money I save on gas can be spent on my budding leatherworking and chainmail making business.

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For reasonable accuracy, fill at the same pump facing the same direction and don't top off. Also, it can be difficult to trust results from a single tank, so you might not want to declare success or failure until you've had a few tanks (while conditions/driving seemed to be the same before and after).
I've stopped topping off so I can get fairly accurate volume numbers. I usually end up at the same pump and facing the same direction just because it's the easiest and quickest entry and exit to the gas station. Convieniently, the station is located just outside my office building, so I don't even have to stray off my normal route. I've now done this for 3 fill ups (with two mileages recorded), and the results are fairly decent so far. According to the numbers, I'm averaging high 20's for a car the EPA has at 19MPG combined. Works for me... I just want to see if I can drive the number higher.

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Your GTI VR6 has a normally aspirated V6 engine, right? I wouldn't be surprised if it has the same transmission as the 1.8T, which is probably geared low even for that engine, let alone yours. How many RPM at 70mph in your car?
Naturally Aspirated 15 degree V6 with 2 valves per cylinder (1 intake, 1 exhaust).
I'm completely new to owning an import car, let alone a European car, so I don't know much about other engines. I'm also not to sure what my gear ratios are, though I know I wish the 5th gear was taller. At 70MPH, the car revs at 3K. I'm used to driving V8 powered Chevrolet Caprices and Camaros that tach about 1200 at 70MPH, so 3K seems high to me. Sadly, I don't know for certain if this is normal or not. You asking does make me want to look this up.
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Old 04-22-2009, 12:49 PM   #6
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The worn out tires might be good for FE, but they're horrible for my nerves.
Yeah, I wasn't actually recommending continuing to use dangerous tires...just pointing it out.

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I'm completely new to owning an import car, let alone a European car, so I don't know much about other engines. I'm also not to sure what my gear ratios are, though I know I wish the 5th gear was taller. At 70MPH, the car revs at 3K. I'm used to driving V8 powered Chevrolet Caprices and Camaros that tach about 1200 at 70MPH, so 3K seems high to me. Sadly, I don't know for certain if this is normal or not. You asking does make me want to look this up.
I've been asking around; I've found that imports and domestic compacts equipped with manual transmissions all run unnecessarily high RPM in 5th (or 6th, if equipped), presumably for lazy drivers who don't like to shift (who should have automatics, IMO). My 2008 VW Rabbit probably has the same transmission as your GTI, my 5th gear is 3000rpm at 70mph. The NA I5 engine is no Chevy V8, but it's pretty torquey for an economy car and could easily turn a 2000rpm@70mph gear.

Even the new V6 Camaro with its 273 ft-lb torque (almost all of which is right there at idle) has short gears on its manual transmission. The V8 model is geared like I think the V6 probably should be, and the V8 probably should have the T56 (with its .50 6th) that was in 4th generation V8 Camaros.
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Old 04-22-2009, 07:09 PM   #7
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Yeah, I wasn't actually recommending continuing to use dangerous tires...just pointing it out.
I assumed you weren't suggesting I keep running on bad tires. I want them off there pretty bad, but I need to wait until Uncle Sam is paying me the way he should be.

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I've been asking around; I've found that imports and domestic compacts equipped with manual transmissions all run unnecessarily high RPM in 5th (or 6th, if equipped), presumably for lazy drivers who don't like to shift (who should have automatics, IMO). My 2008 VW Rabbit probably has the same transmission as your GTI, my 5th gear is 3000rpm at 70mph. The NA I5 engine is no Chevy V8, but it's pretty torquey for an economy car and could easily turn a 2000rpm@70mph gear.
I decided I needed to look for the gear ratios for the Mk3 Golf ('93 to '99 models). Here's what I found:
1 = 3.300
2 = 1.944
3 = 1.308
4 = 1.034
5 = .838
So, 5th gear is a bit of an overdrive, but I'm pretty sure this engine can support an even taller overdrive. From a racing standpoint, I like 2nd gear, and 3rd isn't bad. If I were to change anything, I think I'd go with a 1:1 4th gear and something like a .7 5th gear.


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Even the new V6 Camaro with its 273 ft-lb torque (almost all of which is right there at idle) has short gears on its manual transmission. The V8 model is geared like I think the V6 probably should be, and the V8 probably should have the T56 (with its .50 6th) that was in 4th generation V8 Camaros.
Oddly enough, mainly to keep myself from wanting one, I haven't kept up on the 5th Gen Camaro. I know the V6 is supposed to pump out >300HP, which is awesome. Alas, I have the GTi to have my fun with for now.
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Old 04-23-2009, 06:46 AM   #8
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Yup, 304hp from that 30mpg V6 model. I want one so bad! I ran the numbers, it's 2025rpm at 70mph, respectable but definitely unnecessarily high for that engine in that car.
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Old 04-23-2009, 02:36 PM   #9
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Yup, 304hp from that 30mpg V6 model. I want one so bad! I ran the numbers, it's 2025rpm at 70mph, respectable but definitely unnecessarily high for that engine in that car.
A Chevy reving that high at "cruising" speed is absurd, really.


Back on the original topic... *grin*
I had the trip computer on my car running on the MPG display this morning... I pulled a 30.2MPG average on the way to work this morning! Mind you, this awesome feat was completely negated this afternoon on the way home by an excursion to VA Beach. I don't think I'm going to turn very good numbers at my next fill up. The fuel needle is sitting at 3/8, with the trip odometer sitting at 205 miles. Last fill up, the needle was at 3/8 with the trip odometer at 224.6. We'll see if tomorrow's trip to work (where I will also fill up) evens things out.
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Old 04-24-2009, 06:53 PM   #10
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Well, I had to fill the tank again today. If you check my gas log, you'll see I pulled a 27.06 average. This is down from my last average, but up from the first one I calculated/recorded. Jury's still out on taping over the grill and bumper openings, as it applies to me. Certainly, something good is going on, as I have seen, twice now, MPG figures in excess of 30 on my car's trip computer.
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