VW GTI - Heavy modding done - what next?
 

Sooo - I have had this 1991 VW GTI for almost 3 years now - and for the first 2 it was getting aobut 21MPG. In August of last year we fixed that with an AHU TDI:

MKII VW GTI Gets a TDI Engine in 3 days - YouTube Video

I'ts mostly modded to go fast so I was shocked at how good the MPG was once I started driving it. I'm really hooked now! I even drove a whole 1100 miles as carefully as possible just to see how it does and was able to get it up to 78MPG! :D though the lifetime average is only about 60MPG.

Since the swap I have added the following eco-mods:

1: High temop thermostat (92 rather than 87 degrees)
2: Taller 5th gear (.622 was .756)

My question now is - what else can I do without getting really crazy? I want to keep it looking as stock as possible. Here are my thoughts...

1: Maybe a belly pan of sorts
2: LRR Tires (already in the plans when it gets 5-lug and Porsche brakes)
3: Some sort of tasteful grill block?
4: Maybe eventually go 6-speed with a .59 5th gear

This site has been a great resource so far - and I think the best info for future MPG gains will come from all you you MPG gurus. :thumbup:

Grille block - Coroplast behind the grille. Nobody will see it.

Try water injection, it might work out for you. Remove the vacuum pump from the motor and grab an electric vacuum pump, pressure switch, and reservoir, or just switch to manual brakes. I can't remember how the AHU develops vacuum, but I believe it's the same as my old Golf D 1.6NA, with a vane pump attached to the oil pump. Open the lid, remove the vanes (they slide out) and put the lid back on, then leave about an inch of hose connected and screw a bolt into it, or remove the hose and put a cap on the nipple.

Boost will enhance the efficiency of the diesel. The KKK K03 turbo from a New Beetle bolts on and no intercooler is necessary for low boost, you just need to turn the fuel up to compensate for it. Don't turn it up until you see the haze unless you want more power, just get it to that point, then back it off slightly. You'll just be using less pedal when driving normally.

Electrical mods. You dont' need the radiator fan unless you drive in heavy traffic or let the engine idle frequently. Based on your current reported numbers, I doubt either is the case. If you want protection from overheating, install a tube with holes that will spray water at the radiator and another washer fluid reservoir/pump. If you notice the temps climbing, spray the water to insta-cool the radiator. If it happens frequently, reinstall the radiator fan.

If you don't use accessories frequently, consider an alternator delete and a deep cycle battery or two. Added weight, yes, but the draw removed from the engine will more than make up for it. If you do this, I suggest you pop start as often as possible to keep the starter draw off the system, and mind your night driving (headlights).

I'm fairly certain you don't have PS, but if you do, get rid of it. It's not necessary on such a light car. Best bet is to swap in a manual rack, but looping the hoses works as well. More weight lost there, as well as parasitic engine drag.

Advance the fuel timing. You'll get a more complete burn, more power, and better economy.

Do not advance injector timing
 

I like that behind the grill block idea - and I will want it to be easy to remove as this car isn't just for MPG - it's also my go-fast car. :D

I wonder if water injection would really help FE - I will need to look into that. I know it would help with charge air temps and allow me to run more fuel for more power though. :D

The AHU has the same style pump as the 1.6 NA - I wonder how much power it uses to build and hold vacuum. I suppose I could hook an electric motor to one and measure current draw loaded and unloaded to find out and then see if it's worth the trouble. Manual brakes won't solve the vacuum issue for me as I have installed a VNT turbo and it operates its vanes with vacuum.

The New Beetle is equipped with a Garrett VNT15 stock. the KKK K03 you are referring to is the factory turbo from this motor. I removed it and installed a KKK/Borg Warner BV43 from a European 2.0L 16V 170HP TDI. It's capable of supporting 25psi of boost through most of the rev range.

Radiator fan has never come on. And idling causes my temps to drop - I believe this is due to the unusually lean burn of a TDI at idle. I will be keeping the fans though. This is due to my frequent hard driving and the fact that it will be at the top of Pikes Peak and Mt. Evans this summer along with some other demanding situations. I can't see any advantage of removing them aside from saving the 5.6LBS.

I forgot to mention that I have addressed the Alternator issue as far as I'm willing to. removing it would be a bit more driveability-killing than I want. I removed the stock serpentine belt assembly that went Crank-Idler/Tensioner-120A_Alternator-AirCon and the V-Belt that went Crank-WaterPump-PowerSteering. I am now running a setup that uses the smaller 90A alternator as the tensioner. It goes Crank-WaterPump-Alternator. It is also manually tensioned and not as tight as VW had it. no slipping problems yet. :)

You are correct - I delted the PS pump when I removed the serpentine tensioner and A/C. It now has a manual rack from an 86 Golf.

The tune i have from TDTuning takes timing as far as my tuner (Mike) is comfortable taking it for the power and FE goals.

Thanks for the input Christ! :D

I will keep the IP timing just where VW wants it. :)
I have VCDS
And thanks! :thumbup:

why do you think this? My experience is different if the original engine has "enough" power to keep up with traffic.

I agree - the advantage of the turbo only really comes in when you can use it to produce more power from a smaller engine. This allows for less internal resistance from the engine itself. I think most gains people see are probably due to the typical non-turbo diesels running a little richer than needed and not enjoying the benefits of a complete burn.

Any reduction in pumping losses is a benefit to efficiency. How you use it makes the difference.

Cool swap! You are getting some really good FE numbers with it. I have been thinking a TDI swap into a Mk II or III would be a fun car to have. Less weight and frontal area than my Mk IV TDI. I used black foam pipe insulation stuffed between the bars for my grill block. It is pretty stealth on a black painted grill (see if you can spot it in my avatar). It is really quick and easy to add or remove depending on conditions. The diesel needs surprisingly little grill area because they run so cool. I have the upper blocked year round even climbing the passes and part of the lower blocked in all but the hottest weather. I priced the Snow Performance H2O/Meth injection kit and at $750 it would take a long time to break even on fuel savings. Might be worth it for more power on Pike's Peak but probably not for hypermiling.

If you have the OBDII port from the TDI a Scanguage is very useful. Instant and trip mpg, real time water and intake temps are nice to have. Can really help teach you when to EON (engine on) coast or to overrun (go downhill in gear-@ 9999mpg).

I deleted the passenger side mirror and folded the driver's side with a blind spot mirror glued to the glass. Also, I am sure you know you don't really need a muffler with the turbo and the cat. I substituted a straight pipe for it to make room for a flatter belly pan. I have a full belly pan from the front bumper to the back. No need to worry about exhaust heat anywhere except the cat/con. (see photos in my albums)

I am curious about tunes on a diesel for better mpg. UFO was trying to eliminate EGR for better mpg but it seems to have hurt his warmup times. If you have a tune that you think helps mpg I would be interested to hear your thoughts.

More boost raises engine efficiency on diesel though you get diminishing returns as it increases.
http://web.archive.org/web/200611080...4/A6_1_022.pdf

The question of whether more boost will help on a particular engine depends on how much more energy it takes to create the additional boost, the efficiency of the system doing so, and the increase in friction due to running at higher pressures (note that the above paper showed efficiency increases all the way up to five atmospheres).