THE TDI TRIFECTA
This article is from our archives and has not been updated and integrated with our "new" site yet... Even so, it's still awesome - so keep reading!
Published on Sun, Oct 18, 2009
By: The LACar Editorial Staff
Edie Falco arrives in the new Audi Q7 TDI
THE TDI TRIFECTABy Doug Stokes I guess it falls on me to be the diesel guy here at LA Car. In point of fact, I have only but two qualities for this very important job: (1) I do corporate PR for Gale Banks Engineering, and (2) I once risked bigamy by calling in live to a Detroit-based automotive web show and publicly asking Denise McCluggage to marry me. I also have the seriously insidious torque monkey on my back (who else do you know that drives a supercharged Ford Focus ZX-5?) but I'm taking medication for that. Other than the above, there's honestly no reason (good or bad) to blindly believe anything I say about compression-ignition engines. In fact please don't. You (and a lot more people like you) MUST go out and try new clean diesel-driving for yourself. If you're old enough to have negative memories, or if you are so young that you haven't made up your mind yet ... Please ... go drive a new clean diesel automobile ... It's a revelation and lots of unconditional F-U-N! Our friends at Bosch were the brave ones who slipped us the keys to a low mileage 2009 Audi Q7, and said, "Have fun!" They suggested driving until the fuel gauge read exactly one-half (full or empty) and then turn around and come back ... And, with a diesel, that's a long old trip. We had the vehicle strictly to feel out its engine, but we still put a couple of hundred on the clock and the fuel pointer was still shy of three-quarters full when they came for the car. Watch LA Car for a complete review of the Q7. So, let's talk about this engine. First thing you'll notice is there's nothing to notice diesel-wise. If not for the big BOSCH Clean Diesel stickers on the sides, no one would know. Well, maybe those sleeping drivers who we just walked away from on the freeway by gently rolling on the fly-by-wire fuel pedal. Great gobs of big, smooth, steady acceleration warp one forward and you are left marveling how 5,512 pounds can be shoved ahead so forcefully. The specs are the specs: Three liters (the classic 181.1 cubic inch displacement) but diesel and packing a steep-sounding 16.8-to-1 compression ratio (gas motors get real touchy at 11-to-1, and become potential grenades at 12 or better). In this case it's all the better to make diesel fuel explode and do work by just squeezing the heck out of it ... No sissy spark plugs for us! The block that has to deal with all this cylinder pressure is poured from super strong vermicular graphite cast iron - a new alloy that's far stronger but still 15 percent lighter than standard cast iron. Remember, the diesel makes its fuel explode and work by slamming it into a little declivity in the piston under that 16.8 compression ratio with the fuel squirted directly into the cylinder under the pressure of 2,000 bar (that's a mind-numbing 29,000 pounds per square inch.)
The 3.0 V6 TDI And those injectors, they're Bosch's masterpieces of fuel mastication. These are piezo (you say: "pee-aye-zo", I'll say: pea-zho") injectors electronically-controlled to the what seems the nearest millionth of a cc, they fire off in those ultra-short bursts of low sulfur diesel fuel (almost always more than one shot per compression cycle) to give the exact, precise, minute squirt at the exact, precise moment for perfect power and complete combustion. There's a lot of electronic magic (really a lot of hard work in the test lab and on the engine dyno) in the injection system even including firing an almost imperceptible last shot of fuel into the cylinder after the piston has begun the power stroke. That helps lower emissions and give us a smoother combustion process. Most modern diesel engines have used a form of direct injection (right into the cylinder) for many years now, and that's where the "DI" in the TDI moniker comes from. Again, we have our friends at Bosch to thank for perfecting the art of precise fuel timing. The bore and stroke of this engine are what the tech writers call "oversquare" meaning that the piston travels a shorter distance up and down in the bore than it measures across it's own circumference and that's a good thing making the power delivery perfectly smooth across this engine's entire rev range. If you're a spark ignition aficionado, you might be thinking that I've become so enamored with this delightful diesel that somehow I transposed the horsepower and torque figures when I quote you 225 for the ponies and 406 for the weight-lifters (that's horsepower and pounds-feet of torque). For the record, those numbers are stated in the correct order, diesels are like that. This is a 90-degree even-fire V-6 with 4 valves per cylinder. It's at least as silky as a nice-running V-8 with the compact dimensions (length-wise) of a four the whole engine is only a compact 17.3 inches long and just about the same in width. Of course, everyone knows that the "T" stands for Turbo, and turbos are really what finally brought the Diesels into the civilized light vehicle (pickups, SUVs, and automobiles) world. The turbo (powered by the engine's exhaust gases) squeezes a bunch of extra air into the engine which means that more oxygen gets mixed with the fuel, which means better combustion, which means that more energy is released. This is especially important in diesel because that fuel contains at least 12 percent more energy per unit than gasoline. You can pump a bunch of diesel in and get a whole bunch of horsepower out, or conversely, you can be stingy on the stuff and get almost miraculous fuel mileage, and with the same vehicle. Almost having your cake and ... Truth be told, de-badged of its "TDI" nameplates, no one will ever even guess that this machine is powered by a V-6 diesel engine. There are no, zero, outward or inward, hints of the fact that this engine has no spark plugs. Even a look under the hood won't tip anyone off, this engine has a whole handful of hoses and wires crisscrossing its width and breadth (none of which lead to spark plugs I assure you). Audi handily covers all the (seeming) confusion up with a nice engine shield that cleans up the vista and traps a little engine sound while it's at it. To clean up this engine's act for the U.S. market, Audi chose to go the urea injection route. A small tank of the liquid is carried aboard and sent in minute quantities into the exhaust system just downstream of the engine. There the odorless, colorless (well it's sort of light blue) liquid gives the exhaust gasses a final scrub and matches the Q7's diesel engine to the strict standards that Uncle Sam and Governor Arnold have set for gasoline engines. And, if that wasn't enough to get you kicking up your (Birkenstock) heels, the Q7's diesel engine produces a heart (not global) warming 20 percent less greenhouse gases! The final word on this engine is wondrous. Most of us really haven't had much modern clean diesel seat time. If you're a car person, and just love the tug of torque, like I do, please (and this is the second time I've asked in this single article, by the way) get yourself a drive in an Audi Q7, A3, VW Jetta, Golf or (see our up coming review) a VW Touareg ... Just make sure that the vehicle has those three magic letter on the rear deck: TDI.