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Date:         Wed, 8 Jan 2003 03:41:23 EST
Reply-To:     FrankGRUN@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Frank Grunthaner <FrankGRUN@AOL.COM>
Subject:      Recent Transmission Adventures/ Rest of the Story
Content-Type: text/plain; charset="US-ASCII"

Ah Yes, If anyone is still out there....

For a long time I have been insisting that a heavy vehicle like the Westfalia camper needs all the torque at the tire contact patch that it can muster, consistent with reliability issues in the trans (limits engine choices). In that analysis (archives), I have concluded that the best overall engine for the Vanagon was probably the TDi. But barring the TDi, the best trans for any modern engine swap (I4 or Suble) was probably the DU (5.46 final) or the DZ (5.86 final). These comments were based on NA transmission availability only.

The general wisdom (which has blithely ignored these comments) has held that high rpm requirements of the DZ trans lead to 1. Poor engine life (nonsense!), 2. Decreased fuel economy (nonsense!) and 3. Higher engine noise (true!) as compared to the DK trans.

Well, I have traversed many a mile with the DK/large tire setup. I can confidently report that the only change I made was the trans. Not the engine, not the rolling stock. And now I have 2950 rpm at 60 mph, 3700 rpm at 75 mph and it's a dog. Have to get back to the Audi ASAP!!!

The performance of the current package resembles the 1.6L NA Vanagon diesel but with a serious power band (rpm range). So the rpm's are lower (by 22% compared to the DZ trans), but the noise level (w/o stereo assist) is still substantial, the fuel economy is essentially the same (maybe as much as a 4% improvement) and it has difficulty getting out of its own way. Woof.

Now for some facts. In the past I published the torque curves for the VW/Audi series of engines ranging from the 1.6 NA diesel to the 2.0L Turbo Audi, including the turbo diesel (1.6L), the 2.0L AC and the WBxer series. I had no data on the 1.9L NA and TD options now afoot. Comparing the AC 2.0L torque curve to that of the 1.6L NA diesel, the diesel torque (over the range of 1500 rpm to 4000 rpm) is down by 75% relative to that of the AC engine. Note that the VW factory equipped diesels came with (westfalia's) the DZ trans with 5.86 final drive ratio compared to the 4.57 final of the DK. The first through fourth gear ratios were the same for both engines. The DZ trans (for a given road speed, and the same size tire) offers 22% more torque to the tire contact patch than does the DK. Therefore, when running the diesel through the DZ trans, the available thrust at the road was essentially identical to the AC configuration. Now this does not include acceleration capability because of inherent wind-up differences between gasoline and diesel engines, and it does not address the problem that the diesel engine torque falls off drastically over 4000 rpm. Nonetheless, the reason for the factory choice is clear.

Now there are many convertees out there running the 1.8L engine with the DK trans who pronounce themselves pleased with the result. I have two comments: 1. Stay with the stock tire size. The 8% torque penalty of the 215/75 x 15 tires is really harsh. Will drop the performance of the I4 conversion to that of the AC motor up to 3500 rpm. 2. You like it because you haven't experiences the overall performance of the DZ configuration. 3. You're rationalizing pain and suffering.

Now in fact the lower gear performance of the DK/large tire system is credible. If you compare the effective speed ranges for the DZ trans with stock tires to the DK/ large tire configuration (using an operable power band for the 1.8L gas engine of 1500 to 6500 rpm) one gets the following (all velocities are true mph, not necessarily speedo numbers):

DZ/stock: First: 4.9 to 21.4 mph Second: 9.0 to 39.0 mph Third: 14.8 to 64.0 mph Fourth: 22 to 95.0 mph

DK/Large: First: 6.0 to 30.0 mph Second: 12.7 to 55.0 mph Third: 20.7 to 89.8 mph Fourth: 30.6 to 133.0 mph (100 mph at 5000 rpm)

By inspection, one can see that the second gear of DK/Large covers much of the utility of the DZ/stock third gear. The final drive ratio for second gear DK/Large is 8.66 while the final drive ratio for the DZ/stock is 7.38. Units are engine revolutions per wheel revolution (corrected for revs per mile spec of the tires). DK third gear (5.29 net) is very similar to the DZ fourth (4.98 net). So in the DK configuration, fourth becomes an overdrive gear. The small difference in fuel economy is due to the fact that consumption is given by work done. Drive the same way, same vehicle, get the same mileage.

But there is a big problem! The low gear of the DZ combination went away. Also, if one compares the diesel manual transmissions (DZ,DU,DY) the reverse gear is 3.67 while the gear for the AC trans is 3.28. Comparing the transmissions, the net wheel torque available in reverse for the DK/Large combo is 36% less than that available for the DZ/stock group. Therefore, starting out in reverse (36% penalty) and in first (28% penalty) requires much more clutch slippage in comparison.

Last week, I journeyed to the San Diego Wild Animal Park, fully loaded and including a 350 pound electric wheelchair and ramps. The park was jammed. The entrance is up a long slow grade. Took thirty minutes to get to the parking kiosk. Stop. Go. Stop. Go. Etc. About 30 feet from the kiosk, we could smell something burning. Got really impressive with smoke pumping out from the rear. Smoking clutch. Never experienced before except at the drags. Fact. The DK combo puts much more stress on the clutch for no obvious benefit. I wonder if Ron will warranty the clutch plate?

To summarize, I said this all before (archives) and have verified the engineering with depressing experiment. A top speed of 95 mph actual is more than enough. Engine life of 200,000+ miles is more than enough. 5% gas mileage difference is lost in the noise. The stereo system more than handles the engine noise. I may well end with the DZ with the Audi turbo yet!

Yet it remains to address Robert's comments about how well the 1.9L NA diesel runs with the AC trans. Well, possibly understandable. There is a roughly 20% displacement difference between the two NA diesels. The 1.9 is a later design than the 1.6. I anticipate that the torque output of the 1.9 should be roughly proportional to the displacement difference. The 20% torque difference should give the same performance with the AC trans as obtained with the 2.0L AC motor. Other efficiency gains should enhance. The 1.9 TD should be respectable.

Good night.

Frank Grunthaner


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