Date: Sun, 2 Nov 2003 09:18:46 -0800
Reply-To: David Marshall <vanagon@VOLKSWAGEN.ORG>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Marshall <vanagon@VOLKSWAGEN.ORG>
Subject: Transmission ratios with TDI motors
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Volks
I am getting ready for my Tri-Star to come over from Sweden. It is a great
truck with a bad transmission 3/4 Synchromesh problem.
First, some back ground on the Tri-Star. Other than being a fully equipped
double cab with four doors, it comes with the smaller variation of the
plastic wheel arches. Seeing how this truck is a collectors item, I want to
be able to return it to original spec easily so this means no cutting of the
wheel arches to install some huge tires. 225/75LT16 is about as big as I
can go (29.2"). 225/75LT16 is available in a wide range of tires from the
ever popular BF-Goodrich All-Terrain to the Pirelli Scorpion AT to the
Yokahama Geolander AT
The motor I will be installing will be an ALH TDI from a 2001 Golf with the
Fast Forward mounting kit that is now finally available!
Maximum torque is 155lb-ft at 1900 RPM
Maximum power is 90hp at 4000 RPM
This motor has 32% more torque than a North American wasserboxer motor and
it is at 1300 rpm lower in speed too - right where we need it most. At 3200
RPM where the wasserboxer peaks at 117lb-ft the TDI has around 140ft-lbs
this is 11% more torque than 'stock' at this RPM. The TDI doesn't fall to
117lb-ft until about the red line of 4500 RPM. More pull everywhere! I
feel it is best to concentrate on torque numbers as this is what we really
drive our refrigerators on wheels with - not horse power!
The choice of 29.2" tires will 'hurt' my over all performance. The larger
tires are necessary because they achieve a few things. First, I think they
look much better on a Syncro that the stock 25.6" tall tires and offer a lot
more in tire choices. Second, they lower the RPMs at 100km/h to something
the TDI will actually last at and it will increase my overall top speed
too - not that I enjoy going much over 120km/h in any T3. Going to 29.2"
tall tires will result in a 14% increase in tire size or a 14% drop in
perceived engine performance. The only way to compensate for this is one of
two things, different ring an pinion gears of 5.43:1 final drive to get 12%
more torque to the wheels or get a bigger motor. The problem with 5.43:1 is
the RPM for any given speed will be higher - (not good for a TDI) so this
leaves no choice but the bigger motor - hence choosing the TDI in the first
place. Thankfully the TDI is a lot more than 14% more powerful in all the
RPM ranges I want to use it in!
My usually driving is 100km/h (65mph) through central British Columbia over
some 8% to 10% grades. Some driving in the flat lands of Alberta and
Saskatchewan at 110km/h and hopefully I can take this puppy to the USA to
some of the WA and OR WV shows this summer. I will be doing some occasional
dirt road and off roading with this truck, but not nearly to the extent I
will be with my camper. Bigger tires and different gearing again... Loads
will be mainly light, I doubt if I will ever take this to the 2810kg maximum
weight.
When going up through the gears I feel it is important to 'land' in the
maximum torque range of the next gear and not over rev it to achieve the
next gear on the ladder sort of speak. This means when going from 1st to
2nd, I want the shift point in 1st to correspond to 1900 RPM in 2nd gear. I
think taking the TDI over 3800 isn't going to be that good for it over the
long run so I want to keep the RPMs at most times, under that level.
The transmission is an AAN transmission (4.86 R+P) with stock gearing of:
1st 3.78
2nd 2.06
3rd 1.25
4th 0.85
Suggestions for 'better' 3rd and 4th gears are 1.17 and .77 as they are more
'beefy' that stock and will lower the RPMs. So... with 29.2" tires it would
fall as follows - speeds are km/h:
Gear Ratio 1900 3800 Shift Point
1st 3.78 14 29 3400
2nd 2.06 26 53 3100 3300*
3rd 1.25 43 87 2800
3rd* 1.17 46 93 2900*
4th 0.85 64 128
4th* 0.77 71 142
Common driving speeds (rounding up RPMs):
PLACE SPEED 3rd 3rd* 4th 4th*
Town 50km/h 2200 2100 1500^ 1400^
Back Country Roads 60km/h 2600 2500 1800^ 1600^
Secondary Roads 80km/h 3500 3300 2400 2200
Highway 100km/h 4300^ 4100^ 3000 2700
Interstate and AB/SK 120km/h 5200^ 4900^ 3600 3200
* recommended new gear set
^ out of RPM range
I think there are compromises in both the old and new gears sets with the
TDI motor. I like the shifting points with the new gears - I think you can
say 3300 rpm to 3400 RPM is a good shift point for all gears to keep
everything simple. The jump from 3rd to 4th doesn't seem all that bad.
Back road and secondary roads may be a little tricky with the new gear set
as 70km/h is boardering on the point you should be dropping down to 3rd
gear - seems the original gear set might be better for that. Town and back
country driving will be fine with either set.
So... is the $500 US price worth it for the installed new gear sets? Is
this amount of highway RPM drop going to result in cooler oil and water
temps or not enough for me to notice?
Is there anything else that I can do to prolong the life of my transmission?
Comments - suggestions - thoughts...
David Marshall
Fast Forward Automotive Inc.
4356 Quesnel-Hixon Road
Quesnel BC Canada V2J 6Z3
http://www.fastforward.ca mailto:sales@fastforward.ca
Phone: (250) 992 7775 FAX: (250) 992 1160
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