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PostPosted: Mon Mar 29, 2010 7:30 pm 
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Location: Sammamish, WA
First let me say I've looking around here off and on for about a year. I was watching Top Gear where they race to assemble a Caterham before Stig could get to the track and thought the idea of building a car was awesome. I've been thinking of different ways to build the car, and what to power it with and here's my drivetrain idea:

Engine & Trans donor: 1985 VW Golf Diesel
This is my current car (first car too). I bought it almost 3 years ago and have been steadily fixing and improving it. Recently it stopped starting so right now the engine's getting a full rebuild, bored, honed, new pistions, rings, bearings, valves, guides, and possibly a new head. Big advantage to the engine is simplicity: 12v to fuel shutoff solenoid, coolant and fuel connections and it'll run. The rest of the wiring (maybe a dozen total) on the engine is the alternator and sensors/switches. It should also get excellent fuel economy (50-60 mpg hwy).
The trans is an 020 ACH 5speed transaxle. Rod shifted with a cable clutch it's fairly small, and reasonably light, I can pick it up by myself with oil.

Now how to turn that into an AWD car?
I searched around and found some discussion, but no real results. My idea (which was discussed a bit) was to Turn the drivetrain longitudinally, with the axle outdrives pointing to the front and rear of the car. This, coupled with a Peloquin Torsen limited slip in the 020 would provide full time AWD similar to Audi's Quattro. The problem was front and rear differentials, specifically gearing. Using any standard diff from a RWD car would create a effective diff ration in excess of 9:1, not good for any kind of speed and would ruin any hopes for fuel economy. So my first though was get a gear unit to go in the middle of the drive shafts to remove the diff ratio of the transaxle, but that would add weight, cost and complexity, and we're going for locost here. So the hunt was on.

Solution: Passat G60 Syncro
I'm planning to build this after a TDI swap into the Golf, with a Haldex setup to go with it. That got me looking and I found the Passat G60 Syncro. This car uses a right angle drive attached to the ring gear of the differential in a transmission similar to my 020 to transfer power to the rear when slip is encountered by the front wheels. This is accomplished by the use of a Viscous Coupling (VC) attached to the rear diff. What makes this the solution is that the rear end has a ration of about 1.05:1, which when coupled with the 3.941:1 in the ACH equals 4.138:1. This still isn't quite Ideal, but much better than 9+:1. I'd be loosing some economy, but gaining torque. I could use a larger wheel and tire setup to compensate, but the locost is a small car, and they don't look right with huge tires. This prompted me to look at some of the other 020s out there. VWs are pretty much legos in car form in the A chassis (Golf/Jetta) and especially the mk2s. So I found the Gas engine transmissions have a 3.667:1 diff, giving me a 3.850 ratio, and a 5th gear final drive of 2.869:1 compared to the current 2.936, which is better for stock in my application.

Concerns: VC, drive shafts, and gear loading
The main concern I have is being able to remove the VC from the differential. If I can't use the diff without the VC, then I'm in trouble. Drive shafts are another concern, but I'm thinking of hacking up a couple of axles and using those. I'll probably end up hacking 4 axles into 2 drive shafts with inner CVs on both ends and then making an adapter for the CV to the diff. Another thought I've been wondering about is gear loading. Specifically what will happen if I'm loading the "wrong" side of the gear teeth in the syncro diffs. I'm no engineer and pretty young (just turned 20 a few weeks ago) so I don't know a whole lot, but isn't it true that helical gears are designed to be loaded on one face? I'm thinking I'll have to turn/flip at least one diff case in order to the the wheels to turn the right way and I'm wondering if that could cause problems. I'm hoping that diffs designed for 150 HP and 3000+ lbs would hold with 100 (I'll be upping the output of the engine) and 1700lbs either way.

So what do you guys think?

Edited for maths done with actual ratios


Last edited by FireStorm005 on Tue Mar 30, 2010 5:18 pm, edited 1 time in total.

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PostPosted: Tue Mar 30, 2010 12:48 am 
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build it...


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PostPosted: Tue Mar 30, 2010 1:38 am 
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krepus wrote:
build it...

...and they will come

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PostPosted: Tue Mar 30, 2010 2:17 am 
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krepus wrote:
build it...

That's the plan, after school, a job that will pay for it, time, and the shop space.


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PostPosted: Tue Mar 30, 2010 2:30 am 
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and watch...


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PostPosted: Tue Mar 30, 2010 2:31 am 
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and help if we can...


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PostPosted: Tue Mar 30, 2010 9:03 am 
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Just use the motor trans and front diff from an awd astro van.

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PostPosted: Tue Mar 30, 2010 1:58 pm 
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I'm re-writing some this because of corrections in the math due to finding the actual right angle ratio.

egoman wrote:
Just use the motor trans and front diff from an awd astro van.


What you may not have noticed is my plans for 50-60mpg. I love my diesel because of that and it's torquey, which I'm aware isn't really required for these cars but is a lot of fun. The diesel will also be a breeze to get running because it's mechanically injected and require no computer, I'll post a pic of the engine wiring later since I just wrapped it. I also already have the engine and trans, which saves me times and maybe money depending of the price of syncro diffs. I do realize that this will provably be as expensive or more so than a normal low cost, my saving grace will be having the engine and trans, which are worth at least $2k for what I'm running. The parts I'll be needing for drive shafts are cheap too so that will help too.

To get the speedo to read correctly, I need to either change the gear or adjust with tires. I decided (after finding correct info) to do both. If I use the speedo gear for the gas trans with the 3.667:1 diff I get a speed rating 5% too high, the trans is spinning faster than it normally would for the same speed. The rest is just tires.

I did a little work with this last night: tire calculator. Stock the golf comes with 175/70-13 tires, which have a circumference of 71.1 inches, I found 205/55-15 has a circumference of 75.0 inches, which would make my speedo read 5.4% slow according to the calculator. That's exactly what I want however because the diff ratio of 3.850:1 is 5% lower than the stock 3.667. So with 205/55-15 tires or an equivalent circumference both the speedo and odometer would be correct. I'm thinking I could check that with all the radar signs in my area :P . I'll probably get some 205/55-15 Michelin Pilot Exalto A/S tires for regular driving, and some 225/50-15s slicks for funsies :lol: :lol: .

Also here's a quick sketch I made (in paint) of the drivetrain layout:
Image
The colors are as follows:
Blue: Seats
Brown: Engine, intake and exhaust are on diver's side
Grey: Transmission and diffs, the front diff is being turned correctly the rear is reversed
Red: Driveshafts
Orange: Axles, regular fwd VW axles bolt right up to these
Black: starter


Last edited by FireStorm005 on Sat Apr 03, 2010 3:13 am, edited 2 times in total.

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PostPosted: Tue Mar 30, 2010 2:55 pm 
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If your main goal is mpg rather than AWD for some specific traction purpose then go 2WD. There's less parasitic loss.

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PostPosted: Tue Mar 30, 2010 3:36 pm 
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There is a problem.
The front and rear differenials will have a reduce to them.
At best you are looking at around 2.73:1 in each diff.
Combine that with a 3.67 (about the best that you can find in a 020 trans), you will end up with 6.4 : 1 engine to wheel rotation. With a couple of 020 trans, you should be able to locate a .7:1 fifth gear ratio, but with that you will still end up with 4.48:1.
With the diesel's top rpm (about 4200 ?) you will have a cruising rpm that will be a little high.

And that is if you are able to find a couple of diffs with a 2.73:1.

If you go to Techtonics Tuning, they have a gear chart for the 020 and 02A transmissions. And if you go to scirocco.org, there is a speed / rpm calculator that will make your design job a little easier.

The Rhino's use that configuration for building their 4x4 buggies (Honda powerplant turned 90 degs and driing two diffs) but with a 4x4 vehicle, low gearing is what they want. And the Rhino is not really meant for use on the street.


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PostPosted: Tue Mar 30, 2010 3:45 pm 
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Here is a link to the Gear Up! chart on Scirocco.org:

http://www.scirocco.org/gears/

And if you take a look at the charts, the best final drive that you can get is the 3.67 (in the 4Y, 9A, ACD, AEN, ATH, DFP, and CHE).
The lowest 5th gear that VW made was and is the .71:1 (in the 7D, 7A, FN, FF, FH, and FJ, there may be others).
The neat thing is, you can swap the 5th from any transmission into any transmission (020's).
So you can make a 9A into a 3.67 final with a .71:1 fifth.

But you still have to solve the other differential situations.
And I think you better take a closer look at the Syncro setup. I don't think that it does what you think it does as far as output speeds. Plus, if you turn it 90 degs, you will end up with a different drive train layout then what VW designed.


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PostPosted: Tue Mar 30, 2010 4:08 pm 
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16vvincent wrote:
There is a problem.
The front and rear differenials will have a reduce to them...

Yeah that's what stops everyone when they get to this point. With a couple 1:1 diffs it's a slam-dunk. Unfortunately the slamming part is the cost.

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PostPosted: Tue Mar 30, 2010 5:14 pm 
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KB58 wrote:
16vvincent wrote:
There is a problem.
The front and rear differenials will have a reduce to them...

Yeah that's what stops everyone when they get to this point. With a couple 1:1 diffs it's a slam-dunk. Unfortunately the slamming part is the cost.

Exactly, and the Syncro diffs are pretty darn close and since I already have engine & trans I can use that money to buy them. Vincent probably didn't read the whole first post since I covered in there how the Passat Syncro rears are actually a 1.05:1 ratio using 20/21 tooth gears for the right angle and the diff is off to the side. If you think I'm wrong look at this thread from VWvortex:Syncro to Haldex conversion about half way down he has all the different ratios from Syncro and Haldex AWD rear ends:

Dutch1967 wrote:
Gear ratio's angle drive:

Car type/model:
Golf Rallye/Passat G60 has an 20/21 ratio and 5-speed gearbox
Golf III 1.8 Syncro has an 20/21 ratio and 5-speed gearbox
Golf III VR6 Syncro has an 16/21 ratio and 5-spd 02Q gearbox
Audi TT/S3 4Motion has an 17/27 ratio and 6-spd 02M gearbox
Golf IV 4Motion has an 17/27 ratio and 5-spd 02C or 6-spd 02M
Skoda 4Motion has a n 17/27 ratio and 5-spd 02C or 6-spd02M


Notice Passat G60 is 20/21 which comes out to a 1.05:1 ratio. Since I did my calculations with 1.13:1 I'll have to fix them and I'll update the original post with the correct calculations here in a minute.


Last edited by FireStorm005 on Sat Apr 03, 2010 3:10 am, edited 1 time in total.

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PostPosted: Tue Mar 30, 2010 5:46 pm 
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16vvincent wrote:
There is a problem.
With the diesel's top rpm (about 4200 ?) you will have a cruising rpm that will be a little high.


In it's current form, with an unmodified Turbo injection pump, max power comes around 4500 rpm and redline is just over 5000 rpm (5050 I think). I've heard a guy by the name of Giles at Performance Injection in Canada does amazing work with these pumps and there are rumors that he may be trying to make one that will allow 7000 rpm :shock: :shock: :shock: :shock: :shock: . That's on the naturally asperated pump that stock max power is 4800 rpm and stops at 5300 rpm. These old IDI (indirect injection) diesels can spin alot faster than the DI (direct injection) diesels in newer cars (except the 335d but that's way out of the price range). With some work from Giles ($$$$) I could have one crazy diesel. That work however will probably come after the car is built and running, once I have the suspension and everything all worked out and set up right.

16vvincent wrote:
If you go to Techtonics Tuning, they have a gear chart for the 020 and 02A transmissions. And if you go to scirocco.org, there is a speed / rpm calculator that will make your design job a little easier.

I'm using the gearing info from BrokeVW.com which is an excellent site about the 020 trans.


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PostPosted: Tue Mar 30, 2010 6:08 pm 
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I'll have to echo what's been said, everything was fine up until you said you wanted really good mileage. You're going to have to structure your priorities because you'll be giving up a fair amount of mileage with the extra hardware in friction, complexity, and weight.

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Kimini book: Designing mid-engine cars using FWD drivetrains, http://www.kimini.com/book_info/


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