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Discussion Starter #1
Hello,

I am considering putting a low mileage s4 engine in an S3 spider (89' w L jectronic). I only want to install the long block, not the Motronic bosch system as I know a conversion would be a nightmare. My concern is I understand the Crankshaft design on the S4 is different than the S3. So if anyone could help me answer the following questions I would appreciate it...
1. Can the S3 crankshaft pulley be used on the S4 crankshaft?
2. Are the flywheels different? Do I need to swap the flywheel in order for the starter and crankshaft position sensor to work properly?
3. Can the s3 waterpump be mounted on the s4 engine?
4. In order to keep the s4 ancillaries, waterpump, AC, alternator, (except the steering pump), I understand I would need to install an electric fan for the radiator, would this be complicated? I know the S4 radiator uses a sensor on the radiator. Is this all that is needed? how do I integrate this into the S3 L jectronic wiring harness?

Thanks Again?
 

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Discussion Starter #2
Hello,

I am considering putting a low mileage s4 engine in an S3 spider (89' w L jectronic). I only want to install the long block, not the Motronic bosch system as I know a conversion would be a nightmare. My concern is I understand the Crankshaft design on the S4 is different than the S3. So if anyone could help me answer the following questions I would appreciate it...
1. Can the S3 crankshaft pulley be used on the S4 crankshaft?
2. Are the flywheels different? Do I need to swap the flywheel in order for the starter and crankshaft position sensor to work properly?
3. Can the s3 waterpump be mounted on the s4 engine?
4. In order to keep the s4 ancillaries, waterpump, AC, alternator, (except the steering pump), I understand I would need to install an electric fan for the radiator, would this be complicated? I know the S4 radiator uses a sensor on the radiator. Is this all that is needed? how do I integrate this into the S3 L jectronic wiring harness?

Thanks Again?
Thanks Again!
 

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Hi Mrtzmd

I'm not really a Spider guru but since nobody else is answering your questions here goes


You said
My concern is I understand the Crankshaft design on the S4 is different than the S3. So if anyone could help me answer the following questions I would appreciate it...
I think the only change in the crankshaft after 1972 is that in 1988 they changed the diameter of the rear main seal, made it the same as the seal used on the V6 engine

Rear crankshaft seal used on all V/6 engines in GTV/6, Milano, and 164. Also used on late Spiders from engine number 611278 onwards, approximately 1988-94.

1. Can the S3 crankshaft pulley be used on the S4 crankshaft?
Yes
2. Are the flywheels different?
Yes
Do I need to swap the flywheel in order for the starter and crankshaft position sensor to work properly?
Yes
3. Can the s3 waterpump be mounted on the s4 engine?
Yes, pretty sure
4. In order to keep the s4 ancillaries, waterpump, AC, alternator, (except the steering pump), I understand I would need to install an electric fan for the radiator, would this be complicated?
Yes but is well worth doing. Also you will not be keeping the S4 ac compressor without changing out it's front pulley, as it uses a serpentine belt whereas the S3 car were all conventional Vee-belt designs.
I know the S4 radiator uses a sensor on the radiator. Is this all that is needed?
No
how do I integrate this into the S3 L jectronic wiring harness?
You don't. The L jet system does not control the cooling fan. The cooling fan circuit is it's own separate circuit
I'll try and post some more stuff later

Hope this was helpful.
 

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Discussion Starter #5
Very helpful, thank you!
So if I install an electric fan I can keep the auxiliaries?
 

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Just buy Spider S3.5 and forget about the swap :)

All the answers can be find in parts manuals and ePer. You need to do a cross reference of all the parts. Did it once when swapped the 1.8 TS to 2.0 TS in my old 155.
 

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I am considering putting a low mileage s4 engine in an S3 spider (89' w L jectronic). I only want to install the long block, not the Motronic bosch system as I know a conversion would be a nightmare. My concern is I understand the Crankshaft design on the S4 is different than the S3. So if anyone could help me answer the following questions I would appreciate it...

1. Can the S3 crankshaft pulley be used on the S4 crankshaft?
Yes. The only difference in the cranks was the rear seal size change between 1988 and 1989. Other then that its the same.

2. Are the flywheels different? Do I need to swap the flywheel in order for the starter and crankshaft position sensor to work properly?
Yes. If your running the Jetronic system you will need to change the flywheel. Make sure you line it up to TDC.

The S4 system won't care which flywheel your using.

3. Can the s3 waterpump be mounted on the s4 engine?
Yes.

4. In order to keep the s4 ancillaries, waterpump, AC, alternator, (except the steering pump), I understand I would need to install an electric fan for the radiator, would this be complicated? I know the S4 radiator uses a sensor on the radiator. Is this all that is needed? how do I integrate this into the S3 L jectronic wiring harness?

If you want to keep the S4 stuff including the Motronic full system. But not the p/s pump.

You would take out the 2 jetronic computers and there wiring harness and replace it with the S4 computer and its wiring. You will need to splice into the car harness but it not that bad of a job.

To have the a/c work you will need the 1990 model year front crank pulley. Which uses the Vbelt for the a/c instead of the serpentine belt. If you find one its not going to be chaep. Its a one year only pulley.

You can put the S3 water pump on it and use the cooling system you have. To use the S4 cooling system you will need to install the S4 radiator and its recirculating tank system. The S3 radiator has a plug in the bottom take that the cooling fan switch will screw into.
 

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S3s are Bosch L-Jetronic that have two sensors on the bell housing. One is a crank position sensor (lower one) triggered by a small magnetic post on the S3 flywheel. The other is a speed sensor (top one) that senses the ring gear teeth. These are required for the L-Jetronic to work properly. So, you'll need to swap the flywheel from the S3 to the S4. And, it must be installed properly or else your engine won't start. The crank on the S3 has one flywheel mounting hole that is relieved slightly. That hole will align at the 12 o'clock position when piston #1 is at top dead center. The flywheel has a small line on the edge directly above the hole on the flywheel that must be installed at 12 o'clock when installed on the crank. There's a small V notch in the spacer plate that you align this mark two when installing the flywheel. The relieved crank hole and flywheel timing mark should both be at 12 o'clock. That will place the magnetic pin installed on the edge of the flywheel at approximately 2 o'clock. The distributor rotor should be point forward when all the marks are aligned and the front pulley should be aligned to P (punto). The S3 also has an "empty" distributor. It merely distributes spark to each spark plug. There are not points or pulse rotors in the S3 distributor. Timing is controlled by the ECU (and the crank sensor). So, you'll need to swap the distributors if the S4 distributor is different. If I remember correctly, the S4 Motronic did away with the crank sensor and the distributor actually does initiate the spark plug firing. Of course, you can keep the S4 distributor if it actually initiates spark but then you'll need to eliminate the crank sensor firing message by disconnecting the white wire on the S3 coil. Hope this helps.
 
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