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Howdy all.

 

Long time lurker, first time poster.

 

Quick rundown of the project. 

 

MKV R32 Engine

Custom engine mounts

Precision 6266

3.5" dump pipe

Tial MVR44 and Tial Q50 BOV

800hp Intercooler

 

Here in lies my problem:

My MKV crank is cast. I have verified this. I have a 12v AAA crank in the garage (24v trigger wheel swapped over) that is freshly polished and checked by the machine shop. My software is written for a 24v 2.8 and I have also swapped my MKV exhaust cam, both cam sprockets and hydraulic adjuster unit to work with my software. 

 

Can i just swap in the 12v crank with new rod/main bearings to achieve lower compression (around 7.9 or 8:1 if i remember correctly) and to also lower the piston speed?

 

I know others have done this so I would appreciate any input. The reason for needing such low compression is that I only have access to 98RON fuel, no E85!!

 

I am not planning on much power, 550bhp or so which should be easy for the 3.2 engine. The cost is more or less the same swapping the crank as it is to buy a headspacer and new headstuds, but I would prefer to not mess with the timing chains and the potential for that to stuff up, so swapping cranks seems smartest. 

 

I have done my calculations and with 84mm bore + 90.3mm stroke = 3002cc = R30. 

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I think, (off the top of my head), that someone has done it with a 24v crank that way around which would be the same as the 12v, usually it's other way around, not sure on comp without doing the math. 

 

You're thinking about using a V6 4mo map on a mk5 R32 for FI! Let me know the ins and outs of the ecu so you don't end spending a fortune on that side.

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You need to buy custom vr6 24v pistons with 84mm or larger bore if you are going over bore.

It's not the height of the top of the piston that's the concern although the 7:1 compression ratio you will end up with is a little low for the boost/ power your looking to run. It is the piston pin ratio that may cause you an issue as the piston comes to the bottom of its stroke.

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I think, (off the top of my head), that someone has done it with a 24v crank that way around which would be the same as the 12v, usually it's other way around, not sure on comp without doing the math. 

 

You're thinking about using a V6 4mo map on a mk5 R32 for FI! Let me know the ins and outs of the ecu so you don't end spending a fortune on that side.



12v and 24v crank have the same part number. Different trigger wheel and need three new bolts.

Car is a B5 S4 utilising a 4mo bora ecu with custom code to control 3.2 cams and actuators along with evap output to control mac boost solenoid.

As soon as my 3.6 bearings turn up i will post pictures so others can see you can use stock 3.2 rods/pistons with 12v crank to make the R30 with 8:1 compression.

Also 700bhp should be fine for stock internals. We shall wind the boost up and see how she goes with timing.
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