Nobimmer 694 Report post Posted November 2, 2008 I know surely this must have been covered atleast a hundred times but cant find it for the life of me! Anyways, if noone has that huge writeup that IS on here somewhere I just want to figure out everything I will need to swap my b20 to a b25. Car is a pre f/l 320i with a Getrag 240 (I think) As far as I know I will need to put in a Getrag 260 and change the L/jet etc ? (this is the part I dont understand) Are the m20 bolt on bits ( Alternator, Powersteering etc) interchangable between the b25 and b20. Cheers in advance Ashkan Quote Share this post Link to post Share on other sites
Mark 178 Report post Posted November 2, 2008 Do a 2.7 conversion while you're at it! Quote Share this post Link to post Share on other sites
Nobimmer 694 Report post Posted November 2, 2008 Will see how much funds allow etc. Will be happy with a tidy 2.5 conversion. Will tidy the engine bay up really good too while I'm at it. Quote Share this post Link to post Share on other sites
Kaz 64 Report post Posted November 5, 2008 I would like to know too cause I may be doing the same thing. Quote Share this post Link to post Share on other sites
Guest FrantiC Report post Posted November 5, 2008 (edited) Ok, Blocks are the exact same on the outside as far as mounting the alternator/AC/PS. The B25 motor should have the mounts for them still on it, Unless someone took them off for god knows what reason..... You CAN use your getrag240 and shifter linkage etc. No difference there, Same bellhousing and everything, Just the 240 has closer ratio gears. And YES you will need to take the l-jet ECU / loom out and use the 325i ecu and engine loom. You will need to modify either the engine harness end or fuse box end plug, To suit the plug differences. Early models had a Rectangular c101 (engine harness to fuse box connector) with a C104 3 pin plug by the ECU under your knee panel - The c104 wires exit the engine harness right at the ECU plug into the ECU. These 3 wires are ECU power, RPM for your tacho and I think the 3rd was Fuel consumption for your gauge under the tach. In later models with the round c101 fuse box connector, all wires are routed through there and the c104 does not exist. Here is the diagram you would use to convert the plugs from rectangle to circle to plug into eachother. You will also need to add 2 of the c104 wires to connect to the engine harness if you want the RPM tach etc. But, One problem here is early model ECU's got their power from the c104 (pin 2). Late model e30's do not have a c104. So they get their power elsewhere. Problem is I have never figured out where this comes from, I was following someone elses thread on another forum who did a similar swap with a late model engine into an early model chassis with the c104 and after the swap their car wouldn't start up. I will have to get in touch with the guy see if he figured out why, I always thought it wa because the pin2 of the c104 (ECU power) wasn't plugged in - But no one knows where it would go. I am positive it has been done, though. FWIW, I did a late model l-jet motor swap into a late model body. I researched it for ages and there was VERY little info about it. But the reverse of wiring a c104 plug into a late model car is very straight forward. But I have yet to figure out the definite way of doing it late model motor early model chassis. Edited November 5, 2008 by FrantiC Quote Share this post Link to post Share on other sites
