Turn the 2.5 liter M20 325i motor into a 3.1 liter (M20B31) - the additional torque allows the to pull strongly below 3000 rpm. This kit is a major performance improvement and can be spec'd for any number of builds.
The kit includes:
-Forged OEM steel crankshaft
-Light-weight forged pistons w/rings and wrist pins
Our standard kit includes 85mm bore pistons with 9.75:1 compression. By special order we can supply any combination of bore diameter and compression ratio you want. If you are unsure of what would best suit your build – call us! Custom specs have a 4-6 week lead time.
– Includes a special ring package specified for use with forced-induction along with heavier-duty wrist pins. (Oil squirters available by request for an additional cost).
This kit is intended to run 135mm long connecting rods. This is the length of your stock rods which you can reuse if desired. You can also run 135mm rods from the M52 and S52 engines. Lastly you have the ultimate option of running our high-strength H-Beam connecting rods which is specially priced for use in this kit. Have a machinist inspect and refurbish whichever rods you choose.
Other recommended parts:
To get the most out of this kit we recommend larger fuel injectors, additional tuning (in the form of Miller WAR Chip, Megasquirt, AEM, or similar tuning tools), larger throttle body (or itb's), IE Stg2 Long-Tube headers, free-flow exhaust.
**Your kit may differ slightly than the picture depending on your specs.
***Clearancing may be needed in the block. Have your machinist check and adjust as needed (photos available on request).
**** For information on identifying which main bearings you have, please read our tech article here.