First off...what is the system fuel pressure at the fuel rail for BMW motors? Im aiming for 400-450 crank HP (roughly 300-350rwhp). Im building a 2.1L M44 Stroker motor. Can anyone tell me what size injectors I need and where I can get them at (whether from another BMW or from another source).

Also, what is the best way for going about figuring out what size pistons I will need. Im using a mixmash of parts from a lot of different BMW motors to gain what I need. I will be going with a 86mm bore and a 90mm stroke. Factory is 85mm bore and 84mm stroke.

Lemme know if you guys need anymore info. Thanks in advance for the help.

Injectors I would say at least 36lb or better. I have Ford 30lb's and they are maxed out at a little less than 300rwhp.

Pistons: Contact CP, JE, Wiseco, or however you prefer and obtain a set of custom pistons. Tell them the bore, stroke, and compression ratio you want and you should be good to go.

Isn't an M44 only 4 cylinders? In which case, you will need larger injectors than you would need if you had six of them on an inline 6. It takes roughly 1/2 lb per hour of fuel to make 1 hp and you want to make 450 hp. Therefore you need 225 lbs of fuel per hour. Divide by 4 if you will be using 4 injectors. You get about 55 lbs/hr. You could go up or down a little until you find a standard injector size or you can play with fuel pressure to make any injector flow what you want, within reason (there are fuel flow calculators online that you can use to determine "after" flow if you know the flow at the "before" pressure that is usually the rated pressure or the pressure at 3 bar or 44 psi). You might want 52 lb injectors or 60 lb injectors.

It sounds like you are just getting started and have much to learn. I would find someone who has done exactly what you want to do, successfully, and copy them. Plenty of people who don't know quite what they are doing have assembled lots of expensive parts only to find that they do not all work together as expected. Pistons are sometimes one of those expensive parts, where one is also changing the rod and maybe the compression because one is stroking the motor.

Philip Bradley

Make sure to use a MLS gasket. With an 86mm bore there is only 4mm between bores.

So, you managed to get hold of a M47N crank, does the trigger wheel on the crank interfere with the block? Also, are you fitting the M42 crank pulley, lower timing case and crank trigger sensor to the M44 block?

Isn't an M44 only 4 cylinders? In which case, you will need larger injectors than you would need if you had six of them on an inline 6. It takes roughly 1/2 lb per hour of fuel to make 1 hp and you want to make 450 hp. Therefore you need 225 lbs of fuel per hour. Divide by 4 if you will be using 4 injectors. You get about 55 lbs/hr. You could go up or down a little until you find a standard injector size or you can play with fuel pressure to make any injector flow what you want, within reason (there are fuel flow calculators online that you can use to determine "after" flow if you know the flow at the "before" pressure that is usually the rated pressure or the pressure at 3 bar or 44 psi). You might want 52 lb injectors or 60 lb injectors.

It sounds like you are just getting started and have much to learn. I would find someone who has done exactly what you want to do, successfully, and copy them. Plenty of people who don't know quite what they are doing have assembled lots of expensive parts only to find that they do not all work together as expected. Pistons are sometimes one of those expensive parts, where one is also changing the rod and maybe the compression because one is stroking the motor.

Philip Bradley

Ive done motor builds before, but those were things that had been done before so I was just coping. This build is sort of a new thing. No one has really bored/stroked the M44 and boosted it successfully yet. Gizmo is working on one, and has an NA motor up now, but until things are together, we are both pioneering here.

Didn't even think about the motor being a 4cyl.

Make sure to use a MLS gasket. With an 86mm bore there is only 4mm between bores.

So, you managed to get hold of a M47N crank, does the trigger wheel on the crank interfere with the block? Also, are you fitting the M42 crank pulley, lower timing case and crank trigger sensor to the M44 block?

Paid full retail for it and shipped it in...lets just say it wasnt cheap. :(

Havent fitted the crank on the motor yet...as the motor is sitting at a friends waiting for us to run it to the machine shop. Crank just came in recently. Once the block is machined I'll test fit the crank and we can see how things go. I dont think I will have any problems, but I'll address it as it comes up.

Whats the best source for 60lb injectors?