Scott-EP

i know bimmer engines are strong, but whats making you use stock parts on a boosted engine?

Urinemachine

8.4:1 CR with the HG, forged shot peened connecting rods (have been up to 880+ whp), spheroidal graphite crankshaft, stock 10:1 (on this motor) dished pistons, lowered to 8.4:1 with HG.

Scott-EP

thats cool. hopefully next year i can start on boosting my m3. i need to get my civic dont 1st though. ---- looks good

Urinemachine

The M3 is a little trickier in that its a higher compression motor, but I would have just as soon built a custom turbo M3 as I did a custom turbo 525, same ----.

Scott-EP

my only worry is turbo placement. there is no room. 10psi would be my max just cause the m3 is a daily driver. i want it to be quick(not a race car) but reliable. if i have to sacrafice any reliability im not changing anything.

i cant wait to see more updates on this car

Jcushing

doesnt matter how strong the crank and rods are if the pistons are weak , im not saying they are weak i dont know jack about bimmer engines and im not telling you what you should do but i woulda looked into a slight OS forged piston so you know that when you rehone up to the overbore size you get a nice seal on the rings and that the pistons can take a beating.

Urinemachine

The only reason for forged pistons is if you think your tune is going to be off Or, if your motor has a notoriously weak piston design. These internals have been pushed past 700 whp. The block was straight as an arrow and the hone removed ~0.0015" which is 0.03mm = new piston rings are file fit by an engine builder who was astonished with this particular setup. He was amazed that they used shot peened forged rods, spheroidal graphite impregnated cast crankshaft (no one has ever damaged... crank walked, broke, bent... this crank). The static compression ratio is going to be 8.34:1, and will be professionally tuned. If I break a piston, which I honestly do not foresee, I will consider putting some CP or Ross pistons in. However, the whole point of this project is to see how far it will go.

Once I remove the current engine (identical to this one) from the car, that will be bored and stroked to 3.1L with forged internals.

Jcushing

again i dont know anything about bmw pistons... hondas cast pistons can get broken ringlands cause they just arent strong enough for serious builds.... again yours might be fine though... theres only one way to konw

Urinemachine

Yup - but notice how low the top ring is from the piston surfaces. The BMW pistons are known for a very good firing ring with good depth top-down.

Here is a comparison - Honda piston:



BMW piston:




Notice that particular honda piston (I am not a honda guy, but I can see the weakness in that particular piston) has a 2 ring setup. The mass of between the bottom of the top ringland and piston surface is quite significant in the BMW piston compared to the honda. We rarely, if ever, have ring lands fail. Typically it's due to a bad tune and blowing a hole right thru the piston.

I do have one friend who broke his piston via ringlands, but it was from an S52 engine (3.2L) motor we turbo'd with stock pistons and he didn't exactly know how to tune timing so ran a map, which I haven't seen to this date, and that knocked and blew the ---- apart. But, that was dude to him running a 3.2L 24v with a GT35R T3 .82 housing and not realizing he'd be in boost at very low RPMs in 5th with load.

Neither here nor there - my current set up is at 13.7 psi on 10.0:1 cast stock pistons with pump fuel. Nothing record breaking, but also no issues! It's all in the tune - you'll break forged pistons just as easy if you aren't tuning appropriately.