Planning an engine build, new injector and exhaust ?'s page 2

[digger]

There are a few different piston designs for the M20B25. This pic shows an aftermarket, eta piston, "i" short skirt, and "i" long skirt. There's actually another type of "i" long skirt available. You want the third one from the left, and you still have to trim it down some.


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that's not completely correct

its

ALPINA-SETA-B25-B25

here is view from top they are all pistons for the 885

alpina has shorter comp height for using 135 instead of 130 rod
seta is nearly same as b25 but valve reliefs are smaller



long skirt high comp mahle b25







i also have a long and a short piston and neither have the square raised section.

[Reichart12]

The picture of all 4 side by side was the reason I asked earlier about the flat bottom being short vs rounded/radius being longs. It really does seem like BMW had a bunch of versions that they put in randomly.

[digger]

The picture of all 4 side by side was the reason I asked earlier about the flat bottom being short vs rounded/radius being longs. It really does seem like BMW had a bunch of versions that they put in randomly.

BMW used mahle and KS brand and there are several designs, i think you can get any version to work but some might require more work than others.

[Reichart12]

Well update time... Picked up a 325i engine the other day to use along with the m52 crank. Never realized how heavy the crank is lol. Getting rods next weekend and in the mean time hopefully opening up the engine to see what pistons are there. After that it's off to a machine shop. Still looking for the right one but I think there is a local one with the expertise to do the work.

Also, from what Ive seen it's seeming like I will need a 325i radiator to go with this? Still looking for all the details on whats needed.

Next update in a couple weeks I hope. (also updating in my members ride thread lol)

[Reichart12]

A new option has come up for me....

Custom pistons, yay or nay?

I have the engine, crank, and rods (being mailed) but after talking to a shop they are strongly advising against using I pistons (sure theyd get a sale on customs) so I think it may be better to just get custom pistons. I would be buying new rings and pins anyways plus the machine work to get the pistons to fit. I feel like the extra bit of money to get new pistons with rings (packaged) would make sense.

I would be getting the CP forged 10.25:1 piston set from VAC, with that I still believe the m52 crank and then either I or e rods. That should go with no machining I think? Decisions are not my strong point.

[Reichart12]

Heres the build specs I finalized with, Im posting more updates in my build thread but if I ever get anymore questions Ill go here. Its a slow going process but hopefully done right.

-b25 block bored to 85mm
-m52 crank (84mm stroke)
-cp pistons 85mm with 11:1 compression
-b25 135mm rods

What a difference from the original plan lol

[digger]

what cam are you going to run with 11:1?

what ECU?

[Reichart12]

The ecu will be megasquirt and the cam will be 284/272 I think.

[digger]

you wouldn't really want a cam any smaller with that high of a CR i always recommend an adjustable camgear you can play with the powerband somewhat.

you could step it up duration wise but depends on the application and whether you do use RHD ITB. 284/272 is a good balance daily driver / performance cam with good torque off cam.

[Reichart12]

So things have been going pretty slow but its understandable as the block was dropped off around the holidays and its off racing season and I wasn't in much of a hurry because of money restrictions. My original budget went out the window when I ordered custom pistons so I expected the build to drag out a little lol.

Now on to the important question of the day... the block should be done this week and when I would go to pick it up, I would also drop off the head to get work done but Im not sure if I should go with VAC or Bimmerheads with this.

I know I want some port and polish done and a 284 cam. But what other options do you think are must have? I would like to be able to get a deal and save some money as I still need headers, MS, and clutch but after doing all the block work Id like it to be complemented by the head.

And does anyone have a preference between the two places? Has anyone seen flow data that backs up one over the other?

Thanks

[digger]

John (Forced_Firebird) at WOT tech, knows what he is doing will use a flow bench to work the head. Avoid VAC IMO

http://wot-tech.com/

[SkiFree]

It's a bummer you ordered your pistons, I'm working on something pretty dang special right now. Should have them in a couple months.

-M142 alloy
-slipper skirts
-offset dish head
-coated skirts

[Reichart12]

John (Forced_Firebird) at WOT tech, knows what he is doing will use a flow bench to work the head. Avoid VAC IMO

http://wot-tech.com/

Yeah I wasn't really feeling VAC again but I figured since I have to go there anyways to pick up the block. Thanks for the lead, Ill have to check him out.

It's a bummer you ordered your pistons, I'm working on something pretty dang special right now. Should have them in a couple months.

-M142 alloy
-slipper skirts
-offset dish head
-coated skirts

Sounds like some serious stuff. My original plan would have had the engine swapped in already but I grossly mis-estimated everything lol.

[Reichart12]

Ok so hopefully the last questions from me....

Will pink top m52 injectors fit in without modification? I know I want more than stock fuel injectors but going for m50 ones and calculating the difference of 3.5 to 3.0bar for the systems, they don't seem to be more better. Im looking off Mepeh.com to get already rebuilt ones and the ones listed for m52 seems to fit the specs, Im just not sure if they drop in like normal.

Also my exhaust needs to get worked on too. I've tried to read up on single/dual pipes and Digger's thread about X placement but I think I will be going single pipe after a merge of the headers. I liked sound clips of vibrant products so I am leaning that way. The headers will merge to a 2.5" and have a 12" resonator and vibrant's street power 2.5" muffler. I'm trying to keep it basic and I think this should fit the bill. Any concerns with this setup? And as of now I am not planning on using a flex pipe, is it actually necessary?

[digger]

a longer resonator will be better especially if its just a bottle style without much volume