Blasphemy101's Turbo 24v Build Thread

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Re: Blasphemy101's Turbo 24v Build Thread

Postby blasphemy101 » Wed Jul 22, 2015 7:55 pm

M20_fever wrote:Only thread I know it was discussed off hand is my old engine build thread on tech here: http://www.e30tech.com/forum/showthread.php?t=41594

Not sure where it is in there, haven't looked at it in years.


Lots of good info in there - not so much about M42 pistons. Someone said you would have to machine valve reliefs into the pistons for use in an M20, but that's it.
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Re: Blasphemy101's Turbo 24v Build Thread

Postby M20_fever » Thu Jul 23, 2015 1:04 pm

Hmm, maybe it was another thread where we talked about durability. Can't remember its been so long.
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Re: Blasphemy101's Turbo 24v Build Thread

Postby blasphemy101 » Thu Jul 23, 2015 3:19 pm

I understand. Just let me know if you think of anything. Getting my hands on a full set of pistons may take some time.

So on another note - what is a fair price for a E34 M50 oil pan setup? It looks like the going rate on Ebay is $200, but that seems kind of pricey to me. Unfortunately, it doesn't seem like the sort of thing that would be easy to pull at the pick and pull.
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Re: Blasphemy101's Turbo 24v Build Thread

Postby blasphemy101 » Fri Jul 24, 2015 4:00 pm

I picked up a set of four E30 M42 pistons and rods yesterday. They're pretty heavily used - the rings are almost entirely worn down, and one piston shows light wear. I haven't pulled everything a part to measure them, but here are my first impressions. The M42 piston is the one on the darker rod with the clean(ish) top.

I won't say the rods are identical until I measure them...
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It looks like the M42 piston is heavier, and the M50 piston looks like it puts its material in more important places. It looks like the skirts are thicker. The surface finish on the M50 rod seems smoother. Maybe the result of a different forging process?
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On first glance, I'm not sure about the concern with the ringlands on M42 pistons. They look thicker than those on the M50TU pistons.
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A quick shot of the piston tops. Obviously, I need to clean up the M50 piston to give a real comparison. I'm concerned the valve reliefs on the M42 piston might be too small. The M42 has nearly the same sized valves, but it all depends on the cam profile and the angle of the valves as they open into the combustion chamber.
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This is pretty typical for my cylinders. Those rust spots are completely smooth to the touch. The crosshatching is still very visible.
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Re: Blasphemy101's Turbo 24v Build Thread

Postby M20_fever » Tue Jul 28, 2015 1:17 pm

I don't think either of those pistons are forged. If anything I'd get the valve reliefs machined deeper so you can run a more aggressive cam lift, but that's just me.
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Re: Blasphemy101's Turbo 24v Build Thread

Postby blasphemy101 » Tue Jul 28, 2015 8:44 pm

The pistons are cast. The rods are forged.
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Re: Blasphemy101's Turbo 24v Build Thread

Postby Yoshi » Wed Jul 29, 2015 12:38 pm

don't do it chip!
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Re: Blasphemy101's Turbo 24v Build Thread

Postby blasphemy101 » Wed Jul 29, 2015 6:09 pm

Yoshi wrote:don't do it chip!


Don't do what? Is that a Dave Chappelle reference?
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Re: Blasphemy101's Turbo 24v Build Thread

Postby Yoshi » Thu Jul 30, 2015 12:15 pm

don't use the pistons. and yes it was.

Excuse me officer... excuuuuuse meeeee. I'm a little bit high and lost... Can you tell me where third street is?
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Re: Blasphemy101's Turbo 24v Build Thread

Postby blasphemy101 » Thu Jul 30, 2015 7:30 pm

Why do you hate my pistons so much TT TT
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Re: Blasphemy101's Turbo 24v Build Thread

Postby Yoshi » Fri Jul 31, 2015 12:44 pm

Because they are questionably weak and aren't designed for that engine. I can't find a single person who's actually done it and has proof their car runs.
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Re: Blasphemy101's Turbo 24v Build Thread

Postby blasphemy101 » Fri Jul 31, 2015 6:09 pm

Yoshi wrote:Because they are questionably weak and aren't designed for that engine. I can't find a single person who's actually done it and has proof their car runs.


Then let's do it! For science! -yuush- I don't think it should be any worse than the "2.7i" conversion. I'm going to measure out both pistons tonight and post my results. I'm worried the compression ratio might work out to be too low with the E30 pistons. The pistons should be about 1mm below the top of the block, and I've read that the combustion area on the piston is about 17cc. That seems like an overestimate to me, but we'll see.
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Re: Blasphemy101's Turbo 24v Build Thread

Postby Yoshi » Fri Jul 31, 2015 6:56 pm

Ah god that 2.7i conversion annoys me. Why do it for science? I've decided "Tried and true" is so much more worth not having to bother with the guess work and mistakes.

1mm below the top of the deck is bad. Pistons are designed with a specific type of quench area. It's the same reason custom pistons are preferred over thicker head gaskets. Even if it fits, the physics of catching the combustion change with piston/head design.

You're hell bent on it, I should stop vomiting on your thread.
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Re: Blasphemy101's Turbo 24v Build Thread

Postby blasphemy101 » Fri Jul 31, 2015 7:08 pm

Yoshi wrote:Ah god that 2.7i conversion annoys me. Why do it for science? I've decided "Tried and true" is so much more worth not having to bother with the guess work and mistakes.

1mm below the top of the deck is bad. Pistons are designed with a specific type of quench area. It's the same reason custom pistons are preferred over thicker head gaskets. Even if it fits, the physics of catching the combustion change with piston/head design.

You're hell bent on it, I should stop vomiting on your thread.


Not hell bent on it. I just prefer it to my other options. They still might not work. I haven't measured them yet.

[EDIT] I should clarify I'm not satisfied with the "tried and true" method of the MLS gasket. The best route is obviously custom pistons, which isn't really an option right now. The other option is obviously leaving the compression ratio alone, but I can't find anyone running a stock compression m50 turbo.
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Re: Blasphemy101's Turbo 24v Build Thread

Postby M20_fever » Mon Aug 03, 2015 3:06 pm

don't use the 2.7i conversion as any kind of metric, it sucks ass. Google it, there are tons of people that regret doing it, and almost none that think it was worth the effort. Honestly, IMO your best option if you can't afford custom pistons or rods is leave it all stock and run lower boost. You'll make more power on low boost with stock CR than you would low boost on dropped CR, so it won't be a dog. With a good tune it will make more power than the e30 chassis can use anyway.
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