M20 Turbo Build

[M5W]

Gentleman, Ive been a lurker for quite some time now and I have commited myself finally to an engine build. I had my S38 from my previous M5 built NA but by a shop, I am taking on the M20 myself and would like to document my build here. I have some questions since I have two engines at my disposal (and yet to get my E30 lol, its coming in november).

I have:

1: 1986 ETA engine
2: 1989 i engine

My original plan was to take the e block and then swap the i head and sensors and wiring harness and use my wasted spark megasquirt setup on it. I also have in the works a TCD turbo kit (just the hardware, manifold, turbo, downpipe, wastegate) and my fuel system from my S38 as well (aeromotive regulator, 32 lbs injectors, custom fuel rail, high pressure hose).

I see myself building this setup and once reaching the limit of the 50 trim turbo (300-350 whp) prob pushing my power levels higher. I recently read a member overseas on e30tech runs toyota 86mm bore pistons on his engines and this got me thinking. My ETA block has a bore of 84mm, my i block has a bore of 85mm and change, almost 86 correct ? If so, in theory, could I run a Toyota 2JZGTE stock piston (which have been proven up to 800 horsepower) with a shotpeened stock m20 rod with my stroker crank in the i block and run upwards of 500 hp ? It would be more expensive, but I have found a set of 2JZ pistons for 150 bucks, the turbo motor, and if they could bolt up to an M20 rod, and not interfere with / bang into the head, I would bargain to say Id have one reliable beast of a turbo M20 no ? Im just spitting out ideas guys, Id like to see if there are more options out there and this could be one that could really help the community if it is as easy as it almost sounds.

[quickervicar]

I could be wrong, but not too many people on here are blowing our stock pistons apart--even with big boost. I think your money would be better spent on tuning the software than on different pistons. Besides, running Toyota pistons in a BMW engine is like living with a pig's valve in your heart. You might be alive, but you're still part pig.

[jlevie]

Both the M20B27 and M20B25 use 84mm pistons. I don't think there's enough material in the block for a 2mm overbore.

[SpecM]

Both the M20B27 and M20B25 use 84mm pistons. I don't think there's enough material in the block for a 2mm overbore.

yea, the most people bore an m20 to is 85mm, and thats without boost

[ben312]

Like said above. I would worry less about blowing a piston, then about overboring and throwing one through the block.

[M5W]

Ok guys thats what I needed to hear, stock block it is.

[nando]

Both the M20B27 and M20B25 use 84mm pistons. I don't think there's enough material in the block for a 2mm overbore.

err, what? sure there is, 86mm is a very common overbore. you can even go up to 87mm if you want to push the limits a bit (race only).

the boost argument is silly. People boost the S52 all the time. It has the same cylinder spacing as the M20, with an 86.4mm bore. So how is it that the M20 is going to blow a piston through the cylinder?

also, the top ring landing of the M20 pistons are known to break. Good tuning can avoid this somewhat, but at some point if you plan on more power you will probably want better pistons.

[M5W]

K guys supra pistons on are there way and should be in my hands the 2nd week of november (UPS tracking # , there coming from cali, its a long time but it was cheap shipping so im not complaining). I tore down the 2.7e block to nothing and am going to send it to get sonic tested to see if it has any cracks and then if everything checks out ill have it bored out to 86 mm and o-ringed. That will all happen once I get my head back next week. Pics to come. Took apart the oil pump and cleaned it out with carb spray and then re-assembled it. Got my 60-2 tooth wheel off my 2.5i motor today, awesome little trick to get the crank nut off. Take out your spark plug and slide a piece of 6 gauge or 4 gauge copper wire and then turn the motor over till it locks and then you can get on the breaker bar to break the crank nut loose. Only thing left to do now on the spare motor is get it out of the car and to start on my oil pan for the turbo drain port and to get the short block 2.5i taken apart just in case I need the 135mm rods from it.

With the toyota pistons I want to be prepared in case they sit below the combustion level of the stock piston , then I can use the 135 rods and maybe mill off a mm or less off the toyota piston depending on how meaty it is. What would it cause if the combustion level of the piston was lower than the stock m20 piston ?

(I mean right now the stock 2.7 piston is dead even with the top of the block, what would the result be if the Toyota piston sat lower in the cylinder than the stock piston ? Really low compression ratio ? )

[M5W]

So I finally got around to taking some pics of my stuff.

Block dis-assembled and ready to go to machine shop.



Cart of parts that I have been cleaning up and working on.

Oil pump dismantled and cleaned

Pistons dismantled and ready for oil spray slot to be milled once I find time

60-2 Toothed wheel and sensor from 2.5i motor cleaned and ready

2.5i engine harness ready (thats underneath the table)

Throttle body cleaned but have to add my megasquirt tps adapter to it

Find adapter plug to put into coolant feed from block to throttle body, that way I can use it as a coolant pressure sensor.

Still debating if I should clean up the cam gear or just buy the adjustable one from a sponser on here.

Going to measure the crank and order my bearings soon as well.

[ck_taft325is]

Sweet. Can't wait to see how this all ends up. Very inspiring, man. Made me go out and pull my hood and fenders...

[M5W]

Forgot to post pics of turbo setup from TCD. Thanks again Todd !

[M5W]

Well guys heres some interesting news



2JZ GTE Piston attached to M20 Eta rod using the 2JZ wrist pin. Fits together like factory.

After measuring the combustion stack up thou, the 2JZ is sitting 1.66mm lower in the cylinder than the stock eta piston. Is this enough to make a huge problem in my CR ?







Measuring the M20 eta piston



the eta piston is 1.66 higher than the 2JZ piston



Visually you can see the 2JZ piston wrist pin hole sits slightly lower that the eta pistons



Onto the connecting rods





2JZ factory oil squirter





The toyota rods are alot beefier than the BMW rods



Anyways guys that it for now, hope this helps somebody someday. Ill be giving the 2JZ pistons some fresh rings I bought and have them put into my eta block.

[fiftytakedowns]

Mandatory given nature of what is going on in your build

[nando]

skim the block, buy an adjustable timing gear - problem solved. :)

[M5W]

skim the block, buy an adjustable timing gear - problem solved. :)

Thats what I was thinking. Would you go with that cosmo racing one or the nuke performance one ? Looking for one thats been used by someone on the boards with good results.