M42 Turbo Build! Need to dust a S52

[elcoy]

Posted on R3V as well but figured the M42 knowledge is probably easier to find here!  My little sister drives a S52 swapped E30 and recently got good enough at driving that she can beat me at the track, sooo time for a snail!

So I have read just about every M42 Turbo build thread I could find over the past few years, and finally get to build one!  I am starting a thread to help keep me motivated and hopefully tap the knowledge of the community.  I suppose I should start with the history of the car.  I bought a 91 318is about 4ish years ago that was basically stock.  It didn't last very long before it got lots of suspension parts, as well as a full respray.

Pic of car right after respray:



With the e34 that started the family obsession:



Few years later, no real major changes or mechanical issues.  Electric fan, chip, and some is skirts.  Threw a roof rack on for awhile when I was remodeling a couple rooms in my house and was in work truck mode!



I bought a M42 that had jumped timing to build on the stand so I could drive my car as long as I could without tearing it apart, since it has been (knock on wood) extremely reliable for an unknown miles 23 year old car that is driven hard. 


I happened to stumble across this beauty on craigslist however and made a somewhat impulse buy that has proven to be a ton of fun in Michigan winters:



A 91 325ix auto that will serve as the daily from now on.  The 318 can now sit as long as it needs to once I am ready to swap the motor in!

Now to the actual turbo fun!

Stripped the motor apart and found lots of loose chunks that I am assuming were not designed to be there. As well as some nice dents on the pistons from the valves:





Some of the things found inside:






Sooo the plan now is to take the block to an engine builder to get bored.
From there I believe I have an idea of what the gameplan is, but am open to suggestions and feedback!  I would like to shoot for somewhere north of 300 HP, but would like to build the motor to be stronger than the HP it puts out since I would like to drive it for more than a few months. I plan to have an engine builder polish and balance the OEM Crank and Rods.

Parts list:
Stock Crank
Stock Rods
CP Forged Pistons (85mm)
Turbo Cam
SDS standalone (already purchased)
ARP Hardware
MLS Gasket
Garret GT28 (15ish psi?)
Tial Wastegate
BOV
Biggest Intercooler I can fit

I am unsure about what exactly I am going to do for the head.  I figured port and polish, but was unsure what stock components would be strong enough or flow well enough for my goals.  I will do lots of research between now and when I am ready to make those decisions, as well hopefully get some input from the M42 Turbo Gurus.  I am all about building it right with the correct strong parts, but don't want to waste any more money than I already am! Should be a long ride, but hearing that turbo spool and spanking some expensive cars in my little E30 will be worth it!

Let the hate/love/comments/bankruptcy/general conversation start!

[thebrelon]

no turbo guru here, but if you want 300HP and an engine able to withstand more fore reliability sake you'd better use after market rods.

[Darky]

Hi
You could easily go 86 mm Pistons.
You will also want to drop compression to about 8.5-9
North of 300 means different gearbox and diff.
Cheers Rohan

[elcoy]

Ok while I'm there I guess it would be a dumb idea to not upgrade the rods.  If I am not mistaken a Getrag 260 would bolt up since it has the same bell housing as a 240? Guess I am not sure what to do about a diff yet... any suggestions?

[jrw21]

Awesome. Nice car nice and clean! Lets see the s52 car too!

As for the rods you will be fine at 75hp per cylinder. The stock m42 rods are forged and BEEFY. Just compare them to the s52 rods and you will see what I mean. The s52 rods are proven up to like ~600hp or 100hp per cylinder. But torque is the killer and I am sure you will be fine with the torque at 300hp. But, if you are willing and able go for it!

[elcoy]

I am hoping to keep the stock rods since they are forged and pretty strong.  I am hoping the engine builder will also have an opinion based on dimensions and experience.  Does anyone know if there are dimensions somewhere that compare the stock rods with an aftermarket set? I would be curious to see how much thicker aftermarket rods are since both are forged H beams.

Bonus S52 pic!

[Tgoode318]

The stock rods will do fine But i'm of the opinion that if you have the will and the way (and the $$) DO IT! You cant beat the piece of mind you will get on a great set of aftermarket rods, and if you get power crazy in the future and that 300hp just doesn't do it any more you can crank up the boost !! . If you are on a tight budget and you know 300's where you wanna be skip this mod and save your money for something else more germane to the build. 

By the way nice s52 e30! clean

[elcoy]

Dropped the block and crank off at the engine shop to get magnafluxed for cracks, as well as the head to get ported and polished.  Could be awhile as he is busy building massive drag motors.  The M42 looks almost funny in his shop next to huge V8s! Sorry I forgot to take pictures but am going to drop the rods off next week sometime so I will have to sneak some 'before' pictures!

[econti]

Just some thoughts on rods, someone down here was running somewhere around 500hp at the crank on stock rods in his race car. They did eventually break, but I reckon you'll be right with those power levels.