JRW'S 91 318is turbo build

[jrw21]

Dyno Run #1 265whp 18psi: https://www.youtube.com/watch?v=mx5oh5CHy7s
Dyno Run #2 330whp/281 torque 25psi:
Dyno Run #3 340whp/299 torque 26psi: 80lb/hr injectors @ ~90% duty cycle


Hello all. I am in the beginning stages of a build on my 199k mile 91 318is. I decided to share this project with all of you. This will be a slow build so be patient with me.

I have no goal at this time. Just building..we will see what happens if this ever gets "finished" anyway.

First up was fabbing the manifold, downpipe, and exhaust. I built the manifold out of s52 header and the stock m42 header. The s52 header was from my old 8psi boosted m3 (supercharged). I sold the m3 last year to prepare for this project. The exhaust was built from 2.5" mandrel bends and two "cherry bomb" type mufflers.

[jrw21]

Welded a bung in the lower oil pan at the highest point I could get it.



After the exhuast work was fabbed I let it run for about 15 minutes to verify the turbo and exhuast were to my liking. I honestly was very worried about using the "cherry bombs" but I was pleased with the sound that made its way out of the tailpipe.

Then I pulled it all all right back off to start the build!

The turbo is a Garrett .63/.63 using a tial F38 wastegate. The downpipe has two bungs, one for afr and the other for o2 and a flexpipe.

[jrw21]

It was tough to do it, its been such a reliable strong engine even with 199k miles... But, I pulled the engine today. Going to start playing around with options on the engine build.

[jrw21]

Alright so here are my engine ideas...

1:

m44 crankshaft, s52 pistons, M50B25 Rods

With this combo I will need to shave my s52 pistons about 3 or 4mm to get compression around 8.5:1 (depending on gasket size). s52 pistons have a roughly 4mm dish to them so shaving them 4mm will essential make them flat topped. 3mm shave will put me about 2.25mm below deck and 4mm 3.25mm below deck.

2: WON'T work. I CC'd dish of s52 piston and I recorded 15.5cc dish 6.87:1 compression

m44 crankshaft, s52 pistons, 135mm rods.

With this combo I would not need to shave the pistons, however I will be sitting around 4.25mm below deck and have to calculate in the dish of the piston. So, that limits me to a very thin gasket .06 or .07" compression will be about 6.87:1.

I have a block already bored to 86.4mm and an extra head: supertech valves springs SPR-H1000D/BM and VW 48grams p/n 050 109309 lifters. Planning on using BMW 6mm valves and guides.

Here is a picture of the block (86.4mm) fitted with m44 crank (83.5mm) (just messing around testing deck heights with my calculations) with 140mm rods and s52 piston, m42 piston, and m50b25 piston.



And this is a comparison of a late m42 rod (140mm) and piston on left to a stock m50TUb25 rod 11241721471(140mm) fitted with s52 piston on right.

[wazzu70]

Are the M50 rods/pistons canos or non vanos? Just curious as they are different.

If I remember correct the M42 are on the left and on the right are Vanos M50 assembly. Its been a while since I looked at M42 pistons I cant remember what they look like! Cant remember if they are the newer skirted type perpendicular to the wrist pin, or the old full skirt style all around.

I like your solution for the turbo mani. Looks quite good actually!

[benz-tech]

Based on the picture you have up, the M42 fully skirted piston is on left, attached to an M50 rod possibly?. The piston on the right is the later slipper-skirt style, assuming it is for an M50, it looks similar in style to the S50 and S52 pistons I've had in my hands lately. I'd swear that that rod on the right is an early M42. 12-point bolts and all. Is it possible you mixed them up? the rod on the left is a spitting-image of the M44 and 135mm S52 rods that I have.
Got a cheap set of 135mm rods for sale if you like. I'm going high-compression so they wont work for me.

[jrw21]

As you are looking at the picture the rod/piston combo on the left is in fact from a 93 m42, i pulled them myself. The rod/piston combo on the right is from iirc a m50TUB25 VANOS engine with an s52 piston attached to it. I will get the part numbers off the rods and post them on here tonight just to verify.

I am still trying to weigh the benefit if any of having a higher rod to stroke ratio of the 140mm rod. Not sure if it will be that big of a deal or not. 140mm rod with m44 crank rod/stroke ratio is 1.67:1 vs 1.617 of 135mm crank. Also, trying to determine if shaving the s52 4mm will shorten its life in a turbo engine? Shaving 4mm puts the top ring 4mm closer to combustion so worried a bit on heat issues long term?

[benz-tech]

It appears that you have a later M42 with the "M44" style rods. Realoem definitely has different part numbers for the M44 and the M50. Whats interesting is that they sub to a 'cracked' style rod. My M44 and S52 rods are not cracked, definitely machined. Just curious what type is that M50 rod, cracked or machined?

[jrw21]

Now you have me curious. I am going to get the part numbers off the rods right when I get home tonight. I am unsure what the "cracked" term refers to?

I am going to start disassembling my 91 m42 tonight. Not sure how far I will get but hopefully I will get down to the rods on it. I have never personally touched an early model m42 rod. It will be interesting to see what it looks like compared to the m50tub25 rod. 

[wazzu70]

On a street motor 135mm vs 140mm rods wont make a huge difference. Longer is better, but if you are trying to use OE pistons, just use the rods that are the best match.

Shaving the piston crowns that much could definitely cause issues. The piston crowns on turbo motors are usually thicker than atmospheric engines due to the higher temperatures and combustion pressures.

Really, custom pistons are worth the cost for this. You get the exact CR you want, the ring land spacing you want, crown thickness you want, ect! Small price for many benefits!

[jrw21]

I have the s52 pistons laying around that is basically why I am planning on using them. The reason I wasn't going to go custom pistons is because I see s52 turbo engines with stock pistons making a lot more HP and heat than that I anticipate on making. Maybe my assumption is not accurate?

So, would you say that going with 135mm rods and not shaving the pistons at all would be the way to go? That is the direction I am leaning.
212-(83.5/2)-31-135=4.25mm below deck.

Now with that info with 86.4mm bore assuming 3cc dish on piston (if anyone knows actual s52 dish volume please let me know) and size .06" gasket I compute ~8:1 compression

This would save me time and money milling down the piston as well.

[benz-tech]

Now you have me curious. I am going to get the part numbers off the rods right when I get home tonight. I am unsure what the "cracked" term refers to?

I am going to start disassembling my 91 m42 tonight. Not sure how far I will get but hopefully I will get down to the rods on it. I have never personally touched an early model m42 rod. It will be interesting to see what it looks like compared to the m50tub25 rod.

I'm basing 'cracked' off of what realoem says about the new part number for the rods so I don't really know exactly what they mean. In Mercedes-Benz land, a cracked (rod is forged as a complete unit then cracked in half so that when you bolt it together, the cracked surface mates up with the other half perfectly. Obviously the big end is still machined round but where the bolts go through, there will be a very rough - cracked- edge. An early M42 rod, when you get it in your hands, is approx. 100g heavier and much larger than the later ones. that's why I assumed that it was the one on the right. Keep us posted.

[jrw21]

Will do. Thanks for the info.

Now you have me curious. I am going to get the part numbers off the rods right when I get home tonight. I am unsure what the "cracked" term refers to?

I am going to start disassembling my 91 m42 tonight. Not sure how far I will get but hopefully I will get down to the rods on it. I have never personally touched an early model m42 rod. It will be interesting to see what it looks like compared to the m50tub25 rod.

I'm basing 'cracked' off of what realoem says about the new part number for the rods so I don't really know exactly what they mean. In Mercedes-Benz land, a cracked (rod is forged as a complete unit then cracked in half so that when you bolt it together, the cracked surface mates up with the other half perfectly. Obviously the big end is still machined round but where the bolts go through, there will be a very rough - cracked- edge. An early M42 rod, when you get it in your hands, is approx. 100g heavier and much larger than the later ones. that's why I assumed that it was the one on the right. Keep us posted.

[benz-tech]

I can send you 1 135mm rod for mocking up if you like. I might need it back as the set is for sale. 

[jrw21]

I can send you 1 135mm rod for mocking up if you like. I might need it back as the set is for sale.

I might take you up on that. Actually pm me a price for four of the rods and I may consider it.

Pulled the part number off the m42 rod, I was told the engine was from a 93 car. However, when I ran the part number 1739732 it is showing used on 95-99 m42/m44.

The m50 rod has random numbers that I have not been able to cross reference yet. 473N 473N 23 24 and 380376 stamped on the side