MyE28.com

So, MyE28.com doesn't seem much for bench racing or engine geometry, but let's see if we can change that.

My goal is a street/strip weekend driven E28, probably using my current beater/driver as a platform. It will be an M30B35, or at least start as one.

Timeline for this is way out (Winter 15-16 probably), so this is very much bench racing here. If you're not one for theory or open ended discussion on projects that won't go anywhere in the near future, this is not for you.

It seems the popular methodology around here is to take a good used engine, bolt on a turbo kit, and ride off into the sunset. I like this approach because it keeps it simple, you have an ample power ceiling, don't overthink things, and just focus on tuning and/or driving the thing.

This was my preferred approach in the Volvo world, but as these cars age it is becoming less practical. Starting with a 20+ year old shortblock, rebuilding or refreshing before it goes in seems more and more prudent.

When you get to the point of having the rotating assembly out, I believe it's an important step to consider the geometry of components before you put it all back together, and how it meshes with your overall goals and matches the rest of your components.

What is the weight of a stock piston and rod? What is the rod/stroke ratio using a stock length rod? Rod/stroke is 1.57, which is a little on the low side. My guess is that the pistons are relatively tall and heavy, but this is just a guess as google doesn't readily tell me. How thick are the ringlands? What is the piston's length? What are the most common points of failure at higher power levels?

Here is a post concerning deck height and compression height:
http://www.mye28.com/viewtopic.php?p=83436

It seems every single off the shelf set of pistons and rods out there uses the stock geometry. So you are going to custom-order a set of rods and pistons if you decide it is worthwhile to change.

The main advantages of higher rod stroke ratio are basically that you decrease peak piston speed at a given RPM (this allows you to run higher RPM with all else being equal), and increase in dwell times at top and bottom dead center. You are also theoretically increasing torque on the crankshaft, but that is realistically going too far into the theoretical side for most applications I'd guess.

There are a few benefits to a longer dwell at TDC... For our purposes there are two that are kind of related to one another: Higher resistance to detonation and preignition, as well as easier selection of ignition advance (will be easier to tune an engine with longer dwell vs. one with very short dwell).

Since you are ordering custom pistons and rods, it is up to you to decide what the minimum compression height on a piston would be, and from there how long of a rod you could use, and try to get an idea of how much improved rod-stroke could be... And if it makes a meaningful enough impact overall. I would be extremely interested if anyone can share experience of pushing the wristpin height up on these engines, especially in forced induction applications.

The overall idea is to do more with what we are given to work with.

There may be a case for leaving everything at the stock geometry with upgraded components, doing some meaningful headwork, then throwing a lot of boost through a properly sized turbo with properly designed manifolds. If something grenades, go on car-part.com and get another bottom end for a few hundred bucks. Keep your investment in the part of the engine that most dictates power output... At a certain point though, making peak power and peak torque higher will be needed to increase your ceiling. This is where rod/stroke and other bottom end advantages can be most felt.

But, if you are rebuilding an engine, these are questions that I would want to ask and explore before buying pistons, rods, and doing all the machine work to put something together... Are these questions that have already been answered? My searching tells me no, but I am a lowly noob (here).

A more realistic approach would be to start with a power goal. The entirely stock M30B34 is good for at least 400rwhp. TCD did that with a bolt on turbo kit and an MLS head gasket with studs. Another member made over 600rwhp with standalone injection with his B35. Some people spend an exorbitant amount on a bare block build with very exotic components and end up having more problems than they would have with a factory original motor. Others go to the same extent with expensive parts and lots of labor to achieve power levels that could have been reached easily and reliably with a factory original motor. With these things in mind, start with an honest, reasonable goal and plan accordingly.

BMW set the bar quite high when it comes to building a motor. Most machine shops either don't have the ability or won't put in the effort to perform the same quality work BMW did when these motors were new. The quality of components like pistons, rods, rings and valves is also quite high in terms of machining and metallurgy. You really might be better off with a set of new old stock cast pistons than you would be with fancy aftermarket forged pistons. I've never seen an M20 or M30 fail from a piston coming apart, yet many people throw the stock stuff in the garbage and install unproven aftermarket parts of unknown quality. There is no cost/benefit advantage if the stock stuff is as good or better than the aftermarket "upgrades".

To answer some of your questions more specifically, by far the most common point of failure in a boosted engine is the head gasket. This goes for the M20 and M30, though the M30 seems more prone to pooching the gasket for whatever reason. An MLS head gasket is the best solution for the M30 as long as it is installed successfully. That should withstand boost pressure up to at least 20 psi with a good tune, which is critical for the life of many components. I do not know how thick the ring lands are or how heavy the pistons and rods are but I can say you will have no issue with ring lands at any power level attainable with the 12 valve head and the pistons and rods are light and strong enough to handle regular operation up to 7000 RPM, which is higher than you need to be revving to make power anyway. This isn't a Honda motor and the M30 usually makes peak power below 6000 RPM with a natural VE curve and a good tune.

Well, it sounds like that answers most of my questions. Why talk about it if nobody needs to? Just keep it simple... I'm curious what longevity is in those sorts of setups though.

My background is Volvo redblocks (stout as heck but flow like crap) and Volvo whiteblocks (nice technology but some weaker components). Volvo redblocks can't be troubled to flow enough to break anything without the 16 valve head, and a lot of what you said can be held true about their factory construction as well. There are a couple of versions that are basically indestructible in factory form. With that said, the rotating mass is heavy as hell, and there are still places to make improvements.

Do you know if there are oversize stock pistons available for the B35? Do most people here just hone stock bores and re-ring the stock size pistons? Are rings readily available? I know for a fact that if I pull apart a B35, the bores will be out of round or have upper cylinder wear, just because it's me.

I think my plan will be to focus on top end flow, and just re-seal a B35 bottom end, check bearing clearance/wear, hone/ring, oil pump, etc. I have a B35 head loosely available to me, so may get that on the bench and check out the ports to see if there are any areas for easy improvement before machining. Have done some head work in the past, probably more reading/research than any person should on the topic...

What is the general feeling on turbo up-pipes vs. a new manifold? I would make my own, an equal length header possibly with pulse-paired divided inlet collector.. But for ease of wastegating may stay with a merged 6-1 single collector. Proturbo.fi was a popular manifold in Volvo-land for their good designs, they offer both headers and up-pipe setups... Not sure what chassis they are intended for or if clearance really varies much between E28/E30/E34/etc. There are also a lot of state-side fabricators in that market for Volvos now.

What intake manifold options exist ready to buy? Is there much adaptation of other intakes that flow more evenly between cylinders? Any incestuous swapping potential between the M30 head with one intended for turbo use from the factory? It looks like the same intake is used on M102 and M106... Not surprising I guess given the production numbers. I've seen the stock intake really does not seem to flow evenly between cylinders is the only reason I'd ask.

Am I correct in understanding that the transmission and rear end are stout enough to not really worry about? Basically a proper clutch setup and you are good to go?

I have set up both Megasquirt and VEMS run cars before, but will likely go with Megasquirt unless a VEMS deal falls in my lap at some point before then. It appears the B35 has a nice trigger setup stock. I thank those on here who have done very nice documentation on chassis-specific MS installs... That takes a lot of time on their end and saves everyone else hours or days of work.

In any case, I'm not sure when I will start buying parts, probably after we have our baby that we are currently waiting around for

As far as overall goals, I'd like this to be a longterm project with potential for continous growth, so would like to not corner myself in my early major component selection. Start with nice manifolds and leave it up to turbo selection, injector sizing etc. to really determine what the powerband will look like. This car is probably very very very fun at 400 whp, so let's start there. Peak power has little to do with actual speed, but an HX40 with good manifolding and tuning on a B35 should get there pretty easily I would think and have a great area under the torque curve.

I would be extremely interested if anyone can share experience of pushing the wristpin height up on these engines, especially in forced induction applications.

I've been wondering about this myself. The M30 is based on the M10 four-cylinder design (originally 1.5L) and BMW always used 135mm rods in all of them. So at one extreme we have the big M30 with 86mm stroke and low-ish rod ratio. At the other extreme we have the lower displacement varieties like the M10B18 with only a 71mm stroke and a quite chunky piston with 47.1mm compression height. Certainly one or both of these configurations are not ideal. With the durability of stock blocks being what it is, there's generally not much cause to experiment with custom rods/pistons though.

The S38 uses longer rods, which would fit in an M30. I guess the pistons would then need to have a compression height down around 31mm?

BMW uses shorter pistons in their newer engines, but rod ratios run the whole range. There was a 2.5l with 140/75 rod/stroke, and a 3.0l with 135/89.6.

Do you know if there are oversize stock pistons available for the B35?

I bought some OEM Mahle M30 pistons, .020" oversize, just last year. I don't think they're hard to get.

Not specifically forced induction, but you could look through this:

http://www.mye28.com/viewtopic.php?f=3&t=55585

From Pauters site, it looks like the S38B36 rods (readily available in h-beam form everywhere) are 144 mm with the same big end and size, except slightly smaller width on both ends... Are the rods piston steered or crank steered?

That's 9mm that could come off of the compression height of a piston.. Reduce reciprocating mass and improve rod-stroke ratio. Are there flat top s38b36 pistons out there?

An affordable set of h-beams with ARP bolts, and some flat top pistons to the s38b36 oversize specs would be a significant improvement over stock geometry.

Oversize pistons will have to be custom. Hard to find and expensive OEM. For the price might as well get forged.

Per Paul Burke, using a S38b36 144mm rod does not offer much in the way of improvement over the shorter rod. He recommended I not use the set I have for FI application. I was exchanging emails with him regarding a turbo build.

I do think that a shorter crank from a b28 would be great for revs. Good & Tight was building a motor with this crank until he realized the abuse a stock m30b34 bottom end can take.

I wouldn't go too oversize on the bore. My first motor was an m90 (bigger bore,shorter stroke, I don't remember )and it popped the head gasket between 5 & 6, where it's real thin. That motor wasn't even f/i. The head gasket on these long heads really is the limiting factor.
marc