Stroker Part Questions (2.7i via M52 crank?)

[Sykohtic]

So I recently pulled the motor out of my 325is to do a transmission swap. Refreshing the motor was the original plan, but I thought I'd look into this while it's out.

I've looked into doing a stroker several times. I won't have a huge budget if I decide to actually do it. The motor would be run NA for a while, but it is likely that it would eventually be roots blown (Likely an M62 blower, thought this is irrelevant at this point).

I'm pulling the head, so as it isn't too expensive here locally, the head will be given a spa day with hot tanking, valve grind, valve seats, and head resurfacing. I've been informed by a friend that he recently had this done for $160 (head was disassembled prior to being given to the machine shop).This will open up opportunities for a bigger cam (likely a regrind + oversized eccentrics) and maybe oversived valves (intake only)

2.7-ish is where I'd like to be. I know there are SEVERAL ways to do this. As my car is already equipped with a B25, I'd like to use as much of what I have as is possible. I understand that most prefer the SETA route. However, seems like finding just the bare components locally is difficult. I'd probably end up stuck with I pistons on the eta parts at the current rate and have a less than optimum CR for NA use.

I read a post on E30tech by Digger (assuming the same digger here?? lol) that said using an M52 crank, I-pistons, 130mm Eta rods, and shaving the head about 0.5mm (possible since its already getting machined anyway). He claimed CR around 9.5, which is rather NA friendly IMO. The benefit here is that the M52 crank is much easier to find, and I'm seeing several online right now for sub-$200 (as low as $125 + shipping). That would leave me to find the rods, which I can probably find from people I know here in NC. (I could source a crank from them too I'm sure, but SETA pistons are still hard to find, and just buying rods will likely be pretty cheap). Digger also mentioned that using a crank bigger than the Eta makes power above 7k easier to obtain, should I hazard into that rev-range via tuning.

The M52 seems affordable and easier, though DIgger also mentioned some modifications that needed to be made to make it work. A sleeve for the oil seal and possible machining of he intermediate shaft. Its on these points that my knowledge ends. Whats the cost of these things, and does that cost offset the availability of the M52 crank?

[digger]

The m52b28 crank will make it harder (please show me where i said opposite so i can fix it)to make power past 7k as a bigger engine revving at 7k wants to move more air than a smaller engine at 7k, if you allow the bigger engine to breathe better (it is harder to do this) then you make more power. If you want a high revving engine a smaller engine is better. Strokers don’t make more peak power inherently; they only inherently make more torque.

For M52 You need a sleeve for oil seal, intermediate shaft should be fine I don’t recall when I mocked it up last time (simple fix anyway). crank clearance to block might need a light touch up but a simple job.

The big killer is the clearance between crank counterweights and the piston skirts. With the US M52B28 cranks you can’t trim the skirts alone you need to address the crank counterweights and rebalance if using the short rods. In Europe and Oz people choose the earlier cranks which only require skirt mods so it’s a whole lot easier.

http://www.r3vlimited.com/board/showthread.php?t=285315

[Sykohtic]

http://www.e30tech.com/forum/showthread.php?t=48288

Is there an affordable option in terms of common-ish cranks that only requires modifying the skirts? Common-is being stuff easy to find like 24v stuff. Or am I locked into an eta crank to avoid that?

On the M52 side, can you give an approximation of cost for rebalancing the crank? Or is that going to be entirely by shop?

[digger]

in that thread i meant when youre throwing endless $$$ at it you’re likely addressing the head, cam, CR and manifolding issues so you wont have any issues with a bigger crank choking the induction system to the point of the power falling flat like budget strokers do and actually making less peak hp than a good m20b25.

It wasn’t meant to mean that it will rev harder/higher with bigger crank. In general If you take any given engine pretty much every time you increase the cubic inches (and only the cubic inches) the peak hp rpm will reduce, peak hp will be roughly similar but the torque goes up. This assumes all components are matched properly in the first instance.

The only think the bigger cranks do better at rpm is the forged aspect but on 24V engines they get harmonic issues. These are not apparent with the m20 yet as people aren’t revving the big cranks far enough yet as the breathing of 12V is inferior and the hp falls earlier unless you start getting into really large cams that are far from ideal on the street. there is only two engines i know of that rev really hard with biggish cranks they have epic headwork and 300*+ advertised duration cams

[digger]

http://www.e30tech.com/forum/showthread.php?t=48288

Is there an affordable option in terms of common-ish cranks that only requires modifying the skirts? Common-is being stuff easy to find like 24v stuff. Or am I locked into an eta crank to avoid that?

On the M52 side, can you give an approximation of cost for rebalancing the crank? Or is that going to be entirely by shop?

im not aware of any, but contact forcedfirebird he did an engine recently and can tell you what he did to use the M52 crank

[Sykohtic]

I get what you meant fully now. My initial interpretation was just that it would rev easier than a eta crank, not necessarily easier overall (though now you've clarified I understand the trade off of crank size and revs).

I'll try to get in contact with him, thanks for your help!

[ForcedFirebird]

The last build we did we did cut the skirts, not the crank, but one or the other has to be done. Also in your first post, you mentioned cutting the head .5mm which can't be done without the pistons contacting the head at the squish band, you will need to shave the block .5mm or so (depending on how much your head is shaved, go for .040' quench).

This is a very good combination and as Digger said, it's not going to make power over 7k unless you have a large cam. I have done two of these builds recently. One was a stock rebuild head with a 272 cam and the block was NOT shaved (slightly lower compression), it made 180whp. The other got ITB's, porting and headers and made 217whp, both with power falling off above 6500rpm.

EDIT: The US m52b28 crank clears the oil pump drive...

[Sykohtic]

The last build we did we did cut the skirts, not the crank, but one or the other has to be done. Also in your first post, you mentioned cutting the head .5mm which can't be done without the pistons contacting the head at the squish band, you will need to shave the block .5mm or so (depending on how much your head is shaved, go for .040' quench).

This is a very good combination and as Digger said, it's not going to make power over 7k unless you have a large cam. I have done two of these builds recently. One was a stock rebuild head with a 272 cam and the block was NOT shaved (slightly lower compression), it made 180whp. The other got ITB's, porting and headers and made 217whp, both with power falling off above 6500rpm.

EDIT: The US m52b28 crank clears the oil pump drive...

So for the optimum setup I should shave the block and head, or just the block? Trimming the piston skirts shouldn't be too much of a problem I don't think.

I'll be honest, I would like to go with a more business cam. A friend just put a 284 regrind in his B25 and it's addicting. I was thinking of either doing that or trying the funky dblias cam spec of 290 just to be different. I've priced out a local and well known shop (Doug Herbert Cams) that will regrind the stock cam to any size I want for $125. If the machinst does t charge an arm and a leg, I might also pull a card from my old, over zealously stupid NA build sheet and do 1mm oversized valves (intake) so it will breathe better. Any situation is gonna put me with a need to spend time on the dyno finding the power curve.

Speaking of tuning, what do you guys run your management through? I understand that in reality MS standalone is a good idea, but could I chip the 153 or find a cheap 173 motronic for budget purposes? I understand it won't be as good as MS or another standalone, but doing a chip will be significantly cheaper.

[digger]

The last build we did we did cut the skirts, not the crank, but one or the other has to be done.

that's good news, a crank from a US engine i have here that i cut the entire skirt down the the bottom of boss just for mockup purposes and it still didnt look like it would work without an 1/8" off the crank to.

[ForcedFirebird]

The counterweights will just touch some of the piston castings under the pin area. We lightened the pistons anyway, so it was not much more to modify them. The b28 crank has alternating throws that are longer to account for the opposing crank swing, so some pistons cleared more easily than others.

[digger]

So for the optimum setup I should shave the block and head, or just the block? Trimming the piston skirts shouldn't be too much of a problem I don't think.

I'll be honest, I would like to go with a more business cam. A friend just put a 284 regrind in his B25 and it's addicting. I was thinking of either doing that or trying the funky dblias cam spec of 290 just to be different. I've priced out a local and well known shop (Doug Herbert Cams) that will regrind the stock cam to any size I want for $125. If the machinst does t charge an arm and a leg, I might also pull a card from my old, over zealously stupid NA build sheet and do 1mm oversized valves (intake) so it will breathe better. Any situation is gonna put me with a need to spend time on the dyno finding the power curve.

Speaking of tuning, what do you guys run your management through? I understand that in reality MS standalone is a good idea, but could I chip the 153 or find a cheap 173 motronic for budget purposes? I understand it won't be as good as MS or another standalone, but doing a chip will be significantly cheaper.

i would just m/c the block nominally 0.5mm (actually measure and work out the exact amount as this number is just a nominal number) to give the magic 0.040" clearance.

[digger]

I'll be honest, I would like to go with a more business cam. A friend just put a 284 regrind in his B25 and it's addicting. I was thinking of either doing that or trying the funky dblias cam spec of 290 just to be different. I've priced out a local and well known shop (Doug Herbert Cams) that will regrind the stock cam to any size I want for $125. If the machinst does t charge an arm and a leg, I might also pull a card from my old, over zealously stupid NA build sheet and do 1mm oversized valves (intake) so it will breathe better. Any situation is gonna put me with a need to spend time on the dyno finding the power curve.
Speaking of tuning, what do you guys run your management through? I understand that in reality MS standalone is a good idea, but could I chip the 153 or find a cheap 173 motronic for budget purposes? I understand it won't be as good as MS or another standalone, but doing a chip will be significantly cheaper.

Without ITB using more than a 272 won’t allow you to get the most from the cam (OEM intake is restrictive and tunes for lower rpm) and if you run it on motronic it would be even worse. On an ITB engine id be tempted with an ENEM Z45 NA 280/280/108 cam if I wanted something more than a 272 but less than a schrick 288

[Sykohtic]

Without ITB using more than a 272 won’t allow you to get the most from the cam (OEM intake is restrictive and tunes for lower rpm) and if you run it on motronic it would be even worse. On an ITB engine id be tempted with an ENEM Z45 NA 280/280/108 cam if I wanted something more than a 272 but less than a schrick 288

I've worked out a deal with someone and so I'm getting the rods and crank for an extremely affordable price. I was also told there was a need for a crank spacer of some kind?

I was thinking the larger cam would be good down the road for supercharging purposes, where my intuition tells me the restrictive intake matters less just due to the fact that air is getting forced through it instead of just filling a vacuum. I would say I could just run a stock cam profile until I go FI and then refused the cam then, but that means pulling the head apart all over again to replace the cam. For understandable reasons, I'd like to just do it once if possible. So as another option....

What makes the stock take restrictive? Just the ports? I could (possibly) have a less restrictive intake fabricated that would also work for boost.

For management, I feel like this is gonna be the thing that I have to commit the most to work out and fork out for. Unless I can find a used MS unit a new standalone unit is gonna be expensive, and then I have to account for the loom (probably), at least on a limited budget though MS is pretty affordable. With a chip is there any way I could get it to run right?

[digger]

I've worked out a deal with someone and so I'm getting the rods and crank for an extremely affordable price. I was also told there was a need for a crank spacer of some kind?

I was thinking the larger cam would be good down the road for supercharging purposes, where my intuition tells me the restrictive intake matters less just due to the fact that air is getting forced through it instead of just filling a vacuum. I would say I could just run a stock cam profile until I go FI and then refused the cam then, but that means pulling the head apart all over again to replace the cam. For understandable reasons, I'd like to just do it once if possible. So as another option....

What makes the stock take restrictive? Just the ports? I could (possibly) have a less restrictive intake fabricated that would also work for boost.

For management, I feel like this is gonna be the thing that I have to commit the most to work out and fork out for. Unless I can find a used MS unit a new standalone unit is gonna be expensive, and then I have to account for the loom (probably), at least on a limited budget though MS is pretty affordable. With a chip is there any way I could get it to run right?

I’m along way from being an expert on blower cams but you may want more exhaust duration and maybe wider lobe centers. ENEM do the Z45 cam for a FI application which is nothing more than the NA cam with wider lobe centres. I think it’s a turbo cam but should work well enough. using it in a NA engine should make the idle and drivability better to, but won’t make the same torque. A schrick 272 will be ok for any engine to

The length of the runners tune for about 5500rpm and the runners internally are not great in some areas as they have weird bends and inflexion shape (cut one open you'll see) and they dont align as well with the ports compared to a aftermarket intake from RHD. you could buy the RHD intake manifold and some extensions (without throttles) and fab a plenum with as long runners as you can fit for single throttle body and it would work great.

You’ll definitely want something for engine management if you’re going to use a blower. PNP MS is pretty affordable. On motronic you can run a chip if NA but you leaving a lot of power on the table and drivability will be inferior. In general with OEM manifold and big cam the drivability is nowhere near as nice as it is with ITB thats one of the big advantages and reasons for ITB.

[Reichart12]

I'll throw in along with the idea of sucky stock intake. I have a 84mm crank and 284 cam, my engine is struggling with air flow in the top half of the range. Id figure a good bit of power still out there to be found with better flow. (but I'm also 2.9ish so its not quite what youre looking for)