(US) S50 rods are 135mm and have the same big and small ends as an M20. don't know about euros (or SA).
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He is talking about offset grinding the crank. You weld up material on one side of the journal and you machine the journal to change its center location outward of the rotation axis. Obviously this is not as reliable as a factory forged crank, even if case hardened in a carbon oven. The welded section can sometimes break loose from the origional cast journal for a not so fun time.-Nick
M42 on VEMSComment
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Thanks thats exactly what he was talking about.
Nando... I'm talking about the Euro rods... I know this cause when I was testing the S50B30 pistons, on the M20 rods... they needed smaller bushes 2 be made for the Small ends.
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135/94= 1.44Originally posted by SA E30
even if you use custom rods i dont think you can fit much more than 140mm in there which still gives you a crap ratio of 1.49
As time went on, the factory developed the car each year, making it faster, more comfortable, and capable of handling at higher speeds.
You don’t want this. You want the trickiest, most dangerous, oldest model you can find. Only then can you prove to the world that you’re a man.Comment
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Hmm welding a forged crank? Lets see pictures.Originally posted by wazzu70
And how much do you add to the 81mm crank??79 323iComment
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Very interesting read.
So, using the S52 crank (89.6mm stroke) is not a good idea then? Since, if you did that, the rod/stroke ratio will not be ideal? I ran some calculations, and the only way such a stroke would still have an acceptable rod/stroke ratio would be with a 145mm long rod - about 1.61 - which I'm guessing wouldn't fit in the block? the S14 rods are 144.5mm - but those probably wouldn't fit, huh?
So - the best match is probably the 86mm S50 crank with the S50 rods at 135mm and custom pistons? Which is 1.57 - still not great. Maybe one could use 140mm rods from an m52b25 and yield a 1.627 r/s ratio
Here's my question - will a longer stroke, with longer pistons, cancel out the added torque? Or, does increasing the stroke, and maintaining a good r/s ratio of around 1.6 add torque and maintain a rev happy motor?
I'm trying to find the best match for my stroker! Wnated to go 3.1 or 3.2 - but I'd be happy with a 3.0. ;)Last edited by Sean; 05-29-2006, 06:28 PM.- Sean HayesComment
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Increasing the stroke is what gives you the additional torque down low. Maintaining a good r/s ratio but more importantly keeping rotating parts as light as possible will keep the motor rev happy.
That being said i now need to choose between using the 135mm s50 rods or going balls out and getting some custom 139mm pauter rods. Although itll set me back a grand or more itll boost my r/s ratio up, greatly reduce my rotating mass and be a stronger all at the same time. I just dont know if itll make that big of a difference. I dont mind spending the money if itll keep the original m20 revvability. I wonder how much less rev-happy the 86mm crank/135 mm rod package will be?
As time went on, the factory developed the car each year, making it faster, more comfortable, and capable of handling at higher speeds.
You don’t want this. You want the trickiest, most dangerous, oldest model you can find. Only then can you prove to the world that you’re a man.Comment
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That answers one of the questions I've had in my head. So, increasing the stroke will make it torquey, and I can't do anything to ruin that - bottom end wise.Originally posted by madjurgen
When it comes to rod length - finding the right medium gets the motor to be more rev happy.
So - if you think about it, I'm gonna throw out examples (which may not be accurate)
Say I had a 140mm rod that weighed in at 650 g and a 135mm rod that weighed in at 510 g. Which would be better? A heavier rod, or a better rod/stroke ratio? Is there an equation to find that out?
How about the 89.6mm stroke crank - found in later S52 motors. Whats the longest rod you can use with that crank and still allow room for a piston? It looks like metric mechanic pairs the 89.6mm crank with custom 138mm rods, weighing in at 510g. This also leaves a r/s ratio at 1.54 - so the light rods must make up for that loss in ratio?
Those rods you're looking at look PRRICEYYY. MM makes 138.75mm rods that would work just as well, I think. They also make 140mm rods. If I could afford it, I'd do MM's 140mm rods with an S52 89.6mm crank and their Rally pistons yielding 11.1 compression - but I don't think I can afford it.
I think the 86mm crank paired with the S50 rods would keep a pretty revvable M20. I mean, that's what an S50 has, and it's pretty revvable, all teh way up to 6500 at the very leasyt!- Sean HayesComment
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Originally posted by Sean
This is exactly my concern. Someone with some actual experience needs to drop some knowledge on this thread. Since pistons are paired with rods, if I choose the s50 rods and they suck all the revvability outta the motor Im screwed.
As time went on, the factory developed the car each year, making it faster, more comfortable, and capable of handling at higher speeds.
You don’t want this. You want the trickiest, most dangerous, oldest model you can find. Only then can you prove to the world that you’re a man.Comment
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What about lightening stock rods? Can they "safely" be taken down in some areas to reduce weight w/ out majorly compromising strength?Comment
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lightened stock rods = s50 rods
As time went on, the factory developed the car each year, making it faster, more comfortable, and capable of handling at higher speeds.
You don’t want this. You want the trickiest, most dangerous, oldest model you can find. Only then can you prove to the world that you’re a man.Comment
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I did some research - the M50B25's after 1992 (if this page is right - http://www.bmwworld.com/engines/m50.htm) - had 140mm rods. A local junkyard here has an old M50 motor from a 1993 or 94 325i - he said I could ahve the rods for $15 a piece if I pull them.
Here's what I wodner - and he'll let me check before I remove them - that is, how much they weigh. I can't imagine they'd weigh any more than the stock M20B25 rods (640g) - maybe the same (since they're 5 mm longer). (Stock 91-92 rods weigh 600g, and are 135mm) However, I was thinking I'd take them to the shop and see if they can't lower them about 50-60 grams each, bringing them damn close to teh S50 rods.
But even then - would 5mm longer rods, weighing in say...20 grams heavier than S50 rods, be worth it?
here's my thought right now:
S52 89.6mm Stroke Crank - modified to fit (MM has all needed pieces), and somewhat lightened (maybe take off half a pound, and smooth out the balance elbows)
MM 3.2 Rally Pistons (11:1 CR) (260g) (86mm bore)
M50B25 Rods (140mm) lightened 50-60g (hopefully around 570-590g)
Lightweigh piston pins
This setup would yield 3121 cc's and a shit load of low end torque, and a fairly decent revving motor (at 140/89.6 = 1.57) - not great - but not terrible either.
The funny thing is, the M50B20's and M52B20's have 145mm rods! Too bad those aren't easier to get ahold of - 145/89.6 = 1.62 r/s ratio!
Here's my question - when do we run out of room? (as in - the rod is too long to leave room for a piston) Or should I just do the calculations myself? lol
I'm gonna call Jim in a bit, and ask. ;)- Sean HayesComment
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they are almost definitely lighter than M20 rods
as far as longer, heavier rods vs lighter, shorter rods, I'd go with the lighter ones in that case. with an 81mm crank, your R/S really isn't going to be that bad, but using a heavier rod with a better R/S in search of higher RPMs isn't going to work.
and on the original topic of this thread, now that I have pretty much everything together, I've pretty much concluded that the IE kit is definitely not worth it. Including my crank, MM pistons, rods, and every tiny detail part (bolts, washers, o-rings, gaskets, freeze plugs etc), plus extra things like the IE billet AFPR (which is VERY nice btw), a new ICV and a new oil pump, my stroker will cost about the same as IE's kit which only includes the basic peices (and you have to use your old rods).Comment
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Well youre talking about the 81mm crank, your r/s isnt going to be bad regardless of which rod you use. But Sean and I are going to be using the s50/52 crank both of which properly f up your r/s with stock rods. But i think in the end youre right, lighter is always going to be better.
Been wondering about the quality of the IE afpr since its a rather new product from them. I wonder if it installs as easily as they claim.
I definitely agree that IEs kit isnt worth it. Just take the time to source the parts yourself, youll learn a lot more and save some money, but then again buying used internals is a very risky business. On a similar note, I need to get my crank checked out by a shop. Do they just check for cracks, warping and make sure its balanced? About how much should this run me?
As time went on, the factory developed the car each year, making it faster, more comfortable, and capable of handling at higher speeds.
You don’t want this. You want the trickiest, most dangerous, oldest model you can find. Only then can you prove to the world that you’re a man.Comment
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My shop can check the crank for balance, cracks, condition - etc.Originally posted by madjurgen
I'm going to have my whole rotating assembly balanced for like $40, at least that's what my shop charges me.
Boring is going to be the most expensive thing at the shop - about $130 for 86mm bore.
I just got off a VERY long phone conversation with Jim about engines. It's amazing just how fast times flies when you talking cars. lol
Basically - MM's Rally engines are the MOST you're gonna get - basically, they maxed out the length of the rod that you can go. So, with an S52 crank, their 138mm long rod is the longest you can go and still have enough room for the piston, rings and pin.
He also told me that if I wanted to go even LIGHTER than the H beams, I could get their I beams - their 138mm I beam weighs in at like 480g - and that..my friends...IS LIGHT! (they're about 190-200 each)
If I had the money, I'd get custom rods, but I just don't think I can afford it. it'll be bad enough buying pistons, crank, and S50 rods.
I really wanted to use the higher compression Rally pistons, but the 6 pistons you see listed on their engine brochure are their six pistons - they don't do custom pistons outside of that, which makes sense. They are really the only ones that do 86mm bore, so that's where they lead the pack in displacement.
He also explained all the parts needed to FIT an S52 crank (89.6mm stroke) in the motor. This included:
- Auxiliary shaft - this is what drives the oil pump - this is needed because the crank elbows will make contact with this if it's not machined down - you could have it done or buy it from them, most likely.
- Seal Sleeve Spacer - needed to get the seal to fit on the E36 cranks
- Stepped washer and bolt - bolt lengths are different, this fixes that issue.
I'm pretty sure if you get the above, the crank will fit great! In terms of bearings, MM also has modified bearings that flow more than stock bushings.
Then from there comes the rod/piston combination. On the S52 crank pretty much the only rod you can use from a BMW is a 135mm rod, and that's either from the M52B28 or S50/2. It's either that, or MM's custom H beam rod.
One thing Jim mentioned is that the M52B28 rod is very very strong, stronger on the bottom half than even the S50 rod. One could have part of the rod machined away to lighten it up a bit too.
I asked Jim about teh 89.6 stroke paired with 135mm rods and he said that's its still a very revvable and happy engine. The main reason for this is lightness - so light is better over length - to a certain extent. In our case, we can't even use 140mm rods anyway - so S50 rods would work just fine!
So here's what I'm thinkin now
If I can't afford an extra $1200 for rods (which I probably can't...lol) - yielding 3121CC:
-S52 Crank - 89.6mm stroke (all needed pieces to fit)
-S50/2 Rods - 135mm - 540g (may have lightened a tad - maaybe)
-MM 3200 Sport Piston (310g - 10:1 CR - 86mm bore)
-Customized MM bearings (depending on price - may ask if my machine shop can do it)
-MM Pin bushings
If I can afford rods, I'll get the rods.
This is the best option to get as close to 3.2i as possible. The M20's just don't have the deck height for any more rod length. But, light internals will definately make up for it!- Sean HayesComment
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