engine and drivetrain M10 Forged Piston Specs and Cyl Head Flange Specs for CAD

[TobyB]

Just to add that the 320is pistons can and should be kept. Actually they're an upgrade for the M3 e30 engine builders and this increases compression to around 12:1.

huh? I smell the deposit of a male bovine... 320is is a 2 valve engine,

the S14 has 4, and different chamber shapes.

Everything you read on the internet is true.

t

[PatAllen]

if it where me i would rather spend time trying to make my own casting to build 16v heads rather than pistons...

[john_a]

320is is a 2 valve engine,

the S14 has 4, and different chamber shapes.

Toby, that discussion is about a different 320is, the Italian E30 with the 1990 cc version of the S14 (S14B20)

However, I can't believe that thread quoted from an E21 forum, it has so much obvious incorrect info it does not warrant sharing, except as an example of BS talk by folks that don't have a clue. Maybe that's a bit harsh, what I should say is I don't know why it would get posted here, with all the mistakes it contains.

They are discussing a two liter engine, and they know the bore is the same as the 2.3 S14, but they assume the crank would have 80 mm stroke (same as an M10.) Duh, if an M10 with 89x80 = 2 liter, how do they expect the vastly larger (93.4mm) bore of the S14B20 to also produce only 2.0L with the same 80 mm stroke?

The Italian market 320is (S14B20) has 93.4 bore x 72.6 stroke to produce 1990 cc, which was required to beat the >2.0L vehicle tax in that country. Note that 72.6 mm is not even close to what that writer was speculating.

The rods & the pistons for that engine are unique, and of course rare. And while I don't know the exact compression height, I am inclined to believe it is nowhere near usable in as "upgrade for the M3 e30 engine builders and this increases compression to around 12:1"

For that to be even close, the stock rod for the S14B20 would have to be waaay too long to allow a piston with compression height that would be usable on both it's 74.6 mm stroke AND the 84mm stroke of the M3.

Then the whole subject of crankshaft stroke is described in that post in the most incorrect & tortured way. The writer uses the the word stroke, when in many cases he is speaking of crankshaft "throw". He loses the distinction that stroke = the swept volume of the cylinder, and and that any change in stroke would drive a change in pin location by half that amount (assuming no change in deck ht or rod length.) This is evident where he states "By going from s14b20 80mm to s14b23 84mm stroke we apply the same theory as above so we must relocate the piston wrist pin up the amount of the stroke increase, in this case 4mm."

That should be relocate by 2mm, if you are following along here.

This whole thread has had a too much bad or misleading info tossed around.

I raised a lot of questions for the OP, that were not really addressed, and I am less convinced now there is merit in his experiment.

The pistons I would like to create are

This was followed by a selection of bullet points lifted from KB Pistons (ICON brand) advertising, which is hardly anyplace I'd look to for great product. Why copy the low end of the aftermarket, if you are a competent engineer involved in OEM piston development?

Why borrow an image from Hot Rod, to illustrate a FORGED piston, if that is in fact an LS7 piston. While I agree that the "(LS7 especially) was a very sophisticated piston/piston ring package which is the benchmark in the industry" I think you should know that the LS7 piston is CAST not FORGED. Even though this engine has exotic Ti rods & Ti intake valves,the Mahle pistons are not 2618 or 4032 alloy (neither of which is really common for mass production vehicles) but LS7 pistons are a CAST Aluminum (specifically, Mahle M142S.)

I know what 2618 is, and I have spec'd my own design M10 custom forged pistons with lightweight (thinner) ring packs from different suppliers since before some of our forum members were born.

That experience is what I had to share with DR2002 here, when I offered the ideas of what pitfalls to watch out for. Apparently, he's convinced himself by virtue of a quick second with Google search that finding shiney & round things which fit the same hole size he has means he's good to go and won't run into any problems. I'm about 95% certain that's the position of someone who never actually has taken delivery of there own design of forged piston from Wiseco, Diamond, JE, Ross, or such..

Everyone will also be happy to know that there are many forgings available in the 89mm to 92mm range. Some examples are for Honda/Acura, Cavalier, Nissan 240sx, Toyota, Subura WRX, Dodge Stealth, etc. While they may not be an exact drop in, the forging blank can be machined for a BMW application.

..not an exact drop, can be machined for BMW .. WTF ??, ALL raw forgings would have to be machined. The point I was making about the understanding limitations of available forgings is valid, just because you found that other cars share the bore size don't think you've dismissed any & all issues.

While no one in this thread asked about 92mm forged pistons (again, the thread was started & focused on standard M10 bore) there pops up a find of Subaru piston that has nothing in common with anything an M10 needs. It has 13.5 cc dish, and completely wrong pin height, basically nothing in common.

Looking further I found these below. What is nice is that they are for a 90mm bore, and come in at 1.0 x 1.2 x 2.8mm. Also, the price is $31 for a set. WOW!

That is the price per piston, not such a deal for $124 a set. That detail was part of the specs copied & posted with the Summit product description where it states "Notes Single piston set."

What I had posted about the availability of performance rings in 89mm bore is true, there is not nearly as much as you can get for a SBC. Of course there are other cars with 89mm bores, but that does not mean the rings an experienced race engine builder would desire are used in them.

After reading that the late 70's 320i engine is the subject because it was found at the junkyard, it seems pretty clear that the piston specs found in the Mahle catalog for part 082 10 00 were selected in error. I would bet the junkyard find was a USA spec car, with flat top 08 09 00 Mahle pistons. This does not match the specs in the first post, which are clearly the Euro 320i pistons with 9.3 CR.

I would not be so negative about all this, except I get bugged when folks talk about such ambitious stuff, then don't take initiative to do more that quick internet queries instead of researching & measuring parts they could easily have in hand. A used stock USA E21 piston

has to be worth about $5 tops, and can easily be shipped for about the same cost, and there has to be tons of them available folks would be happy to get rid of.

From a DOE point of view the project seems weak.

I could be wrong, based on what I've heard so far, I'm not holding my breath for any real results.

I can manufacture any piston or ring design required.

There you go -- I guess no one can prove you wrong.

[Tommy]

And while I don't know the exact compression height, I am inclined to believe it is nowhere near usable in as "upgrade for the M3 e30 engine builders and this increases compression to around 12:1"

I hear they do use them with M3 rods and crank. "Slight" machining required. Of course this is not first hand experience so it could be false information spreading from one source.

Tommy

[john_a]

And while I don't know the exact compression height, I am inclined to believe it is nowhere near usable in as "upgrade for the M3 e30 engine builders and this increases compression to around 12:1"

I hear they do use them with M3 rods and crank. "Slight" machining required. Of course this is not first hand experience so it could be false information spreading from one source.

Tommy

Tommy, it just sounds implausible, based on the vast difference between the two engines stroke. Either the original 2.0L rod would have been impossibly long, or the 2.0L piston CH would be too high to use 84mm stroke in the 2.3L

Rough numbers show the issue:

S14B23 = 217.5 deck = 42 throw + 143.5 rod + 32 Piston CH

IF you had a 320is piston with similar CH, the rod would be way too long.

BMW probably did nothing close to this, as the rod ratio would be 2:1. like this example:

s14b20 = 217.5 deck = 36.3 throw + 149.2 rod + 32 Piston CH

Let's back that rod ratio down to down 1.86:1 by substitution of a rod length like an M10 (note this is still a fairly long rod ratio)

s14b20 = 217.5 deck = 36.3 throw + 135 rod + 46.2 Piston CH

Now you have a piston that if fitted with E30M3 rod & crank would be 14 mm out of the hole! That's a lot of machining & I'd doubt there would be any piston top left.

And as the S14B20 had even higher static CR than its 2.3L cousin, the piston heights would have to be greater yet to get there, as it has to overcome the significant loss of swept area from the shorter stroke, while the unswept volume remains the same on both engines.

I don't know where they made up the length lost with the short stroke, but whether they did it with the rod length or piston CH, the results don't appear to support swapping pistons between the S14B20 & S14B23 (when keeping the 2.3L crank/rods.)

Find out what actually happens where folks performed this swap, there must be more to the story. Here in the USA the S14B20 basically does not exist, I don't know what type of experiments have been done.

[Tommy]

s14b20 = 217.5 deck = 36.3 throw + 149.2 rod + 32 Piston CH

Would that be impossible? How would "too high" rod ratio effect?

I'm thinking that s14 was not designed for 2 liter capacity. The version was just made to get into Italian markets. I would assume that they did minimum changes that was possible without sacrificing too much performance.

Tommy

[john_a]

s14b20 = 217.5 deck = 36.3 throw + 149.2 rod + 32 Piston CH

Would that be impossible? How would "too high" rod ratio effect?

I'm thinking that s14 was not designed for 2 liter capacity. The version was just made to get into Italian markets. I would assume that they did minimum changes that was possible without sacrificing too much performance.

Yeah, I might have been too quick to say "no way" but it does seem out of character to have BMW use that long of con rod vs stroke.

Perhaps they picked some compromise where the piston CH was raised just a bit, and the rest of the length increase went to the rod.

The effect of a much longer rod in this application might help slightly just at highest RPM, but there would be a drop in acceleration, and you'd possibly notice the lack of torque pulling away off the corners. Driveability would suffer a bit, as this engine is probably already a bit gutless down low compared to the S14B23

BMW did do a bit more than the minimum here, as they produced unique pistons AND rods (along with the unique crank), when they had decades of experience building 1.8L M10's with a 135mm rod & 71 mm stroke (close to the same stroke as S14B20, with the same deck ht.) They could have saved using the old M10/M30 rod, or even the E30M3 rod, but who knows?

I would like to know what the actual parts do measure.

[Tommy]

I asked from a guy who mentioned the swap. He has had 320is and has now M3 and he knows pretty much about S14's. He didn't have first hand experience either but said they've done them in Germany.

He believed that there is the same difference in rod that comes from crank throw. ->

84-72,6= 11,4mm /2 = 5,7mm

144+ 5,7 = 149,7mm would be rod length.

It would make sense in a way that they kept the same piston design but just made the dome bit higher to compensate loss of CR. Yea - agree they could have done less. Maybe it was still the easy way not to touch much the piston design but just change lengths in crank and rod.

Tommy

Just to mention for future reference that this is just speculating - not 100% sure information.

[BAhyow02]

John and Tommy,

The S14B20 aka the 2.0L 320is Italian engine, does have some long connecting rods. While the standard S14B23 uses rods around 144 mm C-C the S14B20 uses rods around 149.7mm long. I actually have a few of these in my possession that were used in the 2.0L BTCC S14 motors.

I unfortunately do not have a S14B20 piston to compare to the S14B23 usa pistons I have lying around. So I cannot tell you the difference in dish volume.

I hope this helps. I have not actually measured the connecting rods in my possession to verify this data, but have been given this data from some sources in germany.

-Bernard

[Tommy]

Thanks Bernard, I have also gotten some verification about those dimensions. I have now one of those cranks shelved for future use.

Tommy

[BAhyow02]

So I actually went out to the garage and unearthed the box of S14 connecting rods.

My measurement says that the C-C distance of the S14B20 rod is 149.67mm, which is close to the number of 149.7mm from my German sources. The discrepancy could be due to my measurement inaccuracies or the fact that the rods could have been reworked.

I'm attempting to attach a picture comparing the 2.0L rod and the 2.3L rod.

AFAIK, according to the BMW parts guide, the Italian 2.0L S14 used unique pistons compared to any other variant of the S14.

Hope this helps,

Bernard