2.9 stroker pinging

[MillRat]

Sebastian,

When you finally get a chance to get your WAR chip sorted, I have a 2.9L tune you could use (with 272 cam) that will get you started. It sounds like your engine is very similar to mine (with the exception of the crazy CR), so it might be okay as a baseline.

Send me a pm if you are interested and I will email you the file.

[Sebastian35]

Sebastian,

When you finally get a chance to get your WAR chip sorted, I have a 2.9L tune you could use (with 272 cam) that will get you started. It sounds like your engine is very similar to mine (with the exception of the crazy CR), so it might be okay as a baseline.

Send me a pm if you are interested and I will email you the file.

Hi Hichael thats very kind of you! i will pm you my email.

[Sebastian35]

Hi guys back in the land of the living

Hopefully I can get this motor up and running very soon.

I have returned to an email from Top End, my original supplier, and here below is the piston spec you all wanted!


General Information
Date: 9/22/2010 Prepared For: TOP END PERFORMANCE
Promised Date: 10/4/2010 Fax: 764-0155

Customer Supplied Information
Bore Size: 3.346 Dome/Dish Ht.: .065
Compression Distance: 1.181 Ref Job#: 707388



Job Part Information
Part Number Description Ordered
297964 3.346 BMW AUTO 325 6
866-2500-15-51C JE STRAIGHT WALL PIN 6
866-063-MW WIRE LOCK Chrome Si 12
PIN FIT 6
JG1006-3346 1.0-1.2-2.8-3.346 1



Part Information
Motor Type BMW AUTO Head Type BMW Block Type 325
Piston Type Dome Induction Method Gasoline Open-Unrestricted Bore 3.346
Compression Dist 1.181 Dome Height .065 Net Volume 6
Land Width Top .245 Land Width Mid .155 Land Width Bot .085
Groove Width Top .040 Groove Width Mid .048 Groove Width Bot .111
Bot Groove Dia 3.046 Mid Groove Dia 3.024 Top Groove Dia 3.046
OD Finish Turn Bot Dia 3.3425 Cam Type G3 Pin Hole Dia .866
Pin Length 2.500 Lock Type Code JE Wire .063 Intake Depth .136
Exhaust Depth .136 Int Valve Dia 1.820 Exh Valve Dia 1.580
Pin Fit .0006

The email was most welcome as i had removed the pistons on monday to find no ID markings on the pin boss area!

Now Cambridge motorsport are suppling me with a new set but before the order is complete they want the following info:
can anyone tell me where the factory M20B25 piston sits in relation to the deck height at TDC on the standard engine. I think it is + 40 tho above but need facts. The other info was standard head gasket thickness, which is .070ins and head volume that we all agree was to be 40cc even though Top End say factory is 44cc.

The new set is to be 86mm with foctory crown and this time i want CR to be close to factory at 10:1.
I suppose they need to take into account the extra volume of the new bore and need to adjust the deck height of piston to get the required CR, as i do not want a repeat F...up like before! Although you can imagine i want the pistons ASAP i also want there to be no issues this time round. So if you guys can help me with that info excellent!

There was also a mention of a good will gesture in the Email i received from top end but i will let you guys know if that materialise's!

[GeoffBob]

284/272 i,o 32 i,c 72 e,o 66 e,c 26

In which case I get 211psi. Not far off though. At least it shows that these calculations can be used as a general pointer. Ideal pressure (assuming perfectly adiabatic compression and no blow-by) indicates a compression pressure of 236 psi. Your measurement is thus mid-way between "typical" and "ideal", which is spot on for a new engine

[GeoffBob]

Hi Sebastian, welcome back. Hope you had a good holiday.

I have received your e-mails and will get to them when I get a chance. Have been a bit busy passed few days here at work so please bear with me. I'll post my response here on the zone. Hopefully there will be enough info to calculate the dome volume and ultimately what static CR you had. honestly would have been better if you had measured it though since I cannot rule out, for example, that someone may have fiddled with your engines deck height in the past. Simply buying a set of pistons identical to Ezagood's could land you back in the same position if you are not careful. However, all else being equal between yours and Ezagood's engines (block, crank, head, rods, cams etc) you will arrive at the same compression pressure and will not have a recurrence of your earlier problems, at least not at a compression pressure of 225psi you won't.

FYI, looking at your pics I would have to say that the damage to your pistons and bores appears absolutely minimal. There were two spots in the bores that bothered me but on second thoughts I cam to the conclusion that they were a reflection of the crank below? At worst I could see slight vertical scuff marks. At first glance I must thus conclude that your static CR was too high. The question now is, why? If and when I get a chance I'll look at that piston data.

[Sebastian35]

The pistons have not been ordered yet as i am now having an 86mm bore.
They are in the process of trying to work out the spec of the new pistons and need the factory M20 B25 piston deck height or the factory Comp height?

As soon as i have this info they can work out where the new deck height is to be for the 86mm bore to give me a CR of 10:1 or just under using the original crown Design with the crank and rod comb i have.

I must say i all this is not my field, and really need help as to get the info to the guys for then to process my order. Quickly as possible! So i haven't just gone for ezagoogs same spec because of the extra volume, although thanks to him they have a crowm pattern already.

So any help on the info i should be submitting to them i will be very greatful for.

[GeoffBob]

New pics from Sebastian:

[GeoffBob]

Sebastian,

I can see exactly the mistake that has been made here and how it was made. Someone at TopEnd or JE needs a good kick up arse. I’ll explain more in due course.

In the mean time:
Data on the stock M20B25 piston from post 1987 8.8:1 engine can be found here

EDIT: Type in "M20B25M1Z7" where it says "designation" and then click on the "show products" icon on the right.
Then expand the info on part# 081 15 00

What the yanks call "compression distance" I call "compression height", or KH from the German "Kompressionshöhe". Stock KH is 34.2mm for the M20B25 piston. With an 84mm stroke and 135mm rod you'll need a KH of 29.7mm, that's a "compression distance" of 1.170 inches. What JE need to do for you is to manufacture a piston with the same crown as the 8.8:1 M20B25 piston, but with the wrist pin, skirt, rings etc moved up to accommodate a KH that is reduced by 4.5mm from 34.2mm down to 29.7mm. Don’t worry about changing the profile of the piston dome in any way, the change in static CR from 8.8:1 to 10:1 will come about naturally as a result in the change in stroke, although I guess in your case some work will be required due to the increased bore size and oversized valves.

Stock M20B25 deck height is 206.0mm. Before you go ordering pistons you need to measure your deck height as it may not be stock!

I'll post more in due course as to why your flat-top pistons went so badly wrong. CHR1S1990, Reggid and Ezagood, you're going to just love this!

[GeoffBob]

Sebastian,

From the information you posted up above I can now tell you that, assuming your block and head are stock, and all other values are as you have previously specified, your static CR was exactly 12.3:1. Bummer

So how did I arrive at this value, and how did JE and Top-End come to believe that this piston would result in a CR of 11.2:1?

Firstly, with the 885 head and stock 1.8mm gasket the head volume is effectively 40cc + 10cc = 50cc. The low compression (8.8:1) M20B25 piston has a crown volume of -3.3cc (despite its raised crown) due to its exceptional bowl and valve cut-outs. This means that an 8.8:1 CR M20B25 has a compression volume at TDC of 53.3cc. All hunky-dory then.

Now, the JE flat top pistons have a KH of exactly 30mm (1.181”a, as specified by JE) and a crown volume (above the compression height) of +6cc (also as specified). This places the piston at a stack height of 207mm, 0.3mm higher than the stock stack-height of 206.7mm, contributing an extra 1.7cc (on an 85mm bore) to the crown volume. The total compression volume at TDC is thus 50cc-6cc-1.7cc=42.3cc.

Now, you can do this calculation for yourself if you like, but, on a bore of 85mm with a stroke of 84mm with a 135mm rod, a compressed volume of 42.3cc results in a static CR of 12.3:1. Following my usual calculation, this will result in a compression pressure of around 296psi.

So why did TopEnd and/or JE think otherwise? I believe that they are mistakenly under the impression that the combined volume of the head plus gasket is the popularly published value of 53.3cc, which is not the case. This is, as I have stated, the volume due to the fact that the M20B25 low compression piston has a net volume of -3.3cc. The actual head plus gasket volume is in fact only 50cc. If you redo the calculation as I did it above, but assume a starting volume of 53.3cc, and also assume a bore of 84mm, you arrive at a static CR of exactly 11.2:1.

So why didn’t Ezagood land in the same predicament? Simple, they knew that the M20B25 crown profile already worked and that 8.8:1 would become 10:1 by virtue of a change in stroke and rod length only. So Ezagood’s piston is the product of simple geometric copying while in Sebastian's case it was the product of a set of calculations where one of the most critical (if not the most critical) input values was already at fault. A case of garbage in garbage out.

At this point I could easily type all sorts of obscenities aimed at unworthy oversees suppliers, but I shall abstain as it will achieve nothing. I have made my point.

[GeoffBob]

The pistons have not been ordered yet as i am now having an 86mm bore.

Rather go for 85.5mm. After 86mm there is nowhere left for your block to go but in the bin in the event that something goes wrong.

Oh, and looking at those scuff marks in your pics, there is no way that tightness on the bore accounted for your raised combustion pressure. Your problem was well and truly down to excessively high CR.

Sebastian, you did the right thing deciding to change these pistons, What a nightmare!

[CHR1S1990]

Wow, i can't believe what a cock up that is. 12.3:1 would have been nice on LPG though

Il have to look at my calculations again as I worked everything out on the assumed 11.2

[e301988325i]

Geoff you're a legend, I'm surprised someone as large as JE have made this error.

[ezagood]

je just make what they are told. i was specific in what i wanted. i had worked out that the comp would be 10-1 just by increasing the bore and stroke so i asked for the exact same crown shape but with the pin and skirt 4.5mm higher. cambridge motorsport needed my old piston to copy the crown shape and then ordered the new piston from j.e.
simples.

i must admit i feel quite lucky they turn out ok as there are two people with custom pistons on this site that didnt turn out as they should. thumbs up to cambridge motorsport as well. they did a good job copying them. i feel a little bit bad now that i moaned to them for the time it was taking to sort out.

[Sebastian35]

I would have gone 85.5mm but because of the pinging i have in one bore a score that may not be lost by the .5m i am sure it will but in any case what the hell! when this engine is done i will put in the original back in. Why?
It has not been a good winter project as its summer now and im back at square one but with a big dent in my pocket! more to to point, my time and hard work, and the constant ear bashing from my other half lol...Can't quite understand why i have to spend so much time playing with that f....ing car. Do i listen! do i hell! I offten wonder if i will return home to find my workshop burnt to the ground. I keep thinking when those new pistons arrive i will be in there before work and every minute of my free time and then maybe i will get a few months of summer to relax and enjoy the car all by myself at that point!

Anyway thanks again and i will let you know how i get on.
I am sure Chris will get the pistons sorted and i would like to hear what he does with them?

[Sebastian35]

je just make what they are told. i was specific in what i wanted. i had worked out that the comp would be 10-1 just by increasing the bore and stroke so i asked for the exact same crown shape but with the pin and skirt 4.5mm higher. cambridge motorsport needed my old piston to copy the crown shape and then ordered the new piston from j.e.
simples.

i must admit i feel quite lucky they turn out ok as there are two people with custom pistons on this site that didnt turn out as they should. thumbs up to cambridge motorsport as well. they did a good job copying them. i feel a little bit bad now that i moaned to them for the time it was taking to sort out.

Je were supposed to make some pistons to suite my crank and rods I trusted then to caculate all the info as i was not sure what was what. They never asked for the old piston as they had all the info and make these all the time. so they said! cambridge motor sport have had an old piston and it has been sent off to be coppied and they will work out the rest to get me the right comp! as thats what i paid them and JE to do.

[GeoffBob]

[GeoffBob]

FYI Sebastian: All of the data you asked for in the e-mail you sent me is in my posts from yesterday on page 6. Feed that info to Cambridge and your new pistons will be fine.

Also, in response to your statement:

I must say all of this is not my field, and I really need help as to get the info to the guys for them to process my order.

may I recommend that you get your hands on the two books:

How to Rebuild Any Automotive Engine by Barry Kluczkyk



and

The Step-By-Step Guide to Engine Blueprinting by Rick Voegelin.



Both books are published by Cartech and can be ordered online here

The first book will serve to reinforce and remind you of what you clearly already know. The second book will be an education, teaching you in detail what you clearly don’t know about measuring, specifying, fitting and running-in cams, heads, blocks cranks, pistons, rods, bearings etc. Both books are incredibly practical with hundreds of detailed illustrations.

It is this second book that will arm you with the knowledge you require in order that you need not rely on suppliers to fill in unknown quantities on a spec-sheet for you. It will place you in the position to tell TopEnd and/or JE exactly what you require for your project before you part with your hard earned cash on parts that are not to specification. Don’t get me wrong, I am not saying that it is your fault that TopEnd supplied you with the wrong piston (lets not go down this road again). All I am saying is that a little knowledge will in future help you to avoid suppliers who may be prone to making honest mistakes.

As someone said to me the other day (and I swear this is true), a week in the workshop tinkering under the bonnet can save you a whole hour in the library .

[daimlerman]

As someone said to me the other day (and I swear this is true), a week in the workshop tinkering under the bonnet can save you a whole hour in the library .

It certainly is,this is what we used to do before the internet and google came along!

These days,using internet advice should always be tempered with sound,practical knowledge from sources such as those just detailed by GeoffBob.

[MillRat]

I'm just glad that when I ordered my stroker kit, all the parts fitted together like a treat. No problems and once built, the engine fired up and run first try.... Phewww!

[Sebastian35]

Thanks Geoff

I will source those books! I have to say I restore cars to strictly factory as a rule. I am also capable of the measuring things if I purchased the equipment but for a one time application it is not valid. This car is my personal favourite and for a change I wanted to up the power somewhat! Hence I kept the M20 engine as I could have put something else in for less than half the cost with bigger gains but there is nothing like opening the bonnet and seeing originality and knowing its all a facade!

I am very sure when the new set arrive all will be well!

[e301988325i]

Hence I kept the M20 engine as I could have put something else in for less than half the cost with bigger gains but there is nothing like opening the bonnet and seeing originality and knowing its all facade!

+1 on that.

[CHR1S1990]

pistons received from Sebastian (thanks again!) and cleaned up. Heres a quick pic of the best one. 2 others are similar, and the 3 others have some slight signs of detonation but should be fine now i've polished them up. Ill photograph these tomorrow in daylight.

[GeoffBob]

Mmmmm, shiny! So what are your plans for them Chris? Or more to the point, has your plan changed any since we now know that that Sebastians CR was in fact 12.3:1 ?

[CHR1S1990]

Well at the moment I'm searching for some m52b28 rods to suit. The pistons BTW weigh 323g on their own, and a have a gross weight of 451g with the pin, circlips and rings. A stock piston complete weighs 540g so a nice 534g saved there. Stock m20 135mm rods are 624g complete with bolts, whereas the m52 items are 547g complete so another saving of 462g. Nearly a kg saved, not bad!

Im aiming for a CR of stock 8.8, and plan on running plenty of boost on a rotrex c30-94 on LPG. Ive currently 2 blocks sat in my garage, one perfectly fine eta and another b25 block which had some scoring - need to decide how deep the damage is and whether boring to fit the pistons will remove them. Next is to get the block bored to suit the pistons. Firstly i need to research on the gaps for these pistons, and then find a local reputable engine machinist - anybody help me out here? I live near Blackpool.

Now knowing the pistons produce a static CR of 12.3:1 on a b25 block with a standard HG, 885 head and 135mm rods, if I simply swapped the 84mm crank for an eta 81mm crank, the piston would sit 1.5mm lower at TDC giving a CR of 10.3:1. Using the eta block would lower it more to 9.55:1. So, a thicker headgasket will be in order either when i put it together or when I decide to bolt the charger on.

Sebastian is also kindly donating me a 731 head with a combustion chamber more suited to a flat top piston. My thoughts were to port the head larger than an 885, and fit either 885 valves or even larger. Never ported a head before so will need some guidance there too.

I'll deal with the rotrex gubbins once it has all been run in and I'm happy with it

post edited, screwed up on calculations

[CHR1S1990]

Just browsing JE's website as Ill be needing a set of new piston pin circlips (not reusable, right?). Just to make things more interesting, the pistons I have don't have a laser marked ID number. According to JE, pistons with no mark were manufactured before 2004. They just pulled these off the shelf to suit what they thought would "11.2:1" and 85mm? How many other duff 12.3:1 batches do they have?

I'll PM Sebastian anyway and hope he's retained the box, or can I use a different source for the circlips?

[CHR1S1990]

So how did I arrive at this value, and how did JE and Top-End come to believe that this piston would result in a CR of 11.2:1?

Firstly, with the 885 head and stock 1.8mm gasket the head volume is effectively 40cc + 10cc = 50cc....

Hi Geoff, your value of 10cc for the headgasket, im assuming youve arrived at using an 85mm bore. Is this the bore of a standard m20 head gasket for OEM 84mm pistons?

[GeoffBob]

Hi Chris,

Sorry! I missed your above posts last night - I am falling behind in my replies.

With regard to the rods, I cannot comment which are better. Common sense dictates lightest pistons with strongest rods (regardless of rod weight). But then who am I to say that even the lightest rods wouldn't be strong enough for whatever you are considering for your engine. If the lightest rods are sufficiently strong then fit them. I can already see the flood of replies: "I have never heard of an XYZ rod failing under blah blah blah". Likewise I have never heard of a Rastafarian barber being mauled by a penguin while on sabbatical in Antarctica, but that doesn't mean that you won't be the first! Living vicariously can be such fun can't it

Both primary and secondary balance are brilliant on a straight-6 engine provided you have balance between your individual components. I could right paragraphs and paragraphs on this subject, but I simply don't have time today. If I get chance I will scan some stuff in for you. In a nutshell, static component balance is important, and if you want to be anal about it (if you are building a proper race engine) then you might consider having the crank dynamically balanced. I doubt that you’ll want to go that far on your engine though. Component balance starts with pistons. Rods need to be weighed in such a way as to determine which end needs weight removed ”“ you can’t just weigh a rod and match them for absolute weight, the location of the weight is important.

Having said all this, the M20B25 is rev limited as result of the way in which its volumetric efficiency dramatically declines around 6000rpm at wide open throttle. Balancing an engine to handle the rigours of 12000rpm doesn’t count for much when you haven’t a farts chance in a hurricane in getting there.

As for the 731 head ”“ I know nothing about it. Best you measure that head volume as I’d be interested in what you can teach me. I am not even sure if the valves are located at the positions and same angles. 885 head is 2 x 22 degrees. Hence, the plane of the valve cut-outs are at 136 degrees to each other. If the 731 head differs in this regard then obviously you can’t use those pistons. But I assume they are virtually the same head except for volume else the 731 head would not have been suggested as an option?

Yes, I would recommend that you get new retaining clips from JE for the wrist pins. FYI, I don’t believe that those pistons were just ”apulled”a off the shelf. They may be old but they were definitely the product of someone’s acknowledged or unacknowledged fuckup. TopEnd are likely off-loading them on unsuspecting customers whenever and wherever they get the chance under the guise of ”athat’s the way we do high compression motors here in the US”a. If they get a come-back they make good to avoid repercussions. If the customer is none the wiser then so be it. Eight out of ten customers would walk away believing they had a tuning issue rather than question the design of their pistons. Sometimes we forget just how much effort the OEM put into getting our OEM parts right and we fail to realise just how risky the custom and aftermarket parts business can actually be.

That value of 10cc is for the 84mm bore with a 1.8mm thick (compressed) gasket.

[CHR1S1990]

[reggid]

Apparently 731 + B25 pistons = smash, I haven't tested it myself.

I would only be using a 731 if you found someone to develop the ports to outflow the 885. Most places just do a standard port job but there is more meat to raise the port in a 731.

Stock headgasket is atleast 85mm (you can use a 86mm pistons if they are chamfered).

The last head 885 i measured was 42cc.

Looks like those pistons could have been machined to skim the crown or a head gasket slightly thicker I would think, i imagine sebastian is a fair whack out of pocket getting new pistons and machining labour etc?

[eta]

Chris I was under the impression that the eta and B25 block have identical height and that is was the stack height of the crank, rods, and pistons what was 0.5 mm different. So by that reckonningusing an eta block won't change the CR at all. The only way to be sure is to measure the deck hieght of the two blocks.

[CHR1S1990]

Stock headgasket is atleast 85mm (you can use a 86mm pistons if they are chamfered).

good to know, thankyou. Means I can use the standard headgasket that I have for the moment

The last head 885 i measured was 42cc.

I'll be measuring mine anyway to make dead certain what I have

Looks like those pistons could have been machined to skim the crown or a head gasket slightly thicker I would think, i imagine sebastian is a fair whack out of pocket getting new pistons and machining labour etc?

i would assume so!

[CHR1S1990]

Chris I was under the impression that the eta and B25 block have identical height and that is was the stack height of the crank, rods, and pistons what was 0.5 mm different. So by that reckonningusing an eta block won't change the CR at all. The only way to be sure is to measure the deck hieght of the two blocks.

So the stack height is 0.5mm difference not the block height? Damnit, that puts a whole different spin on things. I think I'm starting to confuse myself with all this now the amount of calculations ive been doing..

The stack height of an m20b25 is 75/2 (37.5) + 135 + 34.2 = 206.7mm correct?
The stack height of an eta is 81/2 (40.5) + 130 + 35.7 = 206.2mm correct?

Both pistons come to the top of the bores so theoretically fitting all the m20b25 gubbins into an eta block the piston would poke up 0.5mm? The eta block is actually 0.5mm shorter not taller? I thought that's what i read on here numberous times, thats all.

The stack height of a m20b28 is 84/2 (42) + 130 + 34.2 = 206.2mm. So in a b25 block this would sit 0.5mm down the bore? I thought the wiki states no machining required as the pistons come to the top of the deck?

Please somebody put an end to my madness

[GeoffBob]

I am the last person who should be answering questions on the ETA engine, but according to the zone Wiki "early Eta blocks were very slightly taller (we are talking half a mm maybe)".

However, if the published values of KH=34.2mm and KH=35.7mm for the 325i and 327ETA pistons are indeed correct, then this would indeed indicate a deck height of 206.7mm and 206.2mm respectively (EDIT: assuming the deck clearance = 0mm in both cases). Even though I know nothing about ETA engines I was also under the impression that they were shorter by a 1/2mm, not taller, than the 325i block? But then I could just be sharing in someone else’s delusion.

One thing is for sure though, if BMW did start making Eta engines using blocks of identical deck-height to the 325i block, then they had differing deck clearance between the two, otherwise the numbers simply don’t add up!

When in doubt measure!

[GeoffBob]

Stock headgasket is atleast 85mm (you can use a 86mm pistons if they are chamfered).

good to know, thankyou. Means I can use the standard headgasket that I have for the moment

There’s quite a chamfer there already ”“ it’s called the squishband. FYI Chris, I never rounded that value of 10cc up or down from any other value. I simply understand the stock volume (rightly or wrongly) to be 10cc, as used with the 84mm bore block. Not calculated based upon the 84mm block.

The last head 885 i measured was 42cc.

I'll be measuring mine anyway to make dead certain what I have

Be sure to measure properly Chris. Wipe around your valve seats with Vaseline to stop fluid leaking out and use a slab of Perspex to inhibit the effect of surface tension.

[CHR1S1990]

Ahh, i see Geoff, I didnt know that value was a known used.

Duely noted, the volumes will be measured as accurately as I can (burrette from my chemistry days). Where do I need to measure for the exactly deck heights between the two blocks? I need to pretty accurate seeing as though there is allegedly only 0.5mm difference. Ideally I need the 'tallest' block so I dont have to use such a thick headgasket.

just to quote from one of many examles

206mm CL of mains to deck is the given OE spec Alex(B20B23B25, B27E are 206.5mm)...

which suggests the eta blocks are 0.5mm taller which is what I originally was lead to believe, but this obviously doesnt add up by the stack heights.

I think a good measure up of all my b25 and b27 components are in order, however there are so many variants Im not sure how useful it would be to anyone e.g. the b27 block I have is the very early one with the large core plug, and higher CR pistons