Tech Forum : 2.8 build info

Posted Monday, Apr 26th 5:50pm [Edit] [Quote] [IMS] [View car]

Post nr. 65

Hi Guys pulled this of the e30.zone.uk board froma guy called Master Bates

Jason
2.8 conversion
Block is 325i or 525e. Crank is from M52 2.8 (328i, 528i and 728i). Con rods 130 mm from M20 320, 520i, 323i, 525e. Pistons 325i with 14 mm shaved from skirt to clear crank(early non cat pistion 14mm, later pistions 4mm). This combo works perfectly, no machining of pistons or block is needed.
Crank fits block perfectly without any modifications. All that needed doing is a sleeve machining - use the centre part of the crank front pulley for this. This then replicates the stepped part of the M20 crank where the front oil seal sits. The conical thrust washer needs slimming down by 2mm and the shank of the front pulley bolt needs about 15 - 20 mm taking off. This allows the threads on the bolt to reach further up into the crank. The threads in the M50/52 crank are further up the nose of the crank than the M20.
Also fit the M20 spigot bearing.
And that's it. I'm sure others will reinvent this idea and claim it their own.........

The Yank conversions use a specially made crank and rods which seems like a lot of effort for bugger all gain over what I did to be frank.

The question you're going to ask is....can a 3 litre M52 crank be used? The answer is no. The stroke is too long. The 3 litre M3 crank also. The length of the con rod must NEVER be shorter than the crank stroke x 1.5. Thus a 525e (81mm) works out at 121mm with a rod length of 130 mm. The 2.8 I built has an 84 mm stroke (equalling 126 mm - still okay with 130 mm rods).
The 3 litre M3 crank is 85.8 working out at 128.7 - getting a bit too close and you find a spare M3 crank. The 330Ci crank is a whopping 89.6 which is 134.4 so useless. Even with 135 mm 325i rods it wouldn't be very nice. 3.2 M3? 91 mm stroke thus 136.5 and no good.

How did BMW get around this? They made the M50/M52 (1990 onwards 24v) block much taller. As a result the 2 litre conrods in the 1990cc M50/52 are about 140 mm long.

Posted Monday, Apr 26th 6:36pm [Edit] [Quote] [IMS] [View car]

Post nr. 507

There are many versions of the 2.7/8/9/3.0 stroker build. It all depends what route/output you ultimately want to follow. Just like religion everyone will swear theirs is the best and all other is crap. There is nothing engraved in stone to say that this is the way it has to be done.

Have not heard of the "Yank" method requiring specific special made parts. For instance here is one: Block out of a 2.8l 528e, Overbored 1mm with special ordered forged pistons to match the bore, 325i connecting rods, 524 turbo diesel forged crank, your choice of head.

All BMW parts nothing special except for the buyer specified pistons. You could omit the overbore pistons and keep the BMW pistons that came with the block as well as the conn rods and the eta crank since it has the same 84mm throw as the 524td one. Increase your compression by decking the block and shaving the head,....ad nauseum.

Also remember that the 525e block in europe has a much higher initial compression, 11:1, than the U.S. market etas.

Many ways to skin this cat and BMW provided plenty of hardware for the job. I am sure many will respond with their special way of doing this modification.

Posted Tuesday, Apr 27th 6:08pm [Edit] [Quote] [IMS] [View car]

Post nr. 18

THe one thing to remember about strokers is this:

The rotation (from the crank's journals) are larger in diameter w/ the con rod's angles panning broader

---and----

Because the conrod never pulls the piston down straight, but instead pulls it from side to side, you get wear on the piston skirt. The more wear, the more piston rock and at some point the piston will not seal off the ports properly. The ring also wears and you lose compression.

Strokers are great but they are not long lived motors due to these geometrical conditions.

Posted Tuesday, Apr 27th 7:43pm [Edit] [Quote] [IMS] [View car]

Post nr. 508

that is why the longer 325i conn rods are used. They eliminate the "canting" of the piston and all of the associated wear issues.

Posted Thursday, Apr 29th 3:16am [Edit] [Quote] [IMS] [View car]

Post nr. 67

Ray, do you know if the 323i ever suffered from this canting phenomenon?
I rememeber years ago hearing about 323is throwing con rods and it is interesting that the 325i has longer rods then the 323i but a slighty shorter stoke.I sometimes wondered why BMW bothered to go to the expense of increasing the rod length and stroke of the 325i over the 323i.
It's also interesting to note that the 325i "135" con rods have a larger small end bearing lubrication hole and a small groove at the con rod bearing (compared to the 320/6/323i/eta rods) end also- which is perhaps for lubrication also?

Posted Thursday, Apr 29th 5:45pm [Edit] [Quote] [IMS] [View car]

Post nr. 515

I have taken a couple of 323i blocks apart and they did not have the issue of associated wear with the stock crank. I have also taken apart a 2.8l stroker that had the stock eta crank and rods and it also did not show extra wear on the parallel edges of the pistons and their corresponding bores.

Urban myth?

I can understand why the longer throw of the 325i arm would benefit the stroker on two counts. One you can minimize the need to deck the block to increase the CR of the engine if you use the stock eta pistons (USspec dished). The second would be to provide a longer narrower ramp when the crank is at its farthest position. Actually it "changes" the wrist pin position if you think about it throwing more crown up into the bore. Wow! a whole 1mm worth of extra crown. Something is something especially when dealing with the smaller chambers of the 323i head. Not sure about the wrist pin bushing I can provide pics later. The piston remains centered in its bore and is not pushed against the wall during the compression portion and dragged against the opposing wall at the bottom part of the power stroke like a shorter crown piston would. Regardless of revs.

A shorter rod like the eta would do the opposite of the above and possibly scrape the sides of the bore due to it almost being yanked out of the cylinder at the higher revs. Here is where the theory/urban myth falls in place. Why would it not be possible? Because etas have been running this way since the larger displacement engine was made.

If it was a real issue then I am sure BMW would have done a TSB, a recall, or be more practical and set the rev limit to 5000. Which is just what they did with the US market eta. Personally I think it was to save the much reduced valvetrain and not the block since it has been proven these blocks and cranks can survive in a 6200 rev environment.

Again I always state personal experience higher than heresay and I have a block on the bench that ran with the stock internals, an "i" head, a 6200 rev limited distributor, and does not exhibit any unusual wear patterns.

Posted Thursday, Dec 7th 12:20pm [Edit] [Quote] [IMS] [View car]

Post nr. 2

Hi everybody!

Just read the thread of 2.8 build info
Here in our club, BMW Car Club of Indonesia, this topic is a hot issue now

Consider the following as another option for building the M20 B28
1) Use M20 B25 cylinder block with cylinder block height = 206.2mm
2) Use oversize 50 piston from E46 318i (M43TU B19), the diameter is 85.50mm (Mahle p/n 0831002) and having 30.4mm compression height.
3) Use M20 B25 conrod with 135mm length
4) Use E30 325e or E30 324tds forged crankshaft with 81mm stroke, so we don't need to do a sleeve machining to replicate the stepped part of the M20 crank where the front oil seal sits.

The total height will be 30.4m + 135mm + (1/2 x 81m)= 205.9mm
And we need to have a slight fly cut the block 0.3mm (206.2mm - 205.9mm)
The new displacement is = pi x 85.5 x 85.5 x 81 x 1.5 = 2.790cc, only a 3cc less than B28 engine discussed before with 84mm bore and 84mm stroke from M52 B28m(2.793cc)
The conrod ratio is 135mm : 81mm = 1.67 > 1.50, which is OK

Posted Thursday, Dec 7th 1:58pm [Edit] [Quote] [IMS] [View car]

Post nr. 1289

I am not sure if Ray is around...
but i will add my two cents here.
A common approach to building this engine is like this:

You can use either the 81 mm eta, or 81 mm 524td crank.Then take a 325i block. Bore it to 85 mm..

Use the 325i connecting rods, with custom pistons and 524td crank..and you have your 2.8 stroker.

To build a 2.9 m20
Use a s50 crank, s50 rods, and 325i block.
Again bore the block to 85 mm, and you now have a 2.9 stroker...

Posted Thursday, Dec 7th 9:08pm [Edit] [Quote] [IMS] [View car]

Post nr. 1015

I can't see any reason just to take the super eta block and add an "i" head. If you want the extra ( I wouldn't bother based on the dyno result) 0.1 liters bore the block and put in oversized ETA pistons from Bavarian. The compression ratio comes to approx 9 to 1. You can shave the block if you want to go higher.

My son's doing the 2.7 this way with a 40ES front mount turbo. Using the 173 DME with a TCD turbo chip.

BTW you wouldn't believe how fast his 325e NA motor is with just 24lb 4 pintle injectors a 3bar regulator, 255lph fuel pump, chip and a M30 AFM. With some beehive springs from MM and a better exhaust the thing should kick some serious ass even without the turbo.

I'm just taking a regular 325e with the behive springs, 42lb injectors, 255lph Fuel pump, adding long tube headers , megasquirt,
T3/T4 rear mount turbo and nitrous intake injection to 3psi. I finished all the rust repair, brakes, Ireland suspension, Z3 rack, brakes and pulling the motor this weekend for a freshening. Once I get it on the road it's back to finishing the 357.

Posted Friday, Dec 8th 6:12am [Edit] [Quote] [IMS] [View car]

Post nr. 1290

redmist wrote:

Pete..sounds good.
The super eta is the 2.8 displacement of and eta, with "I" style pistons and rods and an I head.
So it was made around 88, not too common.
Thats why people use the 90 325i 2.5s and bore them out.

24lb and 42 lb injectors are high for stock motronic...but not with a stand alone.
What so you have.

Even just a supereta or built 2.8 in our cars, will move do to the fact that they are so light.

It sounds like you have an interesting setup..
we will have to compare notes and meet up before your son wrecks another fast car.

I have having a few items powdercoated right now,
and I plan on using the 19lb mustang injectors, with motronic, and my MM 2.8 with the knife edged 524td crank. It has the 325"I" rods/

A super eta with a turbo, or a stroked m20 in 2.8/2.9 configuration with a turbo will kick some serious butt.

I will collect the parts to build one in a few years...

later,
J

Posted Friday, Dec 8th 6:55am [Edit] [Quote] [IMS] [View car]

Post nr. 966

ugh...it drives me crazy when people call an eta or super eta a 2.8. It's really not even a full 2.7 liters!

jamie

Posted Friday, Dec 8th 11:55am [Edit] [Quote] [IMS] [View car]

Post nr. 80

You can work out the combinations very easily, simply take the piston compression height + half stroke (which is the throw of the crank) + rod length, then minus it from the deck height of the block.

Example using eta crank rods and pistons (ie a stock eta block).

40.5mm + 130mm + 36.2mm (or 35.7mm, depending on the comp ratio, for this purpose we will use the low comp common eta's) = 206.7mm

M20 deck height = 206.7mm - combination (206.7mm) = 0.00mm which means the combination sits level with the top of the block.

BMW didnt extend the blocks by very much either, people seem to think its a huge figure, its not, its only 2mm and it was to fit the larger stroked cranks of the 3L motors in. What he doesnt seem to know, or simply leaves it from his post is that the larger stroked 2.8L, etc, motors still used 135mm rods.

The thing is, the blocks are more than long enough to contain the larger 2.8 and 3L cranks without a problem. Why? well you dont actually change the rod/stroke ratio, you can keep the crank and existing rod length and simply reduce the comp height of the piston to compensate.

For example, using the 3L crank from the M3 (among others) with a stroke of 85.8mm and the stock rod length of 135mm.

42.9mm + 135mm +?

So take the 206.7mm height, minus the rod and throw lengths and you end up with the comp height of the piston.

206.7mm - (42.9mm + 135mm) =
206.7mm - 177.9mm =
28.8mm comp height.

This is a good combination for anyone building a 3L motor, 28.8mm leaves enough metal on the pistons to still have a good expanse between ring lands and for the crown. It doesnt cause problems with the skirt striking, however some full skirt pistons wont fit, so you need to take note when ordering your new custom pistons.

Ive seen a few people gloss over side loading (well, only just slightly mention it) but have never gone into it with detail which tends to suggest they dont quite understand the motor. If side loading is a problem, why are there large capacity M50, M52 and M54 engines with 200,000+ on them without loss of compression or suffering from piston slap? ive had a good look through quite a few of m50 and m52's, including one that had even seen 400,000 and there isnt a problem with wear due to side loading of the piston. Its usually head gasket failure that is the cause of any problems (quite often due to poor cooling, or cooling issues), and bores being glazed over resulting in poor ring sealing (and using oil).

The angles arent really any different to those already in use in a production engine designed to last the lifespan of a vehicle. So yes, while things are different, they are not extreme nor abnormal, you just have to remember that most of these combinations are already in use today in other engines bmw designed without a problem.

Saying they are great but not long lived is a load of bollocks. See case in point about M50's and M52's above. Im sorry, but like i said, people seem to totally forget they are using the rotating assembly of another engine when building the strokers. Id like someone to come out and tell me that the 2.8L or 3L used in the E36 is a short lived motor, because quite clearly it isnt.

Eta's are pretty much all the same as far as bottom ends go, the crank and rods are the same across all different versions, its the comp height, and in most cases, the piston crown which has been changed in order to generate different comp ratio's.

The problem with all M20's, is vastly owners "abusing" them and weak points in the engine design (and i use that term, weak, lightly as the engine wasnt designed for developing this sort of horsepower, or running under these operating conditions) start to show up. With regards to 323i's throwing rods, its a two part problem.

1) is the very limited number of rod failures on m20 engines get blown out of proportion. Not many people have first hand experienced rod failures, for most people they seem to be relying on experiences from other people, and thus further propogating the myth.

2) the majority of failures occur due to movement of the rod cap under stress. This is partially due to the operation of fasteners and just what happens to them under stress and vibration over long periods of time, but also reduced tensile strength of the bolts suffered first after the intial tightening, then as fatigue sets in over the years of operation.

What is the easiest way to fix the problem? well simply replace your rod bolts as a good start, using aftermarket items like those from arp is even better.

With only a few minor exceptions, all the rod failues i have personally seen (and there have been about 6 of them over the years) have been due to bolts sheering off or the bolts failing to provide adequate torque (so essentially failing). The exceptions have occured in abnormal circumstances such as high revving operation (where a stock rod actually bent) or under forced induction (where again, the rod actually bent under added cylinder pressure due to detonation).

Basically, as far as the bottom ends go, they are pretty robust little engines.

As for why bmw increased the rod and stroke over the 323i. Well, simply, they didnt. They reduced the stroke of the 323i crank and lengthened the rods. The 325i motor actually runs a 75mm stroke which is 1.8mm shorter than the 323i item.

The reason for doing so is one of bottom end design too, especially in regards to the new piston and combustion chamber produced. They couldnt maintain a piston with a good compression height while using the shorter rods already available. What you would have ended up with was a large increase in the phsycial mass of the bottom end due to having to make up the difference in stroke. The only real option was a new combination.

The problem with car communities is too many people talk about it, with the majority of the information they rely on coming from reposted material regurgitated by others. You only have to talk to a few of the old engine builders to know quickly just what is a myth and utter rubbish, and what is actual fact.

Shall we list a few common m20 myths?

eta cranks arent strong enough to rev because they are cast.

i cranks are semi forged.

turbo diesel cranks are best because they are forged, and you need one when building a stroker.

strokers suffer side loading issues, which increase wear.

using 323i heads increase the compression ratio.

Hows that for a few?

Again, like RDAvena, im only relating what i have seen personally and what work i have done on the motors. Ive put together maybe 15 of them in various combinations and ive got a book full of all the notes made when building/machining the engines (if anyone feels like doing loads of typing ill send it to someone with the time to type it all up if you feel game

). And like him, a lot of the stuff that is posted about the m20's is deeply rooted in myth with a liberal dashing or truth.

Might mention that i have a 3L motor sitting on one of the stands here

Only problem is the crank scraper doesnt fit anymore. LOL!

Posted Friday, Dec 8th 2:03pm [Edit] [Quote] [IMS] [View car]

Post nr. 1291

lol.

Madhatter, very good.
Basically the 325i rod, is it the same length as the s50 rod? So in boost applications how robust is the m20 rods compared to the S50??

I have also heard that the m50 2.8 cranks, and rods can be used to stroke the m20, but not to sure about the details.

This round I basically have my 2.8 lower end already done, I am just replacing the eta, with the 524td crank i knife edged.

SO: 81mm 524td crank, 325i rods, 85 mm Metric Mechanic pistons.

I have looked around for ARP bolts for rods..
which part number is correct for this application?

My future plans are to take the 1995 S50 crank(i have already), s50 rods, custom pistons, bore the block or use mine at 85 mm and boost it. Using a CR of 8.5:1.

S0: S50 86mm Crank, S50 rods, 85 mm custom pistons.

**I have heard that you need a certain age m20 block to fit the large crank, and the ones before 89 will not work**

I just had the question about the rods, as I have seen some custom crower ones on ebay for $800, and they seem too much money at 800.

Can S50 rods handle boost.
I want over 300 hp..not anything crazy.

Posted Friday, Dec 8th 3:33pm [Edit] [Quote] [IMS] [View car]

Post nr. 421

Hi

It has been over two years since I posted this, (and credited it source) and I can not belive it has been brought up. But I do note the last paragraph about larger cranks is wrong except for the m3 crank, most stokers using the M3 crank mean the US spec item. The Euro crank has a different bolt pattern for the nose so the crank pulley does not directly fit and the webs are larger and are said to foul the distributor drive on early engines, and come close to the bottom of the cylinder walls

Back when I posted this there was a lack of m20 stoker information now there is loads of threads on rev3 & e30tech, anybody can read the metric mechanic website and become an â€œinternetâ€ m20 guru.

Five years ago before forged pistons were a consumer item, it was cheap just to swap a 2.7 bottom end over, but to do a pukka 2.7 build you took a 325 engine with 885 head (no I v E crap or forged 324 cranks in the UK as they were not sold here) and used the 2,7 crank with 130mm rods 325i pistons and decked the block because that was the tenth of the price of a set of custom pistons, add a shrick cam, 6 branch and a chip and you got about 200HP.

Now you can build what you want depending on your budget, but with the low cost of forged pistions a larger crank makes mopre sense (In the uk a used M20 from a breakers yard is the same cost as a used M52) but a decent induction system & exhaust is going to cost more than the stroker and you will want that to go beyond about 200hp.

As for rod length etc does it mater, I think not look at an 911 engine. Attention to detail during the engine build is going to give more reliability than the â€œrightâ€ rod ratio.

And as I have a 2.7 stroker that makes 250hp would I build another, no I fancy a 2.8 alloy block m52 with an early non vanos head, throttle bodies, six branch and vems for less than the price of a 3.0 m20.

Jason

Posted Friday, Dec 8th 3:55pm [Edit] [Quote] [IMS] [View car]

Post nr. 81

The rods are identical in length. The big difference is the S50 rod is much much lighter with reduced physical dimensions.

here, for example

Thanks to my good friend diego for lining them up side by side and taking a pic

m20 rods are good but there have been one or two failures around the 350-400hp mark with stock bottom ends. But, again, these are stock bottom ends without even being opened up in a lot of cases. With a rebuilt motor and good tuning, you only have to look at results from europe to see 500hp out of high boost setups while still using the stock forged rods.

Yeah you can use 2.8L rods and crank. Just need to match the pistons. Ive got the combination here somewhere (ill have to look it up) when using the 2.8L rods and crank there is another stock bmw piston you can use that fits the dimensions but will maintain a good comp ratio, but without having to do any modifications to it.

Ive got pro series bolts for mine, 201-6102, but ive got matching rods to go with the crank. However, they are very similar between them, i might pull both bolts out tomorrow arvo and take a pic of the different rod bolts side by side. They look to be the same length and pitch, so because they dont have the m20 on their part listing anywhere, might be able to use the later model bolts. Of course, if you give them the length, diameter and pitch, they will match bolts for you though.

Stuff about the blocks doesnt really make sense, they share the same bearing sizes right through the range.

crower make awesome rods, ive got a set of them here which i planned to use on the motor, but i might keep them till its pulled down in the pursuit of real power. They are roughly $180 a rod from them now i think, so for $800 its a pretty good price for a very nice rod.

Hell yeah they can. Even the stock rods will handle it. But if you have a set of S50 items, use them, the lighter rod is going to be better for your bottom end. Just remember you need to have the whole lot balanced again.

Posted Friday, Dec 8th 8:27pm [Edit] [Quote] [IMS] [View car]

Post nr. 1016

Ok so all other things being equal (injectors, electronics, exhaust) what is the HP/torque difference between a 3.0L made from a basket of different BMW parts and a 2.7 (decked to get the same compression) super eta (in order to get the right pistons) with an "I" head (or a super ETA head with a "i" cam)?
My guess would be nominal. Is it worth the cost/effort?
I agree with your all your myths BTW.

Posted Friday, Dec 8th 10:20pm [Edit] [Quote] [IMS] [View car]

Post nr. 422

Okay to help you guys out this is information I have collated from my BMW manuals & Mahle catalogue any errors are my fault please correct me

Jason

Engine type Rod Length Bearing size
M20 2.0 130 45
M20 2.3 130 45
M20 2.5 135 45
M20 2.7 130 45
M40 1.6/1.8 early 135 45
M40 1.6/1.8 late 140 45
M42 140 45
M43 1.6 145 45
M43 1.8 140 45
M43 1.9 140 45
M44 140 45
M50 2.0 non Vanos 135 45
M50 2.0 Vanos 145 45
M50 2.5 non Vanos 135 45
M50 2.5 Vanos 140 45
M52 2.0 145 45
M52 2.3 140 45
M52 2.8 135 45
S50 3.0 142.3 49
S50 3.2 139 50
S50 3.0 US 135 45
S52 3.2 US 135 45

Piston Heights from pin centre to crown
All 2.5 34.2
2.7 Super eta 35.7
2.6 others 36.2

Posted Saturday, Dec 9th 2:13am [Edit] [Quote] [IMS] [View car]

Post nr. 1293

According to Jeff who uses the S50 crank and S50 rods, Matthatter it does depend on what year block you have:

Quote:

The crank will just "Drop" in but there is a "prefered" block to use with this, or on my opinion any performance M20 engine.
That is a block from production of 3/88 and newer. This is because the main brg. were modifyed to help with windage from the oil flow past the ROD brg. This is also the same main brg. used in the M50 to M54 and all the S50 up engines.

And Madhatter can you please check on which Arp bolt to use with the 325i m20 rods, forged pistons and 524td crank..Is it the pro series bolts # 201-6102, Thats a lot..

Joe