2.7 build questions

[eta]

I don't know if this question has been asked but I was thinking (and can't find the answer):

For the e to i conversion on eta engine the simplest method seems to be using the "731" cylinder head from an M20B23 however that engine has a bore size of 80mm. The 2.7/2.5 blocks have a bore of 84mm. So I would assume the 731 head has a cylinder head chamber diameter of 80mm right?
So how can this work efficently on a 84 mm bore cylinder. Not that I doubt the results it just does not feel like a good solution. So if the 731 head has the chamber opened out to a 84 mm diameter would that achieve better combustion or does the smaller combustion chamber diameter not matter.

I also know the 885 head is better option which brings me to my other question. I was adding up numbers and something did not make sense. If you use M20B25 pistions (85-89 9.7:1 compression ratio) in a eta block with the 885 head the pistions at TDC should end up below the top of the bore and give a very low compression right? So:

for a 2.5 block
Block height 206.7mm
Pistion height from centre pin to top of piston 34.2mm
conrod length 135mm
Total crank to piston top heigth 169.2mm and this with the 75mm crank brings the pistons to the top of the bores. Therefore total distance from crank centre line to piston top at TDC = 244.2mm. Is this right? Does the 75mm mean the total width of the crank or is it the distance from the crank centre line to the centre line of the crank arm?

for the M20B27
block height 206.2mm so 1/2mm shorter.
Pistion height from centre pin to top of piston 35.7mm
Conrod length 130mm
Total crank to piston top heigth 165.7mm but the is 81mm so the total distance from crank centre line to piston top at TDC = 246.7mm and this brings it to the top of the bores. So using 2.5 pistons in an eta block with 130mm connecting rods and a 81mm crank would give a total of 245.2mm so the pistons would be 1.5mm (0.15cm) below the bore tops!

so CR = (VC + CBCV)/CBCV

VC = volume of cylinder
CBCV= combustion chamber vol
CR= compression ratio
so VC = 4.2^2*8.1*pi = 448.9 cm^3
CBCV =47.7 (for the 885 head) + volume of the cylinder left by the 2.5 pistons (0.15*pi*4.2^2) =56 cm^3

Therefore CR is 9.0:1 ((448.9+56)/56 = 9)

Now that is not too low! Surely such an engine will run fine? Could it be supercharged or turbo'd?

Also I have found two values of the combustion chamber volume for the 885 head. the value I have used above and 42.5cc used in the 2.7 build sticky. If I use the lower value the CR comes out at 9.8:1. Which is right?

Would custom connecting rods of 131.5mm therefore obviate the need for shaving the block to get higher compression.

Data from http://www.bmwccn.no/rogaland/Mahle_m20.html

Comments please

Malcolm

[daimlerman]

Wow Quite a first post. I am using a 731 head on an eta short motor,no problems. It made 178bhp. I currently have a 200 head being machined to take 325 sized valves.This,or having a 731 head machined in the same way, gets round the C/R snag you mention. Using an 885 head with 325 pistons leaves you with a pityfull C/R unless you deck the block to bring the pistons to the top of the bore. This is fine,but,(there's always a but) the cam timing is now out,to correct this you need a vernier pulley....if you are starting with a 325 motor,check out jazzman's build of a 2.8 somewhere in this section....it's food for thought. Oh,almost forgot,welcome to the zone,you sound like our kind of zoner

[march109]

Second that on the first post bit.

Many people have strapped a turbo to the 2.7 and 9.0:1 should be fine for that (upto a point!)

Apparently the ETA and 731 have the same combustion chambers.

The reason there is too different figures for CR on the 885 may be down to the fact there are to versions of the M20B25, a high compression and low compression version, so both CR's you have may be correct depending if you are using a lower or higher comp engine.

[march109]

it is also possible according to Andyboy to use a 885 head on the eta withought changing the pistons. The later eta engine coupled with a 325 head supposidly gives CR 9.4:1.

Read point 2 in Andyboys post.

I have an eta engine sat in my garden and think if I ever start my build 885 head slapped on the eta, would be easiet and will also save me having to deck the block and add a vernier pully.

I'm not building it for outright power though, I just want something perkier than a 325. I'm more interested in concentrating my time and money in the M52 crank, but I would love to get my greasy hands on a M54 crank.

[eta]

Thanks for the replies. I have read andy's post and from that these questions arose;

1) what is the combustion chamber diameter on a 731 head?

2) would the use of 131.5mm conrods in a eta block with 2.5 pistons allow the pistons to reach the top of bores. While the sums seem to indicate that they will, will the geometry of the block alolw this? I mean would the longer conrods on a 2.7 crank have problems with clearance for the conrods. I just don't like the idea of shaving the block down.

3) Is the chamber volume of an 885 head 42.5 cc as Andy claims or 47.7 cc as I have found on a bmw club site that linked to? Not having any of these heads to measure I have to rely on sourced information.

Before I embark on this project I want to know precisely what I will get.

A 731 head with eta pistons on a eta block with crank may develop ~180 hp but is unlikely to generate significantly more torque than my current stock eta engine. After all the larger valves on the 731 head compared to the 200 head is only going to allow extra torque at high rpm 4500+ (if my thinking is right) I could be wrong but all a see people quote is peak bhp. I am far more interested in the torque and maximising it from low to mid rpms. So what torque is possible.

What I am aiming for is turn eta engine into something with 200 ft/lb torque miminum @3000-4000 rpm. More would be ideal but I don't know what is possible. Hense the thoughts of using the 885 head with it better gas flow.

[Simon13]

"super eta" US and Europe only models came out later on after the facelift on E30's i think, and used an 885 head, and the normal eta bottom end

I don't know about the power or torque figures

[eta]

Simon 13 super eta has 127 hp @~4250 rpm and 170ft/lb or torque at 3250 rpm but this is still using eta manifolds which tune the engine to develop torque at 3250 rpm. That is less power (slighty) and less torque than the stock euro engine so is pointless. The CR is 8.5:1 to minimise NOx emmission by reducing combustion tempertaure. The best fuel they have is 91 octance so I sure knock resistance is also part of the reason for low a CR. But I am not after a super eta engine. Also the piston design was different to stock eta pistons as super eta pistons had a deepish dish in the centre of the piston and no raised crown.

However my questions still stand would 131.5mm conrods work with 3.5 piston in an eta block?

What torque do people get across the rev range from these kind of engines?

Is andy's statement the combustion chamber volume of a 885 head is 42.5cc correct or is the figure 0f 47.7 that I found correct?

What is the combustion chamber diameter of a 731 head?

Please help!

Malcolm

[Simon13]

What are you trying to achieve from all this? if you want 200lbs at 3000-4000rpm i'd say you need to go the 2.5 head route as you'll need to 200bhp to get the torque up to the same and no 731 head conversion makes 200bhp

[reggid]

Simon 13 super eta has 127 hp @~4250 rpm and 170ft/lb or torque at 3250 rpm but this is still using eta manifolds which tune the engine to develop torque at 3250 rpm. That is less power (slighty) and less torque than the stock euro engine so is pointless. The CR is 8.5:1 to minimise NOx emmission by reducing combustion tempertaure. The best fuel they have is 91 octance so I sure knock resistance is also part of the reason for low a CR. But I am not after a super eta engine. Also the piston design was different to stock eta pistons as super eta pistons had a deepish dish in the centre of the piston and no raised crown.

However my questions still stand would 131.5mm conrods work with 3.5 piston in an eta block?

What torque do people get across the rev range from these kind of engines?

Is andy's statement the combustion chamber volume of a 885 head is 42.5cc correct or is the figure 0f 47.7 that I found correct?

What is the combustion chamber diameter of a 731 head?

Please help!

Malcolm

42cc would seem closer to the money give or take a cc or two. To get any better or what would be better said more accurate info will require you to measure the specifics of a head after you've had it skimmed particularly the pone you'll use.

The 731 has been used on many a 84mm ETA and 80mm 323i block and the reason is the piston shape you'd probably need dished or flat pistons to use this head so its probably not important to know to the chamber diameter just don't use m20b25 pistons or have the pistons sit out of the block when using the 200 or 731 head.

The SETA piston actually looks very very similar to a late M20b25 piston which both suit the 885 chamber shape.

Regarding 131.5mm rods it depends on the deck height theoretically speaking a 132mm rods with E crank and I piston and I block should make it sit in the correct position. But its often said that the deck height of the B27 is 206.2mm and B25 is 206.7mm but a few gurus I've spoken to say this isn't the case. The m20b25 is definitely 206.7mm though.
If the B27 is 206.2mm then 131.5mm would do it if its 206.7mm then 132mm would do it, though no sure why you wouldn't deck the block then you will have an excuse to run a vernier pulley which is never a bad thing.

Having said that a M52 crank eta rod m20b25 piston in I block should sit 0.5mm lower but that was not the case in Jazzman's build thread.

[eta]

As I thought and have said in my previous post. But my main questions are still unanswered.

Is my workings for the CR of using 2.5 pistons with eta conrods in an eta block with an 885 head correct (without block modifications)? Which combustion chamber volume for the 885 head is correct 42.5cc or 47.7 cc?
Therefore will connecting rods of 131.5mm work to bring the 2.5 pistons to the top of the bores as this should improve the CR with without modifying the block?

What I am trying to achieve is an engine good for dailly use with the torque at the target rpm that I have suggested so it has decent ( but not earth shattering) performance. I intend to mate this with a manual box and a 3.25:1 diff for a quiet ride (2500 rpm @70mph). Essentially I want to be able to pass alot more comfortably without having to really push the car.

the whole reason why I went for an eta is so I could embark on project like this. I could have got the performance for an M30 but thats boring. Learning about engine design and having one built to give me what I want is whole point. beside the M20 is lighter.

If anyone here does not know the answer to these questions then who are the best people to speak to who can give unbiased advise.

The last thisng I want is to embark on project and spend a whle lot and not get precisley what I want.

Malcolm

[reggid]

What are you trying to achieve from all this? if you want 200lbs at 3000-4000rpm i'd say you need to go the 2.5 head route as you'll need to 200bhp to get the torque up to the same and no 731 head conversion makes 200bhp

I would a 200 head with more port velocity would be better for torque between 3-4k. Having 200bhp bears no impact on the torque between 3-4k.

[reggid]

What are you trying to achieve from all this? if you want 200lbs at 3000-4000rpm i'd say you need to go the 2.5 head route as you'll need to 200bhp to get the torque up to the same and no 731 head conversion makes 200bhp

I would guess that a 200 head with more port velocity would be better for torque between 3-4k. 200bhp bears no impact on the torque between 3-4k.

[daimlerman]

My 2.7 gives 190ft.lb of torque at 3750rpm.The torque line on the graph steady's at 2500rpm and 180ft.lb.,rising to max power(178bhp)at 5250rpm,at this point the torque is down to 180ft.lb. I have just fitted a hottuning six branch with new,standard,exhaust system and my 'arse dyno' tells me I have gained throughout the range with a distinct surge above 4000rpm. As already posted I have another head at the engine shop being worked on, when this is back and I have ported the inlets and installed it I will be off for a mapping session to get the best set up that is available to me.My understanding is that to get the highest comp ratio you need early 325 pistons with eta/320 rods and the block needs decking.Using a standard eta short motor eliminates this problem,the 731(320/323 head) works pefectly well and will pass enough air upto 200bhp,to go higher than this you need bigger valves.The higher the maximum output,the narrower is your powerband.We tend to quote max. power figures as people understand these better.The beauty of my engine is the huge spread of torque,at main road speeds I just plant my right foot,in 5th,and the car takes off. To see the graph of my engine,and others!,have a hunt back in E30 chat in late November.Look for a thread Evolve Rolling Road Day,or similar.

[Simon13]

What are you trying to achieve from all this? if you want 200lbs at 3000-4000rpm i'd say you need to go the 2.5 head route as you'll need to 200bhp to get the torque up to the same and no 731 head conversion makes 200bhp

I would a 200 head with more port velocity would be better for torque between 3-4k. Having 200bhp bears no impact on the torque between 3-4k.

i didn't say it did. Thats rubbish. My 2.7 which was in need of major TLC might i add and down on power had the torque figure this guy is after at that RPM with a standard 325i head+cam on an alpina bottom end. It made 170lbs@2500rpm

Is this going in an E30? because your 3.25 diff calc is wrong. a 3.64 ratio diff with a manual or auto 2.5 M20 box with give 2500@70mph. If you fit a 3.25 diff it would be like a road block and slower than before

[reggid]

What are you trying to achieve from all this? if you want 200lbs at 3000-4000rpm i'd say you need to go the 2.5 head route as you'll need to 200bhp to get the torque up to the same and no 731 head conversion makes 200bhp

I would a 200 head with more port velocity would be better for torque between 3-4k. Having 200bhp bears no impact on the torque between 3-4k.

i didn't say it did. Thats rubbish. My 2.7 which was in need of major TLC might i add and down on power had the torque figure this guy is after at that RPM with a standard 325i head+cam on an alpina bottom end. It made 170lbs@2500rpm

Is this going in an E30? because your 3.25 diff calc is wrong. a 3.64 ratio diff with a manual or auto 2.5 M20 box with give 2500@70mph. If you fit a 3.25 diff it would be like a road block and slower than before

You said you'd need 200bhp to get the torque up to 200 at 3-4k i am not sure how many ways there are to interpret there are

[Simon13]

i've never seen a 2.7 make 200lbs anywhere in the rev range which hasn't made at least 200bhp. Regardless of spec or cylinder head used. Care to enlighten me?

[reggid]

i've never seen a 2.7 make 200lbs anywhere in the rev range which hasn't made at least 200bhp. Regardless of spec or cylinder head used. Care to enlighten me?

My point is that it doesn't mean its not physically possible, at the Evolve rolling raod day there were 2.7s with

225lbft / 205bhp
195lbft / 178bhp

so the bhp has no direct infleunce on the torque at midrange.

200lbft at 4k is 152.3bhp so you can have 200lbft at 4k and still make only 153bhp if the torque drops off really quick...........

Having said that for the OP i would go with M52 crank, eta rod, M20b25 piston and head and either std cam or 272 or 284/272 given that an engine designed for torque alone gets boring after a while and this combo should have a bit of both hp and tq

[eta]

thanks for all the replies this gives me more info and desions to make.

Simon this engine is for my e28 which an eta. It currently has a 2.93 diff in the rear. Based on wheel diameter and gear ratios (top on the auto is 0.73:1), I should be running 2033rpm@70mph (the whole point of the eta engine) in reality the needle is sitting a just beyond the 2k mark. So my workings are right. So a 3.25 diff with a manual box (top 0.81:1) would offer a total ratio 2.63:1 compared to 2.14:1 which is what the 525e have at the moment.

The manual 260 box has completly different ratios to the zf auto.

[Templ8e30]

It's well established that the best way to make a 2.7 is to use the 325i block/head/pistons with eta crank and any non 2.5 conrods.

The only conrods available are either 135mm fitted to 2.5's or 130mm fitted to all other M20's.

While using an 885 cylinder head on an eta bottom end will work, it's not technically correct as the piston and chamber shape don't match losing squish.

The '200' casting eta head is the same as the E21 320i/323i (albeit with 3 cam journals undrilled). The 731 head has the same chambers and valve sizes as the 200 but with larger inlet ports.

Cam choice is critical too, the standard 325i cam is way too tame, Catcams 264 is similar to an alpina c2 2.7 cam. I'm using a 273 catcam and the power kicks in at 3500rpm, I think that's fine for a fast road car.

It's not realistic to say 'X' will give you exactly 'y' bhp and torque.

Cheers,

Iain T

[daimlerman]

If you are using an E28 eta as your base,I would just swap the head for a 320 item with your choice of cam.I would leave the gearbox alone along with the diff!! you will get a useful power boost for little cost.

[Andyboy]

47.7 cc volume includes the head gasket.

[exup]

Eta
I too run a `e28 ETA , and i did the 731 ported head with 325 cam and t body and injectors about 2 year ago
it s a bgood improvement on a std eta ,
But I got ANT to do me a chip for the Eta to raise bhp , you can feel it start to pull well , but then runs out of fuel , the chip did nt work ( etas got a funy ecu etc )it just brought up the auto box warning light locking it into 3 rd gear , so before you put alot of time and money into this project check to see if yors cars chippable ( mine is a 88 e plate version )
hope this helps
re the head the 731 works well on a good eta bottom end as does the 325 cam injectors and t body / manifold
wish you well with your project , but for torque biuld a 2.8 with a mild cam if you want toque low low so to be drivable , My ETA is a London traffic car and the power / torque is great for traffic

[daimlerman]

Why not switch to motronic,using a zone 2.7 chip in a 325 ECU? You will need the loom,cam driven dizzy etc,but it should solve your running issues.

[reggid]

47.7 cc volume includes the head gasket.

The 885 head itself is about 42cc and since the gasket is more than 5.7cc i don't see where the 47.7cc comes from unless its after the head is skimmed.

[Andyboy]

The 885 head itself is about 42cc

Hmm, the appliance of science............

Total cumbustion chamber volumes of course also include any piston crown dish. That's why the total volume on an early 325i is 47.7cc and the later one with deeper dish pistons is 53.25cc.
Do the maths and the early engine seems to come out at 47.5. I used a burette with parrafin with a used BMW gasket glued on and it came out to 47.7. I'm 99% sure that head was original and unskimmed too.

So, where has Mr Eta gone? Were his questions answered?

[eta]

Oh yes they have been thakns everyone. The up shot is before I was sure I want to get a 885 head and pistons from a 2.5 or custom pistons, I am now not so sure. Further reding about engine design make question that for the kind of engine I want.

I quite like Oakley's engine but it sounds like he gone to town on the engine management. So I now thinking why not stick with the standard pistons and 731 head and spend the money saved on engine mangement. Alot more to investigate for sure!

Malcolm

[reggid]

The 885 head itself is about 42cc

Hmm, the appliance of science............

Total cumbustion chamber volumes of course also include any piston crown dish. That's why the total volume on an early 325i is 47.7cc and the later one with deeper dish pistons is 53.25cc.
Do the maths and the early engine seems to come out at 47.5. I used a burette with parrafin with a used BMW gasket glued on and it came out to 47.7. I'm 99% sure that head was original and unskimmed too.

So, where has Mr Eta gone? Were his questions answered?

I see where the 47.8cc comes from since i have been basing my calcs on late m20b25 which does have total chamber volume of 53.3cc assuming the CR is actually 8.8:1 The early ones are 47.8cc using the same calculation mehtod.

The 42cc i was referring to is the casting only so does not include the gasket or the dish / dome of the pistons or the deficit. If you place a piece of glass with small hole over the face of the head and with a syringe and add fluid in until no more can be added that's what i get (~42cc) and i have seen it quoted by Metric Mechanic on their website.

Since you know total volume 53.3cc (or 47.8cc) and can measure the head casting to be 42cc and calculate gasket volume to be say 9cc then the net effect of the piston + deficit is a + 2.3cc contributor to overall chamber volume.

[Andyboy]

I used perspex, a smear of PRC to glue it all down and a crushed head gasket.....and I came up with the figure mentioned. But it doesn't matter, it's an old M20 not an F1 engine.

For a 525e, don't even take the engine out. Just fit an 885 head to your existing engine, it will work fine and give a decent CR. If you're talking about removing the engine, you may as well sell the thing and get something else. By converting the engine to an 885 head etc with a standard 325i cam, all you will end up with is about 185 bhp and a car that's not a lot better than a £500 528i. A complete waste of time, in other words. The 3.25 diff won't do you anjy favours at all. If you want it to really go, you'll need a 3.64.
A 525e will respond to a remap - a bit more timing and fuel and you'll gain 5-10 bhp and much better response. A bigger throttle body will add another 2-3 bhp but after that, the camshaft will just slam the door shut.
As the Yanks proved, adding a 325i cam to a standard Eta and remapping the ECU gave a massive improvement but you're still up against weight and silly tall gearing.

[eta]

I bought a £500 528i once and that was a waste of time. Engine problems power steering problems and suspension collapse, rust in jacking points. A cheap E28 is cheap for reason as it can be pile of scrap as mine turned into. A good 528i will be inexcess of £1500 but try finding one. The one that appear on e-bay for few notes are in the same catagory as the one had or are poverty spec and I hate that. It a five series after all.

I now think after all your input I going to be on the lookout for a 731 head and intake manifold, exhaust, and other related bits. Diff is the difficult choice but a 3.64 does sound like a good comprimise.

Anyway the point of this car it is lighter than a 528i by ~60kg and importantly has a lighter engine and is no longer poverty spec and besides this sort of project is fun so when converted will be quicker (with the right diff).

Anyway fun is the reason why we buy maintain and modify old cars isn't it?

If I was sensible about cars I would have a Ford or a Nissan or maybe wait for it a Toyota!

Malcolm

[Andyboy]

Fair enough! What year is your car? Just that earlier ECU's aren't mappable.

[eta]

1986 so I think it is mapable and least that chipped UK said! I take they are right.

[Andyboy]

Yes, a 1986 will be doable. It's the really old ones (83-85) that can't really be done. You'd be surprised how much extra urge a remap can make on a standard 525e.

[eta]

A couple of questions;

1) When I convert the engine my existing tachometer will be useless. How will I be able to get a new tach face in the instrument panel so it displays the corect rpm while still keeping the existing odometer.

2) The ZF4hp auto box curently shifts at 4000 rpm when in kickdown (yawn!!) blatently this will be a problem does anyone know how to alter the shift points in these auto boxes? The box is a standard eta unit no sport/economy 3-2-1 twisty knob.

3) What is best exhaust manifold. I going to guess the eta one is not an ideal candiate so will the 2.5 exhaust maniold fit a 731 head?

I'm getting a few bits next weekend so it should start comming together for summer.

Malcolm

[daimlerman]

Guessing on most of this!! How about a tacho from another E28? I would expect it to be plug and play,unless anyone knows different. Autobox,hav'nt a clue!! I would approach your local autobox specialist. Current value exhaust manifold is the hottuning item at £200 delivered. But will it clear your steering gear? JAM172 has an E28 and an M5,the 528 has an aftermarket manifold of some sort,he may be able to guide you on clearence issues. We realy are better informed on E30 issues. Have you tried the 5 forum?