m20b27 block skim super/turbo charger advice

[mongomushroom]

Good afternoon all. I'm looking for some advice on block skimming for 2.7 super charger/turbo.

Firstly I'll give a little background info since i'm a longwinded kind of person. I bought an abandoned project last year which i'm just getting round to properly starting. included was 325ise in need of some tlc big brake kit, lsd, m3 leather interior, m20b27 engine lying out in the rain with head removed, unknown make of centrifugal supercharger(with brackets, pulleys etc), 7th injector set up, piggy back ecu and a few other bits and pieces. The supercharger had been fitted to the m20b27 engine and produced 211bhp and 300ft/lb with print outs to prove. this engine is f*cked though with rusty cylinders from lying outside and piston/valve contact which I only noticed after buying it. my plan was to fit this super charger to what i thought was a good m20b25 and adding bigger injectors, intercooler, modern management blablabla etc hopefully improving on previous power.

I've encountered a few problems though. It seems my supercharger is not suited to this engine size. It seems that its better suited to a smaller engine as explained to me by a very knowledgeable and helpfull zoner. http://www.e30zone.net/modules.php?name ... ger+advice (my appologies for my cheekyness in that post. i was pretty drunk when using the laptop which is never a good idea). was thinking of fitting it anyway since it worked before and going for something else later but should probably sell it now and get myself a turbo. still deciding on that one.

next problem is the 'good' m20b25. turns out that the crankshaft was in good condition except the thrust bearing was totally shagged and had worn into the webs and is now beyond economical repair. I pulled the crankshaft from the 2.7 which looks to be in good order apart from the key for timing belt pulley is proper f*cked (i think thats the correct term). Not sure what happened to the engine, timing belt snapped maybe selecting 3rd instead of 5th at very high speed, not sure but something caused the pulley to force the key into the shaft. Spoke to someone at my local machine shop who reckons he can machine a bigger key into it and cut a bigger key groove into the pulley which I know would risk altering the timing but would require a vernier pulley on the cam anyway as the block will need skimmed (using 325i head, block, pistons, 320 rods). before I make any decision the crankshaft is getting measured to see if any other work is required.

The advice I'm looking for is how much to skim off the block for a forced induction application. I realize that this is probably covered on here somewhere but have spent a long time searching and cant seem to find it. I want the compression ratio low enough so that I can have a fair amount of boost but not so low that I could encounter other running problems. I dont have an exact boost figure in mind yet as I'm still not sure which turbo/supercharger i'll end up using. This is my first m20b27 build and also my first forced induction build so any advice would be very much appreciated

[daimlerman]

Not too sure that the eta 2.7 crank is tough enough for a supercharger application,these were designed with a modest rev limit in mind.

The tuning houses,Alpina-Harge-Racing Dynamics-Les Stannard etc seemed to use the M21 diesel crank to go to 2.7,snag is that as this engine(324d)was never imported officialy,these are a little like rocking horse manure in the UK!

As your crank already needs work,and may need more by the sound of it,may pay you to have a hunt on German ebay for the tougher crank.

Another alternate is the crank from the later M52 family of engines,more easily available due to the Nikosil issue and just needs a spacer machining up to fit the M20 block,have a hunt for some build threads,users 'stonsie','goosiegander' and 'jazzman' spring to mind.

As far as machining the block to suit forced induction is concerned,you will need to calculate c/r and things,hunt out posts by 'geoffbob' for help in this direction.

Good luck with your build,keep us informed!

[GeoffBob]

Hi Mongo, welcome back. Seems last time we communicated you were heading "offshore"? Successful I hope?

I remember your last thread quite well. No offence intended, but it sounds as if you have managed to pick yourself up a right bucket of nuts and bolts for an engine.

As I said in your last thread, you're best off looking at a Rotrex C30-94 if it's a centrifugal blower that you are after. God knows what that old supercharger of yours really is, and unless you have a substantial research and development budget to cover your engine in the event that something goes wrong, I wouldn’t even bother giving it a try. As a rule I never use parts that I don’t have data on.

There are many options at your disposal if it's a turbocharger that you'd prefer. I'd advocate a buying a Garret since it's easy to choose the right one based upon the amount of data that Garrett make available surrounding their products. There are, however, plenty of successful recipes for turbocharged M20's on the zone using other turbochargers (Holsetts are very popular) despite an absence of data with which to match the turbo to the engine.

As for CR and pistons, I am sure that we can help you to work out something to fit. Eta and CHR1S1990, amongst others, will also be able to offer advice in this regard I should think. In the mean time I’ll see what I can work out for you. Pity though that you don’t want to use a post 1987 M20B25 as this is ripe for turbocharging with a stock CR of 8.8:1. Opting for the ETA crank does make it rather likely that you will have to fit custom pistons (although I can’t say for certain at this stage). One thing I can say, however, is that compared to the cost of a new turbocharger, intercooler, plumbing, ECU, pistons, rods, injectors, turbo-manifold, fuel pump and all the other usual sundries, the cost of picking up an 8.8:1 M20B25 from the scrappy will be negligible. Might be worth mulling this over before committing to an ETA engine whose crank is non-ideal and already in need of repair, just a thought.

[mongomushroom]

Thanks very much for the quick replies. Hello again Geoffbob. Ye was just heading off to work the last time we spoke. The reason I was wanting to use the 84mm crank was simply because I had it and was thinking I could get the desired CR depending on what I had skimmed of the block but its not necessary to use it and its not looking very cost effective anyway. The block I've got is from a 1990. I swapped it out of my other 325 for this project because of the CR. Maybe I should see if that crank can be repaired. Been told it wouldn't be cheap. All bearings looked pretty good apart from the cooked thrust bearing (from heavy clutch use apparently) so that could be my best option. I'm just trying to work with what I've got at the moment since I've got a garage and garden full of 'crap' and will get shot if I get more. If I get another engine the crank might need reground anyway and from when I was rebuilding a tractor for my father I remember it was about £300 for grinding the Crankshaft. I've got money to spend on this but not to burn so I dont want to get custom pistons if I don't need to.

I'll go with your advice on that supercharger Geoffbob. I'll sell that 1 probably and go for a turbo instead. What size of turbo would you advise for the m20b25 engine with standard size head gasket and very light skim taken off the cyl head?

[CHR1S1990]

Thanks very much for the quick replies. Hello again Geoffbob. Ye was just heading off to work the last time we spoke. The reason I was wanting to use the 84mm crank...

Eta crank is 81mm. Using the combo you described (885 head, 325i pistons, and 320i rods) will give you a compression ratio of either 9.4:1 (using late low comp pistons) or 10.4:1 (using early high comp pistons). Which ones do you have? Decking the block removes around 1.5-2.0mm according to the wiki so yes you could remove a little less for a CR of 8.8:1 for example - you would need to mock build the engine first though and measure the actual volume contributed by the piston crown/bore to be accurate enough IMO as the 1.5mm etc is only a guide.

If it was me, I would get a decent m20b25 crank and rebuild into the engine you have (assuming it has low comp pistons) or simply by a low comp block. No skimming headaches etc just 8.8 out of the box. I do see the obvious appeal of the extra 2.7 capacity though but messing about with crankshaft repairs may not be the best thing for a 'charged motor, and eta cranks arent exactly common anymore.

[GeoffBob]

If it was me, I would get a decent m20b25 crank and rebuild into the engine you have (assuming it has low comp pistons) or simply by a low comp block. No skimming headaches etc just 8.8 out of the box. I do see the obvious appeal of the extra 2.7 capacity though but messing about with crankshaft repairs may not be the best thing for a 'charged motor, and eta cranks arent exactly common anymore.

Agreed, although I'd probably buy a set of 0.050" oversize pistons pistons from Mahler and do a +1 rebore on the block to get it all good as new. I'd also grind the crank and fit +1 bearings. These engines are getting old and you can almost guarantee that you won't be starting out with an engine in tip-top condition.

[CHR1S1990]

how much are "standard" new pistons from Mahle? Surely in the region of custom/forged items? Speaking of pistons, I received Seb's pistons today Geoff. Ill clean them up and report back.

[GeoffBob]

[GeoffBob]

[CHR1S1990]

Very quick indeed! I hate to see such beatuiful items go to waste!

[mongomushroom]

81mm/84mm typo sorry. Its a late engine I've got with code 25 6K 1 taken from a 1990 325ise. If I can get a decent amount of boost on 8.8 CR then messing about with building a 2.7 is starting to look like a ball-ache. I've seen that a few people have used a thicker head gasket and could do this if 8.8 is going to limit boost level too much. If 8.8 is suitable enough I was thinking of using standard head gasket with uprated head bolts. Another option could be leave the block unskimmed and use the eta crank with 325pistons, head and 320 rods. i've read that this would give a compression ratio of about 7.7. Could anybody give an opinion on how this would run ie idling or starting problems?

[mattrs]

Subscribded.

My track car is a 2.7 and I would also like to go down the supercharger route....I have been unable to get hold of Ant, who else could supply and fit one? Roughly how much should i be looking to pay?

Sorry for the thead hijack (if indeed ones occured that is, I never quite know the etiquette )!

[CHR1S1990]

youre probably aware of what dropping the compression ratio achieves for boost and det, but dropping as low as 7.7 would probably see you with crap fuel economy due to the reduction of thermal efficiency (not so great at todays prices) and crap off boost torque. Depends on how you want it to drive on the road?

[CHR1S1990]

...forgot to add youre probably much better off using a higher 'octane' fuel to avoid the detonation and efficiency problems of low comp motors

[mongomushroom]

Thanks very much geoffbob, I'll need to study everything you've said there and come to a decision.

Thanks aswell chris1990, all taken on board

[GeoffBob]

[CHR1S1990]

lost of eta/2.7's charged to silly levels on youtube, seems like a popular thing to do in the US.

[GeoffBob]

lots of eta/2.7's charged to silly levels on youtube, seems like a popular thing to do in the US.

I see. Are repairs to your 2.7 totally out of the question Mongo? I mean, I know you can get the keyway in the crank fixed, but what about the rest of it? Too badly rusted to restore or is there life left in her?

Personally, if I had no choice but to use the 81mm ETA crank in the 325i block I’d stick with the 325 (135mm) rods and have a set of custom JE pistons made up (similar to the ones Sebastian is having made by Cambridge Motorsport). I’d keep the deck of the block exactly as is (206.7mm) and have the pistons made up with the required compression height and a deeper bowl to give me my desired CR suitable for turbocharging. I’d do it this way to keep the shape of the combustion chamber as it should be, not to mention that the JE pistons are ideal for the application. Sadly, not a cheap solution. If it’s of any use I can spec the pistons to give you the required CR Mongo.

[daimlerman]

lost of eta/2.7's charged to silly levels on youtube, seems like a popular thing to do in the US.

Larger pool of available cranks?

Point is,there are stronger cranks available that are more suitable for a FI engine.....if Alpina had deemed the eta crank suitable then they would have used it.

[CHR1S1990]

i totally agree, however I have never heard of a crank actually failing under excessive torque (more likely something weaker attached to it), however im only 21, theres still time yet

No doubt, the m52 forged item is much better and a lot easier to come by and similarly priced

[Gunni]

I have been around the E30 scene a while and seen what people have done to the M20.

I have NEVER EVER EVER ,,,,, EVER EVER heard of a crank fail under any circumstances.

I´m talking any amount of torque or engine speed done so far.

[eta]

Eta cranks don't fail under boost unless there is something wrong with them. there ia chap, turbodan on mye28.com who has his 528e running 450 hp on a stock eta internals I believe. Seems to work for him. Metric mechanic in the U.S also go by this. Read there catalogue. They have never had a eta crank fail but have seem some M21 cranks fail.

[mongomushroom]

Thanks very much to everybody for their input. Much appreciated. As for as failing crankshafts go, I cant see it myself. I would expect a rod to snap before a crankshaft would fail. I've never seen it on any pump, compressor or engine although plenty of rods and bearingas. Thanks for the offer geoffbob but I definately won't be going for custom pistons. If I was building something race spec that would definately be in my budget. As far as grinding crank for oversize bearings I dont want to do this unless I need to. My thinking is a ground journal would make a smaller load bearing area on the bearings and would cause it to wear out more quickly.

I'm thinking that using the eta crank, 325 pistons, head 320 rods and standard block with a 7.7 CR wouldnt make a very usable road car due to fuel economy and i'm thinking pretty dead at low revs.? Although could get away with fitting a pretty big turbo to this. Might hang on to this crank for the next project, track/drag car. Geoffbob I understand your frustration with using spacer head plates/thicker head gaskets and making up engines with out of spec piston to head clearances but if it works then it works and i dont think it would be cost effective using an m20 if i was going to go with the expense of getting custom pistons etc made up. would probably go for old m5 or something. If I decide to use a thicker head gasket I would go for the first oversize and no bigger. But if I can get away with the standard 8.8 CR then I'll be much happier. This project is for fast road use and some occasional track use so i'll stick with the 325 8.8 CR I think if i can get enough boost into it? I'll keep everybody posted once I've made some interesting progress. has anybody had any problems with thrust bearing before. if this is a weak point then i should prob be looking for something more robust or improving oil supply or somrehing like that? been told heavy clutch use can wear these out pretty quickly.Thanks again for eveybodys input much appreciated.

[GeoffBob]

[Gunni]

Thanks very much to everybody for their input. Much appreciated. As for as failing crankshafts go, I cant see it myself. I would expect a rod to snap before a crankshaft would fail. I've never seen it on any pump, compressor or engine although plenty of rods and bearingas. Thanks for the offer geoffbob but I definately won't be going for custom pistons. If I was building something race spec that would definately be in my budget. As far as grinding crank for oversize bearings I dont want to do this unless I need to. My thinking is a ground journal would make a smaller load bearing area on the bearings and would cause it to wear out more quickly.

I'm thinking that using the eta crank, 325 pistons, head 320 rods and standard block with a 7.7 CR wouldnt make a very usable road car due to fuel economy and i'm thinking pretty dead at low revs.? Although could get away with fitting a pretty big turbo to this. Might hang on to this crank for the next project, track/drag car. Geoffbob I understand your frustration with using spacer head plates/thicker head gaskets and making up engines with out of spec piston to head clearances but if it works then it works and i dont think it would be cost effective using an m20 if i was going to go with the expense of getting custom pistons etc made up. would probably go for old m5 or something. If I decide to use a thicker head gasket I would go for the first oversize and no bigger. But if I can get away with the standard 8.8 CR then I'll be much happier. This project is for fast road use and some occasional track use so i'll stick with the 325 8.8 CR I think if i can get enough boost into it? I'll keep everybody posted once I've made some interesting progress. has anybody had any problems with thrust bearing before. if this is a weak point then i should prob be looking for something more robust or improving oil supply or somrehing like that? been told heavy clutch use can wear these out pretty quickly.Thanks again for eveybodys input much appreciated.

The old M20 can handle alot.

I´d say a nice and tidy M20B25 with 8.8:1 compression ratio engine will be able to push out about 400-450lbs torque and 400-450hp or so without failures of any of the components.

This turbo here along with the right turbo manifold is the ideal candidate for said performance range.

http://www.e30zone.net/modules.php?name ... c&t=193194

It happily runs and performs nicely from 300hp upwards.

I have one friend with this on a 2.8 M50 and it´s just the best. Had a friend with this on a M20B25 and that setup was also the best performing turbo setup I have seen on a M20 in the 400-450hp range.

On the M50B28 you´ll see positive pressure above 1200rpm
In low gears you´ll see your max boost at 3200rpm, in higher gears it´ll be at 2300rpms. On my frien

Here is an example of the M50B28 at 0.5bar boost

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[youtube][/youtube]

[GeoffBob]

[Gunni]

Stock internals (oem spec parts) can reach quite some numbers on a M20

As seen here
http://www.e30tech.com/forum/showthread.php?t=105048

That is with E85 fuel and I don´t see that ever happen on a M20 with normal petrol alone.

I also don´t reccomend people attempt those numbers without being willing to see things fail as that is a knife edge trick getting stock stuff that far without it just collapsing

[mongomushroom]

I've got both crankshafts in the machine shop right now getting measured up and priced up for all new bearings. cylinders will also get honed and new rings fitted. I've got 3 used oil pumps here and will be measuring them all. if I have a very good 1 I'll be using that but if all are close to their wear limits i'll be getting a brand new 1. Cyl head has already been pressure tested, cleaned up, new stem seals fitted, valves lapped in and very light skim taken off. hoping to use standard head gasket with uprated arp studs. new timing belt, tensioners, water pump and all new gaskets will be used. Intercooler - was thinking of the biggest i can fit onto it ( not the most technical approach but the bigger the better i reckon). Havent decided on injectors yet but again the bigger the better probably. Was thinking about fitting COP and M50 non vanos loom but if theres no significant advantage to this I might just leave it as it is. If i was to fit this would this mean different impedance injectors? For management i was thinking of seeing what the local specialists have to offer.

That figure of 7.7 I read on here somewhere.Possibly for an eta block which is taller?just a thought. Thanks very much for taking the time to do them calculations. I'll need to think about which route to take. It might just come down to which crankshaft needs the least work. Was given a quote of £90 for skimming the block. plus it'l be prob another £80 odd for vernier pulley. saw some cheaper on ebay but was probably made at tea break in some factory/garden shed.
Like I say I'll need to think about it. If I could get 400hp I would be grinning from ear to ear for the rest of my life. Any more and I would be ejaculating repeatedly and would be kind of embarrassing in public although probably awesome at the same time but not when i'm visiting my granny. but seriously I wouldn't like to put so much faith into 23 year on diff gearbox etc
Thanks very much for all vids and links. very inspiring

[Gunni]

Don´t worry about diffs and getrag 260 boxes, those will not fail at the 400hp limit / 350-450lb depending on the application

[mongomushroom]

Cheers Gunni, thats reassuring. I've got a choice of 3 getrag 260's here so will see which is best. Have seen a sport getrag 245 for sale here locally but not sure whether its worth fitting. Same 5th gear ratio anyway and with a boosted engine I dont think the difference in other gear ratios would be noticable.

[GeoffBob]

I've got both crankshafts in the machine shop right now getting measured up and priced up for all new bearings. cylinders will also get honed and new rings fitted. I've got 3 used oil pumps here and will be measuring them all. if I have a very good 1 I'll be using that but if all are close to their wear limits i'll be getting a brand new 1. Cyl head has already been pressure tested, cleaned up, new stem seals fitted, valves lapped in and very light skim taken off. hoping to use standard head gasket with uprated arp studs. new timing belt, tensioners, water pump and all new gaskets will be used.

Sounds like you have all of this under control Mongo. If the keyway isn’t too badly damaged on the ETA crank, then that sounds like a good option to me Just be sure that your bloke at the machine shop manufactures your new key from something like EN24 tool steel or similar, and then has it properly hardened and tempered (heat treated). Else you could risk the same happening again. A 2700cc motor at 8.5:1 CR has huge potential compared to a 2500cc at 8.8:1, although there is technically nothing wrong with the latter.

Intercooler - was thinking of the biggest i can fit onto it ( not the most technical approach but the bigger the better i reckon).

Pipe diameter in and out of the cooler is important and keep bends down to a minimum. Cooler area is more important than cooler thickness and if at all possible, flow your air across the short dimension of the cooler, not the long dimension (sadly not possible on many applications). Cooler size is ultimately determined not by your engines hp, but by for how long you intend to run the engine at that hp value for. Engines that sustain high hp for short durations (such as for short bursts of acceleration on the street or drag strip) can get away with smaller intercoolers than pure track cars that have to sustain high hp for extended periods without the intercooler outlet temperatures rising substantially due to heat-soak. As a rule (of physics) the higher the boost pressure you run the more heat the compressor will put into the air it is pumping, hence the larger the required intercooler. It is possible to calculate the exact size intercooler for an intended application, but this usually results in something bigger than you can fit, so fitting the biggest you can get in your available space is actually not such a bad idea.

Havent decided on injectors yet but again the bigger the better probably. ).

At such time as you know exactly what turbo you will be using and we have an exact hp and boost figure in mind it is possible to calculate exactly the required size injectors. Fitting the biggest possible is not a good idea.

Was thinking about fitting COP and M50 non vanos loom but if theres no significant advantage to this I might just leave it as it is. If i was to fit this would this mean different impedance injectors? For management i was thinking of seeing what the local specialists have to offer.

Wasted-spark COP is quite easy to do and has the advantage of getting rid of the distributor. You are going to want an ignition system that is capable of generating the higher voltages required to arc-over the spark-plug electrodes at boost. The stock ignition is not ideally suited to this task, but ultimately depends upon just how much boost you plan to run. Most aftermarket ECU’s aren’t fussy as to whether you use high or low impedance injectors.

Like I say I'll need to think about it. If I could get 400hp I would be grinning from ear to ear for the rest of my life.

Just be realistic with regard to the size turbocharger you will have to fit to get you to 400hp Mongo. Don’t get me wrong, I’m not saying it’s not doable (to the contrary), but you won’t get there with the assortment of Chinese T3/T04E’s and Mitsubishi TD04’s and TD05’s that are to be found on e-bay and down the scrappy. You’ll need to be on the look out for a compressor that chokes (red-lines) at around 50 lbs/min airflow at 1bar boost (that’s at least a 57mm compressor inducer), not to mention a turbine that’s big enough to drive that compressor (at least >64mm). That immediately puts the relatively cheap and civilised GT3271 right out the door and moves you well and truly into GT3582R and equivalent territory. Gunni’s BorgWarner K27 sounds about right to me. Also have a look at that Turbonetics I recommended in the other thread as Turbonetics are good value for money. All I am saying is, make sure you get the right turbocharger for the job or you will be disappointed!

Also, don’t discount the cost of a decent external wastegate. Your wastegate should be sized according to the difference between the mass-flow-rate of air at which the turbine begins to choke and the mass-flow-rate of air that you have to flow in order to achieve your hp target.

[Gunni]

Here is the ignition coil that will suffice to 600+ hp
http://cgi.ebay.co.uk/NEW-VAUXHALL-OPEL ... 45ed4f77ca

It´s cheap, it´s easy to get, works with the stock plug leads and it works like a charm

With a good ecu you can run any injector size you want. So you should consider buying larger then you need cause you WILL want to up the power after some time. No need to buy things twice.

42lbs will work for most power goals I have heard of in the UK (so far at least)

[GeoffBob]

With a good ecu you can run any injector size you want.

Too big injector and metering of the fuel will be poor at low duty-cycle (such as at idle). ALL injectors have a finite temporal resolution, regardless of how "good" the ECU is. This is due not to the digital resolution of the ECU, but rather to the finite rate-of-rise of current through injector (due to the finite inductance of the injector solenoid). Low impedance injectors were created in part to help overcome this problem, but have their limitations since the lower the inductance of the injector solenoid, the lower the MMF (magnetomotive-force) which drives the pintle-valve of the injector open and closed. This requires that the injector be operated at progressively higher and higher current until the limiting factor becomes the impedance of the driving circuit and the wiring that connects the driving circuit to the injector. This is all well documented.

Size of injector is also dictated by whether you decide to run the injectors batch-fired or sequential-fired since this dictates the injector minimum dead-time (and hence maximum duty-cycle).

I advocate fitting the correct sized injectors for the application.

[Gunni]

2000cc injectors on a 4cyl 2liter engine good??

If the car can drive around with Lambda 1.0 at idle and cruise I´d consider them not to big.

[GeoffBob]

That's your subjective opinion Gunni and you're entitled to it. You're pissing in the face of common sense, and not to mention on quite a few well respected engineers. I don't think that this is the sort of thing that Geoff Goddard would have taught you at Brookes.