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M20 Conversion For Dummies

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****this isn't a complete guide yet, I have had a lot of questions recently so I decided to post what I've written so far. Pics will come soon, hopefully the guide will be completed by the end of the month and converted to PDF for downloading.

The M20 Into 2002 For Dummies Swap Guide

This is not complete yet, I will update it periodically until I finish it. Once it is finished I’ll make a pdf and host it on mediafire.net. For those looking to do the project it will help with the first 80%+, especially once I get some pictures uploaded.

If you have any other advice or experience, especially with helpful hints or other parts which will work, please post them

The pitch --> Are you tired of a measly 100hp in your 2002? Want to show up some of those boy racers, get better mileage, and have a smoother running ’02? Can you or a friend weld? Do you possess at least basic mechanical aptitude? Then this swap is for you, unless you have a Tii(don’t castrate it). I wrote this guide as a kind of updated version of 6 goes into 2, which I did reference when performing the swap myself. I think it’s an excellent guide but there were a few things I felt could be improved so I’ve written this up in an attempt to make this swap even easier. I added a bunch of pictures and tried to list a wider selection of parts which will work for the swap in addition to where I bought them and for how much. Some things have changed since 6 goes into 2 was written, this guide reflects that. I also took many a picture, I’m a very visual learner and I think it helps people’s confidence to have a visual reference of something written down when performing something like this for the first time.

This swap does involve welding, there’s no way around that. I make motor mounts right now, hopefully I’ll be doing an exhaust downtube, transmission mount, and center bearing mount soon too. As far as motor swaps go, it is very straight forward and almost 100% bolt in. With all the parts collected the conversion can reasonably be finished in a week by two people with a standard set of tools, a few car jacks, and an engine hoist. Specifically I used two car jacks, a 1-ton hoist, power drill, hand held grinder w/cut off discs, mig welder, complete set of box wrenches/sockets, a 3lb small sledge hammer, and a soldering iron.

This parts list will detail what I used for the swap. Additionally, in the swap notes I will try to list all optional parts which I know will work. Optional parts to what I used will be mentioned in italics at the bottom of each list. If you have questions just search “M20 into 2002 for dummies” on www.bmw2002faq.com.

Engine

• BMW M20B25 found in 1988-1991 BMW E30 325i

• Passenger side ’02 mount and one E30 motor mount for the drivers side

• Custom motor adapter mounts

There are two different M20’s we received in the states, the M20B25 and M20B27. Occasionally you can find an M20B23 as well from the E21. The last two digits represent the displacement, so a M20B25 is 2.5L. The M20B25 is the motor you want and it came in the E30 325i(s) from 88-91. It is rated at ~170hp/160tq, check out Wikipedia for a overview of the M20. The M20 has a wide range of stroker possibilities all the way up to 3.2L and there are a few people running around with turbo M20’s in their ‘02s if you want to go nuts, back on topic.

Like all builds, it’s better to err on the side of caution and perform some basic maintenance before you put the motor in. M20’s are an interference engine(valve will hit the piston if the timing belt brakes) and unfortunately BMW’s only timing belt(instead of timing chain) engine. Timing belts are cheap and it’s best to replace the belt, tensioner, and water pump all at once, this will run you $70-100. That’s the minimum maintenance I’d do before putting the motor in, I would recommend replacing seals too, they’re so much easier when the motor isn’t in the car. Unless your motor mounts are new(in which case you can use a 2002 drivers side motor mount) replace the motor mount. A single E30 motor mount(they’re identical on both sides) works just as good, if not a bit better, than the driver’s side ’02 mount and it’s about ¼ the price of the ’02 mount. You will need to use the factory ’02 passenger side mount.

Transmission/Driveline

• Getrag 260 from an E30 325i or 325e

• E30 325i or 325e shift linkage, preferably the earlier platform style vs aluminum rod version

• Slave cylinder for Getrag 260

• M10 228mm or 88-91 E30 325i “singlemass” flywheel

• 88-91 E30 325i Clutch kit

• Manual transmission driveshaft from E30 325i or e(*note below)

• 22” clutch cable with 2 male M10x1.0 fittings

• 325i or 325e transmission mounts (2)

(*note, some eta transmissions had a “big six” output flange so you’ll need the driveshaft that matches. Side by side it’s pretty easy to tell the difference, if you’re going turbo M20 try to find one of these driveshafts)

One super neat thing to note which was recently discovered by a 2002faq member is the E30 325 driveshaft fit perfectly in the ’02. I’ve tested this and I’m using the E30 driveshaft in my two conversions. Recently I discovered the M10 and M20 flywheels are identical, every measurement checks out. An M20 single mass is 18.4lbs while a stock M10 228mm is 17.2lbs. I have one odd flywheel, possible an E21 323i or 1602, which has not been lightened but weighs 14.2lbs. For some rev happy fun, an aluminum flywheel is 8lbs.

I chose the Getrag 260 because it’s widely available, inexpensive, and can handle more power than you should have in an ’02. It is physically larger than the other two transmissions which will work, the dogleg E21 323i transmission and 90-91 E30 318i Getrag 240. The E21 is the easiest transmission to use, but expect to pay $600-1000 if you can find one. The M42 powered 318i transmission will work too, but it sits cocked about 10 degrees so the shifter will be leaning to the side. On top of this, you won’t be able to use the 325 driveshaft which saves a lot of money and time. I encourage you to experiment and post your results though, there is a lot of cross compatibility in driveshafts if you’re willing to move the center bearing mount. Most bmw’s after the mid 80’s have driveshafts with slip joints, it’s possible the M42 E30’s driveshaft will fit the ’02 as well.

The transmission has a few tabs which need to be cut off before installing it. This side bulge is from two sensors used in the 325e, it needs to be trimmed to clear the throttle linkage. These ears are good to cut off just to save some room.(I’ll try to add pics soon)

Cooling

• 83-85 VW Scirocco radiator, core dimensions ~20 x 12.5 x 1.25”

• Slim 12” electric fan ~1500cfm

• Hoses from the E30 and some adapters to mate to the scirocco radiator

• Scirocco radiator temp sensor if you’re using that radiator

• Radiator overflow tank from Volvo 740(round bottle)

The Scirocco radiator is a double pass so the fluid travels right to left, down, and then back to the right. The radiator I used does not have a filler neck, it’s filled through the overflow tank(Volvo 240’s and 740’s from 1986 on have a nice small round one). I bought mine from parts train for $38 shipped, it’s not the nicest looking radiator but weighs nothing and has about the same cooling capacity of the E30 325i radiator. Unfortunately I have no summer testing with this radiator yet, there is another version which is 26” wide if you live in a warmer climate If you’re down in the warmer parts there is also a wider 26” core Scirroco radiator which doesn’t cost much more. Afco makes a “Scirocco style drag radiator” which is 3” thick, 20” wide, and 13.5” tall if you want some more bling. I’m not sure how easy it would be to fit though, the stock 1.25” core scirocco radiator doesn’t have too much extra room.

I bought my fan off ebay for $25 shipped, it’s the same manufacture as you’ll receive with the ’02 e-fan kits. I bought the straight blade one, curved blade fans are quieter but about $10-15 more.

I’m sure there are multiple radiator overflow containers you can use, but the Volvo 740 one is nice and small, cheap, and has the right size in/outlets for the e30/scirocco.

Exhaust

• 88-91 E30 325i factory exhaust manifolds and collector pipes

• 2 into 1 merge collector for twin 1.75” pipe to single 2.25” pipe

• 2.25” exhaust tubing recommended, 1 16-24” glass pack resonator + 1 muffler under trunk

Exhaust is one place where bigger really isn’t better. What you may gain in top end HP will be lost in low down torque with too large of an exhaust. From a book by David Vizard, “A pipe will flow 115cfm per square inch of cross-sectional area. You need 2.2cfm of flow capacity per horsepower.” 2.25” 16g tubing(standard) is ~2.13” ID which is adequate for about 200hp, or about the level of a cam’d, chip’d, lightly worked over M20.

The 2002 doesn’t have much room to place mufflers. Under the trunk between the gas tank and spare tire well a 14”x 7” x 4” muffler would fit perfect, unfortunately that’s an uncommon size. You may be able to position a 14x5x8 case muffler which is much more common. Ahead of the rear subframe a 20” case resonator(or glasspack) fits well. I would highly recommend getting a Thrush or Dynomax glasspack, they are a true perforated core instead of that louvered crap. Perforated core is a tube with holes in it, standard glass packs are louvered where the tube is punctured and the metal is pushed in. These restrict flow compared to the straight through perforated cores, I can’t comment on the noise level yet, my m10 car is getting an exhaust with two perf core mufflers and it should be running again soon. Thrush makes them in stainless, 304 iirc, so you can still have a sexy stainless exhaust if you want.

I made my exhaust in 3 pieces, exhaust down pipes to end of tranny, tranny to front of rear subframe, and a last piece over the rear subframe out the back. I used slip fit band clamps and less tubing than I anticipated, a single 4’ straight section and two 180 degree U bends is enough for the whole system. It is possible to modify the E30 downtube to fit but it takes a lot of cutting and re-welding. MSDS and IE headers fit, TEP should as well, but they might need a bit of modification . I may be making an exhaust downtube for the swap soon, depends on how complicated it will be but I’m leaning towards doing it. In the future I’ll do an MSDS header adapter too once I have the cash for a set of them.

Exhaust is a touchy subject, many companies claim good increases in HP/tq with their headers. I have never seen any dyno charts to back it up and I’m a bit skeptical. If the engine is modified, especially if it’s a stroker then I would go with headers but even a chipped/slightly modified M20 isn’t restricted much by the exhaust system. So if you’re going with a relatively stock system I’d stick with the OE manifolds.

Fuel system

• External fuel pump above 120LPH flow capacity

• Generic Bosch metal canister fuel filter

• 5/16” metal hardline

• 5/16” high pressure fuel hose

Unless you have a tii the fuel feed line is low pressure hose for a carb. Fuel injection can run pressures of up to ~100psi and requires a reinforced fuel line vs the carb’s <10psi line. The factory return line on 72 and later cars is metal and works great as the return line for the M20, earlier cars don’t have one. You’ll have to make another fuel line for the feed line. I used the factory line from theE30 and re-bent it to match the factory ’02 return line. This was just in an attempt to complete the build for as little as possible. Summit racing sells 25’ rolls of zinc coated steel hardline for $16, stainless steel is available in 20’ rolls for ~$40 too. They have aluminum as well, but I wouldn’t recommend that for a street car as it’s not as durable. 25’ is more than you need, 20’ would suffice. High pressure fuel hose is fairly expensive, around $3/foot. I reused all of it from the E30, cheap option is the junkyard and pulling it from a newer car. In the spirit of safety I would recommend buying some new hose though. 10 feet of it will be plenty. For bending the fuel lines I used one of those $10 cast aluminum units available everywhere. Just be mindful of what you’re doing and you can easily do kink free bends, test a scrap piece or the end of your roll of tubing first.

The Volvo 740’s and 240’s from 86-93 have a nice little external fuel pump and filter together on a mount with rubber feet. I stuck it in the trunk and then put the battery in a box. If you run the fuel filter and pump separately(not on the Volvo mount) they will fit under the car near the rear subframe. If you’re browsing the junk yard Volvos have it either under the driver seat or driver’s side in front of the rear axle. You can also use the in-tank fuel pump from an E30 325i or late 318i, it’s a little bit shallow but fits in the stock ’02 sender location. Tii tanks are nice because you can have a pump and sender due to the two holes. On a different project I pulled the E30 tank and cut its sender mount out. You can also wire the 325i sender to work with the ’02 I believe, it would not read accurately due to the shallower depth, but that’s actually a good thing because it will read empty when the fuel pump isn’t able to reach the last maybe gallon of gas. I believe Dave Aardvark can modify the E30 intank unit to the factory ’02 length so you’ll get full use of the fuel tank. Pretty much any external fuel pump for a 2+ liter car will work.

Electrical

• Electric speedometer, or oem if you have an E21 m20 transmission

• ECU chip(Turner, MarkD, Dinan, ebay, etc…)

• Complete engine wiring harness

• ECU computer with #153, #173, or #308

• Engine wiring harness male plug from the E30 car wiring harness

The M20 swap does require moving the battery from the engine bay. The most common placement is in the trunk using the E30 battery cable, this has been covered in the “faqs” section of the BMW 2002 faq. It is possible to place two slim batteries under the rear seat if you can’t give up your precious trunk space. Dave at 02again.com makes a mounting kit for the batteries and Zenon Holtz did a nice write up on the conversion, it can be found at http://www.zeebuck.com/bimmers/bmvseite/

Electrical is usually the biggest hurdle for people when working on cars, it absolutely is for me. I ran into a lot of problems the first time I did this conversion; however, most were from me being dumb and not checking connections. There are only 7 wires you need to splice and one you need to install to do this conversion, it is very simple and anyone can do it. The wires are as follows,

On the e30 connector_on the 2002_______________Function_____Location on ‘02

#1 Blue____________blue from voltage regulator___Alternator___back of alternator, or B+ terminal

#4 Brown/Violet_____Brown/White_______________Coolant temperature

#5 Black/Brown _____Brown/Green______________Oil Pressure__Sender near distributor

#6 Green___________Green____________________Ecu power___Coil

#7 Green___________Same Green wire as above___Coil Power

#9 Black____________2 18g black wires__________Tachometer__Coil

#13 Voilet/Red_______N/A______________________Fuel pump___Run one from #13 to your fuel pump

#18 Black/Yellow_____Black 10g_________________Starter

Now with the E30 harness you will have a few wires to hook up to the ’02. The E30 harness has its own alternator wires(red ~8g + blue 16g), it has a group of ground(brown) and power(red) wires as well, with the wiring harness installed and the ECU going to the ’02 glovebox, these wires will be on the passenger side. My battery relocation setup included a terminal block on the driver’s side near the factory flasher relay. That is where my battery relocation cable terminates and the power cables for the starter, fuse panel, and any relays hook up. I cut the factory e30 wiring harness sheath and moved the power cables over to this terminal block. The ground wires were moved as well, being bolted to the engine block for a better connection.

Electrical issues

-relays are not working. The two orange relays are for the fuel pump and O2 sensor, the white relay is the main relay. When you turn the key the main relay should click, the other two won’t. These relays are cheap and something you should carry spares of in the glovebox, the O2 sensor relay isn’t necessary to the car starting, but the fuel pump one is.

-coil should have maximum resistance of 7 ohms, both of mine measured around 3 ohms.

-should have 12 volts when checking between the starter + terminal and ground, less means either the battery is dead, battery isn’t hooked up, or some connection between your battery + terminal and the starter + terminal is not solid.

-starters have 2+ terminals, one terminal is the grounding terminal which you need to connect the yellow/black wire to. The other terminal I believe is for devices which need power only when the starter is turning over. Early starters(fat, ~17lbs, look like original ’02 starters) have the (–) terminal below the solenoid, you can’t see or feel it unless you get under the car. If you are not connected to the correct terminal nothing will happen when you turn the key. The later small starters have all the terminals visible on back of the solenoid, if nothing happens when you try to start the car, switch the yellow/black wire to a different terminal

-If the car starts and dies almost immediately, unhook the MAF and try again. This puts the car into “default” mode and if the MAF is bad the car will start, if the car still doesn’t start then it’s probably not the MAF.

-remove the ecu and unhook the battery when welding on the car, I’d even unhook my ignition switch and any other items which could be damaged by the electrical current from the welder.

-The black wire heading off the ignition switch should only get 12v when the key is in position 4(starting). Position 1 = key in or out of ignition, not rotated. Position 2 = rotation you do to get electronics like the stereo to turn on, position 3 = position the key returns to after starting the car

-Check/re-check your grounds, they need to be absolutely solid for everything to work.

Custom parts

• Motor mounts

• Transmission mount

• Driveshaft Center support bearing mount

• Shifter platform

• Exhaust downtube/whole exhaust

Installation

Prepping the car

Starting at square one with a complete 2002, the first step is to remove the exhaust from the transmission back to the tailpipe. This will clear the way to pull the old motor. The easiest way to do this, and most beneficial in the long run, is to drop the engine/tranny as a single unit with the front subframe. The subframe has 3-bolts per side, the struts are bolted to the control arms with 3-bolts each, the steering box guibo has 4-bolts, and don’t forget the throttle linkage/wiring/water hoses to the heater box. The transmission has the clutch line and a single mount. You’ll also have to undo the 4 bolts holding the driveshaft to the diff and the 2 bolts for the diff center bearing. This way doesn’t require unhooking the brake calipers from the lines and makes the motor easier to slid out since you don’t have the struts to deal with. It does still require you to remove the calipers so you can pull the rotors/hubs to get at the bolts holding the control arm to the strut tube. Once you have removed all these bolts the whole engine/transmission can be slowly lowered down, personally I used two car jacks while the car sat on jack stands. After unbolting the subframe, if you have an engine hoist, picking the car up by the bumper mounts or shocks on ’73 and later cars is no problem. With an earlier car you’ll need to jack the car up higher and lower it onto stands, then proceed to lower the motor out. This job isn’t too difficult, two people makes it easier, but I’ve done it solo.

With the motor out of the car, now unbolt it from the subframe and start to clean the subframe up. You’ll need to reinforce the driver side engine mount, a common weak spot on even stock ‘02s. This requires removing the steering box(which you should adjust and change the fluid in since it’s easy to access now). I went overkill on the reinforcement because I was having fun with my welder, a single strip of 1/8” steel inside the motor mount arm will suffice.

On the chassis, you’ll need a 2-3lb hand sledge hammer to pound out the transmission tunnel. It’s easiest to make two slits on the top of the tunnel and two down near the pedal assembly on both sides of the transmission tunnel. This way you can bend the metal easier and just weld in a patch to cover the portion that expanded. You may be able to hammer the tunnel out enough without cutting it out, I have not tried this yet.

Mount the engine on the subframe as a longblock assembly without the exhaust manifold or intake. Line up the clutch and attach the transmission before installing in the car. Installing the front half of the driveshaft with guibo, the shifter assembly, transmission grime guard, speedometer sensor wires, and clutch line to the transmission before jacking the whole assembly up into the car. It’s not absolutely necessary to add the driveshaft, but I find it easier than trying to tighten all 6 bolts once it’s in the small tunnel. The shifter will be relocated back about 3” if you’re using the stock E30 shift linkage. Personally, I find this nice as I feel the shifter is too far forward from the factory. If you use the stock e30 linkage it will clear the e-brake handle but you’ll need to do something about your console shift surround unless you have an early short console. You must install the clutch line on the slave cylinder as you will not be able to get a wrench on it once the transmission is in the tunnel. Another mod which may make bleeding the clutch easier would be to add a 6-8” hose on the bleeder nipple hole and mount the bleeder nipple to the end of the line. When you need to bleed the clutch you could pull that line down instead of struggling with the bleeder nipple in such a tight space.

Once you’re ready, use two floor jacks if possible. Place one under the subframe and one towards the rear of the transmission. Jack the assembly up until your shifter is touching the transmission tunnel and you can see where you need to make a new cut out if you’re using the stock linkage. It’s possible to install this by yourself but much easier with a helper to align the subframe while you install the bolts. A helpful hint for those without a 3” holesaw, cut out a rectangle in the trans tunnel around the stock shift hole and flip it around, then weld it back in place to match the shifter. This is where the earlier shift platform is nice, it’s similar to the ’02 setup and can be modified to mount only to the transmission instead of using a bushing on the tunnel behind the shifter mount. I just happened to have one of these, on my second swap I’m going to look into either making a custom one or modifying a 2002 or e21 platform to mount to the transmission.

My rant/random fact paragraphs

One of the first things people will point out about the engine is the weight, it only weighs ~80lbs more than an M10. The transmission is heavier as well by 20lbs or more so the entire swap will add around 100lbs to the ’02. That may sound like a lot, and it is almost entirely on the front axle but it’s really not bad. You have to move the battery to the trunk which takes 35lbs off, the whole AC system on an ’02 adds about 30lbs to the front of the car, remove the smog pump plus other misc stuff and you’re almost up to the 100lbs added. A roundie M20 swapped 2002 will have an equal or lower front axle weight than a 74-76 ’02 with AC. An S14 conversion is only 35lbs less than an M20 conversion.

There is a wealth of information on R3v, bimmerforums, and especially E30tech about modifying the M20. The '02 rear diff becomes the weak link with the M20 and getrag 265 which can both handle around 400lb-ft TQ reliably, while the '02 rear diff in 3.64 is rated at 260lb-ft TQ

Other Considerations

Now that you have close to double the power of a stock ’02 it might be time to consider upgrading the suspension/brakes. A few stores like Ireland Engineering, Top End Performance, and Korman sell everything under the sun for suspension and brake upgrades. The standard setup is 22/19mm sway bars, eibach sport springs, bilstein HD dampers, Volvo/E21 front brake upgrade, and E21 rear drums or VW discs. With the subframe out it’s really easy to replace all the bushings…not so much once it’s back on the car, do it now and you’ll thank yourself later. Poly or rubber, it’s up to you. I’ve had both and the poly bushings aren’t that bad on a street car, especially once they wear in. Just make sure to use a lot of the special poly bushing grease they give you with the bushings.

Frame reinforcement. If you’re not tracking the car and adding a cage there are thing you can easily do to stiffen the body. US composites makes pourable closed cell expanding urethane foams in various densities. I used a 16lb kit of 8lb foam, about $65 from them. This filled the rockers + frame rails and made a huge difference in chassis stiffness. The car no longer creaks when entering driveways or when jacking by the factory points. It also rides a bit quieter while feeling more “sporty”. To take it a step further you can use 2lb injectable foam from _________ in the a/b/c pillars and roof structure, this is a bit more work requiring removal of the headliner, but worthwhile if you’ve already removed the headliner. One thing to note, if your car sits outside in the rain or in cold/damp climates this foam can accelerate corrosion in the rockers because it traps moisture in.

Cost

I’ll try to give a rundown of what you should expect this conversion to cost. As always, it depends on your patience, location, and fab/mechanical skills. If you get lucky and find a running $500 325i w/5spd and can do the fab/mechanical work yourself $1000 or less for the complete conversion isn’t out of the question.

If you’re piecing the kit together expect to spend 200-600 for the M20 w/wiring/computer, 100-250/Getrag 260, 50-80/flywheel, 200/clutch kit(new), 50/driveshaft, 125/guibo tranny mounts clutch slave & clutch line, 75/radiator & hoses, 3-500/exhaust, 75-150/fuel delivery, and 300/misc parts. So a reasonable estimate is $1500-2250. That may not sound too cheap, but it’s the cheapest way to get S14 power (chipped) in a 2002 and have it super reliable.

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Until I finish the guide, I'll post all the updates here so they're easier to find.

Another good radiator option

Aluminum, upper left/lower right openings, 22x13x2" standard crossflow two core w/o filler neck. Griffen 2-25185-H, ~$240

you'll just need some adapters for the hoses as the radiator has a 1.5" and 1.75" inlet/outlet.

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Nice write-up. I like the fact you were able to fit the 325i trans in the tunnel. A picture of that surgery you did on the trans and body to make it fit would be helpful. Also the radiator mounting. Are you cutting up the nose panel to make it fit?

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Pics will come soon, I've been splitting my time between 3 2002s...

We did have to cut the nose panel, I spent a really long time trying to cut as little as possible. The only way you could get away with out cutting it would be a custom radiator or converting to megasquirt, installing an electric water pump, and modifying the thermostat to re-route the hoses. That would likely give enough room to use a stock, maybe IE aluminum, radiator with a pusher e-fan setup. Instead of megasquirt you could probably use a block mounted distributor, but I'm not sure how that fits with the standard "i" intake as I don't know anything about the early E21 M20s which had block mounted distributors.

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By the way, for those not interested in chipping their stock M20 ECU, DIY Autotune makes a Plug and Play Megasquirt System. It basically plugs into the standard wiring harness in place of the standard ECU. So you'd have programmable EFI. Just another option to consider.

http://www.diyautotune.com/catalog/megasquirtpnp-g2-b8793-for-the-8792-bmw-e30-325i-p-502.html

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Is there a particular reason the M20b27 can't be used/isn't recommended? I haven't found an explanation yet, but I am still reading up on it.

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I've driven one, with the dual mass flywheel, low compression, and limited rev range it felt like a bit of a dog.  Key to making the M20 feel proper in the 2002 is by raising the compression, and lightening the drivetrain a reasonable amount to make it a bit snappier. 

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So theoretically, a b27 bottom end and an 885 head swap from the b25 would do the trick?

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So theoretically, a b27 bottom end and an 885 head swap from the b25 would do the trick?

That still makes a relatively low compression engine. Great for a turbo...

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(edited)

Odd... the numbers I keep finding for USA models are:

 

M20b25 = 8.8:1

M20B27 eta = 9.0:1

M20b27 Seta = 8.5:1 

Edited by Spyke

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Is there a particular reason the M20b27 can't be used/isn't recommended? I haven't found an explanation yet, but I am still reading up on it.

there is no reason it CAN'T be used.  it would actually be a pretty darn good option if you wanted great mpg, quiet cruising, and good punch off the line.  the engine was known as the "eta" for "efficiency" by BMW.  lots of torque down low from the displacement bump over an M20B25, but lower compression, mild cams and soft valve springs mean lower redline and less drag for better economy.  combine it with a really tall diff ratio (2.93:1) and you would have a killer highway cruiser.  my e30 325e is turning about 1800rpm at 55mph.

 

like andrew said, an m20b25 from a 325i will definitely be more lively if your goal is listening to an engine sing at higher rpm.

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(edited)

Odd... the numbers I keep finding for USA models are:

M20b25 = 8.8:1

M20B27 eta = 9.0:1

M20b27 Seta = 8.5:1

Where are you sourcing your info spyke? To do a proper stroker you're going to need to go forged pistons, there are lazy ways to mix match oem bits but no ensemble of stock parts is without some big compromise. Edited by AceAndrew

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R3vlimited has a big thread on it, with tons of people cross referencing all the specs. Wiki also matches.

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