M42T 2.1 Build Thread

[Retoropak]

https://www.bimmerforums.com/forum/f...975-1983-(E21)

Hello hello



The time has come to upgrade the drive train in my e21 to a bit more modern unit and to add 8 extra valves.
I used to rock the m10 turbo for almost two years. I run a moderate 15-18 PSI on stock m10 but always wanted to build it and squeeze 400 out of this unit.
The biggest problem with m10 was to find a getrag 260 or 265 transmission to suport my power goals.
After this years fiasco with my turbo manifold idecided to ditch the m10 and go with m42.

M42 will allow me to run zf320 tranny which can support everything that the poor m42 will be able to produce.

Here is the outline of the build

Engine:

Bottom end:
m42 with m44 timing cases and serpentine belt setup
m47 crank ( already ordered)
m5x main bearings
135mm eagle rods
86mm wisecos
9.5:1 compression

Head:

if budget allows
Cat cams turbo cams and solid lifters
6mm valves
light port and polish

or i will run stock head for now.


Drivetrain:

zf320
medium case swap using e28 subframe ( already have it just need to add adjusters and powder coat it)


ECU, Fueling and other gizmos
MAXX ecu race standalone
E85, ID 1300, Honda B series intake
Drive by wire, traction control, boost by gear and some other goodies
This ecu is really versatile and fairly affordable.


Suspension:
Rear E28 trailing arms and koni race shocks ( the one i currently have in a car)
Front e28 spindles, koni race shocks, tubular control arms, some sphericals here and there

Brakes:
Some variety of the OEM BMW brakes that will fit E28 spindles:
I will try to stik with 15" wheels for now untill i figure out what flares i want to use.
I will need some 245s or bigger tires in the back. Possibly 17s at some point.


It will be fairly slow progress i think 1-2 years to get this back on the road and probably 3-4 to finish whole thing.

Plan for this year is to prep the chassis for new drivetrain and finish the suspension setup. We will see if i have a time and budget to build the motor next summer.







Here is the original m10t build thread

https://www.bimmerforums.com/forum/f...975-1983-(E21)

[WantingAfunE21]

Liked the original thread, imagine this one will be better.

[EauRouge2002]

Good luck with your build. I know 17 inch rims are a contentious issue with most e21 owners but personally I like them and well, I have to have them given my car has the e36 treatment up front with among other things e36 M3 LCA's, spindles/brakes so 17's are needed for clearance. Here's a pic of my car with e46 style 68's. When my build is complete, I will get something that fits the period a bit better but these do the job for now. Tires are 215/40r17 up front and 235/40r17 at the rear. Up front, everything fits fine with enough clearance. At the rear, no idea yet!
IMG_0936.jpg

Good luck!

[Retoropak]

Lets talk about vert mounting m42. I would love to vert mount it for better manifold fitment and i will be able to mount the turbo a bit lower and still gravity drain it.

Oiling should not be an issue once i modify the pickup and oil pan. Head is symetrical so i dont expect any oil pooling.
However the transmission rotation might be a problem.

I think i will be able to modify the shifter to accommodate different angle. However i am not sure about the lubrication. It shouldn't affect it by much since the part of the gears will be submerged in oil but who knows maybe I'll will have to adjust the oil levels a bit.

But if the shifter mod won't work i might have to cut and shut the bellhousing.
Does anybody have any experience cutting bellhousings? How do you keep it concentric? Any ideas for the Jig?
I can weld up to a 1/4" aluminum "in-house" or can take it to my friend to do 3/8"-1/2" if needed/.

I know 17 inch rims are a contentious issue with most e21 owners but personally I like them and well

For me bigger issue than looks will be traction. I will have to go with the flares at some point. With the power goals in my mind i might need 255-275 in the back.
Thanks

[Retoropak]

I picked up e36 subframe for mockups.
I want to swap whole e36 front setup with power steering control arms etc.


Looks like i will have to shorten the subframe by around 3” and relocate the steering rack mounts.

E36 Control arms should give me similar track width to e21. E46 arms will be 1” wider per side which should nicely match my e28 rear subframe swap.


I need to get some e36 spindles and control arms and start chopping things.


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[Somjuan]

It ends up being slightly narrower in the rear suspension with an e28 rear and an e36 front. But if you run staggered setup the widths end up being only nominally different. Are you chopping the three inches in order to square up the front to rear and then redoing the control arms to place them where you want?

[Retoropak]

I need to chop 3" to mount the e36 subframe to e21 frame rails.

e36 subframe mount-mount is 790mm wide
e21 subframe mount to mount is 710mm wide.


e21 control arms mount almost below the frame rails and are approximately 11.75" long e36 control arms mount 2-2.25" further inboard and are slightly longer at approximately 13.5".

It seems like the wheel position and track width will be almost the same and if i need more width up front i can always swap e46 arms which are i believe around 1" longer.

[Somjuan]

Ah, so you’re using the old mounting spots. I think you’ll need more width in the rear, but don’t quote me on it. We have about the same measurements for the subframe, but I’m using e32 trailing arms in the rear which have a different hub.

Mounting it like you’re describing (if I’m understanding right) would bring in the control arm mounts as well, so you’ll probably be about in the right spot. Sounds good to me anyhow

[Retoropak]

...,but I’m using e32 trailing arms in the rear which have a different hub.

Any advantage in going with e32 trailing arms over the e28?

Do you also have a large case diff?





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[Somjuan]

Medium case. The e32 has sealed linear bearings instead of bushings and also has stronger bracing, which helps flex under load. Granted both are for cars 1000+ lbs heavier, so either will be overkill. The stock brakes for the e32 are also compatible, you’ll just need bias adjustment if you’re putting them in place of the stock stuff.

[Retoropak]

I guess ill grab some e32 arms next time i see e32 on the junkyard.


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[Somjuan]

FYI, you can only find them on the 740i e32 and larger. The linear bearings were used on that model as well as the e28 m5, and they’re really robust. New OEM bearings are more expensive than pulling the whole trailing arm setup from the yard, with the added bonus of stiffer arms and replacement parts. The hubs also interchange with the e28 hubs, so there’s no versatility lost if one ends up being a better track width than the other in comparison to the front end. In a nutshell, keep your eyes peeled for an earlier model with the m60. The design changed for later ones, and there’s a thread about it on myE28 somewhere.

Sorry to hijack, looking forward to seeing the rest of the build!

[Retoropak]

Sorry to hijack, looking forward to seeing the rest of the build!

All good information and very relevant to my build. Thanks.

Now i will have to find out what to do with the fender flares to fit some 9” 17s.

I want something in between group 2 and stock.

I really like what my neighbor’s son in law did to his falcon.
Check “Project FalcOff” on fb.

I would definitely entertain something similar







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[AndronPrime]

This build sounds like it will potentially be amazing! looking forward to watching you progress!

Also I didn't realized the 740i, 750i, M5 trailing arms were such a large upgrade. If I keep the trailing arms in the rear of my car ill have to look into them eventually also.

[autox320]

The e28 arms are improved by using wider track in combo with 12 degree sweep (e21 is about 22 deg). Less arc of the suspension during travel and lowering. Gives more predictable camber and toe change. Allows more sane settings at lower ride height. They also have a "pitman" arm that also controls part of the arc when in motion.

IMO i'd be careful just swapping rear parts especially for trackwidth changes. If don't increase the front to match or have adjustment then the car will tend to plow(understeer). The 12 degree sweep arms will improve rear geometry and one of the main reasons I made mine 12 degrees.

[m60b30530i]

The e28 arms are improved by using wider track in combo with 12 degree sweep (e21 is about 22 deg). Less arc of the suspension during travel and lowering. Gives more predictable camber and toe change. Allows more sane settings at lower ride height. They also have a "pitman" arm that also controls part of the arc when in motion.

IMO i'd be careful just swapping rear parts especially for trackwidth changes. If don't increase the front to match or have adjustment then the car will tend to plow(understeer). The 12 degree sweep arms will improve rear geometry and one of the main reasons I made mine 12 degrees.

Do you know what the e30 arms are ? I have a full e28 rear but didnt want to go 5 lug.

- - - Updated - - -

I had a 62 falcon, sold it once I found my 71 chevelle.

That one is pretty bad ass, whats under the hood ?

[autox320]

Do you know what the e30 arms are ? I have a full e28 rear but didnt want to go 5 lug.

- - - Updated - - -

I had a 62 falcon, sold it once I found my 71 chevelle.

That one is pretty bad ass, whats under the hood ?

E30 arms are 15 degree sweep and would work well also IMO. I mean e30's have been knocked for semi-trails rear suspension but their track record proves otherwise.

[Retoropak]

I had a 62 falcon, sold it once I found my 71 chevelle.

That one is pretty bad ass, whats under the hood ?

Fairly mild 302. I think it made 230 whp

He also has s54 swapped e36 track car

Check @ryanjamesupham

[Somjuan]

The e28 arms are improved by using wider track in combo with 12 degree sweep (e21 is about 22 deg). Less arc of the suspension during travel and lowering. Gives more predictable camber and toe change. Allows more sane settings at lower ride height. They also have a "pitman" arm that also controls part of the arc when in motion.

IMO i'd be careful just swapping rear parts especially for trackwidth changes. If don't increase the front to match or have adjustment then the car will tend to plow(understeer). The 12 degree sweep arms will improve rear geometry and one of the main reasons I made mine 12 degrees.

They’re the same dimensions otherwise, and hub swapping makes them the same as the e28 setup. As a bonus they still have the same setup as the e21 for the Macpherson strut.

Where’d you find the data on the rear arms? I’d love to get a copy

[autox320]

They’re the same dimensions otherwise, and hub swapping makes them the same as the e28 setup. As a bonus they still have the same setup as the e21 for the Macpherson strut.

Where’d you find the data on the rear arms? I’d love to get a copy

Data floats around on the net, but I've measured sets myself to know for sure.

[Retoropak]

What is your opinion on the rod lengths?

I have an option to go with 140mm m52 rod or 135mm m42 rods.


I still need to verify clearances with 140mm and stroker crank. But it should fit





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[autox320]

What is your opinion on the rod lengths?

I have an option to go with 140mm m52 rod or 135mm m42 rods.

I still need to verify clearances with 140mm and stroker crank. But it should fit

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For NA I'd opt for long rod combo. For boosted maybe lean on the shorter rod ratio and heres why with my thinking. The piston design and ring pack for boost and heat. Longer rods means the piston design gets compact so a factor I'd investigate. I've never built a high boost engine so really couldn't tell ya what limits are. For NA though all day I'd choose longer, longest can get in the block making short ring pack and custom piston pin height. In some cases means notching the bottoms of the cylinder liners to clear longer rod combo's. My 147mm(vs 144mm) rod S14 2.7L is this way. Light die grinding to the sides of the block to clear rod bolt heads etc.
can search factors like
piston speeds, dwell @tdc, cylinder filling, VE, ring pack and piston design

I'd say with boost the rod ratio is less critical IMO. With NA it's another neat tuning tool to build around. 5mm difference rod doesn't sound like much, but can change the curve. If enough piston for your expected boost maybe go for it. I'd look around to see if someone else has successfully built the combo your after.

[Retoropak]

For NA I'd opt for long rod combo. For boosted maybe lean on the shorter rod ratio and heres why with my thinking.....

.....I'd look around to see if someone else has successfully built the combo your after.

I really appreciate the time that you dedicate to these forums. Helpful as always. I wish all responses were so detailed and to the point as yours.


There are not that many boosted m42s around and most of them are running moderate boost on stock blocks.

There was a 600+ Swedish build but i believe it was based on stock 135mm rod.


I agree longer rod will move the pin further up in the piston and reduce some crown thickness which might not be optimal for high boost.

I still have about a month before i get my cranks plenty of time to educate myself on rod ratios for boosted applications.


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[autox320]

I really appreciate the time that you dedicate to these forums. Helpful as always. I wish all responses were so detailed and to the point as yours.


There are not that many boosted m42s around and most of them are running moderate boost on stock blocks.

There was a 600+ Swedish build but i believe it was based on stock 135mm rod.


I agree longer rod will move the pin further up in the piston and reduce some crown thickness which might not be optimal for high boost.

I still have about a month before i get my cranks plenty of time to educate myself on rod ratios for boosted applications.


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Glad to help or at least get the thought process going. Keep in note the "squish" or "quench" when calculating piston to head clearance. I know we've posted about it before but keep it with some asterisk's when your plugging in numbers and figuring on which "o-ring" or gasket thickness compressed. 0.035" range, less chance of detonation, less timing needed for power goals, less octane needed to avoid detonation.

My lady and I daily drive M42 cars. I've had thoughts of one day building one of them all out. Being a NA guy I'd probably opt for something similar like this. Large'ish cams and ITBs. S42ish without the price etc.

[Retoropak]

According to my calcs i will be at 9.5:1 with 0.04”(1.016mm) gasket at it will give me 0.035” squish.

This is assuming 33cc chambers and 25cc dish, 135mm rod,88mm crank and 33.147mm compression height.

I can easily drop the compression 3/4 of a point with thicker gasket if i get to much ping.It will screw the squish tho.




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