M20 B3x Naturally Aspirated Stroker build past, present and future

[digger]

So, 18 months ago I finally did a major interior overhaul that I had been planning for many years.
The main objective was to

• Replace the cracked dashboard (new 2^nd last made for a RHD)
• Put in a “replacement carpet” carpet as the old one was torn near clutch pedal footrest (found a good used carpet from Brutus on R3v/E30zone)

I look the liberty of doing a whole lot more, I replaced

• New Centre console
• New Centre console
• New lower dash cover
• New lower sill pieces
• New M-tech sill cover
• New Interior handles
• New floor mats
• New Power window switches
• Installed powered USB port
• New blower and resistor

I rebuilt the heater box (not as bad as it looks) just taken 4000 photos like I did but not much of the assembly

• New Evaporator
• New Heater Core
• New Heater Valve
• Re foam all the flaps
• Replaced crack flaps and links
• Replaced cracked vent slider assembly
• New heater core pipe and found a good used one that was NLA

I installed the A/C solutions full kit noting I already had the parallel fin condenser so now it blows cold air in summer

The worst part was half assed speaker wiring done by previous owner it was threaded through carpet and connections not properly made and just pulled apart with barely any tension so lucky I took a lot of pics and labelled everything thoroughly.

What a mess


CARPET


Did give a light dye with a closely matching spray dye to uniform the colour


DASH
Old dash fitted out vs new dash bare




HEATER BOX



SOUND PROOFING/ DEADENER
I added the Resonix CLD square ( butyl rubber with Aluminium backing) to any panel that was flat without much pressing/beading that sounded tinny or prone to resonance when It was tapped. This include inside of door skin, inside of rear quarter panels, the floor, the rear seat base and backing. I kept some of the factory sound deadener but removed some to.


I added Resonix lockout into the front doors and the rear quarter panel

But importantly I added mass loaded vinyl sheeting/panelling under the carpets and under the rear seat bottom vertical cushions but had to keep the thickness only like 1/8” so things could go back together. I added thicker mass loaded vinyl into the rear quarter panel cavity



The shit aint cheap and must add like 50kg maybe more (can’t be effective if a bunch of mass isn’t being added) but it works well and I would do it again and people who have been in the car have noticed without any prompting.

REASSMBLY



“FINISHED”

[digger]

Back in 2023 I decided to change to 17” Maxlite 17x7.5 ET25 wheels for the following reasons

• I wanted better tyres
• Able to fit better brakes (A setup that used an OE pad compound) ended up with 300mm.de 312/297 e34 540i setup
• needed to be Alpina style

Impressions on quality is they are pretty good and well packaged but some minor gripes

• Centre caps are much lower quality than Alpina (aluminium) and are non locking they use a capscrew
• Some of the drilled hole chamfer needed to be lightly deburred on a one (1) wheel. Would have installed fine but pedantry
• Centre caps are PITA to remove but I use a suction cap and that sorted that
• I had to machine the Alpina stick on emblems 2” vs 50mm difference

I used GYEON ceramic coating on them to make easier to clean.

I have always been a Michelin fan having tried Michelin Pilot Exalto 2, Michelin Pilot Sport 3, and 4 fitted to the Alpina 16x7. So I fitted 205/45/17 Michelin Pilot Sport 5 to front and 215/45/17 to the rear with the Pilot Sport 5 similar to 4 but much longer lasting and not to be mistaken for a pilot sport 4s replacement.

I ran 205/45 instead of 215/45 at front because I didn’t want to rub as I was running the offset CA bushes which pushes the wheel about 7 or 8mm forward so rubs the front arch plastic liner on hard lock. I could run 205 at rear but maybe 215 provides a bit more rear traction probably marginal.

I opted not for 215/40/17 which is the “correct” diameter because there is less sidewall and I was concerned the harshness and the look would be a bit extreme.

I do have 5mm spacer at rear but only because the thickness of rear rotors is a smidge thinner than the step on the hubs so the wheel would bear onto the hub properly and might wobble (same issue with the corrado rotors I had before on front which I ran a 3mm spacers/shims which is the minimum that can be attached semi permanently).

I use longer lug bolts with the spacer to maintain the thread engagement. I currently do not run the concentric CA bush anymore so 215 would fit the same as 205 but would need to run a 5mm spacer to clear the 2.5” GC spring perch (I have chamfered them already)

215/45 is about as big as you would want circumference wise as at 110km/h on the speedo the GPS speed is 110km/h so need to watch out for speed cameras. At 60km/h there is still a few km/h buffer.

Overall the Michelin are good tyres for street and excellent in the wet. They are not an all out dry max grip tyre but are good in all areas wet, dry, comfort, noise and wear. I may try Continental MC7 next time as they review just as well or higher.

The 17’s do ride rougher than the 16” and 15” obviously but with the pressures at 30-32psi it is ok now that I have toned things down on the suspension at front downing the spring rates to 250lb/in from 375lb/in and anti roll bar sizes from 24mm to 22mm and employing the bump stops appropriately to stop coils going solid

Here are some pics. The front is about 5-7mm higher now so not as much rake

[digger]

This a writeup of the vibration damper
Here is the damper CAD section view


And the real prototype


It uses ATI inertia ring and their o-rings 80 duro
Manufactured by CNC providers Xometry and Protolabs with Electroless nickel plating to offer some corrosion resistance (would not use this on longer term) and I did lightly scuff key interfaces with very fine scotch bright as it felt slipperier than ATI products and didn’t want o-rings to skate. It is assembled with the ATI recommended silicone spray which is not supposed to stay slippery.
I designed the rest with some initial dimensions from ATI from many years ago so the interface of the inertia ring and o-ring and the ensuing compression are correct and wall thickness falls inline with ATI recommendations and easily above SFI minimums.
I have mock this up on a bench engine and it fits no problem sans mods below

• lightly shave lower timing cover (easily done with file or disc sander/linisher
• longer bolt S55/58 trimmed
• should check clearance to intermediate cam gear leading edge (a mm can be ground off front of gear if needed depending on stack up tolerances)
• should check water pump pulley clearance (a mm can be ground off pulley lip if needed depending on stack up tolerances)

It will fit a factory timing gear and normal bolt setup (still needs clearance of timing cover and other checked) but ATI advised it is best to transfer the torque via a press fit onto the crankshaft snout rather than thrust friction drive so this would need to be foregone and the reason why the new gear exists. To me the factory set up works fine on mild setups (BMW still use this approach but diamond coated washers on some) but on some serious builds one would probably want to listen to ATI.

The parts


Inertia Ring (7”)
This is a standard ATI part taking their o-ring kit

Inner hub (steel)
This interfaces with the cam gear and is dowel for alignment and receives small bolts for keeping the damper together when the unit is off the cam gear.

Outer Shell (steel)
Retains factory 60-2 trigger and water pump pulley

Pulley (PS and A/C) (Aluminium Anodized)
Stock Vee design and angles
Cam gear (heat treated 4140)
Cam gear basically a replica of the OE except smaller bore for press fit ( I had the prototype ID ground locally to suit crank dimension) and longer snout to allow other parts to be concentric located. The bore ID has a clearance step to make the key easy to align since it need to be oriented at the correct angle to press it correctly. The gear is separate to the inner hub to make timing belt easier to install (same as stock)


Assembly



The unit is much heavier than the stock one but is obviously rebuildable and the price to pay for not breaking a crankshaft. Some parts could be replaced with aluminium and/or lightened

I don’t know what I am going to do with this other than my own testing. If an established reputable vendor wants to take the design and get to production through ATI, then I could part ways with the design as this is not the space I want to be in as they will no longer do a one of would do a min of 10 units iirc. This is provided it is followed through and made available for the community.

[digger]

Definitely let me know when you have a new exhaust system as I may be interested in the old one depending on how insane the shipping would be...

always exciting to see what comes with the new setup

ill be using a bunch of elements from the exhaust but replacing the header and depending how successful i will probably need to decide to sell either btb2 or btb3 version but this is realistically not happening this year.

[2mAn]

Definitely let me know when you have a new exhaust system as I may be interested in the old one depending on how insane the shipping would be...

always exciting to see what comes with the new setup

[digger]

Here is the “short” update list (high level). I will try expand in due course with happy snaps where these were taken for the stuff that has been done:

1) I installed new set of wheels mid 2023 to allow bigger brakes and step up the number of quality tyre options

• 17x7.5” Maxlite 4x100 Alpina style wheels ET25
• 205/45/17 Michelin Pilot Sport 5 (front)
• 215/45/17 Michelin Pilot Sport 5 (rear)

2) I did a major update to steering/front subframe late 2023

• I purchased a reinforced front subframe from Dan Grooty (Grooty’s Race and Resto)
• I got a re-manufactured purple tag rack from LPSR and their steering linkage
• New PS lines from Dan in UK (BM Conversions)
• New OEM engine mounts
• New Lemforder e46 inner tie rods and e36 outer tie rods
• New Lemforder Control arms
• New GC 8641 1198 SPORT shocks (old ones were blown)
• Powerflex offset CAB (replaced worn OE eccentric)

3) I did a major update to brakes early 2024

• 300mm.de BBK 4 lug 312/294 E34
• New braided lines
• E90 Booster and M/C
• 2002 Remote reservoir

4) I did a major interior update late 2024/early 2025

• Replaced torn carpet (purchased a good used crapet from the UK)
• New dash
• New centre console (both)
• New under dash cover (driver side)
• Installed A/C solutions full kit
• Rebuilt the heater box
• New Evaporator
• New Heater Core and Valve
• Added a bunch of noise insulation/barrier (Resonix CLD and Lockout) also used mass loaded vinyl

5) I got a used subframe and welded the eccentric bolt adjusters

• Got multiple alignments and readings showing toe out at rear of varying magnitudes 1mm to 3mm
• Rear has about 1mm toe out per side confirmed and now getting consistent numbers and checked with stringline
• Will use either OE bushes or powerflex

6) I did a major front suspension overhaul earlier this year

• New shocks (again as started rattling)
• Rebuilt GC street top mounts (axial/thrust bearing and poly bushes)
• New Coilover Springs 250 lb/in x 9 inch 2.5" ID
• New GC bump stops properly setup

7) I got a ATI Vibration damper functioning prototype made (to be tested). Note this was my project (not in conjunction with them) and ATI didn’t produce any new parts.

• Used ATI Inertia ring and their o-rings
• Custom crank hub for light press fit to snout
• Inner and Outer shell outsourced to Xometry
• Dynamically balanced

8) I messed around with front suspension some more to try and improve comfort, tramlining and potentially bump steer.

• Tweaked camber to get LH to RH consistent
• Went back to concentric bushes (still Powerflex)
• Went back to 22 mm bar (H&R) from Whiteline 24 mm
• Happy with results on rough roads compared to before but may still look into bumpsteer correction through rack or tie rod end and may still go to OE rubber concentric CA mounts

9) I actually spoke to a engine machine shop the other week so will probably be dropping stuff off in the next month or two i am just doing a stock take of parts to make sure i have everything but at least moving forward.

10) Future Works - There are a couple of higher priorities before engine can go in

• I need to install rear sub frame and bushes first so i can align it properly and do some R&R on fuel system / brake system above tank and diff speed sensor wiring based on what i find.
• Fix cluster indicator and spurious speedo dropout
• Get the Haltech Elite installed with dual WB and tuned so that i have a good ECU up and running before swapping engine so when i start it is good tune. My current ECU is functional but archaic
• New airbox to try and incorporate strut brace and improve filtration
• I will likely be doing a 6 speed swap but will do this when swapping engine
• I will also be doing a new header and exhaust but will do after the new engine is in as any testing on current one is a moot especially since the power feels like it has fallen off since the last dyno which is like 10 years ago

[2mAn]

A year later & we still havent gotten our update digger

[leez]

Any updates for us digger

[skarlqvist]

If you want to run classic wheels and a big brake kit. K-sport is a nice alternative. This kit has 3 piston callipers and 350mm rotors. I have tested it to work with all the 18" wheels I like.
Order a 325mm rotor and it will clear 17" also.

[litu]

Nam nam

[skarlqvist]

A proposal for the ultimate screamer:
Move to dry sump, Use a 2.5l crank, Port the head, Bore the cylinders from 80 to 87mm, Use hi-comp pistons 12:1, Use RHD itb and roller kit with 316 cam.
Add a really light fly wheel and clutch pack and rev this 2,7l m20 to 10K.
This will give you more than 300whp at piston speed 25m/s and with the right exhaust a sound like a Honda CBX1000 ;-)

[litu]

It is all about the total package head. This awd dyno result is from my m20 low comp na stroker build. It pulls harder than an original s54. With a bigger cam there is a lot more to gain.

Wow, that engine in ix. We want more, way more info...Is there any where i can follow this project

[skarlqvist]

280 whp in an ix on a awd dyno with perhaps 15% drive train loss is a dead race against an original S54 (tested on the same dyno).
There is room for an additional horses if you go for the 302/309/316 roller cams (street-ability will suffer, this is none vanos engines).
The RHD roller setup allows for revving to 10K but the 89,6mm crank in my car translates to a pistonspeed of 25m/s at 8400 rpm.
Piston speeds of 25m/s is the upper limit in most engines.
The original m20 oil pump will start to cavitate at 8000+ so the real max rpm is actually 8000 (one must move to dry-sump for higher revs).
My engine is build for boost and >500Whp. If I was to keep it na I would have gone for RHD itbs, any day.
I have been talking to DBilas and they have pressure tested the plenum and itb construction for 2 bar.
For this car I have bought an Australian "Raptor V" supercharger and since the ix front diff is the weakest part I will limit power to 500whp on pump gas.
The engine needs a lot of air in and out. I use AEM Dry flow 76/135mm and the custom build 2x2,5" exhaust below.

[digger]

~240whp (281bhp) seems about right for that, though i would expect it to peak at higher rpm with the short runner dbilas intake but this might be a lazy dyno tech not setting up rpm correctly. Personally i would consider the RHD inlet it is far superior perhaps except for the OEM looks or lack thereof

[hasa]

Thats better than what I'd expect for standard compression and 173CFM head! Nice packet.