M20 B3x Naturally Aspirated Stroker build past, present and future

[lindskrot]

thanks

what cam are you going to be running?

I have schrick 288 degrees in the car.

Do you guys have E85 fuel accessible down under? We have it on basically every fuel station, so im running E85.

[digger]

It's a street engine so I'm not looking to push it too high as it gets quite hot here in Summer and a heat soaked engine is significantly more prone to knock . It's diminishing returns with compression anyway doesn't make much sense to be on the ragged edge. I might even go a bit lower than 11.5

[digger]

I have schrick 288 degrees in the car.

Do you guys have E85 fuel accessible down under? We have it on basically every fuel station, so im running E85.

There are a few places, I did think about running flex fuel but seems like more hassle than it's worth.

[digger]

Is the 11.5CR pistons the highest compression you could go coupled with the 292 cams?

I've been in thought putting the pieces together for a 3L stroker (s50 86mm crank, s50 135mm rods, catcams 1300530 camshaft, CP 85mm 12:1 pistons, supporting valvetrain mods, ITB's down the road)

Not sure if the cams ive selected would be too big for my car being a daily.

Your build is coming along nice though. Cant wait to see how it turns out

thats a pretty aggressive cam (lots of overlap) for a daily driver, especially if the ITB arent until down the road. with standard manifold thats going to idle like a pushrod drag car. what valve springs and rockers are you planning on using?

http://www.catcams.com/products/camshafts/datasheet.aspx?ENGINE_id=111&CAMSETUP_id=269

i contemplated using it with mine but thought id start quite mild to begin with but the pistons will be designed with a big overlap cam similar to this

[skitzy777]

thats a pretty aggressive cam (lots of overlap) for a daily driver, especially if the ITB arent until down the road. with standard manifold thats going to idle like a pushrod drag car. what valve springs and rockers are you planning on using?

http://www.catcams.com/products/camshafts/datasheet.aspx?ENGINE_id=111&CAMSETUP_id=269

i contemplated using it with mine but thought id start quite mild to begin with but the pistons will be designed with a big overlap cam similar to this

Oh, yeah I thought it would have been to much of an aggressive cam for daily use, but I wanted the highest compression motor I could use on aus 98 octane.

I would be using the catcams springs they provide, and either the MM inspected rockers or IE.

What piston manufacturer are you going with? I might just end up doing the same compression and piston design as you as well as the same camshaft but instead using a different crank. I’m still not sure yet I feel planning is essential.

Where are you sourcing your crankshaft from?

[digger]

Oh, yeah I thought it would have been to much of an aggressive cam for daily use, but I wanted the highest compression motor I could use on aus 98 octane.

I would be using the catcams springs they provide, and either the MM inspected rockers or IE.

What piston manufacturer are you going with? I might just end up doing the same compression and piston design as you as well as the same camshaft but instead using a different crank. I’m still not sure yet I feel planning is essential.

Where are you sourcing your crankshaft from?

i bought the crankshaft from ebay

i am not sure on piston supplier yet, it will be either JE, CP or Mahle MS. i am designing my own dome to suit my particulars using 3D CAD. i got it printed in 3D and did a mock assembly to check squish and valve pocket placement, i just need to fine tune the CR once i get back into looking at it.

you would need to ask Rama if he has any more rockers/cams as he may not have any in stock

[BUDNUNTA]

Rama suggested Tighe cams in QLD to me

[digger]

Never used them, Another I know of is franklin cams in nz

http://www.camshafts.co.nz/bmw.aspx

[BUDNUNTA]

I've heard good things about Clive Cams in Victoria too

[Schlander]

The stroke is 93.80mm and bore is 86.00mm so its 3,269 cc (199 CI)

Is it a custom crank or from what engine? ;D

[digger]

its a OE crankshaft made by BMW for the Alpina engines found in the B3S and B3 3.3 which are based on the S52

A custom crank is quite expensive not to mention you are fast running out of room to fit it without severely compromising the stiffness of the intermediate shaft which i think would dramatically reduce the life of those bearings. IMO there are too many hurdles to go more stroke than that.

[The Dark Side of Will]

There's no reciprocating load on the intermediate shaft, so stiffness is a FAR less important concern than it is for a crankshaft.

[digger]

There's no reciprocating load on the intermediate shaft, so stiffness is a FAR less important concern than it is for a crankshaft.

its the timing belt tension + valvetrain drive loads that are cantilevered off the end, if you neck down the middle then you get too much rotation in the front journal. i have verified this with FEA and hand calculations.

the strength you can mitigate with a 4340 heat treated steel but stiffness is a different matter. all you can do is replace cast iron with steel but its a D^4 term so it catches up with you pretty quick. it wont last at 12 mm OD with a 5.5 mm ID.

the only solution i see for something bigger stroke than 93.8mm is a smaller crankpin and rod. as it stands many aftermarket rods are too wide even for the 93.8mm

[ForcedFirebird]

There's no reciprocating load on the intermediate shaft, so stiffness is a FAR less important concern than it is for a crankshaft.

I have seen multiple intermediate gears shatter, even on stock engines (one turbo). This is why the gears were upgraded to sintered vs stamped steel.

The timing belt setup on an m20 takes more back lashing that people think. There's no live spring tension on the belt. Tension from the tensioner spring only sets initial tension, once the belt starts stretching, the spring is invalid.

[ForcedFirebird]

the only solution i see for something bigger stroke than 93.8mm is a smaller crankpin and rod. as it stands many aftermarket rods are too wide even for the 93.8mm

You mean wide as in the cap bolt area has less intermediate shaft interference?

The bigger problem I see in the m20 and huge strokes is the deck/compression height. Once you start getting over 84mm stroke, the rod/stroke ratio goes to crap. Your piston TDC dwell gets very short, so you have to add a lot of advance, and the error margin goes small window for ignition tuning. Also because of the short deck height, you start running into piston pin/ring interference (why BMW decreased pin diameter on the s54).