M20 B3x Naturally Aspirated Stroker build past, present and future

[Nutzy]

Stellar work Digger! Looking forward to seeing the results. :)

[digger]

The limitation on stroke is the clearance to the intermediate oil pump shaft. im getting a custom one made as even with slim rod shoulders of the Molnar rods it needs to neck down too much for my liking with crappy quality material (cast iron?) its made from becoming apparent when you start to cut into it

[ForcedFirebird]

Bang up!

[digger]

didn't think you could go bigger than the s52 crank. Are you running the 135mm rods?

The longest rods I've heard is the MM stroker kit which are like 137mm so this crank will really shorten that piston!

135mm rods, which coincidentally is the same length rods that the donor engine had. This means the piston compression height is larger than my MM pistons which use a 138mm rod.

[downforce22]

didn't think you could go bigger than the s52 crank. Are you running the 135mm rods?

The longest rods I've heard is the MM stroker kit which are like 137mm so this crank will really shorten that piston!

[FredK]

Wow. That is a tasty burger!

[digger]

incredible. where did you source the Alpina crank?

eBay, a new one cost about 5k from alpina and you need a VIN, you could get a custom one for that so i waited a couple years until one came up on ebay

[AwakenNoMore]

This is fantastic, I'm quite curious to see what the dyno graphs look like for this monster.

[bradnic]

incredible. where did you source the Alpina crank?

[suruba]

I want tony to do a head package for my 3.1 soooooo bad. this thing looks great. I can't wait for you to get it into a vehicle.

Dave

[digger]

Yeah most was done a few years back though lol, while he waited for me to send the final parts etc , just did finishing touches and assembly a few weeks back

[LJ851]

Hot Damn ! That head looks A+. You had Knight do the headwork, right?

[digger]

I think it’s time for an update.

So my head is 99% assembled minus some studs, sprayer and the shaft plugs

RHD rockers and 292/292 cam installed. 110 lobe separation with just under 13mm lift. Think schrick 288 but extra 1.5mm lift and a few degrees duration more so nothing too wild (yet).

Valve lift seems to be what a big stroker needs to get VE at any sort of rpm approaching 7000rpm, the roller followers enable a higher valve velocity than you can get with stock type rocker pad giving a nice fat lift curve.

i was going to go for the 306 cam but i thought id start mild to begin with as i want to still drive it on the street without too much compromise, maybe im getting old or just soft ;) however everything is being designed around being able to fit the 306 cam with 106 LSA at a later date.

port work is mint 45/36 valves lots of chamber reshaping (remember that the chamber is an extension of the port...), the RHD intake was fully port matched to.

you can feel the shapes are right with your finger the short side profile is miles better than any head ive had ported before.















Time for the bottom end to get serious. Lightweight 93.8mm stroke crank from an Alpina B3 3.3 / B3S should do the trick for some midrange torque. I wouldn’t expect anymore topend hp compared to 89.6 crank all else being equal but shouldn’t have to rev it as hard.

[digger]

i certainly agree that with intake length the filling just before BDC (quite alot before BDC) to IVC is the key to better output

[The Dark Side of Will]

Are you saying the additional mass that enters between IVO and piston “suction” starting proper (say 50cc volume worth possible more ) is less then the benefit from just starting the flow early and getting better filling due to better “ramming” from BDC to before IVC and less reversion at that point? My main discussion point was you want the flow to start early as possible there are benefits to this. My guess it might not be clear cut. you could probably do a few what ifs with the sim to check but its hard to isolate one thing without affecting something else

Put numbers to it...

At 11:1 compression, the clearance volume is 1/10 of the displaced volume. For a 500 cc cylinder, that's 50 cc's. The max additional charge you can get from scavenging the overlap is therefore 50cc's. That's certainly nothing to sneeze at and should absolutely be an objective.

However, the volume in the cylinder between BDC and IVC is... What? 100 cc's? 150 cc's? I don't know your cam specs.
They're both important, but the air below IVC is most likely a bigger chunk.