Is it worth to build high rev M20B22?

[Jasu]

Hi guys.

I've always wanted to build a high revving short stroke M20 engine.
And now it seems to be time to finally do it.

Mainly in the planning stage, so I don't have all parts yet.

Idea is something like the following
-M20B25 block
-B20 66mm stroke crank
-145mm rods
-85mm 12.5:1 - 13.0:1 pistons
-885 head (40ml) with std. valves, new original rockers
-~280º @1mm ~12mm lift cam
-42mm itb

Fuel will be ethanol (RE85).

Is there anyone here who has planned or made similar?

[goarmy]

They will probably tell you to swap and go m50 or go s54

[LateFan]

Hi guys.

-B20 66mm stroke crank
-145mm rods
-85mm 12.5:1 - 13.0:1 pistons

School me on how this works, please anyone.

You go with a shorter stroke crank, then put longer rods and/or taller pistons in to reach deck height for compression?

So you have a short stroke, but more reciprocating rod mass? (unless you have really light rods?)

It obviously works - most of the great race engines are short stroke, over square designs. I'm thinking of the Porsche 2.5 flat 6, or any F1 engine. I just want to understand the physics of the extra mass shaking up & down when you're trying to reach an existing deck height.

-Engine design noob

[nrubenstein]

It's interesting, but how many revs will that actually turn for a reasonable amount of time?

If you want revs and low displacement, why not just get an S14? It'll be better in pretty much every way.

[raudonis]

The problem with high revving m20 is not in the bottom end.
It is in the head, poor lubrication between cams and rocker pads at high rpm because rocker geometry to be precisely.
It appears that no sliding rocker design is up for the job. The only working solution so far is this roller rocker design http://www.racehead.com.au/?wpsc-pro...roller-cam-kit. The creator and seller of this is here http://www.r3vlimited.com/board/member.php?u=35745 He ran 2.7l in 8000 range, then stroked it 3.0l for better midrange torque and better general powerband.
On the other hand, you can get m20 to 86mm bore with custom MLS gasket and for something small as 2.2l better use 731 head with bigger valves of 885 + flattop pistons.
Also you will need properly sized ITBs instead of the factory manifold. Factory "crab" manifold is tuned for the midrange very strongly.

You can try contacting this guy about high rpm m20 problems, he is Eesti ;) www.youtube.com/watch?v=xJO3C0j8F3U
He used really expensive PPF billet rockers and most aggressive dbilas camshaft, but they just kept on grinding each other to death.
His build thread is here, although most of the pictures are no longer working :(

http://www.e30tech.com/forum/showthread.php?t=78727

[ThatOneEuroE30]

I got a m20b20 crank sitting in the block in my drive way.

[digger]

id start with a 731 or 200 head and heavily work it, as you wont need/want the same port volume that the 885 has in a small cubic inch engine and with a small cubic inch you want the small chamber volume to make it easier to achive a high CR.

on e85 i wouldnt go below 13:1 especially with a huge cam like that

also 40mm ITB will be plenty

[TobyB]

OP is from Finland. They do NUTS shit there.

I say go for it.

But you WILL want a DOHC head to do it. That shouldn't be a problem, right?

Frm M10 experience, the rockers really do limit you at a certain point, and that's
probably going to be lower than the bottom end can take.

Swap in an M88?

Hee.

t

[raudonis]

OP is from Finland. They do NUTS shit there.

I say go for it.

But you WILL want a DOHC head to do it. That shouldn't be a problem, right?

Then swap over s50b32 head ant turn over 10 000 :D BTW swaping s50b32 head over m20 block has been done, there are a couple of vids on youfube from some German dude

Sent from my GT-S5570 using Tapatalk 2

[digger]

sounds like a bad idea

[Cabriolet]

OP for that cost, just get an s14. they can be wound higher and are in the same Liter-age as you are looking to get. they are lighter and pair with a much better transmission. i had a lot of fun winding the crap outa my m3.

[Jasu]

id start with a 731 or 200 head and heavily work it, as you wont need/want the same port volume that the 885 has in a small cubic inch engine and with a small cubic inch you want the small chamber volume to make it easier to achive a high CR.

on e85 i wouldnt go below 13:1 especially with a huge cam like that

also 40mm ITB will be plenty

I have in stock -731 and -885 ported heads (both with 42/36 valves and 40cc)
I know that with so short stroke it is difficult to get so high compression ratio, but the idea is interesting, and have had it more than 10 years in my mind.

OP is from Finland. They do NUTS shit there.

I say go for it.

But you WILL want a DOHC head to do it. That shouldn't be a problem, right?

Frm M10 experience, the rockers really do limit you at a certain point, and that's
probably going to be lower than the bottom end can take.

Swap in an M88?

Hee.

t

Doch head is not a problem, but money is. :D
Std rockers are ok ~9000rpm, if cam and springs are "correctly selected".

OP for that cost, just get an s14. they can be wound higher and are in the same Liter-age as you are looking to get. they are lighter and pair with a much better transmission. i had a lot of fun winding the crap outa my m3.

Basically, it would be wise. And my big dream.
But I have those M20 parts damn much. And one new Cosworth YB race spec engine. I should get rid of those first.
And now is not the seller's market.

[raudonis]

Std rockers are ok ~9000rpm, if cam and springs are "correctly selected".

[Jasu]

Believe it.
Course I would like to use roller kit, but the price is too high for me.

[digger]

standard rockers are not ok at 9000rpm for an extended period. gotta do it right if youre gonna do it. the billet rockers from VAC are cheaper than the roller rockers, then there is the heavy duty rockers (cast) that have been around for a few years now.