How about High CR Stroker

[ForcedFirebird]

People often dismiss the Motronic, but it is more than capable of powering the m20. It's a very simple engine with a single coil and exceptional detonation resistance. Probably shouldn't say it in public, but I have witnessed an m20 running 14:1 at 10psi on a small 56mm turbo - where most engine blow up, this thing just wanted more!

I don't hate Motronic. I am one that gives the hand held calculator more than it deserves. lol. I tried making it do an Alpha-N by feeding back a variable TPS to the AFM input, but it's just too dumb. :(

[ForcedFirebird]

That sounds like a true German hot rod.
I made the mistake of building an M50 with too high of a static compression ratio, 12:1 (because at the time that’s what I thought I wanted).
Running on 93 I won’t even floor it, because it pings so badly. However if you do keep your foot down long enough the Knock sensors will intervene and pull timing. (Which feels like you just lost 25 whp)
I have to run a can of Torco every fill up, which claims would raise the octane to 98. This mixture eliminates the pinging completely, but costs $23 every fill up.
I was going to throw some cams with some decent overlap in to see if I can get away with pump gas, or just use a thicker head gasket. I think 11:1 would be ideal.
Anyways, I just wanted to share my experience with high compression engines. Hopefully others don’t make my mistake and go too high and have a engine they can’t beat on all the time with pump gas.



Sent from my iPhone using Tapatalk

sorry, but it's no m20!

The 24v engine follow a more modern flat piston and pent roof design, you will never get the detonation resistance of a BMW 12v. Sorry.

OTOH. A local is making well over 700whp in his e39m5 with 1bar and a completely un-opened engine. They react great to boost, but when you try and tweak a high-strung 24v engine, you are going up against all the top notch BMW engineers. As of late BMW has become a penny-pincher of production and longevity/reliability. The id10t's couldn't even extrapolate the bearing clearance when they moved to ~2" rod pins on the s54 (or any other "S" designated engine after the millennium). Sure .0015" worked great for years, but not when you increase the journal by ~50%., :(

[apostate]

That was I talking about. Thank you, sir, for the incite.
Now I am really out, kids.
Good time and all the best!

[LowR3V'in]

14:1cr & 10psi sounds good but 200hp is still 200hp. ;P

[ForcedFirebird]

14:1cr & 10psi sounds good but 200hp is still 200hp. ;P

Closer to 250whp/300wtq on a 56mm, but yes, an e30 with 250+whp is loads of fun. I have no idea why guys bring in e30's and want 500+ when the chassis isn't built for it (and they couldn't keep up with a good driver in a 150hp e30)...but whatever floats your boat. :P

One local is well over 500whp. WTF do you need a 500whp e30 for?

[LowR3V'in]

you don't have to use the entire 500hp going around turns ya know.

[digger]

That sounds like a true German hot rod.
I made the mistake of building an M50 with too high of a static compression ratio, 12:1 (because at the time that’s what I thought I wanted).
Running on 93 I won’t even floor it, because it pings so badly. However if you do keep your foot down long enough the Knock sensors will intervene and pull timing. (Which feels like you just lost 25 whp)
I have to run a can of Torco every fill up, which claims would raise the octane to 98. This mixture eliminates the pinging completely, but costs $23 every fill up.
I was going to throw some cams with some decent overlap in to see if I can get away with pump gas, or just use a thicker head gasket. I think 11:1 would be ideal.
Anyways, I just wanted to share my experience with high compression engines. Hopefully others don’t make my mistake and go too high and have a engine they can’t beat on all the time with pump gas.

Sent from my iPhone using Tapatalk

Yeah it’s one of those things were there isn’t any big gain in going overboard especially on a street car that gets heat soaked and lugged up hills in high gears or might get shit fuel at the bowser once in a while as the gain from compression alone is small especially if you are at 10 or 11 already.

The static cr alone doesn't tell you that much about knock though.
if you add in cam timing it tells you a little more. Baby stock duration cam with advanced vanos closes the intake valve way early if you could do a compression test in the advanced position it would probably read 300psi lol not good with pump gas.

Even then inlet valve close point and "dynamic" compression dont tell whole story either you need to factor in VE, if the engine fills better then you have more trapped mass and higher pressure and temp at end of compression stroke. For the same static CR and cam timing the 24V engine will have more VE than the average m20 so more pressure and temp.

Some ways to mitigate knock:

The purpose of moving the piston close to the head is to generate squish, i.e. to squeeze and squirt mixture from between close surfaces out into the chamber introducing mixture motion when there isn’t much happening and also those surfaces run cooler hence the name quench also used.
The biggest benefits are seen most a relatively low rpm as at high rpm the increased port velocity produces more mixing motion inherently e.g. swirl, tumble etc. but it is always a good thing.
The truth is few have tested squish clearance properly they almost always just run a thinner gasket which changes the squish and compression ratio. It isn’t a proper test of squish. There are a few SAE papers I’ve got and it’s proven worth power, lower BSFC and higher knock resistance but it would be engine specifics involved to. Anecdotal evidence suggests that knock resistance is the largest benefit its no silver bullet as there is only so much it can do.

With squish it’s important to note it is all about squish velocity which is a function of squish area and clearance and the less area you have that provides squish then the less clearance you must use to generate the same squish velocity

other things that help.

- Suitable cam timing helps
- plug heat range colder helps
- no sharp edge in the chamber and no nooks and crannys (issue with high CR vanos engines the piston dome looks like ass)
- feed the engine cold air

Retarding timing cost power, if you run a little less compression and don’t need to retard you always make more power.

[bmwmaster81]

People often dismiss the Motronic, but it is more than capable of powering the m20. It's a very simple engine with a single coil and exceptional detonation resistance. Probably shouldn't say it in public, but I have witnessed an m20 running 14:1 at 10psi on a small 56mm turbo - where most engine blow up, this thing just wanted more!

I don't hate Motronic. I am one that gives the hand held calculator more than it deserves. lol. I tried making it do an Alpha-N by feeding back a variable TPS to the AFM input, but it's just too dumb. :(

The FI 14:1 Cr engine sounds really increddible. Sure it runs on e85 ? Im asking me what is the key to be able to run this combo?

Im building an m20 2.7 actually where i will pay a lot of attention to good squish area and distance, have also polished the chambers to prevent knock as much as possible. CR will end up at about 10.5 and I will run it with emu standalone.....it was planned to run on rhd itbs and 280 deg cam.
But now i read your post and because i have an nice 3076 gtx turbo laying around I would really like to combine it with this engine.
How good is the chance to make this work with abiut 8 to 10 psi on premium fuel?

[varg]

One local is well over 500whp. WTF do you need a 500whp e30 for?

He might not want that kind of power if he lived somewhere where there were turns in places other than intersections, but you won't find many roads where a momentum car is fun to drive here and out-accelerating a corvette is a cheap (not in the financial sense) thrill.

[digger]

The FI 14:1 Cr engine sounds really increddible. Sure it runs on e85 ? Im asking me what is the key to be able to run this combo?

Im building an m20 2.7 actually where i will pay a lot of attention to good squish area and distance, have also polished the chambers to prevent knock as much as possible. CR will end up at about 10.5 and I will run it with emu standalone.....it was planned to run on rhd itbs and 280 deg cam.
But now i read your post and because i have an nice 3076 gtx turbo laying around I would really like to combine it with this engine.
How good is the chance to make this work with abiut 8 to 10 psi on premium fuel?

E85 + huge cam in the 320* range + not being lugged around the street

[bmwmaster81]

E85 + huge cam in the 320* range + not being lugged around the street

So I assume that low boost of about 8 PSI with 10.5:! CR m20 isn't the best idea?
Here my thoughts:

I would run 102 octane premium fuel on it. 280 deg cam with about 2mm lift in TDC should already lower dynamic compression.

See attached the pics what my Idea was for the NA setup.
I have customized the stock pistons so that I can use them with 2.7l crank and still 135mm oem rods.
With the modification the squish area is bigger and completly around the outer edge of the piston.
For me this should prevent knock even better than stock. I also payed attention to keep the gap very tight....but have to measure the next day the real result. But from the looks it seems good

left side oem piston / right side modified

https://drive.google.com/open?id=1xnwxIUEAzfNxp3hxb7N08WgqUiuuOu6Q

Here piston further modified with round edge which (should) fits to round area in head: Piston is in TDC on pic

https://drive.google.com/open?id=1ednaHIESIVb9Xg0B7Hr6riYTbLyFZQHF

Im curious how the piston will fit into head. Squish should be tight. I hope the shape will fit also well and maybe it will be well resitent against knock so that I could use this ::devil:

https://drive.google.com/open?id=1zbNarfuog2pFF0xmyGjwAPxLuHQPpca9

https://drive.google.com/open?id=1NGLEGQ1FT6Dr9kA8tQ_lMekcpWSikfHr

Should it be real that the m20 ist as knock resistant as ForcedFirebird says? Then I should be able to boost this thing a little.......thats somehow my hope;D
Where would I and up with 8 PSI Boost ? 300 HP?