Yeah, but as pertains to our M10's what is the highest anyone runs in a daily driver?

I would think that very high compression 10:1 + might be accomplishable by substantially fattening up the mixture via a re-tailored kugelfisher or an appropriately jetted carb. I know it isn't a slam dunk. I have been wondering about where to go now that my 9:1 bathtub piston'd plant is really showing its age. A huff'n and a puff'n.

I don't keep up with current bmw technology but you can be sure that if BMW is going to be doing direct gasoline injection. Applying that sort technology to an m10 would be a fools pursuit imho. But maybe there is a 4cyl in the pipeline that could be transplanted. Does the 1 series offer a 4cyl gasoline motor?

I don't think going higher than 10.1 would be recommended. The m10 motor is dated in cylinder head and matching piston design. You are not going to be able to do much more than what it has been able to support since it was designed. If you are willing to experiment, there are somethings that could be tried to push the detonation limit higher. Like ways to improve swirl in the chamber and acheiving maximum squish. And small things like indexing the spark plugs and smoothing the chamber/pistons for reduce impedence to flame travel and hot spots.

I;d stick with 10.1 or less

Initial findings with AvGas (100 LL) seem to indicate that 11.5:1 is
safe. Barely, if you're a bit careful with timing.

So going to the high side of 10 is probably not a set- and- forget operation.

t
_________________
I have a car disease. There is no cure.
I'm not even managing the symptoms very well...

Ultra High Compression ratio in a M10 ?

not without "knock" sensor technology,
Ignition, and Fuel delivery map controls
of the 1990+'s.

you will not get anywhere with a M10 distributor,
mechanical fuel injection, carburation, and without 'digital' electronics.

Direct injection into combustion chamber is now in the present day BMW motors.
Direct injection into combustion chamber started with the 12-cylinder M73 motor, and now has worked its way into most 2007+ models.



Mercedes-Benz had Direct Injection (not into the intake port or
intake manifold) with injectors screwed into the side of the cylinder
block pointing at the piston tops. The injectors cannot be seen because they are 'under' the motor, down on the drivers side. The BOSCH fuel
injection pump is also down under there with all the metal fuel pipes.
None of the injection system is seen here up on the intake side of the motor. Just alittle 'direct fuel injection ' history lesson
_________________
1976 BMW 2002 #2743711(sorry I sold it 12/25/06)
1986 BMW R65 650cc twin 19k miles
1964 BMW R27 250cc single 15K miles
2002 BMW 325xiTouring 29k miles
1984 MERCEDES-BENZ W123 300D Turbodiesel-188k miles fein-DIESEL

c.d.iesel wrote:

Ultra High Compression ratio in a M10 ? not without "knock" sensor technology, Ignition, and Fuel delivery map controls of the 1990+'s. you will not get anywhere with a M10 distributor, mechanical fuel injection, carburation, and without 'digital' electronics. Direct injection into combustion chamber is now in the present day BMW motors. Direct injection into combustion chamber started with the 12-cylinder M73 motor, and now has worked its way into most 2007+ models. Mercedes-Benz had Direct Injection (not into the intake port or intake manifold) with injectors screwed into the side of the cylinder block pointing at the piston tops. The injectors cannot be seen because they are 'under' the motor, down on the drivers side. The BOSCH fuel injection pump is also down under there with all the metal fuel pipes. None of the injection system is seen here up on the intake side of the motor. Just alittle 'direct fuel injection ' history lesson

Thanks for the responses. I obviously live in the horse and buggy era since I am currently fiddling with carburetors from a vintage ski boat that hasn't seen the water in 40 years and have not stayed current with the newest offerings. I have since been informed that Honda and BMW and most others are all running much higher compression ratios. In fact, I am so ancient that I can remember reading about Mercedes racing with a straight 8 engine similar to the beautiful picture posted by C.D. (Sorry he sold it!). CD: what are those chrome stacks/elbows sitting between the gray aluminum intake runners? Ever worked on one of their straight 8's. I also remember when the C111 was brand new and powered by a rotary rather than a diesel.

Great site here! Thank you again.

Where would you add the sea foam? lol

http://www.ultimatecarpage.com/pic.php?imagenum=6&carnum=362&no_cj_c=1

the "chrome' visible between the gray aluminum intake runners
is the one sheet aluminum exhaust shield.

Tubular exhaust headers exit the head on the same side as
those long intake runners. This is the sheet aluminum
heat sheild protecting the intake from the header heat.

different motor here - with better exposure:
you can just see the single pipe at the rear,
outside of the rear two intake runners,
and in between the middle runners at the gap in the heat shield.

Note the twin-coil ignition on the firewall.
Your looking at a 300SL Roadster - which had 2 coils for better
coil saturation, and 'better' dwell for the higher output cam fitted to the later Roadsters. Roadsters also had front disk brakes. The earlier
Gullwings had front drums and only one ignition coil - slightly less horse
power rating.


300 SL Roadster


One can learn a lot about car construction under the hood of early Mercedes-Benz. Plumbing, wiring fastening, routing, fasteners,
securing brackets, rubber mountings, materials, sealing methods .....
It's how I served my early apprenticeship
Work Safe - protect your eyes, and lungs !
_________________
1976 BMW 2002 #2743711(sorry I sold it 12/25/06)
1986 BMW R65 650cc twin 19k miles
1964 BMW R27 250cc single 15K miles
2002 BMW 325xiTouring 29k miles
1984 MERCEDES-BENZ W123 300D Turbodiesel-188k miles fein-DIESEL

I ran my 10.1 compression motor on the street on pump gas for many years........no problem
_________________
68' 1602
98' ///M3 Sedan

88' ///M3 Sold *
06' ///M3 Competition Pkg Sold *

http://www.bmw1602.com/