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Hi all! Theoretical question (and I'm not very technical person): is there any potential of increase in the displacement of the M20B20 engine (2l) to increase the power output? Basically to make it slightly closer to the 323i spec? I guess this could affect the compression rate. If yes, what other options should be included?

Thanks!

Get a M51D25 crankshaft, M54B22 pistons and M20B25 (135mm) conrods, then modify the pistons by milling correct valve pockets, and you'll have a 2.5L M20B20 with a CR of 9.6

This is very professional advice BertjeConti, thank you very much. I assume that this was previously tested by someone and it worked?

Any potential problems with this modification? Excessive heat or likelihood of block cracking etc?

I guess this setup is never tested.
I just gathered as much information as possible about various M20 setups with parts of other bmw engines.

Problem with the M20B20 and M20B23 blocks rebore them to 84mm, there is probably not enough material to do it savely. (They say older blocks have more material)

The M54B22 pistons are designed for a aluminium block and need oil squirters for extra cooling, M20 blocks don't have oil squirters, but could be installed. If using these pistons in a iron block would give problems? Don't know.

The setup mentioned by me doesn't require block reboring or decking.

There are many other setups possible up to 2.8L, but require a 84mm bore. M20B20 have a 80mm bore.

Most safe solution would be getting M20B23 pistons and crankshaft.

If your M20B20 is a carburetted engine in good health, you could gain some horses by converting to EFI, and a more agressive camshaft would give even more HP.

a b23 crank conrods and pistons fit without and problem in your b20 block .. they are identical. You will need to get a set of oversize pistons and bore the cilinders accordingly.

I think a b23 engine as a package would be easier and cheaper

What works fine aswell is an eta engine with your head bolted on .. gives you a 2.7 stroker and all parts are just bolting on one another .. power should be 140hp with a single carb .. with a set of double webers you can increase that still

You can also get a set af double webers on your b20 engine .. that will give you around the same power as an original b23

In fact I'm considering triple 40 DCOE Webers at the moment.



Weber triple DCOE kit for BMW M20 2.3/2.5 engines

Comprises

1 x British made intake manifold
3 x Genuine Spanish Weber 40DCOE carburettors
1 x Weber rod linkage set
6 x Weber mesh filters
Studs, nuts washers and mountings.

The carburettors are supplied with the following calibration

Venturi 30mm
Auxilliary venturi 4.5
Main jet 115
Air corrector 200
Emulsion tube F11
Idle jet 45F9
Pump jet 40

This calibration will allow the car to start and run, and it is recommended that the carburettors be set up on a rolling road to achieve satisfactory results.

Excuse me butting in here, I spent a long time pondering an increase in displacement before deciding to stay entirely stock and collect lots of parts to build a variety of engines.

M20B20 bottom end
M20b23 bottom end
M20b25 bottom end
325i 885 cylinder head
Very rare 324td crank, this has the same throw as the 2.7 ETA but is forged rather than cast and therefore much stronger

All the parts are available for sale if required.

e21Keith wrote: Wed May 06, 2020 10:08 am Excuse me butting in here, I spent a long time pondering an increase in displacement before deciding to stay entirely stock and collect lots of parts to build a variety of engines.

M20B20 bottom end
M20b23 bottom end
M20b25 bottom end
325i 885 cylinder head
Very rare 324td crank, this has the same throw as the 2.7 ETA but is forged rather than cast and therefore much stronger

All the parts are available for sale if required.

I'm doing excactly the same, but that's not what the topic starter asked.
I'm trying to get the most out of a original M20B20, at the moment my old tired B20B20 is dynoed at 130hp with a good tuned EFI.
A fresh engine with 9.8 compression pistons and overhauled 731 head and motronic manifold should do even better.

I don't mind if the topic is slightly drifting towards other options of increasing power. Unless it is against the rules of the forum.

I'm definitely not going to go towards electronics. My car hasn't got any electronics and I want to keep it that way.

Of course, I'm spoiled.

But as soon as you drive, calibrated and so on, from the rolling road, you're off. The carbs I mean. And you won't have a way to adjust them without the rolling road and DCOE's... You keep adjusting them. If you are not technical, I would absolutely stay away from DCOE's.


So, lets' be realistic. What do you want and what can you maintain When you do something to the engine so that the heart itself is intrinsically capable of more horsepower is the easiest and what I would suggest for your situation. On top of that follows a list of things one can do to increase it even more but, the downside is, to more cost and more knowhow required. EFI brings some points of that list to a point where less knowhow can maintain it, to the cost of higher complexity.

I couldn't stand breaker points and the dizzy anymore. And I couldn't stand the carb anymore. So I built myself an engine that idles not very well, it seems to smell a bit, it makes a hell of a lot of noise, but above 4000rpm, it's sweeeeeet. But against all those aforementioned points.


I would suggest to list some pro's and con's the ideal car or engine does not exist, at least, not without Koenigsegg's Freevalve system. So it is really necessary to have pro's and con's clear in order to prioritise. And that process can, and should, take months in order to get to the point that you are really sure of what you are doing, otherwise it is destined to fail.

Amur73 wrote: Wed May 06, 2020 10:06 pm I don't mind if the topic is slightly drifting towards other options of increasing power. Unless it is against the rules of the forum.

I'm definitely not going to go towards electronics. My car hasn't got any electronics and I want to keep it that way.

Ok, no electronics, and what about the electronic distributor?

To be honest, if you really want to benefit those lovely webers, your engine needs at least a camshaft upgrade, and if you still have the 200 cast head with the small inlet ports, consider a swap to a 371 cast head, which has bigger inlet ports, but stil the same combustion chambers as the 200 cast head.

BertjeConti wrote: Wed May 06, 2020 10:29 pm

Amur73 wrote: Wed May 06, 2020 10:06 pm I don't mind if the topic is slightly drifting towards other options of increasing power. Unless it is against the rules of the forum.

I'm definitely not going to go towards electronics. My car hasn't got any electronics and I want to keep it that way.

Ok, no electronics, and what about the electronic distributor?

To be honest, if you really want to benefit those lovely webers, your engine needs at least a camshaft upgrade, and if you still have the 200 cast head with the small inlet ports, consider a swap to a 371 cast head, which has bigger inlet ports, but stil the same combustion chambers as the 200 cast head.

I am gathering ideas and opinions, asking experts and listening to everyone. I'm grateful for your input and advice.

Interesting topic. I have one question for Rob though, I read that you dont recommend to increase the bore of a M20 from 80 tot 84 mm. But the later 2.5 and 2.7 models use the 84 mm pistons. Is the design of the engine change for this specific engines? As they are still the M20 design.

Thegs wrote: Thu May 07, 2020 12:42 pm Interesting topic. I have one question for Rob though, I read that you dont recommend to increase the bore of a M20 from 80 tot 84 mm. But the later 2.5 and 2.7 models use the 84 mm pistons. Is the design of the engine change for this specific engines? As they are still the M20 design.

The 84mm bore blocks are different casting as the 80mm bore blocks, in 84mm blocks there is no open space between the cylinders, and in the 80mm bore blocks there is open space between the cylinders.

I've measured wall thickness of my '87 80mm bore block, which was aprox 6mm, if you bore this block to 84 mm, there will be 4mm cast iron material left, seems not that much to me.

However some say it can be done, there is more information about this in de E30 forums.

Older 80mm blocks should have thicker casting (they are heavier), but i can't confirm that by now.

It is a very interesting option now the good M20B25 and M20B27 blocks getting more rare and expensive.
A M20B20 block still could be found for little money, and then bore it to 84mm is a cheaper solution as a set of oversized M20B25 pistons.

(found on: http://mywikimotors.com/m20b20/#Tuning)

M20B20 Stroker

M20 series have been well-known for many years already. This is why there appeared lots of ways which make it possible to increase its capacity. The most common way is to use stroker due to the fact that the height of cylinder block is the same. If you want to upgrade your M20B20 and turn it into M20B23, all you need is to buy crankshaft, pistons, connecting rods and flywheel which are used in M20B23. You will have a chance to build engine with at least 150 HP.

At the same time you can also upgrade your M20B20 into M20B25. We decided to go even further and increase capacity from 2.0 liters to 2.8 L. First of all we need to bore cylinders up to 84 mm (3.3 in). We also need to buy M52B28 crankshaft, M20B25 Kat pistons as well as M20B20 Carb flywheel. Keep in mind that you should also replace the radiator as the old one will not be able to handle with such capacity.

If you want to gain maximum power, follow instructions which are given HERE: cams, porting, inlet, exhaust…

At the same time you need to have a clear understanding that after you boring cylinders up to 84mm, the walls of cylinders will be rather thin. This will reduce the lifespan of your engine. You should not expect your motor operate after 6,000 – 13,000 miles (10,000 – 20,000 kilometers) of mileage.