Hi all,

I'm in the process of building a 3.4 kompressor engine based around the m104.980 block, and I'm going to need to reduce the piston height in the bore by a fair bit. Ideally I would like to machine a safe amount of metal from the top of the pistons, then use a decompression plate to take it the rest of the way.

Pics of my problem!

This is the block of a normal m104.980, the piston sits .6mm above the deck in standard form:

Now with the new crank/rod combo the piston is sitting 3mm above the deck:


The blower setup I will be using:



Now for my questions!

-Since the engine will be boosted by up to 1bar of pressure, what compression ratio would I need to achieve?

-How much can I safely machine from the crown of a standard piston?

-The normal m104 piston is .6mm above deck, how much below deck should it sit to achieve the ideal compression ratio? .4mm maybe?

Thanks in advance guys!

__________________
87 w124 zender 3.6 - 3.0 kompressor in progress!
96 w124 e300 diesel - slowly being modded
98 w208 230 kompressor - m103 testbed SOLD.
96 s124 om606 superturbo diesel 508bhp

why not use a thick gasket made by gaskets llc.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Sorry, should of mentioned that I'm in the uk.

I could use a thicker gasket, but what thickness should it be?

__________________
87 w124 zender 3.6 - 3.0 kompressor in progress!
96 w124 e300 diesel - slowly being modded
98 w208 230 kompressor - m103 testbed SOLD.
96 s124 om606 superturbo diesel 508bhp

The height of the piston protruding from the block should be about 0.8mm or so. (You need to find this specification to be sure - 0.6mm sounds a bit low to me - but I've never taken a M104 to bits before)

3mm is really wrong - what sort of connecting rods do you have fitted to get that?

I don't think it is a good idea to remove much meat from the piston crowns to change the compression ratio. Not only do you have to make a large volume change but the engine will probably be running hotter and dealing with greater pressures - weakening isn't a great step forward in my opinion...

Here's a link for the effective compression ratio calculation =>

Effective Compression Ratio Calculator | GTSparkplugs

And here's some advise (OK for an Alfa) saying about 11:1 effective compression ratio is about enough!

Turbo and Supercharged Engine Compression Ratio Calculator

I've seen threads where people have said they have added turbos to M102s and such with 0.5 to 0.8 bar boosts but these people don't seem to stick around for long!

A M104 has a 10:1 compression ratio which means about 4PSI / 0.27 bar is about the most that will possibly work with petrol to give you an effective compression ratio just about 11:1 (this might be too much)

You can calculate the additional volume in the cylinder if you want to lower the compression ratio by fiddling around with the formulas in this thread =>

Does anyone have any nifty ways of measuring the true volume of an engine's cylinder?

Alternatively this might help

Not2Fast: Compression Ratio Calculator

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Thanks for the links, I'll have a play around with those.

The .6mm was measured before the engine was taken apart, But I'll try to find the true spec for it.

The engine is fitted with the crank from a c36 (350sd), 143mm honda h-beam conrod's, with the standard m104 pistons. Unfortunately I cant fit shorter rods or the piston will hit the crank , I already had a clearance problem with the under piston oil cooling jets!

I was thinking of using a decompression plate to increase the block height to where it needs to be, I'm trying to avoid a solid copper headgasket though as they seem to be very hard to seal properly.

__________________
87 w124 zender 3.6 - 3.0 kompressor in progress!
96 w124 e300 diesel - slowly being modded
98 w208 230 kompressor - m103 testbed SOLD.
96 s124 om606 superturbo diesel 508bhp

I don't know if they do this type of modification work but Roe Engineering in Fleet used to be a good place to visit about 20 years ago - they are the only people who I can think of who are close(ish) to you - perhaps they can help.

Timing chain with a raised deck solution will be interesting.

The main design requirement you need is to work out the effective compression ratio that you are aiming for and then calculate the additional swept volume you need and then remove the area of the bore you have to get the height...

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

You might prove me wrong on this but most likely you are going to end up with a big pile of broken parts. The 3.6 engines have the wrist pin moved up into the oil ring land to get the piston height correct and keep the rod ratio correct. The crank is machined and the pistons are cut for clearance.
If you mill the top of the pistons that much and add 1bar of boost then they will fail.
You could go with a copper headgasket but as mentioned to do this and get the compression ratio where you want it then you are going to have to go a lot. You would have to mill the cam sprockets to make them adjustable for getting the timing correct. It is possible that you could retard them one tooth and be close enough.
As far as what compression ratio to go with as Stretch mentioned you can go with those formulas. That is a good indicator for running pump gas. But remember that the higher the compression the lower the boost needs to be to make hp. You should not have as much trouble with knock on this project due to the fact that the boost is linear. So you are not making big boost at low rpms. It also depends on intake temps, timing, quench, etc.

Thanks for the info, I've got a 3.6 lump here but didn't like the idea of the wrist pin being in the ring land, or the thinner cylinder walls. The rod/crank combo I'm using doesn't have any clearance problems, but it is close.

With the cam sprockets I was thinking of drilling a second set of bolt holes like amg did on the 3.6 exhaust cam sprocket, once the cams are timed with the crank I should be able to mark where they need to be. I hope!



I think I go with the advice and keep the pistons as they are. Has anyone tried using 2 head gaskets, either side of a steel plate to give more block height? Any pro's and con's with that idea vs a copper head gasket?

Thanks guys.

__________________
87 w124 zender 3.6 - 3.0 kompressor in progress!
96 w124 e300 diesel - slowly being modded
98 w208 230 kompressor - m103 testbed SOLD.
96 s124 om606 superturbo diesel 508bhp

Spacers/thicker/multiple head gaskets tend to effect the combustion dynamic in the cylinder head...
New pistons or shorter rods are the best way to lower compression.

You'd be surprised how much power you can make a .5 bar and 10:1 CR.

BMW runs 10.2:1 CR on the production N54 and N55 motors with .6+ bar boost.
Dinan cranks the boost up to .95 bar and gets 400+ HP and 440+ torque.

Most important, regardless of CR is that you have optimum control of your AFR's and ignition if you are looking at very high boost.

Ed A.

__________________
http://i19.photobucket.com/albums/b1...c/GOWIDE-1.jpg
1971 280SL ROADSTER
1988 300CE TWIN TURBO WIDEBODY
1994 E320 CABRIOLET
1999 C43 AMG
2005 G55K AMG
2008 CLK63 AMG BLACK SERIES

Hi Ed,

The rods are about as short as they can go without hitting the crank, they are 143mm h-beam type ment for a honda.

400hp is what I would like to see out of this project, if that can be achieved with 10.1 cr I'd be happy.

I've got an emerald standalone ecu for the engine management, with a ford edis6 coil pack setup to give a decent spark.

__________________
87 w124 zender 3.6 - 3.0 kompressor in progress!
96 w124 e300 diesel - slowly being modded
98 w208 230 kompressor - m103 testbed SOLD.
96 s124 om606 superturbo diesel 508bhp

If you've done a compression and leak down test to assure that all cylinders are within spec and cleared up any vacuum leaks then your engine should handle .5 bar @ 10:1 CR. A proper fuel/ignition control should get you close to the 400BHP you're trying to attain without worrying about your engine coming apart.
The critical component in any engine is the AFR under boost.

Ed A.

__________________
http://i19.photobucket.com/albums/b1...c/GOWIDE-1.jpg
1971 280SL ROADSTER
1988 300CE TWIN TURBO WIDEBODY
1994 E320 CABRIOLET
1999 C43 AMG
2005 G55K AMG
2008 CLK63 AMG BLACK SERIES

W124 Build thread coming soon!

__________________
87 w124 zender 3.6 - 3.0 kompressor in progress!
96 w124 e300 diesel - slowly being modded
98 w208 230 kompressor - m103 testbed SOLD.
96 s124 om606 superturbo diesel 508bhp

That looks beautiful

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

For 400hp you can use the stock m104 980 engine with just a thicker head gasket. I'm currently running ~480 hp on a bone stock m104 980 motor with 1.0bar boost and a compression ratio (static) of ~9.2-9.3:1 with 2.64 mm head gasket and that's on pump gas .

As to decompressing the setup you are building, I'd do it (apart from custom pistons) using a decompression plate with two head gaskets, that way you wouldn't weaken the pistons.

__________________
190E 3.0-24v (M104 980) turbo @ 0.8 bar
1/4 mile: 2.483 / 13.540 / 175.17 km/h (street tires)

hi, i am thomas and i own a w124 with the same motor 104980 stock. How the project is going? i am thinking of installing a kompressor and i would like to know if this is possible and which are the difficulties and moddifications that must be done.