Can a lower compression 60x be built? - PeachParts Mercedes-Benz Forum

trik · #1 06-16-2004, 06:22 PM

Allright, I finally found a decent forum with lots of info and enthusiasts for Mercedes Diesels!

After reading too many Cummins websites, I see how a lower compression diesel can make some serious power when fuel and boost is turned up. At 22:1, the Mercedes is too close to the edge for me to tinker with a lot. So I was thinking of how to drop the compression ratio down. Well, I can't find the bore and stroke specs on all the 60x motors easily. I do know that the 601 went from 2.0 to 2.2 and the 603 had a 3.0 and 3.5. I have to assume that an increase in stroke occurred in these expansions. So, unless block deck height changed or the combustion chamber changed, the longer stroke cranks needed shorter connecting rods. Well, I know dirt about these motors, but if bearing sizes were kept the same, can the stroked connecting rods be coupled with the smaller cranks to drop the compression ratio? It may be too drastric of a change, but I was hoping to find out if it was possible. If anyone has any specs, please share!

leathermang · #2 06-16-2004, 06:31 PM

I don't know anything....
but a shorter piston would be another way to decrease the compression ratio.....

#3 06-16-2004, 06:41 PM

...or a thicker head gasket. I don't know these are available for a Mercedes, but VW sells head gaskets in three thicknesses. IIRC, the difference between each one is about half a compression point.

Some of the TDI guys have been removing their glowplugs to reduce compression. This is fine on a TDI if the outdoor temperature is above 30 degrees, but it wouldn't work on a Mercedes.

Add an intercooler, and you will have room to tinker without having to reduce compression.

trik · #4 06-16-2004, 06:41 PM

Well, I read a little info on the 2.0 and 2.2 and found 87x84 for 2000cc and 87x92.6 for 2200cc. If this is correct, the stroke difference is 8.6mm, which means a 4.3mm shorter rod for the 2200cc (all other things the same). 4.3mm constitutes 102.2 less cc. This part, I'm not sure of, but I get a ratio of 10.4:1 using the 4.3mm shorter rod with a 2000cc crank. That's too low for a diesel, so probably couldn't work. Can anyone back up my calculations? Is my info correct?

As far as shaved pistons, I don't know if you can buy new pistons for a Mercedes with less compression.

leathermang · #5 06-16-2004, 06:45 PM

I guess after you get the compression figure down you could put spark plugs into the glowplug holes.....

Hatterasguy · #6 06-17-2004, 09:49 AM

The only modification I have found for the 603 is an intercooler kit made by Mosselman, it cost $2,000 and will need some modification's to work on US cars. Unfortunitly their is no aftermarket for old MB diesel.

TonyFromWestOz · #7 06-17-2004, 10:09 AM

Quote:

Originally posted by trik
Allright, I finally found a decent forum with lots of info and enthusiasts for Mercedes Diesels!

After reading too many Cummins websites, I see how a lower compression diesel can make some serious power when fuel and boost is turned up. At 22:1, the Mercedes is too close to the edge for me to tinker with a lot. So I was thinking of how to drop the compression ratio down. Well, I can't find the bore and stroke specs on all the 60x motors easily. I do know that the 601 went from 2.0 to 2.2 and the 603 had a 3.0 and 3.5. I have to assume that an increase in stroke occurred in these expansions. So, unless block deck height changed or the combustion chamber changed, the longer stroke cranks needed shorter connecting rods. Well, I know dirt about these motors, but if bearing sizes were kept the same, can the stroked connecting rods be coupled with the smaller cranks to drop the compression ratio? It may be too drastric of a change, but I was hoping to find out if it was possible. If anyone has any specs, please share!

Reducing compression ratio will have downsides too:
* - Hard to start, heat of compression will be lower, resulting in need to glow longer.
* - lower efficiency, higher compression ratio is diesel's advantage over SI engines.
Why reduce compression ratio, only to have to pump air into the combustion chamber to make it work again?

trik · #8 06-17-2004, 03:19 PM

Lowering the compression ratio is not for those who want better fuel economy. It is for those who want to introduce more boost and fuel into the engine for more power. The cylinder pressure rises dramatically with a little more pressure and heat from turning up the turbo and this is amplified by the compression ratio. Cummins can make big numbers without detonation due to their lower compression ratio. Mercedes will grenade if pushed to hard by the turbo and extra fuel. It is much like slapping a turbo on a honda and an older mustang.

gsxr · #9 06-17-2004, 07:48 PM

I'd leave the CR alone and seriously investigate the intercooler method. That should be good for a safe 20% power gain. Beyond that you will need massive internal modifications that cost way more than it's worth. A guy posted details of how he pumped up a 617 a few years ago to somewhere near 200hp but he also said he'd NEVER do it again, it took hundreds of hours labor, and a disgusting amount of money (nearly $10k, IIRC).

Hatterasguy · #10 06-17-2004, 07:52 PM

What about putting a 3.0 crank and connectiong rods into a 350 block? It wouldn't be a rod bender anymore at least.

gsxr · #11 06-17-2004, 07:59 PM

No need. Just put in the redesigned (stronger) 3.5 rods in the 3.5 block and it will live a long and happy life. It's a low-RPM stump puller though, not the rev-happy powerhouse (well, relatively) that the 3.0L is. I still think intercooling the 603.96x is the only way to go. That assumes you have already gotten the full 148hp that it came with from the factory - proper cam & IP timing, good injectors, full boost and fuel enrichment, etc... easy way to test is by checking the 0-60 time against factory specs (with stopwatch, GPS, etc to ensure accuracy.)

boneheaddoctor · #12 06-17-2004, 08:21 PM

Has anyone given thoughts to custom Connecting rods? with centers a tad shorter? should be able to be done By Eagle, Crower, Carrillo or one of the aftermarker guys as a one off. Could get lower comression that way with stock pistons. Maybe studs to replace head bolts (stronger) and get it O-ringed or use copper head gasket............where there is a will there is a way.

trik · #13 06-18-2004, 01:31 PM

VeeDubTDI and boneheaddoctor's ideas of thicker gaskets and custom rods are definetly one good way. gsxr's idea of intercooling is a must. All good info. A slightly thicker head gasket might drop the count to 21.5:1 and still be safe for holding pressure. Custom rods would be ideal and if I get serious about this, it will be the way I may eventually go. Anything force induced should have a way to drop the intake charge temps. An intercooler works best and for a little more measure water injection 6" before the intake manifold. Now, VeeDubTDI had an interesting idea about removing the glow plugs to drop compression. Obviously this is not for building a daily driver. The 2.2 or 3.5 rods plus a 2.0 or 3.0 crank is not feasible if my specs and calculations are confirmed. Just thought I'd summarize for those who search and find this.

psfred · #14 06-18-2004, 08:43 PM

Trik:

Sorry to rain on your parade, but the 60x engines are the "other breed" of diesels, those that have high mechanical compression and fairly low boost.

You are not going to find "low compression" pistons, and you also do not want to manufacture a set -- stock are $2500 a set. There are no, and are never going to be, aftermarket pistons for such low production number engines.

What you should think about is the fact that these engines produce quite a bit of horsepower on quite small displacements with very simple boost systems. You can up the boost and generate considerably more power (so long as you can also get more fuel!), but what for? My 300D does 0-60 in roughly 9 sec and goes 130 mph, and gets 31 mpg doing it (less if I floor it all the time). I did the math, and by displacement, the 603 turns out more hp and torque than a GM Vortec engine!

You trade high revs for that low compression, long stroke engine -- rev limit on the 60x engines is around 5000 rpm, and they will go faster at the expense of durability (normally 500,000 miles and more on the bottom end -- in fact, other than the bent rod problem in the 3.5L, I've never heard of one failing short of being run out of oil!).

The 601 is a four cylinder, the 602 is a five cylinder, and the 603, 606, and 607 engines are sixes. Bore, stroke, and pistons are identical except for the non-turbo engines (no oil cooling passages in the pistons). Turbos have oil jets, non turbos don't, I believe. 606 and 607s are DOHC engines rather than SOHC, with the injection port in the center. Rods are common on all engines, I believe. Certainly the crank throw is the same.

Make sure you have an EGT gauge if you overboost, else you risk roasting something or melting the pistons!

Note that the different thickness head gaskets on the VW/Audi/Volvo engines are to compensate for piston projection above the block. If you have "tall" pistons, you cannot lower the compression by using a thicker gasket.

Peter

boneheaddoctor · #15 06-18-2004, 11:08 PM

Quote:

Originally posted by psfred
Trik:

Sorry to rain on your parade, but the 60x engines are the "other breed" of diesels, those that have high mechanical compression and fairly low boost.

You are not going to find "low compression" pistons, and you also do not want to manufacture a set -- stock are $2500 a set. There are no, and are never going to be, aftermarket pistons for such low production number engines.

What you should think about is the fact that these engines produce quite a bit of horsepower on quite small displacements with very simple boost systems. You can up the boost and generate considerably more power (so long as you can also get more fuel!), but what for? My 300D does 0-60 in roughly 9 sec and goes 130 mph, and gets 31 mpg doing it (less if I floor it all the time). I did the math, and by displacement, the 603 turns out more hp and torque than a GM Vortec engine!

You trade high revs for that low compression, long stroke engine -- rev limit on the 60x engines is around 5000 rpm, and they will go faster at the expense of durability (normally 500,000 miles and more on the bottom end -- in fact, other than the bent rod problem in the 3.5L, I've never heard of one failing short of being run out of oil!).

The 601 is a four cylinder, the 602 is a five cylinder, and the 603, 606, and 607 engines are sixes. Bore, stroke, and pistons are identical except for the non-turbo engines (no oil cooling passages in the pistons). Turbos have oil jets, non turbos don't, I believe. 606 and 607s are DOHC engines rather than SOHC, with the injection port in the center. Rods are common on all engines, I believe. Certainly the crank throw is the same.

Make sure you have an EGT gauge if you overboost, else you risk roasting something or melting the pistons!

Note that the different thickness head gaskets on the VW/Audi/Volvo engines are to compensate for piston projection above the block. If you have "tall" pistons, you cannot lower the compression by using a thicker gasket.

Peter

A popular way to get over 300 reliable HP out of a GM 6.5 diesel is replacing 22-1 compression pistons for 18-1 pistons intercool it crank up the boost and turn up the fuel...............Peninsular (spelling) Diesel does it.

putting ever so much shorter rods to drop the compression does nothing that will hurt the power band. It just lets you safely pump so much more fuel and air into it.

Your stroke remains the same as the crank is not afected.

Head gaskets are a common way to fine adjust static compression ratios on turbo gasser cars...............