Update on 280SL / 3.0 performance engine

[Tom Colitt]

Here is an update on my 280SL / 3.0 engine rebuild.

I have built the first iteration of my 3-liter engine project using a stock 1970 280SE engine as the basis. My goal is to create a performance enhanced 280SL engine that you couldn’t tell visually from a stock engine, is as reliable or better than the stock engine and can be built at a reasonable cost.

I have increased the displacement mostly by increasing the engine stroke by 5mm using the stock crankshaft at a reputable shop here in Southern California that is known for their vast experience in doing this type of work. I had always planned to pull the engine apart again after my initial testing was complete, to fit it with oversize, lower-weight and lower-friction 3 ring after-market pistons, adjusted to the new compression height that I have now determined. As of now, I have had no problem at all with adapting the fuel injection pump to the new, higher fuel demands of the larger displacement engine. The resulting engine runs very smoothly (this may also be due to the fact that I balanced each individual piston and connecting-rod assembly) and has great torque. I cannot detect any differences from the smooth-revving characteristics of the stock engine. In my test Pagoda, the new engine was coupled to the taller (3.27) rear end gear ratio. These differentials commonly make a Pagoda, equipped with the automatic transmission slightly sluggish when accelerating from a standstill in second gear. With the increased torque of the new engine, the car pulls strongly from a standstill in second gear and revs as high as previously. When you start in first gear, the combination of the 3.0L engine and the tall rear gear ratio works so nicely and smoothly that it feels like it was always designed to work that way. Acceleration is naturally even better, but the first gear is actually very usable and the shift from first to second is smooth as well.

I will soon do some HP tests, so that I can compare the improvements between this first test engine and the next generation, for which I plan to bore the cylinders to the next repair size (To save on development costs, I had not done any work to the block except hone the cylinders and install new rings. This resulted in a slightly larger than allowable piston the bore clearance and ring end gap). The new, custom pistons will be lighter weight and lower friction. I will also rebuild the head and fit the Euro specification camshaft in this next iteration.

Regards, Tom Colitt
ClassicAutosLA

[Paddy_Crow]

I don't understand. How did you increase the stroke using a stock crankshaft? Did they reduce the rod journal diameter to increase the throw?

[Tom Colitt]

Yes, that is one way to increase the crank offset, but it would result in a smaller big-end journal and one would now have to use different connecting rods as well. The better option, (since I come from an engineering background, this initially caused me some concern) which sounds very invasive, is to actually build up the diameter of the crank journal and then be able to offset grind the journals in the new "location" using the stock bearing size. The crankshaft is then heat treated to relieve stresses from welding, any distortions are removed and the bearing journals are re-hardened. This procedure has been used by reputable race engine builders for many years with great success on engines that have even higher specific power output (HP/liter) than the M130E.

Regards, Tom

[Paddy_Crow]

I shudder to think of all the potential imperfections that could be induced in such a process, which could be an issue with long term durability (high cycle fatigue).

[Benz Dr.]

Did you use the stock connecting rods? Something tells me that the piston would be the same 5mm lower in the bore at TDC as it would be at BDC due to the 5mm off set. Or, did you change the connecting length somehow? There must be some optimum amount you can go before the rods would start to have clearance problems at the bottom of the cylinder bore.  One way this could be done is to change the position of the piston pin 5mm lower but this would require custom made parts. Still, all in all, a neat project because it's all internal.

I ran into this piston height in the block problem before on several different engines. The 921 and 928  190SL engines are the same stroke but the 928 has shorter connecting rods by about 3mm. If you try and use 921 pistons in that engine they will pop out of the block. I got a set of 220Seb rods mixed up with 230SL rods once and the guy said the pistons were all out of the block, as he put it.

[Tom Colitt]

Dan

You're right about the stroke. My 5mm stroke increase comes from a 2.5mm increase in crank offset. This is the maximum amount one could do without getting interference at some point, either the lower end of the piston skirt hitting the crankshaft weights, but primarily, the stock connecting rods will hit the inside of the crankcase walls. I did have to do some mild work on the lower (aluminum) half of the crankcase for clearance.

Paddy: I agree with your concern. Also, I was somewhat concerned about losing the ductility and other qualities of the forged MB crankshaft through the welding process (oxidizing, introduction of high temperatures, the possibility of changing the composition of the alloy, etc). Like I said. In the end, I was convinced by the long term success of the process that has been shown over the years. The finished crank journals showed no trace of any inclusions or even pits and were polished to the same mirror smooth finish as you would find on any re-ground crankshaft.

Best Regards, Tom

[waqas]

Hey Tom,
Very cool project. Can we expect a neat write-up in Pagoda World (with pictures!) when your project is finished? (or close to finished, since these projects tend to proceed asymptotically towards completion)

Also, did you do anything to enhance engine cooling? (to handle the excess heat inevitably produced)

In any case, thanks for sharing!

[Tom Colitt]

Hi Waqas

Thanks. I really like the project too. Especially, since I was able to do it with all MB components so far (although I am planning on changing/ improving? that on the next generation :-)

I also am very happy with the results so far and have just decided to go ahead and install the 280SL Euro camshaft on this 280SE head very shortly, before I even take the engine block apart again for completing the short block. That way I can run some comparative HP tests between the various modification stages....

As far as the cooling is concerned, I believe that most of the cooling issues that are reported on Pagodas are associated with some part of the cooling system not being up to specs. I will concede that an AC equipped car, sitting in traffic, idling, on a hot day in the Arizona dessert (they have traffic, right?), runs at the limits of its cooling capabilities, but I have no indications that my increase in displacement/HP has, so far, increased the demands on my cooling system. We still are having a pretty warm summer here in Southern California and so far the temperature does not much exceed the 180 degree mark. Granted, I do not currently have the AC installed, nor even the AC condenser that blocks flow of cool air to the radiator.

I welcome any more questions from people who are interested. While I've done a lot of research on the project, more questions will only give me the opportunity to address and work out any issues that may come up...

Regards, Tom

[Benz Dr.]

Are you getting a full 3 liters from this conversion? What compression ratio do you expect?

[seattle_Jerry]

I was watching an old episode of Top Gear last night. They were reviewing a tuner shop new SL... Some AMG equivalent.

They kept the V12 block and threw everything else out and started over....new heads, pistons, etc.

So whens the new head coming

[Tom Colitt]

Yes. The displacement is just over 3.0L
Of course, the compression ratio ending up too high was my main worry with this engine. My early calculations showed that, even with my modification of the stock pistons, the ratio would be in the low tens, even using what appears to be a low compression head (Epsilon symbol and 9.5 on head is omitted and the combustion chamber is clearly enlarged vs. the regular 9.5 late model 280 head) From Joe Alexander's cylinder head chart it appears that this head casting number 130 016 3201 should be a 9.5 ratio head, but this one clearly has not been modified and as far as I know came off a US spec. 280SE. I would like to know which engine this was from because apparently US version 280SE were supposed to come with the same 9.5 ratio as a 280SL....

Anyway, after the modifications so far, I am getting compression readings between 135 and 145psi (remember, I have not yet bored out the cylinders, so I expect those numbers to be just a bit higher in the final version. In other words, they are not as high as I had feared, but right where I would want them to be, with a little room to spare for a skim off the cylinder head, if needed.

Regards, Tom

[Benz Dr.]

I can't imagine 135 PSI even on that stroker engine to have very much more power than a egular 280 engine with 175 PSI but I suppose the only way to tell would be on a dyno. Using emprical data, we can conclude that something would change but that's hard to say until you're done.

[Tom Colitt]

Hi Dan

How are you reaching that 175psi on a stock 280Sl engine? In other words, is that the maximum reading that you can attain from each cylinder on your compression gauge?

Tom

[Benz Dr.]

Actually, it's a 250SE engine and they're all in the 175 - 180 range. This the most I can get using a standard compression gage. The actual running compression* would be maybe 110 PSI. I milled the head only once about .010'' from a stock unit. The block was decked about .025'' to get the pistons slightly above the parting surface. All the ports were matched and the cumbustion chambers were polished a bit. The runners going into the head were cleaned out but not opened to any great extent.
This engine has the early exhaust manifolds, visco fan clutch, late ribbed oil pan and a distributor from a 300SE. I also added the oil cooler which wasn't on the engine at the time.
I used a 230SL cam that I avanced about 5 degrees to match the euro 280SL specs as closly as I could. The pistons are .050mm oversize.
I also used a 280SL clutch and pressure plate in front of a ZF 5 speed trans. Everything runs with some sort of synthetic oil ( engine, trans, diff and steering ). I get about 10KM per liter on mid grade fuel.

* Running compression is lower than total or maximum compression figures taken from a tester or gage. If you run your engine with a compression gage on one cylinder you will find that it runs about 40% lower ( at maybe 110 PSI ) than your maximum compression reading. This has to do with valve overlap. If I ran my engine at a maximum 175 PSI it would spark knock and fly apart quickly.
During compression testing the very first pump and the reading on the gage at that point will be very close to running compression on our engines. Everything else above that is what's stored in the gage due to the check valve on the tester.

[Tom Colitt]

Dan

What I was getting at with my question was, what is your procedure/ revolutions, etc. for doing a compression test, so that we can see whether our numbers can be compared side by side. The numbers I quoted were achieved after 8 revolutions of the engine. If I continue the test, the compression continues to built up to a maximum of 180psi after 18 revs and as high as 200psi after 22 revs. Also, don't forget that I have not yet rebuilt the cylinder head and I am using the original (modified compression height) standard size pistons in a block that has just been honed and fitted with new standard size rings. The theoretical compression of this modified engine came in at over 10 to 1 and so at this stage I am glad that the compression did not turn out to be too high. Once I have fitted the custom pistons, I always have room to raise the compression again, if needed, by taking some material off the top of the block or off the head....

Regards, Tom Colitt
ClassicAutosLA

[Benz Dr.]

Oh, OK. Well, I suppose I spin it about 8 times or until it doesn't go any higher. I think most people do this as they're looking for what the maximum number is.
Spun until it stops climbing, it runs around 175 - 180 PSI which is pretty good for one of these cars. Most won't go higher than 165.

[mdsalemi]

Don't the instructions (listen to the manufacturer, right?) for most compression gauges tell you to crank the engine 6-8 times?  That's what I've seen.

What are you getting when you do it more?

There's also "dry" and "wet" tests.  If you keep on cranking the engine for 20 times or more, doesn't your "dry" test kind of come, by default, a "wet" test with all that un-burned fuel in the cylinder now?

[Benz Dr.]

No, you pull the fuse to the pump so no fuel gets into the cylinder.
You can only get so much and then it goes to a max amount. I don't see that much difference between hot or cold but there can be a difference wet or dry on worn engines.

[dixy2k]

Hi Tom,
I hope this info helps in expanding your research horizon:


The AMG 3.6 M104 was rated at 276 horsepower (206 kW) at 5,750 rpm and 284 foot-pounds force (385 N·m) of torque at 4,000 rpm using the HFM engine management system.
The boost in power was obtained by stroking the 2,8 litre M104 using the crank from the 350sd engine.


http://en.wikipedia.org/wiki/Mercedes-Benz_M104_engine

[dixy2k]

One more thing on M130 from wikipedia again.

The M130 was the ultimate variant of the ‘mid sized six’ with a capacity of 2,778cc gained by increasing the bore to 86.5mm from the 82mm of the 2.5 litre engine while retaining the 78.8mm stroke. This represented the maximum practical enlargement of the engine given the limitations of the engine block as evidenced by the deletion of water passages between the cylinders.


http://en.wikipedia.org/wiki/Mercedes-Benz_M130_engine

[Tom Colitt]

Hi Dixy

Thanks for the info. I agree that the bore could not really be increased beyond the 2nd repair size. And the stroke increase of 5mm is about as far as you can go too, especially with the stock connecting rods. I'm not sure if the AMG 104 engine has much (if anything) in common with the M130E engine, however.

Michael. I did try going beyond the recommended 8 engine revolutions and got as high as 195psi after 20 revolutions and one cylinder even went to 200psi after 22. I'm not how this number is useful or translates into information that means anything to anyone. That is why I was happy to find that the engine would not detonate at those relatively high numbers, obviously due to the fact that the numbers are lower at smaller numbers of revolutions (i.e. one, when the engine is running...).

[dixy2k]

Hi Tom, I don't think M104 has much in common with M130, however the text was about using a diesel engine crankshaft in that M104. By analogy I thought there was a different engine which would be compatible (crankshaft I mean) with the M130.
Usually Mercedes engines are an evolution over the previous model. Lot of specs remain constant over time, unless something drastic changes, like a V6 engine.
I understand that M110 engine block is very similar to the M130. If that theory holds true, Maybe M104 has something in common with the M130, so the crankshaft would hopefully fit.
It does not automatically mean it is a perfect fit, there will be many other concerns, but just an idea worth exploring if the parts are available to you.

All I am trying to do is to give you an idea, assuming the risk of being totally wrong on the matter.


By the way, if my math is right that 5mm increase in stroke would give you about 2957cmc of displacement. If clearance is a major concern with a longer stroke, then the crankshaft from the 3.5 L6 diesel is out of the question, but the one from the 3.0 OM603 or even M104 would fit. Again, I'm just guessing here.

[Benz Dr.]

The M110 engine and the M130 engine are very different. I've already thought of that idea and it won't work. I didn't check the crank but it's the same displacement so I didn't see any clear advantage over what's already in the engine.

[dixy2k]

Hi BenzDr
I didn't imply to swap the crankshaft from the M110 into M130, but rather the one from M104. If it works, which I have no clue.
My dream was to swap the head from the M110, but I think we all know that is just impossible.

[wbain]

The M104 is a variant of the M103 used in the W124, W126 and W102. The M103 is a SOHC 2.6, 2.8 or 3.0 engine while the M104 is a DOHC. The M104 DOHC uses a more advanced engine management system than the M103 which uses the CIS-E.