Fuel economy & power & lpg

[craigb]

Just an update now that I seem to have my car sorted, last 2 fills have been 17.2 and 16.8 l/100km which has involved bumper to bumper commuting and the occasional 'blat' when I feel the urge. I filled this morning and have a sprint tomorrow, so it will be interesting to compare 'track' mileage! Of course that is on lpg and I love the bill after filling up!

One interesting point,  last week we had a bit of a workshop day preparing other cars that will run tomorrow and I offered to take some of them out for a spin, particularly the one that was saying the 280 was a 'gutless wonder' (don't you love that when people make those sort of judgements based on driving one car of possibly dubious condition!). My car seemed to be running fine, but just didn't have the same top end pull I had become used to. I remembered the lpg mechanic saying that it will run better if you can keep the temp up toward 100, and i put the hotest thermostat in that I could at 87 and removed the fan (which may need to go back in warmer weather). Whilst my car was well and truly warm when I was thrashing it, the guage was only at 80 at first. We had to wait for some lights etc and then the temp was up to 90 or so, put my foot down and it was away with the sort of power I had got used to. So based on that I would say temp is very important to lpg. While I will admit the 280 is no powerhouse, particularly pulling a W116 around, I think a lot has to do with the tune of the car and being prepared to get into those upper rev ranges.

So just raising the concept of getting your car to run at its optimum, which is not only tuning but also what temp your car is running at. I have had cars in the past where people have chucked away thermostats, probably due to a blocked radiator, had to replace the radiator anyway and left the thermo out, and these cars are never going to run at their optimum and you are never gonna get your best fuel economy.

And of course beware of non original restrictive mufflers which by far is what killed my car in both power and economy.

[oscar]

I've found the last couple of days with the warmer weather mine is not only much easier to start but gets to that optimum temp quicker.  But overall, when the engine is completely hot, it's really responsive.  Now I don't know about my thermostat but I can feel the rad get hot up top when the engine gets to about 80degC, but remembering mine doesn't have a mechanical rad fan the engine keeps getting hotter until the dual electric fan comes on.  The thing is the fans come on at about 100degC.  I swear, whilst I thought that might be too high, the engine performs really well.  The temp will drop to about 90 before the fans cut out.  Of course this is all on petrol rather than LPG but goes to show how important "operating temp" is.

Back to tuning, couldn't agree more and rather than start another thread, one of you guys from Adelaide (Andreas or Bandolero) asked sometime ago about power and camshaft timing and using offset woodruff keys.  The beauty of the M110 with DOHC being that intake and exhaust can be timed separately.  So here's some food for thought.  Is there still room for improvement on yours Craig.

From a mercedesshop thread :

I have a 1981 w123 M110 280CE and I would like to share some performance mods with u guys, case anyone feels like trying them.
A few years back when this was my daily driver I needed to increase the engine's top end pull, the M110 is a powerful unit considering it small capacity of 2.8L and since my car had rear end ratio of 3.58 I was in real need of top end revs.
So I ordered the offset cam pins from the dealer, those pins come in 2deg, 4 deg, and 5 deg offsets and they connect the cam gears to the cam.
Usually they r used when work is done on the head to reset the timing chain to specs, but in my case purpose was to shift the power band.
First attempt: I advanced both intake and exhaust cams by 4 degs, and boy did I get low end torque ok I lost even more top end as now revs hardly moved beyond 5800, but the low end was tremendous
I mean and I am sure of this, that any one will be stunned by the torque from 1000 to 4500 rpm range, flooring it in 3rd mid corner gives one big drift. First became almost useless as most of was spin.
Unfortunately it turned out that the small autobox on the w123 can't handle all that torque, I broke a gearbox every 10 days, I swear I went thru three boxes in one month. In the end I had to change the setup. After all even with new internals the gearbox wouldn't last more than 10 days.
Attempt 2: I retarded both cams by 4 deg. Now I had zero low down, I mean below 3000 u need to shift into first to see any movement, by 4500 u feel some power but at 5500 it feels like a turbo has kicked in and the power keeps coming all the way to 7400 (my cut out). Fromm 5500 on the engine is so smooth and so powerful, u don't get spin as its HP and not torque but when overtaking cars once u go past 5500 u would think cars have braked as u don't feel the push but see ur self moving a lot faster than the cars around u.
I know most of u would think I am exaggerating, but tell me how many m110 w123s u know of that can keep revving all the way to 7300 in fourth and clocking 235km/h??
I remember I once raced a w124 320 E from 150km/h on to max, we were equal from 150 to 170, then from there I pulled with ease all the way to my top speed of 230km/h.


in the end though, top end ended costing me lots of fuel as u always had to kick down to have the car moving, so i switched to a 2 degs retard setup, it was ok but not that gr8.
Also my engine had taken a beating with all that over reving from the original redline 6500 to my new 7400. oil consumption increased drastically in the end, and the fact that i ran the car with no filter during winter months didn't help at all.

[koan]

The section that "oscar" quotes from the Mercedes shop forum makes sense, all to do with where the piston is when the intake valve closes and what RPM the engine is doing, con rod length comes into it as well.

But I'm a bit surprised a few degrees this way or that makes such a big difference at low rpms.

This wikipedia article explains what's going on and if that's not enough try this article by Jeffrey Diamond.

Happy reading.

koan

[craigb]

Very interesting reading, and I might have to read it a few more times to properly absorb it! So does anyone know how long my rod is without pulling the motor apart?

John Green was telling me once that on his M110 rally car, he shifted a cam one tooth (can't remember which one and what direction) and gave significantly more power but crap economy. Andreas and Bandolero where there and that may be what is being referred to.

[koan]

So does anyone know how long my rod is without pulling the motor apart?

Have a look at job 03-313 "Repairing and squaring connecting rods" for your engine.

The figure given for 280 looks a bit odd, 130.050mm to 131.950mm almost 2mm tolerance which sounds a bit broad, the tolerance on a 450 con rod is 0.1mm. I'd guess at a 280 rod being 131.00 +- 0.05mm.

Maybe the correct figure is hidden in a late paper manual somewhere.

koan

[oscar]

I read those links koan the day you posted them and enjoyed the content and whilst the formulas were a bit lost on me it led me on for two nights of googling other pages about cam timing and compression ratios and high octane fuels to stop detonation in high compression motors and skimming heads and a bunch of other things in conjunction with the above like forced induction.  I've got no exact plans how I'm going to achieve more power but I want to experiment.  Cam timing will be one of those variables to change once the theory is concrete in my head.

I'll look in my books tomorrow and see if I find anything different in the conrod length though I doubt my stuff is any different.