News:

The ORG - No back-slapping boys club!

Main Menu

Tuning tips

Started by Mr AMG, 05 April 2009, 06:36 AM

Mr AMG

Hi guys i know we all want our motors to sing and go as well as they possibly can, so here is a couple of pointers to get them going good.

One of the most important things with any engine is the ignition timing, and with todays fuels being alot slower burning than the older fuels it is critical that you set your timing to suit.

  My advice is to set the timing about 15 degrees advance on all the old cars and with the k-jet (mechanical injected) models you can prbably go a bit more. You can pretty much run at 20 degrees advance but you tend to lose the bottom end take off. One way around this is to connect the vacuum advance hose of the distributor straight to constant vacuum from the manifold (find somewhere that the central lock hoses come off etc) this will give you more advance at low throttle and will retard the timing under increasing throttle to give you a bit more torque when your foot is down, it also makes sure it can't ping, and will give you a heaps better idle. It is also the best way to do it on the older   d-jet (electronic injection) cars as you dont want to move the ditributor too much because then you lose the injection timing a bit. A little bit of discression is needed and you might find you go a bit more or a bit less once you drive it.

   The other thing people are frightened of is spark plugs, and they think that if they go hotter then the engine will run hotter. That is completely un-true and in fact anyone with a pre-1990's merc should a least go one heat range hotter so as to match the burn rate of modern fuels which burn slower and tend to leave more deposits on the plugs. You see the heat range only determines the heat at which the porcelain centre runs in the plug and the hotter it is the more ability it has to burn soot from the electrode, especially on a 30yr old engine.
      A lot of people are seeing the 4 electrode plugs and platinum, iridium etc, and I'll give you the tip, they make no difference in an old car, they are designed for late model very high output ignition systems and compression ratios which do benefit from them but I've tried all of them over the years in many different cars and to be honest a good set of "NGK BP5ES" is the way to go as bosch and most european plugs tend to foul up quick and bosch especially will not fire if they get even the slightest bit wet. 

    The other major thing I suggest is that you get rid of the old rev limit rotor buttons with the spring thing on them as you can never trust whether or not they are arcing out a bit at lower revs and i don't know about you but i don't want that. Don't be scared to put the later model rotor buttons in your car it makes no difference to the running, but with give you constant and reliable spark all the way to the redline, and I'm sure you all know where to stop revving your motors anyway.

    Also you should make sure you have a good set of ignition leads on the car too, as many little hiccups in the idle are almost always spark related, this means dist. caps, rotor buttons and leads.


       Anyway good motoring and good luck, lets here those motors sing !!!

1974450SEL

I completely agree.  I had a import shop that has a mech who has worked on these 116's do just that, he advanced the timing just enough so I can run the regular (87 octane US)  instead of 91 in my car and it works very well.  I've replaced all the ignition components and have a set of those NGK plugs ready for the next change but the Bosch Platinums I put in and set at the proper gap 3 years ago are still performing very well.  I don't drive the car very much as it is my hobby/cruising vehicle but this set up runs well.  You can't go wrong with new fuel and air filters as well.  what's your opinion on the high flow air filters, would they make that much difference on an older engine? 

oscar

In the 350 d-jet when the engine's warm I can only manage about 8deg advance on idle before it pings on WOT or hard acceleration.  That's on 98RON as well but I suppose the relatively high 9.5:1 CR has got a lot to do with it.  I've never really contemplated the effect of the d-jet injector timing changing.  It's a shame the two can't be separated without some improved ignition system.  I agree though that factory specs on most w116's dictate a very conservative ignition timing. 

As for NGKs, so true from my experience too.  Most of the time I've used BP6 plugs but recently went to BP5.  Although I'm a bosch fan the W7DC or W8DC used to foul too often for my 350 which doesn't get on a highway all that often.  The spark would too easily track around a fouled plug and lead to a crappy idle.  Never had that problem with an NGK.
1973 350SE, my first & fave

koan

#3
Quote from: oscar on 07 April 2009, 09:43 AM
In the 350 d-jet when the engine's warm I can only manage about 8deg advance on idle before it pings on WOT or hard acceleration.  That's on 98RON as well but I suppose the relatively high 9.5:1 CR has got a lot to do with it. 

Much the same on 6.9 with 98 RON (what the AUS supplement recommends), I run 6 degrees, any more and it pings.

EDIT: That should be 95 RON, wasn't thinking

koan
Boogity, Boogity, Boogity, Amen!

TJ 450

My 450 is set by the book at TDC and there are no problems with pinging on 98RON. Is there some performance to be gained by advancing a few degrees?

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

Bandolero

When he says to set the timing at 15 BTDC, he is not taking into account the vac retard system (on idle) on a lot of our 116s.

If you were to set the timing on a 116 with a correctly working vac retard system to 15 advanced, you would have detonation.

On your 6.9 you may be able to advance the timing by a couple of degress with a performance gain but watch out for "pinging".

On most V8s that don't have vac retard at idle, you can run about 12-15 degrees advanced, I did on my old 318 Plymouth that I owned and noticed an improvement.

(If you disconnect the vac retard, you will notice the timing will go to about 10 degrees advanced.)

The vac retard is used for the air con to keep the idle speed the same when it "cycles".
Russell Bond - (Adelaide, South Australia)
1978 450SEL 6.9 .... #5166 .... 12/78 (Sold.) [url="//www.ezycoat.com.au"]www.ezycoat.com.au[/url]

oscar

They're good points bandolero.  To be honest, although I've tried with and without vac lines attached in the past I can't remember what i did before summer, the last time I did timing.  I know that if I set it as per fac spec without vac lines attached at 5deg advanced at 700-800 rpm it'll tend to almost stall under load due to the effects of the vac retard.  I think I'll have to take a closer look at this next time I do it to see what's what.   I can't remember off the top of my head what exact settings i've experimented with. 
1973 350SE, my first & fave

Bandolero

Yes, if your vac retard is a bit "sus" it makes it hard to do the timing to specs.

Disconnect the vac retard and set the timing to about 10 degrees advanced and you will be close to the correct timing.
Russell Bond - (Adelaide, South Australia)
1978 450SEL 6.9 .... #5166 .... 12/78 (Sold.) [url="//www.ezycoat.com.au"]www.ezycoat.com.au[/url]

scraf

Took my 450 SEL into the Mercedes dealer today to get the timing checked ( has a flat spot around the 150 kmh mark ), they couldn't do anything due to it not having a "diagnosis plug", a half hearted attempt with a strobe light later and I was missing 41 euro.

Ho hum.

koan

#9
Quote from: TJ 450 on 07 April 2009, 08:05 PM
My 450 is set by the book at TDC and there are no problems with pinging on 98RON. Is there some performance to be gained by advancing a few degrees?

Production of oxides of Nitrogen increase with the higher combustion temperatures that result from advanced ignition timing. These pollutants are difficult to deal with so the solution on emission engines is to back off the ignition advance.

Also, an engine with a few kms on is probably down a bit on compression, this allows a few degrees of extra advance before pinging becomes a problem.

Yes, our aging engines that don't have to face emission testing can gain a little extra performance with a bit more advance.

Watch out for pinging though, on a cold morning with a warmed up engine give it full throttle and listen for metallic rattling sounds at low to medium RPMs.

Thanks Bandolero for the correction regarding the vac retard on or off, Mr AMG's figures now make  sense.

koan

EDIT: after "cold" added "morning"
Boogity, Boogity, Boogity, Amen!

chinny4290

goddamn this stuff is complicated lol.
1975 W116 280S - SOLD
1994 W124 E320 Coupe - Gone

CURRENT - 1974 450SEL

carl888

Great info, and my experiences mirror yours.  In my M110 W126, I managed to get the fuel comsumption down from a totally apalling 21 mpg on a trip to 27 mpg from just giving it 5 degrees advance (On the crank) and running 98 RON fuel. 

The biggest issue I have found is not the timign itself, is the advance curve, for some reason, they are very soft in the mid range, that's where most of the gains are if you can be bothered to change the curve.

Regards,

Carl.


GreaseMonkey

Hi guys,
and thanks to all for a timely thread as I am trying to find the right settings for my '75 280SE.
It has the electronic injection and the points type distributor.
It is currently set at 13° advance at idle, but it 'pings' like crazy as soon as it is under load, and at the same time the temperature gauge immediately climbs to hot.
I normally set myy cars up to run on 95RON as 98 is not always available locally, and this is fine in my other Benzs.
I suspect there is a fault with either the vacuum advance or the centrifugal mechanical advance springs, but I have a spare distributor to try.
I will check what plugs it has, I did change them not long ago, and although I normally use NGK I think I may have used a spare set of Bosch WD7 I had in the shed.
I am going to tkae it out agin this morning with the timing back at 5° to see if there is an improvement, then try it with the vac disconnected and plugged and work through the choices to see if I can pin this down.
I will report back with my findings as soon as I have any answers, hopefully this weekend.
Chris M.

WGB

I don't know what CR's your 280's are running but the V8's are 8:1 for Oz spec cars and 8.8:1 for euro's.

My two Euro's V8's definitely prefer 98 octane and being K-jets their ignition timing is TDC with all vacuum lines connected and A-C off. They will detonate and run hot with any advance in timing.

I know the D-jet V8's are supposed to be set at 30 degrees advanced at 3000 rpm and assume the 280's are similar - is this what you mean - the figures you are talking about seem way to far advanced for 95 octane unleaded fuel to me.

Bill

Papalangi

I don't remember which rating system the US uses but I'm running 87 octane at 15-18 degrees advanced and it made a huge difference in idle quality and completely eliminated the dieseling problem I had.  Mileage went up 1 MPG so I have to fill up every 15 days instead of 14.

I'm considering bumping it up a hair more till I get pinging and switching to mid-grade, 89 octane I think.

Michael
'83 300SD, I'm back!  It's the son's new car (12/2020)
1976 450SEL, 116.033  Sold it to buy a '97 Crown Vic.  Made sense at the time.
1971 250C, 114.023
1976 280C
1970 250/8