6.9 Performance Upgrades

[Oversize]

Well I'm going to reveal all my performance thoughts now, as I'd like to see every MB enthusiast get more HP from their rides. And keep the rice burners at bay! I agree with another thread that most current 116 & 107 owners are a very different group to MBs original target market. Although repairs still cost the national debt, purchase prices have never been better.
It seems to me that even MB herself has a completely different attitude to street performance; who'd have thought they'd adopt AMG? And maybe they'll start racing in V8 Supercars? How good would that be for them to win at Bathurst!!!!
Back to the topic: It's very rare to see a 6.9 (or any 116 / 107) now and when the public see one I'd like them to say wow! Note that there's other performance upgrades available, but they involve disconnecting systems that I believe should be retained on a MB (eg A/C). I'll start small & work my way up....
Make sure you have no vacuum leaks,
Make sure your timing chain isn't stretched,
Check ignition timing & advance mechanisms,
Obviously check fuel supply - including rubbish in the tank, screen, filter. Check flow, pressure & mixtures,
EGR - shouldn't operate at full throttle, so check it,
Engine oil - as thin as possible without knocking,
Cold air intake - get one!
Engine heat - vent the bonnet (tastefully of course),
Engine driven cooling fan - get electric fans,
Exhaust - Extractors & high flow pipes / muffler (sounds better too) ,
Diff - get a new ratio, or upgrade to a GM Trutrack / IRS 9" (where can you do over 110kmh anyway?),
Transmission - get a four speed with shorter ratios (Big Boys Toys transmission adapters).

The following's not legal in Vic, or not legal without being engineered:
Aust delivered air pump - Does rob your engine of hp ,
Throttle body - fit a larger one,
Replace the camshafts - years ago it would've been easier (seems no-one in Aust can make them now) ,
K-Jet - get rid of it & go for electronic injectors & a new ECU (that damn original airflow flap's a huge restriction),
Intake manifold - custom fabricated from sheet aluminimum with up to 8 throttlebodies (Hogan),
Pistons - increase the compression ratio,
Nitrous - Not legal at all in Vic,
Supercharger,
Turbocharger/s.

Another way to improve acceleration (and decrease fuel consumption) is to remove weight:
Washer bottle - does it really need to be that big?
Spare wheel - get rid of it & sign up for roadside assist,
Battery - get a light dry cell one.

My cars all seem to like clean air!!!!!

 

[Oversize]

Oh & I forgot boring & stroking.........

 

[Oversize]

Make sure you're getting full throttle & all the linkages are well lubricated,
The original throttle balls always break, so make sure they're replaced,
Try a weaker throttle return spring,
You could also lighten & knife-edge the crank....

And now you'll need a parachute (sorry)!!

My brain hurts, so that's it for now!

 

[Fotografa]

And maybe they'll start racing in V8 Supercars?

Will never happen, Mercedes-Benz, and most other respectable manufacturers aren't interested in going backwards to pushrod V8's.

Taxi racing is losing fans and interest, and will be dead and buried in a few years. Hooray!

GM and Ford would not be interested in racing if the formula moved away from 1960's technology, because they would get owned all over the racetrack.

Hopefully we will get proper touring car racing back in this country, so we can see some interesting racing like they have in the DTM.

 

[Fotografa]

You mention engine bay heat, but no mention of ceramic coating the exhaust. I would have thought that would be one big way of reducing the temp under the bonnet.

 

[Oversize]

Agreed that MB would never go back to pushrods and that was never suggested. It was announced in March 2010 that the V8 Supercars 'Car of the Future', would allow for other manufacturers. Yes, it is unlikely (but not impossible) that MB & BMW would be involved, as $$ capping & 'parity' would be issues yet to be addressed. It would seem this form of racing is more about the driver & team, rather than the manufacturer's product. Not sure if I agree with that phylosophy, but that might be a topic for another thread...

And no, I'm not ashamed of the fact I love ANY V8 racing (ok Nascar's a little boring). I don't care if they're a side-valve, pushrod, DOHC, or mounted in a hot rod, boat, or Top Fuel dragster. To me, if you can't appreciate the sound of any V8 under full noise, then you're not a true petrol head...

Back on the topic of mods, I'm not suggesting my list is exhaustive (as can be seen I've added more as they've come to mind). I was simply offering some ideas of my own and I'd welcome any other opinions, or thoughts. I've seen many cars (not just MBs) where the owners have performance aspirations, but they'd seemed to have missed even the basics.

More to add to the list include:

Heat insulated (or cooled) fuel supply,
Indexed spark plugs,
Distributor-less ignition,
Porting & port matching,
Heavy duty valve springs,
Bigger valves with smaller stems,
Roller rockers (obviously custom ones),
Thorough balancing of all moving parts.

 

[Fotografa]

Agreed that MB would never go back to pushrods and that was never suggested. It was announced in March 2010 that the V8 Supercars 'Car of the Future', would allow for other manufacturers. Yes, it is unlikely (but not impossible) that MB & BMW would be involved, as $$ capping & 'parity' would be issues yet to be addressed. It would seem this form of racing is more about the driver & team, rather than the manufacturer's product. Not sure if I agree with that phylosophy, but that might be a topic for another thread...

And no, I'm not ashamed of the fact I love ANY V8 racing (ok Nascar's a little boring). I don't care if they're a side-valve, pushrod, DOHC, or mounted in a hot rod, boat, or Top Fuel dragster. To me, if you can't appreciate the sound of any V8 under full noise, then you're not a true petrol head...

Back on the topic of mods, I'm not suggesting my list is exhaustive (as can be seen I've added more as they've come to mind). I was simply offering some ideas of my own and I'd welcome any other opinions, or thoughts. I've seen many cars (not just MBs) where the owners have performance aspirations, but they'd seemed to have missed even the basics.

More to add to the list include:

Heat insulated (or cooled) fuel supply,
Indexed spark plugs,
Distributor-less ignition,
Porting & port matching,
Heavy duty valve springs,
Bigger valves with smaller stems,
Roller rockers (obviously custom ones),
Thorough balancing of all moving parts.

From your list of cars I never would have guessed you like V8's.

 

[Oversize]

And the fuel retailers love me for it!!!!

 

[Oversize]

And I wish I had more money (and time), to do just a few of the things suggested!!!

 

[motec 6.9]

Hi Mark if you go back through some of Cams post sel450 and my post you will see most off the mods you sugest have been or are being done by us at the moment i currently are building a stroker and the heads have been ported and polished with thinner valve stems fitted Cam has access to custom cams and my original motor died from a NOS lean out as far as i am aware i was the first to fit after market injection to a 6.9 in oz Haltech 2002 Motec 2003 i already have extractors and exhaust and yes they are ceramic coated

 

[Styria]

Now, now, Oversize - how many of your mods and improvements will you effect ? Many of them require serious money to be outlaid, and you'd only need to ask Motec 6.9 and to some degree SELfour50 what they are up to in total dollars on their modifications.

Unfortunately, 6.9s and, of course, the Mercedes range in the olden days (post 1958) were not meant to be muscle cars. You've only got to look and compare with the Yankee V8s with their huge inlet and exhaust ports, and even carburettors performing the jobs they are looking for - gobs and gobs of power and, dare I say it, torque. Mercedes engines were not built that way - the design principles are totally different. Yes, it helps and it is important to maintain all facetrs of fuel, electical and air supplies as best as possible, and to ensure accurate adjustment of freeplay in linkages etc., as well as ignition timing and quality of spark. Regards Styria

 

[SEL_69L]

When it comes to racing, Mercedes made an engine for Indy Cars that had a pushrod OHV V8, and so doing could retain the (then) 4 litres semi grandfather engine capacity for pushrod engines.

It was a little different, though from then current 4 litre formula. To begin with, it had 4 valves per cylinder, and NO overhead rocker shafts. The camshaft was in the normal place low between the Vee. There were 32 pushrods (titanium) at the top of which in the top each head, were 16 rocker posts which transmitted the cam lobe info. to the inclined valves. The inclined valves allowed for hemispherical combustion chambers.

Performance wise, it was at least the equivalent of the 3.9 litre Cosworth engines of the time.

 

[SELfor50]

Mark, I just connected the dots with the list of cars and the username. Nice one.

I saw Mark's collection (well 1 in the flesh the other covered) of 6.9's on Friday. Good to see you posting up here mate.

We spoke briefly about performance mods, and it's good to see you on here.

The list of items you mention above are exactly what need to be checked to regain any lost horsies in the stable. Less weight always helps, hence why I paid more for my custom SE6.9. I was happy for it not to have hydro suspension, sunroof, shorter wheel base.. etc etc.. And going forward I think getting it lightened to about 1500kgs should make it very very head jerking.

As for engine mods. Motec's going down one path, and I'm taking a slightly similar route but not touching the bottom end at all. Motec is grinding the crank to offset it and boring out to 8.2L.

I understand where you're coming from Styria.. They aren't the engines that have off the shelf horsepower modifications - but as for design, the guy who currently has my 6.9 heads (Motec know's him well and recommended him) has complimented on their design. Saying for the era they're actually a very well designed set of cylinder heads. And the manifold he said is a little different in design, but very accessible.
The main restriction on these engines is the K-Jet hardware on the top and the Throttle body. 80% of that being the throttle body.
A 560 Throttle body can be adapted and bored out more.. or something like an LS1 throttle body will fit quite easily.. and getting one of those in say an 85mm setup will increase the size by 10mm. At least. Still remains as mechanical operation too, so no reason why with correct plumbing you couldn't put K-jet back on and use the LS1 throttle body.

Motec posted his results of his Dyno run with extractors, MotecM48 fuel injection etc etc...
(and the extractors are so sexy and well done)
2 things.. the dyno ramp rate might be influencing the output which seems to be not that much at 215rwhp... .and he stil lhas stock throttle body. I think with an LS1 or even 560TB attached and polished, there's at least another 20% + in that setup... quite easily.

 

[Oversize]

If all goes well, I'll have one I can drive on the street in the next few weeks (just in time for summer)!

I won't take credit for any of the suggested modifications, as it's obvious that a few are already well down the track of undertaking things I've mentioned. All I was trying to achieve was to list all the possibilities in one thread & create some discussion on the options available. Indeed, many of the mods have been around since Adam was a boy.

As well designed as the MB engines were, it seems there's still scope for improvement, particularly with the technological advances over 30 odd years. From what I've seen, only a handful of 116 & 107 owners (worldwide) have attempted significant engine improvements (and you all live too damn far away from me) . Whilst I agree that the cost of replacement parts can be bordering on the obscene, machining on a MB engine should be no more expensive than any other V8.

On the subject of cylinder heads, it should be noted that port size is not the be-all, end-all for the street. Port design was found to be more important than outright size, which led to the development of aftermarket 3V heads for the Ford Cleveland. The 4Vs flowed too much for the street and air velocity, low speed fuel delivery, vacuum & driveability suffered.

Here's a question for those more knowledgeable on these subjects: What's limiting revs on these engines? OHC infers that they should be able to achieve more RPM (quicker & more reliably), than OHV. After all, why would MB bother which the technology if there wasn't an advantage? Why is it that some OHV engines (of the same capacity) can rev harder than OHC? Do these MB engines have a longer stroke than most larger capacity engines; hence their impressive torque? Historical material I read quite a while ago stated that MB believed they'd reached the limit of piston speed in these engines. Has there been any huge leaps in technology, since these cars were produced, to break this piston-speed 'ceiling'?

 

[SEL_69L]

Normally the reason why an engine is overhead camshaft (OHC) is used is to lessen valve train flying weight, and therefore allow the engine to rev. faster, because you do not have pushrods. With a V8 engine with 4 valves per cylinder, you would need 48 pushrods. That's a lot of extra mass. That's the theory. 4 valves per cylinder should give better engine breathing.

I can't understand why Mercedes have persisted with driving the camshafts with a chain. They are much heavier than a tooth rubber belt, considering their mass. The camshaft chain for a 6.9 engine is almost 1.5 metres long! Most modern engines use a toothed rubber belt to do this. Ferrari first did it with road cars when they saw the success that the nitro drag boys had when using a toothed rubber belt to drive their superchargers. Nearly 1000 horsepower is diverted to the supercharger in this way.

A limiting factor on engine revs is the strengthen of the valve springs. It doesn't matter if you have OHV or OHC if the valve springs are not strong enough. When the engine is revving hard, the valves slam shut on their seats harder, and if revving hard enough, the valves bounce off their seats against valve spring tension. When this happens, engine breathing becomes very inefficient, and the engine cannot rev any faster beyond revving speed that produces valve bounce.

This problem can be solved in three ways:

1.) By replacing the valve springs with stronger ones,
2.) Changing the engine design by having cam opening and cam closing valve gear, otherwise known as Desmodromic valve gear. Mercedes did that with some of their racing engines,
3.) Changing the engine design by operating the valves hydraulically ( have never heard of this) or pneumatically. Renault went with the pneumatic option when they first introduced this to Formula one.

The valves can also be opened and closed by means of a vertical jackshaft driven by bevel gears from the crankshaft, thence to the valves at the other end of the jackshaft. This has been done in a number of aircraft engines in the 1920' and '30's. Another way is to drive the camshafts by a gear train from the crankshaft to the overhead camshafts This was done on a few racing engines during the 1960's, but is very noisy and only suitable for racing engines. Ford did this with an Indy racing engine.

I am very tempted to think that most engines in the future will have pneumatic valves. The reason for this has to do with simple maintenance. You can pull out the injectors from the head, you can pull out the spark plugs from the head. It is also possible to pull out complete valve assemblies (valve complete with it's actuation) directly from the head without having to remove the head itself.

 

[motec 6.9]

Hi Mark the 6.9 engine is very much an undersquare motor in that the bore is4.21 inchs and stroke is 3.76 inchs so piston velocity is not a problem one of the worst motors for that problem is the 5.4 ford modular motor and the 3.8 buick at 6000rpm there pistons are just under supersonic that is why there was no chance to extend the rev range on those motors but supercharging works great on both motors

 

[Oversize]

And now we have adjustable cam sprockets for the 6.3 & 6.9. Soon I'll be looking into custom throttles & lower manifolds