Author Topic: AMG cams for 6.9?  (Read 393 times)

raueda1

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AMG cams for 6.9?
« on: 14 March 2020, 09:43 AM »
I was recently on the periphery of a 1977(?) AMG 6.9 sale.  The seller claimed that AMG made special cams for the 6.9 resulting in a 100 HP boost.  I'm very skeptical of that.  In fact, I'm skeptical that it wasn't a homemade MAG look-alike.  But....  what if it's true?  And if it is, could stock cams be reground to whatever the AMG design was?  Or for that matter, does anybody have any info on 6.9 cam regrinds?  Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

john erbe

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Re: AMG cams for 6.9?
« Reply #1 on: 19 March 2020, 07:11 PM »
Agree that 100 hp boost sounds like he was on medication. Relatedly, looked into regrinds a few years back and was shocked to find a shop in LA that could do both for less than $400.

raueda1

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Re: AMG cams for 6.9?
« Reply #2 on: 20 March 2020, 09:00 AM »
Agree that 100 hp boost sounds like he was on medication. Relatedly, looked into regrinds a few years back and was shocked to find a shop in LA that could do both for less than $400.
Interesting!  I guess you didn't go down that road or you'd have some comment on the results.  Regardless, can you say who the shop was? Maybe I'll give them a call.  I've got a pair of spare cams to play with.
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

john erbe

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Re: AMG cams for 6.9?
« Reply #3 on: 20 March 2020, 01:02 PM »
Cant find that binder I had my Benz notes in but at that time I just went net surfing for engine mod or rebuild shops if I recall. They were a know entity in the NHRA world. Sorry.

Randys01

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Re: AMG cams for 6.9?
« Reply #4 on: 20 March 2020, 11:40 PM »
A cam regrind never gave anyone a 100hp increase in 300.  ::)......  not even Mickey Thompson.!
I had this discussion with a very learned colleague only a fortnight ago...the influence of worked over cams when using K jetronic.
One needs to tread carefully. Excessive overlap breeds inlet tract back volume flutter.  the ole K jet is not thrilled about positive back pulses at low rpm.
Thus, if AMG or anyone else ever came up with regrinds,  duration and in turn overlap would be inhibiting factors.
I see the exhaust side of the M100 as the Achille's heel...this has been discussed before but the ports are small with  nasty bends. If there was one side of the motor that needs attention it is the exhaust. My focus would be optimising the exhaust cycle before getting too excited about the inlet.
The more one looks at the M100 6.9, it is a veritable smorgasboard of opportunity to extract more safe horses.
Plenty of folk have had a crack over the years. supercharge..turbo charge..convert to EFI..etc.
My favoured route is back to carbies..I'm not sure if anyone has done this... successfully or otherwise.
Each has its challenges.. EPA compliance is but one.





raueda1

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Re: AMG cams for 6.9?
« Reply #5 on: 21 March 2020, 10:25 AM »
A cam regrind never gave anyone a 100hp increase in 300.  ::)......  not even Mickey Thompson.!
I had this discussion with a very learned colleague only a fortnight ago...the influence of worked over cams when using K jetronic.
One needs to tread carefully. Excessive overlap breeds inlet tract back volume flutter.  the ole K jet is not thrilled about positive back pulses at low rpm.
Thus, if AMG or anyone else ever came up with regrinds,  duration and in turn overlap would be inhibiting factors.
I see the exhaust side of the M100 as the Achille's heel...this has been discussed before but the ports are small with  nasty bends. If there was one side of the motor that needs attention it is the exhaust. My focus would be optimising the exhaust cycle before getting too excited about the inlet.
The more one looks at the M100 6.9, it is a veritable smorgasboard of opportunity to extract more safe horses.
Plenty of folk have had a crack over the years. supercharge..turbo charge..convert to EFI..etc.
My favoured route is back to carbies..I'm not sure if anyone has done this... successfully or otherwise.
Each has its challenges.. EPA compliance is but one.
Yeah, I laughed to myself when the seller made the 100 HP claim.  He made a lot of wild claims.   ::)
 I've been struck by the oddness of the manifolds and their total asymmetry.  Not much room under there....   In any case I'm not really interested (or capable) of going down the path of serious tuning. A regrind seems like pretty simple thing in the scheme of things - provided there's somebody out there with the knowledge and skills to do it right. 
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

john erbe

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Re: AMG cams for 6.9?
« Reply #6 on: 21 March 2020, 01:48 PM »
Back at the time my thought was to do a cam grind and use the 560 throttle body to get my domestic performing more towards a Euro. I found a shop that could machine a bolt on base for the later. However, the question that put the hole project on hold was if I would ever even feel any additional hp increase? My feeble brain told me the Euro's extra performance mainly comes from the piston heads.

raueda1

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Re: AMG cams for 6.9?
« Reply #7 on: 22 March 2020, 08:03 AM »
Back at the time my thought was to do a cam grind and use the 560 throttle body to get my domestic performing more towards a Euro. I found a shop that could machine a bolt on base for the later. However, the question that put the hole project on hold was if I would ever even feel any additional hp increase? My feeble brain told me the Euro's extra performance mainly comes from the piston heads.
I suspect the same (higher euro compression) but certainly also the lack of all the smog stuff.  I've been slowly deconstructing a US engine.  It's amazing how much little diddley fiddley smog stuff is actually there, between all the valves, little pipes/tubes etc etc.  It really does make the euro engine seem simple and uncluttered by comparison.
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Randys01

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Re: AMG cams for 6.9?
« Reply #8 on: 23 March 2020, 03:05 AM »
Just imagine if DB had used the D jetronic on the euro 6.9. ?! 330 din hp would be around the mark.
Cars of the weight like the W116 need about another 40 hp for you to feel it.ie 20hp per ton.
the key to more urge out of the venerable old M100 is more torque not more revs. 5and half is probably about all you want to swing it to but if you can get greater "volumetric efficiency"  and improve torque by 15 percent you will of course get more horsepower without having to rev the the daylights out of what is an old design motor.
This motor was conceived probably late 50's.   introd early 60's and lingered until 1980. yes it had some running improvements etc along the way but fundamentally a motor which relied on huge capacity to get the job done.
That said, the 6.3 on mechanical injection is a spirited beastie and for the era a bit of a revver for its size. I've been doing a bit of work on a 600 and wow.!!..that motor must deliver every drop of its rated horsepower .
It beats me how the Americans can get mid 60's  era production pushrod V8's 6 to 7 litres to swing to 6000+ rpm.


3l33ter

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Re: AMG cams for 6.9?
« Reply #9 on: 24 March 2020, 02:52 AM »
Just spit ballin' but maybe the AMG cams came with AMG valve springs, which allowed a higher redline, which is where most of that 100hp gain claim comes from. The stock redline is really low.
'75 280S
'77 6.9
'82 300TD

Randys01

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Re: AMG cams for 6.9?
« Reply #10 on: 26 March 2020, 01:00 AM »
Valve springs are not the inhibiting factor.......reciprocating mass. the ratio of bore versus stroke.....these are fundamental constraints.

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Re: AMG cams for 6.9?
« Reply #11 on: 27 March 2020, 12:17 AM »
My red 6.9 is a real AMG, and what I do know is that the rocker arms are ground down and lightened.  The valve springs and hydraulic lifters look standard to me.  The cams do have a code number stamped on the rear ends, but it's a long time since I looked in there.

'76 6.9 Euro, '78 6.9 AMG, '80 280SE, '74 350SE, '82 500SEL euro full hydro, '83 500SEL euro full hydro , '81 500SL

s class

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Re: AMG cams for 6.9?
« Reply #12 on: 27 March 2020, 12:21 AM »
I may soon be in a position to know more, because the car has a problem with low compression on #2.  I've done extensive tests, compression, borescope etc etc and it seems the issue is a bent conrod. So the next step is to take off the heads and check piston protrusions to confirm the diagnosis.  It was a one owner car, and he claimed it was bored and stroked.  There is the usual evidence like headbolt molestation tgat at least confirms the heads have been off.

Once I have them off I will be able to measure the bore and stroke.  If it is indeed stroked I could be in for a fun time solving the issue of a bent rod.

'76 6.9 Euro, '78 6.9 AMG, '80 280SE, '74 350SE, '82 500SEL euro full hydro, '83 500SEL euro full hydro , '81 500SL

Randys01

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Re: AMG cams for 6.9?
« Reply #13 on: 27 March 2020, 02:29 AM »
An opportunity to compare many aspects of the motor with a stock one.   [with which you are very familiar ]..so any little mods should pop out to you.
Perhaps you could elaborate for the viewers on what you currently know to be an /your  AMG variant..so much myth..folklore.so little fact surrounds the 6.9.
I'd love to see the trimmed down rockers.

From memory the only nos on the back of the cams relates to lh versus rh.  The actual cam p/no is moulded into the shaft itself. If AMG fiddled with the cams, you'd be looking for a bespoke etched identifier.
I'm bemused by the current generation of tossers who brag about their newish "AMG" Mercs.....only to discover they have nothing more AMG floor mats.!!.........yes at the top end there are plenty of decent AMG  derivatives but c'mon guys...get a grip. ......... ::)


raueda1

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Re: AMG cams for 6.9?
« Reply #14 on: 27 March 2020, 08:23 AM »
I may soon be in a position to know more, because the car has a problem with low compression on #2.  I've done extensive tests, compression, borescope etc etc and it seems the issue is a bent conrod. So the next step is to take off the heads and check piston protrusions to confirm the diagnosis.  It was a one owner car, and he claimed it was bored and stroked.  There is the usual evidence like headbolt molestation tgat at least confirms the heads have been off.

Once I have them off I will be able to measure the bore and stroke.  If it is indeed stroked I could be in for a fun time solving the issue of a bent rod.
Jeez. :o  Bent rod is challenging enough with stock engine.  Can't be that bent if the car still runs....  Still, it's quite a rabbit hole.  Good luck!
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0