M117 engines and HP

[subforry]

I was looking through my copy of Illustrated Buyer's Guide, Mercedes -Benz and noticed the M117.984 (in my 280SE) is stated as 230 SAE HP. The M117.982 (from a 450SL) is stated as 180 SAE HP.


Are these numbers correct? What causes the lower HP? Cams, compression, fuel delivery?


I am asking because I have a line on a long block from a 450SL that I was thinking of buying, but if there is a loss of 50 HP that I cannot reclaim with parts from my M117.984, then I am not interested.


Thanks.

[Frank Reiner]

If the heads are off or can be removed from the candidate .982, you can get a good idea of its potential. At TDC the piston should be effectively at the top of the block. There were low compression versions for the US market that will have the piston .060-.080" down in the hole. If the pistons come to the top the power can equal that of the .984 with the same cams.

[TZ_280SEL]

The euro M117 4.5 had 8.8:1 vs the us 8:1 CR. The euro 4.5 in my 280SEL had visibly different heads and piston tops vs the US 4.5 that came out of the car. My US 4.5 had flat to pistons and larger combustion chambers. My Euro 4.5 has valve pocket in the pistons and small chambers.

[subforry]

Excellent info. I can get a handle on all of that with a borescope. FYI: My 4.5 is a euro delivery car. It seems way stronger than my old US 4.5. I have wondered if there is some cam or compression ratio difference.

[Tomguy]

I have found a thread comparing 4.5 low comp, 3.5, and what 4.5 high comp heads would look like (not having had a set of those handy). 3.5 being the highest compression and a direct bolt on to a 4.5 low compression block/engine. Also with the piston not going to the top of the block, I'd imagine with today's machinists who can do on-demand parts from billet stock, that you could get some high compression, even domed pistons, and put whatever heads you wanted on any block and get the power you want. Yes, it'd cost money but it'd be interesting to build out, to me.

Piston at TDC:
https://www.peachparts.com/shopforum/vintage-mercedes-forum/124227-my-headjob-progress.html

If you go to this thread, specifically posts 17 through 20, you can see pictures of the different heads and what they came on.
https://www.peachparts.com/shopforum/vintage-mercedes-forum/318200-300sel-3-5-anyone-installed-117-cylinder-heads-116-engine.html

Euro 4.5s were likely at least 8.8:1. But if they had pistons that go to the top, they'd likely be around 9.5:1 I'd speculate, without info, because 9.5:1 is what the 3.5 was.

[Tony H]

That's similar to what I am doing with my "5.6" build. I am having pistons made and specifying a dish volume that will result in my desired CR. Also to note-D-Jet heads do not have squish pads (at least US) and K-jet heads do. Last time I checked custom pistons were about $1200 but it would require a total engine rebuild to go that route.

[TZ_280SEL]

Here is the low compression head and cylinder from my 72 4.5 M117.

[TZ_280SEL]

These are the high compression head and piston from my current engine. This is from a euro 450SL from 1974. Both are solid lifter cars and both had the same serial of cam shaft.

[Tomguy]

It's been a while but to my knowledge the early m117 (and m116) cams had the same part numbers on them and the way to tell the "Grind" was the number stamped in the back, with 52/53 being the sought after pair for 4.5s and 57/58 being "Dogs" but I don't recall why - and I may be off with the numbers. You can search the forums for more details I imagine, or if you happen to have the m117 service manual(s). I lost my copies in a HD crash.

[Tony H]

I have the PDF with the cam grinds I can post if there is interest. From my experience the greatest difference in cams was the amount of cam retard ground in. Being smog engines, low compression and retarded cam timing was used to reduce NOx. It resulted in a kind of passive EGR.

[alabbasi]

Originally Posted by TZ_280SEL

These are the high compression head and piston from my current engine. This is from a euro 450SL from 1974. Both are solid lifter cars and both had the same serial of cam shaft.

Is that engine still treating you well?

[TZ_280SEL]

Running great. I love the euro with Megasquirt. Lots of fun

[alabbasi]

That's great. I now have a 300SEL 3.5 which feels lively. It needs some suspension work to make it a driver.