Actually you engine is low compression which started in 1972. You should be fine running regular, but if you have pinging, move up to mid grade, but you don't need supreme.

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Auto Zentral Ltd.

Way back, I "borrowed" the battery out of my dads boat because it was way cheaper than buying a new one. It didn't live long for the exact reason autozen posted, and I had to buy my dad a new boat battery. It was a expensive lesson for a high school kid working part time.

Anyone who doubts this should drive any 1971 M116 3.5 powered MB. I never liked 4.5 motors, they were so detuned and the cars bloated without air suspension to support the extra pounds. The M110 was a better motor, but I couldn't see MB selling high end cars in the USA without a v-8.

I suppose you don't check in the Vintage section often - I put 3.5 heads on my 4.5, and have calculated actual compression (using a reading from cyl #7) at 9.9:1. I can notice the difference on cranking, it has a slightly different tone. Very slight, but noticeable.

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Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

Hey. You borrowed those last two lines from me. Here's another: What happens if you get scared half to death twice?

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Auto Zentral Ltd.

Why was the m110 a better motor? It still had less power and torque than a 4.5 - sure, 4.5's in 116s after 1975 really suffered, but the ones used before then with DJet were still not bad, I believe even the 8.0:1 versions had as more torque 3.5's.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

You're right. I don't check the vintage section often. I did the new car preps on those cars at the dealer, but I have no interest in them. The blocks are the same so if you put 3.5 heads on, you no longer have a 4.5. The 3.5 was imported for only the year 1971 and it was high compression. I have a 3.5 coupe buried under a bunch of stuff in my garage next to a 67 230SL. One of these days I'm going to drag them out and drive them.

__________________
Auto Zentral Ltd.

The blocks aren't the same That's why one is a 116, the other a 117. The 4.5 is taller (30mm) and therefore a bit wider up top because of it. You can verify this, if you don't believe me, by trying to put a 3.5's manifold on a 4.5 (it will be too small to fit between the heads) or vice-versa (too big). The 3.5's crank also accounts for the shorter stroke. I believe the rods are the same, and the rings, but the pistons themselves are different too. 3.5 heads are identical in external dimension to 4.5 ones, only the combustion chamber itself is different.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

I agree, the D-Jet motors were pretty good overall in terms of quality and power. A D-jet motor seems so much crisper than a CIS injected motor.


IMHO, the post 1975 motors were junk:

1. Low rev limit due to hydraulic lifters.
2. Crude CIS injection.
3. Wimpy distributer advance curve.
4. Wimpy cam lift and duration design.
5. Poor quality steel used, causes rapid valvetrain wear.
6. Restrictive exhaust manifolds.

They went from 230 hp out of a 1971 3.5 to 170 hp in the late '70s 4.5 motor.

OK. If you have done all that reseach, I'll concede that one block is taller than the other, but I still have no interest. What has all this got to do with a battery?

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Auto Zentral Ltd.

I'm leaving the rest of this thread to you kids. Enjoy.

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Auto Zentral Ltd.

Mea culpa.

I started it with my comments, sorry.

Jeeze, I'm not the smartest guy in the world but gotta wonder how in the world MB squeezed one full litre displacement difference from blueprinting and recutting a fresh set of cylinder head designs alone.

I assume you're talkin about American export here w/soft camshaft cuts, cat converters and slow distributor advance. Owned a Euro import 4-spd 280SEL w/ m110 that was hotter than a $2 pistol, fastest MB I've ever owned. And is primitive CIS injection really a step below D-jet EFI? Never owned one, but from what i understand the EFI was hell for maintainance. Dunno about import Russian/Italian steel going into longblock and cyl head components either. Seem to remember somewhere it was *only* the sheetmetal stuff that was not Ruhr valley stock from 1973-79. The strike never entirely shut down the mills. Immigrant scab labor (Turks and others) kept em running from what i understand.

(edit: And otherwise returning to topic y'all am stickin to my guns on diesel batteries, gotta be millions of ways to hang the windshield/washer bladder on the wheel well if the battery hold down bracket dont fit. And you can strap it to prevent bouncing off the hood, if thats your worry.

I just noticed that you are from Fairfield. I grew up in Fairfield in the 60's when it was just a cow town. Lived in Vacaville for a while then moved to Nevada City 16 years ago.
Tony

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT