PeachParts Mercedes-Benz Forum - View Single Post

Tomguy · #11 08-19-2016, 12:46 PM

The 3.5 and 4.5 cams are spec'd the same, IIRC. The heads are nearly identical, with the 4.5 having more of the chamber ground out to lower compression (and I have personally seen two 4.5 head designs, which seem to correspond to differing 4.5 power numbers and compression ratios). Otherwise, the valve specs are the same, springs, etc... so valve float would not be why the 4.5 redline is lower. Couldn't be. The only difference in the engines is the 4.5 has a longer stroke, so it's GOT to be why the redline is lower. That being said, I'm fairly sure I went above 6k on my 4.5 after I put on 3.5 heads, maybe with stock compression the engine power drops so much it just tops out @ 5800 or whatever and has no guts to go higher in top gear?

Since a pic is worth a thousand words, here's a 3.5's combustion chamber. Yes, dirty in the pics, but you can see that the only portion that would extend above the deck/gasket is the wedge around the valves. On the 4.5, what is pictured on the bottom half is cut out - with more cut out for the 8.0 heads than the 8.8 heads. I measured volume with a syringe and although it isn't 100% accurate I was within about 90% accuracy... you would need to use the forum's search to find it, I did it years ago.