Sacrificial D-Jet Dizzy? - Page 2 - Mercedes-Benz Forum

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post #11 of 13 (permalink) Old 08-09-2012, 08:58 AM Thread Starter
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Originally Posted by GGR View Post
A well sorted megasquirt may help you save a bit of gas compared to the D-jet, mainly because your D-jet components are old by now and because Megasquirt allows you to tune the engine much more precisely.

But the stock US 4.5 engine is not the right one to start with if you're after fuel savings. The compression ratio is low, 8:1 or somethink like that, it is heavy and I'm not sure the cam grind is ideal as it was designed at the beginning of the smog regulations.

You should consider sourcing an early euro 500 engine. 100lb lighter and 9:1 CR. You would already have a better ignition and you could transfer the 4.5 intake manifold and D-jet hardware like I did.
GGR- Was that early 5.0 in anything besides the 450SLC? i.e. a 500SE?

Also; GGR, I know you have seen this already, but FWIW there is a chap on peachparts called Tony H who is figuring out how to stroke a 4.5 to approximately 5.0 using stock parts (560 crank and rods and machined 4.5 K-Jet pistons) that puts the crown of the piston at the top of the bore where it belongs rather than several mm down (EVERYBODY did this for emissions purposes in the seventies.) If it actually works it would mean a reasonably high 9.5 to 1 static compression ratio (the pistons are reverse dome) along with something resembling proper quench, effecting a more efficient burn that would be somewhat detonation resistant. A compression increase would allow for more cam timing, which a megasquirt system can take advantage of. This could be another option for people with early cars.
You can follow his progress here: m117 4.5 block measurement - PeachParts Mercedes ShopForum
and here:
Project: Iron block 5.0 - PeachParts Mercedes ShopForum
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post #12 of 13 (permalink) Old 08-09-2012, 09:11 AM
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Any Gen I euro 5.0 will do. They were found on the r107 SL/C and the W126 series. Quite a few made it in the US on the gray Market. Any 560 engine, euro or not, would also do as they were 9:1 CR. But then a Gen 1 ignition system should be sourced.

Yes, I'm following Tony's project. I find it quite an interesting exercise, though I prefer the later alloy blocks as they are lighter and keep the car better balanced. It's also less work as the long blocks are kept stock.
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post #13 of 13 (permalink) Old 08-11-2012, 12:53 PM
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Date registered: Jul 2004
Vehicle: 1971 280SE 3.5 Coupe
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5.0 progress

Glad to see someone is interested in my project. I agree a alloy 5.0 would be much less work and lighter but it is a rare engine and to find a known history, good engine would take a bit of searching. This way I will have a drop in, duplicatable, engine that uses common parts and the piece of mind knowing what's inside. The only real extra cost to this engine over a quality stock rebuild is balancing(+- $250) since I'm machining the pistons my self.

280SE 3.5 Coupe
Stick shift
3.27 Axle
5.6 Iron block build in progress
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