2 mph increase in speed on a local hill I use for testing. 40 mph at top of hill stock, rack limiter adjusted to max gives 45mph, fuel pressure increased, now 47mph. All tests in third gear. Not sure what the grade is but would guess about 7-8 percent.

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1977 240D turbo

I suspect if the fuel pressure had been increased first the gain would have been greater than 2 mph. Perhaps the rack adjustment would have given you only two or three mph if done after the fuel pressure. Both directly affect fuel delivery.

Higher fuel pressure tends to increase energy and engine efficiency. I always suspected by feeding all cylinders more equal amounts of fuel . We have never had a really good report on what transpires on fuel milage on long highway trips.

Some 616 engines give about 5 miles per gallon better fuel millage than others. I never have absolutly pinned the cause of this down yet totally. Some of it might l be in the fuel supply pressure. I just do not know yet.

In theory fuel economy should be better. Certainly not worse as the engine power strokes are more in balance than at low fuel pressure. It appears that both things in combination gave you about a 14 percentage point power increase.

I have to wonder if the engine is near or sitting on the injection pumps speed limiting internal govenor at 47 mph in third gear. You might want to do the calculations to establish the rpm. Or their may be three red lines on the speedometer that may indicate the govenors proximity.

Fourteen percent is really important as we tend to use maximum power quite often with those 616 engines. Good going.

It is my intention and desire if I ever get any spare time to really do some serious tests on the 616 engine. One last thing is since you used a gauge your increase was from 10 psi to 21 psi. Many 240ds are running at this time at far less than 10 psi.

Actually the engine will not seem too bad at say four psi or even less sometimes. The differential you experience is going to directly affect the amount of power you gain. Four pounds to twenty one for example would have given you more power gain from you original weaker starting point. Same as if your starting point was say 14 pounds initially you would not have gained as much.

Are you on diesel fuel or wvo? I expect diesel but am not certain.

The three dots on the speedometer are at about 60 for third gear. Yes I could well be near or at the top speed governer if it is set a bit soft. I am not doing anything further to the injection pump until I get an EGT gauge on though. Last thing I need is to melt some pistons. Had my Dodge at a steady 1200 today, 15,000lbs of trailer....

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1977 240D turbo

I have a 5 speed waiting to go in my 240 4 speed when the time is right (clutch change comes to mind!) The FD would be a much easier one day job so I might just give it a try. I wonder what it will be like with both? Dreams of cruising at 80 MPH dance in my head. Of course it will take 2 minutes to get there but that's another matter. And I wouldn't have to wear my noise canceling headphones anymore. I just got a ticket for that last week

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'70 F100 shortbed
'82 Diesel Westy
'83 Euro 300TD
Curtlo Viper
Yeti ARC
Surly long haul trucker

speaking of noise, my 240 did not have any insulation under the rear seat, is this true for all 240's ? I took the insulation out of a wrecked 300, and it made a big difference.

Is the 5 speed an overdrive in 5 ? If so I would not change to a five speed and lower rear.

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1977 240D turbo

It's an OD tranny. All W123 cars came with the under seat insulation so someone must have liberated yours once upon a time.
My car did NOT come with under hood insulation and that is something I should take care of first. It makes a huge difference. That and maybe some header wrap on the exhaust pipe as well would help.
There is something about the pitch of a 4 cyl diesel at high RPM's that makes me feel as though someone is driving an ice pic into my ears

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'70 F100 shortbed
'82 Diesel Westy
'83 Euro 300TD
Curtlo Viper
Yeti ARC
Surly long haul trucker

So which diff are you recommending? What ratio?

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

My well-worn, automatic 240D has that 'icepick in the eardrum' effect at highway speeds. Mt first, rusty, manual 240D was much better, but the solid, manual 240D that replaced it is the best of the bunch. Actually quite pleasent at speeds up to around 70.
If I was converting that one to a 5-speed, I'd hold off changing the rear for awhile, until I had some mileage and experience with the new tranny.

Happy Motoring, Mark

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DrDKW

That would be the prudent move but it's just so easy to swap the pumpkin in the back I might go ahead and get myself into trouble anyway. I can always switch it back if I don't like it later.
Just think, I could do a "Top speed for a 240" thread!

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'70 F100 shortbed
'82 Diesel Westy
'83 Euro 300TD
Curtlo Viper
Yeti ARC
Surly long haul trucker

I'd stick with the 369 with a fiver in a 240d. My prediction is top speed will not be affected and will remain about the same in fifth as it is in fourth. At least that is the case with my 240/300d with the euro 300 na and 307 rear end. 99 mph in fourth or fifth.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Maybe you could set a 240D record with enough downhill ahead of you.
On my '84 5-speed Euro TD, with 3.46 rear, I rarely use fifth-gear anywhere except on the highway.
Also remember the rear-end change will require a matching speedometer. Something I'll need to deal with on my TD as I suspect a PO 'federlised' it with a speedometer for a 3.07-rear US turbo model. It now reads and clicks off the miles about 9% too fast!

Happy Motoring, Mark
.

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DrDKW

Speedometer. What's that?

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'70 F100 shortbed
'82 Diesel Westy
'83 Euro 300TD
Curtlo Viper
Yeti ARC
Surly long haul trucker

Well, if your car doesn't have one, don't worry about it.
Otherwise, on these cars the speedometer calibration is matched to the rear-end ratio. So a rear-end swap, without the matching speedometer, will throw off the speed and mileage readings.

Happy Motoring, Mark

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DrDKW

I forgot the sarc / tag!

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'70 F100 shortbed
'82 Diesel Westy
'83 Euro 300TD
Curtlo Viper
Yeti ARC
Surly long haul trucker

mines a manual, and reasonable up 70 or so. I have a muffler from a 300 on it with no resonator. I little bit of a growl, but a nice growl, not an unpleasant sound. By the way I love the sound of a detroit 2 cycle, so maybe I'm not really well qualified to judge sound

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1977 240D turbo