Why not comprimise a little farther? I think the NA five cylinder engined cars of the late 70s and early 80s had the 3.47 ratio rear ends. Not a lot quieter at speed but signifigant enough to consider in my opinion. 3.69 is going to be too noisy in my opinion. The na rear 3.47 end should be easy to get your hands on. I do not see any demand for them.

Without being defensive, I use the best built helmet money can buy, which is
an Arai Quantum which protects my "knowledge base".

And the best hearing protection money can buy ,
which happen to be in-ear Etymotic ER4S headphones and/or hearing protectors.

For road trips, I power the headphones with a portable Bose 1401 amp with a total loss dedicated battery, in various cars.

Or to protect against my collection of noisy machinery and noisy hobbies, when
I'm in my shop, I use the headphones with a pocket radio; or the hearing
protector version -- which have interchangeable fit adapters.

Its an audiophile solution for long distance travel comfort,
in a car. At dB levels lower than typically required in a 30 year old car,
unless you've applied some noise abatement product to the sheet metal.

I can do it with the top down/off, when that's an option. See Porsche 914/6.
YMMV.

If you haven't tried it, perhaps you should not knock it. If you have, what's the problem, again?

__________________
--frankb

1982 300TD 617.912 <NLA> . 1975 2002 E10-EFI . 1976 914c6 . 1983 MG LMIII <NLA>. 1988 Montero / 616<NLA> . 2001 TLS . 2005 Saab 9-5 Wagon

Technically you could buy noise cancelling headphones. They pick up the noise and apply a counter noise that cancels out both noises. Just do not wear them in the presence of the wife or girlfiend. You could land up as dead meat.

Barry,

I think you'll grant that a n/a 617 is quieter than a n/a 616 at
same rpm. Side effect of 5 cylinder "natural" balance. See audi ads from the 80's fwiw.

So, a 3.69 is less objectionable than pre-1982 240D -- right? 3.69's, I think. I'm open to correction.>
Later 300D's have different/better/more insulation -- perhaps in better condition.

So, is the compromise real + necessary? I have the fuel receipts from the 3K trip
to submit if there are any doubters. 24.37 mpg at peak. 23.1 'worst case', which was
in/around Boston traffic.

__________________
--frankb

1982 300TD 617.912 <NLA> . 1975 2002 E10-EFI . 1976 914c6 . 1983 MG LMIII <NLA>. 1988 Montero / 616<NLA> . 2001 TLS . 2005 Saab 9-5 Wagon

headphones of any sort are not legal here in Virginia, check your local laws. Everyone has their own idea of what is to much noise. I am fine with the way my 240 sounds at 70, over that and it is getting more then I want to hear.

__________________
1977 240D turbo

I believe all 240s regardles of year are 369 diff. A long wheelbase probably is 3.90. 220s standard wheelbase are 3.90. Long wheelbase 220s are probably 4.10.

I have never compared a na 300 to a 240 with the same gear ratios so I have no basis for comparison. I doubt there is much difference in noise though at same rpm.

So are you saying your tank which got 23.1 was all town driving and the other was all highway? Did you change your speedometer when you changed your diff gear? Did you fill the tank to the brim each time? What speeds do you drive? Did you check your odometer against the mile markers? Are your tires standard size? Your stated fuel economy is about the same as I experienced in my 300d na with a standard 347 diff, highway but for me town driving with the automatic was under 20 for sure.

Sorry to be a doubting Thomas but these in town mileage claims are a bit on the high side unless you actually were driving on urban interstates mostly at sustained speeds.

__________________
[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.

I also own a five cylinder 77 300d. To me the 3.47 it is about as low a rear end ratio as one wants to go on the highway. You could do the math but in my opinion the 3.69 is getting borderline. Not that it will not work.

How much weight are you intending to pull? There are limits to how strong a hitch can be used on the 123s.

Not.sure.on ex.weight id.say.almost 2 4 wheelers 600ccs.plus maybe extra 600 lbstougne weight 350 lbs.at the hitch...i think? Have to look again...its almost road.ready

Oh 5/14.open tralier.too. Single axle

Tom,

I used my etrex GPS' "daisy chain" recording for ALL mileage records, as well as actual speed reports.
So, its more accurate than all of the changes below, combined.

As far as fuel, I just pulled the numbers right off the pump receipt to the nearest 10th.

My tires are 185/65-14's Blizzaks, which are larger than standard by .2". Not that it matters for this calc.
And yes, the low number; 23.1 mpg, included dropping a friend who lives in Boston. Other than that, and some two lane roads around Camden, ME;
and a brief stint in Holyoke for my daughter's graduation ceremony; the entire trip was freeway, much of it turnpike.

My speed at full throttle is ~73.5, average, as reported. Uphill drifts a bit
to about 69mph. I can maintain "above 65" in all conditions experienced, which I could NOT with the 3.07 diff I pulled out.

Most of the "use a longer diff" advocates on this list seem to be wildly inconsiderate of an 18-wheeler bearing down on you, from behind,
locked into your lane by traffic, uphill, as your speed drops below 60.

68hp. Use it wisely.

__________________
--frankb

1982 300TD 617.912 <NLA> . 1975 2002 E10-EFI . 1976 914c6 . 1983 MG LMIII <NLA>. 1988 Montero / 616<NLA> . 2001 TLS . 2005 Saab 9-5 Wagon

totally agree on the "noise is perceived" issue. And in this world of cellphones,
what in the WORLD are VA legislators thinking? A brick plastered to your head
is safer than an earpiece? How "last century".

In some states its illegal to use a cellphone WITHOUT an earpiece behind the wheel!

My favorite "in-travel" phone pauses the music, switches the call, and re-queues the music without missing a beat -- which is why I switched to
"in ear" phones for travel in the first place. It made it much easier to understand the caller's words, when compared to the tinny, 4 inch dash
speakers in a TD.

Add the caucauphony of noise created by even slightly leaking window seals ... it is a 30 year old car, after all.
The rear speakers aren't even worth considering for music OR voice calls.

__________________
--frankb

1982 300TD 617.912 <NLA> . 1975 2002 E10-EFI . 1976 914c6 . 1983 MG LMIII <NLA>. 1988 Montero / 616<NLA> . 2001 TLS . 2005 Saab 9-5 Wagon

Ok i got my 83 300d on the road at last.at 60 mph. Iam taching appx. 2950 rpms.with the 3,07 gears....if i swap to say a 2.88 gear how many rpms.would that drop it down to.?

i think the 3,69s are going to tach way too high. Dose any know.for sure what rpms at What speed ?

So i might have to use my truck for the heavy.trailer loads after all.

The 2.88 will run 2700-2800 rpm depending on tire size.

Putting shorter gears into the 617 turbo doesn't ever make much sense. If the taller gear cannot pull the vehicle and the load in high gear, you always have the option of using third and slowing the vehicle slightly. In fact, some have put a 2.47 in the vehicle with perfect results. They run about 3300 rpm in THIRD gear on the highway, if they need it.

I'm currently in the process of putting a 2.47 in the 300SE for the exact same reasons. The I-6 will perform perfectly well using gears 1-3 and fourth gear will be for cruise on the highway.

Right now my gps shows 12.8 miles.traveled so far and shows 13.2 on the.odometer.with stock size tires. So whats up with that .

Did you swap in the spedo from the donor the diff came from? The spedo`s are geared to the differential.


Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works