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Old 02-17-2010, 05:27 PM   #8 (permalink)
EcoModding Apprentice
Join Date: Oct 2008
Location: Chile
Posts: 222

Mercedes 89 D - '89 Mercedes 300 E
90 day: 33.86 mpg (US)

Skodie - '09 Skoda Octavia TDI PD
90 day: 38.84 mpg (US)

1993 Mercedes 300D Turbo - '93 Mercedes Benz 300D Turbo W124
90 day: 26.19 mpg (US)

Crossie - '16 Subaru XV Crosstreak
90 day: 9.61 mpg (US)

Crossie - '16 Subaru XV Crosstreak
90 day: 33.34 mpg (US)
Thanks: 15
Thanked 9 Times in 7 Posts
RD28 diesel engine in a NASH: final ratio issues.

Hi Mauricio,

You wrote: "I'm trying to fit a RD28 in an old Nash 1956 (rambler model). This car has an original rear ratio of 4.2 (too slow, I thought)..."

I say: No, I think this ratio is PERFECT for the Nash. The original ratio of the Laurel diesel was 4.08. It may be too short, but only a little. You can fit larger tires and it will be nice.

You wrote: "and I bought a Dana 30 with 3.07 ratio". Here there are no hills but maybe this ratio is too fast. How was your car with this relation in horizontal terrain?"

I say: My car had a 3.07 final ratio standard. The car was too slow in horizontal terrain. No sprint at all. The fifth gear (lock, actualy) entered only at 110 km/h. This is very bad, as it is the gear with maximum yield. So the car yielded poorly also.

Yoy wrote: "Have you some technical information about laurels and skylines gearbox and differential available? I've a 5 speed gearbox, and you have an automatic gearbox. Is it relevant?

I say: Manual gearbox will give you a better control and some more yield. With a 3.07 ratio the car will move smootly, no doubt. But a little Citroen 2CV will surpass you on a hill.

You wrote: "You say that in the original car it was a 4:1 final ratio, isn't? It is the only available ratio or there are also faster? I thought that RD28 are similar as a naturally aspirated merc. 300D (88hp) and this engine comes with a 3.0:1 final ratio.

I say: I think you are wrong. Merc diesel has a 3.0 ratio, but Laurel and Skyline doesn´t. See for exampe these link:

R200 Diff Ratios -

You wrote: "But maybe the RD28 has less moment and higher rpm?! Maybe i must try the car first with the original ratio (4.2:1) and if it is too slow, I must change for the 3.07:1. What do you think about? Thanks and best regards",

I Say: Well, RD28 I have is a 1996 with 18 valves, and 100 HP of power. There are some older engines with 92 HP only (12 valves). And RD28 has higer revs.

I agree you should start with the 4.2 final ratio and see how it works.
There may be a gearbox influence between Merc and Skyline, because Mercs do not handle as high relations as Skyline.

Take you notes, make some tanks drives, see more comfortable speed for changing gears, and so on. Hopefully, use a tachometer.

Then, if you think it is not good, try your 3.07 differential and compare.

Good luck,


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