Grey motor performance...3.55:1 and 3.36:1 diff ra

[FB_MAD]

   G'day all.I posted this question on FB/EK forum...no replies so was hoping someone here could answer.I'm after tacho readings (top gear) with 3.36 and/or 3.55 diff ratios using 13 inch rims and standard profile tyres at say 30,40,50,60 m.p.h. I did have a formula to work out theoretical rpm using different speeds/tyre/rim combinations but can't find it now.
  Also is there anyone running either of these ratios behind a grey???.Disappointed or happy with performance???.I'm building up an FB standard and want to run either of these ratios to ease engine revs on highway running and maybe help with economy($1.40 litre Grrrrrr !!!).I've only ever run the standard 3.89:1 diff in all my previous projects over the years.Hope someone can give feedback.....good excuse now to go for a spin on the weekend!!!!  Regards Terry.

[colt]

Terry, 3.55 seems to be a good ratio for greys. A number of guys with stockers run this ratio. My car has 3.55 with a modified grey, from memory around 3200-3300 revs at 60 mph. I have a lightened flywheel which knocks the torque around though.
Colin

[FB_MAD]

Thanks Colin for taking the time to reply.I'm going to be running a stock grey until the ministeress-of-finance releases funding for some engine mods or I go the way of a 149 red motor (see wanted ad this forum).Do you reckon a 3.36:1 ratio with a stock grey would be asking too much of the engine to get the car along without the need for the the accelerator pedal needing to hover close to the floor?.    Terry.

[EJ_Dave]

I've run all three ratios behind my fairly stock grey and the 3.55 is the pick. The revs work out to almost spot on 20mph/1000rpm (32kph/1000rpm). Much better than the 3.89 at speed but much easier to get going around town than a 3.36.

Dave

[RET]

That seems to be the consensus of opinion.  They're all fine on the highway, but it's the city cycle where you strike trouble.  Anything taller than 3.36 puts a lot of strain on the clutch and first gear.

Hope that helps,
RET

[FB_MAD]

Thanks Colin,Dave and Ret. All this info appreciated.I'm in the bush so most of my driving is highway (couple of small hills around the area)with a bit around town so I might give the 3.36 a go first and see how it goes.Dave,I had a FC Wagon years ago with the stock 3.89 and I sort of remember it was reading about 3400 rpm @ 60 mph with the old crossply 13's so your 3.55 ratio @ 60 mph = 3000 rpm sounds right.I'd guess a 3.36 would run around 2800 rpm @ 60 mph or so.I wonder where the stock grey's high point of the torque curve sits???   Thanks fellas for the input......Terry.