Opinion Re Differential Gear Ratio

[alexiskai]

Originally Posted by Bob Bidonde

I will opt for the 3.27:1 gear set, so the search for the gears begins. I live on Long Island which is mostly flat. My annual long distance touring is to the New England Meets which can be a hilly ride. As I mentioned earlier, the engine in my Victoria is a Model B with a 6:1 cylinder head, a chopped flywheel and a V8 clutch. My guess is the this motor has between 50 & 60 HP.

Just for clarification, the gear sets sold currently are 3.25:1, not 3.27:1. I believe it's due to a change in the tooth numbering. The old sets were 36:11 and the new sets are 39:12.

The current sets are manufactured by Italian company Motive Gear. I think they must do them as a custom part run because this particular gear set is not listed in their catalog. Either Snyder's or Bert's sells the 3.25 gears for about $525. Sacramento Vintage Ford lists the old-style 3.27 gear set in stock for $750.

[Synchro909]

On 2 of my cars, I run 5.25X21 tyres on the back and a stock 3,78 rear end. That gives me an effective ratio about the same as running a 3.54 diff (to within 1%). By the time I engage the 26% Mitchell O/D, the effective ratio is 2.81 - way higher than anything spoken about so far. There have been times when I have forgotten to take the car out of O/D when I stop and try to move off in high 1st. It doesn't like it but once moving, I love high 2nd and high 3rd gears. Even towing a trailer that weighs as much as the car, 50 mph on the flat is easy.
The motor has a 5.5 head on it but I'm sure it is higher now that it's been planed a few times. It cranks 105 - 110 psi compression. It has a mildly modified cam and a down draught Stromberg carburettor that has a throat the same as the first barrel of a Webber (26mm) I estimate it puts out about 70 hp.
That combination has been all around this continent (same size as your lower 48) a couple of times and more and loves the flat outback country. Around these parts, I don't tow very much and that setup is great for solo car touring. I wouldn't change what I have for versatility.
In short, with the right engine, 3.25 should be good ratio but with a less modified one, I wouldn't go higher than 3.54 and be prepared to travel slower.
It is worth noting that the engine will be working harder with a high ratio and cooling could then become an issue. Ask the man who knows!