Moss Motors, Ltd

What is considered the standard gearing ratio for a 71 Spit.  It seems that I've turning too many RPMs for the MPH.

kc,

Yes, that's standard for a Spitfire.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

The Moss parts manual lists a 3.89:1 gear set as standard for US spec Spits. I think there was a slightly lower ratio available for the GT6 when fitted with over drive. Most of us in the US just aren't used to engines turning the rpms like the British cars, but to get the performance with the small displacement motors they had to use relatively low gearing. If you can find an overdrive transmission for your car it would make highway cruising a lot more relaxed.

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'73 Midget (V6)
'59 MGA (I6) under construction
'73 Lotus Europa
'52 MG TD kit car body project.
'98 Jag XK8

"There is a fine line between a hobby and mental illness"

I guess that what you say is true.  My Merc Sable is about 2000 at 60 mph and I'm used to that.  I do hate to see the tach wind up to that 4500 mark though.  Thanks.

 

Are you saying your tach indicates 4500 rpm at 60 mph? If so, then I'd get the tach checked out, it needs calibration. You shouldn't be turning over around 3700 to 3900 rpm at that speed if I remember correctly from my Midget. It had a 3.9:1 rear axle ratio with the same size 13" tires, so the final drive rpm should have been about the same. Here's a link to a calculator which will help you decide if your tach is accurate, just plug in the axle ratio, the tire size, and see what happens. http://www.f-body.org/gears/

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'73 Midget (V6)
'59 MGA (I6) under construction
'73 Lotus Europa
'52 MG TD kit car body project.
'98 Jag XK8

"There is a fine line between a hobby and mental illness"

Thanks a lot Bill.  I'm going to have to wait till spring and then check the gearing.  I was quoting from memory on the RPM's but it did seem like it would be winding pretty tight if I wanted to hit 70 with her.

By the way.  I couldn't stand it any longer.  It warmed up a bit today, 32deg F and I had to fire her up.  She's been sitting for over three months but with a lot of pumping the gas and a good bit of choke she fired right up and ran smooth as she did when I put her down.  Gotta love those little cars.

 I have a 1969 Spitfire with overdrive and a different rearend from another Spitfire. I'm turning 3000 RPMs at 80 MPH. It's like i'm idleing down the freeway. My fuel milage is pretty darn good to as you can guess.

i have a 69 spit with a 4:11 rear end and i just upgraded to a 3:89   i also found a tr7 5 speed for her to put in but can't find out what parts i need to swap to get it in    any ideas ?

stealthrt,

To the best of my knowlege there are no parts at all for making such a conversion. I must say that you have picked a very heavy gearbox to use. It's also kind of bulky for a Spit, though it'll certainly be strong enough if you dsecide to go that way.

If you do, there is a lot to consider. It's really a bit of a minor engineering job to make a gearbox which is comnpletely unrelated to a given engine fit that engine. You must consider such things as: the protrusion and diameter of the pilot bearing and input shaft's rel/ationship to it, An engine backplate which fits the bellhousing bolt pattern, AND puts the input shaft of the gearbox EXACTLY concentric with the flywheel and clutch, along with that input shaft bearing in the back of the engine. Then you must accomodate the physical size of the gearbox, which sometimes involves modification of the tunnel and/or floor. You must overcome the challenge of a proper mount at the rear of the gearbox. You must find a way to accomodate the slave cylinder, and you have to find a clutch disc which is the correct diameter but will accept the splines on that darned input shaft on the donor box.

All this and more is why various companies make and sell kits. They take the time to engineer all this stuff and to set up tooling and produce and market it.

Many folks feel that many of the five speed kits out there are too expensive. I've even heard folks call them a ripoff. For all the reasons stated above, and the fact that those companies have to then stand behind the product, they are actually a bargain offered to a pretty small niche market. I'm NOT shilling for Moss here. I just recognize the difficulties encountered in trying to develop such a thing.

Now, if you want to persue this thing, my hat's off to you for your determination at the least. BUT, I do believe you can find a better gearbox for this particular application, even if you decide not to use a kit. The TR7 Transmission, if it's still good, is worth money to someone who is making a five speed Rovre/MG V8 engined MGB or such, though they'll have to find the proper bell housing from a TR8 or a Rover SD-1.  Good luck, and let us know how it's going.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon