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Rear End Gear Ratio

C

Carmen Sauro

Donation Time
Hello Club Members:

I have a 1960 Alpine with over drive set up for VSCCA racing. I need a higher rear end gear ratio. I have plenty of horse power. The car just won't go. Can anyone please tell me what rear end gear ratio I need?

Thanks in advance,
Carmen
 
R

RootesRacer

Donation Time
Higher numerical (lower ratio) or higher speed (lower revs)?


There were at one time a bunch of ratios available for various cars that used the same axle system.

Ratios you can find today are 3.70, 3.89 and 4.22.

In addition to these, there were (at one time) rootes cars that used 4.44, 4.86 and numerical ratios to 5.78 on the older 15 inch wheeled cars.

On any rootes small car axle, there were two types of gears. The newer hypoid and the older spiral bevel type.
They and their third members are NOT compatible with each other, but entire third members can be swapped from axle to axle from the mid 50s into the 70s.
The caveat is that you must find the appropriate axle spline for the third member, or swap out the spider gears to the spline axle you will use.

I used to run a 4.55 spiral bevel third member (from a 15 inch wheeled rapier) in an SII alpine axle case.
Great for acceleration, but runs out of poop pretty low in the road speed department.
 
DanR

DanR

Diamond Level Sponsor
Quote .....a 4.55 spiral bevel third member (from a 15 inch wheeled rapier) in an SII alpine axle case.
Great for acceleration, but runs out of poop pretty low in the road speed department. Unquote.

Running out of poop with the 4:55 is where a good OD comes in Handy!:D
 
DanR

DanR

Diamond Level Sponsor
Carmen,

Rootes gave you some good info on the various gears....

My question would be.... What gears are you presently running?

Suggestion: Go from there to what Rootes mentioned and make a pick!
 
R

RootesRacer

Donation Time
DanR said:
Quote .....a 4.55 spiral bevel third member (from a 15 inch wheeled rapier) in an SII alpine axle case.
Great for acceleration, but runs out of poop pretty low in the road speed department. Unquote.

Running out of poop with the 4:55 is where a good OD comes in Handy!:D
Click to expand...

No D type overdrive will survive the shock and torque my engine would put through it. The factory twisted OD shafts with far less power.

The 4.55 was fun but totally impractical both for street or the track.

Someday I hope to do a J type OD conversion, even still I doubt I would go lower gearing (higher numerical) than a 3.89.
I know I could top out a 3.70 right now at 7000+ RPM without OD.
 
George Coleman

George Coleman

Gold Level Sponsor
Just a note I have a 3.70 in my car great! I did notice that Roots Post Vintage no longer list the 3.70 gear sets they had, good luck finding one.:cool:
 
RootesRooter

RootesRooter

Donation Time
Carmen Sauro said:
Hello Club Members:

I have a 1960 Alpine with over drive set up for VSCCA racing. I need a higher rear end gear ratio. I have plenty of horse power. The car just won't go. Can anyone please tell me what rear end gear ratio I need?

Thanks in advance,
Carmen
Click to expand...


You need to clarify. Are you lacking top end speed or acceleration? Do you know what gear ratio you currently have?

If its top end, I think Doane Spencer's "Project Sunbeam" Alpine ran 4.44's with OD and was competitive in its class against the last of the bathtub 356's, etc. That the 4.44 was a posi probably helped in the corners, but I don't think they ran out of rpms on most tracks. Are your local road courses particularly long-legged (ie. incorporating a 1/4-mile drag strip as part of the main straightaway)?

If its a matter of acceleration, switching from 3.89's to 4.22's is the most straightforward strategy. If you're already running 4.22's, see RootesRacer's post.

As mentioned many times here, the Achilles heel of Alpines are the crown wheel bolts and their soft tab washers. Whatever gears you select, make sure the bolts are fresh and tight!
 
C

Carmen Sauro

Donation Time
Hi RootesRooter,

All of these response are great thank you! Please bare with me I'm not very mechanically inclined. I have a series I with OD the 4.22:1. The car has no low end or high end speed (max 80mph with OD on).

I have 13" tires with a diameter of 23". Will a tire or rim adjustment help me out? If so what to I want to run?

Thanks again everyone on this site is awesome. What a great club!

Carmen


RootesRooter said:
You need to clarify. Are you lacking top end speed or acceleration? Do you know what gear ratio you currently have?

If its top end, I think Doane Spencer's "Project Sunbeam" Alpine ran 4.44's with OD and was competitive in its class against the last of the bathtub 356's, etc. That the 4.44 was a posi probably helped in the corners, but I don't think they ran out of rpms on most tracks. Are your local road courses particularly long-legged (ie. incorporating a 1/4-mile drag strip as part of the main straightaway)?

If its a matter of acceleration, switching from 3.89's to 4.22's is the most straightforward strategy. If you're already running 4.22's, see RootesRacer's post.

As mentioned many times here, the Achilles heel of Alpines are the crown wheel bolts and their soft tab washers. Whatever gears you select, make sure the bolts are fresh and tight!
Click to expand...
 
RootesRooter

RootesRooter

Donation Time
If your max speed is only 80 with O/D (should be 95+), your problems lie elsewhere. (ie. carbs, electrics). Also, are you sure the OD is engaging correctly?
 
C

Carmen Sauro

Donation Time
Hello RootesRacer,

Please bare with me I'm not very mechanically inclined. I have a series I with OD the 4.22:1. The car has no low end or high end speed (max is actually 90mph with OD on).

I have wire rims with small 13" tires they have a diameter of 23". Will a tire or rim adjustment help me out? If so what do I want to run? If I need to change the 4.22 ratio are others obtainable? Can you suggest one please?

The car's been recently been fully race prepped. Webers are dialed in completely rewire.

Thanks again everyone on this site is awesome. What a great club!

Carmen



RootesRacer said:
Higher numerical (lower ratio) or higher speed (lower revs)?


There were at one time a bunch of ratios available for various cars that used the same axle system.

Ratios you can find today are 3.70, 3.89 and 4.22.

In addition to these, there were (at one time) rootes cars that used 4.44, 4.86 and numerical ratios to 5.78 on the older 15 inch wheeled cars.

On any rootes small car axle, there were two types of gears. The newer hypoid and the older spiral bevel type.
They and their third members are NOT compatible with each other, but entire third members can be swapped from axle to axle from the mid 50s into the 70s.
The caveat is that you must find the appropriate axle spline for the third member, or swap out the spider gears to the spline axle you will use.

I used to run a 4.55 spiral bevel third member (from a 15 inch wheeled rapier) in an SII alpine axle case.
Great for acceleration, but runs out of poop pretty low in the road speed department.
Click to expand...
 
R

RootesRacer

Donation Time
Yeah, if you cant get near 100mph either your OD isnt working, you dont have the ratio you think you do or your engine is woefully under powered.

Even the 1494 should be able to get near 100mph, probably with a slightly higher speed out of OD than in.
 
RootesRooter

RootesRooter

Donation Time
For starters, stock Alpines have never been road burners. Not by the standards of 1959-68 and definitely not by today's. The Series I's 1494cc was the least peppy of the bunch. Still, test drive reviews when the car was new nibbled on the 100mph mark. And that was with Zeniths.

If a good shop has gone thru the Webers and wiring, then you have to consider the history of the motor itself. Is compression strong? Any headwork? Does it have a stock cam? If not, who installed (or mis-installed?) the replacement cam and what kind of profile does it have? Any chance the lobes have flattened out? You also might consider another shop for a fresh set of eyes and a 2nd opinion.

Do you have twin 40DCOE's or single downdraft?
 
mototron

mototron

Donation Time
Hello
I run 4:22 ratio without overdrive in a series II Alpine with a 1725 .
and just break the 100MPH mark at most of the tracks I run at .It sound like you are way low on power do a comp. check , set valve lash , and check max ignition advance

Rocco
 
B

Bill Blue

Platinum Level Sponsor
Back to basics. Is the 90 mph actual? Old dash instruments are notoriously inaccurate.

"Back in the day", with about 20,000 miles on the clock, my Series II averaged 100 (95 and 105) mph on a two way run. Overdrive engaged, cool November day, temperature was probably in the 30's. Top up. Dead stock.

Bill
 
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