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Discussion Starter #1
Looking to buy a new or used 4.77 Ring and Pinion for the smaller (1.6) liter GTA rear end housing.

Bob

1965 RHD GTA Corsa Ex-Horst Kwech 1966 Trans-Am and B-Sedan Champion
 

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Discussion Starter #3
These are the only pieces I know of. ThisCrazyGarage.com
The seller is Curtis Wood. He is a good guy and the prices seem fair from what I have seen.

Andy
Andy thanks for the reference, but I called him yesterday a hour after he cut a deal with Anthony.

Bob

1965 RHD GTA Corsa Ex-Horst Kwech 1966 Trans-Am and B-Sedan Champion
 

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I still have a 5.12 rear end with the sliding block pin and a brand new O.S. Giken LSD in it for sale. I think you are only talking about 5-6 mph difference in top speed with the same size tire.
using a 24" tire and a .85 5th gear a 4.77 will give you about 17.3 mph/1000 rpm.
" 5.12 will give you about 16.2 mph/1000 rpm.

Andy
 

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Discussion Starter #5
I still have a 5.12 rear end with the sliding block pin and a brand new O.S. Giken LSD in it for sale. I think you are only talking about 5-6 mph difference in top speed with the same size tire.
using a 24" tire and a .85 5th gear a 4.77 will give you about 17.3 mph/1000 rpm.
" 5.12 will give you about 16.2 mph/1000 rpm.

Andy
Andy,

I bought a NOS 5.12 from Re-Originals but Roman has urged me to get a 4.77 for the long tracks like Road America, Road Atlanta and even Watkins Glen.

So I may trade away the 5.12 or stock three diff set ups. In the Can-Am car we change the gears and to be competitive you need a similiar investment in various ratios to do the popular tracks. I have also settled on using the Gripper diff from Alfaholics as my standard diff.

Bob

1965 RHD GTA Corsa Ex-Horst Kwech 1966 Trans-Am and B-Sedan Champion
 

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I know one other guy I can call next week. He doesn't use the internet so I will let you know. You could also try Larry Ogle in the Chicago area. I do not have any contact info for him, but he is reported to have some nice nos Alfa Racing stuff.

Another thought would be to get the 15" GTA replica wheels for the long tracks to get more top end by just changing wheels to a larger diameter tire.
Andy
 

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Bob, sorry I don't have a 4.77 for you. And it sounds like the one my brother had got away just before you called. But here are couple thoughts. First, although Roman has forgotten more about these cars than I will ever know, I would bet that a 5.12 would be fine with one of the smaller engined cars. I assume you are running a 1600 in the GTA. I run a 4.77 with a .85 fifth and 225/50-14 tires with a 2L. At Road America, on laps as low as 2:41, I don't run over 7700 rpm at the ends of the straights. With a 1600, even a GTA motor, I doubt you will see top ends that high, and therefore the 5.12 would probably work okay. Second thought was that I believe OS Giken (i.e. Anthony Rimicci) is making the 4.77 gears for the early diff. That's where I sourced them for my 2L, but I thought they were making them for each type for about $1500.

Erik Wood
 

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Discussion Starter #8 (Edited)
Bob, sorry I don't have a 4.77 for you. And it sounds like the one my brother had got away just before you called. But here are couple thoughts. First, although Roman has forgotten more about these cars than I will ever know, I would bet that a 5.12 would be fine with one of the smaller engined cars. I assume you are running a 1600 in the GTA. I run a 4.77 with a .85 fifth and 225/50-14 tires with a 2L. At Road America, on laps as low as 2:41, I don't run over 7700 rpm at the ends of the straights. With a 1600, even a GTA motor, I doubt you will see top ends that high, and therefore the 5.12 would probably work okay. Second thought was that I believe OS Giken (i.e. Anthony Rimicci) is making the 4.77 gears for the early diff. That's where I sourced them for my 2L, but I thought they were making them for each type for about $1500.

Erik Wood
Eric and Andy I checked your calculations and get close to the same numbers.
I will be shifting at close to 7700 and have a 205/60r14 tire. With a 5.12 CWP and a .85 fifth gear I would get 133.8mph and with a 5.12 CWP 124.7 mph.

Not that I can hit 133.8 mph at Rd America, but my Scott Gray engine made good hp and I would not want to be lifting before the end of the straight;hence I would chose the 4.77 CWP for Road America. I don't know much about GTA times but 2.41 at Rd America seems pretty good compared to Spec racer times.
I would hope a GTA with a good motor and driver could do similiar times to your 2 liter GTV (?), but once again I am new to this Alfa world.

Do you guys have similar information for Road Atlanta and Watkins Glen?

Thanks for your input.

Bob


1965 RHD GTA Corsa Ex-Horst Kwech 1966 Trans-Am and B-Sedan Champion
 

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Bob FYI, 2.41 @ RA is the fastest time I have ever seen for a Alfa GTV/GTA body on treaded tires. More common is 2.44-3.05 lap times. I know the GTA is lighter, but top speed will likely be limited by HP vs wind resistance. I believe Eriks car had a lot of fiberglass (light weight) and was making 167hp at the rear wheels when he did the 2.41. The GTA driven well will make up it's time under braking and 3 wheeling through the corners!
 

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Bob and Andy, first let me say that I have run a total of one lap in the 2:41's at Road America. But my point was that I didn't run out of revs with the 4.77 with that lap time. Peter Stark says he runs about the same revs with a 4.55, but then he is faster than me. He was in the 2:40's at the last event. Of course I blame that on weight. Our cars each weight the SVRA minimum of 2000 pounds, but I weigh 265 and Peter wouldn't way half that dripping wet! Well, okay...he can also drive!

As Andy pointed out, the GTA could end up as quick, even with the smaller motor. But I doubt it would hit similar top speeds. That is more limited by aerodynamics and horsepower. So what kind of power is your 1600 making? If I were in your shoes, I'd be tempted to run the 5.12 for now and see how it goes. You can always put a 4.77 in it later. If you must have it now, you may want to buy an OS Giken one for a 2L style diff. Of course if you have already bought the Gripper LSD for the early style, that wouldn't be an option. Or, if you have the early diff set up for a sliding block, it might not go right onto the later style diff.

As for Watkins Glen, I don't remember running very high top speeds there. On the front straight, I was just getting into 5th. And the long uphill pull toward the bus stop didn't get me near redline in 5th.

Erik

Bob FYI, 2.41 @ RA is the fastest time I have ever seen for a Alfa GTV/GTA body on treaded tires. More common is 2.44-3.05 lap times. I know the GTA is lighter, but top speed will likely be limited by HP vs wind resistance. I believe Eriks car had a lot of fiberglass (light weight) and was making 167hp at the rear wheels when he did the 2.41. The GTA driven well will make up it's time under braking and 3 wheeling through the corners!
 

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Don't forget that the 1600 with it's lighter rotating internals should be able safely outrev the 2L
 
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