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Spaceman
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339 Posts
Discussion Starter #1 (Edited)
Gentlemen,

If any (European / EU) members of this great forum should have a 3:89 ring & pinion for a GT 1900, (1971) (NOS or in very good condition) lying around, or know anyone who have one that they will part with do not hesitate to give a PM.

I won't bother you with the a story about a dishonest dealer, but for some reason 3.89 seems to be as rare as hen's teeth.

Thanks in advance.
 

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Opel Key Master
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5,014 Posts
Any of those ring gear sets are very hard to find in the States as well. I know of some, but I do not believe they are for sale. Todd at Opels Unlinited probably awaited some recently with Rogers parts, but they are all mismatched and a mess. Who knows what goes with what.
 

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Spaceman
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339 Posts
Discussion Starter #4 (Edited)
Gents,

I have purchased a used (but in good condition) 3.67 from https://viadanny.com/, and he will ship it tomorrow. It will be a "workaround" solution for my rear diff rebuild project. I have already all other parts (bearings, NOS spider gears, and NOS carrier for a 3.67 / 3.89)

I would have preferred a 3.89, but the one dealer who claimed he had it didn't when it came to reality.

Danny Sohns from https://viadanny.com/ do have a used 3.89 in stock, but it has rust on 5 teeth on the crown wheel, which Danny has been quite honest about :yup:, but the diff wizard who is doing the rebuild for me told me not to purchase it :no: when he saw the pictures of it, and told me I would be better off with a good condition 3.67 :)

Still if someone inside the EU should have a NOS or in good condition 3.89, I'm still interested, as I can just flip the 3.67 for greens, but if I do not get a positive response in the next couple of days I'll go with the 3.67..- plenty of those by the way!

Cheers
 

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Registered
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123 Posts
Differential gears...

Gents,

I have purchased a used (but in good condition) 3.67 from https://viadanny.com/, and he will ship it tomorrow. It will be a "workaround" solution for my rear diff rebuild project. I have already all other parts (bearings, NOS spider gears, and NOS carrier for a 3.67 / 3.89)

I would have preferred a 3.89, but the one dealer who claimed he had it didn't when it came to reality.

Danny Sohns from https://viadanny.com/ do have a used 3.89 in stock, but it has rust on 5 teeth on the crown wheel, which Danny has been quite honest about :yup:, but the diff wizard who is doing the rebuild for me told me not to purchase it :no: when he saw the pictures of it, and told me I would be better off with a good condition 3.67 :)

Still if someone inside the EU should have a NOS or in good condition 3.89, I'm still interested, as I can just flip the 3.67 for greens, but if I do not get a positive response in the next couple of days I'll go with the 3.67..- plenty of those by the way!

Cheers
So I looked around in my "spares" and I have a 4.22:1 Gear Set... Anyone have any interest...? Ernie Bello
 

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686 Posts
You can change the tire size to 185/60 13, which will make your 3,67:1 ratio feel like a 3,89:1. According to my calculations, a 3,67:1 ratio with 185/60 13 tires has a speed of 106,13km/h @3000RPM, almost the same as a 3,89:1 with 185/70 13 tires which has a speed of 106,73km/h @3000RPM.
0,5522 x 3000 / 2,95 x 0,189 vs 0,5892 x 3000 / 3,13 x 0,189
 

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1,876 Posts
You can change the tire size to 185/60 13, which will make your 3,67:1 ratio feel like a 3,89:1. According to my calculations, a 3,67:1 ratio with 185/60 13 tires has a speed of 106,13km/h @3000RPM, almost the same as a 3,89:1 with 185/70 13 tires which has a speed of 106,73km/h @3000RPM.
0,5522 x 3000 / 2,95 x 0,189 vs 0,5892 x 3000 / 3,13 x 0,189
Interesting math!!!!!

Here's my set up

175 70 r13 , (22.5" tall mounted on car) stock 3.44 ratio rear

At 100km/h (on gps) @ 3400 rpms

So that would "simulate" final theoretical ratio of?


P.S My apologies to the original author of this thread for this off topic post....
 

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Spaceman
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339 Posts
Discussion Starter #8
@Commodåren,

Thanks for your calculation, but I'll stick with my 185/70/r13 (Pirelli CN36) :yup:

I guess that my up-coming engine rebuild will provide some of the necessary extra hp to compensate, as my initial plan is to go for a ENEM Y12 cam..- so who knows the 3.67 might turn out to be a good choice.

The important part is that it'll (still) be good drive on the streets. If I go in track-day mode again I plan to have set of street legal tires / wheels, and there I can aim for 185/60/r13

Cheers
 

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686 Posts
The stock 165 13 tire diameter is 0,5942m if we assume it's a newer 80-profile. The diameter of a 175/70 13 is 0,5752m.
I assume the tranny is an original four speed with a 1:1 fourth.
0,5942 x 3400 / 3,44 x 0,189 = 111km/h @3400RPM vs 0,5752 x 3400 / 3,44 x 0,189 = 107,45km/h @3400RPM
The lower tire makes the ratio feel like a 3,55:1.
 

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686 Posts
@Commodåren,

Thanks for your calculation, but I'll stick with my 185/70/r13 (Pirelli CN36) :yup:

I guess that my up-coming engine rebuild will provide some of the necessary extra hp to compensate, as my initial plan is to go for a ENEM Y12 cam..- so who knows the 3.67 might turn out to be a good choice.

The important part is that it'll (still) be good drive on the streets. If I go in track-day mode again I plan to have set of street legal tires / wheels, and there I can aim for 185/60/r13

Cheers
I believe the 3,67:1 ratio will be good, and there is still the 185/60 tire option if needed. Just don't forget to increase the static compression to about 10:1 if you are going to use the Y12, otherwise you probably will lose some needed low end torque.
 

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686 Posts
Interesting math!!!!!

Here's my set up

175 70 r13 , (22.5" tall mounted on car) stock 3.44 ratio rear

At 100km/h (on gps) @ 3400 rpms

So that would "simulate" final theoretical ratio of?


P.S My apologies to the original author of this thread for this off topic post....
Your private message inbox is full, so I couldn't reply to your PM.
 
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