Alfa Romeo Forums banner

1 - 20 of 37 Posts

·
Registered
Joined
·
179 Posts
Discussion Starter #1
Not sure what LSD this is but I think its a 4:10 is there anyway to confirm? it had a blue F stenciled on the side of the housing before I cleaned it ip.

can someone please confirm what I have here? thanks guys
 

Attachments

·
Richard Jemison
Joined
·
7,080 Posts
LSD

Stock LSDs come with 1 clutch disk per side and lock up rate is about 20 %. Adequate for street use. Reconfiguring the internals, and using 2 clutck disk on each side of the unit results in about 40% lock up. Good for track, but not street use.
 

·
Registered
Joined
·
216 Posts
It is stamped on your ring gear; 2nd picture. It appears to be 8/41? which would be a 5.125:1 gear ratio. If you count the teeth, calculating the ratio is driven/drive or ring/pinion.
 

·
Registered
Joined
·
179 Posts
Discussion Starter #8
none of this makes sense to me...
I looked at the PDF and I don't see anything that translates
 

·
Registered
Joined
·
179 Posts
Discussion Starter #9
Counted the gears. 9:41 what is this good for? quick acceleration or speed?
I want to use it for my 71 gtv 2L
 

·
Registered
Joined
·
841 Posts
It is stamped on your ring gear; 2nd picture. It appears to be 8/41? which would be a 5.125:1 gear ratio. If you count the teeth, calculating the ratio is driven/drive or ring/pinion.
Much more likely to be 9/41, which would be the 4.55.
The stamping in that pic is very unclear for the first digit.

Steve
 

·
Moderator
Joined
·
9,944 Posts
Counted the gears. 9:41 what is this good for? quick acceleration or speed? I want to use it for my 71 gtv 2L
41 / 9 = 4.55, which is the most common ratio used on 60's - 70's era Alfas here in the US. As Hans-Peter wrote, 4.55 is better for tight turns on mountain roads than for freeway driving. Once Alfa introduced the higher torque / lower rpm 2L engine, it is puzzling why they retained the 4.55 (it made more sense in the days of 1600cc engines).

But if you have a 4.55, go ahead and try it. A lot of this is subjective. Alfas engines are free-revving, and listening to your's turning 4,500 rpm at freeway speeds may be music to your ears.

If that revving drives you nuts, the common swap is to install a differential from a Bosch injected spider from the '80's-'90's era. Those had a 4.1 ratio, which will drop you rpm's by 10%. The low 1st and 2nd gears in the Alfa transmission still allows great acceleration with that ratio.
 

·
Registered
Joined
·
179 Posts
Discussion Starter #14
The red paint is also the ID mark I just discovered well that makes things easy wish I knew before
 

·
Premium Member
Joined
·
13,090 Posts
I like my 4.55. 6800 in 4th gear is 100 mph. I have a rebuilt 4.1 that has taken up space in my garage for years and I doubt that I will ever install it. Now if I had a diesel engine in the Spider....
 

·
Registered
Joined
·
3,518 Posts
Well you have it figured out thanks to others.

The stamping on the gear, that is not well done in your case, must be 9/41 for a ratio, as others say, of 4.55 or 4.56 as some say. So a good stamping tells the story but counting teeth and doing a division is best.

It also possible to lock one axle and rotate the input, while noting the input's rotations and counting the rotating axle's number of turns. Then one number, and here I forget, has to be halved or doubled before division to get the ratio to make sense.

Here is what I found for available axle ratios in Comp Advisory Service Manual. The Manual also gives the applications as of date of publication.

RATIO Teeth
3.73 11/41
3.91 11/43
4.10 10/41
4.56 9/41
4.78 9/43
5.12 8/41
5.38 8/43
5.86 7/41


FWIW

Ken
 

Attachments

·
Registered
Joined
·
2,336 Posts
It also possible to lock one axle and rotate the input, while noting the input's rotations and counting the rotating axle's number of turns. Then one number, and here I forget, has to be halved or doubled before division to get the ratio to make sense.
When you lock one wheel and rotate the drive shaft(pinion) the other wheel that rotates spins twice as fast as it would if you let both wheels rotate. So on the 4.56 if you turn the pinion just over 4.5 turns you will get 2 turns from the one wheel that can rotate. If you let both wheels turn at the same rate 4.56 turns of the pinion will give one revolution of each rear wheel.
 

·
Premium Member
Joined
·
6,347 Posts
I've swapped them back and forth and with a modifed 2L with a few extra torques and hp s I've landed back in the 410. Then again this is akin to whats better, B&W or Color. It depends is really the only correct answer.
 

·
Registered
Joined
·
556 Posts
Unlikely that even Alfa Romeo would make a 43:10 ( 4.3 ratio ) as found in 2 litre Berlinas and a 39:9 ( 4.33 ratio )
 
1 - 20 of 37 Posts
Top