Zf tranny...what diff?

[mightywhitey]

This thread makes me laugh.

Your fenders make me laugh

[Chris916]

Im in the same boat! dropping an m50 in 318is. will be using the zf with the stock 4.10. Its my track car though so its gonna be a blast! :D

[kalib0y]

got a zf with my S50 and I have both the 2.93 and 3.25. I like the 3.25 becuase of the acceleration but I like the 2.93 becuase of the less RPMs at 80mph ~3700 in 5th. The 3.25 is ~4100 at 80mph in 5th. 2.93 is a good diff with strong acceleration for a daily driver.

The reason why I choose to keep the 3.25in there is becuase the S50 and ZF comes out of a car that uses 3.15lsd stock. So a 3.25 would be the closest to stock but a tiny bit faster if you can bear the ~4100rpm highway RPM.

[Wh33lhop]

got a zf with my S50 and I have both the 2.93 and 3.25. I like the 3.25 becuase of the acceleration but I like the 2.93 becuase of the less RPMs at 80mph ~3700 in 5th. The 3.25 is ~4100 at 80mph in 5th. 2.93 is a good diff with strong acceleration for a daily driver.

The reason why I choose to keep the 3.25in there is becuase the S50 and ZF comes out of a car that uses 3.15lsd stock. So a 3.25 would be the closest to stock but a tiny bit faster if you can bear the ~4100rpm highway RPM.

Your speedo or tach is off, or you have your diffs wrong. A 2.93 should be at 3400rpm or so in 5th at an actual 80mph, a little less even at an indicated 80mph (speedo reads high).

A 3.25 should have you at around 3750 at 80 and a 3.46 should be about 4050.

[kalib0y]

Your speedo or tach is off, or you have your diffs wrong. A 2.93 should be at 3400rpm or so in 5th at an actual 80mph, a little less even at an indicated 80mph (speedo reads high).

A 3.25 should have you at around 3750 at 80 and a 3.46 should be about 4050.

It might be my tach becuase I verified these diffs but my tach shows that my care idles at about ~800-900 rpms and sounds fine...any other reason that might lead to a difference between your findings and mine?

[shiboujin]

You guys are all dumb asses. Tossing numbers and shit around like you know WTF you're talking about and not answering the OP's questions properly.

1) And E36 diff will not fit into an E30. The diff cover has 2 mounting points while the stock E30 one only has one. You need the M3/328 drive shaft with a 4 bolt rear half that will mate up to a stock E30 differential. Also an E30 M3 DS will work (so I hear. never seen it done).

2) See this image as a reference (big pic) http://www.slidewaysonline.com/images/gears.jpg

The very left column set is a GR 260 with a 2.93 LSD. Middle column set is a ZF with a 2.93. And the right most is a ZF with a 3.25 LSD.

This is assuming a 195/65/14 tire (24 inches in diameter according to http://www.miata.net/garage/tirecalc.html). Gear ratios are from my own research (http://e30performance.info/viewtopic.php?f=22&t=941). The math is done via =(((A2*D2)/(C2*B2*336.13552))) (check my math if you don't believe me).

According to the excel sheet, highway cruising at 80 mph:
2,659 rpms with the GR260 + 2.93
3,300 rpms with the ZF + 2.93
3,650 rpms with a ZF + 3.25

Now if you want suggestions on picking your diff, shorter will be quicker accel but faster shifting. Longer diffs will be better for highway cruising. The choice is up to you.

[Wh33lhop]

When you want to call people idiots, you might also want to add some new information to the thread. The e36 diff was covered in the first few posts, and if you look a few posts above your own you'll find I just went over the cruising rpms.

[shiboujin]

When you want to call people idiots, you might also want to add some new information to the thread. The e36 diff was covered in the first few posts, and if you look a few posts above your own you'll find I just went over the cruising rpms.

Just because you say something doesn't mean it's true. Evidence is key. You just blurted out numbers and facts and expect people to believe them. Don't believe everything you read on the net. The fact that it has taken that long in this thread to get any reasonable information is astounding.

[kalib0y]

Just because you say something doesn't mean it's true. Evidence is key. You just blurted out numbers and facts and expect people to believe them. Don't believe everything you read on the net. The fact that it has taken that long in this thread to get any reasonable information is astounding.

Mind giving me ideas to figure out why my RPMS are no where near the excel sheet results? Maybe my trans is geared differently? I would like to rule out as much as possible for my own curiousity

[shiboujin]

What are your numbers? Are you sure your wheel diameter is 24 inches? 0.1 inch difference will make a huge diff at speed.

[Wh33lhop]

Just because you say something doesn't mean it's true. Evidence is key. You just blurted out numbers and facts and expect people to believe them. Don't believe everything you read on the net. The fact that it has taken that long in this thread to get any reasonable information is astounding.

Sure--thanks for gracing us with your presence and saving the thread with your redundancy.

What are your numbers? Are you sure your wheel diameter is 24 inches? 0.1 inch difference will make a huge diff at speed.

His speedo doesn't care about his rolling diameter, and if you took a few seconds to read the thread you'd see he posted his numbers, again, a few posts above yours.

[shiboujin]

You're damn fucking right you're happy I came into this thread and put a gleam of awesomeness in an otherwise useless thread.

[kalib0y]

What are your numbers? Are you sure your wheel diameter is 24 inches? 0.1 inch difference will make a huge diff at speed.

Yes they are since I am running 235/40/17. I may be wrong ,but my thinking is that is the overall rotation is larger then the RPMS should be lower right?...Well actually I know I am probably wrong but I would love a technical explanation if possible...

[Wh33lhop]

Yes they are since I am running 235/40/17. I may be wrong ,but my thinking is that is the overall rotation is larger then the RPMS should be lower right?...Well actually I know I am probably wrong but I would love a technical explanation if possible...

Yes, a higher rolling diameter will raise your gearing in general. However your speedo will not read any different since your VSS is in your diff and only counts axle rotations.

Here's how it works

If you have 23.9" (stock iirc) tires on your car with a zf and a 2.93 your tach will be at 3300 and your speedo will be at 80, and you will be doing 80.

If you have 48" tires on your car with a zf and a 2.93 your tach will be at 3300 and your speedo will be at 80, but you will be doing ~160 (wishful thinking). So your gearing is lowered, but if you were just looking at your speedo you wouldn't notice since tires do not change the gear ratio between the engine and the diff (speedo pickup).

Therefore while in real life your tire diameter can raise or lower your gearing, it will have nothing to do with the gearing relation between your tach and your speedo.

[pandaboo911]

Just because you say something doesn't mean it's true. Evidence is key. You just blurted out numbers and facts and expect people to believe them. Don't believe everything you read on the net. The fact that it has taken that long in this thread to get any reasonable information is astounding.

I changed from a 2.93 LSD to a 3.25 with a ZF and it added the equivalent of 12.6534 horsepower.

Heres the evidence:

https://www.tinyurl.com/2ud2y8c