CS vs CSi diff difference; 5 speed effect?

snj5

snj5

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Since I just bought the car (CSi), I was reading the owners' manual and it shows the CSi with a 3.24:1 final drive as opposed to the CS 3.45 final drive. The accompanying chart in the manual shows a reduced cruise of 2800rpm for the CSi at 100kph and 2950rpm at 100 kph for the CS. The final ratio differnce is about 0.93, very close to the overdrive ratio of 0.89

So, with an overdrive 265 Getrag, is the overdrive 5th gear still comfortable in a CSi with the longer diff ratio? The math suggests that a 5speed in a CSi would give a 100kph cruise of ~2500rpm

Any experience or comments?
Many thanks.
 
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Cruising speeds of ALL E-9's

In every E-9 I have ever driven covering numerous 2800CS, 3.0. 3.0CSi, 3.0CSL--they all like to cruise/tour at 78-80 MPH-irrespective of which Diff ratios they are fitted.

!00 kph--62.4 mph is not a healthy speed for an E-9--not even breathing!!
 
IMO an overdrive Getreg with the CSI diff is to tall. I would suggest putting some miles on it as is (assuming stock configuration) and see how you like it around town and at speed. Then drive a CS with a 3.45 and overdrive if you can arrange it.

If you just have to have a 5 speed, I'd consider a close ratio paired with the CSi diff or if you go overdrive then move up to a 3.45 or 3.64.

A stock well sorted out CSi is a pleasure to drive with the stock gearing.
 
Too tall? Bah! My E34 540 has a 2.81 rear with a top gear of 0.81.

If you plan to cruise along in 5th, it should work fine for highway work. The other gears are very close to the stock ratios, so it will behave the same.
 
It's all about how you use the car I suppose. I bought a CSi a while back that the PO had installed an overdrive in but kept the original CSi diff. Very hard to find a place to use 5th unless you live in a state/country with no speed limits. My perception after driving it a few thousand miles was that it was a complete waist of a perfectly good gear.

x_atlas- your 540i has 1/3 more max torque than his CSi and probably even more of an advantage at the low rpms that would be turning in 5th with that gearing (gotta love more displacement and a modern EMS).

snj5- I'd put some miles on it first if you can and then you'll know what you want to do.

I've owned 3 CSi's and a 2800CSA converted to a CSi hotrod- all had their own unique personalities but my favorite was a stock CSi engine and diff w/ a close ratio 5sp- no wasted gears and always the right gear available.
 
E911 said:
I've owned 3 CSi's and a 2800CSA converted to a CSi hotrod- all had their own unique personalities but my favorite was a stock CSi engine and diff w/ a close ratio 5sp- no wasted gears and always the right gear available.
Click to expand...

This right here is the trick. I installed a 265 not knowing the first four gears were the same (or at least felt like it) as the 4 speed. I didn't like the "wide ratio" feel of the original 4 speed.

I still like the 5 speed better. Drops the engine revs to about 2700 or so at 80 MPH. Normal speed around Texas.
 
E911 said:
It's all about how you use the car I suppose. I bought a CSi a while back that the PO had installed an overdrive in but kept the original CSi diff. Very hard to find a place to use 5th unless you live in a state/country with no speed limits. My perception after driving it a few thousand miles was that it was a complete waist of a perfectly good gear.

x_atlas- your 540i has 1/3 more max torque than his CSi and probably even more of an advantage at the low rpms that would be turning in 5th with that gearing (gotta love more displacement and a modern EMS).

snj5- I'd put some miles on it first if you can and then you'll know what you want to do.

I've owned 3 CSi's and a 2800CSA converted to a CSi hotrod- all had their own unique personalities but my favorite was a stock CSi engine and diff w/ a close ratio 5sp- no wasted gears and always the right gear available.
Click to expand...

True, but the 540 also has an extra 800+ lbs of weight.

As for the 5th gear, I didn't have much of a problem driving the E9 at ~2000 RPM at 65, since that is usually a highway-only speed. Great for long-haul fuel economy.

With the stock wheel/tire/3.45 combo and a Getrag 265, I am running about 2500 RPM at 75 in 5th. I still feel that is a little high for prolonged highway driving, as I don't exactly need a lot of passing power at speed.
 
Thanks everyone for the great discussion. I think I will spend a bit of time with the car as a 4 speed before deciding for sure. The car will see some road trips, so the overdrive would see some 70 mph+ use. Steve at Korman have a kit with the doodads to install, and Erik CK has an appropriate transmission.

Based on previous experience, will also upgrade the brake and clutch lines while on the lift.

All opinions and advice appreciated.
 
5 spd OD with 3.64

I like the slightly higher rpm's at speed. With the 5spd OD and 3.64 LSD I hit 3,000 rpm at 75 mph (in 5th gear) - which is usually plenty of power for the hills and some passing.
 
I've driven my 3.5l 5-speed Bav for thousands of miles and love the overdrive gear. Presently I have some 225/45/16 KDW's and 3000 rpm is about 71 mph.
 
yup, it's lazy

I have a 3.0CSi with a 3.25 diff and a Getrag 265 5-speed, and it definitely is lazy (low RPMs) on the highway. Next time I'm crusing I can give you some numbers.
 
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