engine and drivetrain 5-speed ?'s

[Guest Anonymous]

I've got an E21 5-speed ready to bolt in but I'm questioning a few things so I'm looking for opinions & suggestions.

The car is used as a daily driver, fuel economy is a non-issue really, I'm looking for sporty, fun & reliable as well as something that will cruise on the highway nicely. I do mostly either city/traffic driving or extended highway driving at moderate to higher (but safe) speeds.

I have a stock diff currently but will be installing a 50% LSD with the 5-gear transmission. I'm wondering about diff ratio as well as gearbox choice. I have a feeling that what may be reccomended is a 3.91 with the economy 5gear rather than the dogleg CR box. What advantages would a dogleg (sport) gearbox give and would it be best to pair it up with a 3.91, 3.64-or stock, or higher up to a 4.10, or even much lower to a 3:45??

My thought was that the CR gearbox would be more fun and if kept with the stock 3.64 RPMs would stay reasonable. If I go up to a 3.91 and a CR won't the rpm's go up higher than the stock 4-speed because the overall ratio is increasing? What do you guys run and what works best?

My driving is exactly as I said: either city where a 2-gear transmission would be fine, or highway crusing for extended periods and distances on open roads (80 mph give or take conditions). I think the CR box would be a "cool" piece to add to my car however I'm not really after "cool", I'm after functional performance.

9.5 comp, 292 cam, lightweight flywheel with 4-puck clutch (stock PP), bav-auto header, urethane all around, Ireland swaybars, Billy HD's X 4, ST springs X 4, vented fronts & rear disc upgrade, 38/38, etc.

Thanks for your valued suggestions & opinions!

[Paul7002]

be loud and wound out on the interstate - same as if you put a 3.91, 4.11 or whatever with a stock 4 speed. The 5 gear of the CR box is just about the same ratio as 4th in the regular 4 speed.

If you want to go squirty fast, by all means use the CR box and the lowest rear end you can find (3.91, 4.11 etc)

If you want to be a more relaxed, go with the OverDrive 5 speed and a 3.91 which will have some quckness advantage over the standard 3.64 but will still decrease rrpms in 5th over what they'd be with the stock 4 speed and 3.64. The OD with 3.64 will be pretty much like the regular 4 speed and standard rear end set up in 1-4, but with a relaxed 5th gear for the interstate.

This topic has been talked to death on the board - you'll find as many opinions as there are people posting them.

[_z_]

Here is a program that will tell you final speed at various RPMs given your tire size, dif & transmission choices. This should give you an idea of what to expect with the different choices

http://www.jeffersonfreestate.org/gears/

I was going to make it graph too, but haven't gotten around to it -- so its kind of rough looking

enjoy!

-z

also the faq

http://www.bmw2002faq.com/content/view/56/32/

[Guest Anonymous]

I don't mind the revs and since I've installed Dynamat soundproofing under the carpets, on the firewall and in the roof. I'm a little worried about blowing up my motor if I start cruising on the highway at 6,000 rpm. How much will the CR & 3.91 shorten the life of an engine? Also I've started a new motor with a completion date somewhere out in the future. Would it be best to build it for HIGH RPMs and go with the CR?

How much of a difference is there really between the OD & CR boxes? Are we talking HUGE differences in power and performance as well as noise and RPMs?

What was the setup on the Turbo cars? Wasn't it a 3.45 and a CR box?

[BarryA]

My '69 runs an E21 OD 5 speed & the original 3.64 open diff.

Until about 6 months ago, it had a set of E30 325iS 14x6.5 BBS alloys and 195/65x14's installed, and pulled about 3500 rpm at 75 mph.

Late last summer, I found a set of period-correct Ronal 13x5.5 alloys and went back to 185/70x13's (largely to get away from fender lip interference issues with the 14's) - with no other changes, 3500 rpm now comes up at about 70 mph.

[Guest Anonymous]

I'm thinking about going with the 3.64 50% lockup LSD and the overdrive. I'm assuming that my engine now will be fine with that and the new motor will have enough power that the OD 5-gear will pull and accellerate fine being that it will be a 2.2ish 130ish RWHP car. This will also mean that I don't need to change any of the speedo gearing because the rear end will stay the same - correct??

The LSD that I have needs to be rebuilt and I was contemplating either a Quaife or the 50% lock that's currently in it. What's the real story with % lockup? Does it mean that the second tire spins at the lockup % rate instead of 100% like the drive wheel?

What would be a good % for a non-race but performance street application?

[Lupin3]

Well, there are 5 speed CRs and there are 5 speed CRs. If you're referring the original equipment optional Getrag 235/5, I'd be wary of putting that trans in a daily driver - particularly if tracking/auto-x is not part of your intended use and if you plan on spending a fair amount of time on the highway.

Engine life is one consideration - though in this case more to be considered in terms of the differential you choose than the CR trans, since the transmission's final gearing will be the same as a four-speed.

Parts availability is the real issue, though - and that means expense and downtime if you can find parts at all - if your trans breaks.

On the other hand, it is my understanding that BMW also offered close ratio 5 speeds for the 320is models as well - in addition to the standard overdrive 5 speeds. I'm not sure how parts availability compares, but I assume it is better for these later transmissions than the earlier ones - and therefore more economically practical to run in a daily driver.

On the other, other hand - I know shops will rebuild overdrive 5 speeds with new gearing to create a close ratio trans. This is probably quite expensive, though likely less expensive than an original equipment close ratio trans rebuild.

I would think that an overdrive 5 speed would be the best option, all around, for a daily driver. It is both more common and less expensive than a CR 5 speed, as well as being more flexible for daily driving needs (being stuck in traffic with a CR wouldn't be much fun, as far as I can see).

Lastly, Metric Mechanic had a chart somewhere on their site for estimating rpm usage on engine life - a must read for all the auto-xers out there. You may want to check it otut.

[Guest Anonymous]

I'm starting to think that the only advantage of a CR box is the "cool" factor of having first where it is. It would give a valet a hell of a time driving away. I think that if I go to a CR box I'd go up to a 3.45 rear end because of the top end gearing on the highway. I will have to look into this further and report back.

Does anyone know if the 5-speed OD conversion kits including shortened driveshaft will work with the CR box as well?

[Lupin3]

The driveshafts are different lengths for the OEM CR 5 speed and the later 320is overdrive 5 speeds, so they will not - to the best of my knowledge - be interchangeable. However, I'm not sure all the extra components needed to mount the Getrag 245/5 to the '02 will be necessary. Probably more complicated than replacing the 4 speed, but less than a high-quality 5 speed conversion.

CRs maximize the acceleration for a given engine by leveraging the additional gear multiplier, but more importantly they better match gear selection to a race engine, which usually only makes power in a narrow, high rpm range. For street use they are limited.

[Guest Anonymous]

Unless you do nothing but race, the CR is, IMO a waste of money. Its the same theory as putting a 6-spd into miatas and other small cars, the more gears compensate for a lack of power. (6-spd is basically a CR and overdrive combined) If you had more power you wouldn't need (or want) the extra gears. Personally I would rather have fewer gears, because shifting wastes time. But the OD and CR have the same number of gears, you say? Not really, you aren't going to use the OD 5th in racing. OD gets a 1:1 ratio in 4th, CR gets a 1:1 in 5th, so thats 3 gear changes verses 4 to get the 1:1 ratio. Plus you get the nice overdrive gear for cruising which enables you to lower the diff ratio and in turn gain more low speed acceleration.