engine and drivetrain 3:45 ratio - any one running in there 2002 ?

[Conserv]

I believe the true reason US cars adopted the 3.64 was because they weigh more than those sold in the rest of the world. Remember that the body shells have additional reinforcing, big bumpers, aircon and emissions crap. They may be as much as 10% heavier....

Perhaps, John, but there is little weight difference before the square taillight cars, i.e., 1974 models. In August 1971, when BMW decided to use the 3.64 in the U.S. version of the tii, the weight difference between a Euro and a U.S. tii was negligible. And neither U.S. nor rest-of-the-world examples were ever offered with overdrive transmissions -- even as an extra cost option, and even on the factory turbo...

Regards,

Steve

Edited November 18, 2015 by Conserv

[tzei]

Me too, even though I have a 5spd OD now. I drive sorta on the fast side on two lane roads and the 3.45:1 ought to give some more 3rd gear passing capability to go around a 55mph driver. Although the S14 solved most of my needs in that area.

I have S14 + 5spd OD + 3.45:1 LSD combo and i absolutely love it! Very nice on a long stretches when speed limits are here in 50 - 75 mph region (80 -120 kmh).

[LarsAlpina]

3,45:1 was only available in early non-US tii´s. LHD sedan up to VIN 2712822, RHD sedan up to VIN 2751004, touring tii up to VIN 3423670. For LHD sedan and touring the end came about mid 1972, a bit later for the RHD cars.

AFAIK the change to 3,64:1 took place at about the same time when the tii engines were updated from plastic intake runners to metal and got the newer E12 cylinder heads instead of the 121(TI).

 

A combination of 3:45 with 5-speed OD in a stock 100hp carbed 2002 will cause you to shift back to 4th at even smaller hills the road might be leading up if you want to keep your initial velocity at medium speeds. tii or otherwise power improved engines with 130hp or more will not show this phenomenon. But a 3,45 will do no harm to your engine if you´re not going to drive "untertourig" (don´t know that one in English - maybe something like under-revved).

 

5-speed OD was never available for 02 from factory because at the time the 02 was produced the use of that current multi-gear gearboxes wasn´t common among german car manufacturers - four gears were considered enough. Even a Porsche 911turbo (930) came from factory with only a 4-speed first. Only for racing purposes a 5-speed was considered necessary and according to the rules of FIA homologation BMW had to offer the 5-speed CR as an option for everyone from factory on to be allowed to use it in the german and european production car racing classes of the time. 

 

Fuel consumption (and with that getting the engine revs down at higher speeds) first became really interesting in Europe after the second oil crisis in 1979. Then the manufacturers started to produce (as Volkswagen called it at that time) 3+E and 4+E gearboxes. E is for economic and means a longer gear ratio for the highest gear available. In nearly every manual of that time you could´ve read: "Top-speed only to be reached in 4th gear." At the start of production of 3-series E21 in 1975 there still wasn´t a 5-speed OD available, it started with the 5-speed CR only (at least it was like that in Europe). 5-speed OD was added to the options list later, about 1978 or 1979 if I remember right.

 

Best regards, Lars.

[gastephens]

I regularly drive my car at 80+ mph and find even 5th gear a bit buzzy with my 3.91 as it nears 4000 RPM. I wasn't aware of a 3.64 but that sounds like a good compromise between 3.45 and 3.91. I'm going to look into it.

 

With the 3.91, I regularly use 5th gear around town. I would be fine with using 1-4 for normal driving and 5th on the highway. I think that might have been the original intent of overdrive.

[avoirdupois]

Perusing this thread reminds me of an early 02 with particularly slow acceleration but wonderful cruising attributes.  Originally, the engine was wrongfully blamed for Subaru 360'ish acceleration.  Took some head scratching to determine the curious performance was partly due to a 3.45 transplant although the engine set up was not the best.  Probably would not have been a favorite in the hilly, Bay area.

A short answer to why the 3.45 axle ratio was disused is a series of complicated business decisions dictated by sales and profits - rather than a narrow view of performance preferences.  It is also a reputed cause for the brief appearance of the 02 turbo.  This compromise contributed to the drive train eventually used in the majority of the E10's  successor, the E21.  E21 sales began in 1975, starting with the same 'ol four gang Getrag as the E10.
 
Reasons for factory choices are not as obvious as they may seem.  In the '70s, design and production occurred well in advance of hoped-for sales.  Design and construction had to be predictive of both fickle customer interest coupled with world events.  It is hard to quantify how hard many manufacturers were hit by the first so-called "’73-oil crisis."    In addition to fuel economy becoming of paramount importance, emission control implementation and the implementation of lower octane unleaded fuels also took their toll on both economy and performance.  For those who can remember, this was when smaller displacement and lighter weight Asian imports began to strut their stuff over their US counterparts.

 

Most manufacturers targeting US markets in the '70s adapted by relegating performance to the wayside in favor of fuel economy balanced by a need for reduced emissions.  What Lars did not cover in his post was the negative reception by many US, if not international, consumers to these changes.  One might guess BMW was somewhere in the middle of this sales free-for-all, since its market share was relatively small - in the early ‘70s.  After the crisis, BMW, like others, emphasized the “lux” and “handling” and understandably less of the straight-line “go.”  In the US, it introduced lower displacement, lower compression, power plants, such as the 2.5ltr M30 engines.  The E10 wasn’t excepted from fuel economy and reduced emissions concerns.  Like other manufacturers - before the advent of lambda sensors - compression ratios were reduced and carburetor jetting pushed the lean end of the scale.  (This was probably a big reason for the aftermarket Weber popularity.)   With the imposition of legal speed limits in major markets, top speeds were less significant - to most consumers.  A few manufacturers maintained a modicum of performance by offering lower (numerically higher) axle ratios and (when reasonably available) transmissions with an over-driven fifth gear.  Fledgling fuel injection helped too.  Before introducing the replacement E21 model, BMW's ability to maintain a semblance of performance was to make the best of the troublesome situation.  One means of doing so was equipping (its 1976 49-state E10s and a few 1976 CA-state E10s with a 3.9 ratio. (Edit per Conserv's excellent observations)  (This was probably a necessity in the already performance hampered automatic transmission models.)

 

 

Top speed and performance was probably of little concern to most motorists in late-'73-74.

 

 

 

 

 

 

Sammy Hagar's lament, "I can't drive 55" did not make it to the airwaves until approximately 10 years after the oil crisis, i.e., 1984.  Viewer discretion (for those who seek to dial the message down) advised.

Edited June 28, 2016 by avoirdupois

[Conserv]

On 6/26/2016 at 4:04 PM, avoirdupois said:

.... One means of doing so was equipping (most of its later “golden state” E10s with a 3.91 ratio.  (This was probably a necessity in the already performance hampered automatic transmission models.)

 

All good points you make.  I also note that the ability of U.S. '02's to use "regular gas" was apparently important from BMW's point of view.  They even printed a version of the following on the window sticker of all BMW NA-imported cars (early '75 through the end of '02 production), as seen on the accompanying sticker from my '76:

 

EMISSION CONTROLLED ENGINE RUNS ON REGULAR FUEL WITHOUT CATALYTIC CONVERTER

 

This, of course, cost both power and fuel economy, but must have been viewed as an important marketing point.  Contrast it to today when many (most?) U.S. models of German cars require premium fuel, and we -- well, I -- don't complain.

 

One minor quibble, or I mis-understood what you said.  The U.S. '76 models did use a 3.90 diff, but only in the 49-state version.  The CA-only '76 continued to use the 3.64.  My understanding at the time was that the introduction of the E21 head allowed a thermal reactor-less car to meet the Federal standards, but not the more stringent CA standards, and even a change in diff ratio would require re-certifying the CA version, with little or no assurance the 3.90 would pass muster. Thus, BMW left the CA version alone.  A '76 CA version is, therefore, identical from an emissions perspective to a '75 '02, when a single version was sold in all 50 states.  I'm a little hazy on whether the '76 49-state 2002A used a 3.64 or a 3.90.  Others here will know.  The 3.90 is a true 3.90 -- 10-tooth pinion, 39-tooth ring -- and a bit of an oddity, whereas the 3.91 -- 11-tooth pinion, 43-tooth ring -- became the "go-to" diff for 5-speed e21's.

 

Regards,

 

Steve

 

 

[avoirdupois]

On 6/26/2016 at 4:41 PM, Conserv said:

 

All good points you make.  I also note that the ability of U.S. '02's to use "regular gas" was apparently important from BMW's point of view.  They even printed a version of the following on the window sticker of all BMW NA-imported cars (early '75 through the end of '02 production), as seen on the accompanying sticker from my '76:

 

EMISSION CONTROLLED ENGINE RUNS ON REGULAR FUEL WITHOUT CATALYTIC CONVERTER

 

This, of course, cost both power and fuel economy, but must have been viewed as an important marketing point.  Contrast it to today when many (most?) U.S. models of German cars require premium fuel, and we -- well, I -- don't complain.

 

One minor quibble, or I mis-understood what you said.  The U.S. '76 models did use a 3.90 diff, but only in the 49-state version.  The CA-only '76 continued to use the 3.64.  My understanding at the time was that the introduction of the E12 head allowed a thermal reactor-less car to meet the Federal standards, but not the more stringent CA standards, and even a change in diff ratio would require re-certifying the CA version, with little or no assurance the 3.90 would pass muster.  Thus, BMW left the CA version alone.  A '76 CA version is, therefore, identical from an emissions perspective to a '75 '02, when a single version was sold in all 50 states.  I'm a little hazy on whether the '76 49-state 2002A used a 3.64 or a 3.90.  Others here will know.  The 3.90 is a true 3.90 -- 10-tooth pinion, 39-tooth ring -- and a bit of an oddity, whereas the 3.91 -- 11-tooth pinion, 43-tooth ring -- became the "go-to" diff for 5-speed e21's.

 

 

 

My mostly-anecdotal reply was off the top of my head (from memory) and started out only about the 3.45 ratio.  I had not intended the reply to be too academic, but I think you got me.

 

For the most part, I agree with your assertions regarding the '76 E10s.  The problem with certitude as applied to '70s BMWs - are the numerous exceptions to each so-called written-in-stone rule.  I am certain, for example, that I have seen one or maybe more examples of the '76 CA-equipped models with thermal reactors and E21 (versus the earlier E12)  heads.  I know this because I remember tearing down a warped head, wondering whether it came from a dealer named Frankenstein with a chief mechanic named Igor.  As I recall, the vin and related underhood/door jam stickers clearly indicated a CA delivery that stated compliance with applicable CA rules for the '76 model year.  It was a long time ago, and the vehicle had low miles and still belonged to the original owner who claimed it was just as he received it.  Since the car was not in CA at the time, the CA-only information was not deemed terribly significant - other than it might be something to avoid.  Some of my info came from shops a few may remember e.g., Miller & Norburn, Vasek, and CTC/Circle Tire.  None of them were particularly stymied by deviations from "the microfiche." 

 

Regarding the 3.91 ratio, no sooner than I typed it, I realized it would have been better to hedge things with "3.9" but I was distracted until your post.  Even so, the last best lsd I had was a 3.91 with the 4 bolts on each side that came from a CA '76.  Could it have been a non-original replacement from a '79 E21?  The answer is lost, like vaporized seafoam.

 

I am unable to presently access the few hard copy records I might have on this subject (if they still exist).  However, I note the Forum has plenty of info that substantiates your position.  Again, it is not that I disagree with you.  However, given the passage of decades, facts and data can become blurry.  Reading the quoted material below, while the 49-state version of the '76 E10 is extolled as "02 perfection" the CA '76 version implicitly inherited many of the detriments attributed to the "least desirable" '75 49-state version.  The problem with this conclusion is it is premised on the notion that all versions remain exactly as they were - when originally sold.  It fails to account for factory-sanctioned warranty repairs that fixed some of those original shortcomings.  Nor does it account for numerous pro forma valve jobs and CARB-approved aftermarket replacement parts that negated so many of the early criticisms.  One hastens to add that when it comes to CARB data, there seems to be fewer and fewer absolutes with each passing year.   In fact, it probably can be argued that the passage of time has created more and more exceptions and variances.                 

 

 

Quote

1975 brings no visual changes. The engines are highly modified with emission controls. Thermal reactors were added, EGR's and air pumps, and also the '75's yield lower compression. The '75's are the least desirable as a result.

1976 is the last year of the 2002. No major exterior changes were made, but the emission controls were removed for the 49-state version (non-California) cars. Thermal reactors are no more, which was a welcomed changed. Rear axle ratio is lowered on 49-state cars to improve acceleration up to a higher numerical 3.9:1 vs the original 3.64:1. A new cylinder head (designated the E21 2.0) is used which is the same one the 320i's eventually adopt. The non "49 State" version California cars are identical to '75 models. The '76's are by far the easiest to maintain and own. By 1976 BMW had ironed out all of the problems and as a result the '76's are the most reliable all around models. These are perfect for the first time 02 owner.  http://www.bmw2002faq.com/articles.html/technical-articles/history-and-reference/2002-buying-tips-how-to-find-a-good-one-r65/

 

 

 

 

Edited June 28, 2016 by avoirdupois

[chargin]

3.64 + 5 speed OD @  3k rpm = 70 mph, 3.6k = 80 mph.

 

How much do you want?

[kbmb02]

I'm working on a build with a quick-revving street M10 combined with a 4 speed and 3.45 final drive; I'm looking forward to providing seat-of-the-pants data to the discussion. -KB

[avoirdupois]

4 hours ago, kbmb02 said:

I'm working on a build with a quick-revving street M10 combined with a 4 speed and 3.45 final drive; I'm looking forward to providing seat-of-the-pants data to the discussion. -KB

 

Looking forward to it too!

 

When you say "quick-revving" one assumes you implicitly mean more torque and hp.  

 

(This was one of the reasons injected E9s with 4-speeds and a 3.25 final drive ratio managed to post similar, if not better, performance numbers than their 20hp less (equally weighted) cs brethren with the same 4-speed and a 3.64 final drive.  The biggest difference being top speed numbers, all of which became somewhat less consequential to sales  .  .  .   after the '73 oil crisis, mandated speed limits, and the then-apparent need to reduce compression ratios for unleaded fuels.)

Edited June 28, 2016 by avoirdupois

[kbmb02]

20 hours ago, avoirdupois said:

 

Looking forward to it too!

 

When you say "quick-revving" one assumes you implicitly mean more torque and hp.  

 

Yes - plus lightened / lighter crankshaft, rods, pistons, flywheel and careful balancing. -KB