Metric Mechanic - Competition Gear Boxes

Background
Prime Directive - getting from point A to point B as quickly as possible. The basic variables in the "quickest - time" equation are:

• Engine size (horsepower)
• Vehicle weight
• Gearing
• Driver's ability.

By classifying cars by model, engine size, types of performance modifications, etc., the range of these variables narrows dramatically. Furthermore, the more restrictive each class becomes, these figure more like constants. This, in theory at least, leaves driving ability as the single most controlling factor, which is as it should be. However, in practice, classifying cars really forces a driver to scrutinize and 'fine tune' every aspect of his/her race car to gain some kind of "edge" over one's competitors. For instance, squeezing a bit more horsepower, trimming some excessive weight or perfecting one's driving skill can mean the difference between a good performance and a winning one.

Gearing
as a variable, has always had the narrowest of ranges for two reasons. First, with respect to differential options, the number of readily available ratios is four; 3.45, 3.64, 3.90 and 4.11. Although 3.64 is most common, most racers prefer at least the 3.90 (also the most common limited-slip ratio) and often even the 4.11. Even though tire diameters vary somewhat, most drivers are limited to basically two choices.

Furthermore, as far as transmissions are concerned, gearing really is a constant in the "quickest - time" equation. With the exception of a minor ratio change from 3.8 to 3.7 for first gear and an insignificant one of 2.05 to 2.02 for second gear in late '78 and '79 320i's, all four speed gear ratios are the same. The only gearing alternative from the factory was the 5-speed close ratio transmission. This was a European option that offered five gear selections between the normal range of the stock four. This is totally different from the "overdrive" 5-speed that has become standard equipment on all '80 and later models.

The distinct advantage of a close ratio gearbox is that there is less rpm drop between gears, which keeps the engine in closer proximity of its peak horsepower range. Theoretically, if you can avoid dropping out of the engine's power band you're maximizing horsepower to the rear wheels, which translates into quicker track times.

The disadvantage to the close ratio 5 speed is that you still have another gear to shift through which does cost some time, besides being an inconvenience. The rationale is that there is still a net gain. There is more time lost when the engine rpm falls further from peak horsepower as with the stock 4-speed, than the time lost by making an extra shift. In addition, even though 1st gear is somewhat taller (3.4), by using the preferable 3.90 or 4.11 differentials, you have effectively returned 1st gear to "stump - puller" status which renders it nearly useless. And finally, if you are lucky enough (or wealthy enough?) to acquire a close ratio 5 speed in good working order, you are still faced with the cost of the additional parts and labor needed to make the conversion (usually over $3000.00). Some classes prohibit the use of anything but a 4-speed anyway, which eliminates any 5-speed transmission as an option.

At the Present Time
Given the above situation, what the vast majority of racers ultimately do is resign themselves to a stock 4-speed gearbox but have two or more differentials to choose from. This strategy takes the most advantage of their engine's power range, depending upon whether they are road racing or autocrossing and according to whether the particular course is basically “slow" or "fast". Even though a "slow" course calls for a "shorter" (higher ratio) differential and a "fast" course needs a "taller" (lower ratio) one, all courses have characteristics of both types in them, therefore the challenge.

An Alternative
In answer to this dilemma, a new racing transmission has been developed that incorporates the advantages of the 5-speed close ratio (the closeness of the gearing) and the convenience of the 4-speed (no complicated conversion necessary).

The Logic Behind The 44LCR and 64CR Competition Gearboxes
Let's face it, a 3.8 ratio first gear is all but worthless for a road racer and has debatable value for an autocross driver. We all know that even a stock 2002 or 320i can barely get through an intersection before you feel the need to shift into 2nd. The lower (higher ratio) first gear is the wider the proportional distance between the remaining gears, since fourth gear is, by design, necessarily 1 to 1.

The greater the distance between 1st/2nd, 2nd/3rd and 3rd/4th, the further away from its horsepower peak the engine is and the longer it takes to work its way back into its power band after each shift. However, by raising first gear to a ratio (3.0) approximately halfway between first and second in a 5-speed close ratio (3.4/2.2) you have a much more useful gear. It can take you up over 40 miles per hour (see shift charts). Even as tall as 3.0 it is still a shorter first gear than any BMW automatic transmission (2.83). At this point, we have narrowed the total shift range by nearly a whole number (1.0-3.8=2.8 compared to 1.0-3.0=2.0). As it turns out, third gear ratio is best left in the stock position due to what we want to accomplish with second gear.

In competitive situations that occur in both road racing and autocrossing, the two shifts that will be of greatest benefit will be the ones from second to third and third to second. A ratio of 1.6 was chosen because it allows second to be as close to third as possible and yet no further away from the new first position than it is in the stock 4-speed. What the 44LCR/64CR evolve into is second, third and fourth gears closely resembling third, fourth and fifth, respectively and first gear being a compromise (but actually more useful) between first and second in the close ratio 5-speed (see above chart).

Applications
Because of their unique combination of gear ratios, the 44LCR and 64CR Gearboxes offer distinct advantages for competitive drivers.
Let's say, hypothetically, that you're on the track approaching a turn that you want to take at 55 mph. Let's also assume the following; your engine's power band is between 4,000 and 7200 rpm, your rear end ratio is 3.90 and you're still using a stock 4-speed. First, you know that you are going to have to slow all the way down to nearly 55 to downshift into second because setting up at even 60 will rev the engine to nearly 7000. And even at 60, your rpms in third are below 4500, so there's little time to be made by staying in third, at the bottom of your power band. So, you decide to downshift into second after you have entered the turn. Just before you're coming out, with the revs already at 6300, you have to shift again on reaching 7200, only 7 or 8 mph away!

If by chance you are using the new 44LCR Racebox, you could downshift into second well before the turn, let's say at 70 mph, (8,000 rpm with the stock gearbox but only 6350 now), and by the time you have slowed to 60 for the turn, your rpm is well placed into the lower-middle of your power band instead of nearly at the top end. Furthermore, you need not shift until you are well out of the turn at 80 mph (7200 rpm), instead of 63 mph (7200 mph, stock ratio 2nd).

The same reasoning applies in road racing and autocrossing for an advantageous upshift from second to third. With the same car as above, for instance, you might have a straight-away that you would like to be doing 70 mph on, but you're in second (stock 2.0) and are already at 7200 rpm. Upshifting now into third would drop the rpm all the way to 4600, just barely into the bottom of your range. However, if you are in the 44LCR's second (1.6), you are already in the middle of your peak horsepower and you can run all the way to 80 mph if you so desire.
Another special advantage for the autocrosser is the ability to run some of the "tighter" courses entirely in first gear! Because of its unique ratio (3.0), you have the advantage of taking the tightest turns in a gear that's tall enough to still reach 45 mph (see charts), which thereby eliminates the need to waste time shifting.

Testing
Prototype 44LCR and 64CR Gearboxes have already been in the field in road racing, autocrossing and even street applications for more than three years. As a matter of record, at the Tulsa BMW Oktoberfest (1987) autocross event, Lee Terry and Margo Potheau won first place trophies in 2002’s fitted with this transmission. Also, a road racer in Ohio informs us he has been consistently placing either first or second with the help of the 44LCR.

Conclusion
In the true spirit of the Metric Mechanic's philosophy of promoting creative ideas and mechanical innovations, comes the first gearing alternative for competitive driving. Beyond being simply an alternative, the 44LCR and 64CR Competition Gearboxes offer solutions to racing situations by providing a competitive "edge" in a particular area previously not addressed.