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Straight Cut Close Ratio Ribcase Gearset Sprite & Midget

Straight Cut Close Ratio Ribcase Gearset Sprite & Midget

Straight Cut Close Ratio Ribcase Gearset Sprite & Midget
The stock ribcase gearbox of any Sprite and Midget can be transformed into a superb racing box with the installation of straight cut gears! Not only does the straight cut design provide more strength and take significantly less power to drive but the ratios of the various gears are ideal for high performance racing! Yes, the nature of straight cut gears is that they are louder than the stock helical, but if you are racing you shouldn't care about noise, only performance. This gear set when installed will make a 948cc engine feel almost like a 1275, and a 1275 will feel like a 1500! You can always be on the proper power band of any motor! The gearset can be fitted to any ribcase that originally used the 22G1100 laygear. The first gear and the reverse gear in the stock box is retained. The installation of these gears is often done at home but it is better left to the experts. GSK106 is the gasket set to use if you do it yourself! Mini Mania can supply either just the gearset or can provide you with a ready to race gearbox! Ratio Comparison: Stock S/C Close ratio 2nd 1.916 1.722 3rd 1.357 1.255 4th 1.0 1.0
Technical Information:
Synchromesh Transmissions vs Dog engagement

Synchromesh Transmissions

Most modern cars are fitted with a full synchronized engagement gearbox. This relatively old design concept assure the delivery of smooth, reliable, and quiet operation.  This is an absolute must have for any car that is a daily driven vehicle. Synchromesh transmissions operate using a special collar that applies force to a cone-shaped area attached to the gear. The collar allows the shaft speed of the gearset and the input shaft to be matched or “synched” to the output shaft prior to the collar locking into place and initiating a shift.

As even a street racer is driven at relatively slow engine speeds (Below 6,000prm) Synchromesh gear engagement is ideal and requires a bit more time compared to a dog box, to facilitate shifts. Limitations of synchromesh gearboxes in high-performance applications include slow upshifting at very high engine speeds—e.g. 8,000 rpm—and slow downshifting, as well as the need to fully use the clutch.

Dog Box Transmissions

Dog engagement is typically limited to racing applications where fast, precise shifting is needed. Dog gear engagement works by having numerous large teeth or ‘dogs’ that mate into matching openings machined into the opposite surface of the drive gear. Unlike the synchro engagement, there is no synchronizing mechanism to assist in equalizing speed. Ideal gear selection—e.g. minimal clashing and wear of the dog rings—is achieved by quick shifts; the motto here is “the quicker the better”, so bang away.

Unlike a conventional synchro gearbox that a clutch MUST be used, it is far better in a dog box to lift your foot off the gas momentarily to give a little break in engine load until the shift is achieved. The driver will then experience the dog ring engaging with the next gear and the throttle can be reapplied. With practice this can be done in milliseconds. In fact, a driver can preload the stick shift in the direction of the next shift, and then when he either blips the throttle or clutch the shifter will quickly click in the desired gear.

With all else equal, dog-engagement gears are much stronger than synchro-engagement gears because without needing to make space for synchro rings, the gears themselves can be made thicker. The number of dogs (teeth) and the size of the openings determine the window of opportunity that the dogs have to engage during the shift event. Rings with a smaller number of teeth provide a more efficient, smoother shift quality. The downsides to this easier engagement are increased noise and abruptness on the shift.
The most destructive method of shifting dog gears is attempting to change gears in a “passenger car” or “synchromesh” manner. This involves slow shifting and use of the clutch—i.e. lifting off the throttle, depressing the clutch, moving the gear lever slowly, releasing the clutch, and applying the throttle—a scenario typically found in stop-and-go traffic.

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These closer ratios, in conjunction with the very high rev limits of my Bonneville racing MG Midget put the power band right where it needed to be. Additionally, the straight cuts gave less parasitic power loss and less fore and aft strain on the transmission case. Watch the tach in this video, and keep in mind we're running 4:22 gears in the pumpkin. We took a push start to 30 mph, and I dumped the clutch at 9500 rpm. Note the rev drop on gear changes - considerably less than one would encounter with a stock ratio set. This run was for 126.684 in the flying mile. Once launched, the engine never left the power band, and the transmission held up beautifully . . . https://www.youtube.com/watch?v=aRYNKIMGCEs&feature=youtu.be If you install these yourself, get a piston ring compressor to hold the spring loaded ball bearings in place under the speed hubs, and be mindful of the pins holding the gear sets to the mainshaft - they're tricky. It's not an easy do-it-yourself project, but if you are patient, and work in a clean area, an average mechanic can do this with some difficulty, but to great success.
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