From: "mark (m.d.) roberts" Date: Thu, 7 Nov 1996 13:33:00 -0500 Subject: Gear Ratios made easy in E-types I'm not sure if this answer got around yet for the query on what the gear ratio was for a particular E-type. The easiest way to find out what your rear-end ratio is, assuming no one has been playing with the speedo gears, is the little number on the face of the speedometer itself. The key to the numbers is: Series 1 3.8l E-type 6.40x15 RS5 tires/tyres SN 6322/00 3.31 miles SN 6322/01 3.31 kilometers not for Germany/Italy SN 6322/02 3.31 kilometers for Germany/Italy SN 6322/03 3.54 miles SN 6322/04 3.54 kilometers not for Germany/Italy SN 6322/05 3.54 kilometers for Germany/Italy SN 6322/06 2.93 miles SN 6322/07 2.93 kilometers not for Germany/Italy SN 6322/08 2.93 kilometers for Germany/Italy SN 6322/09 3.07 miles SN 6322/10 3.07 kilometers not for Germany/Italy SN 6322/11 3.07 kilometers for Germany/Italy Series 1 4.2l E-type tires/tyres SN 6322/00A 3.31 miles 6.40x15 RS5 SN 6322/02A 3.31 kilometers 6.40x15 RS5 SN 6322/03A 3.31 miles 6.40x15 SP41 SN 6322/05A 3.54 kilometers 6.40x15 SP41HR SN 6322/09A 3.07 miles 6.40x15 RS5 SN 6322/11A 3.07 kilometers 6.40x15 RS5 SN 6322/13 3.31 kilometers 6.40x15 SP41 SN 6322/14 3.54 miles 6.40x15 SP41HR SN 6322/27 3.31 miles 6.40x15 SN 6322/28 3.31 kilometers 6.40x15 SN 6322/29 3.54 miles 6.40x15 SN 6322/30 3.54 kilometers 6.40x15 SN 6322/31 2.88 miles 6.40x15 SN 6322/32 2.88 kilometers 6.40x15 SN 6322/33 3.07 miles 6.40x15 SN 6322/34 3.07 kilometers 6.40x15 SN 6322/35 3.31 miles 185x15 SP41 SN 6322/36 3.31 kilometers 185x15 SP41 SN 6322/37 3.54 miles 185x15 SP41 SN 6322/38 3.54 kilometers 185x15 SP41 SN 6322/39 2.88 miles 185x15 SP41HR SN 6322/40 2.88 kilometers 185x15 SP41HR SN 6322/41 3.07 miles 185x15 SP41 SN 6322/42 3.07 kilometers 185x15 SP41 I don't have any numbers for series 2 and series 3 E-types....sorry. Regards, Mark Roberts Phone: (613) 763-2924 Ottawa, Ontario, CANADA Fax: (613) 763-3970 1988 VDP - SIII V12 e-mail: markdr@nortel.ca 1963 3.8L E-Type Coupe - 16 years into a 3 year project ------------------------------------------------------------------------- Date: Fri, 17 Oct 1997 From: Michael Frank Subject: [E-Type] Differential swap Vs 5-speed If you have a Jaguar 4 speed, then you have the following overall gear ratios: Rear axle 3.07 3.31 3.54 1 9 9.70 10.39 2 5.85 6.31 6.74 3 4.26 4.59 4.92 4 3.07 3.31 3.54 Assuming that you pick 3500 rpm as your shift point, you will shift at roughly the following speeds: Rear axle 3.07 3.31 3.54 1-2 29 27 25 2-3 45 42 39 3-4 61 57 53 So a 3.07 will lead to quieter cruising at normal highway speeds. If you drive to excess, you will be 'reaching for fifth' at the following speeds: 4-5 85 79 74 The 3.54 will give powerful acceleration, and is optimized for the ol' double nickels at the top end. The 3.07 gives you more 'headroom', but will add maybe a second to yor 0-60. Now let's suppose you replace the Jag 4 with a JT 5, but keep the 3.54. Overall ratios will be: 10.443 6.8676 4.7436 3.54 2.832 And shift points will be: 25 38 55 73 Which is similar to the Jag 4, but when you reach for fifth, it will be there, and will carry you quietly to 92 :->. So you have all the original punch, plus quiet cruising beyond the limit. Now let's look at the same thing, but with a Moss 4-speed. Your overall ratios will be: Rear axle 3.07 3.31 3.54 1 10.3459 11.1547 11.9298 2 5.7102 6.1566 6.5844 3 3.9603 4.2699 4.5666 4 3.07 3.31 3.54 And the shift points would be: Rear axle 3.07 3.31 3.54 1-2 25 23 22 2-3 46 43 40 3-4 66 61 57 "Reach" 85 79 74 At least on paper, the Moss box with the 3.07 looks like a great combo...fast off the line, and quiet at speed. I've always felt this box had an undeserved poor reputation. Any thoughts? Mike Frank 1969 E-Type 2+2 Thema: Re: Gear ratios; supercharging Datum: 22.11.1996 05:02:32 From: mfrank@westnet.com (Michael Frank) The gear ratio is computed by dividing the number of teeth in the differential ring gear by the number of teeth in the pinion. This works outto be the same as the total ratio in fourth gear because fourth gear is 1:1. I don't have the ratios for the other three gears handy, but a typical 5-speed has a fifth gear ratio of .85 or therabouts. A ratio of less than one is an overdrive, which means that the transmission input shaft spins slower than the output shaft. For example, my Supra has the following gearing: 1st 3.28 2nd 1.89 3rd 1.27 4th 1 5th .86 To get the overall drive ratio, multiply the rear axle ratio by the transmission gearing ratio. Generally, the slower the engine turns, the better the gas mileage will be, and the higher the eventual top speed. Numerically high gear ratios will give better acceleration at the expense of top speed. Supercharging improves performance by providing a denser mixture. Unless there is careful design of the head and sophisticated engine management, compression ratio would need to be reduced to prevent preignition. Supercharging uses some engine horsepower to create more horsepower, which is somewhat less efficient that turbocharging, which uses waste energy from exhaust gases to do the same thing. On the other hand, turbocharging slightly increases back pressure, which robs some HP. The advantage of supercharging is that the effect is instantly proportional to engine RPM, while turbocharging suffers from a characteristic lag. Fuel economy need not suffer in a well designed blower setup, but usually does. Wear and tear on turbos and supercharges used to be a horrendous problem. You may recall that WO Bentley was dead set against the blower cars, and they nearly blew (pun!) his racing record. Modern alloys and ceramics have made these units acceptably reliable. Homologation rules may have prohibited blowers at the time of the C and D cars, but I'm guessing. Reliability, cooling, and engine bay space were likely large factors. Hope this helps. Mike Frank 1969 E-Type 2+2