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Bajaj Discover: How to select out of seven models.

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Choosing a Bajaj Discover Commuter bike up to 125cc.

NOTE:

Prices differ from state to state and city to city because of local taxes. They also keep on increasing because they are directly dependent on price of ONiONs! Please check ONiON prices in your city today to know correct bike prices.

Bajaj does not mention Compression Ratio [CR] on its website for any of its models except the Three Discover100 bikes: Discover 100 DTSi (94.38cc) 2valve of which CR=9.8;                             Discover 100T DTSi (102cc) 4valve of which CR=10.75;                             Discover 100M DTSi (102cc) 4valve of which CR=10.5o.                              

<1>Starting with the cheapest and simplest engine Bajaj bike, the cheapest is probably Platina which has a SiNGLE spark plug and is not DTSi. Engine is 99.27cc (not the smallest) and produces 8.1bhp=6.03kw of power at 7500 and max torque 8.05Nm at 4500. Assuming a Compression Ratio of 9.5, the Engine Life Factor (ELF) of this bike would be 1.4, which would be highest among all bikes in the hole of Bajaj. Therefore Platina should have longest life of all Bajaj bikes.

<2>Almost in the same price range would be Discover100 DTSi, which has the smallest 94.38cc engine among all geared large wheel bikes (excluding scooters) in this hole cunt ree! It produces slightly less power=7.6bhp= =5.66kw at 7500 and less torque=7.85Nm.at 5000 than Platina. The CR of this engine is given as 9.8. Hence~notional, not effective~ELF=1.36. To get effective ELF, since this engine is DTSi, we have to apply correction, and divide this by 1.2 to account for DTSi 20% heat factor, (Platina does not have DTSi so heat factor is not applicable to Platina). So, 1.36 divided by1.2=1.133. Now since max torque in this bike happens at 5000rpm (in Platina it happens at 4500rpm which is 90% of 5000), the EFFECTiVE ELF of this bike is 1.133 x 0.90=1.02., which is 27% less than 1.4 of Platina which means its life will be 27% shorter than Platina. If life of Platina is taken as 10 years, this bike engine will live 7.3 years. Since it is DTSi, it will give 6% more mileage than Platina.

In performance both above bikes will be almost 99% same.

<3>Next bigger engine is the 102cc Discover100T DTSi. The most important difference in this bike is that it has a 4valve engine while the above Discover100 without T, has a 2valve engine. Also this engine revs max at a higher 9000rpm producing10.06bhp, and max torque 9.2Nm at 6500rpm. CR is actually given (not assumed) as 10.5. So ~ notional, not effective ~ELF will be 1.058. To account for DTSi and 4valves we have to divide this figure by 1.32, which gives effective ELF=0.80, which is 57% of the ELF of Platina. Thus if life of Platina is taken as 10 years, this bike life will be 5.7 years. Yet this one of the most powerful, high tech, small (~100cc) engines, in this hole world since hardly any other bike maker in the world has a 4valve DTSi engine of such small size. Producing @25% more power than the above two, and highly fuel efficient given the power it produces, its mileage will be 8% less than the above two bikes and life will be 15-20% shorter than above two bikes yet is the most fun to drive ~~100cc bike.

<4>Next higher in the Discover series of Bajaj is Discover125 DTSi which has a 2valve, 124.6cc engine producing 8.1kw=10.85bhp at 8000rpm and max torque 10.8Nm at 5500rpm. Assumed CR being 10.5, the notional, not effective ELF of this bike will be 1.19. Applying 1.2 DTSi correction, the semi-effective ELF of this bike will be 0.99. Since his bike revs at 500rpm higher for torque, real effective ELF will be 0.99 x 0.95=0.94. So if life of Platina is 10 years, life of this bike will be 6.7 years. It has almost 40% more power & torque than the above three~~100cc bikes. Mileage will be @ 15% less than the above two bikes but will be more fun to drive. While the above three bikes come with drum brake both front and rear, this bike comes with a choice of 200mm disc brake in front.

<5>Next higher is the 4valve Discover125T DTSi having the same 124.6cc pot which revs at the same high 9000rpm as the 102cc 4valve Discover100T and both will have the same life span, which is 5.7 years. This bike produces 12.33bhp at 9000 and torques 10.8 Nm at 6500. Mileage will be 10% less; top speed will be 90+ and comes with an optional 200mm disc brake in front.

<6>Top of the table of Bajaj bikes up to 125cc is the 4valve Discover125 ST. While producing 12.8bhp at the same 9000rpm as the 100T and 125T, it max torques 11Nm (=1.1kg-M) at a higher 7000rpm as compared to 6500rom of the 100T & 125T. Assuming CR=10.5, the notional ELF is 1.058. Applying DTSi (divide by 1.2) and 4valve correction (again divide by 1.1), the ELF comes to (1.058/1.32)=0.80. Further applying torque rpm correction (0.8 x .95), the effective ELF is 0.76. Since Platina (ELF=1.4) life is assumed at 10 years, this bike life will be 5.4 years. This is the most powerful 125cc bike from Bajaj. Mileage will be 3% less and power & performance 5% higher than 125T. Max speed will be close to 100.

<7>Bottom of the table is the latest Bajaj Discover100M. This is a toned down version of the same 102cc 4valve DTSi engine having specified CR=10.5, with reduced 9.17bhp = =9.3PS=6.84kw at reduced max rpm of 8000 (instead of 9000) and reduced max torque rpm at 6000 (instead of 6500). So notional ELF is 1.19. Further applying correction for lower rpm for max torque, the effective ELF becomes 1.19 x 1.05=1.25.

Thus if Platina life=10 years, this bike life=8.9 years, which is an extremely long life for a 4valve DTSi engine! With just 0.9PS less power, this bike will give @5.5% more mileage and 94% of the performance of Discover100T DTSi.

Explanation of the WHY, HOW and HOW MUCH for the above EngineLife estimations:                                                                                                              

Bajaj does not mention Compression Ratio [CR] on its website for any of its models except the Three Discover100 bikes. Therefore for all other models in the hole of Bajaj the CR is assumed (and mentioned as assumed in the calculation of ELF).

To get an indication of life of engine, we define a measureable and quantifiable FIGURE which we call Engine Life Factor or ELF for short. ELF gives RELATiVE life span of various engines, and is defined as:100000 divided by (CR x max RPM) that is: ELF ==100000/(CR x max RPM at which max bhp is produced).

Now the math gets slightly KompliKated.

While above is the basic formula, THREE additional factors need to be considered and corrections applied. These are

<1>Engines having same bore x stroke producing max Torque (not max power) at Different RPMs: The rpm may be higher or lower, and is always in multiples of 500. For this correction, the %age=percentage increase/reduction is used. For example, in two engines having same bore X stroke producing (same or different) max power at same rpm (say 6500 rpm), but 0ne of them produces (same or different) max torque at 5000 rpm and the other produces (same or different) max torque at 4500 rpm then, if the ELF of the engine producing max torque at 5000 rpm is ‘L’, then the ELF of the engine producing max torque at the lower 4500 rpm will be: L x 5000/4500, that is: L x 50/45= L x 10/9= L x 1.11.

Another mathematical procedure for the same ELF calculation could be: L divided by 9/10= L /0.9. It is a mathematical fact that any number divided by 9/10=0.9 will give the same answer if multiplied by 10/9=1.11.

The 0perative factor for calculating ELF is RPM, not power.

<2>Engines of same bore x stroke having TWO spark plugs: While most engines use 0ne spark plug, some engines (e.g.,Bajaj and Royal Enfield) use TWO spark plugs. (Bajaj calls it DTSi and Enfield calls it TwinSpark). Two spark plugs do better utilization of fuel and burn more of the fuel in cylinder than single plug. More fuel burning in the same space (cylinder) means the temperature of the TWO PLUG cylinder will be higher than ONE PLUG cylinder, and it is a fact that at higher temperature wear and tear will be more than at lower temperature, and its corrected ELF will be LOWER than single plug engine. ASSUMiNG that two plug engine temperature will be 20% higher (=1.2 times higher) than single plug engine, we need to further divide the ELF of a two plug engine by 1.2 to account for two plugs.

<3>Engines of same bore x stroke having 4valves instead of 2valves: Engines having 4valves have better combustion efficiency=better fuel utilization than 2valves, which also raises temperature and reduces engine life. ASSUMiNG the temperature in a 4valve engine is 10% higher than in 2valve engine, we need to further divide the ELF of a 2valve engine by 1.1 to account for 4valves.

Further, if an engine (of same bore & stroke) has TWO PLUGs (as well as 4valves, we need to divide the ELF by 1.2 x 1.1=1.32.

While the higher temperature due to two plugs may NOT be exactly 20% HiGHER (since no actual measurements have been made, it could be lower or higher), and the higher temperature due to 4valves may NOT be exactly10% HiGHER (since no actual measurements have been made, it could be lower or higher), dividing by 1.2 and 1.1 may not be exactly accurate, it doesn’t matter, since ELF is an INDICATiVE relative figure, NOT an EXACT measured quantity. ELF only gives relative life expectancy, not exact life duration, which is good enough to compare relatively higher or lower life expectancy to make a buying decision.

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