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I dont quite follow your logic there David.

5000 RPM in 4th will be slower than 5000rpm in 5th. When I mean slower I'm referring to road speed. Acceleration is dependent upon torque the engine generates.

* Acceleration (quickness) is dependent on torque
* Top speed is dependent on HP

It may take a looong distance to achieve top speed, since the torque decreases as high-RPM horsepower increases.

In circuit racing the goals are different from top speed contests. I would guess that in your type of racing, you want to select the steepest gearing (quickest acceleration) that allows the highest top speed for the given length of track, while also keeping in mind gear ratios used for slower corners.

That is rarely the goal of a street driven car, as even a stocker A12 will exceed the highway speed limits. So instead most owners will focus on either acceleration (steep gears) or fuel economy (tall gears) or some compromise of the two (middling gears). Perhaps the best performance combination for highway use (120 or 140 kph maximum) is steep final drive gearing (say 4.111 or more, which allows 120+ kph top speed) along with overdrive for cruising. The overdrive does not improve performance/power/acceleration but does reduce noise and increase fuel economy, and is used when not accelerating.

Ok i'm a little confused! :/ so if i use the standars 4 speed of the a15 would be fine with a 100 hp motor?

YES, the A15 4-speed is fine to use with an A15. It can do 150kph in a Datsun B310 with stock gearing (rear final drive).

ok good :) so what do i do if i want to achieve more than 150kph?

btw just so you know, the B310 i have is the one with the round headlights. i know that its called also 210 but B310 is what there is on that plate on the firewall.

Another thing which i wanted to ask was: could i swap the a15 for an L series? Is it better than an A series? Does it require more work to fit and does it cost more? I just want to know, not thinking of putting an L series

Datsun model series B310 is only called the 210 in North America. In other countries it is badged as Sunny or 120Y/140Y/150Y.

Quote:Put your foot down and let the engine rev to 6000 RPM, which is below the red zone. If your B310 has the common 3.700 final gear, and is running the stock-size 155/80R13 tyres, it will do approximately 160 kph given enough room to accelerate up to speed.

You can swap an L-series engine into a B310, it has been done many times. The L-series engine is not better, just heavier and bigger and therefore makes more HP. It requires a conversion, including some fabrication and some upgrading, whereas the A-series simply bolts in. The engines cost about the same in most places. The factory L-series runs to 7000 RPM so makes a bit more HP than stock A-series which only does 6000 RPM. For example, L14 made 85HP@7000 RPM while A14 made 80HP@6000 RPM.

So if i install a 7000rpm racing camshaft would it achieve a higher top seed? Also, what is the 3.700 final gear that you mentioned?

I will probably put on wider tyres on it, and maybe slightly shorter tyres. Will this have a great effect on top speed? I really don't want to stick with the original tyres, apart that they look horrible, they have no grip at all. I enter at a roundabout in 2nd gear barely moving and floor it the back just slides out like nobody's business with the stock a12 which has been running daily for 33 years... So yeah you can imagine what its like in the wet! Ihave to change them