I used the formula used earlier (above).

**Answer is you've much more than 150 hp net at the flywheel** 5000 rpm in 4th is 185 km/h, enough to do a 12 second quarter. Perhaps yer rev counter is out, or you got such bad wheel spin that the 450 odd hp that your not telling us about is having trouble getting through!!!!! :rolflmao:

Here are the calcs to you can see if I'm a bulls**ter or not!

**Calcs:-**
my rear gears are 3.23 and i run 225/65 r14 and i have a w55 supra box 3.55 first gear. what sort of power am i looking at having?

(not by any of the formulas given in other books, this one is based on factual info from all reputable British car mags from 1970 until 1990, it allows for the reduction in tyre diameter due to wheel load which can be 4% on a Mini, to 2% or less on a large car with big tyres)

The fourth gear is 1:1, so Km/h at 5000 rpm is worked out this way

225*0.65+225*0.65+(14*25.4)= unloaded tyre height of 648.1 mm with full tread. Take off 2.2% for crush. Its a radial, how can the tyre balloon at 150 km/h? Actual loaded diameter is 634.1 mm.

Divide by 1000 to get meters, multiply by 60 to get the units (revs) into hours, and multiply by pi (3.1416) and divide by 3.23:1 (diff ratio) to get km/h in a 1:1 fourth gear.

Answer is 37.0 km/h in fourth per each 1000 rpm.

**At 5000 rpm, that's 185 km/h**
Ist is 10.4 km/h per 1000 rpm.

A 15.8 second quarter mile needs

**a minimum of 112 kw (150 hp) at the flywheel** if an XT Falcon is 1320 kg ar the kerb, has 80 kg for one driver, and 3/4 of a 77 litre tank is 77*0.75*0.75=43 kgs. All up 1363 kgs.

The terminal speed for that is around 143 km/h.

For gearing to be optimised, car must haul through the traps at an rpm reading

**10% above the point where maximum power is reached**.

In most six cylinder 250 Falcons, red line can't exceed 5400 rpm, or sump surge, crank vibration and piston speed start causing problems. In most cases, a cammed 250 with more than 280 degrees of cam and a good head/carb will do 160 kw(215hp) at 4900 or less. A Falcon 250 engine can hit 112 kw at 3800 rpm, and 4200 rpm is the best change up point. So a flat 15.8 could be done with only a 3.5:1 diff ratio giving 34 km/h per 1000 rpm and only 112 kw!

Quarter Junior:-

The quarter Junior seems to over estimate things, saying you'd need 172 hp at the flywheel. With 3.23:1 gears, it'd be doing 3860 rpm through the traps in fourth.

For an XF EFI Falcon S 4-speed , thats 188 hp

an EB S-XR6 Falcon 5-speed 252 hp

an EA SVO 3.9 Falcon 3-speed, 214 hp