[eschaider]

Here's some stuff that'll work your noodle a bit but also give you some insights into possible areas for improvement.

To make 100 HP it takes 10 lbs of air per minute or 600 lbs of air per hour assuming you are fueled correctly with maximum brake torque timing (optimized advance) good gas and no detonation.

There are any number of calculators on the net that will do the mental calisthenics for you and come back with a lbs of air per unit time that your engine processes at a given rpm. I did a calculation for a 418cubic inch engine with 98% volumetric efficiency. I am likely high for your engine so you may want to factor the volumetric efficiency to a number you feel good about.

At 98% volumetric efficiency a 418 cubic inch engine at 6500 rpm will process 54 lbs of air per minute. Divide 54 by 10 and multiply by 100 and you will get 540 hp at 6500 rpm. That translates into about 435 ft/lbs of TQ at 6500 rpm and probably around 480 maybe 500 at a lower rpm.

Unless your heads are particularly bad, improving port flow is not going to give you bottom end, it will give you top end. My bet is your complaint is bottom end related not 6500 rpm related. If that is true then increasing upper end breathing does nothing for and might hurt bottom end performance.

I suspect that any additional torque you will find will be related to cam phasing, compression ratio, gasoline octane rating and ignition timing. If you run poor quality (low octane) gas and therefore low ignition timing, to prevent knock, you are going to be disappointed by the engine torque output. Torque is what your seat of the pants dyno measures.

The solution is either to get better fuel, better timing and better cam phasing or get more inches. Don't forget, 10 lbs of air per minute is 100HP. The only way to get more air is more inches or supercharging.

If you want 20% more torque then you need 20% more displacement at the same rpm. 418 inches multiplied by 1.2 is 501 inches. There is a reason that big inch engines are popular in these cars. You can spend a lot of money to improve your heads and discover your bottom end did not step up at all and even worse stepped down — this would be a sad discovery.

The cheapest fix is to advance the cam for low speed and midrange torque, go to a dyno and get your fuel delivery system brought into focus for your engine's air appetite and while you are there take advantage of the dyno time to optimize your ignition timing and ignition curve.

You will spend about the same amount of money, the big difference is the visit to the dyno will actually make a difference. If you still want more then it is time for more displacement.



Ed


p.s. Nothing gives the seat of the pants dyno a blip like a positive displacement supercharger. My daily driver is a supercharged 4.4L (268 inch) v8 that produces 480 or 490 ft/lbs of torque at 1500 rpm, I don't recall anymore. When you touch the gas pedal, to say the car is responsive is an understatement.

My Cobra produces right at 650 ft/lbs of torque at 1500 rpm and is over a ton lighter than my daily driver. At 7000 rpm the engine still produces 642 ft/lbs of torque. This is the beauty and the bane of supercharging.

You don't know fear until you roll into your throttle at 100 mph and start to smoke the rear tires, in fourth gear! Until I turned on the traction control in the MS3Pro, the car was dangerous in the extreme at any speed and in any gear — so be careful what you wish for.