Timing Curves

[Todd Hedges]

How does the HP Curve and rpm range effect the way your car works.

What I'm trying to ask is, given the exact same HP curves but with one really getting strong starting at 2300 rpms thru to 4500 rpms verses one that starts getting strong at 3000 rpms thru to 5200 rpms. (let's say a 400hp engine in a 2800# car w/ a 5 speed)

What is the difference?
Is one suited better for a light car?
Is one better for the 1/4 mile?
Is one better for a twisty road course?
Is one easier to drive?

I have an idea that the quicker you can build HP, the quicker you will get up to speed, but once up to speed do you need the HP to keep the car accelerating in the higher RPMS where drag take over?

[RallySnake]

Todd,

This is an interesting subject. I'll bet you'll get some differing opinions over it.

The difference in the horsepower range is controlled by the camshaft. I had a BIG solid lifter cam in my engine when I built it and the upper rpm power (4000 to ?) was amazing. I could dip the clutch for a second to let the engine rev and then pop it and spin the wheels at most speeds. Pulling away from a stop sign on an incline with the tall first gear and 3.31 rear was NOT so much fun. The best part was buzzing around canyon roads with the close ratio 4 speed. It was easy to keep the motor on boil. The NOT so good thing was the constant high rpm on the freeway.

Now, I have a milder hydralic cam, Rhodes lifters and a Tremec 5 speed and the car is much more relaxed. Power is made from 2200 to 5000. Crusing the freeway at 80 at 2700 rpm is perfect. The low 3.27 first gear launches the car easily from a stop in any mode. The transmission's wider ratios are not as much fun on the twisties though, I pretty much leave it in second. It's the same on an autocross track, second gear all the way.

Sometimes, I wish for a 6-speed, to have the best of all worlds. However, I suspect that, in practice, the 6 speed could be confusing. I would need a little digital display to show which gear I'm in.

I hope that answers your question,
Paul

[Cracker]

I have two FE's with completely different personalities. The 427 is a screamer with power coming in @ 3,500-7,000 (and beyond if you'd let it!) and the 428 w/webers which is basically off idle to 5,000 rpm's. For street use there is no doubt that MOST Cobra owners would probably prefer the torque low and broad like the 428 in the car now. I, however really enjoy the rush of a higher rpm BB that will easily bump the rev limiter without trying! The old saying goes 1st gear is used just to get rolling. Well in my case I say the same is true about the late surge of the 427. With any spirited driving the engine never falls out of the power range between shifts and you know it still not that bad at 2,500 either! Enjoy whatever you choose.