396,427,454 High Performance camshaft question?

[Duke W.]

Re: May not be completely true in practice

I think you may have missed the point of my argument. (See Taylor's IC engine textbook for a further explanation if you like.) The engines in question are all IDENTICAL except for stroke - same bore, CR, heads, ports, valves, inlet and exhaust system.

The VE for all three will be the same for any given piston speed, and all three will achieve peak power at the SAME piston speed, but the 302 will be revving higher by the ratio of the inverse of the strokes.

Once you start changing engine compoents on any one of these engines and then install them in different chassis you introduced new variables and all bets are off.

Duke

[mike cobine]

May have missed part of the point

Duke,
you are right about the power for a given VE and at a given piston velocity. For example, the 377 with 3.75 stroke will have 750 fps at 6000 RPM and produce 457.0 hp per FAA. The 302 will have 750 fps at 7500 RPM and produce 457.0 RPM per FAA.

Givens: 4.00 bore, 200 cylinder pressure, 3.00 stroke for 302, 3.75 stroke for 377.

In the real world, peak power doesn't always come at the same piston velocity in various engines because engines are not built out of identical components but out of components tailored to match the operating characteristics desired.

[mike cobine]

OOPS! 750 INCHES , not feet

That was 750 INCHES per second which is 62.5 feet per second.

RPM 3 3.75
-------------------------------------
1000 RPM 8.333 10.417
1500 RPM 12.500 15.625
2000 RPM 16.667 20.833
2500 RPM 20.833 26.042
3000 RPM 25.000 31.250
3500 RPM 29.167 36.458
4000 RPM 33.333 41.667
4500 RPM 37.500 46.875
5000 RPM 41.667 52.083
5500 RPM 45.833 57.292
6000 RPM 50.000 62.500
6500 RPM 54.167 67.708
7000 RPM 58.333 72.917
7500 RPM 62.500 78.125
8000 RPM 66.667 83.333
8500 RPM 70.833 88.542
9000 RPM 75.000 93.750
-------------------------------------

[mike cobine]

It would help if you could read it

That was 750 INCHES per second which is 62.5 feet per second.





RPM 3 3.75
-------------------------------------
1000 RPM 8.333 10.417
1500 RPM 12.500 15.625
2000 RPM 16.667 20.833
2500 RPM 20.833 26.042
3000 RPM 25.000 31.250
3500 RPM 29.167 36.458
4000 RPM 33.333 41.667
4500 RPM 37.500 46.875
5000 RPM 41.667 52.083
5500 RPM 45.833 57.292
6000 RPM 50.000 62.500
6500 RPM 54.167 67.708
7000 RPM 58.333 72.917
7500 RPM 62.500 78.125
8000 RPM 66.667 83.333
8500 RPM 70.833 88.542
9000 RPM 75.000 93.750
-------------------------------------

[Duke W.]

Re: It would help if you could read it

Mean piston speeds are usually stated in feet per minute.

Mean piston speed = two times stroke (in feet) times RPM

For a 377 at 6000: 2 x 3.75/12 x 6000 = 3750 ft/min = 62.5 ft/sec

The current practical limit with the best cylinder head technology is about 5000 ft/min. Above this mean piston speed there is just not enough time to efficiency fill the cylinder and VE begins to drop off rapidly. Current F1 engines are running at about 5000 ft/min, and with bore/stroke ratios of about 2:1 for a 3.0L V-10 the corresponding revs are about 18,000.

Duke