Cam duration

[Steve.k]

Everything is the same other than front carb sits 1inch higher. However before jet change fuel consumption equal.

[SchmidtMotorWorks]

You can play around with this
Estimate Cam Intake Duration Needed @ 0.050" http://www.magneticlynx.com/carfor/calccam.php

Stan

Why does a duration calculator take number of cylinders as input?
Test it with an input of 1 cylinder.

Engine Size = 375.5ci -- Number of Cylinders = 1 -- Max RPM = 9500
Volumetric Efficiency = 125% -- Head Flow - Intake CFM = 444

The result of your calculation is:

2092.28 Duration @ 0.050" Lift

[Stan Weiss]

You can play around with this
Estimate Cam Intake Duration Needed @ 0.050" http://www.magneticlynx.com/carfor/calccam.php

Stan

Why does a duration calculator take number of cylinders as input?
Test it with an input of 1 cylinder.

Engine Size = 375.5ci -- Number of Cylinders = 1 -- Max RPM = 9500
Volumetric Efficiency = 125% -- Head Flow - Intake CFM = 444

The result of your calculation is:

2092.28 Duration @ 0.050" Lift

Jon,
How many people without thinking about it will know what the size of one cylinder of their engine is verses their engines size?

You are right it does no validation. So GIGO

Stan

[SchmidtMotorWorks]

Jon,
How many people without thinking about it will know what the size of one cylinder of their engine is verses their engines size?

You are right it does no validation. So GIGO

Stan

Bore and Stroke would be a better choice of inputs than displacement and cylinders.

Regardless of the inputs, a return in the thousands of degrees indicates a scaling problem.

[GARY C]

Engine Size = 375.5ci -- Number of Cylinders = 8 -- Max RPM = 9500
Volumetric Efficiency = 125% -- Head Flow - Intake CFM = 444

The result of your calculation is:

261.53 Duration @ 0.050" Lift

?

[SchmidtMotorWorks]

Engine Size = 375.5ci -- Number of Cylinders = 8 -- Max RPM = 9500
Volumetric Efficiency = 125% -- Head Flow - Intake CFM = 444

The result of your calculation is:

261.53 Duration @ 0.050" Lift

?

That was the default calculation.
Change the number of cylinders to 1 and the the duration goes to the thousands (which is impossible).
That indicates a scaling problem in the formula.

[digger]

Engine Size = 375.5ci -- Number of Cylinders = 8 -- Max RPM = 9500
Volumetric Efficiency = 125% -- Head Flow - Intake CFM = 444

The result of your calculation is:

261.53 Duration @ 0.050" Lift

?

That was the default calculation.
Change the number of cylinders to 1 and the the duration goes to the thousands (which is impossible).
That indicates a scaling problem in the formula.

The real answer to your question is it's not possible to achieve the result, it is not necessarily a scale issue. 444 cfm cant feed a 375ci engine sufficient to achive 125% VE at 9500rpm. a number greater than about 330 tells you that

[GARY C]

Engine Size = 375.5ci -- Number of Cylinders = 8 -- Max RPM = 9500
Volumetric Efficiency = 125% -- Head Flow - Intake CFM = 444

The result of your calculation is:

261.53 Duration @ 0.050" Lift

?

That was the default calculation.
Change the number of cylinders to 1 and the the duration goes to the thousands (which is impossible).
That indicates a scaling problem in the formula.

I see, I thought it was designed for 8?

Wouldn't the math be different for 1 cylinder vs multiple cylinders due to lack of scavenge from the other cylinders?

[randy331]

I will have to add a list of different type engines and what a reasonable VE range would be.

Stan

The ve tables may help, but to me the more duration equals more ve is flawed.
Maybe some limits on duration inputs based on the rpm entered.

By that calculator our emc engine should have been 3% higher ve with the largest cam vs smallest tested. That would be about 20-25 Lbs of tq and it wasn't near that difference, and the smaller cam was the better one.

I just don't think the relationship of cfm-duration-ve is like the calculator shows.

Randy

[digger]

In pipemax VE seems to be about lift which makes more sense but things are not so simple all the time

[Erland Cox]

Stan! Is the duration on the valve or on the lifter?
If it is on the lifter what rocker ratio does the equation use?

Erland

[MadmanMark]

Unless they changed the formula on the website, I get 261 for the duration with 8 cylinders. If you change the input to 1, I think you need to divide the displacement by 8, which gives you the same result (261). I get "Invalid Result" with a 375.5ci single cylinder.

[Stan Weiss]

Stan! Is the duration on the valve or on the lifter?
If it is on the lifter what rocker ratio does the equation use?

Erland

Erland,
This is at the lifter. This is just a basic calculation which will get you close in most cases.

Stan

[Erland Cox]

OK, with 1,5 rockers?

Erland

[Stan Weiss]

OK, with 1,5 rockers?

Erland

Yes

Stan