Cam duration

[Steve.k]

For any given camshaft per cubic inch motor is there a duration number that gives you a rpm amount? For example you have 262@ .050 and engine peaks at 6700. How much more duration needed to get peak to 7100? All other things being equal or no change.Im thinking of utilization of head flow here mostly.

[andyf]

It would only be that simple if the engine was severely under cammed. If you took a race engine an put a small cam in it then you could probably make a chart showing how the power peak would move as the duration was increased. I don't think the curve would be linear, it would most likely flatten out as you approached the natural limit of the rest of the parts.

I've worked on a bunch of race engines where adding duration kills power. So in your example, adding duration past 262 might reduce the power level rather than increase it. It all depends on what else is going on in the engine.

We had a guy bring a "pro street" engine into the shop a while back. It was a "summit racing" special where he ordered a bunch of parts and built an engine. His cam was huge for the compression ratio and heads that he had on the engine. The engine sounded bad ass but ran like crap on the dyno. We finally talked him into letting us try a different cam. Went with something that had 20 degrees less duration and the engine picked up 100 hp. It also didn't sound so "bad ass" anymore but I guess he learned to live without the noise!

[blykins]

It all depends on the cylinder head. With some heads, you may not be able to add enough duration to move the peak hp rpm.

[andyf]

Another data point for you to chew on is the dyno test I just finished up. I have a nice pump gas race engine that made 760 hp with a 264/268 solid roller. I've been working with a cam mfg who thought their newest stuff would make more power and figured that a 268/271 cam would be the ticket. A bunch of testing later the engine makes slightly less power with the bigger cam. It seemed to all of us that the more aggressive cam with slightly more duration should make more power but it didn't. Bigger isn't always better with cams. The engine only needs what it needs and anything more is too much.

[Stan Weiss]

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

Stan

[randy331]

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

Stan

That calculator was good for a laugh or two, but not much else.

Andyf is on with his posts. His results are similar to what I've seen. More duration doesn't always equal more power, or more rpm.

A small cam can hold an engine short of it's peak HP rpm potential, but a big cam can't move the engine past it.

Induction and exhaust tracts run the show more than the cam.

Randy

[user-30257]

For any given camshaft per cubic inch motor is there a duration number that gives you a rpm amount? For example you have 262@ .050 and engine peaks at 6700. How much more duration needed to get peak to 7100? All other things being equal or no change.Im thinking of utilization of head flow here mostly.

What if I told you none and all we did was move the centerlines a couple degrees, and kept your duration the same.

[swampbuggy]

Andyf, How many cubic inches was that 760 HP engine and what static compression ? If you don't mind, Mark H.

[engineguyBill]

For any given camshaft per cubic inch motor is there a duration number that gives you a rpm amount? For example you have 262@ .050 and engine peaks at 6700. How much more duration needed to get peak to 7100? All other things being equal or no change.Im thinking of utilization of head flow here mostly.
[/quote

Steve,
There is not an EXACT correlation between camshaft design (duration) and maximum RPM potential. There are many factors involved in designing an engine that will attain high RPM levels AND produce torque/horsepower at elevated RPM ranges. With that said, the camshaft must be designed correctly in order for an engine to operate at higher RPM, in conjunction with intake manifold, head porting, exhaust system, etc., etc. Then the vehicle needs to have the correct gearing in order to utilize the RPM range effectively. Just remember though, that when you are producing torque/horsepower at high RPM levels you will be sacrificing power at lower RPM levels . . . . . .

[Steve.k]

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guys here is a 436 ford i just did.Notice peak hp at a leisurely 6700.Heres flow sheet. Go off bottom sheet. Im thinking raising rpm to utilize head flow. Ur19 manifold with dual 1050's. Cranes r-262 cleveland roller in there now.

[MadBill]

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

Stan

For my 498" BBC, the calculator came out with one degree more duration than the solid roller Mike Jones did for me.

[randy331]

Narrow spread from peak TQ to peak HP rpm.

Randy

[swampbuggy]

Randy-----what would you consider an excellent spread ??? Mark H.

[Steve.k]

Randy the old motor with single 1050 peaked at 5100 however that was 571ftlb. Now its 595 at that same rpm. Will the car not accelerate faster all things being kept equal?

[Steve.k]

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

Stan

For my 498" BBC, the calculator came out with one degree more duration than the solid roller Mike Jones did for me.

According to this calculator to run 7200 with my headfow 285@.050. From 262