Head flow chart, cam lift - how does it all come together?

[turbogrill]

Hi,

 

Let us pretend that I get the following flow improvements with a head port. (tested in flow bench)

 

Intake

0.1 Lift, 1% Improvment

0.2 Lift, 4% improvement

0.3 Lift, 10% improvement

0.4 Lift, 10% improvement

0.5 Lift, 14% improvement

 

Exhaust

0.1 Lift, 10% improvment

0.2 Lift, 15% improvement

0.3 Lift, 27% improvement

0.4 Lift, 25% improvement

0.5 Lift, 25% improvement

 

Given this data, could someone elaborate a little on how that would affect cam choice and also HP gains? Make up a scenario if you want!

 

Trying to understand how all this stuff comes together...

 

[HuD 91gt]

I am by no means an expert and I will delete this as soon as someone corrects me but....

 

 

A cam lifts a valve to it's max lift with every two rotations of the crank.

 

This means, you want an increase in flow up and until max lift of your cam. Simple.

 

Increase duration of your cam means the valve is open longer. A more extreme ramp of lift would mean the higher flow at higher lift would be much more desirable. I'd assume this is more applicable to a race engine.

 

A street engine, which is meant for reliability and longevity will have lower lift and more then likely a softer ramp to be easier on the valvetrain.

 

Long story short, max flow at your max lift in my mind makes the most sense. The numbers at lower lift are important, but your duration and how quickly your cam goes from

Open to close determine how important those

In-between numbers actually account for.

 

 

Is there ever too much lift? Besides valve train wear and reliability, can you have too much?

 

Of you have no increase in flow from a lift of .400"-.700" there is no need to go for a larger cam. Cap it at .400" and keep it open. Less wear, less movement, less noise, less heat.

 

Having a chart with % increases doesn't mean much. I'd think absolute flow numbers would be what would help you choose a cam. This is all drunk ramble from a guy who's only dissassbled one or two motors. Eager to learn.

Edited September 14, 2016 by HuD 91gt

[clarkspeed]

Google is your friend. There are things called emissions, economy, driveability, that factor in.

[turbogrill]

 

This means, you want an increase in flow up and until max lift of your cam. Simple.

Thanks for the input.

 

Seems like you can't get good flow both at low lifts and high lifts. So it's important to optimize for the average lift. If the lift is 0.300 then it is more important to have a nice lift there than at 0.400.

This article (www.datsport.com/racer-brown.html) even suggests that it might be a good guideline idea to have flow fall of a little before max valve lift (maybe typical for Datsun heads).

 

HOWEVER! I guess all these flow charts are true at 100% VE. Highest VE is achived at torque peak (right?).

I wonder how a flow chart looks for the same engine running at 3000 RPM and 6000 RPM....

 

Anyone knows?