Using Blair to spec a Cam

[Stan Weiss]

Jon,
I am not looking to write a program do to this and I do not think very many on here are either. I was hoping that someone had some algorithms that people could plug into something like an Excel spreadsheet.

Stan

[digger]

Paging Vannik to the courtesy phone...

Neels does caution that the STA values are rough guidelines, which help "creating a new engine or when analyzing an existing engine".

Jon's Camflowrpm did some of this, but was a bit less sophisticated. With Neel's you adjust the BMEP and RPM and import a measured (ideal) or simulated (ideally to every 1*) valve lift profile.

what program is that? 4sthead?

EngMod4T,

This is the 1D software that is both affordable and very capable.

Vannik posts in Advanced

http://vannik.co.za/

ive been using it for 2 years but not seen that window lol

[SchmidtMotorWorks]

ive been using it for 2 years but not seen that window lol

I thought I remembered you posting images of it.

I had not used it either, but the UI style is a give away, where it came from.

[GARY C]

Is this engine going to be dyno tested to confirm that the cam works?

[vannik]

ive been using it for 2 years but not seen that window lol

It is the STA button on the main dialog box of Dat4T - I sometimes wonder why I do Help files, but seeing that most of the time I also do not use them, I understand it

[vannik]

A good background read is the following SAE paper:

Empiricism and Simulation in the Design of the High Performance Four-Stroke-Engine, Gordon P. Blair, 983046

The problem is that Bair's STA value targets are based on a limited number of engines with different porting configurations. There are engine builders that has refined the values for their specific group of engines and use it with great success. They obviously do not post those values.

[digger]

ive been using it for 2 years but not seen that window lol

It is the STA button on the main dialog box of Dat4T - I sometimes wonder why I do Help files, but seeing that most of the time I also do not use them, I understand it

its funny i click the button basically next to it every time i use it, but until now i never remember seeing it

[Stan Weiss]

Is this engine going to be dyno tested to confirm that the cam works?

Gary,
This is all just a theoretical exercise. Meaning no engine is being build.

Stan

[Stan Weiss]

I was hoping that others would step in and offer some help.

I am not sure if the term normalize is correct here or not.

These steps are easier said than done

Step 1 is to remove the time / RPM factor from STA as the same cam at different RPM will produce different STA's.

Step 2 is to remove the valve size from STA as the same cam at the same RPM with a different valve size will produce different STA's.

I believe I will now have the needed cam area for each segment.

Step 3 is to create a duration / lift profile for the cam area for each segment.

What do you think?

Stan

[hoffman900]

I was hoping that others would step in and offer some help.

I am not sure if the term normalize is correct here or not.

These steps are easier said than done

Step 1 is to remove the time / RPM factor from STA as the same cam at different RPM will produce different STA's.

Step 2 is to remove the valve size from STA as the same cam at the same RPM with a different valve size will produce different STA's.

I believe I will now have the needed cam area for each segment.

Step 3 is to create a duration / lift profile for the cam area for each segment.

What do you think?

Stan

Stan,

To be honest, I don't own any Blair literature... just seem to have too much going on and I already have a huge stack of books in cue, so I haven't looked at any of his writing on this. Busy day, I'll post something tomorrow.

Normalize would be to adjust the values so they could be scaled to a common scale. Like area of the bore to valve diameter won't scale, as area the radius is squared, but Valve area to bore area would be considered normalized and is dimensionless.

Your Step 1 seems correct. I believe Step 2 involves calculating a coefficient of discharge for some valve size flow area and velocity. No?

[SchmidtMotorWorks]

I was hoping that others would step in and offer some help.

I am not sure if the term normalize is correct here or not.

These steps are easier said than done

Step 1 is to remove the time / RPM factor from STA as the same cam at different RPM will produce different STA's.

Step 2 is to remove the valve size from STA as the same cam at the same RPM with a different valve size will produce different STA's.

I believe I will now have the needed cam area for each segment.

Step 3 is to create a duration / lift profile for the cam area for each segment.

What do you think?

Stan

I think removing RPM and Valve size makes it meaningless.
Different RPMs demand different cam values.

[hoffman900]

I was hoping that others would step in and offer some help.

I am not sure if the term normalize is correct here or not.

These steps are easier said than done

Step 1 is to remove the time / RPM factor from STA as the same cam at different RPM will produce different STA's.

Step 2 is to remove the valve size from STA as the same cam at the same RPM with a different valve size will produce different STA's.

I believe I will now have the needed cam area for each segment.

Step 3 is to create a duration / lift profile for the cam area for each segment.

What do you think?

Stan

I think removing RPM and Valve size makes it meaningless.
Different RPMs demand different cam values.

Swept volume?

[pcnsd]

Stan,
I am not able to post the Blair pdf's due to size, but I think you likely already have them since your original post includes a clip from his "Back to basics'" article. If not all may be located here for download:
http://www.profblairandassociates.com/RET_Articles.html

There are 4 articles related to camshaft design that may be of interest.
The right lift
Making the cam
Bucket operation
Pushrod operation

I have a pdf of Clyde Moon's "Cam design". It was a primer for industrial engineers employed by Camco. It was published in the early 1960's. I will email you a copy. You may find it useful.
Attached are two files. One is an edited Doc. file I clipped from Dick Jones website giving his camshaft equations or at least some of them related to drawing the lobe.
The other is an excel spreadsheet I started, but did not complete using them. There is some useful information provided, but it is not finalized. It reports a macro, but there is no code. I was going to use the macro to build an array and fill the cells when I gave up and bought his software package instead.

Camshaft calc.doc

Camshaft calc DJones.xls

[DrillDawg]

If you have a HP and rpm target for a certain size engine and not allow for a known air flow air when picking the cam makes no sense to me. There would be no way the same cam would be right for an engine that heads flowed 380 and the same engine with heads that flowed 430 and depending how weak or good the exhausted flowed should also be worked into the equation.

[Stan Weiss]

I was hoping that others would step in and offer some help.

I am not sure if the term normalize is correct here or not.

These steps are easier said than done

Step 1 is to remove the time / RPM factor from STA as the same cam at different RPM will produce different STA's.

Step 2 is to remove the valve size from STA as the same cam at the same RPM with a different valve size will produce different STA's.

I believe I will now have the needed cam area for each segment.

Step 3 is to create a duration / lift profile for the cam area for each segment.

What do you think?

Stan

I think removing RPM and Valve size makes it meaningless.
Different RPMs demand different cam values.

Jon,
Just what does Blair's calculation telling me?

I am understanding to tell me what time area I need for a give BMEP.

So how would you do it?

Stan