Using Blair to spec a Cam

[Stan Weiss]

Let me start by saying if you are not going to post anything that adds something technical to the thread PLEASE don't post. I know that could mean this will be the only post in this thread.

Let see how using Blair will help me select a cam.

I am going to use a 535 ci Pontiac engine for this example. bore = 4.35", stroke = 4.5", rod = 6.7", cr = ??? (Pump gas), Intake Valve = 2.22", Exhaust Valve = 1.77".

I want 900 HP @ 7500 RPM

Torque = (Horse Power * 5252) / RPM
► (900 * 5252) / 7500 = 630.24

BMEP = (Torque * 150.8 ) / Cubic Inches
► (630.24 * 150.8 ) / 535 = 177.645

Since Blair uses metric 177.645 = 12.2482 Bars

► BMEP_BARS = 12.2482
► (5.02 * BMEP_BARS + 57.78 ) / 10000 = 0.0119265964
► (1.7775 * BMEP_BARS + 74.822) / 10000 = 0.009659317549999999
► (4.1185 * BMEP_BARS - 17.985) / 10000 = 0.00324592117
► (3.0296 * BMEP_BARS - 11.363) / 10000 = 0.002574414672
► (1.6329 * BMEP_BARS - 7.1871) / 10000 = 0.001281298578
► (2.4022 * BMEP_BARS - 14.57) / 10000 = 0.001485262604

OK, so what is my next step?

Stan

Blair.gif

[RevTheory]

Looks simple enough, Stan

What's in parenthesis on the right?

[DrillDawg]

I have no clue about Blair, but I'd use 11 to 1, 280/294, .800 lift 113lsa\110icl, due to the "small" valve size close the intake valve late to keep the VE up, the heads need to flow in the 380 to 400 cm area and the intake and exhaust tracts have to be sized right. I would say you might struggle to make 900hp on pump gas without very good heads.

[pcnsd]

Looks simple enough, Stan

What's in parenthesis on the right?

Equations 18 through 23.

Stan,
I have a number of articles from Blair and others on camshaft design I will dump here if you concur. Despite Blair's comments about camshaft design no longer being the realm of experts, I will disagree. I can understand the basic concepts but building up the complete spreadsheets with visualbasic programming is still beyond my ability. I also have the equations posted by Rick Jones in spreadsheet form when he closed his original website but they only draw half a lobe and I assume the landing of the valve is much different from it's launch.

[statsystems]

I have no clue about Blair, but I'd use 11 to 1, 280/294, .800 lift 113lsa\110icl, due to the "small" valve size close the intake valve late to keep the VE up, the heads need to flow in the 380 to 400 cm area and the intake and exhaust tracts have to be sized right. I would say you might struggle to make 900hp on pump gas without very good heads.

Are you going to show your math? Otherwise it looks like a guess. Or you've done it enough to use empirical evidence to determine cam timing.

[DrillDawg]

Lol, it is my best guess, who turns a 535 pontiac 7500 using a 2.22 valve, without head flow, everything you do is a guess.

[Stan Weiss]

Looks simple enough, Stan

What's in parenthesis on the right?

Equations 18 through 23.

Stan,
I have a number of articles from Blair and others on camshaft design I will dump here if you concur. Despite Blair's comments about camshaft design no longer being the realm of experts, I will disagree. I can understand the basic concepts but building up the complete spreadsheets with visualbasic programming is still beyond my ability. I also have the equations posted by Rick Jones in spreadsheet form when he closed his original website but they only draw half a lobe and I assume the landing of the valve is much different from it's launch.

Paul,
That would be great. Anything that will farther the technical discussion is very welcome.

As far as the spreadsheet you are working on, there are 3 different ways that I see.
1) Pure symmetrical lobe and ramp
2) Pure symmetrical lobe and different ramp on close
3) Non symmetrical lobe and different ramp on close

1 and 2 should not be very hard to add.

Are you looking to do a pure Visual Basic Program or use VBA with Excel?

Stan

[Stan Weiss]

Lol, it is my best guess, who turns a 535 pontiac 7500 using a 2.22 valve, without head flow, everything you do is a guess.

I am trying to use Blair's and time area. Nowhere's does it need flow numbers. Sorry, I just looked and the head I would use on this example has a 2.23" intake valve (432 cfm @ .800") and while I am correcting myself the exhaust valve is 1.72".

Stan

[statsystems]

Lol, it is my best guess, who turns a 535 pontiac 7500 using a 2.22 valve, without head flow, everything you do is a guess.

I am trying to use Blair's and time area. Nowhere's does it need flow numbers. Sorry, I just looked and the head I would use on this example has a 2.23" intake valve (432 cfm @ .800") and while I am correcting myself the exhaust valve is 1.72".

Stan

Thanks for the clarification. Following this thread closely to see what comes up for cam timing.

[Scotthatch]

I wondered how to get there too from those equations then read this

15260743910440.jpg

[SchmidtMotorWorks]

Sounds like a good project.

At the top of the dialog, a menu that classifies engines into groups of BMEP.

One good thing about the Blair method is that the cam is defined in several regions with a separate formula for each one.
It is also good that it is time & area, so that the aggressiveness of the cam is considered.

If you have a lot of refinement done on a particular type of engine to where you can say, "for this specific type of engine, region x needs to be larger", then you can edit that one specific formula.

If you make it in a program, it would be a good idea to make a text file that goes along with it that is read when the program initializes.
That way, you could continue to refine formulas and then every time you load the program it would use the latest file/formula.

Further, for someone that works on more than one type of engine and notices that each of them have different characteristics; like for example if you worked on both Harley and Japanese 4 cylinder engines, you could consider putting an option menu that allows you to choose from a variety of configuration files.

With regards to approximating the cam quickly, there are a few ways to go about that; if that becomes a time consumer, just ask, I may be able to provide some options depending on what language you are using.

[Stan Weiss]

John,
I have written in a number of different programming languages depending on what the computer / operating system was. Under Windows I use Visual Basic (pre .NET)

The point of this thread, I hoped was to show all of the work needed to use this method here so that anyone could try it.

Stan

[hoffman900]

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.

[SchmidtMotorWorks]

John,
I have written in a number of different programming languages depending on what the computer / operating system was. Under Windows I use Visual Basic (pre .NET)

The point of this thread, I hoped was to show all of the work needed to use this method here so that anyone could try it.

Stan

That choice is a little tricky.

The factors to use when choosing a language to code in are:

1. What development software is best to work on?
Hands down, that is Microsoft Visual Studio, the other options are only practical for non-beginners.
Microsoft visual studio can be used for free if you are not a big company.
It has more functionality to help the coder than anything else my multiples.

2. What language can I find free code on the web to use as part of my project?
This is super important, the speed of a good modern programmer (not working in a company) is how fast they can find good code to reuse and assemble into your program.
Of the code and tutorials you will find on the internet C# is far better quality that VB.net because it is used in more professional projects.
There are more simple VB.net examples, but for hard things, there will be more C# examples.

3. If I can't figure out how to do something, what do I do?
C# will be a better choice here, too.
If you are struggling with something, you can find people on forums or Freelancer.com to do stuff for you. There are literally thousands of people in 3rd world countries that will do amazing work for $20. I use them 100's of times.

4. What language is worth the most for a job if I learn to use it and like it and want to get a job doing it?
For sure C#.

[hoffman900]

And to go along with Stan's first post:

Since Blair uses metric 177.645 = 12.2482 Bars

► BMEP_BARS = 12.2482
► (5.02 * BMEP_BARS + 57.78 ) / 10000 = 0.0119265964s/m (intake pumping)
► (1.7775 * BMEP_BARS + 74.822) / 10000 = 0.009659317549999999s/m (exhaust pumping)
► (4.1185 * BMEP_BARS - 17.985) / 10000 = 0.00324592117s/m (intake overlap)
► (3.0296 * BMEP_BARS - 11.363) / 10000 = 0.002574414672s/m (exhaust overlap)
► (1.6329 * BMEP_BARS - 7.1871) / 10000 = 0.001281298578s/m (exhaust blowndown)
► (2.4022 * BMEP_BARS - 14.57) / 10000 = 0.001485262604s/m (intake ramming)

OK, so what is my next step?

Stan, I added the bold to help people follow along.

The units of "time-integral of area per unit swept volume" or "m^2s/m^3=s/m