Using Blair to spec a Cam

[GARY C]

Will you be able to adjust for valve angle and different seat angles?

I think it was mentioned those STA values don't require flow CFM.
Also noted if you had a set of values perfected for a certain port design you would need to re-evaluate for a deviation. Port, valve angle, seats etc.

I was just thinking window area of 45* vs 55* would have an effect or 23* vs 12* head just for example?
So you would calculate different values for these changes?

[Vincenzo]

Stan
of all the engines that have pased through my hands, and they have been many and varied, only one was a top performer that had STA values closely comparing to the targets in Dat4T (Vannik's software).
This engine was a single cylinder, 2 valve DOHC of 500 cc capacity, and the purpose behind my interest was to evaluate the design, I had no involvement whatsoever in either the design or manufacture of this unit.
Said engine was and still is the top competition engine in it's racing class (Classic Motorcycle racing) and was a modified version of an existing engine, the modifications being made by two former Cosworth employees.
There were other engines that had near matching STA values, but they were not in the same top performance bracket as was the above.
The STA targets should be regarded as guides only, not values to be matched at all costs.

[Stan Weiss]

Stan
of all the engines that have pased through my hands, and they have been many and varied, only one was a top performer that had STA values closely comparing to the targets in Dat4T (Vannik's software).
This engine was a single cylinder, 2 valve DOHC of 500 cc capacity, and the purpose behind my interest was to evaluate the design, I had no involvement whatsoever in either the design or manufacture of this unit.
Said engine was and still is the top competition engine in it's racing class (Classic Motorcycle racing) and was a modified version of an existing engine, the modifications being made by two former Cosworth employees.
There were other engines that had near matching STA values, but they were not in the same top performance bracket as was the above.
The STA targets should be regarded as guides only, not values to be matched at all costs.

Thanks, I have to find sometime to wrap my head around your PM.

Stan

[Stan Weiss]

Thanks Neels,

While I have only had time to look at and not read it. SAE paper 983046

Empiricism and Simulation in the Design of the High Performance Four-Stroke-Engine
Gordon P. Blair
The Queen's University of Belfast

This might be of interest to others.

Stan

[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

While I have not worked out away to convert the STA's back to a cam, I am still working to see what the cam could look like. Using what is my second intake lobe design and shifting it around I have come close to the Intake Pumping and ramming numbers. the overlap which could cause me to go back to the drawing boards will not matter until I get an exhaust lobe. Please note that I use cm^2 and Blair uses M.

Stan

Code: Select all

Intake BTDC (IVO to TDC) = 7.463
Intake Pumping (TDC to BDC) = 119.310 <<<<<<<<<<<<<<
Intake Ramming (BDC to IVC) = 14.737 <<<<<<<<<<<<<<<
Intake Overlap (IVO to EVC) = 7.463

VALVE     Lift      Opens   Closes  Duration
                 Deg BTDC  Deg ABDC             Area
         0.00000    58.00 |  77.00 | 315.00 |  70.07
         0.00600    55.21 |  74.21 | 309.42 |  70.06
         0.01000    53.56 |  72.56 | 306.11 |  70.05
         0.02000    49.91 |  68.91 | 298.83 |  69.98
         0.04000    43.97 |  62.97 | 286.94 |  69.80
         0.05000    41.43 |  60.43 | 281.86 |  69.71
         0.10000    31.00 |  50.00 | 260.99 |  68.88
         0.15000    22.47 |  41.47 | 243.95 |  67.87
         0.20000    14.85 |  33.85 | 228.70 |  66.47
         0.25000     7.72 |  26.72 | 214.43 |  64.88
         0.30000     0.86 |  19.86 | 200.72 |  62.94
         0.35000    -5.86 |  13.14 | 187.29 |  60.99
         0.40000   -12.51 |   6.49 | 173.98 |  58.38
         0.45000   -19.17 |  -0.17 | 160.65 |  55.39
         0.50000   -25.94 |  -6.94 | 147.13 |  52.55
         0.55000   -32.88 | -13.88 | 133.24 |  48.89
         0.60000   -40.13 | -21.13 | 118.75 |  44.29
         0.65000   -47.84 | -28.84 | 103.32 |  39.91
         0.70000   -56.31 | -37.31 |  86.38 |  33.84
         0.75000   -66.11 | -47.11 |  66.78 |  26.56
         0.80000   -79.01 | -60.01 |  40.98 |  16.45

[Stan Weiss]

OK, the reason I did not post the cam lobe information last night was I started with to big of a cam lobe and produced those numbers using 1.4:1 rocker arm. I have adjusted the cam lobe and am now using 1.65:1 rocker arm.

Stan

Code: Select all

Intake BTDC (IVO to TDC) = 7.463
Intake Pumping (TDC to BDC) = 119.310
Intake Ramming (BDC to IVC) = 14.737
Intake Overlap (IVO to EVC) = 7.463

VALVE     Lift      Opens   Closes  Duration
                 Deg BTDC  Deg ABDC             Area
         0.00000    58.00 |  77.00 | 315.00 |  70.07
         0.00200    57.02 |  76.02 | 313.04 |  70.07
         0.00400    56.09 |  75.09 | 311.18 |  70.06
         0.00600    55.21 |  74.21 | 309.42 |  70.06
         0.01000    53.56 |  72.56 | 306.11 |  70.05
         0.02000    49.91 |  68.91 | 298.83 |  69.98
         0.04000    43.97 |  62.97 | 286.94 |  69.80
         0.05000    41.43 |  60.43 | 281.86 |  69.71
         0.10000    31.00 |  50.00 | 260.99 |  68.88
         0.15000    22.47 |  41.47 | 243.95 |  67.87
         0.20000    14.85 |  33.85 | 228.70 |  66.47
         0.25000     7.72 |  26.72 | 214.43 |  64.88
         0.30000     0.86 |  19.86 | 200.72 |  62.94
         0.35000    -5.86 |  13.14 | 187.29 |  60.99
         0.40000   -12.51 |   6.49 | 173.98 |  58.38
         0.45000   -19.17 |  -0.17 | 160.65 |  55.39
         0.50000   -25.94 |  -6.94 | 147.13 |  52.55
         0.55000   -32.88 | -13.88 | 133.24 |  48.89
         0.60000   -40.13 | -21.13 | 118.75 |  44.29
         0.65000   -47.84 | -28.84 | 103.32 |  39.91
         0.70000   -56.31 | -37.31 |  86.38 |  33.84
         0.75000   -66.11 | -47.11 |  66.78 |  26.56
         0.80000   -79.01 | -60.01 |  40.98 |  16.45
CAM
         0.00200    64.77 |  83.77 | 328.53 |  43.83
         0.00400    62.30 |  81.30 | 323.59 |  43.83
         0.00600    60.23 |  79.23 | 319.45 |  43.82
         0.01000    56.79 |  75.79 | 312.57 |  43.79
         0.02000    50.25 |  69.25 | 299.51 |  43.70
         0.04000    40.94 |  59.94 | 280.89 |  43.40
         0.05000    37.22 |  56.22 | 273.44 |  43.27
         0.10000    22.31 |  41.31 | 243.63 |  42.17
         0.15000    10.03 |  29.03 | 219.06 |  40.69
         0.20000    -1.30 |  17.70 | 196.40 |  38.60
         0.25000   -12.31 |   6.69 | 174.38 |  36.12
         0.30000   -23.35 |  -4.35 | 152.30 |  33.08
         0.35000   -34.80 | -15.80 | 129.40 |  29.51
         0.40000   -47.20 | -28.20 | 104.60 |  24.63
         0.45000   -61.67 | -42.67 |  75.66 |  18.66
         0.50000   -82.90 | -63.90 |  33.19 |   8.65

[pcnsd]

Intake lobe centerline is 99.5. I am not saying it is wrong, but when looking at others, it is not what I would have expected in a 900HP big block spinning 7500 rpm either.

[SchmidtMotorWorks]

Intake lobe centerline is 99.5. I am not saying it is wrong, but when looking at others, it is not what I would have expected in a 900HP big block spinning 7500 rpm either.

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.

[GARY C]

Intake lobe centerline is 99.5. I am not saying it is wrong, but when looking at others, it is not what I would have expected in a 900HP big block spinning 7500 rpm either.

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.

[pcnsd]

Intake lobe centerline is 99.5. I am not saying it is wrong, but when looking at others, it is not what I would have expected in a 900HP big block spinning 7500 rpm either.

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.

Gary,
Could you please not crap on every camshaft design learning opportunity until they are dead. I have had enough of the elementary school antics. Jon's response was specific to myself. It is complete and I understand the answer given to my oblique question. It also implies that knowing the ICL is around 109 should allow you to adjust the STA's until you have a engine type match that can be added to a library of engine types.

Please stop!

[GARY C]

Gary,
Could you please not crap on every camshaft design learning opportunity until they are dead. I have had enough of the elementary school antics. Jon's response was specific to myself. It is complete and I understand the answer given to my oblique question. It also implies that knowing the ICL is around 109 should allow you to adjust the STA's until you have a engine type match that can be added to a library of engine types.

Please stop!

Just playing with Jon, I am interested to see what Stan comes up with, I know he will post some usable info... I will play nice.

[hoffman900]

Intake lobe centerline is 99.5. I am not saying it is wrong, but when looking at others, it is not what I would have expected in a 900HP big block spinning 7500 rpm either.

Stan,

There seems to be a lot of ways to play around with STA.

Do you get the lift from duration? Lift? Valve / valve throat size?

The latter may be fixed for whatever reason. Then it's a game of how aggressive can the valve lift curve be? For small hemi, with a 32ci/bore displacement (valve size I: 1.900", E: 1.48") with a 7000rpm peak power target, I was coming up with 104-106* centerlines. I can move things around based on the cam profile used.

All I've changed here is the peak hp rpm. Noticed the STA changes:

[GARY C]

There seems to be a lot of ways to play around with STA.

Could someone explain STA in laymen terms so it is more understandable for general engine tech. I can make assumptions on the term but would probably be wrong.

[af2]

There seems to be a lot of ways to play around with STA.

Could someone explain STA in laymen terms so it is more understandable for general engine tech. I can make assumptions on the term but would probably be wrong.

Specific time area. Inverted radius comes to mind.

[GARY C]

There seems to be a lot of ways to play around with STA.

Could someone explain STA in laymen terms so it is more understandable for general engine tech. I can make assumptions on the term but would probably be wrong.

Specific time area. Inverted radius comes to mind.

Thanks. Terminology is one of the things that creates a division in these discussions and most will not ask and I fail to ask when I should.