Using Blair to spec a Cam

[pastry_chef]

2.28/1.70 valves and 48cc chambers.

http://forums.maxperformanceinc.com/for ... ostcount=2

Possibly these larger valves were version 2 of the heads.

[Big Speed]

Just for reference ,about 9 years ago we built a 535 Pontiac at 10.9 cr .Tiger heads at 535CFMs 2.250-1.800 45 degree seats.1/16 rings .Very compromised Tiger manifold cut to fit under hood.Vacuum pump .Made 896HP at 6900RPMs.CAM was 272-292-114 Mid 800s lift.Typing from home do not have build sheet here.4.350bore .4.500 stroke 6.700 rod .spherical dish.Bill C.

[Stan Weiss]

Just for reference ,about 9 years ago we built a 535 Pontiac at 10.9 cr .Tiger heads at 535CFMs 2.250-1.800 45 degree seats.1/16 rings .Very compromised Tiger manifold cut to fit under hood.Vacuum pump .Made 896HP at 6900RPMs.CAM was 272-292-114 Mid 800s lift.Typing from home do not have build sheet here.4.350bore .4.500 stroke 6.700 rod .spherical dish.Bill C.

Thanks Bill.
Did you run this on Pump gas?

Stan

[GARY C]

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

Stan, did you ever make any progress on this program?

[Big Speed]

Correction That set of Tigers flowed 435 CFMs Engine was 535 Cu In

[PRH]

CAM was 272-292-114 Mid 800s lift

This is quite a bit different than the calculated 101lsa, almost single pattern 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

Stan, did you ever make any progress on this program?

Gary,
No I did not. This thread can to an end about 10 months ago and this just got behind other things to do.

Stan

[Stan Weiss]

It is difficult to keep up with all of the changes in the engine data, but the models shown on Controlled Induction 7.08 have different values for port flow and rocker ratios. The math is also incomplete and not completely accurate and is why Rick created 2020. Also the 119%VE is unobtainable by that port.

The model displayed on 2020 have user errors, as is evident by the intake port flow of 368 CFM at .555" lift and the 300 fps design velocity displayed. You should download the new Version 3.01 Stan, it will prevent those kind of mistakes.

I modeled this engine using 11:1 mcr, an intake port flow of 330 CFM at .558" valve lift, 1.8:1 rocker arm ratio with .014" lash at 7500 rpm. Controlled Induction calculated a required TRAPPED VE% of 107% to achieve the 900 HP, and a mean port velocity of 353 fps to achieve that VE%. The Peak Piston CFM Demand for 107% VE was 429 CFM, which using a max port flow of 434 CFM at .800" was barely obtainable. The Potential VE was calced at 119%, but was not available as the Peak Piston CFM Demand for 119% VE showed 479 CFM which that port cannot deliver.

At a mean port velocity of 353 FPS the cam calculated as follows

.050" 284 - 295
.100" 259 - 268
.200" 221 - 228
.300" 188 - 192
.400" 153 - 154
V Lift 1.084" - 1.052"
lobe c/l 113 - 115

This is not a good model as is evident by the cam requirements, especially when the port stops increasing flow at .800" and is not capable of 353 fps mean velocity.

Modeling the 535 Pontiac that "Big Speed" posted as a reference, Controlled Induction 2020 version 3.01 calculated a 272-288 with .858"-.833" on a 113 LSA compared to the actual 272-292 with mid .800 lifts on a 114 lsa. Although, the CBHP was 50 shy of the reported 896.

After reading all of this information being shared, I don't believe the timing events are terribly useful for comparison. IMO, with the same cid at the same RPM, it seems that the port volume and flow characteristics, VE%, area of the valve opening curve and opening curve itself drastically change the intake valves optimum closing point.

Thanks I do have CI 3.01. But I think you have missed the point of this thread. The point was not to find a cam for the engine. It was to see if we could go from Blair's time area numbers back to the needed cam profile. I am not even sure where some of my files for this are anymore. What I had done with a few cams was to take their lobe lift files to see how they matched up to Blair's number.

Stan