Anyway to calculate vacuum from camshaft overlap?
03-04-2017, 01:01 PM
#1
Anyway to calculate vacuum from camshaft overlap? As the title says... is there any rule of thumb way to do this?
I know rings, compression, engine size, and intake manifold design all play a role in vacuum... but the cam is still the biggest variable in how much vacuum you'll pull.
Is there a way to calculate this?
On my two cams, I've run in this motor, one with 5.5 degrees of overlap idled at 850 I was around 58kPa @ 850 or 13" hg. The one with 16 degrees saw 70kPa @ 950 or 9.5" hg.
I'm trying to figure what a cam with 22 degrees of overlap would look like on a 408. And what one with 10 degrees would like like.
I know rings, compression, engine size, and intake manifold design all play a role in vacuum... but the cam is still the biggest variable in how much vacuum you'll pull.
Is there a way to calculate this?
On my two cams, I've run in this motor, one with 5.5 degrees of overlap idled at 850 I was around 58kPa @ 850 or 13" hg. The one with 16 degrees saw 70kPa @ 950 or 9.5" hg.
I'm trying to figure what a cam with 22 degrees of overlap would look like on a 408. And what one with 10 degrees would like like.
03-14-2017, 11:36 PM
#3
Hi Lance,
What specs do you need?
The 408 would be 4.03" bore, 4" stroke, 2cc flat tops, -.010" out of the hole, .040" gaskets 4.130" bore, 67cc chambers. Rings gapped .018/.020.
Cam specs:
@ .006" 293/306
@ .050" 244/256
@ .200" 166/173
Lift: .627/.615
114 LSA 111 ICL
Spring Seat Pressure 170lbs @ 1.750" height, 440lbs @ 1.200"
Heads flow:
0.100 69 55
0.200 146 122
0.300 237 199
0.400 294 250
0.500 336 277
0.550 348 284
0.600 353 290
FAST LSXR 102 Intake Manifold
Kooks 1-7/8" Primaries, 24-28" length, 3" collector 6" long, 3" dual exhaust
What specs do you need?
The 408 would be 4.03" bore, 4" stroke, 2cc flat tops, -.010" out of the hole, .040" gaskets 4.130" bore, 67cc chambers. Rings gapped .018/.020.
Cam specs:
@ .006" 293/306
@ .050" 244/256
@ .200" 166/173
Lift: .627/.615
114 LSA 111 ICL
Spring Seat Pressure 170lbs @ 1.750" height, 440lbs @ 1.200"
Heads flow:
0.100 69 55
0.200 146 122
0.300 237 199
0.400 294 250
0.500 336 277
0.550 348 284
0.600 353 290
FAST LSXR 102 Intake Manifold
Kooks 1-7/8" Primaries, 24-28" length, 3" collector 6" long, 3" dual exhaust
Last edited by JakeFusion; 03-14-2017 at 11:52 PM.
03-15-2017, 11:54 AM
#4
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Wow! Jake those are some incredible exhaust #s, can you tell
me about those heads? and with 84%-82% E/I Ratio why
the 12* exhaust split? 300 N2O shot?
me about those heads? and with 84%-82% E/I Ratio why
the 12* exhaust split? 300 N2O shot?
03-16-2017, 11:40 AM
#6
FormerVendor
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Eap @ 23 cfm 15 hp Hi Jake, there where some choices :
Auto Trans in gear.
Spark Advance set for best HP
Air door set to 23 CFM.
Results :
500 = 2.9 Hg
600 = 3.1
700 = 4.2
800 = 5.3
900 = 6.4
1000=7.5
1100=8.3
1200=9.7
YES your chosen camshaft has AGGRESSIVE lobes.
Lance
Auto Trans in gear.
Spark Advance set for best HP
Air door set to 23 CFM.
Results :
500 = 2.9 Hg
600 = 3.1
700 = 4.2
800 = 5.3
900 = 6.4
1000=7.5
1100=8.3
1200=9.7
YES your chosen camshaft has AGGRESSIVE lobes.
Lance
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03-16-2017, 04:36 PM
#9
I was trying to see how bad it would be to aim for a 550+rwhp 408 vs just putting the Procharger on my current setup (which sees 13.5" of vacuum @ 850). So the choice is pretty clear now. Any less cam and it wouldn't be worth the upgrade. Not when the Procharger will make significantly more power and drive better.