Volumetric Efficiency
Thread Starter
Instructor
Joined: Mar 2007
Posts: 169
Likes: 0
From: Tullahoma Tennessee
Volumetric Efficiency
I've been playing around with a dyno program and noticed that along with giving the power and torque at given RPMs it also gives you the "volumetric efficiency", which it explained was the percent of air/fuel that is able to enter the cylinder before the intake valve closes. Using different cam profiles and valve sizes I've been able to get just about the same power curve regardless of the efficiency. So my question is, do I want high efficiency or low efficiency? At first I thought the closer I got to 100% the better because I would get more power out of every stroke, but then I messed with the cam specs more and got my efficiency up to about 120% and realized that this would cause close to no vacuum at the intake. 
I also realized that if I can get the power I want with very LOW efficiency I would burn less gas per cycle and get better mileage. So do I want high efficiency or low?
I also realized that if I can get the power I want with very LOW efficiency I would burn less gas per cycle and get better mileage. So do I want high efficiency or low?
Melting Slicks
Joined: Mar 2008
Posts: 2,336
Likes: 1
From: North Bellmore Ny
St. Jude Donor '09
Thats hard to answer, you want the closest to 100 percent while keeping it streetable. Also the only real way to go over 100 percent is the use of a turbo or supercharger.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Desktop dyno isn't exact. You will get better performance and mileage @ close to 100% VE. My build is 100% VE from 4500 to 6000 RPM according to Desktop Dyno...............which isn't exact.
Thread Starter
Instructor
Joined: Mar 2007
Posts: 169
Likes: 0
From: Tullahoma Tennessee
Here's what my dyno's telling me, sounds too good to be true but I'm looking at almost 500 ft/lbs just off idle. 
Cam would have to be a custom grind since I'm pretty sure nobody makes anything like this. I'll post the specs on that as soon as I get them printed. 
RPM HP. TQ. Eff.
2000 178 468 94.5
2500 235 493 96.3
3000 281 492 96.8
3500 328 492 98.5
4000 370 486 99.4
4500 404 472 98.4
5000 421 442 95.9
5500 418 399 91.9
6000 396 347 86.0
6500 352 284 79.0
7000 300 225 72.6
Cam would have to be a custom grind since I'm pretty sure nobody makes anything like this. I'll post the specs on that as soon as I get them printed. RPM HP. TQ. Eff.
2000 178 468 94.5
2500 235 493 96.3
3000 281 492 96.8
3500 328 492 98.5
4000 370 486 99.4
4500 404 472 98.4
5000 421 442 95.9
5500 418 399 91.9
6000 396 347 86.0
6500 352 284 79.0
7000 300 225 72.6
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Thread Starter
Instructor
Joined: Mar 2007
Posts: 169
Likes: 0
From: Tullahoma Tennessee
Here's the cam specs, I'll admit I just messed with the numbers to get the efficiency up. I don't really know what they mean in terms of idle quality and vacuum.
Camshaft type- High Performance Street
Lifter- Roller
Cam Specs @- Seat To Seat
Int. Lift @ Valve- .500
Exh. Lift @ Valve- .500
Lobe Center- 114.9
Valve Overlap- 34.0
Int. Duration- 240
Exh. Duration- 287.5
Timing @ Adv. 15.0
IVO (BTDC)- 0.0
EVO (BBDC)- 73.5
ICA (ATDC)- 120.0
IVO- 15.0
EVO- 88.5
ICA- 105.0
IVC- 45.0
EVC- 19.0
ECA- 124.8
Camshaft type- High Performance Street
Lifter- Roller
Cam Specs @- Seat To Seat
Int. Lift @ Valve- .500
Exh. Lift @ Valve- .500
Lobe Center- 114.9
Valve Overlap- 34.0
Int. Duration- 240
Exh. Duration- 287.5
Timing @ Adv. 15.0
IVO (BTDC)- 0.0
EVO (BBDC)- 73.5
ICA (ATDC)- 120.0
IVO- 15.0
EVO- 88.5
ICA- 105.0
IVC- 45.0
EVC- 19.0
ECA- 124.8
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
only use existing numbers from cam cards.
DD2000 is way off of reality because it rewards massive exhaust valve timing. So use real life cam card numbers and the .050 numbers increase the accuracy
DD2000 is way off of reality because it rewards massive exhaust valve timing. So use real life cam card numbers and the .050 numbers increase the accuracy
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
When you order a custom cam each manufacturer only has a list of so many lobe designs and machinable blanks of certain Lobe Center angles.
So you look for the type of lobe that you want H-flat, Solid Flat, h-roller or S-roller. Then you choose the intake lobe duration and exhaust lobe duration and then tell them what LSA you want
I have free flowing exhaust so on my 383 solid roller I went with 236/242 @ .050 on comp cams XR profile at 112 LSA
Instructor
Joined: Nov 2004
Posts: 110
Likes: 0
From: Texas
Go to the AFR website and click on small block chevy heads, then check out cylinder head dyno results and cylinder head magazine articles, this may help out with motor combinations if its something your not real sure of.
