Camshaft discussion: CFM requirements by RPM.
#281
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Let's say 210 cfm at .400 with a 1 3/4 inch pipe on exhaust.
#283
6600 rpm clutch dump of death Administrator
From Jay's site.
http://www.absolutespeedls1.net/page5.html
LS1 FLOW NUMBERS
STAGE 1X STAGE 2 5.3l LS6 stg 2
LIFT- INT- EX LIFT- INT- EX LIFT-INT-EX
200- 147- 104 200- 151- 115 200-154-118
300- 200 144 300- 204- 163 300-208-171
400- 243- 183 400- 257- 198 400-258-204
450- 257- 201 450- 275- 209 450-278-212
500- 274- 212 500- 292- 218 500-296-221
550- 289- 215 550- 305- 222 550-310-227
600- 284- 219 600- 313- 227 600-320-229
650-326-230
http://www.absolutespeedls1.net/page5.html
LS1 FLOW NUMBERS
STAGE 1X STAGE 2 5.3l LS6 stg 2
LIFT- INT- EX LIFT- INT- EX LIFT-INT-EX
200- 147- 104 200- 151- 115 200-154-118
300- 200 144 300- 204- 163 300-208-171
400- 243- 183 400- 257- 198 400-258-204
450- 257- 201 450- 275- 209 450-278-212
500- 274- 212 500- 292- 218 500-296-221
550- 289- 215 550- 305- 222 550-310-227
600- 284- 219 600- 313- 227 600-320-229
650-326-230
#286
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Originally Posted by John B
Remember, exhaust flow numbers are inflated in the range of 15% or so with a pipe. I would recommend using an exhaust number closer to 240 cfm for a ported LS6 head since Julio has gone on record with his heads flowing 205CFM without a pipe attached and I would imagine Jay's flow similarily.
#287
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All right, Exhaust duration split lesson:
Now, this just comes from years of f#^%*&^ with engine builders and cam profiles. Proof to me it works is my happy customers.
For CID under 400, 75% exh ratio to intake dictates a single pattern cam, for over 400 CID, 80% dictates a single pattern. For every % point over you need to crutch the intake 1/2 degree of duration. . .GENERAL RULE OF THUMB. Now high RPM, over 8K will affect this somewhat. . .so I have to use an R&D guess.
Now with J-rods numbers supplied:
247 with intake on LS6 and 210 exhaust.
we have a 85% ratio of exhaust to intake.
Camshaft:
Stock 346 CID
Compression 11to1
Max RPM 6500
Max effort street car
Duration
233 Int.
229 Exh.
Max HP at 6100 will pull till 6500
Max Torque at 4300
Chris
Now, this just comes from years of f#^%*&^ with engine builders and cam profiles. Proof to me it works is my happy customers.
For CID under 400, 75% exh ratio to intake dictates a single pattern cam, for over 400 CID, 80% dictates a single pattern. For every % point over you need to crutch the intake 1/2 degree of duration. . .GENERAL RULE OF THUMB. Now high RPM, over 8K will affect this somewhat. . .so I have to use an R&D guess.
Now with J-rods numbers supplied:
247 with intake on LS6 and 210 exhaust.
we have a 85% ratio of exhaust to intake.
Camshaft:
Stock 346 CID
Compression 11to1
Max RPM 6500
Max effort street car
Duration
233 Int.
229 Exh.
Max HP at 6100 will pull till 6500
Max Torque at 4300
Chris
#288
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And you guys thought you weren't going to get anything out of this...
On a serious note, the purpose of this thread was never to give you a hard and fast formula or tell you how to design the perfect camshaft. That takes more work, time, and effort than any of us care to contribute. On top of pure theory, years of experience are must be applied.
Before anyone goes out and buys a cam ground to those specs, keep in mind that Chris has effectively given you jack ****. You don't know the centerlines, the lift, the ramp rates or anything else about the lobe...no .100", .200" lift durations, etc.
It does serve as a wonderful example of how meaningless the "cam specs" everyone throws around are.
On a serious note, the purpose of this thread was never to give you a hard and fast formula or tell you how to design the perfect camshaft. That takes more work, time, and effort than any of us care to contribute. On top of pure theory, years of experience are must be applied.
Before anyone goes out and buys a cam ground to those specs, keep in mind that Chris has effectively given you jack ****. You don't know the centerlines, the lift, the ramp rates or anything else about the lobe...no .100", .200" lift durations, etc.
It does serve as a wonderful example of how meaningless the "cam specs" everyone throws around are.
#289
Originally Posted by DenzSS
And you guys thought you weren't going to get anything out of this...
It does serve as a wonderful example of how meaningless the "cam specs" everyone throws around are.
It does serve as a wonderful example of how meaningless the "cam specs" everyone throws around are.
joel
#290
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iTrader: (4)
Originally Posted by Cstraub
All right, Exhaust duration split lesson:
Now, this just comes from years of f#^%*&^ with engine builders and cam profiles. Proof to me it works is my happy customers.
For CID under 400, 75% exh ratio to intake dictates a single pattern cam, for over 400 CID, 80% dictates a single pattern. For every % point over you need to crutch the intake 1/2 degree of duration. . .GENERAL RULE OF THUMB. Now high RPM, over 8K will affect this somewhat. . .so I have to use an R&D guess.
Now with J-rods numbers supplied:
247 with intake on LS6 and 210 exhaust.
we have a 85% ratio of exhaust to intake.
Camshaft:
Stock 346 CID
Compression 11to1
Max RPM 6500
Max effort street car
Duration
233 Int.
229 Exh.
Max HP at 6100 will pull till 6500
Max Torque at 4300
Chris
Now, this just comes from years of f#^%*&^ with engine builders and cam profiles. Proof to me it works is my happy customers.
For CID under 400, 75% exh ratio to intake dictates a single pattern cam, for over 400 CID, 80% dictates a single pattern. For every % point over you need to crutch the intake 1/2 degree of duration. . .GENERAL RULE OF THUMB. Now high RPM, over 8K will affect this somewhat. . .so I have to use an R&D guess.
Now with J-rods numbers supplied:
247 with intake on LS6 and 210 exhaust.
we have a 85% ratio of exhaust to intake.
Camshaft:
Stock 346 CID
Compression 11to1
Max RPM 6500
Max effort street car
Duration
233 Int.
229 Exh.
Max HP at 6100 will pull till 6500
Max Torque at 4300
Chris
Would that suggest something like a 230/220 in your opinion or a 235/225 etc?
#292
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Originally Posted by Cstraub
All right, Exhaust duration split lesson:
Now, this just comes from years of f#^%*&^ with engine builders and cam profiles. Proof to me it works is my happy customers.
For CID under 400, 75% exh ratio to intake dictates a single pattern cam, for over 400 CID, 80% dictates a single pattern. For every % point over you need to crutch the intake 1/2 degree of duration. . .GENERAL RULE OF THUMB. Now high RPM, over 8K will affect this somewhat. . .so I have to use an R&D guess.
Now with J-rods numbers supplied:
247 with intake on LS6 and 210 exhaust.
we have a 85% ratio of exhaust to intake.
Camshaft:
Stock 346 CID
Compression 11to1
Max RPM 6500
Max effort street car
Duration
233 Int.
229 Exh.
Max HP at 6100 will pull till 6500
Max Torque at 4300
Chris
Now, this just comes from years of f#^%*&^ with engine builders and cam profiles. Proof to me it works is my happy customers.
For CID under 400, 75% exh ratio to intake dictates a single pattern cam, for over 400 CID, 80% dictates a single pattern. For every % point over you need to crutch the intake 1/2 degree of duration. . .GENERAL RULE OF THUMB. Now high RPM, over 8K will affect this somewhat. . .so I have to use an R&D guess.
Now with J-rods numbers supplied:
247 with intake on LS6 and 210 exhaust.
we have a 85% ratio of exhaust to intake.
Camshaft:
Stock 346 CID
Compression 11to1
Max RPM 6500
Max effort street car
Duration
233 Int.
229 Exh.
Max HP at 6100 will pull till 6500
Max Torque at 4300
Chris
Hmmmm.....
Street car???
What exhaust system and tubing size???
I "may" disagree somewhat Chris... but WTF do I know?????
I also noticed you left out a couple of "other" key numbers in your profile Chris. Getting the seeds planted???
Ed
#294
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Originally Posted by 99 Black Bird T/A
J-Rod, do you know what the heads on the car mentioned above flow with the intake in place?
I think the key point that often gets missed is very seldom do people have flow numbers with the LS6/LSX intake in place. These intakes can cut as much as 50 cfm off the intake flow numbers depending on the cylinder head.
My guess is the Absolutes on the car above flow ~325 without intake and 270 to 280 with the intake in place. These would be excellent flow numbers with the intake. I've had an older set of LS6 heads that would only flow 239 with the intake in place.
7000 rpm seems reasonable for the C5 above...lets do a little ghetto math...
346/2*7000 divided by 1728 = 707 cfm needed for the engine
707/8 = 88.4 cfm need per cylinder
Lets say the head flows 275 WITH INTAKE for this calculation
88.4*X=275 solve for X and X is .321
the cam need .321 of 720 degrees of crank rotation to get the air in the cylinder
so a 231.4 degree cam is needed
we know the ghetto math isn't exact so a couple of degrees either way might need to be tweaked. A low 230 something cam say between 231 and 235 sounds like a good starting point.
John speculated the G cams are low 230's as the ghetto math suggests they should be.
I think the key point that often gets missed is very seldom do people have flow numbers with the LS6/LSX intake in place. These intakes can cut as much as 50 cfm off the intake flow numbers depending on the cylinder head.
My guess is the Absolutes on the car above flow ~325 without intake and 270 to 280 with the intake in place. These would be excellent flow numbers with the intake. I've had an older set of LS6 heads that would only flow 239 with the intake in place.
7000 rpm seems reasonable for the C5 above...lets do a little ghetto math...
346/2*7000 divided by 1728 = 707 cfm needed for the engine
707/8 = 88.4 cfm need per cylinder
Lets say the head flows 275 WITH INTAKE for this calculation
88.4*X=275 solve for X and X is .321
the cam need .321 of 720 degrees of crank rotation to get the air in the cylinder
so a 231.4 degree cam is needed
we know the ghetto math isn't exact so a couple of degrees either way might need to be tweaked. A low 230 something cam say between 231 and 235 sounds like a good starting point.
John speculated the G cams are low 230's as the ghetto math suggests they should be.
#297
6600 rpm clutch dump of death Administrator
Ok, so lets summarize some of that.
Lets look at a couple of heads, and how you would select lobes.
Lets look at a couple of heads.
A LPE/GMPP CNC ported head with a 250CC runner
A AS CNC ported head with a 220 CC runner
A AFR head with a 205CC runner
Now, why did I select these three heads. Well, because flow is about the same on the heads, but runner volume (hence velocity is different).
Now, we all know that head porter do different things to get to the same end goal. With that in mind how do you select a lobe when you have a port that is fatter and lazier than a port that has better velocity.
My understanding from Chris' post is that he would use a slower opening port for a port with a more efficient port. So, would you use a port with a fast opening and closing in a port like the GMPP head where the port has a lot of volume, and velocity may be down over another head?
Would you look at something like the lobe that TR uses on its OMC cam 215 duration .600 lift which has nearly the same area under the curve as a TR230 lobe? (230/.575)
Hey Ed,
Since you might disagree with Chris a bit, what would you do on the little exercise above with the AS heads that Chris gave us .050 specs. I'm not asking for lift, LSA, etc... specs, but what you would do @ .050 and why.
Lets look at a couple of heads, and how you would select lobes.
Lets look at a couple of heads.
A LPE/GMPP CNC ported head with a 250CC runner
A AS CNC ported head with a 220 CC runner
A AFR head with a 205CC runner
Now, why did I select these three heads. Well, because flow is about the same on the heads, but runner volume (hence velocity is different).
Now, we all know that head porter do different things to get to the same end goal. With that in mind how do you select a lobe when you have a port that is fatter and lazier than a port that has better velocity.
My understanding from Chris' post is that he would use a slower opening port for a port with a more efficient port. So, would you use a port with a fast opening and closing in a port like the GMPP head where the port has a lot of volume, and velocity may be down over another head?
Would you look at something like the lobe that TR uses on its OMC cam 215 duration .600 lift which has nearly the same area under the curve as a TR230 lobe? (230/.575)
Hey Ed,
Since you might disagree with Chris a bit, what would you do on the little exercise above with the AS heads that Chris gave us .050 specs. I'm not asking for lift, LSA, etc... specs, but what you would do @ .050 and why.
#298
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Originally Posted by J-Rod
Hey Ed,
Since you might disagree with Chris a bit, what would you do on the little exercise above with the AS heads that Chris gave us .050 specs. I'm not asking for lift, LSA, etc... specs, but what you would do @ .050 and why.
Since you might disagree with Chris a bit, what would you do on the little exercise above with the AS heads that Chris gave us .050 specs. I'm not asking for lift, LSA, etc... specs, but what you would do @ .050 and why.
Without all the low lift flow numbers... (.050" - .500")
"Disclaimer"
Using a 3600# C5 with real dual exhaust...
Long tube 1-3/4" headers...
LSX Intake - 80 MM TB
.585" Int - .575" Exh
232* Int - 234* Exh @ .050"
111* LSA - 110* ICL
Now...
I left out a few tidbits on ramp speeds and lift as well as rocker ratio... OK??
Ed
#299
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Originally Posted by Cstraub
Yep. To back up what I have said here. Look at stock Honda cams.. . . exhaust on those things are in the 85 and 90% range. Duration favors those little bastards about 12 degrees on the intake over the exhaust.
Chris
Chris
#300
TECH Senior Member
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Originally Posted by Beast96Z
Calculations like this don't seem to favor for the larger CI motors. In my figuring, using this equation, a 383 with a head flow of 265 with the intake on will need a 255 duration camshaft to peak at 6800 rpm's. Seems rather big for a 383 and the numbers just keep getting bigger the more CI you add. Seems a bit out there to me, but seemed to work ok for a 346.
I'll crunch a cam size based on Jay's LS6 2.75's thru the LS6 intake. I bet it will need a ~230 to 236 sized cam for a 383. Maybe a 240 at the max.