Lift vs Duration
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Lift vs Duration
Which is more important when choosing a high HP/TQ cam? Are there downsides to having too much of either? If heads generally flow better at higher lift numbers why not have the most lift possible with your drivetrain? Does either effect torque peak or area under the curve?
Im trying to find a good cam for my stage II /M6 combo with my stage II GTP heads. Looking for as much HP as possible with good area under the torque curve. Throw out some possible custom grinds or generic grinds for examples/etc.
Thanks
Im trying to find a good cam for my stage II /M6 combo with my stage II GTP heads. Looking for as much HP as possible with good area under the torque curve. Throw out some possible custom grinds or generic grinds for examples/etc.
Thanks
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From: 51°N 114°W, 3500' elevation
There's more to a cam than just lift and duration. LSA, valve overlap and valve timing play just as big a part.
In simple terms lift makes HP and duration makes torque. Roller cams can make more torque because of the lobe design. They can get more duration out of the cam than a flat tappit cam will. Maximum lift doesn't always provide the most power.
Look at a Stock Eliminator car. They're limited to a maximum lift of .430 or OEM whichever is greater. Most of us wouldn't even consider a cam with this small of a lift. Everything else about the cam can be changed. A stocker cam slams that valve open very quickly, holds it open for a long duration then slams it closed. Stocker cams don't like to idle below 1500 rpm. With such radical cam profiles and low lift these cams produce enormous amounts of power.
Your best choice for a cam is to call a cam manufacturer. Once they know your car's combination of parts they can recommend the best cam to use for your situation.
Use DD2000 and try different cams. You can even try other makes of cams. If a ford grind works better then order a GM cam with that ford grind.
In simple terms lift makes HP and duration makes torque. Roller cams can make more torque because of the lobe design. They can get more duration out of the cam than a flat tappit cam will. Maximum lift doesn't always provide the most power.
Look at a Stock Eliminator car. They're limited to a maximum lift of .430 or OEM whichever is greater. Most of us wouldn't even consider a cam with this small of a lift. Everything else about the cam can be changed. A stocker cam slams that valve open very quickly, holds it open for a long duration then slams it closed. Stocker cams don't like to idle below 1500 rpm. With such radical cam profiles and low lift these cams produce enormous amounts of power.
Your best choice for a cam is to call a cam manufacturer. Once they know your car's combination of parts they can recommend the best cam to use for your situation.
Use DD2000 and try different cams. You can even try other makes of cams. If a ford grind works better then order a GM cam with that ford grind.
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Pretty simple actually.. the higher the engine is built to spin, the more duration it's going to need to fill the cylinders at that higher speed. You can build alot of engine speed without a ton of lift... just need lots of duration.... but you won't make as much power throughout the powerband as you would with more lift per degree of duration. More lift per degree = more area under the curve and generally equates to stronger average power numbers.
-Mindgame
-Mindgame
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Re: Lift vs Duration
Originally posted by 96z
Which is more important when choosing a high HP/TQ cam? Are there downsides to having too much of either? If heads generally flow better at higher lift numbers why not have the most lift possible with your drivetrain? Does either effect torque peak or area under the curve?
Im trying to find a good cam for my stage II /M6 combo with my stage II GTP heads. Looking for as much HP as possible with good area under the torque curve. Throw out some possible custom grinds or generic grinds for examples/etc.
Thanks
Which is more important when choosing a high HP/TQ cam? Are there downsides to having too much of either? If heads generally flow better at higher lift numbers why not have the most lift possible with your drivetrain? Does either effect torque peak or area under the curve?
Im trying to find a good cam for my stage II /M6 combo with my stage II GTP heads. Looking for as much HP as possible with good area under the torque curve. Throw out some possible custom grinds or generic grinds for examples/etc.
Thanks
From what I recall your heads flow pretty well, getting the exacts on them would help.
If we get a accurate flow chart of them, which we can go do, and cc them we will be alot closer to picking out a new cam or chosing that it's not worth it. A drive down here and $35 will get them flowed and we'll cc them while we are at it.
Is the engine out yet?
Gotta know more about the goals, rpm range and how crazy of a cam you can afford. There is no need to put a cam in the car that is just going to break things down the line. Yeah, you can get away with somethings, but doing things the right way is really the cheapest way to go in the end.
Bret
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I have a better understanding now guys....
Bret, I know we talked about this but you had me than lost me through out the whole conversation and got me thinking later at night.
I was digesting things you said 5 min before while you were explaining something new.
The motor will be out within the next couple weeks if not days. Ill have some time on my hands with thanksgiving break from school.
Ill most likely be down your way this winter and we'll flow the heads and check the specs. Im still waiting on the numbers from GTP themselves. Ill email and let you know when stuff starts to happen.
Bret, I know we talked about this but you had me than lost me through out the whole conversation and got me thinking later at night.
I was digesting things you said 5 min before while you were explaining something new.The motor will be out within the next couple weeks if not days. Ill have some time on my hands with thanksgiving break from school.
Ill most likely be down your way this winter and we'll flow the heads and check the specs. Im still waiting on the numbers from GTP themselves. Ill email and let you know when stuff starts to happen.
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Cool,
Yeah when I talk I get ahead of myself sometimes too, and never remember where I am. I hope you understood the overlap, LSA, duration thing. I'm much better at writing, that might be hard to belive after reading some of this stuff.
Yeah, getting the numbers on the head is the first step to deciding what you need. I'm going to look at some simple things for your bottom end. I understand the college kid budget, I was there a few years ago!
Bret
Yeah when I talk I get ahead of myself sometimes too, and never remember where I am. I hope you understood the overlap, LSA, duration thing. I'm much better at writing, that might be hard to belive after reading some of this stuff.
Yeah, getting the numbers on the head is the first step to deciding what you need. I'm going to look at some simple things for your bottom end. I understand the college kid budget, I was there a few years ago!
Bret
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What's already been said seems to cover things pretty well. Just a quick comment on what Stephen said, which I generally agree with: I have never had much luck calling cam manufacturers. I suppose if you know a specific person to talk to, it would be very useful. But the people who usually answer the phones seem pretty ignorant. Typically, they can answer very specific technical questions about the product, like: "can a certain cam be ground with a 116 vs. a 112lsa?", but not general questions like: "what cam is best for my application?" YMMV though.
In terms of the question here, sounds like Bret is on top of things! I can't resist throwing in my $0.02 to this extent though: cams are a great example of TINSTAAFL (there's no such thing as a free lunch). You can not get something without giving something up. Want more high end power? Than you will give up low end, etc. For a given combo and usage, there will be an optimal design that will minimize the compromises, but the TINSTAAFL principle still holds. Most street and street/strip cam designs seem to give up too much low end for top end power, not taking into account that acceleration occurs over time. It the "area under the torque/hp curve" over the rpm range the car is operating in which determines acceleration, not peak numbers.
In terms of specific design considerations, many "off the shelf" cams fail to exploit the maximum lift/degree that is available. Maximum lift/degree is a way of minimizing the compromises for a given duration. I have been told by one of the big cam manufacturer's engineers that it's a marketing thing. According to what he said, performance enthusiasts insist on buying cams with longer durations than are optimal. To maintain drivability they must limit excessive overlap. To do this, they resort to a "trick". They chose a wider than optimal LSA. I don't know if this is true, but I do know that off the shelf cams do not maximize lift/degree, also perhaps due to psychological considerations. According to what this engineer said, people want to rev their motors beyond where it's necessary. To avoid valve float and other nasty consequences, they provide lobes with less than opitaml lift. I tend to believe this. One thing that always amuses me is to see someone rev a motor past where it makes power. It is very common on cars that are dynoed to see that the owner has been shifting 500-1000rpm beyond the power band. For example, there's no reason to rev a stock LT1 over 5,500rpm. It just stops making power when revved above that speed. But people do it all the time.
So, my general principles for a street or street/strip NA cam relative to the "usual" designs: shorter duration, higher lift, narrower lsa.
Rich Krause
In terms of the question here, sounds like Bret is on top of things! I can't resist throwing in my $0.02 to this extent though: cams are a great example of TINSTAAFL (there's no such thing as a free lunch). You can not get something without giving something up. Want more high end power? Than you will give up low end, etc. For a given combo and usage, there will be an optimal design that will minimize the compromises, but the TINSTAAFL principle still holds. Most street and street/strip cam designs seem to give up too much low end for top end power, not taking into account that acceleration occurs over time. It the "area under the torque/hp curve" over the rpm range the car is operating in which determines acceleration, not peak numbers.
In terms of specific design considerations, many "off the shelf" cams fail to exploit the maximum lift/degree that is available. Maximum lift/degree is a way of minimizing the compromises for a given duration. I have been told by one of the big cam manufacturer's engineers that it's a marketing thing. According to what he said, performance enthusiasts insist on buying cams with longer durations than are optimal. To maintain drivability they must limit excessive overlap. To do this, they resort to a "trick". They chose a wider than optimal LSA. I don't know if this is true, but I do know that off the shelf cams do not maximize lift/degree, also perhaps due to psychological considerations. According to what this engineer said, people want to rev their motors beyond where it's necessary. To avoid valve float and other nasty consequences, they provide lobes with less than opitaml lift. I tend to believe this. One thing that always amuses me is to see someone rev a motor past where it makes power. It is very common on cars that are dynoed to see that the owner has been shifting 500-1000rpm beyond the power band. For example, there's no reason to rev a stock LT1 over 5,500rpm. It just stops making power when revved above that speed. But people do it all the time.
So, my general principles for a street or street/strip NA cam relative to the "usual" designs: shorter duration, higher lift, narrower lsa.
Rich Krause
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Rich, I couldn't agree with you more. Listen to him, guys!
"Free lunches" don't exist, and what you said about marketing longer duration/wide LSA is true. I've thought that cam manufacturers should just fib about 10-20 degrees on .050 duration, and build the cams they know work. I'm ancient enough to remember when .050 duration wasn't published, and everyone bought 280 or 300 degree cams. Some had 190 degree .050 duration and some had 240. It depended on the ramps.
I once asked a top cam company engineer about using certain lobes for a specific engine design. He said, "That's the lobes I would use if I were doing that engine." It was a series I've never seen advertised, but, if you use the correct lifters, pushrods, rocker arms, and springs, is almost the proverbial free lunch.
You are VERY familiar with this series of lobes, and their virtues/limitations, Rich. He was correct, IMO.
Keep up the good posts.
Jon
"Free lunches" don't exist, and what you said about marketing longer duration/wide LSA is true. I've thought that cam manufacturers should just fib about 10-20 degrees on .050 duration, and build the cams they know work. I'm ancient enough to remember when .050 duration wasn't published, and everyone bought 280 or 300 degree cams. Some had 190 degree .050 duration and some had 240. It depended on the ramps.
I once asked a top cam company engineer about using certain lobes for a specific engine design. He said, "That's the lobes I would use if I were doing that engine." It was a series I've never seen advertised, but, if you use the correct lifters, pushrods, rocker arms, and springs, is almost the proverbial free lunch.
You are VERY familiar with this series of lobes, and their virtues/limitations, Rich. He was correct, IMO.
Keep up the good posts.
Jon
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$35 is a good deal Bret, I have another set of head here that need to be flowed. They actually might be going to Matt for his car. GTP Stage 3's.
Here is my opinion on cams for you Matt. If you want to make thing simple, then a 306 is a proven performer. However, I think that you could make more power with more lift (keeping the duration the same as the 306 or in that ballpark). I really like the power my car is making, but I initially thought that my goals could'nt have been met unless I ran a cam with more duration. Instead, Mark toned down the duration some, and jacked the lift. Now I have the power I was hoping for, great driveability, and great throttle response. On top of that, I dont have alot of overlap, so the exhaust system becomes a little less crutial.
You are going to be on your 3" exhaust with this new setup....which is why I would suggest you to stay with a 112-114LS cam. Having a tight LS is supposed to aid in scavaging but with a smaller exhaust (3") just causes more reversion and contamination of the intake charge. I would never run any tighter than a 112LS on a street car (ie, not open headers, full exhaust).
However, lift on the exhaust side is not as critical as on the intake in that the exhaust side doesnt react as much to the increased lift. The exhaust has much higher cylinder pressure than the intake side....therefore duration is a little more important on the E side, whereas the intake side is the opposite.
Kinda sounds like a CC306 huh? I think (in part) why that cam has been so sucessful in 6spd cars.
One thing I have learned (the hard way) is not to complicate things when doing buildups like this. Its good to have the knowledge and technical info behind it all, but for average "joe's" like us with limited resources, simple is better.
Jason
Here is my opinion on cams for you Matt. If you want to make thing simple, then a 306 is a proven performer. However, I think that you could make more power with more lift (keeping the duration the same as the 306 or in that ballpark). I really like the power my car is making, but I initially thought that my goals could'nt have been met unless I ran a cam with more duration. Instead, Mark toned down the duration some, and jacked the lift. Now I have the power I was hoping for, great driveability, and great throttle response. On top of that, I dont have alot of overlap, so the exhaust system becomes a little less crutial.
You are going to be on your 3" exhaust with this new setup....which is why I would suggest you to stay with a 112-114LS cam. Having a tight LS is supposed to aid in scavaging but with a smaller exhaust (3") just causes more reversion and contamination of the intake charge. I would never run any tighter than a 112LS on a street car (ie, not open headers, full exhaust).
However, lift on the exhaust side is not as critical as on the intake in that the exhaust side doesnt react as much to the increased lift. The exhaust has much higher cylinder pressure than the intake side....therefore duration is a little more important on the E side, whereas the intake side is the opposite.
Kinda sounds like a CC306 huh? I think (in part) why that cam has been so sucessful in 6spd cars.
One thing I have learned (the hard way) is not to complicate things when doing buildups like this. Its good to have the knowledge and technical info behind it all, but for average "joe's" like us with limited resources, simple is better.
Jason
Last edited by Jason Short; Nov 25, 2002 at 10:12 PM.
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Wow.
you guys really know your stuff, and Im actually understanding it good now too! The 306 is what Im leaning towards now b/c of Jason says, it can be had cheap, and because many guys seem to go fast, even on stock heads with that cam.
So the general consensus is short duration, high lift and short LSA.....Ill probably go with a 112 LSA no matter what.
Thanks guys! You really got me thinking/schemeing now.
Bret thanks for extending a helping hand.
you guys really know your stuff, and Im actually understanding it good now too! The 306 is what Im leaning towards now b/c of Jason says, it can be had cheap, and because many guys seem to go fast, even on stock heads with that cam.So the general consensus is short duration, high lift and short LSA.....Ill probably go with a 112 LSA no matter what.
Thanks guys! You really got me thinking/schemeing now.
Bret thanks for extending a helping hand.
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Just to take Jason's idea to the next level, I'll be soon running a Hydraulic roller cam with essentially the same duration figures as the 306....but with a LOT more lift. I'll be either running a Jesel system, or a custom made stud girdle to keep things in place. I'll let you know how I make out....
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Interesting talk here...I've thought about the things mentioned and it mostly makes sense. I went looking through Crane's, Lunati's, and Comp Cams pre-ground offers for the LT1 and none have a lot of lift except the ones touting a lot of duration.
I'm currently running a CC 220/230 .544/.544 112 grind (M.O.R.E. custom on 1.6s) on my 396. It's a great cam - lots of torque, good idle, basically no surge, but it won't make power past about 5,600 on my motor. The other cams available just don't appeal to me. I've looked at the CC 230/236 .544/.555 112 (on 1.6s) - it has very little extra lift, but 10 more degrees on the intake duration. The exhaust duration is "OK". The CC306 is an old grind with pretty slow ramps (adv duration - 290/307) compared to the eXtreme series. To me, that means more overlap with the same duration @ .05".
I've continued looking and came across this custom grind by Speed Demon :
"This is a naturally aspirated street grind for a hot 355 or a milder 383. The specs are 224/230 at 0.050 276/282 adv. 112lsa 108IC 0.605/0.544 (1.6rr). Cast core. Comp "R" series pro magnum lifters reccomended."
I like the LS and the duration numbers aren't too high...but what really caught me was the .605" lift. That is a whole .061" more than the exhaust side even though the exhaust side has a duration advantage. That's like the move from stock lift to aftermarket cam lift, if you know what I mean. Interesting...
Anyone have experience with this cam? Would it be a complete waste of time to put this cam in place of my current one? I have a complete exhaust system (Hooker LTs w/Mufflex y-pipe and SLP 2OTL catback), so I'm thinking I don't need much of a split. My head flow numbers :
lift I E
0.100 65 33
0.200 136 84
0.300 192 142
0.400 232 170
0.450 251 179
0.500 263 187
0.550 266 189
0.600 268 193
0.650 268 193
Seeing as my intake and exhaust flow numbers are basically stalling at .550, would the extra lift help at all?
-Alex
I'm currently running a CC 220/230 .544/.544 112 grind (M.O.R.E. custom on 1.6s) on my 396. It's a great cam - lots of torque, good idle, basically no surge, but it won't make power past about 5,600 on my motor. The other cams available just don't appeal to me. I've looked at the CC 230/236 .544/.555 112 (on 1.6s) - it has very little extra lift, but 10 more degrees on the intake duration. The exhaust duration is "OK". The CC306 is an old grind with pretty slow ramps (adv duration - 290/307) compared to the eXtreme series. To me, that means more overlap with the same duration @ .05".
I've continued looking and came across this custom grind by Speed Demon :
"This is a naturally aspirated street grind for a hot 355 or a milder 383. The specs are 224/230 at 0.050 276/282 adv. 112lsa 108IC 0.605/0.544 (1.6rr). Cast core. Comp "R" series pro magnum lifters reccomended."
I like the LS and the duration numbers aren't too high...but what really caught me was the .605" lift. That is a whole .061" more than the exhaust side even though the exhaust side has a duration advantage. That's like the move from stock lift to aftermarket cam lift, if you know what I mean. Interesting...
Anyone have experience with this cam? Would it be a complete waste of time to put this cam in place of my current one? I have a complete exhaust system (Hooker LTs w/Mufflex y-pipe and SLP 2OTL catback), so I'm thinking I don't need much of a split. My head flow numbers :
lift I E
0.100 65 33
0.200 136 84
0.300 192 142
0.400 232 170
0.450 251 179
0.500 263 187
0.550 266 189
0.600 268 193
0.650 268 193
Seeing as my intake and exhaust flow numbers are basically stalling at .550, would the extra lift help at all?
-Alex
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From: Upstate NY
Originally posted by AlexA
"This is a naturally aspirated street grind for a hot 355 or a milder 383. The specs are 224/230 at 0.050 276/282 adv. 112lsa 108IC 0.605/0.544 (1.6rr). Cast core. Comp "R" series pro magnum lifters reccomended."
I like the LS and the duration numbers aren't too high...but what really caught me was the .605" lift. That is a whole .061" more than the exhaust side even though the exhaust side has a duration advantage. That's like the move from stock lift to aftermarket cam lift, if you know what I mean. Interesting...
Anyone have experience with this cam? Would it be a complete waste of time to put this cam in place of my current one? I
-Alex
"This is a naturally aspirated street grind for a hot 355 or a milder 383. The specs are 224/230 at 0.050 276/282 adv. 112lsa 108IC 0.605/0.544 (1.6rr). Cast core. Comp "R" series pro magnum lifters reccomended."
I like the LS and the duration numbers aren't too high...but what really caught me was the .605" lift. That is a whole .061" more than the exhaust side even though the exhaust side has a duration advantage. That's like the move from stock lift to aftermarket cam lift, if you know what I mean. Interesting...
Anyone have experience with this cam? Would it be a complete waste of time to put this cam in place of my current one? I
-Alex
I'm not sure about the cast core, however. I've only seen them on steel cores for roller lifters.
I think you'd like the 3192, but keep the revs reasonable, say 6500. Not sure about the less agressive (3315) exhaust with the 3192. That would take more study.
These lobes are on page 230 of Comp's (online) catalog. If I were thinking of this cam, I'd probably go directly to Comp.
My $.02
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Posts: 229
From: NorCal
Originally posted by 96z
4drLT4 thanks, Ill be interested in seeing that....What is the lift on the 306 with 1.6rr as it is? What was your reason for doing this? Your .600 + flow numbers?
4drLT4 thanks, Ill be interested in seeing that....What is the lift on the 306 with 1.6rr as it is? What was your reason for doing this? Your .600 + flow numbers?
Flow numbers are the pre-dominant reason for the large lift..yes. That and the fact that I'm not willing to fight with the knock sensors when going solid. So we'll try this......