The truth about LSA
On The Tree
Joined: Aug 2005
Posts: 103
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Until the stock cam in my car broke all those rules,just like the LS cylinder heads perform unlike they appear on paper.for a 117+lsa the cam sure works nice,25mpg and approaching 100k miles of beating.Again I'll say this is why variable valve control is so necessary--there is no optimal valve timing.
Originally Posted by Nine Ball
Increasing Lobe Seperation Angle moves your powerband higher in the rpm range, and lowers your low/mid rpm torque output. It also helps with emissions testing and makes the idle smoother. "Increasing LSA" means the same thing as "decreasing overlap". So, a 114 LSA cam will idle better, make less emissions, and show peak HP higher in rpm than a 112 LSA cam.
Increasing intake duration will move your powerband up also. It also will hurt midrange torque most of the time. Bigger is NOT better, and alot of people make that mistake. Increasing duration makes the idle rougher also.
Increasing exhaust duration is intended to extend the HP curve a little further on the high rpm. Not always the case. It is meant to help support a restrictive (stock manifolds and cats) exhaust setup. If you have headers, you will most likely see no gains by having more exhaust duration than intake duration. This is known as a "split duration" cam and those tend to idle worse than single pattern cams and cause more misfire SES codes. "single pattern" means cams with the same intake and exhaust duration.
Increasing lift moves the entire power curve upwards if all else is kept equal. More lift means those valves open up further. Has no effect on drivability, but more lift does wear out your valvetrain faster.
Increasing intake duration will move your powerband up also. It also will hurt midrange torque most of the time. Bigger is NOT better, and alot of people make that mistake. Increasing duration makes the idle rougher also.
Increasing exhaust duration is intended to extend the HP curve a little further on the high rpm. Not always the case. It is meant to help support a restrictive (stock manifolds and cats) exhaust setup. If you have headers, you will most likely see no gains by having more exhaust duration than intake duration. This is known as a "split duration" cam and those tend to idle worse than single pattern cams and cause more misfire SES codes. "single pattern" means cams with the same intake and exhaust duration.
Increasing lift moves the entire power curve upwards if all else is kept equal. More lift means those valves open up further. Has no effect on drivability, but more lift does wear out your valvetrain faster.
I'm sorry if this has been answered. I only read the first three pages.
I'm looking at the Thunder Racing 224/224 @ 112 LSA cam for my M6, stock gears daily driver. I want to be formidable in a race to the end of four telephone poles, but the feel of high off-idle to 2500 RPM power is most important. I realize what gears can do, but they aren't in my budget currently. I would rather buy a 12-bolt later than gears for my 10-bolt now.
I have viewed graphs of the TR224 cam and like the way they look. I also love the sound of the idle.
Would I be able to get more power, but with a similar power curve, with another cam?
Thanks!
Sharpe
Originally Posted by Sharpe
Wouldn't you then be able to keep lowering LSA (numerically) while increasing durations and lift to continue to produce more and more power without sacrificing the low end of the RPM range?
Sharpe
Sharpe
Rick
This is the equation for overlap, correct?
[(intake duration + exhaust duration) / 4] - LSA * 2
So, the overlap of a TR224@112 would be 0 (zero) degrees, while a TR224@114 would be -4 (negative four) degrees, right?
[(intake duration + exhaust duration) / 4] - LSA * 2
So, the overlap of a TR224@112 would be 0 (zero) degrees, while a TR224@114 would be -4 (negative four) degrees, right?
TECH Enthusiast
Joined: Mar 2004
Posts: 647
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From: Australia
Its not as simple as that. If it were, there would be one optimal cam designed purely from cam math. You also need to consider wave theory when debating overlap, something a cam spec cannot hope to predict since it is dependant on things other than the cam - like ports, headers, exhaust, RPM, AFR etc.. Other factors like dynamic compression, fuel, heat etc. also also play a part in the production (or limitation) of power.
You never really know how a cam will perform on THAT car until you install it.
You never really know how a cam will perform on THAT car until you install it.
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TECH Resident
Joined: Dec 2004
Posts: 845
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From: K-W, Ontario
If you want to learn more about overlap, remove LSA from the equation.
Look at the individual valve timing specs on the cam card, and also notice
the overlap at 0.006" and 0.050" lift.
From there, you need to consider (along with everything else mentioned)
rocker ratio, pre-load amount, how the valve follows the lobe profile at certain
RPM, shape of the lobe (to name a few).
When we're discussing overlap, we need to think degrees of overlap at a certain
lift, not LSA values IMO.
Look at the individual valve timing specs on the cam card, and also notice
the overlap at 0.006" and 0.050" lift.
From there, you need to consider (along with everything else mentioned)
rocker ratio, pre-load amount, how the valve follows the lobe profile at certain
RPM, shape of the lobe (to name a few).
When we're discussing overlap, we need to think degrees of overlap at a certain
lift, not LSA values IMO.
Originally Posted by Sharpe
If so, would a 230/230 cam with 115 LSA make more power but have a similar curve as a 224/224 with 112 LSA?
Originally Posted by Sharpe
So this question cannot be answered as it is stated. Alright.
Originally Posted by DAPSUPRSLO
Those cams will have very different valve events and hence their power and powerbands will be fairly different.
FMS Custom Grind Camshaft - 224"/224" .588"/.588" 112LSA - aggressive profile with a 1800-6600 RPM range, fair idle
FMS Custom Grind Camshaft - 230"/232" .595"/.585" 114LSA - aggressive profile with a 2500-6800 RPM range, rough idle
Powerbands are quite different.
DAPSUPRSLO, in the threads that I have been reading, it is your posts or posts about what you are doind that has spurned my curiosity. It seems that you are trying to make low end power with bigger cams. I read where you had a 224/224 @ 110 LSA cam, for starters, and that you had a large cam that you were advancing like 8 degrees.
Can you see where I'm going with my line of questions?
The cam was advanced 6 degrees and yes I see where you are going. Don't get too caught up in my stuff though. It is application specific. You will give up power in the area you should be most concerned with if trying to go as fast as possible drag racing. However, if you only want big block like torque then these advaced cams are for you. It seems the 38 degree at .050" IVC point worked well for what I was trying to do when I spec'd that cam (224 110lsa cam) and that was not turn the motor that hard and make great power. It suceeded very well for me.
My new cam will not close the IVC till 57 ABDC at .050", but then again we are not talking about a 346 anymore or an intake restricted motor. So many variables, so little time, and so much to read out there to draw your own conclusions from.
My new cam will not close the IVC till 57 ABDC at .050", but then again we are not talking about a 346 anymore or an intake restricted motor. So many variables, so little time, and so much to read out there to draw your own conclusions from.
Originally Posted by Adrenaline_Z
If you want to learn more about overlap, remove LSA from the equation.
Look at the individual valve timing specs on the cam card, and also notice
the overlap at 0.006" and 0.050" lift.
From there, you need to consider (along with everything else mentioned)
rocker ratio, pre-load amount, how the valve follows the lobe profile at certain
RPM, shape of the lobe (to name a few).
When we're discussing overlap, we need to think degrees of overlap at a certain
lift, not LSA values IMO.
Look at the individual valve timing specs on the cam card, and also notice
the overlap at 0.006" and 0.050" lift.
From there, you need to consider (along with everything else mentioned)
rocker ratio, pre-load amount, how the valve follows the lobe profile at certain
RPM, shape of the lobe (to name a few).
When we're discussing overlap, we need to think degrees of overlap at a certain
lift, not LSA values IMO.
Overlap can be looked upon heavily in the .006 duration range than the .050 range. Seat timing says alot more about the camshaft IMO.
Rick
TECH Addict
Joined: Jul 2005
Posts: 2,153
Likes: 3
LSA Dyno Test After reading 6 pages of theory, I remembered an old dyno test where they kept everything the same and changed LSA. You guys might find this useful.
Car Craft, June 1999, "Cam Lobe Separation Comparo"
Engine: SBC, 357 cid, 10.8/1, Dart Iron Eagle heads (275 i / 190 e), Super Victor intake, Holley HP 950 carb, mechanical flat tappet cam.
Cam spec's: 262/266 @ .050, .580"/.585"
LSA .. TQ@ 4500 .. TQ@ 5500 .. HP@ 7000 .. HP@ 7250 .. Idle "Hg
110. . .450 . . . . . . .480. . . . . . .584. . . . . . . .465. . . . . . . .6"
108. . .465 . . . . . . .489. . . . . . .578. . . . . . . .512. . . . . . . .5"
106. . .484 . . . . . . .504. . . . . . .580. . . . . . . .562. . . . . . . .4"
Everything looks just like theory suggests, except over-rev hp. I would have expected the wider LSA to make more power past peak, but just the opposite is true. The only comment that the article made was that they believed the rapid dive in power was caused by valve float, which doesn't totally make sense either because it would happen with all the cams.
Mike
Car Craft, June 1999, "Cam Lobe Separation Comparo"
Engine: SBC, 357 cid, 10.8/1, Dart Iron Eagle heads (275 i / 190 e), Super Victor intake, Holley HP 950 carb, mechanical flat tappet cam.
Cam spec's: 262/266 @ .050, .580"/.585"
LSA .. TQ@ 4500 .. TQ@ 5500 .. HP@ 7000 .. HP@ 7250 .. Idle "Hg
110. . .450 . . . . . . .480. . . . . . .584. . . . . . . .465. . . . . . . .6"
108. . .465 . . . . . . .489. . . . . . .578. . . . . . . .512. . . . . . . .5"
106. . .484 . . . . . . .504. . . . . . .580. . . . . . . .562. . . . . . . .4"
Everything looks just like theory suggests, except over-rev hp. I would have expected the wider LSA to make more power past peak, but just the opposite is true. The only comment that the article made was that they believed the rapid dive in power was caused by valve float, which doesn't totally make sense either because it would happen with all the cams.
Mike
Last edited by engineermike; Jan 8, 2006 at 12:30 PM.
Mike, any test that's done on most motors in terms of LSA usually wants more overlap, almost every time. Mike Petralia did a good test in a EM mag article last year as well..... his did show average power and that too little LSA can hurt as well.
Bret
Bret