Cam talk
#865305
11/28/10 03:58 AM
11/28/10 03:58 AM
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Anonymous
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Anonymous
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What would the difference be with a cam at 108* LSA and one with 112* LSA? The motor being the exact same and the cam specs being the same except the LSA. What difference will it make to the motor and the performance on the car?
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Re: Cam talk
[Re: ]
#865306
11/28/10 11:43 AM
11/28/10 11:43 AM
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Joined: Dec 2008
Posts: 1,200 UK
602heavy
pro stock
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pro stock
Joined: Dec 2008
Posts: 1,200
UK
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Take these two cams , both have exact same duration @ seat , although one is ground on a 112* lobe sep the other a 108*.......... Cam #1 280int/280ex (seat to seat) 112 lsa/112icl (installed straight up) IO/28 IC/72 EO/72 EC/28 overlap @ seat 58* Cam #2 280int/280ex (seat to seat) 108 lsa/108icl (installed straight up) IO/32 IC68 EO/68 EC32 overlap @ seat 64* As you can see the #1 cam opens intake valve LATER BTDC & closes LATER ATDC , #2 engine will suffer more intake charge contamination due the extra 6 degrees of overlap......#2 cam will close intake valve earlier increasing cylinder presuure. There's a lot more to it than this , hopefully you get the basics.
Last edited by 602heavy; 11/28/10 11:55 AM.
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Re: Cam talk
[Re: Pacnorthcuda]
#865310
11/28/10 02:40 PM
11/28/10 02:40 PM
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Joined: Jan 2007
Posts: 3,695 nc
emarine01
master
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master
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Posts: 3,695
nc
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Quote:
A narrow LSA (in this case 108) will create more high rpm power, the wider LSA will create more low end torque, all other things being equal.
Rut Row Something dont sound right
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Re: Cam talk
[Re: emarine01]
#865311
11/28/10 02:55 PM
11/28/10 02:55 PM
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Joined: Jan 2003
Posts: 15,439 Val-haul-ass... eventually
BradH
Taking time off to work on my car
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Taking time off to work on my car
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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Quote:
Quote:
A narrow LSA (in this case 108) will create more high rpm power, the wider LSA will create more low end torque, all other things being equal.
Rut Row Something dont sound right
Let me take a shot here... Wider LSA - better (smoother) idle, will come on cleaner at a lower RPM, won't make as much torque, may make more HP at peak (not a sure thing, though), less cranking pressure.
Narrower LSA - rougher idle, more sensitive to exhaust back pressure, comes on harder once above the point where the engine cleans up, may not make as much peak HP (again, not a sure thing), more cranking pressure.
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Re: Cam talk
[Re: S/ST 3040]
#865313
11/28/10 03:07 PM
11/28/10 03:07 PM
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Joined: Jan 2007
Posts: 3,695 nc
emarine01
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master
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nc
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Quote:
Hey.... quit hiding behind the popcorn....
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Re: Cam talk
[Re: emarine01]
#865314
11/28/10 05:33 PM
11/28/10 05:33 PM
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Joined: Jan 2003
Posts: 5,486 SoCal
Brian Hafliger
master
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master
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Posts: 5,486
SoCal
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Generalizing cam behavior is wrong IMO. I've done a few engines where I started with the customers cam he picked out and then changed cams with one I pick out and I have to say I've been surprised more than once in what I've found. I've seen tighter lca's broaden the HP and Tq curve...I've seen more lift add TQ below TQ peak...I've seen just 6° of duration of the same lobe family add 20HP. And I've seen both .010 of lash and .035+ lash make great power. Go figure....
Brian Hafliger
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Re: Cam talk
[Re: ]
#865317
11/28/10 07:41 PM
11/28/10 07:41 PM
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Joined: Oct 2005
Posts: 8,879 Ontario, Canada
Stanton
Don't question me!
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Don't question me!
Joined: Oct 2005
Posts: 8,879
Ontario, Canada
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Quote:
What would the difference be with a cam at 108* LSA and one with 112* LSA? The motor being the exact same and the cam specs being the same except the LSA. What difference will it make to the motor and the performance on the car?
The only answer to this "general" question is a "general" answer. Simply put the overlap decreases with the increased LSA. Decreasing the overlap "generally" increases bottom end torque and HP BUT also decreases peak torque and peak HP. The idle will smooth out.
HOWEVER, the cam profile you're comparing may already have a low enough overlap to idle smoothly and provide sufficient low end torque and HP. Increasing the LSA would yeild no improvement what-so-ever.
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Re: Cam talk
[Re: ]
#865322
12/04/10 04:47 AM
12/04/10 04:47 AM
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Joined: May 2008
Posts: 5,399 Aurora, Colorado
451Mopar
master
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master
Joined: May 2008
Posts: 5,399
Aurora, Colorado
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I don't buy into the "magic" cam hype. All cams have trade-offs. Wider LSA cams are usually installed to take advantage of an earlier exhaust opening point and to reduce overlap. Most common reasons are forced induction, Nitrous, or to crutch a poor exhaust system. Also, wider LSA cams (in theory) have a wider power curve, but less peak torque. Narrow LSA cams increase overlap, generally have higher peak torque, and a narrower power band. Here is a link to CompCams web page on LSA: http://www.compcams.com/Pages/413/cam-timing-lobe-separation-angle.aspx
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Re: Cam talk
[Re: 451Mopar]
#865323
12/04/10 08:40 AM
12/04/10 08:40 AM
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Joined: Feb 2007
Posts: 6,295 U.S.
moparniac
master
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master
Joined: Feb 2007
Posts: 6,295
U.S.
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What about the same cam grind with small cubes vs big cubes ...
Mopar Performance
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Re: Cam talk
[Re: moparniac]
#865324
12/04/10 10:19 AM
12/04/10 10:19 AM
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Joined: Jan 2003
Posts: 10,010 Frostbitefalls MN (Rocky&Bullw...
gregsdart
I Live Here
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I Live Here
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Posts: 10,010
Frostbitefalls MN (Rocky&Bullw...
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port size is important. A very large engine like a 535bb mopar with poor flowing 906 ported heads will swallow most all the cam you can throw at it and it won't pull power past 5800/6000. Try that with a 1970 ford boss 302 (huge Big block type ports)and you have an engine that won't get out of its own way till 6500 rpm. BUT, with the right cam it will make 650 hp at 9500! That was done in a HotRod article back in the seventy s. All they did was blue print the motor, no head porting, put in a big rollercam, and went modified class racing. AS I recall they were shifting that deal close to 10,000 rpm with stock ports. The 906 head motor has so much port velocity it is hard to screw up with cam specs that are off. I went from a 590 cam installed at 108 to 112 and I didn't see any difference! A 286 @ .050 roller with .750 lift went in, and it only raised the power peak about 300 rpm, but the motor responded with a 5 mph gain in the quarter. The Boss motor would be very touchy about late intake closing, because there is no velocity to help cover it up till very high rpm. It also will need a lot less duration for the same rpm. The 286 duration cam in that motor might even be too much at 9500, because the ports flow so well they don't need the extra time to fill the cylinder.
Last edited by gregsdart; 12/04/10 10:33 AM.
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Re: Cam talk
[Re: gregsdart]
#865325
12/04/10 11:51 AM
12/04/10 11:51 AM
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Joined: Aug 2006
Posts: 614 Michigan
Get-X
mopar
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mopar
Joined: Aug 2006
Posts: 614
Michigan
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Quote:
port size is important. A very large engine like a 535bb mopar with poor flowing 906 ported heads will swallow most all the cam you can throw at it and it won't pull power past 5800/6000. Try that with a 1970 ford boss 302 (huge Big block type ports)and you have an engine that won't get out of its own way till 6500 rpm. BUT, with the right cam it will make 650 hp at 9500! That was done in a HotRod article back in the seventy s. All they did was blue print the motor, no head porting, put in a big rollercam, and went modified class racing. AS I recall they were shifting that deal close to 10,000 rpm with stock ports. The 906 head motor has so much port velocity it is hard to screw up with cam specs that are off. I went from a 590 cam installed at 108 to 112 and I didn't see any difference! A 286 @ .050 roller with .750 lift went in, and it only raised the power peak about 300 rpm, but the motor responded with a 5 mph gain in the quarter. The Boss motor would be very touchy about late intake closing, because there is no velocity to help cover it up till very high rpm. It also will need a lot less duration for the same rpm. The 286 duration cam in that motor might even be too much at 9500, because the ports flow so well they don't need the extra time to fill the cylinder.
Greg, Nice reply, very informative. You're absolutely right on cylinder fill and duration. The cam out of my Hemi99 engine has 20* more duration on the exhaust side. They are trying to help the poor exhaust port with it's puny(compared to the intake) valve keep up with the huge port and valve of the intake.
The valve is also being lifted 1.050" so the efficient, huge intake port with a 2.55 valve diameter doesn't need a ton of intake duration to cylinder fill. The exhaust is a different story as it's an afterthought in a pro stock head and needs all the help it can get!
The cam in your 440-1 headed engine probably has more duration @.050 on the intake than my PS Hemi!!
'65 Belvedere '68 GTX '57 Dodge pickup
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Re: Cam talk
[Re: Get-X]
#865326
12/04/10 12:28 PM
12/04/10 12:28 PM
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Anonymous
OP
Unregistered
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Anonymous
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Unregistered
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Great info coming.
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