would someone define LSA for me please?
i have part of the clue; lobe seperation A?
does that indicate amount or advance :confused:
thanks, john

Lobe Seperation Angle

Simply the distance in cam degrees between the intake lobe center & the exhaust lobe center.
;)

Now explain the relation with power. I small LSA would create a small difference in between combusts, and a large would slow down the rate of combustion. I guess what I'm trying to say is that smaller angle will open the valves quicker than a larger one. PLEASE ( smile.gif ) correct me if I am wrong.

thanks. i no about lobe seperation, but we used to just call it lobe seperation never saw or heard the A for (angle) reference before until joining this site. graemlins/thumbsup.gif
john

Lobe seperation is just that, the measurement in degrees between the intake lobe peak and exaust lobe peak {peak not being an actual term but easy enough to visualise}. It is ground into the cam and cannot be changed. A wider LSA of lets say 112 will give you a broader torque band, better idle quality and more vacum and is "nice" on the street. These cams have less overlap than a narrow LSA cam. This is more taylored to an automatic trans.
A narrower LSA of lets say 108 will give you that wicked sound, along with a more "peaky" but narrow power band and is better suited to a stick shift or a race car and has more overlap. There are exceptions im sure but in general i hope this is what your looking for. Also the wider LSA is more suited tward nitrous cars and supercharged cars but i cant give you a GOOD answer why, i believe it has to do with overlap and scavenging, maybe somone will chime in on that. Hope this helps a little.....
Nick

Originally posted by Adman:
Now explain the relation with power. I small LSA would create a small difference in between combusts, and a large would slow down the rate of combustion. I guess what I'm trying to say is that smaller angle will open the valves quicker than a larger one. PLEASE ( smile.gif ) correct me if I am wrong. What determines how fast the valve opens is the lobe design.
Basicly what happens with lobe seperation is a tighter one like 106 will develop more torque sooner & be in a norrower rpm range than one with a wider lobe seperation like 110 which would have less peak torque but a wider torque curve. The shorter lsa will develop more cylinder cranking pressure & in general have a worse idle because it has more overlap. The wider one will have less cranking pressure but will have less overlap.
This is assuming you are talking about a cam with the same lobe designs.

Hi Nick,
You happen to be goin to the PRI Show? :D

What is the 'scavening' effect? Thanks for entertaining my mind smile.gif

Originally posted by Adman:
What is the 'scavening' effect? Thanks for entertaining my mind smile.gif At the end of the combustion cycle the exhaust valve opens BBDC & what's left of the combustion pressure starts forcing the exhaust gas out. From this point to about BDC is called blowdown. Then the piston is on it's way up & pushing the gas out. As you approach TDC the intake valve start opening but you are not at TDC yet & there is very little pressure left in the cylinder but there is exhaust gas flowing out the port & pipe. The gas does not like to stop & creates a "suction" on the cylinder which helps to suck the remaining exhaust out & also if timed right it starts the intake flowing. This is the part that is referred to as scavanging. It is also where you get reversion at lower speeds with big cams & lots of overlap.

And the wheels on the bus go round & round :D

And I forgot to add,,,,,,this is the stuff that makes us real glad there are people like Harold to call :D

Hey there Mike....ill go if i can but i dont know what it is??? Whats the PRI show? let me know and maybe ill go.
Nick

Sorry about that graemlins/clonk.gif
It's the Performance Racing Industry deal in Indy & is HUGE!! But it is trade only.
We like to go & drool on all the new stuff :D
Thought you might be going with your friendly local machinist or something.
It starts Thur the 4th & ends Sat.

Nahh sorry, love to but i cant, Indy is probably a 12hr drive and i have to spend my money where it counts right now....new MSD ignition,Caltracs, and a Mighty Demon carb come to mind :D Ive also been looking at a 66 el-camino for a winter driver {im sure somone just lost there cookies} yes i said winter driver. BUT hey if your driving by any chance stop through Waterloo and say hi, we could probably go find oldani {even though i have yet to meet him} and go grab a cold one.
-Nick graemlins/beers.gif

Mike,

You do just fine with your replies. I enjoy reading them.
I'll be at PRI all 3 days, as Holley has changed their minds once again.....

John,

LSA, or Lobe Seperation Angle, is what we grind into the cam to give the torque curve that you want. ICL, or Intake Center Line, is where we tell you to put the Intake's max lift point, to give you the characteristics you want to make your combo work. Most of my cams like 4 to 6 degrees advance on their LSA, ie---A 106 LSA likes a 100 ICL, and a 112 LSA likes a 106 ICL. Generally 2 degrees less ICL also works OK.
When my cams are advanced this much, they like a good fuel system....

UDHarold

Thanks Harold,
We will see you there. My wife is coming but they won't let us bring the wolves :D

Another couple points about LSA's ---

The tighter the lobe separation angle the more valve overlap you will have; the wider the LSA the less overlap you will have. Overlap is the period when when both the intake and exhaust valves are open at the same time. This occurs at the end of the exhaust stroke and at the beginning of the intake stroke.

At high RPMs a larger overlap period causes scavenging - where the exhaust pulse moving at high speed in the exhaust pipe helps "suck" the intake charge into the cylinder (with very big cams some of this charge is actually "sucked" straight through the cylinder and into the exhaust pipe causing that "gassy" race-car exhaust smell).

At low RPMs there is not enough velocity in the exhaust pipes to suck fresh mixture into the cylinder, instead pressure from the exhaust actually pushes back into the intake --- causing the mixture to be diluted by the exhaust gasses. This leans the mix and causes that classic big cam rough idle.

More overlap is what causes a tight LSA cam to be peakier --- a large area of overlap causes reversion at low RPMs hurting low end power and causes more scavenging at higher RPM increasing the top end power.

Of course you can increase or decrease overlap by increasing or decreasing duration too, but changing LSA has a BIG effect on overlap.

The exhaust valve open point is also effected by changing the LSA and also effects how much power an engine will make. The Exhaust Valve Open timing is important because it can cause pumping losses if too late or waste cylinder pressure if too early. Wider LSA cams open the exhaust valve earlier while narrower LSA cams open the exhaust valve later. N2O and blower cams need wider LSAs and extended exhaust duration so blow down starts early and allows adequate time for an extended blow down to get rid of all the extra exhaust gasses.

Sorry I got rambling . . .

Also to re-emphasize what Mike (Wolfplace) said earlier. This is when comparing two cams that are otherwise identical from the same manufacturer and the only variable being changed is the LSA.
When comparing two cams, a slightly small cam on 106 LSA will sound lumpier than a slightly longer duration cam on 112-114 LSA.
Basically, with LSA changes you're able to fine tune the power curve of a cam that's otherwise close to perfect for your combo.

Randy