Lobe separation

explosives87

explosives87

powder monkey
Joined
Aug 14, 2008
Messages
953
I am looking to buying a cam and I am trying to find out what the advantage of having a narrower lobe separation over a wider one would be. Some manufacturers swear by narrow LSA and other swear by wider LSA. How would this affect the performance of the engine.
 
lobe sep.

if your getting a cam get something in the area of 104 to 106 degree lobe sep. anything higher than that with a big charger will be very laggy and seems very hard to light one off. keep in mind tho if you have stock pistons you can't go real low on lobe sep because youll be taggin valves and you don't want that.haha.
 
I once ran a cam with a .530+ lift and a 112 LSA, real good on top but doggy on the bottom, had another one cut the same grind except with a 105 LSA and it was really nice, spool-up was 500 RPM's sooner.

Jim
 
Big stick is 105.5 LSA, I was told there is a 107LSA big stick that runs a little hotter, but will light a big charger faster.
 
I've got a 107 LSA Big Stik and it lights my Super B Special like stock, and even at elevation (7500ft) lights with ease.
 
2007 5.9 said:
I've got a 107 LSA Big Stik and it lights my Super B Special like stock, and even at elevation (7500ft) lights with ease.
Click to expand...

Did you notice any difference in egt's and fuel mileage? I have the same cam here for the new motor.
 
The Helix 2 is 110.2 LSA.

Wider LSA gives a broader TQ range. Not as peaky.

Narrower builds TQ faster. Higher peak

Both of these statements are general in nature. Not an exact.

LSA is mostly secondary to where the lobes actually are though. I am currently running a 114 LSA in my truck for testing. It is far from "doggy".

Opening the exhaust valve sooner or later can effect things much more on the Cummins. And as RPM increases that really plays the biggest part. One could open the EX valve at 39 BBDC and run a 105 LSA or still open at 39 BBDC and use 116 LSA and not have a huge effect on how doggy it is.

LSA that is too narrow ( as we found in the early days ) is a bad idea with a turbo that runs a higher back pressure than boost pressure. Reversion is the result. Ex gases flowing backward. Mixing with your fresh intake charge. Lowering oxygen content of the air charge in the cylinder. I have seen plenty of intake manifolds filled with black soot using a narrow LSA.

Wider LSA is almost always better for higher RPM range work. As the RPM passes 3500, a wide angle is king. HP will increase as well.

Here is a chart for general use of LSA's:


NARROW............................... WIDE

int opens earlier.................... int opens later
int closes earlier.................... int closes later
ex opens later....................... ex opens earlier
overlap is more...................... overlap is less
TQ is peakier......................... TQ is flatter
RPM range drops off............... RPM hangs on longer
 
Soup Nazi said:
The Helix 2 is 110.2 LSA.

Wider LSA gives a broader TQ range. Not as peaky.

Narrower builds TQ faster. Higher peak

Both of these statements are general in nature. Not an exact.

LSA is mostly secondary to where the lobes actually are though. I am currently running a 114 LSA in my truck for testing. It is far from "doggy".

Opening the exhaust valve sooner or later can effect things much more on the Cummins. And as RPM increases that really plays the biggest part. One could open the EX valve at 39 BBDC and run a 105 LSA or still open at 39 BBDC and use 116 LSA and not have a huge effect on how doggy it is.

LSA that is too narrow ( as we found in the early days ) is a bad idea with a turbo that runs a higher back pressure than boost pressure. Reversion is the result. Ex gases flowing backward. Mixing with your fresh intake charge. Lowering oxygen content of the air charge in the cylinder. I have seen plenty of intake manifolds filled with black soot using a narrow LSA.

Wider LSA is almost always better for higher RPM range work. As the RPM passes 3500, a wide angle is king. HP will increase as well.

Here is a chart for general use of LSA's:


NARROW............................... WIDE

int opens earlier.................... int opens later
int closes earlier.................... int closes later
ex opens later....................... ex opens earlier
overlap is more...................... overlap is less
TQ is peakier......................... TQ is flatter
RPM range drops off............... RPM hangs on longer
Click to expand...

Thanks for the breakdown:thankyou2:
 
94 12valve said:
Thanks for the breakdown:thankyou2:
Click to expand...

x2.

That's more like what I would have expected based on my other turbocharging experience. I was really surprised at the narrow LSA numbers I was seeing when I started looking into cams for the Cummins.
 
Looking purely at LSA's can give a clue as to what the timing events are for both valves.

Wider LSA's will open the exhaust earlier ( typically ) in terms of where the piston is in its downward stroke. As the RPM increases on a Diesel we found you must open the EX earlier and earlier. It helps to lower pumping losses. Opening earlier begins to drain the cylinder of hot gases sooner. This keeps the piston from having to "pump" or force exhaust gas out with the piston. This raises power in the upper bands. At a price though: The TQ can be less at peak values compared to a cam that opens the exhaust later. Simply because the piston will have hot combustion gases pushing on it longer. But a big concern becomes how long do you want that piston to be soaking up the heat from the combustion? Adding fuel only makes it worse for piston crown temps and leaving the exhaust valve closed too long can get one into melt down conditions.


Wider lobes also serve to increase piston to valve clearance. As an example the piston to valve clearance is increased with a Helix 2 VS all of the stock Cummins cams. Valve float becomes less of a concern. Also, overlap is reduced to avoid exhaust gas reversion. One can run a higher exhaust gas pressure than boost pressure and not get into reversion. This is very important for stock turbo guys or even twin turbo guys with stock or small secondary chargers. Finally, a lower piston crown temperature was measured with the final product VS all the cams we tried in 2004. This was a larger concern in the overall idea of a Helix 2.

If you are a pretender in the HP game, run little to no additional fuel, and/or keep the RPM range under 3000, a tighter lobe cam might work best for you.

On the other hand if you need the best peak horsepower................
 
Don I am glad to see you posting some specs. You are correct to a point

Because lobes can have more duration on closing ramp than the opening or the other way around LSA numbers don't always have to fall into a specific category to achieve a cams purpose.

Take for example our 181/210 on a 107. Thanks to its moderate LSA and its aggressive ramp rates, it spools Much sooner than the Helix 2 making much more power below 3000rpm. Going by what Don is saying it would not match the helix 2 at high rpm. Not so. It continues to make more power than the helix all the way until redline. Our 107 in short, spools like a cam with a 104.5LSA but makes power on the top-end like a 111. Numbers don't lie here is a graph.

http://i240.photobucket.com/albums/ff203/zacheryhamilton/Scan_Pic0002.jpg

Posted by Don....."If you are a pretender in the HP game, run little to no additional fuel, and/or keep the RPM range under 3000, a tighter lobe cam might work best for you.

On the other hand if you need the best peak horsepower................"

That is a half truth!

The reason? That's simple, well engineered parts that can take advantage of very aggressive ramp rates. LSA's are sometimes but not always indicative of where a particular cam will make power. When I design a cam, opening and closing events are my first priority , LSA's will end up where they end up based on ramp rates.

Zach
 
Last edited:
Hamilton Cams said:
The reason? That's simple, well engineered parts that can take advantage of very aggressive ramp rates. LSA's are sometimes but not always indicative of where a particular cam will make power. When I design a cam, opening and closing events are my first priority , LSA's will end up where they end up based on ramp rates.

Zach
Click to expand...


The Helix 2 has very aggressive ramps, but has a lower overall wear rate VS all the stock Cummins cams. We did the testing to find out.

Part of the reason it is duration of the cam lobe gives us some additional real estate to use. I have the software acceleration and jerk graphs of the H2 VS all the stock cams. It is much more aggressive.
 
Hamilton Cams said:
Take for example our 181/210 on a 107. Thanks to its moderate LSA and its aggressive ramp rates, it spools Much sooner than the Helix 2 making much more power below 3000rpm. Going by what Don is saying it would not match the helix 2 at high rpm. Not so. It continues to make more power than the helix all the way until redline. Our 107 in short, spools like a cam with a 104.5LSA but makes power on the top-end like a 111. Numbers don't lie here is a graph.

http://i240.photobucket.com/albums/ff203/zacheryhamilton/Scan_Pic0002.jpg
Click to expand...

Now I want that cam even more!
 
mondtster said:
x2.

That's more like what I would have expected based on my other turbocharging experience. I was really surprised at the narrow LSA numbers I was seeing when I started looking into cams for the Cummins.
Click to expand...

you gotta realize, these cams have such small lobes compared to aftermarket gasser cams, overlap on one of these cams at 107LSA is still less than a healthy gasser cam at say 112LSA
 
Soup Nazi said:
The Helix 2 has very aggressive ramps, but has a lower overall wear rate VS all the stock Cummins cams. We did the testing to find out.
Part of the reason it is duration of the cam lobe gives us some additional real estate to use. I have the software acceleration and jerk graphs of the H2 VS all the stock cams. It is much more aggressive.
Click to expand...

Posted by soup nazi- "The wider lobe is not needed with the Helix 2 grind.

Longer duration allows a slower lift on the lobe compared to stock. The wider lobe also slows tappet rotation which adds to higher wear on regrind cams. Rotating the tappets ( called sliding tappets also ) are key to slower wear.

The Helix is harder at the lobe as well. The lighter overall rotating mass/weight helps avoid breakage under heavy loads. Simply less mass.

When the molds are produced, we can make them any configuration we like. Wider, not as wide, etc. A larger diameter, etc. The Helix is made this way by design.

The only load we dont like on the Helix cast cams is a 13mm inline P pump. Actually it is not the load to turn the P pump, but the unloading and shock that can oocur if a driveline piece breaks and the load is removed quickly."

The Helix lobes are the same width as the 12V cam, but not as wide as the 24 and CR. Some discussion has occured on paying for another mold, but this has not been needed. Our wear rates are the lowest we have seen on any of the cams available."
__________________




So which one is it? In one post you say it is faster and one you say it is slower.

Also I am still laughing that you said "when we have them cast we can have any width we want." If you have them cast for you, why on earth did you grind off all of the part numbers and the name of the manufacturer? And the part about having less mass makes it stronger is the biggest lie of the post. Like I said, If less mass means it's stronger a Sherman tank should be as strong as an eggshell.

There are numerous inconsistencies in your post. Care to elaborate?

Zach
 
Last edited:
You must log in or register to reply here.
Back
Top