Lobe Separation Angle (LSA) Specs—What Does a Plus Signal Imply?

Lobe Separation Angle (LSA) Specs—What Does a Plus Signal Imply?


I’ve been cam specs for the Summit Racing Professional LS Truck camshafts and I’ve a query. I’ve seen that lots of the specs now listing the lobe separation angle (LSA) spec with a plus quantity added. The cam I’m is the Professional LS Truck 8718R1 cam. The LSA specs are listed as 112+2. However the precise specs say the LSA is 112 levels. So what does the +2 discuss with? It’s one thing new that I’ve by no means seen earlier than and I’m undecided what it means.


This can be a nice query with, for as soon as, a easy reply.

However don’t fear, we’ll increase our reply simply so everybody understands what we’re speaking about. The brief reply is that the +2 refers to how the cam is floor relative to the LSA and the cam’s consumption centerline. The +2 on this occasion means it has been machined with two levels of advance constructed into the cam, inserting the consumption centerline at 110 levels BTDC.

However let’s take a more in-depth look to ensure everybody understands this clarification. Lobe separation angle is the angle between the consumption and exhaust lobes for a given cylinder and is expressed in camshaft levels. Utilizing the COMP Cams illustration on the backside of this text, you possibly can see that the consumption lobe centerline (the left lobe) and the exhaust lobe centerline (on the best) are each displaced 116 levels away from the TDC centerline.

The lobe separation angle is the sum of the 2 angles divided by two or 116 + 116 = 232 / 2 = 116 levels. If we advance the consumption lobe two levels to 114 levels BTDC, then the LSA can be 114 + 116 = 230 / 2 = 115 levels. That is completed in the course of the precise grinding of the camshaft and can’t be altered. Cam firms typically add this advance as a result of this improves low-speed torque. Not all cams are floor with advance inbuilt, however it is extremely widespread.

Earlier than this shortcut description, the easiest way to determine if the cam had been floor superior was to test the consumption centerline determine. If the consumption centerline quantity and the LSA quantity are each the identical, then the cam shouldn’t be spherical with advance. But when the consumption centerline is 110 levels and the LSA is 112 levels, then the cam has been floor with 2 levels of advance constructed into it.

Within the case of the Summit Racing Professional LS Vortec Truck Swap Camshaft, the LSA is expressed as 112+2. As you suspected, the cam is floor with a 2 diploma advance with a LSA of 112 levels. Which means that in case you had been to diploma the cam, you’d discover the consumption centerline would measure 110 levels BTDC. On this case, there isn’t any purpose to additional advance the camshaft as a result of the manufacturing facility has executed it for you. The brand new itemizing as 112+2 merely factors out that the cam has been floor with two levels advance within the cam. This shorthand description tells you all the pieces it’s essential to know.

Summit Racing Professional LS Truck Camshaft (SUM-8718R1) Specs

Length at
Consumption 279 230 0.625″ 112+2
Exhaust 291 242 0.605″
Consumption Centerline on this case is 110 levels BTDC.

This illustration from COMP reveals how the lobe separation angle (LSA) is decided. On this case: 116 + 116 = 232 / 2 = 116 LSA. If we had been to advance the consumption lobe (transfer it towards the centerline) by two levels, this is able to change the LSA:  114 + 116 = 230 / 2 = 115 levels. A tighter (smaller) LSA quantity additionally will increase valve overlap. (Picture/COMP Cams)
The LSA can’t be modified as soon as the cam is floor. Nonetheless, degreeing the cam will point out the place the cam is relative to consumption centerline. Within the case of the Summit Racing cam SUM-8718R1, the +2 signifies the consumption centerline shall be at 110 levels BTDC. (Picture/Jeff Smith)

Jeff Smith has had a ardour for automobiles since he started working at his grandfather’s gasoline station on the age 10. After graduating from Iowa State College with a journalism diploma in 1978, he mixed his two passions: automobiles and writing. Smith started writing for Automotive Craft journal in 1979 and have become editor in 1984. In 1987, he assumed the function of editor for Scorching Rod journal earlier than returning to his past love of writing technical tales. Since 2003, Jeff has held numerous positions at Automotive Craft (together with editor), has written books on small block Chevy efficiency, and even cultivated a powerful assortment of 1965 and 1966 Chevelles. Now he serves as an everyday contributor to OnAllCylinders.


Leave a Comment

Your email address will not be published.*



September 2022