importance of LSA?

[Jalolo]

I often see that camshafts with LSA 113 or 114 are recommended for EFI engines.

What are the advantages and disadvantages of these compared to lower LSA?

Factory Jeep 4.0 engines used LSA 112 and even 107.5 camshafts, and they work fine with stock ECUs.

[Cheromaniac]

A wider LSA tends to produce a smaller valve overlap, more vacuum at idle, a smoother idle, and a flatter wider torque curve whereas a tighter LSA tends to produce more valve overlap, a lopier idle, and a peakier torque curve. Despite the tight LSA, the later OEM camshaft still has a smooth idle due to the shorter duration.

[Jalolo]

A wider LSA tends to produce a smaller valve overlap, more vacuum at idle, a smoother idle, and a flatter wider torque curve whereas a tighter LSA tends to produce more valve overlap, a lopier idle, and a peakier torque curve. Despite the tight LSA, the later OEM camshaft still has a smooth idle due to the shorter duration.

Thanks for your reply. I was wondering whether to buy a Comp Cams 68-231-4 with LSA 111 or a 68-301-5 with LSA 113. I don't see the .050 valve opening and closing specifications for the 301.

[Cheromaniac]

Both are good all-round cams but the 68-301-5 is designed for the '99 and later blocks where the cam is held in place by a thrust plate rather than the older spring/pin set up. That cam has a 113* LSA and is installed at a 109* ICA.

[Cheromaniac]

Here are the seat to seat valve timing events for the 68-301-5 camshaft:

Intake Centerline: 109.00° ATDC
Exhaust Centerline: 117.00° BTDC
Intake Open: 16.00° BTDC
Intake Close: 54.00° ABDC
Exhaust Open: 66.00° BBDC
Exhaust Close: 12.00° ATDC
Overlap: 28.00°

and the 0.050" lift valve timing events:

Intake Centerline: 109.00° ATDC
Exhaust Centerline: 117.00° BTDC
Intake Open: -6.50° BTDC
Intake Close: 31.50° ABDC
Exhaust Open: 43.50° BBDC
Exhaust Close: -10.50° ATDC
Overlap: -17.00°

[Jalolo]

Both are good all-round cams but the 68-301-5 is designed for the '99 and later blocks where the cam is held in place by a thrust plate rather than the older spring/pin set up. That cam has a 113* LSA and is installed at a 109* ICA.

Are you sure of what you're saying? Aren't you confusing it with the 163-301-5 cam?
My preference leans slightly more toward the 68-301-5 because it has LSA113 and, according to the Comp Cams website, it's nitride-coated. It also specifies that it's for pre-1998 engines.
Here's the link.
https://www.compcams.com/xtreme-4x4-205 ... 8-cpg.html

[Cheromaniac]

Are you sure of what you're saying? Aren't you confusing it with the 163-301-5 cam?

You are right. The 68-301-5 cam is for '98 and earlier engines while the 163-301-5 is for the '99 and later. Both have identical specs though.

[Cheromaniac]

Here's my updated spreadsheet:

https://www.angelfire.com/my/fan/Jeep4.0Camshafts.htm

[Jalolo]

The decision is made then. I'm going to buy the 68-301-5.

Thanks for the information, you've helped me a lot.

[Jalolo]

Here's my updated spreadsheet:

https://www.angelfire.com/my/fan/Jeep4.0Camshafts.htm

I'd like to take this opportunity to point out a possible error.

When I enter the data into the calculator to find the DCR, if I select the 1999/2004 OEM camshaft (mine is 97' but I understand it has the same degrees and advance), the calculator shows an intake closure angle of 53.95 degrees, resulting in 8.24 DCR.

IMG_20250504_005551.jpg

If I do the calculation using the degrees of closure indicated in the camshaft list, i.e. 60.9 degrees, it calculates 7.88 DCR.

IMG_20250504_005521.jpg

IMG_20250504_002749.jpg

What would be the correct result?

[Cheromaniac]

The second picture is correct. In the first picture you entered an advance or retard of 0 degrees when you should have actually entered -2.5 degrees.

[Jalolo]

To get the same result as the second image, I have to put -7 degrees in the advance or delay box.

[Jalolo]

IMG_20250505_001723.jpg

[Cheromaniac]

Yeah I get the same result when I enter the seat to seat valve timing events: 107.3* LSA and 114.3* ICA or 7 degrees of retard. When I enter the 0.050" lift events I get 107.5 & 110 respectively or 2.5 degrees of retard. I'm not sure which I should believe.