Comp XFI Lobes
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Comp XFI Lobes Is anyone here running a cam with these lobes? Looking at Comp's lobe catalog, on a 224 lobe for example, the advertised duration is 274 on the XFI lobe for a ramp rate of 50, slighty less than an XE-R lobe. The duration @.200 is 149 for the XFI vs. 146 for the XE-R, making the XFI bigger. But I can't find any info on this site about the XFI lobes. More lobe area is a good thing, right?
You would need to make sure that they could grind that lobe on a a LS-1 journal. It dosen't give the journal size on Comps website, but LS-1 jornals are a bit larger than other cams out there. I noticed they listed XFI's for Mustangs and LT-1's, which makes me leary of wether they would fit the LS-1 journal. You could however look into the LSK lobes for the LS-1's. They have a diffrence of 50 also with the same .200" duration, but th elift is extremeley high, which may cause P/V problems.
LSK lobe 2126- 273 (.006) - 223 (.050) - 149 (.200) - .636" lift
LSK lobe 2126- 273 (.006) - 223 (.050) - 149 (.200) - .636" lift
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Comp was actually who suggested them to me. The guy said they had them on an "R" master, so they could grind them on any core. I asked if Comp was planning to make any shelf grinds like the other motors, and the guy said he didn't know.
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Springs depend on profile, valvetrain mass and stiffness, and dynamics of the spring itself. A stock LS1 has a lightweight valvetrain and the beehive springs have unique characteristcs. Just make sure you tell Comp the whole story. If you are running a heavier 2.1 valve, it may need a different spring.
On profiles and base circles, note that the LS1 has the largest journal except for race blocks. This is writeup is from Crane Cams:
On profiles and base circles, note that the LS1 has the largest journal except for race blocks. This is writeup is from Crane Cams:
Important: Lobe Design Size When Choosing a Roller Grind
Our roller profiles are designed for a particular finished lobe size, as determined by engine types or base circle radius requirements. We have provided a column indicating the Lobe Design Size for each of the listed profiles. Coding is as follows:
A. 1.786” nominal journal diameter (Buick V-6 and V-8, or special small base circle diameter. Chevrolet 262-400 V-8 requiring connecting rod to cam clearance in long stroke applications.)
B. 1.868” nominal journal diameter (Chevrolet 262-400 and 348-409 V-8 and Pontiac 265-455 V-8)
C. 1.948” to 1.968” or 50 mm journal diameter (Chevrolet 262-400 V-8 LRB, Chevrolet 396-454 V-8, Plymouth-Dodge 273-360, 350-440, & Hemi V-8’s)
D. 2.036” nominal journal diameter (Ford 221-302 and 351C-400 V-8’s), AMC
E. 2.125” nominal journal diameter (Ford 429-460 and other engines)
F. 55 mm or 2.165” nominal journal diameter (Chevrolet LS1 V-8, Chevrolet Vortec V-8, Ford LRB, and other engines)
G. 60 mm or 2.362” nominal journal diameter (Large cubic inch race only engines)
Some lobe designs have had masters generated for more than one size category. These have been indicated where applicable. When a roller lobe designed for one journal size is applied to an engine having a different nominal journal size, a duration change will occur. For example, an “A” lobe ground on a “C” engine camshaft will realize a four-degree increase at 0.050” cam lift. There is usually a two-degree change between design size series. Caution must be used when selecting a larger sized lobe for a smaller lobe application. If a “D” lobe were used on an “A” application, not only would a duration loss of eight degrees take place, but also a negative radius of curvature (inverted flank) may try to occur in the grinding process, resulting in a finished lobe shape that is not representative of the actual design shape. This may result in unstable valve train, possibly causing component failure. Lobes that are intended to have this inverted flank (Crane’s IR series) were carefully designed and manufactured using a special process to prevent this condition. Even so, IR camshafts are not normally advised for high RPM applications.
Our roller profiles are designed for a particular finished lobe size, as determined by engine types or base circle radius requirements. We have provided a column indicating the Lobe Design Size for each of the listed profiles. Coding is as follows:
A. 1.786” nominal journal diameter (Buick V-6 and V-8, or special small base circle diameter. Chevrolet 262-400 V-8 requiring connecting rod to cam clearance in long stroke applications.)
B. 1.868” nominal journal diameter (Chevrolet 262-400 and 348-409 V-8 and Pontiac 265-455 V-8)
C. 1.948” to 1.968” or 50 mm journal diameter (Chevrolet 262-400 V-8 LRB, Chevrolet 396-454 V-8, Plymouth-Dodge 273-360, 350-440, & Hemi V-8’s)
D. 2.036” nominal journal diameter (Ford 221-302 and 351C-400 V-8’s), AMC
E. 2.125” nominal journal diameter (Ford 429-460 and other engines)
F. 55 mm or 2.165” nominal journal diameter (Chevrolet LS1 V-8, Chevrolet Vortec V-8, Ford LRB, and other engines)
G. 60 mm or 2.362” nominal journal diameter (Large cubic inch race only engines)
Some lobe designs have had masters generated for more than one size category. These have been indicated where applicable. When a roller lobe designed for one journal size is applied to an engine having a different nominal journal size, a duration change will occur. For example, an “A” lobe ground on a “C” engine camshaft will realize a four-degree increase at 0.050” cam lift. There is usually a two-degree change between design size series. Caution must be used when selecting a larger sized lobe for a smaller lobe application. If a “D” lobe were used on an “A” application, not only would a duration loss of eight degrees take place, but also a negative radius of curvature (inverted flank) may try to occur in the grinding process, resulting in a finished lobe shape that is not representative of the actual design shape. This may result in unstable valve train, possibly causing component failure. Lobes that are intended to have this inverted flank (Crane’s IR series) were carefully designed and manufactured using a special process to prevent this condition. Even so, IR camshafts are not normally advised for high RPM applications.
Last edited by DavidNJ; Feb 10, 2006 at 08:11 AM.
I'm using the 242 at .050 exhaust lobe on a customers car right now. They do recommend 918 springs with these but we are using 921 shimmed .050" from coil bind cause we are using the monster lsk 239 at .050 lobe on the intake. I like them cause they are slightly easier on things from advertised to .050 then they become more agressive then the xe-r from .050 to .200.
And yes, they do have these lobes on the ls1 core. Comp can do almost any lobe on the ls1 core cause it's so damn big compared to everything.
I believe comp may also be the only company in which lobes don't grow by going from one master size to another (ex. from sbc journal to 55mm ls1 journal). Crane (as indicated above) and cam motion do grow. LSM, i'm not sure about.
And yes, they do have these lobes on the ls1 core. Comp can do almost any lobe on the ls1 core cause it's so damn big compared to everything.
I believe comp may also be the only company in which lobes don't grow by going from one master size to another (ex. from sbc journal to 55mm ls1 journal). Crane (as indicated above) and cam motion do grow. LSM, i'm not sure about.
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so, in a nutshell, the xfi lobes would sacrifice a little power low in the band, then come on really strong to redline? like...the xe-r lobes would make power sooner, but not as much on the top end, whereas the xfi lobes would take longer to make power, but make MORE when they do?
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Verdad Gallardo This is something I posted in another forum about the 918 springs. It may break it down for you some what. good luck!
"The 918s don't go into coil bind until 1.085, so take 1.800 (installed height) and subtract 1.085 and you get .715 lift before coil bind. Now subtract another .050 from .715 to account for the distance you should have safely before coil bind and you get .665. That's .665 lift you can safely run with these springs but it's not quite that easy as most cams with that kind of lift have crazy agressive ramps and the 918s will not have enough pressure to control them, unless you use titanium valves or some other crazy stuff or a crazy crazy slow lobe. Now, let's say you plan to use a cam with .615 lift. You could shim up the comp 918 springs till they are .050 from binding when that lift figure is taken to account. To do this simply take the .665 lift number and subtract .615 lift and you come up with the shim thickness that you need to run this spring at .050 from coil bind with a .615 lift cam. In this particular case you would need .050" worht of shims.
You would do this to increase the pressure of this spring to aid in controlling the agressive ram rate cams. Just an example."
"The 918s don't go into coil bind until 1.085, so take 1.800 (installed height) and subtract 1.085 and you get .715 lift before coil bind. Now subtract another .050 from .715 to account for the distance you should have safely before coil bind and you get .665. That's .665 lift you can safely run with these springs but it's not quite that easy as most cams with that kind of lift have crazy agressive ramps and the 918s will not have enough pressure to control them, unless you use titanium valves or some other crazy stuff or a crazy crazy slow lobe. Now, let's say you plan to use a cam with .615 lift. You could shim up the comp 918 springs till they are .050 from binding when that lift figure is taken to account. To do this simply take the .665 lift number and subtract .615 lift and you come up with the shim thickness that you need to run this spring at .050 from coil bind with a .615 lift cam. In this particular case you would need .050" worht of shims.
You would do this to increase the pressure of this spring to aid in controlling the agressive ram rate cams. Just an example."
Originally Posted by s346k
so, in a nutshell, the xfi lobes would sacrifice a little power low in the band, then come on really strong to redline? like...the xe-r lobes would make power sooner, but not as much on the top end, whereas the xfi lobes would take longer to make power, but make MORE when they do?
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Yes, the LS1 can use just about any profile. However, it can also use profiles that the smaller journal cams can't. In a stock small block engine size, this new for Chevy. Typically, Chevy has had the small journal sizes, small lifter bore sizes, and small rocker arms that have all been limiting factors. The LS1 has none of these problems.
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Originally Posted by Ragtop 99
I've talked to comp about using them too. Since the XE-R does not go below 220*, the XFI would give me the ability to use a faster ramp on a small duration cam.
Originally Posted by DavidNJ
Yes, however the LS1 uses roller cams, eliminating the problem.
Staging Lane
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From: AUSTIN, TEXAS
Now over three months later sense the XFI discussion began, do we have any real evidence on how this lobe changes when ground on the LS1 core?
Is really close to the LSK lobe, fast ramp but with less lift or is it closer to the XER lobe?
The XFI questions seem to be piling up.
Is really close to the LSK lobe, fast ramp but with less lift or is it closer to the XER lobe?
The XFI questions seem to be piling up.
TECH Apprentice
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I just ordered a cam Thursday from Jonathan @Thunder Racing. It has an XFI exhaust lobe, (274, 224@.050, 149@.200, .609 lift) but they didn't have an intake profile that matched what I needed. What I wound up using was a lobe not in any catalog, but found by one of the Comp Techs in their files. It specs out at 269, 220@.050, 145@.200, .597 lift. It's between a XER and a LSK lobe. It won't be installed until July, so I can't give you dyno results yet. But I'm having it Cam Doctored if you guys would be interested in the results.
Staging Lane
Joined: Oct 2004
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From: AUSTIN, TEXAS
Originally Posted by Gearhead1
I just ordered a cam Thursday from Jonathan @Thunder Racing. It has an XFI exhaust lobe, (274, 224@.050, 149@.200, .609 lift) but they didn't have an intake profile that matched what I needed. What I wound up using was a lobe not in any catalog, but found by one of the Comp Techs in their files. It specs out at 269, 220@.050, 145@.200, .597 lift. It's between a XER and a LSK lobe. It won't be installed until July, so I can't give you dyno results yet. But I'm having it Cam Doctored if you guys would be interested in the results.