Pure Stock Drag Racing tips & tricks

[Chevy454]

Marlin:

Just curious...is this your current cam (from Comp)? Check the part number & specs and let me know...

[YENKO DEUCE REGISTRY]

Rob;
That's the one! Part number matches.

Sam;
No day two for me, I'm actually considering putting the original Crane cam in [img]/ubbthreads/images/graemlins/smile.gif[/img]

[COPO PETE]

[ QUOTE ]
Rob;
That's the one! Part number matches.

Sam;
No day two for me, I'm actually considering putting the original Crane cam in [img]/ubbthreads/images/graemlins/smile.gif[/img]

[/ QUOTE ]
OH MY GOD!!!!!!!! BE STILL MY LITTLE HEART!!!!
Peter [img]/ubbthreads/images/graemlins/biggthumpup.gif[/img]

[Salvatore]

Crane was not the original cam! Chevy was. Try to find an early nos cam, because chevy standardized these cams and I personally don't think they are as good or as accurate as the originals. I have a Crane speck cam in my Z/28, and frankly it just does not have the snap as the early chevy sticks had. I don't know why you would go to all that trouble any how. sam [img]/ubbthreads/images/graemlins/crazy.gif[/img]

[Chevy454]

I can understand the 106 LCA helping with the low compression, but the 106 LSA sounds REALLY tight to me! How does that thing idle, Marlin? Does the advanced LCA make up for the tight LSA? Anyone?

As for the Crane vs. GM discussion, I tend to believe it's the opposite. JJ's "143" (from Crane) was spot-on when they checked it at the Certified Stock tech. And, as I mentioned earlier in the thread, Lerum put an NOS GM "143" on a cam doctor and all of it's specs were all over the place, from LSA to lift. Just my opinion though...

Whatever you decide on cams is your business, but I expect to see that thing on the track!

[YENKO DEUCE REGISTRY]

Rob;
Not sure what LCA and LSA mean, and how they might relate to each other? My car idles a little high, but I think the secondary throttle plate is hung up a little. I took it off to adjust that, but not sure if I corrected it or not. Other than that, the car idles fine, 18inches of vaccuum at idle so....

The durations of the two cams have not changed, so why would I have a problem with the vaccuum supplied to the brakes? Only the lift is up, and when you check the cam profile the increased lift has minimal effect due to the same duration. Plus, the original manifolds, heat riser and smog stuff stifle any lift advantage [img]/ubbthreads/images/graemlins/frown.gif[/img]

Thoughts? Constructive ones, Pete [img]/ubbthreads/images/graemlins/smile.gif[/img]

[JLerum]

Marlin,

LCA (Lobe Centerline Angle) is a term that tells you how advanced your cam is. If you have a cam that has 114 degree LSA (Lobe Seperation Angle)and you put the LCA at 106 degrees you've advanced you're cam 8 degrees.

This would generate good static compression at low RPM but hurt high RPM cylinder fill. It will close the intake valve approximately 8 degrees sooner. What you get on the bottem end you give up on the top end. Alot of how the cam should be put in depends on your car set up. ex. 4 speed or automatic, 4.10 gears or 3.55, high compression motor or low low compression motor. [img]/ubbthreads/images/graemlins/beers.gif[/img]

JIM

Hope this helps! [img]/ubbthreads/images/graemlins/flag.gif[/img]

[Chevy454]

Sorry about that, Marlin! Jim's right on the money with the acronyms:

LSA - Lobe Seperation Angle
LCA - Lobe Centerline Angle

The LSA is the amount of serperation, or overlap, between the intake and exhaust lobe. The "wider" (larger) the number, the less overlap, and the more fuel/air that is trapped in the cylinders at low/mid engine speed, and vice versa. This is ground into the cam, and thus, can't be changed. This also has a great effect on idle, and anything under 112 will generally have a pretty good lope to it (that's why I questioned the 106 LSA of the Comp unit). I believe the LSA of the 143 cam is 114, and I think the original LT-1 cam is the same (114). The LSA is independant of the LCA.

LCA is the centerline of the intake lobe, and like Jim said above, tells you how much your cam is advanced/retarded. This is changed by degreeing your cam to whenever you want it to come in. I believe most of the older/original cams were ground advanced (the 143 cam was ground with 6 degrees advance!), which is fine on the stickies, but is hard to handle if you are running on the skinnies!