Re: Correct me if I'm wrong ............
 

Marlin,Marlin,Marlin, Please just GO to day 2. And all your troubles will be gone! [img]/ubbthreads/images/graemlins/no.gif[/img] [img]/ubbthreads/images/graemlins/naughty.gif[/img] [img]/ubbthreads/images/graemlins/dunno.gif[/img] [img]/ubbthreads/images/graemlins/confused.gif[/img] [img]/ubbthreads/images/graemlins/haha.gif[/img] Sam

Re: Correct me if I'm wrong ............
 

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]

Re: Correct me if I'm wrong ............
 

[ 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]

Re: Correct me if I'm wrong ............
 

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]

Re: Correct me if I'm wrong ............
 

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!

Re: Correct me if I'm wrong ............
 

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]

Re: Correct me if I'm wrong ............
 

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]

Re: Correct me if I'm wrong ............
 

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!

Re: Correct me if I'm wrong ............
 

Thanks Rob/Jim;
I think I have a little better understanding of the LSA and LCA. When I installed this cam I was looking for better driveability, not for Certified Stock!

I think the stock LT1 cam is 116 degrees of LSA. Is it possible to have the LSA and LCA both at 106? It doesn't seem possible to me, but my cam card doesn't show LCA, it only says 'these specs are for cam installed at 106 intake center line'.

The idle seems fine to me, but I would have to be standing next to a 182 cam'd LT1 to really notice any difference.

So, does the 106 LSA give me more bottom end? Does that limit the upper rpm range?

Re: Correct me if I'm wrong ............
 

Ok, Marlin, I just got off the phone with both Crane and Comp Cams, and here is what I found out:

Crane Blueprint Cam (1970-1 LT-1):
Part# - 969551
Grind# - 3972182
Gross lift (int./ex.) - .459"/.485"
Duration (@ .050", int./ex.) - 242/254
LSA - 116
LCA - 110
Notes - 1 , 2

Comp Cam (your current cam):
Part# - 12-511-5
Grind# - CS 272 TLS-6
Gross lift (int./ex.) - .510"/.530"
Duration (@ .050", int./ex.) - 242/250
LSA - 106
LCA - 106
Notes - 1 , 2

Now, some observations. What jumps out at me first, and what I questioned above, was the LSA difference between the 2 cams. The original cam had an LSA of 116, which should have a little "lope" to the idle, yet still have plenty of vacuum. Your current cam, on the other hand, has an LSA of 106...this is extrememly tight, even for a race cam! The Comp unit should provide a VERY lopey idle, and would be poor in the vacuum department. I asked both Comp and Crane about that 106 LSA, and they both said "no way" for a street car, and that with that tight of an LSA that you would have little or no vacuum and it would be a dog on the low end. But, what confuses me is that you said the idle is fine and you have plenty of vacuum? The Comp unit is clearly directed at top end, which would be fine if you are looking to race on the skinnies, but it's not necessarily what you were after. The LCA of the Comp unit is advanced 4 degrees ahead of the original, which would help with the bottom end, and all of the other "minute" differences (lift, duration, LCA) would have small effects, but the difference in LSA is what has me confused...am I missing something here fellas? Oh, just curious...did you assemble the engine and put the cam in yourself? Not criticizing, just curious!