L81 Camshaft selection... What do you think?
 

I think I finally found the kind of cam I need for my L81 but still hesitate between the CompuCam 114132 and the COMP Cams XE256H:

114132: Duration 210 int./216 exh, 0.440 int./0.454 exh. lift, 114 lobe separation and operating range 2000 - 5000.

XE256H: Duration 212 int./218 exh, 0.449 int./0.456 exh. lift, 112 lobe separation and operating range 1200 - 5200.

I believe the ratio for the rear axle is 2.72:1. And I want to keep the Computer and maybe go TPI in the future. Does this look acceptable as far a compatibility?

What do you think Crane or Comp cams?
Thanks

:cheers:

Hi,
I've got the 114132 (the camshaft formerly known as CompuCam 2040) & the computer is happy with it. Am I? Well, you're never happy once you get used to it :D The cam isn't what I'd call a performance cam & I got far more seat of the pants dyno effects from fitting true dual exhausts. However, & this is crucial, the cam is designed to be used with a decent CR & I've still got the stock heads & pistons, so there's no surprise that it didn't give a big increase in power. An ex forum member has the same cam in conjuction with a set of decent heads & is very happy with the power spread/increase.
A forum member ran a Comp Cams non computer cam with good results. I think it was a 268H???? See if you can get hold of Dallanex (Justin) for more info. Choice of cam for the L81 only really depends on what manifold vacuum it holds at idle (within reason). If it gets too low (the lopey area) the computer thinks that the throttle is open, so starts supplying more fuel, causing a bog when you do open the throttle. The problem is that I can't remember what the min vac level must be & a lot of the L81 owners have long since left the forum, so it would be worth searching the archives (there's bags of info on L81s in there somewhere).
Something worth doing to an L81 is to advance the base timing from 6BTDC to about 12BTDC (or 2* under the point where pinging starts occuring). I've set mine to 11BTDC & it gave much better throttle response, specially at low speeds.
I'm away for 3 weeks so it would be worth seing if sensie is still around as he's a mine of info on L81's.
:cheers:

Thanks a lot for your input UKPaul, this is great information. I went around the archives in this forum and there is a lot of information.

I just called Comp Cams hot line and the guy suggested a smaller cam to be able to run the computer. He thinks that the 256H might be too big :ack:

The one he suggested is the XE249H: duration 206 int./212 exh, 0.434 int./0.444 exh. Lift, 112 lobe separation and operating range 1000 – 5000

I guess I’m finally going for the CompuCam 114132 that you, UKPaul have. It looks like it works well on your L81 and the price tag isn’t that bad. That will be my first major retrofit on an engine ever! :D

Looking forward to do it ….

:party:

Do some research on the sites (www.chevelles.com, www.camaros.net, etc) before you throw your jack on an XE cam. There's a high failure rate and many of those that do survive break-in are reporting valve train noise,..though the grinds you're considering are pretty conservative.

Good luck!

I also heard a lot of good thing about the GM151 (GM P/N#3896962): 222/222 duration, 450/460 lift, and 114 lobe separation. I know it's a pretty old design but is this camshaft computer compatible? It seems to be a little bigger than the Compu Cam 2040.

Does anyone run this GM151 cam with the computer? I guess the main concern would be to have enough vacuum at Idle.
Thanks

:cheers:

X962 cam known as an L82 cam ... 'cuz it is. Yep ... it's an OLD design. Take a look at comp's other cams that don't have such aggressive ramps; ie "dual energy" 265DEH or 275DEH.

-edit- summit's K1103 kit will probably work as well as any of the ones listed so far ... right now it's $63 including lifters.

Not saying they won't work, but wouldn't a wider LSA than the 110* the DEH's have be advisable with computer control? :confused:

Might want to consider one of summit's cams to use with your computer. Maybe the 1104 or 1106, which are symmetrical. The computer should tolerate those. Great thing about a summit cam is you can get the cam and lifter kit for like $60 or $80.

OE L81 has relatively low compression ... anything bigger than 1103 on street may be too much cam for L81 compression.

As for L81 computer ... L81 is carbureted ... not FI ... not throttle-body ... comp controls ignition timing advance and leans/richens carb. L81 comp does not control ignition pulse timing (rotor & cap does that)nor does it control fuel pulse timing (it's a carb). Seems to me L81 comp is kinda rudimetary & has a rather wide operational range

OK, good info. Wasn't sure whether or not those LSA's posed an issue for this one.

very true. you can throw alot of cam at this computer. it's too stupid to know any better. the only thing you really have to be careful of is too much valve overlap. you'll end up making the computer think it's running too rich and it will cycle the metering solenoid accordingly.
some people who don't visit as often as they used to have been quite happy running up to about 270* and .490 lift with a built L-81. that may be a bit much for a stock L-81 but if the bottom end checks out, it would probably like the 262 alot.

Great input so far guys! Thanks!
I'm still learning all that stuff and don't really want to get a cam that will cause me more trouble in the end...:willy:
How do you determine the overlap? I guess the biggest the difference between intake and exhaust duration is, combined with a larger LSA, should reduce the overlap and so increase the vacuum at idle right? The bigger the lift the more horse power you get? Please tell me if I'm wrong :cry :banghead: !!! Now, what about oxygen sensors and emission?
Although if I get a cam too big with the stock 2.72 rear axle ratio I will not get enough torque to the rear end even though it’s a stick. This won't be good if I want to keep good drivability all around. I‘m not looking for a strip racer but more of a nice cruiser. I’m thinking of upgrading to a 5 speed transmission in a far future so I could really do something with the rear axle....

:cheers:

Street cruiser... Get the summit 1103. PERFECT cam for you. I'm running that same cam and it's great for the street. Now that I have vortec heads and Z28 valve springs I'm thinking of maybe going a little bigger.

I had the Comp 260H in my 81' with all stock fuel and ignition parts and it ran great. True duals with no cats and that came really made the car come to life. I still have that motor laying around somewhere. The stock carb will handle a lot of motor just fine. I ran my stock carb and dist. on the 406 that I have in the car now for 1 year before I got the DFI injection installed and it worked fine there too.


-Justin

You may live in one of many states that have adopted SEMA's custom vehicle registration language into law. If so, you don't have to worry about emissions equipment or inspections anymore, if this isn't a daily driver and you register properly. And, yes, the EPA's on board! Here's a link to the model language...

http://www.semasan.com/images/CustomRods.pdf

to answer your question in simple terms, most manufacturers list the LSA in their spec cards along with the individual intake/exhaust duration. it's not a hard and fast rule but a smaller duration cam, i.e. <270* with a wider LSA 112-114* will typically yield the least amount of overlap. more computer and emissions friendly.
while i seriously suggest you replace the cam as pretty much all the cams GM used in the late 70's to early 80's were very weak iron, an L-82 type cam in addition to a good set of heads like what kalway suggested will give you the best of all worlds. good power, efficient combustion, everything. plus, if you can get rid of the factory cat, even if you have to put something like the random technologies, it will make a world of difference.
BTW, if you keep the factory 2.72:1 rear gears, i highly recommend the richmond 5-speed or even their six speed.

Thanks Clutchdust! This is exactly the kind of info I was looking for... :thumbs:
I have one more question: According to what you said and looking at the Comp 268H (not XE268H) with an advertised duration of 268/268; 218/218 at 050 inch but only 110 for the SLA. Do you think the SLA might be to small for this kind of duration and could create vacuum problem?

Now I'm down to 3 choices, crane 2040, summit 1103, and Comp 268H. Hopefully I will place my PO before the week-end! I will eventually change my heads and I currently have no cat. I guess the stock headers got to go too :lol:

I need to check what TheSkunkWorks was saying about this SEMA's custom vehicle registration thing. That was a great info too…

Thanks!

:cheers:

I have to wonder about the Comp techs that recommend cams. The XE256 will NOT be too much for your engine. I'm running the XE262 with a mildly modified engine and the computer has no problems. I'm pretty sure the XE268 would be fine too, but I do have a bit more compression than stock. I'm sure you would probably be happy with the XE262, but my best advise is to go ahead and spend the money for a roller cam retrofit. With the oil they are making nowadays, you'll be glad you did. I'm probably going to spend more on Lucas and synthetic racing oil than it would have cost to go roller in the first place! God bless, Sensei

I guess I'm going for the Comp268H. I had a 79 with the L82 before and I just loved the way it sounded. Looks like the 268H is the closest to the L82 GM151 accept for the SLA (110 instead of 114). I went through a lot of threads and it seems that the 268H fill fit my application and the computer will work with it. Roller lifter? almost $1000 :ack: ! I think I'm just gonna go easy on my first camshaft swap and go for a flat tapped hydraulics lifters and roller tip rocker arms.
Can I get the 1.6 ratio rocker arms with stock valve springs without binding??

:cheers:

I finally placed my order::hurray:

Comp 268H Cam/ Lifters/ Timing, Hydraulic Flat Tappet + Comp Rocker Arms, Roller Tip, 1.52 Ratio with pushrods + Hypertech Thermostat, 180 Degree + EMP/Stewart Stage 1 Water Pump.

Went with Summit racing, free ground shipping and I'll get a free cap :lol: Man that was a really hard to select this cam! I learnt a lot though

Many thanks for everyone's input! Really appreciated

I'll let you know how it went!

:cheers: