Just out of interest, I'm trying to research the specs of a standard L48 cam - ie the type that would have been in my 80 before the previous owner swapped it out for a Crane 290.
The GM service manual for the 80 vette has only very limited details - ie the cam lift and that's about it!
Is there another source of info, more specific to the engine, that would have these details?
I'd also like to see specs for the L82 Cam, just to see how it compares to the Crane cam currently residing in my motor....
Can anyone point me to a good publication??
:cheers:

 

L-48 not enough cam for a Corvette. L-48 about 195 202 @.050 .390 .410 114LS

L-82 224 224 @.050 .450 .460 114LS

 

Cheers Ganey,
I realise the L48 isn't much of a cam for a vette, the stock 1980 figure of 195 bhp speaks for itself there, doesn't it?!
That kind of power from a nearly-six-litre engine is a bit poor to say the least. Still, plenty of scope for us to open them up a bit!

Hate to sound thick, but can you elaborate on your figures a bit..
195 202 - this is duration right? I assume this is 195 for exhaust and 202 for inlet?
.390 and .410 .... lift, yeah?? Is that at Cam or at Valve?
And 114LS, sorry but I can't even hazard a guess what you mean there :)

I'm sure those numbers come from your head, but there must be some literature out there (as i said, GM manual is quite limited) do you know of any books etc?
Cheers
Theo :cheers:

 

LS is lobe separation angle. Check out this link, I found it informative for a cam noob like me.

http://www.chevyhiperformance.com/te...148_0405_lobe/

 

The 195 is the duration at .050 of tappet lift. Most cams are measured this way. The .202 is for the exhaust. Most of the time the intake is listed first then the exhaust. The lift figures are at the valve. For a Hyd. cam these are in theory and will vary slightly but close enough. The stock L48 cam is a dowel and is good for passenger cars but not for a Vette. Slide a little more aggresive cam in there and you will be pleased.

 

Ok, so the the intake and exh. lobes have different lifts? Never seen that before, but then I'm FAR from expert here, as you can see!

I assume the lift figures are with the stock rocker ratio? That's 1.5 isn't it?
I do actually have a slightly hotter cam in her (Crane 290, installed before I bought the car) - i was interested really in seeing how different it is to the L48, and how close to the L82.
As a matter of interest, the Crane 290 is 290deg advertised duration (obviously!) and without the data sheet in front of me I have to go from memory, but I think 216deg at .050 lift The lift is .454 with a 1.5 rocker ratio.

Cheers for all the info - -but the one question still remains, where is there some published technical data for the L48/82 cams?? I just want some figures to get a hard copy of !
:cheers:

 

Hi Theo,
That link should explain cams well. I think I've also got something I found on the Net tucked away somewhere. If I find it (& it's not a copy from that link) I'll email it to you. I'd take Ganeys' figures as fact, that man knows his cams. The L82 cam specs were interesting, kind of makes my 210/216 .440"/.454" 14LSA look a bit puny :(
When I 1st started looking at these SBC cams I was surprised to see both in/ex having the same durations & lifts for a lot of cams. It was completely alien to me, but I guess it depends on what you're used to :)
:cheers:

 

Hi Paul, hows tricks?

I was surprised at the figures on the L82 also, my Crane cam is definitely 216 at 50 thou lift, I've just checked the specs online. So by having that cam installed, I'm essentially approaching L82 with my 48, although obviously other components are not to be forgotten. Not sure what the LSA is on the crane though. Did you mean 14LSA or 114LSA, in your figures??
In short, the cam i have is a good reason to re-curve the dist, which is next on the agenda!

Cheers!
:cheers:

 

Hi Theo,
Tricks are OK, life is just too busy though!
Yep, sorry, 114LSA (keyboard is playing up - must be all the coffee & crumbs in it). Posted just before finishing work & drove home wondering why I put less cam in than a stock L82 had? Then it came to me, Eureka! What the figures don't tell is the opening & closing rates of the lobes. I know that my cam is fairly aggresive in this area, as it's designed to keep a high manifold vacuum at idle to keep the computer happy. So, a cam with 224 duration @ 50 may not be as "good" as one with, say 216. If the 216 cam accelerates the valve open to max lift asap (or as fast as a hyd lifter cam can), holds it there as long as poss & then slams it shut (decreasing the closing rate dramatically just before it seats) then it may well flow more than a 224 cam that opens & closes the valve at a really leisurely rate. I guess the telling info would be the integral of the opening/closing curve ie the area under the curve, but I'm not going to try to work it out :lol:
So now I'm feeling a lot better about my cam :D No doubt somebody will now post & tell us that a stock L82 cam is better than both our cams :lol:

I can't recurve my dist as it's computer controlled. What I did do was swap the chip out for a better one. Got a small power increase. I then advanced the base timing (effectively doing a full re-curve like you'd do) & wow, big difference. Don't know if it's boosted the power, but the off idle response was massively improved. Do it, you could be pleasantly surprised (the exhaust note will sound a lot "healthier" as well).
:cheers:

 

Reading your post I don't think you quite understand the duration. The 216 is a measure of how long the valve is off the seat. So 216 at .050 means that the valveis off the seat for 216 degrees of rotation. 226 at .050 is off for 226 degrees of rotation. One being better than the other depends on the engine combo. The longer the duration the higher rpm the motor will spin. A short duration will give good throttle response and low end torque where as a long duration will be soggy on the bottom end but really scream at high rpm. There is a whole lot more to this than that short explanation but cam Also the duration has nothing to do with how fast the valve is opened. Most solid cams have a faster rate of opening than hyd. cams. You can have two cams with 225 duration but the rate at which the valve opens is different. A solid roller keeps the valve at higher lift much longer than a hyd. flat tappet. You have to look at the area under the curve to see how high and long the valve stays opn.


[Modified by Gordonm, 7:44 AM 4/23/2004]

 

My L48 is equipped with the Crane Energizer 272-H10. This cam produces CRISP throttle response and combined with the parts listed in signature, this car smokes the tires. It is so 'bad' now that I have to ease into the accelerator off of the line to get decent traction. The engine is a torque pig (very high torque compared to the L48). As you can see, the Rear Wheel HP and TQ numbers exceed even what the L82 could deliver at the flywheel so this engine is now much stouter than both the L48 or the L82; approx 300hp/380tq at the flywheel assuming drivetrain losses with the 700R4 in the neighborhood of 22-25%.

So, if you are considering a little less can than the Crane 290, I'd strongly recommend either the 272, 278 or 280 Energizer from Crane. BTW, these are single-pattern cams; same lift duration on intake and exhaust and have closer lobe separation angles (110 if I recall correctly)so you will get a little less vacuum and more 'rumpety' idle characteristics.

 

Gordon,
I understand duration, but what I'm tying to say is surely the opening/closing rate of the valve has a large part to play eg. if one cam had lifted the valve 0.1" 10deg after it first started to open it, whereas a different cam had only lifted it 0.05" after 10deg of opening it, then there'd be greater area around the valve head for the charge to enter (or exit) with the 1st cam during all points of the opening phase (or closing phase in the case of the exhaust)? And then there's all the extra considerations of where the piston is in the bore & the pressure differential etc.
An example is a Kawa 1360cc engine we were playing with years ago. The owner had a cam in there that was opening the valves at such a time as to be on the limit of them hitting the piston crowns. He wanted an ever bigger cam and, after a while, found a cam that forced the valves open a lot more aggresively. The overall specs on duration & opening/closing points were the same as the existing cam, but because the valves were opened/closed at a higher rate, the valves were more open at the same angular position in the opening/closing cycles, giving more area for the charge to enter/exit. Hope I'm explaining this OK? We had to lighten the valve gear & fit stronger springs to cope with the very aggressive ramps, but the net result was more power, proven on a dyno. Unfortunately, the owner missed a part of the small print saying that the cam was manufactured for drag racing only. He was supposed to infer from that info that it hadn't been nitrided/case hardened for street use & 400 miles later there wasn't much activity regarding valve lift! And the metal from 8 lobes had gone round inside the (expensive) engine :(
I'm used to what you call flat tappet cams (normal cams to me, hydraulic lifters are new-fangled stuff :D ). If I've used a cam with very aggresive ramps then I have to sometimes use a different radius on the lifter (as well as all the other stuff with the vavle train). What I'm wondering is: Is there much variation possible with opening/closing rates when using hydraulic lifters. Or is the rate severely limited (scuffing/pick-up between the lifter & ramp), meaning that for what I'd call a mild lift rate, a flat tappet or roller cam would have to be used?
Or think of it this way. If I had 2 cams, one of which gently opened the valve up to full lift & then gently closed it, & the other that belted the valve fully open & held it at full lift for as long as possible, before slamming it shut (a valve seat killer) you'd be able to draw graphs of lift against angular position of the crank/cam. The interesting parts of the graph would show an upturned "V" for the soft cam (gentle on mechanical parts, quiet operation, crap performance) & almost an upturned "U" for the other. Total area under the graphs would be obviously different, with more gas able to pass the valve for the cam with the U graph. In the real world cams aren't like this, but I hope I've explained myself a bit better?
:cheers:

 

Yes, seems like its all too easy to get carried away with numbers here, when what I guess you really need is a full profile of the cam, to integrate as you mentioned. That's why I originally asked for any detailed info on the L48/82 cams. With a full profile, i could use excel or matlab or something to fit a function to the valve lift profile and then integrate it for the lift vs Crank angle curve area. The info must be out there somewhere, probably from someone who's worked it out themselves with a degree wheel and a Dial guage. Oh well, I'll just have to keep an ear to the ground...
I suppose it's not worth having a cam that opens the valve too much quicker than the L82, because then the stock valvetrain becomes the weakest link, being accelerated quicker than what it was designed for.
As for the timing, I notice the L82 is 12 degrees static, plus 16 mechanical, all in by around 2000 rpm. The L48 is 6 degrees static, plus 22 mech, which doesn't fall in until something like 4500.
So I'm hoping it will be a really good "bang for buck" improvement.
I wonder, with your 81 can you reprogram the chip yourself, is there any software for doing that?

You could get into the joys of chip mapping then - probably need the dyno for that.....

:cheers:

 

TedH,
I'm not actually considering a cam, as I already have the 290 installed. I was just looking to make a comparison between the L48/82 cams and the crane 290.
I was informed by the previous owner that the motor is 350 hp at the flywheel. BUT I make apoint of not believing figures like that, even if they are meant honestly. SO i don't know what the real figure is, but would say it is safely in the high 200's. It's enough to push her to 60 in a ****** over 6 seconds, as measured with a race technology performance meter. But I just don't know if the dizzy has been optimised with that new cam, and having not put a timing light on it yet, it could still be in stock L48 trim. Hence the recurve kit.

 

So is the L82 and the old 300hp cam's close to the same in spec's ?????
i don't know them off the top of my head :confused:

 

NO! NO! NO! the L82 cam is actually slightly bigger than the popular 350HP 327 motor camshaft. The 1970 300HP 350 motor IS an L48 engine with the small cam, it makes it's power with it's 10:1 compression ratio (too uch for today's pump gas.) There are far better alternatives in the aftermarket than any of the cams discussed in this thread.

 

Another important issue esp. for a street motor and
throttle response is your static or mechanical
compression ratio and it's relationship with the
intake closing event of the cam - the later it closes
the more compression pressure it bleeds off.

So you need to take into consideration both your
static compression ratio and your cam opening
and closing events, esp. the intake closing, to
give your dynamic or running compression ratio.

I've got a handy calculator program to figure that,
will post it or a link if I can find it. Also has some
info as to what to look for.

The wider lobe center angles are known to generally
give a broader torque and power range with a little
less peak power than the closer centerline cams.
Cams with more duration on the exhaust are usually
best on the street where you have more exhaust
restriction than with open headers. Engines with heads
with better flowing exhaust and without a need for a wide
torque range (i.e. at the strip) often work better with a
close lobe center cam that's even on intake and exhaust.

 

Here's a link to figuring your dynamic comp ratio,
and some other stuff.
http://cochise.uia.net/pkelley2/index.html