NewbVetteGuy

I just attempted to generate the DCR for an L82 from the factory, and unless I did something horribly wrong the DCR fully explains why these things have no low end and can't do burnouts.

Static CR: 8.91:1

8 Cylinders, 4" bore, 3.48" stroke, 76cc combustion chamber, Deck clearance 0.025", Gasket Thickness 0.017", 4" gasket bore, 6cc valve reliefs, connecting rod 5.7",

Advertised Cam Duration: 346?!? For a 222 @ 0.050" duration?!?!? Holy Moly these were insanely lazy slow ramps.

LSA: 114

Advance / Retard: -3 degrees (3 degrees retard ground in for SMOG-era L82s).

This is also assuming a timing chain that hasn't stretched AT ALL and we know that these things can stretch and cause an additional degree or two retard.

DCR: 4.14:1


I know the cylinder pressures will be the equivalent of about a 1 CR improvement higher because of iron heads vs. aluminum heads, but, dear god, the seat-to-seat duration of these old flat tappet cams is just HUGE for the static CR and the retard just makes it far, far worse.



I can't believe I bought the old "The L82 cams are pretty good street cams" ---yea for the 1960s, with 1960s compression ratios, maybe.

These things need new cams. Look a modern grind seat-to-seat duration with teh same @ 0.050" 222 duration and the cam installed straight up or advanced a few degrees and it should be a world different.


Adam

REELAV8R

Back when my L-48 was still the stock engine and I had added hooker side pipes and re-curved the ignition and rebuilt the carb It was running pretty good for a stock engine L-48.

I came upon a stock config L-82 on the freeway and we sort of raced them down the freeway several times.
Each time my L-48 beat the L-82 off the line and through the acceleration.
His was a 78 L-82 completely stock.
So, yes the L-82 in stock config is a bit of a dog. The L-48 was no barn burner for sure, but with slight modification it could take a stock L-82.

Where did you get the info for the seat to seat duration? That may need to be converted to .006" duration for a fair comparison.

Dynra Rockets

Welcome back from your 35 year coma.

Yes, an L82 cam is a L46 cam with a touch of advance.

Yes, The L82 cam does not work well with low CR, but in the mid 70s when it was introduced that's all they had to work with.

Yes, adding CR to an otherwise stock L82 wakes it up nicely.

Yes, a modern cam profile will outperform it easily, apples to apples.

stingr69

The typical DCR guidelines are for typical aftermarket cams, not factory grind ramps. No way to compare GM ramp grinds to aftermarket. Apples and Oranges.

You can run about 10.5 actual CR with the L-82 (L-46 350/350) cam, iron heads and run pump gas. It works very well, idles close to a stock 929 cam, and is reliable. The L-82 suffers from low static compression and poor flowing heads.

Steeper ramps do make a little more power but that comes at the expense of reliability and durability. Upgrade the whole valve train to match or just go all the way to a roller if you need more power than that. Just a compromise.

jb78L-82

Just a touch of reality here:

The Base L-48 78 C3 was a dog especially the automatic....0-60 L-48 auto in 1978 was 7.8 sec with a compression ratio of 8.2:1 with a low lift passenger car cam which is what the L-48 essentially was.

The L-82 4 speed in 1978 was the fastest American production car that year with the L-82 4 speed bone stock with 0-60 MPH time of 6.5 seconds, which was pretty darn respectable back then! In fact the only cars faster in 1978 were the Porsche Turbo and the Ferrari 512. The 79 L-82 auto ran 6.6 sec 0-60 mph.

I drove my friends L-48 auto 1980 and it was a dog compared to my 78 L-82 4 speed..no comparison.

Headers, duals and timing adjustment on an L-82 and the car was even quicker...bone stock motor.

My 78 L-82 with no emissions, shorty headers and 2.5 duals did 233 RWHP with a weak #6 compression cylinder..fully healthy it would have done at least 240-245 RWHP...A base stock engine L-48 could NEVER achieve those types of numbers.

Sorry!

63mako

That cam was designed to run 10.25-11 to 1 compression. Drop it below 9 it is overcammed and a dog in normal operating RPM. At high RPM it is much better but most street cars spend 95% of their time out of the true power range of the combination.

cv67

the quickest production (american anyway) back then was the dodge lil red express pickup..the one with the diesel stacks

Had a 360 engine and ran 14s stock.
Gm had to make puky ramps for 1)emissions and 2) so they lasted they had thier hands tied.

Dynra Rockets

Very true, but you really had to wind the sh*t out of it and power shift to get those results.

Tooling around town and punching it at 2500 rpm to 50 mph and the L48 felt quicker than the L-82.

jb78L-82

Yes true with the L-82 auto which was lazy down low since the revs were kept down and poorly suited to an automatic tranny but not the case with the 4 speed and 3.70 gears..........................L-82 4 speed cars with the 3.70 gears are a very different car than the L-82 auto and the L-48, either tranny.....

63mako

True, 4 speed and 3.70 gears allow you to get into the powerband pretty quick.

NewbVetteGuy

This is nonsense. DCR to DCR comparisons are literally apples to apples.

Static CR accounting for the intake close event (DCR) accounts for the two most important indicators of cylinder pressure.


If I have an L82 engine with the GM L82 CAM and a 222 Duration @ 0.050" and a 360 "Advertised" Duration (assumption 0.006") and do nothing but replace that cam with a fast ramp cam that has a 222 duration @ 0.050" and an "Advertised" duration of 280 or 300 (and maintains the stock ICL of 112), it's going to have a DRAMATICALLY improved DCR/Cylinder Pressure / Torque and far less overlap. -This is about as "apples-to-apples" of a comparison as you can get.


The L82 cam is horribly matched to the static CR and L82 automatic TC stall of 1,800 RPM; GM should've made a new cam for the L82 instead of reusing a CAM that was designed for a high static CR; they also shouldn't have installed it 3 degrees retarded.


The L82 cam was ground/installed 3 degrees retarded, not advanced.



Adam

NewbVetteGuy

Example: Same 222 @ 0.050" duration with a 290 deg advertised duration and a 3 deg advance instead of a 3 deg retard = 6.61 DCR.


Dramatically better.

Dynra Rockets

GM should have done lots of things. They should have used aluminum heads and intake manifold in 1973, they should have offered a 5-speed in 1978, they should have never introduced the Aztek. This list goes on...

Either add more CR to your existing L-82 or put a different cam in better suited to 8.2CR, but complaining about decisions made 45 years ago (when there was a poor economy, gas crisis and new emissions regulations so no budget to do any of those things) is nuts and will get nothing accomplished. As stated above, even with that camshaft they were still about the fastest thing on the road at the time so there was no incentive to make it better ether. It is what it is.

I regularly shake my head at designs I see in cars but I wasn't invited to give my opinion in their planning sessions.

7t9l82

An L-82 with an ignition recurve and a free breathing exhaust and some carb tuning was a low 14 second car with a manual transmission you would be high 13 second range. I have never I repeat never driven an L-82 with the timing adjusted that wouldn't burn the tires.
The lil red truck was indeed faster mainly because in 78 it lacked a catalytic converter, there was about 35 horsepower in a dual exhaust.
The cam in the L-82 is capable of 12 second quarter miles in a c3 Corvettes so I don't see it being that bad.
At some point I will run my L-82 stock cam short block down the track and I'd bet it will suprise alot of people
​​​​​​

NewbVetteGuy

I think you are confused on the point of my post; it wasn't to complain, but, as the title strongly suggests, to suggest that the prevailing opinion that "the L82 is a pretty good streetable cam" (in these lower compression 350s) seems to not be so true far more streetability and power is possible with a modern cam grind.

-I've heard both of these opinions touted on here, but seeing a DCR of 4.1 is just pretty shocking and makes the lack of low-end and all the complaints of an inability to do a burnout make sense.


Adam

NewbVetteGuy

The myth of the L82 cam being a good street cam just needs to be killed.

Voodoo 262/268 cam for comparison:

Advertised Intake Advertised Duration: only 262 compared to the L82's astronomical 346
Duration @ 0.050": 219 --ALMOST hits the L82's 222 duration still here
LSA: Same as L82 @ 112, but advanced 4 degrees instead of retarded by 3
RPM Range: 1,400-5,800: Appropriate for both the L48 autos' 1,600 stall and the L82s' 1,800 stall.

DCR: 7.43:1 compared to 4.1.


Friends don't let friends run L82 cams, at least not with L82 heads and static compression ratios...

L82 cams belong in museums behind glass.


Adam

63mako

The L82 cam advertised duration is figured at .000 lift, right on the ramp to .000 going off the ramp as speced by GM. I have seen this number quoted at 312 also. Modern cams are rated from .006 on the ramp to .006 going off the ramp. I believe Crane uses .004 to .004. The beginning and end of the ramp is a gradual slop that intensifies so the advertised duration numbers are very deceiving on the GM cams if you use the advertised duration base circle to base circle. This is why Duration @ .050 is used for comparison purposes. The Factory blueprint 3896962 cams are advertised at 292/288 which is at .006 lift. This is what you need to use to compare and figure DCR comparisons. This also seems to correspond to the numerous forum members I have talked to regarding detonation on L46 engines. Right at the verge with Iron heads, factory compression running premium fuel and optimal timing. Most need to dial the advance curve back a touch. I would like to see someone actually measure the Chevrolet Performance 3896962 from .006 lift to .006 with a degree wheel and get an ACTUAL number that is carved in stone but I have never been able to find that information. I am betting the 292/288 @ .006 lift is really close. A guy running a stock L82 bottom end with good gearing swaps out to 64CC aluminum heads or modified Vortecs and a .015 shim gasket can add 1.6 rockers to that L82 cam and have a very good, durable combination that will pull well to 6000 RPM.

NewbVetteGuy

FINALLY, someone made sense of what I'm seeing. Those DCR #'s just didn't make any sense until this post. Totally agree; need 0.006" duration #s for the L82 cam.

That number makes sense; 300+ just made no sense at all.

I like your 292/288 guess, too. Woudl be so great to be able to make an actual comparison.


Adam

REELAV8R

I gave you reality. If you can't accept it that's your issue not mine.

It was a STOCK automatic 78 L-82 vs my automatic 77 L-48 slightly modified.

The results were what they were.

You understand that peak HP numbers really don't dictate street performance, right?

63mako

The strong points of the L82 cam is it makes 350 HP in a higher compression engine with iron, crappy flowing heads. With better heads, intake, headers, exhaust and tune it has 400 HP potential in a 350 . With the late intake closing point and 114 LSA it allows you to run 10.5 to 1 compression or 11 to 1 with good quench and careful tune with IRON HEADS while getting decent fuel mileage. It has the mannerisms and RPM range of a 222 duration cam with extended RPM potential and a flat torque curve because of the 114 LSA. It is durable because the ramps are a little slower, less hydraulic intensity, good if your running flat tappet. It is an ideal cam for some builds.