AirBusPilot

Keep in mind “closed loop” versus “open loop”.

In open loop, the O2 sensors are not read. The engine A/F and timing are written in the engine management software. Meaning, at full throttle the engine switches to open loop and doesn’t rely on O2 readings.

Closed loop occurs at less than full throttle and only then are the O2 sensors utilized, as it makes adjustments to A/F, timing, etc.

Part of what a “tuner” does is rewrite the open loop engine management coding for better performance.

I have no doubt the next wave of engine management systems will self tune for any engine demand.

Edited to correct terminology.

Dynra Rockets

That was me. My point was why complain about a decision the factory made 44 years ago. Either put a cam in that better fits the low CR or add more CR for the existing cam.

I don't think a lot of people on this forum think the L82 engine is comparable to a modern designed engine. In its day it was the fastest thing around. Your argument is like telling the old timer with the hopped up flathead ford that that their engine was a bad choice because two cylinders shared an exhaust port.

63mako

The L82 short block in stock form with a set of AFR 180 64CC heads, A .015 shim head gasket, Headers, good exhaust and an intake upgrade will make 400 HP with that cam, have the mannerisms of a 222 duration cam, get decent fuel mileage and pull past 6000 RPM. What is so horrible about that? It made 350 HP in a 70 350 with crap heads.

resdoggie

I think its the other way around. Open loop kicks in at wot and the fuel maps are not used. I played with the Harley screaming eagle software maps a few years back. In closed loop, they had a ranges for the different parameters that you couldn't exceed but the maps were ignored for fuel in open loop which occurred at wot.

Priya

The Isky cam at the link is 44.5 degrees of overlap. Isky used to have a much more complete list of valve timing events on its site for its cams but don't list much now.

AirBusPilot

It’s been awhile, I may have misspoke on which word is correct, but how I described the operation is correct. At full throttle the O2 sensors are out of the loop, and don’t do anything. To make changes, they have to be over written on the stock tune parameters.

EDIT:

Yep, “open loop” doesn’t rely on the O2 sensors, just a written engine map, “closed loop” is part throttle and makes minor adjustments using the O2 sensors.

http://www.enginebasics.com/EFI%20Tu...Loop%20o2.html

cv67

Hope they stick around, if I had the dough Id buy one of ea of their many good grinds. They are old but work, love the way they pull.
stuck a set of smogger 882s on a 9.5:1 cheapo bottom end, performer rpm and Isky 270 w/edelbrock carb in a not so light 82 shortbed that truck had super strong midrange, made a great daily driver

NewbVetteGuy

Not a horrible match for that cam with a static CR of 10.2:1.


BUT, you can definitely gain an easy 30 hp (this is a SUPER rough guestimate I haven't dyno sim'ed anything) and have more low rpm torque, vacuum for brakes, and a small fuel economy improvement with a better cam.

Those AFR heads come with good springs that can deal with faster ramps and there's 20 more CFM of air available on AFR 180s from 0.400" lift to 0.500" lift- so there's no added cost beyond just buying the better cam/lifters.

The L82 is a terrible match for low static compression ratios; it's better with 64cc and 58cc chambers, but a faster ramp with a bit more lift for AFR heads is still much better all the way around.


Hmm... L82 cam with 64cc Iron Vortecs might be a really good match...
Especially as their peak airflow is at even lower valve lifts still from the AFRs and they're valve-lift limited.


Maybe there is a realistic, common scenario out there where doing a head swap on a L82 and leaving the L82 cam in place makes sense...


Adam

NewbVetteGuy

I think you misread my intent; I agree completely with what you're saying. My point is also "either put a cam in that better fits the low CR or add more CR for the existing cam" -I would just add to that, that if you're adding more CR by getting new heads you probably have a lot to gain by replacing the L82 cam, still.


My intent is not to "complain" about a decision made by the factory 44 years ago, but to try to push-against a pretty commonly repeated statement on here which is "The L82 cam is a pretty good street cam" (for most builds that we see on here) and to push back using the data.

The L82 is NOT "a good street cam" in 2017 terms; definitely not for 76cc chambers and even most 64cc street heads would such much better street manners and low-end torque, vacuum and fuel economy with a modern grind that gets DCR into an acceptable range.



A pretty weak strawman argument; a false equivalency; borderline intellectually dishonest. I've not commented on the L82 engine; only a single, very replaceable component. My comments are not on how bad the engine was, simply how poorly matched the cam was for the motor and "street" goals; that's pretty undeniably true and the data supports that statement. The DCR is abysmal.

I know they were trying to ensure that they hit the EPA emissions goal first and foremost and did the best that they could at the time, but in order to do it, they chose a cam that was a really terrible match to the engine with crappy cam timing and ignition timing. These L82 engines have HUGE potential because the components are great (other than teh cam) and the from-the-factory tune and exhaust were so horrible from a power perspective. The cam is one of the components that's a part of the over-all "smog package" and should also be removed and replaced from a performance perspective.


The L82 cam, in an L82 engine should not be considered a "good street grind" and definitely not a good match for the engine or typical street goals; the L82 cam is an integral and major power-stealing component in the "smog package" that came from the factory with the mid-to-late 70s Corvettes; it makes the car LESS streetable.

NewbVetteGuy

I externally process information and it's taken me 5 pages to get there, but I think my point can be summarized that the L82 cam, in the L82 engine should be considered a "smog / emissions compliance component" and not a performance component.

It helps emissions and hurts performance and streetability in these motors; the majority of L82s would be better off with a modern grind with a far better DCR. There are exceptions to the rule and if you have 64cc or smaller combustion chambers, ultra thin head gaskets, and change the cam timing from being retarded to advanced or straight up, the L82 cam certainly gets way better and can put up better #s, but that doesn't make the L82 cam "good" or even "Streetable" in 2017.


Adam

Priya

Given that it was basically the L46 cam I would think it actually was pretty poor at controlling emissions and GM could have had even better emissions control with a cam designed specifically for the lower compression ratio in the L82.

I think you make a pretty convincing argument but perhaps a little strong on the tone.

resdoggie

Maybe GM knew their market better than you think they did. They gave L-82 owners a great platform - forged crank, pistons, 2.02 heads, 4 bolt mains L-46 cam - that they didn't need to for the given power rating. Way over built unless of course you up the cr, port the heads, add headers. "Hey, I'll buy that L-82 and make those couple of mods!" Well, maybe GM did think that way. Sold gobs of vettes in the smog era. Wonder why?

NewbVetteGuy

That's a good thought. I put Jeep buyers in that exact same market / mentality today. Who's got a stock jeep? No one!


Adam

63mako

Oh yeah, you can definetly make more power with a modern cam. Durability comes into play for some builds. The slow ramp is MUCH more durable long term. Hydraulic intensity was engineered into these to give a 100,000 mile life expectancy even driving it hard. Lighter springs required, less valve float, ECT. The modern grinds are competing for sales. The way to more dyno power is faster ramps. This is the race to sales now, peak power results sell cams. A hydraulic intensity of 54 is considered the highest safe intensity on a flat tappet cam. This is the difference between advertised .006 and duration @ .050. This means a 276 cam can have a maximum duration@.050 of 222. That is a maximum. Many modern grinds are faster. Many solid lifter cams are way faster and they have far surpassed the engineering safety margin. A 1.6 rocker loads the lobe lifter interface harder as do higher rpm and heavier springs to control fast ramps and rpm. You start combining these long term durability drops drastically. The vortec head on a base L82 is probably a good, safe, durable build with excellent power and operating range. We are bench racing here but it is a good thread. Look up hydraulic intensity David Vizard or Harvey Crane hydraulic intensity.

cv67

Lots of those "older" grinds lasted a long time cause they didnt go overboard. Its when you start putting a lot of spring on them or these "extreme" ramps trying to get a FT cam to act like a roller you run into problems. Ask the designer of that line about them see for yourself. Went from the mega cam line to the XE when they came out there was a slight difference but wasnt impressed. Sure was a pizzer when they failed quickly.

Is risking failure really worth 10 lbs of torque or an inch or two of vaccum hell no. Its just a gimmick to sell parts thats all people still buy into it.
Ill take an older but known good grind any day over the "koolaid". Look for power elsewhere or just build bigger
Its amazing GM is building 400+hp engines with .600 lift AND warrantying it young people are spoiled and dont know how good they have it

Used to take 11:1 some heavily ported 2.02 heads, a "292" cam single plane to even come close to 400hp.

Now a small modern head and cam will get it done


if youre stuck for money go get a boneyard 400 a reasonable flat tappet cam and cheap modern head the car will haul azz worry free.
Wish they would start making that block again they would sell like hotcakes if they could price it under a grand

resdoggie

11:1 is now common these days.

dabreeze

So , bottom line , in todays world is it not even worth the time to do any bolt-on mods to my 78 L48 ? If so , what are the ones that you would actually feel and could be done by one of us old school sixty's motorheads...? I've been through the go-as-fast-as-possible phase , now , in my old age , I'm looking for a nice stock everyday driver/cruiser . Stock ( which includes bolt-on's ) is king...

TedH

It is amazing what a distributor recurve can do to waken a small block. Stock, advance curve is for emissions compliance. Recurve for power can add 50hp!!! Accomplished with an Accel performance replacement HEI and performance curve.

Along with better heads, cam, intake, carb jetting, headers/exhaust, compression and you get all kinds of complimentary benefits.

Toss in a 700R4 with lower 1st gear and non-stock 3.54 gears in back and it gets really fun.

My warmed over L48.

TedH

In this order:

1. recurve for power
2. re-jet carb to compliment the recurve
3. ensure all vacuum connections are tight and not leaking (loss of vacuum hurts power)
4. If you can, limit the vacuum lines to those only essential for advance signal from carb, PCV and EVAP (elim the thermal actuator lines, thermal switches in intake, EGR, EFE actuator).
5. K&N air filter with freshened cold air intake and seals around radiator

These improvements alone will make your L48 embarrass any stock L82.

To have more fun, see my signature.

7t9l82

Assuming the L-82 had a spark plugs missing. What if lhe l--82 had the same thing done to it?