Jebbysan

This are copies of the stock L-48 pistons and they come in at -12 cc. With a .015 gasket, .035 in the hole at 4.020 bore with a 64cc head....you get 9.36 to 1.
These are the same pistons that came in millions of 350 Goodwrench "targetmaster" crate engines.......
The gasket I used is the Fel-Pro shim gasket.....#1094.
I do not deviate from my cam selection at this compression.....if it scares you then go to a 262 Comp piece....a "belly button" all around good camshaft that is very flexible for application.
Compression is good....but don't get too hung up on it at this level.....the stock L-82 had maybe 9 to 1 and a 222@.050 camshaft.....you will see about 15 hp and torque increasing one whole point of compression......now if you increase duration more than this then the compression should be raised to compensate......
Some will pop in here and give you DCR numbers.......I don't pay attention to DCR (Dynamic Compression Ratio) too much for a couple of reasons.....One, the dynamic number does not account for camshaft area under the curve, and two, it doe not account for VE (Volumetric Efficiency) which is how much you can cram into the cylinder at BDC (Bottom Dead Center). The VE of your new heads will be WAY more than a stock head......VE compensates for low compression and this is fact. A small, bad *** flowing head with the right cam on a 9 to 1 engine will still work VERY well.......DCR calcs are an arbitrary tool to get one close into the ballpark if they have no clue what to use.
I say continue with your plan. I have put several different 64cc heads on the Goodwrench 350 and made great power.......my Dad's 32' Coupe had RPM heads on a Targetmaster 350, with the RPM no gap intake and a way too big 292H Magnum cam and threw down 335hp at the tire in 1999! This had the same pistons as yours....I measured 9.4 to 1 at the time.....that engine STILL is running down here although he choked it with Muffler Shop special mufflers and killed the power.......

Jebby

derekderek

where did you measure the .035? they are not that deep unless somebody welded the deck up and re-machined it .015 taller than stock. or did something else equally impossible like custom shorter connecting rods. a lot of piston makers raise the compression height a little to reduce the .020 depth. nobody is gonna make a deeper piston that costs a point or more, low compression pistons for turbo or supercharged apps still have the correct quench height and a deeper dish. and they are not cast. you measure at the SIDE of the piston where the smooth ring goes around the circumference. i think you measured in the middle of the dish. chevy and most builders put the pistons .015 to .020 in the hole. mainly to help the top ring live longer.

Jebbysan

I agree to a point the number sounds deep but I have an L-46 350 here with flattops rebuilt circa 2000 that the pistons are .040 in the hole! So not out of the question if someone used freakin dump truck pistons with a lower C/D……
I opened a 69’ 350 from a C20 pickup….never cracked,ten years ago and those were .070 in the hole!!!
But I agree….remeasure this…..they should be about .15 or so in the hole….

Jebby

Lamouree351

I thought it seemed awfully high also.... I checked it on two different cylinders and used two different methods. First I used a plunger style indicator and a mag base. I put it in the bore on the tallest part of the piston and rotated the crank until I got the cylinder to TDC and zeroed the indicator. I then rotated the mag base to the deck and wrote down the difference. I also put a straight edge across the cylinder and used feeler gauges. I got about the same number both times

Stormin_Normin

A lot of rebuilder pistons are .010 short to make up for decking the block, so if the block wasn’t decked it sounds about right. I had the same issue with mine that was rebuilt in the early 90’s and not decked.

Lamouree351

Thanks Jebby,
I got the thinner head gasket and the comp cams XE262H on order, The Howards cam was on back order so decided to go with the comp cams. I will update here once I get everything back together

Dino_'72

Yes keep us posted. You seem particular in your thought process. If you could also post idle vacuum readings and cranking cylinder pressure numbers after mods are completed that would be helpful. These L48 upgrades are common on the forum and I'm sure would be of interest to other members in the future. Good choice I believe. Should work out well. Good luck. Thanks.

Krystal

The L82 needs more than headers.

In stock form the only good stuff is in the block. The heads, intake and cam should all be jettisoned as emissions era weaklings that don't/won't make base line SBC performance power.........headers or not.

On a more positive note. The L82 did pack a stout bottom end short block. 4 bolt mains, Flat top forged pistons are perfect for todays available pump gas. Everything above the short block should go when it's time to get serious about building in performance to an L82.

Don't let the 2.02/1.6 valve sizes fool you on the L82 heads. They're JUNK, same as the L48 head with the smaller valve and the very same chamber design that will rob torque and power across the RPM range with the single worst open chamber design Chevy ever came up with. Never forget that low compression was all about meeting emission standards in the 1970s. Don't dare be fooled into thinking that bigger valves always mean "perfromance". In this case they absolutely do not! That chamber design is guaranteed to cost you all across the RPM range vs the use of most all pre-emission era heads or any of great many after market heads currently available.

Here's a pretty good run down on what to do if your set on the idea of keeping an L82 between the fenders. I especially like the idea of that over 400HP figure achieved with just a top end build up. Today's cars are super tough competition for any 40+ year old car to match up to and these days the bar has been raised significantly. Can anyone still be satisfied with much less than 400HP in any Corvette? I don't think so. You're still not gonna make a serious move on a modern Corvette but it takes this much power to at least manage some basic level of respectable. In the 1980s and 90s 300-350HP was good enough. Today? 400HP seems like a base line.

wilcar

Agree with the old school Comp 268. I went with the Isky 201264 mega cam on my 76 L82 with T 400, 3.36 rear and single cat exhaust. Had better low and mid range power than the L82. 214 214 .450 lift 108 lsa. I used the stock l82 springs.

Lamouree351

I attempted to fire the engine tonight and break in the cam. Initially the car started and ran poorly for a few seconds I tried to bring up the rpm and it died. It did this twice in a row. I then tried rotating the distributor to play with the timing and now I can't get it to do anything other than spit every once in awhile.... Does anyone have any suggestions? I'm thinking I will go back and check TDC and firing order, but not sure why it would fire initially if it was wrong. How worried should I be about the new cam? Will excessive cranking wipe out a cam lobe? Everything was coated with Lucas assembly lube when I put it together. I primed the oil pump before attempting to start and I'm reading 40psi when cranking.

augiedoggy

I had 2 wires crossed after my recent cam install. It wasnt as stressful as the flat tappet cam break in though. I would double check your wires for sure

Jebbysan

I doubt you have hurt it any.......it tales a lot of valve openings with the lifter not spinning to wipe a lobe.....but my one issue id the Lucas assembly lube.....I never use lube on a flat tappet, Moly paste only.....all assembly lubes drip off eventually while sitting......paste stays in place for a bit til it is washed off by oil spray when the engine finally fires and is up to speed.....if you had used Moly paste here, I would say just go for it.....but I just can't here......you have to make a decision......and like I say, you are probably ok, but it is your call.
Anyway....put it on #1 (blow your thumb off with a helper).....pull the cap and check rotor position. Look at the rotor tang when you have the rotor where you want it and use a Sharpie to mark that straight down from the tang to the distributor base.....put the cap on and line up #1 on the cap with this mark......now here is the fun part, grab the distributor and turn it a smidge counterclockwise, about 3/8"......this will get you around 10 degrees initial......snug up the clamp just so you can turn it, have the timing light hooked up and ready.....ok, if the firing order is correct, then you are ready to start assuming the carb has fuel supply and is in good shape.
Me personally....I would go for it......pour a bottle of Lucas ZDDP in there for piece of mind right now.......the first minute is most important, it determines if the lifters are spinning.....

Jebby

7t9l82

The L-82 cam was not a smog era cam. GM indtalled it. With zero advance.. add 4 degrees and it's a strong running street cam. Yes the heads wére garbage and the intake too. Changing the top end and set of headers and tuned properly it runs pretty well.
I can't say I've had any run ins with c7 corvettes but I have no problem with the more modern versions with my current flat tappet cam.
You guys underestimate flat tappet cams ,alot.

Did someone really refer to car and driver from 1974? The same car and driver that named the Ford pinto the car of the year? They were a joke those clowns knew nothing about performance and nobody gave them any credibility.
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7t5

Get a cell phone borescope. All different types on Amazon. Then you don't have to pull a head until you are ready for upgrades.

Nevermind. I read the rest.

Lamouree351

Over the course of the week I got the engine running and broke in the cam. I got a little worried by what I thought was a noisy lifter, but it turned out to be an exhaust manifold gasket leak. After break-in I changed the oil, fixed the exhaust leak, and fine tuned the timing. I took it for a quick shakedown run around the the neighborhood, but didn't want to push it too hard until I get some miles on the new setup. It did feel pretty good under 1/4 - 1/2 throttle.

To summarize the changes:
I changed to Edelbrock E-Street 64cc chamber heads, 0.015" head gasket (this puts me at about 9.25:1 compression ratio), and a Comp Cams extreme energy 262H-14 cam and lifters. It already had an Edelbrock Performer dual plane intake manifold which I am still using.

The cam specs are as follows:
Duration @ 0.050: Int 218 / Exh 224
Lift: Int 0.464 / Exh 0.470
Lobe separation: 114
Advertised Duration : Int 262 / Exh 270

With this setup I am getting 160-165psi cranking pressure across all cylinders and 15" of vacuum at idle. The new cam and lifters do seem a bit more noisy than the old setup, but from what I have read the extreme energy cams tend to be. The noise is a bit like a sewing machine. I can't isolate the noise to one area and it does not get louder with rpm, so I think I'm ok. Here is a video of the car idling after the shakedown drive: . Let me know what you guys think.

7t9l82

Don't baby the cam get out and run it get the oil splashing on it and get it run in good. Broke in. Is broke in.