L82 cam in a stock L48

[DCShark]

I have not posted here in a long time. Usually, everything I need is in the archives.
I have a 1979 Corvette with a L48 engine, auto, 3.55 gears. The compression checks out at 150 in all cylinders. I'm getting a lot of lifter noise at about 3000 to 3500 rpm. I bought the L82 350hp reproduction cam from GM performance parts. Will this cam perform well in my stock engine? What other parts need to be replaced besides the cam,lifters and timing set.
The concern I have is that the compression ratio is 8.2 to 1 in a L48 while the L82 has a 9 to 1 compression ratio. Will this make any difference?

 

[MMM]

I plan on doing the same thing with the base 200hp 350 in a '72 Vette. The caution is the block, crank, rods and pistons. The L-82 uses a four-bolt block, forged crank and pistons and upgraded rods to handle the higher rpm the cam will provide. The L-82 cam will easily rev beyond 6000 rpm. I have been told by some knowledgeable people that to rev a two-bolt main, 350 block (with the cast crankshaft) past 5500 is risky. As far as I know, all L-48's are two-bolts with cast cranks. While I have seen this combo (2-bolt, cast cranks) regularly used at or above 6000 rpm and live (in circle track racing), I defer to other's expertise and advise you watch your rev limit. Maybe others have additional experience.
Mike

 

[DCShark]

Thanks, Mike for the reply. I'm mainly using the vette as a cruser and I don't think I will be revving the motor past 5500.

 

[motorman]

I have not posted here in a long time. Usually, everything I need is in the archives.
I have a 1979 Corvette with a L48 engine, auto, 3.55 gears. The compression checks out at 150 in all cylinders. I'm getting a lot of lifter noise at about 3000 to 3500 rpm. I bought the L82 350hp reproduction cam from GM performance parts. Will this cam perform well in my stock engine? What other parts need to be replaced besides the cam,lifters and timing set.
The concern I have is that the compression ratio is 8.2 to 1 in a L48 while the L82 has a 9 to 1 compression ratio. Will this make any difference?

you will have less bottom end torque and the corvette will seem lazy on take off. you can help this by installing a higher stall speed convertor. we did this on stock L-82 even when they were new because the stock convertor was so"tight"

 

[DCShark]

motorman, thanks. I guess I would be better off with the 300hp cam. Right?

What is the stall speed on my engine.

Am I right to assume that by lazy on take off, the car will feel like it is bogging down.

 

[GerryLP]

motorman, thanks. I guess I would be better off with the 300hp cam. Right?

What is the stall speed on my engine.

Am I right to assume that by lazy on take off, the car will feel like it is bogging down.

Typically, a higher Horsepower rating on a motor cam sometimes equals to trading-off torque for horsepower. For example, a larger exhaust system would affect your engine as you know it right now. The top end will be more responsive and perhaps gain horsepower, but you could loose torque at the bottom end.

GerryLP:cool

 

[Tom Bryant]

"Quote motorman, thanks. I guess I would be better off with the 300hp cam. Right?"

Not necessarily. All of these old GM grinds will work fine in applications similar to what they were designed for or even in lesser engines if the gearing (and/or converter) is right. Your 3.55 gears will help. What you need to realize more is that all of these old GM grinds are just that, old. Anything from the base 300 horse cam to the famed Duntov to the L82 are based on technology that is anywhere from near 35 to almost 50 years old.

Camshaft tecnology has advanced in leaps and bounds over the last several decades and has kept pace with todays available fuel and compression ratios. If you go to a modern cam profile you can get better low end than the 300 cam and also get better performance throughout the rpm range of your engine.

A call to the tech line at Crane, Comp ext. will get you a recommendation for a cam that will match your car without additional mods if that's what you want to do. I also like and use the cams from the GM performance parts catalog. They are manufactured by Crane. I used 12353918 in my recently completed 355. It is designed to match the usage of my vehicle that the engine is going in. In this case I set the compression at 9.3:1 with street ported heads, shorty headers, performance intake and small Holley and 3.73 rear gears but a stock Turbo 400 trans.

Looking at your stock engine specs I'd take a serious look at GM performance cam #12353917. It's designed for your compression ratio range and cruise rpm with your gearing and stock trans/converter. It should give you a boost all across the board and maybe a slight lope too.

Here's the specs from the GM site:

12353917 Camshaft Kit
8.0 - 9.5 to compression ratio, 2200 - 2600 cruise rpm. Basic rpm range 1500 - 4000, 6500 rpm attainable with proper valve springs and lifters. All model small-block Chevrolet V8 1955-66 California, 1955-68 with federal emissions. All non-emission trucks, and 1966-92 for off-highway applications.

Technical Notes: These are hydraulic flat tappet camshaft kits. The duration at .050 lift (intake/exhaust) is 204/214 degrees, and the valve lift is .420"/.442". Lobe centerline is 112. This camshaft kit is designed and manufactured by Crane Cam Co.&reg. It contains one camshaft and 16 tappets

Here's the specs for the "929" cam that was used in the base engines includine 300 horse 350s. You can see that the 917 is a better deal and I think you will like it.

12364051 Camshaft kit, Hydraulic
Dual pattern, blueprinted replacement for factory P/N 3896929 with 300 hp and 327 cu. in. camshaft.

Technical Notes: Basic rpm range is 1000 - 3500; cruise rpm at 60 mph is 1600 - 2200 and compression ratio is 7.75 - 8.75. The duration at .050 lift (intake/exhaust) is 195/202 degrees, and the valve lift is .390"/.410". Lobe centerline is 112. This camshaft kit is designed and manufactured by Crane Cam Co.&reg. It contains one camshaft and 16 tappets.


I don't think you will have to change valve springs if you are planning on not trying the 6000 rpm thing. As for push rods and rocker arms if they aren't worn or show galling in the ball area they can be reused. I used the GM Performance self aligning stamped rockers and thick wall push rods simply because what I had was junk. I found both on Ebay at a fraction of the cost from GM in sealed packages. I got lucky.

Here's the link to the small block cam page on the GM site:

http://www.gmgoodwrench.com/perfpartsjsp/partlist.jsp?cat=9387&section=ep

Of course you can order this cam from any GM dealer or online from places like Scoggins-Dickey or Pace Chevrolet. http://www.paceparts.com

Tom

 

[MMM]

I may be full of it, but my seat of the pants feel has always liked the L-79 hydraulic cam better than the later L-46/L-82. I feel there is less loss of low end torque with the L-79 cam even though the specs for the two cams are very close. I plan to advance the L-46 cam I will install by 4 degrees (brings the timing events closer to the L-79's).
I had a '75 L-82 Convertible with 3:55's and a M-20 wide ratio four speed. The car felt sluggish at low end with the stock cam. During restoration I replaced the L-82 cam with the L-79. Maybe it worked better because of the gearing, but it was a TOTALLY different car after the cam change and a real blast to drive.
Mike

 

[maxrevs85]

I thought I might add, that one thing you should take a look at is your harmonic dampner. These are often overlooked and if not in good condition can lead to problems. I found my 85 had moved about 3/8 of an inch. check for cracks and weathered elastimer...There are many aftermarket dampners out there that are not high dollar. For your application a new stock one is more than satisfactory.
Just food for thought.
Hey also it might be a good time for roller rockers. Harland /Sharp are your best bet.
Dave

 

[DCShark]

Tom,

Thanks, that was a lot of information. I will give the #12353917 a serious look. It seems to match my driving needs.

I am planning on installing a dual exhaust without cats. I would like to install shorty headers. Will either of these help with the lack of lower end torque because of the L-82 cam. Or will this only help the upper end horsepower.

I have a 2101 performer intake that I may install. Will all these upgrades work well together.

I usually cruise in the 3000 to 4000 rpm range. I do hit 5000 when passing.

Thanks to everyone who has replied.

 

[Tom Bryant]

The 2101 is for milder engines like yours and helps in the low to mid range more than high rpm. The headers and duals will help even your stock engine across the board. I think both mods would compliment that 917 cam well.

 

[WayneLBurnham]

Man, It may be impolite...But I *LOVE* solid advise like that!

With all respects to the hard corps NCRS set, and I do respect perfect restorations and examples of original designs - really, thanks for throwing in the light of reason for a driving enthusiast application Tom!

Look, L48, L82...whatever....all these engines were lots of trade offs with mileage concerns, emmissions concerns, and a host of other things having damned little to do with the purity of vision of The one, true American sportscar the Corvette has always been meant to be.

There are a dozen great cam grinders who make cams that with all other things the same in a low to mid compression engine increase performance dramatically at all engine speeds and loads. Factory engineering was under a host of concerns irrelevant to the enthusiast and, as Tom accurately points out, lacked a quarter century of research.

Keep all the external aspects of your vehicle perfectly stock if that is your preference, but swap out anything that can't be seen for that which simply works better. Talk to the techs at the quality aftermarket suppliers, and GM's performance people too, and pick something that does what you want.

Since you have to do all the harassment of pulling the radiator or the engine, consider other options more money intensive but less work intensive at the same time too. The headers and duals are one such thing. $400-500 installed increases performance significantly whatever your setup, even if you have to put on another cat. A decent aluminum intake and roller rockers are cheaper ($250 and $150) and real simple operations. A rebuilt carb or new is in the same category and even more productive in terms of increase per dollar (from $50-450.) Changing ingnition components also can yield great improvements in power and responsiveness and can range from $150-600 or even more depending on what you change. The stock HEI with a better coil and wires is usually pretty decent as is.

Some cams available are even retrofit hydraulic roller versions which offer even better performance but most require some clearance machining and the cost is significant over a regular hydraulic flat tappet design of the same range (typically $750 additional) for not all that much extra performance.

Nice aftermarket aluminum heads which, as well as greatly improving flow, also easily raise compression from 8.5 to 9.5-10 are about $1200 NIB with all the stuff needed like gaskets and such. It's easier to swap heads than a cam! That's really the highest end of the top end bolt on approach.

With many of these cam and head packages, getting 1:1 ftlb torque and 0.9 hp per cube is both reasonably expectable and not significantly harder on your stock bottom end.

Your somewhat weaker bottom end won't run into lots of problems unless you are silly enough to turn 6500+ - and, since in most "best area under the curve for torque" selections, all your hp is yielded by 5500 and peak torque is over by 4750, you really don't have to go up there anyhow. Keep in mind, whether it's a Ford 460 or a Honda 2L, higher rpm always magnifies both stress and wear - and why it's always good for a long duration design to not aim for it.

Even with all cast components and two bolt mains, your weakest links are the rod bolts, main bolts and caps themselves, followed by the rods. Fortunately, you can change the first three of those the next time you pull the pan with stronger components by just removing and replacing.

Changing rods, pistons and crank, is of course the last and most dedicated level build up and in an older motor is better left for a complete engine teardown and remachining of all bearing surfaces and bores. Of course at that stage it is really tough to pass up the packaged and tested stroker assys (377, 383, 388, etc.) since the component cost is the same and you thus get a big free boost in cubes to base power off of.

Whatever you decide to do - whatever components you decide to upgrade -plan it all out in advance to meet your budget, expected down time and need for outside help - and bolt on a 30-50% overage for "whatevers".

 

[Jack]

Even with all cast components and two bolt mains, your weakest links are the rod bolts, main bolts and caps themselves, followed by the rods. Fortunately, you can change the first three of those the next time you pull the pan with stronger components by just removing and replacing.

NO, YES, NO!!! You can successfully change the main cap bolts without attention to anything else ... BUT ... NEVER attempt to change rod bolts without also having rods resized (machine shop) and NEVER attempt to swap main caps without also having block align honed (machine shop). No offense, simply wishing to prevent what would most likely be a VERY costly mistake.
JACK:gap

 

[DCShark]

Jack

Thanks. If the bottom end needs attention I would end up doing a complete rebuild. I had the main seal done last year to determine if I was just leaking oil or burning oil. So far the verdict seems to be I was leaking oil. I will pull the plugs and do another compression check before the cam swap. No point putting in a cam and then have to do a rebuild.

 

[WayneLBurnham]

That's good advice, but not absolutely a must...

No offense, simply wishing to prevent what would most likely be a VERY costly mistake.
JACK:gap

Oh, none taken! That is the best approach, but many are put together without these operations.

On rod bolts the ability to do this has a lot to do with the design of the rod, the type of rod bolt it comes with and the type you select to replace it. Some replacement bolts are merely stronger materialed versions of the originals. Even changing a rod bolt that is thirty years old to an exact copy can buy a little insurance against overstress from so many cycles.

Some makes of main caps too are designed to be a straight bolt on replacement to factory. I would probably want to plastigage the new bearings on those to see if there was a high/low side or fit.

To be honest, I've never done either of these "slap together" replacements or even just changed main cap bolts. If I'm that concerned about the load I'm putting on weaker cast components, I change the rod (and, hell, while we're at it! put some nice cheapy forged or hypereutectic higher compression slugs on those new forged rods!) I also can't resist putting those nice new four bolt splayed caps on it if I'm going that far in - only $300-500 when having the rest of the block machined...

Nevertheless, people have been swapping those parts with decent success for years without the recommended machining....

Still, all in all, the bottom end is not usually that weak at these power levels, especially without a higher shock power added thrown in, like nitrous or a blower - or the older higher compression that won't even work on our "cheap" 91-93 octane....

 

[Tom Bryant]

I don't see any reason to pull the pan and change all of the fasteners. I would be more worried about the engine after doing this than just leaving it alone. Now if you have bottom end noise or low oil pressure from worn bearings then changing the fasteners would just be a waste of time anyway.

If there is enough doubt in the strength of the rod and main bolts to worry about them at 5500 rpm or less I would definately avoid even starting the engine to move it out of the garage until I pulled it for a complete rebuild. Your engine seems to be a sound, good running engine with good compression so this cam change should not cause any undue stress on the bottom end if you continue to drive it in the manner you say you do. If you turn it into a weekly drag racer then you may have a problem sooner than later.

Since it was brought up I have some definate opinions on rod resizing and plastigage use too( don't use it, don't like it, don't trust it. Learn to use proper measuring tools and believe the real numbers when you see them.) but that is getting off topic here. But briefly, if a used rod is clean and straight and measures to specs all the way around the big end bore and front to back what are you gaining by resizing? I'm not being argumentive, just throwing this out for discussion. I think that the magazine guys and their sponsers have fostered this notion that you can't re-use a fastener and everything has to be machined like it's going to Indy even if it's just the wife's grocery getter. Never used to be this way and failures were few.

Tom

 

[Jack]

Tom:
Same as you, no offense intended or taken ... just friendly discourse.
With one exception, I agree with everything you say above. Talking rod bolts here ... those with nuts ... not cap screw type. Changing rod bolts often deforms the rod and the rod-cap alignment slightly; sometimes enough to matter. Because a dummy like me did, I'm sure most folks can also learn to use accurate-proper measuring tools (gaging). But I doubt if most folks have decent gaging or wanna buy it. If (after installing rod bolts) the rod remains round & sized right ... then by all means there's no need to resize. But without "someone" measuring it, who knows? BTW, a local race builder with good reputation had two separate failures with new Eagle 5.7" SIR rods. When subsequent batches were checked for size, turns out Eagle had not properly torqued some bolts prior to sizing. On the failed rods ... builder had not checked size prior to install ... rods were not round when properly torqued ... two broke in two different different motors. Brand new $200+/set rods not round and several have to be resized. Typically, machinist does not resize the ones that check round or size OK ... only the ones that don't check right. SIR's continue to need checking & some resized ... but no further rod failures since checking/resizing first. Never see this problem with pricier Carillo/Crower/Howards rods ... you get what you pay for. I have a mitutoyo dial bore gage now, but for years used a good mike & telescope gages with no problems ... still using the telescopes for some stuff.
JACK:gap

 

[Tom Bryant]

I guess that shows that just because it's new doesn't mean it's perfect. I had a friend that used to pull apart new 327 short blocks and check all of the clearances when he was prepping them for the local dirt track back in the 60s. I thought he was nuts. I don't recall if he ever found a problem but It was obviously the smart thing to do.

 

[dfw81shark]

Look, L48, L82...whatever....all these engines were lots of trade offs with mileage concerns, emmissions concerns, and a host of other things having damned little to do with the purity of vision of The one, true American sportscar the Corvette has always been meant to be.

You mean the original designers didn't intend for my true American sportscar car to only have 190hp? :confused :L