L82 Cam

[Jim Callan]

Is this cam still available from GM ? If so, what is the part number ?

I'm rebuilding my '71 350/270hp with TH400, and it was suggested that I use this cam. Is there a better cam to use ?

Thanks

Jim

[Duke W.]

Re: L82 Cam

The L-82 cam,3996946, was also used on the earlier L-46. It has slightly more duration than the L-79 cam - 224@.050" lifter rise versus 221. Also, it is effectively retarded four degrees relative to the L-79 cam with points of maximum lift of 114/114 versus 110/118 for the L-79. For reference your base engine cam is 194/202, 108/116.

The 946 is a very good top end hydraulic cam, but with an auto trans, I would recommend either advancing it four degrees or using the L-79 cam.

The L-46 was not available with autos. L-82s were, however, they were generally equipped with higher numerical axle ratios than base engines due to their lower low end torque and had a slightly higher CR (9:1 forged pistons) than the 8.5:1 base engine. The base engine was stronger up to the range of 3000-3500. Using the L-79 cam or advancing the 946 cam will slightly mitigate the loss of low end.

It should be available from Federal Mogul (as are all OE cams) but I don't have a number.

Depending on what torque curve you are looking for I would pick among these three OE cams including the optional indexing, and not even consider an aftermarket cam. I would also recommend raising the CR to 10-10.5 with either the of the SHP cams. This will require premium fuel instead of regular, which is what all '71 engines were designed for.

The base engine with higher CR and pocket ported heads will actually be a very good performer in normal driving, where low end and mid range is relatively more important than the top end of the power curve, especially if you have a lower numerical axle ratio than 3.36.

With any engine rebuild, regardless of what cam you choose, I always highly recommend pocket porting/port matching the heads with a three angle valve job because this will yield up to ten percent more top end power without affecting low end torque. Any cam that improves top end power will hurt low end torque.

Duke

[Jim Callan]

Re: L82 Cam

Thanks Duke,

Looking at the link below, the L79 cam is # 3863151 for the 327/350hp. Is this the same cam that you reference ?

http://www.kendrick-auto.com/chevrol...y_cam_spec.htm

According to the machine shop - the bores will +.030 and I'm going to have the final honing done with a torque plate installed. We're planning to use a Summit rebuild kit that "should" give 9.7 CR, but they have a 10.5 CR kit - both kits are for the 64cc heads, which I have with 2.02/1.60 valves. I plan to use the stock intake with the Q-Jet, stock exhaust manifolds with 2.5" pipes, and a Pertronix ignition system.

If I have understood you post - the L79 cam should give me better low - mid range torque with the auto. I'm not looking for Z06 performance, just more "fun".

Thanks

[Barry Chappell]

Re: L82 Cam

I have used the L-46/L-82 cam in several applications and it is an excellent cam.
However, I have always used 3896962 as this cam.
I'm not familiar with "3996946".
Is this a change up number for that cam?
Or, Duke, are you having a bad typing day.

Barry

P.S. The L-79 cam, works well also. The L-79 is more "lumpy" at idle.
I'm not really convinced the the "modern" cams of today are actually
any better. It's easy to advertise that.
These old cams work very well.

[Clem Z.]

the big problem with later year corvette

with auto trans is the stall speed of the convertor is too low making the takeoff from a dead stop feel very sluggish. the taller rear gear also add to the problem. a cheap fix for this is to use a convertor from a V-6 engine that matches your transmission. we did that to some L-82 engined corvettes and it makes a big difference in off the line performance.

[Patrick H.]

Re: L82 Cam

Jim,

What pistons come in the kit?

I suspect they are regular old dished cast pistons. Those are fine, but for "free" hosepower and longevity, consider F-M hypereutectic pistons. I used them with NO dish and only 2 valve reliefs in my own 71, and they work great. Rework the heads, have your distributor recurved and you're good to go.

The Summit kit is fine for your truck. I wouldn't trust it without a complete list of specs for my Corvette. Make sure, too, you use FelPro high performance gaskets.

Patrick

[Duke W.]

Re: L82 Cam

Typo - sort of. To make a short story long, the part number for the finished camshaft is 3896964, and this number or at least the last four digits should be molded into the casting of an OE cam. The cam and dowel pin ASSEMBLY, which is the service part number is 3896962.

Utilization is '69 to'70 L-46 and '73 to '80 L-82.

Duke

[Duke W.]

Re: L82 Cam

Stated CRs are based on an ASSUMED piston/deck clearance and head gasket thickness. I would NEVER, EVER trust some mail order parts house stated compression ratio even if they stated the "assumed" deck clearance and head gasket thickness, which they usually don't. It should always be measured on each specific engine. This starts with measuring piston/deck clearance on the original engine BEFORE the block is disassembled.

Then you get all the piston specs - compression height and "dome volume" (which is usually "negative" - subtracts combustion chamber volume - for real domed pistons, and positive - adds volume - with flat top pistons with valve notches or dished pistons). Now with various available head gasket thicknesses and head chamber volume you can actually calculate the CR and select a gasket that gets you into your target range. If the heads are unmodified you can use the spec volume. If they've been modified, the volumes should be checked and equalized.

With a L-79 cam I would shoot for no more than 10.5 if you have 93 PON fuel available, 10.25 if you only have 91 PON. With the base cam use 10 and 9.75.

The L-79 cam (3863151 or equivalent clone) would provide slightly better low end torque than the 962 (L-82) cam, but keep in mind it will be weaker up to mid range than the base cam and, especially with a 3.08 axle, may not be a good combination for normal driving. The base cam with massaged heads will be a very nice combination for a cruiser with a TH400 and tall axle. L-82 axles with TH400 ranged from 3.36 to 3.70 depending on year and availble axle options. The higher numberical ratios were used with L-82 because of its less low end torque than the base engine TH 400, which had a 3.08 in '71.

If you are using 64 cc heads they must be earlier verisions and not original to your engine. If they don't already have the 2.02/1.60 valve I would not enlarge them. Use the 1.94/1.5 combination if that's what they currently have.

I'd suggest you do more reserach. HP Books "How to Hot Rod your SB Chevy" is a good reference as is the old Chevrolet Power Manuals from the seventies.

Reputable piston manufacturers publish the piston data you need to accurately calculate CRs when you know the deck height, head gasket volume, and head chamber volume.

Duke

[Brian Monticello]

Re: L82 Cam

Jim,
I highly suggest measuting several things before selecting a rebuild kit and cam. These things are:

1. Combustion chamber volume
2. Piston/deck clearance

The compression ratio quoted for the pistons makes many assumptions. This data (along with head gasket info and proposed dome (dish) volume) will help you compute your actual static compression ratio and will help you select components and make adjustments. If attention is not paid to these measurements you have the possibility of ending up with a lower performance motor due to low compression or a money guzzling beast with an appetite for racing gas.

Brian

[Duke W.]

Re: the big problem with later year corvette

Good point! When you install a "bigger cam" you need a higher stall speed converter and shorter gears to make up for the loss of low end torque. Otherwise you could end up with a combination that actually feels slower in normal driving. A looser converter and shorter gears will also noticeably reduce fuel economy.

Unless the entire drivetrain combination is properly system engineered it may be disappointing.

The base cam with TH400 and a 3.08 axle is a nice combination for cruising and touring. A big cam might improve quarter mile time and MPH a bit, but could be a worse combination in terms or normal driving situations.

Massaging the heads with any cam will improve top end power by 5-10 percent and add about 500 useable revs at the top end. Considering that low end torque will not be affected to any signficant degree with normal pocket porting and port matching, the base cam will yield the same normal driving characteristics with more SOTP top end power and is probably the best combination with the TH400 and 3.08 axle.

Duke

[Jim Callan]

Re: L82 Cam

Patrick,

The pistons are hypereutectic or forged 'flat tops' with 4 valve reliefs. Complete FelPro gasket set, moly ring set, cam/main/rod bearings, hi-vol oil pump. I would have to add new timing set. I am going to wait until the machine shop finishs it's inspection before I buy anything. The reason I'm doing a rebuild is because the car has sat for 10 years, only has 95K on it. The bores look 'glazed'. This whole thing started because I wanted to detail under the hood and just repaint the engine. Now the engine is out, the heads have been
done, and I feel that as long as I have committed to a rebuild I may as well try to get "a little more". If the shop says the bores just need a hone and stay std, I'll go with new bearing/rings and keep the same cam. BUT if I need new pistons anyway I might as well use a new cam. My wife says I have "mad car" disease ...

Jim

[Scott Marzahl]

Re: L79 Cam

Duke,
So did I screw up when I rebuilt my L79 using flat tops with a computed static CR of 9.4:1 with the stock cam, I did install it advanced 2 degrees for a little more low end.

Scott

[Jim Callan]

Re: L82 Cam

I replaced the original heads with these 'camel hump' heads in '73 - I don't remember why... now I do... I put a set of Hooker side pipes on and I thought it would sound good (it did). They do have the 2.02/1.60 valves.

Can I 'guesstimate' how far 'in the hole' the piston is with a feeler guage at TDC ?

Jim

[Duke W.]

Re: L79 Cam

No, but you could have gone about anouther point in compression, however, with only 9.4 you can run a more aggressive igntion advance map with premium fuel.

With only 9.4 you might be able to run it on midgrade or even regular.

Duke

[Duke W.]

Re: L82 Cam

No, these are precision measurements that should be carefully measured to the nearest thousanth. A depth mic or feeler gages with a machinist's bar is the way to measure deck clearance. At TDC you rock the piston back and forth until the measurement is equal on both sides, which eliminates inaccuracies from piston rock.

Usually the clearances are fairly close on each side, which indicates the deck is parallel to the crankshaft axis. Often one side is a little higher than the other. If the high side is on the left you can deck it down without destroying the number pad, or you can use different thickness gaskets to get equal quench clearance.

Duke