I received two suggestions from Comp Cam techies for which cam I should use in my "new" 350 build going into my C1. Either the HE 260 or the HE 268. After hemming and hawing for a couple weeks on which one to buy I chickened out and ordered the 962 cam from Chevrolet. That is the semi-hot hydraulic from the L46/L82 engines. I'm looking for good low RPM performance rather than drag strip get up and go. Hope I made the right choice. Bob

 

If it's not too late, I'd back up and opt for the one of the Comps. Which one depends on the rest of your combo. Cam technology has come a long way since the GM 962 was designed. Modern profiles like the High Energy series open the valves faster, giving you more performance with a shorter seat duration. The GM cam was also designed with emission requirements, warranty repair issues, and other limitations in mind, most of which are contrary to the performance interests.

BAC

 

not enough info in your profile to answer.
need CR, trans, rear, shift rpm, mpg desired.

 

That's mostly marketing hogwash - there's no such thing as "new cam technology", unless you're selling them and looking for hype to put in 4-color brochures. Factory high-performance cams have years and years of development behind them, use ordinary valvetrain components that aren't over-stressed, and are bulletproof and utterly reliable; there are plenty of different grinds to pick from depending on the rest of your combination and driving style, and they'll meet the needs of 99% of owners. Race motors are a different animal, but that's not what we're dealing with here.

 

This is myth promulgated by aftermarket cam manufacturers. The dynamic characteristics of the lobe are limited by valve train stiffness, and GM had a very good handle on how much acceleration and jerk the valvetrain could handle back in the sixties. OE cams are dead-on reliable and won't wipe lobes of bust valvetrain parts. It doesn't take too many cruises throught various discussion boards to see that wiped lobes and valvetrain problems are not uncommon with many aftermarket cam designs.

The 962 cam is an EXCELLENT choice, however one thing I might suggest is advancing it four degrees. The duration at .050" lifter rise is 224/224 compared to 221/221 for the L-79 cam. The 962 cam points of maximum lift are 114/114 versus 110/118 for L-79, so it's effectively retarded. Low end torque can be enhanced with a slight loss of top end power by advancing it four degrees to achieve the same indexing as L-79.

Use all OE or OE equivalent parts in the valvetrain including the standard '67-up "068" OE valve springs. Adjust the lifters properly and you can forget about the cam and valvetrain for a LONG time and it will rev stongly and reliable to 6000.

With massaged heads the 962 cam will pull almost as much top end power as the LT-1 cam, but you give up 500 revs at the top end.

Duke

 

Not to argue with the list gurus, but 100,000+ mile reliability is not a priority for me in a limited-use performance vehicle like my midyear will soon become. While they *may* be best for Claf's application, the 60s-era factory grinds with relatively slow valve acceleration and wide LCAs are just not what I'm looking for. I'm definitely not an engineer, but I am an old street racer (gasp!) and sometimes drag racer from years ago. Half the fun for me is trying to put together something that betters the all-around performance (subjective, I know) of 40 year-old GM vehicles and I don't mind breaking the very occasional part in that quest. The world has come a long way since the 60s, so y'all will never convince me that "factory" can't be improved upon. Besides, half the flat-tappet cams in the GMPP catalog are "designed and manufactured by Crane Cam Co."

I really do appreciate the valuable information and opinions you guys post, but the pro-GM bias is clear... and understandable. And I'm really hard-headed.

BAC :^)

 

Duke: I'm using this cam along with a set of ported and polished 2.02 heads (67 Z28 oem) and I expect the limiting factor on this motor will be the relatively low CFM of the AFB carb and 1965 factory alum manifold but I'll cross that bridge when I come to it. My question is, how do I advance the cam? Do I need an adjustable cam gear? Or?? Thanks, Bob

 

Offset keyways for the crank sprocket to advance or retard the cam are commonly available from cam manufacturers and sold by hot rod shops. To advance the cam you want it to be positioned two degrees clockwise from the OE location. Hopefully the offset key will have some intelligible instructions. Getting it right can be confusing.

Your are correct. With massaged heads, the 327 SHP manifold is the limiting factor - more so than the 550 CFM AFB.

You should really consider the LT-1 cam. See if you can search posts by Dave McDufford. His blueprinted, pocket ported L-79 with LT-1 cam made about 360 HP @ 6500 SAE gross on a dyno and it was still climbing. The LT-1/Z-28 manifold probably would have yielded another 15-20 HP, and a FI with a massaged air meter would have been knocking on 400. All this with 80 percent peak torque at only 1600!

A production L-79 would make in the range of about 300 HP @5500. The OE ratings were grosslly inflated.

Duke

 

I used the '962' L-46 cam in my 327/300 hp engine. Everything in this engine was pretty much stock with the exception of .030 over forged flat top pistons, screw-in rocker arm studs, and a later version electric choke 625 cfm AFB carb. .. Exhaust was through the stock 2 1/2 inch cast iron manifolds.
I felt the 962 cam had good idle quality and decent low end torque in my engine. I could take off from a dead stop in second gear (M20, 4:11 rear) and pick right on up to speed from there, no problem. There were no hiccup or bog issues. Mid range performance with this cam as installed in my engine was very good, IMO. Top end performance past 5K revs did seem to leave a little to be desired, though. Perhaps a better intake manifold and distributor ignition advance map would have helped. Lighter spring tension advance weights were installed in the distributor but the advance curve was never checked. It's possible there may not have been enough total ignition advance to suit the top end. The initial ignition timing was set at 12 degrees BTC.
I did make the mistake of installing valve springs that had too high spring pressure. Concave lifter bottoms were the end result though the cam lobes themselves appeared to be ok . .
Overall, I felt this cam had good street manners and was a good choice for my application. I certainly wasn't disappointed . .

John

 

Again with all due respect to the GM engineers of the day as well as those on this forum, but new and/or modern cam design is not a myth.

Everything in the way of R&D in the auto industry has grown by leaps and bounds.

If the old GM grinds of the 60s were as great as everyone suggests, and have not been improved on in 40 years, then why aren't they still being used in todays motors? or at least being used as a basis for stock cams in the new LS1s and various other performance engines?

Breaking parts and reliability is always a concern, but I'd put a Comp Cams 292Magnum Hydraulic up against an LT-1 anyday of the week and the comp will make equal vaccuum, idle better, make better lower end torque and pull harder. And thats in stock trim with cast log type manifolds in a Camaro. Not to mention it will easily go 100k miles.

I've done it, and don't need dyno sheets to prove what the seat of my pants tell me. I'm sure there are better cams than the 292Magum out today. Even that cam is now a 10-15year old design.

The GM designs are great, and i'll continue using them for Restoration purposes, but there certainly better cams out there that are as reliable,easy on parts, and will make more power and better vaccum throughout the entire curve.

 

i think the other reason we see alot of wiped cam lobes and failing lifters and such like that is becasue people never seem to listen to the reccommendation of the cam manufacturers.

they will flat out tell you where the line is between street and race applications, however I have found that some of the guys on the other end can barely read a catalog any better than I can so one really needs to get more than a single opinion on a cam selection.

but you can't blame the design of a cam, if the user or installer isn't using the correct componants along with it.
any times I've been a speed shop or something, and someone walks in thiking they know everything there is to know and procedes to make incorrect decisions based on what they've heard, or what they want.

that isn't a fault of the cam or design, its just stupidity.

 

I love the L-79 cam in my L-79

I have been able to make 272 rwp (calculated) with that cam straight up, untouched heads, 490 intake, and 3367 carb through exhaust manifolds and factory sidepipes............


I am sure there are better cams out there, but this grind works for me.......

 

MRG,

I have used the 962 cam (as well as several others of the well known grinds - both factory and aftermarket). I felt that the 962 was the weakest of the batch (especially compared to the 151 cam of the L-79). It does exactly what you say (idle well, but falls off @ 5K, but never pulls as strongly as the 151). The sim program actually gives a slight edge to the 692 cam at the higher end, but my experience does not agree (based on the same vehicle and engine).

Duke is slowly converting me over to a believer of the LT-1 cam. I have not tried it myself, but do have experience with it via a friend's original Z-28 that I maintain. It pulls very strongly and works great with the Turbo 400 trans (with both 3.70 and 4.11 rear gears).

In using the EA dyno sim program, I have found what might be a better alternative to the LT-1 with a higher rear gear. It does not have the peak HP of the LT-1, but does have similar torque band performance with comparable BSFC numbers. If typically running 3300 RPM or below, I would like to try this Comp Cam #282S, but for engines running typically above 3300, the LT-1 seems to be the best I have found (for my setup).

Note that the below numbers are only relative to my engine combination, so caution is advised. The numbers are low, since the engine currently has 9:1 CR, which certainly is not optimum for either of these 2 cams! I have not run the sim program with a higher CR, but will in the near future.

For comparison purposes, the following are the "numbers" at a few RPM points:

Comp Cams 282S cam (Intake: 106 CL, 236 duration @ .050", lobe lift .330", Exhaust: 114 CL, 236 duration @ .050" lift, lobe lift .330").

The LT-1 cam data (@.050" lift was via the EA data supplied (Intake: 106 CL, 242 duration @ .050" lift, lobe lift .306", Exhaust: 122 CL, 254 duration @ .050", .323" lobe lift).

1500 RPM LT-1 = 213 Torq, 60.7 HP, .666 BSFC
1500 RPM 282S = 235 Torq, 67.2 HP, .638 BSFC

3000 RPM LT-1 = 347 Torq, 198 HP, .505 BSFC
3000 RPM 282S = 350 Torq, 200 HP, .508 BSFC

4500 RPM LT-1 = 356 Torq, 305 HP, .519 BSFC
4500 RPM 282S = 351 Torq, 301 HP, .565 BSFC

5000 RPM LT-1 = 339 Torq, 323 HP, .596 BSFC
5000 RPM 282S = 333 Torq, 317 HP, .604 BSFC

5500 RPM LT-1 = 315 Torq, 330 HP, .644 BSFC
5500 RPM 282S = 295 Torq, 309 HP, .667 BSFC

Just food for thought!

Plasticman

 

The model you are using for the LT-1 cam WILL NOT YIELD ACCURATE RESULTs, nor will manufacturer's published .050" data for ANY mechanical lifter cam. The published .050" lifter rise data for both GM and aftermarket hydraulic cams is okay to use. See the nearby "30-30 cam..." thread to understand why, and all the timing data is there to create accurate models for all the GM SB mechanical lifter cams.

Cam evaluations using EA should ALWAYS include exhaust back pressure assuming you are working on a street engine. For the Corvette exhaust system I use 250 CFM flow per side, which generates about 3 psi on a good SHP SB at 6500. Even this relatively small amount of back pressure can make a big difference on cams with too much overlap, which includes most of the aftermarket cams of similar duration to the LT-1 cam.

The L-46 cam should make more peak power on any configuration than the L-79 cam, but less low end torque because the L-46 has three degrees more duration, but the big difference is that the lobes are effectively retarded four degrees relative to the L-79 cam.

Duke

 

Duke,

Your above statement implys that I am not using a proper exhaust model, when I think I am - for my system). I am using the 400 CFM exhaust (total) since I do not have the most efficient mufflers/system (headers into 2.25" pipes - with "H" pipe, into typical aftermarket no-name turbo mufflers, and then 2" pipes on a C1).

As for using your revised cam numbers, I ran through both versions for comparison. Your revisions certainly make the LT-1 cam look much better, but since I do not have the same revised numbers for the Comp Cams 282S, I cannot compare them using your method. Whereas with the "published" numbers, a direct comparison (agreed flawed) is obtainable.

Using the EA "Optimizer" for valve event revision, comes up with some pretty wild exhaust duration numbers! Wonder where I can find a 212 intake duration and 252 exhaust duration cam.

Plasticman

 

Plasticman ..
At the time, I thought the 962 cam would be a good way to go compared to the 151. Timing specs were fairly close between the two cams, IIRC. I wished, later on, that I had gone with the 151 cam instead of the 962, as your experience showed.
As it happened I did have for use a brand new GM 151 cam that I had planned on using. Well, one day a guy I knew personally and once worked with asked if it would be ok if he could 'use my cam' in his engine. The agreement was that he would buy another brand new GM 151 cam as payback when the time came to install a 151 cam in my engine. Long story short......... I never saw the guy - or more importantly, a replacement 151 CAM - again .. ! .. If I ever do see that guy again the first thing I'll ask is if he's 'done using my cam' .. .. Funny the things we remember after more than 30 years.
My latest engine rebuild included the LT-1 cam. For various reasons I've had to mothball my resto project, for the time being. The engine rebuild is complete, but on the engine stand. I was originally going to cam my rebuild with a Comp Cams XE 262 grind, as per Comp Cams recommendation. After reading up on specs and cam dynamics right here in the forum related to fast acting lobe ramps and long duration cams I decided against using the XE 262. Yes, Duke influenced that decision .. ! . .
In addition to power and performance I'm also hoping to attain respectable gas mileage. I would like to do some major league travelling in my car so this is an important consideration. The tighter lobe centers and thus shorter duration of the LT-1 cam would seem to complement this function. IMO the LT-1 cam offers reliability and durability in a proven design even if it is 'vintage' ..

John

 

I use 500 CFM total for the C2 2.5" exhaust, so your 400 CFM is probably okay - maybe even 450.

I don't have the optimizer, so I must have an earlier version of EA.

The OE 461 head exhaust ports only flow about 65 percent of the inlets, so a cam with a relatively early opening is best. Assuming you keep the closing point reasonable, duration is longer than inlet and the centerline is advanced. I don't know of any other SB cams that have a 122 BTC exhaust point of max lift like the LT-1 cam.

Massaging the heads improves the exhaust flow more than inlet so you end up with an E/I ratio of .75-.80, which implies equal or even a little less duration on the exhaust side. I put together a "supercam" for massaged 461s that uses the OE LT-1 lobe and indexing on the inlet side and the old Duntov lobe/indexing on the exhaust. This opens the exhaust valve later, but closes it at the same point as the LT-1, which yields maybe one percent more power in the lower rev range with no loss up top, so it's not worth pursueing, However, since the Duntov acceleration is so mild, if you used a titanium inlet valve the valvetrain would probably run to well over 7000 without trouble on OE valvesprings. It would be a good setup for a 283 or 302.

The exhaust opening point has the least effect on the torque curve as long as you don't open it too late, and it really doesn't hurt much to open it too early.

Duke

 

While on the subject, I ran across an old magazine article written by Dave Emanuel in 1986 comparing the "151" cam with a Crane HMV-272.

Engine used was a 355, Performer intake, Holley 0-4777 (650 cfm) carb, headers (size unknown), MSD ignition. Heads were 76cc w/ stock ports, & 1.94/1.5 valves.

Here are a few data points:

1750 RPM: "151" cam = 297 Torq., 99 HP
1750 RPM: Crane 272 = 309 Torq., 103 HP (+3 HP)

2500 RPM: "151: cam = 323 Torq., 154 HP
2500 RPM: Crane 272 = 311 Torq., 148 HP (-6 HP)

3000 RPM: "151" cam = 340 Torq., 194 HP
3000 RPM: Crane 272 = 346 Torq., 198 HP (+4 HP)

4000 RPM: "151" cam = 362 Torq., 275 HP
4000 RPM: Crane 272 = 376 Torq., 286 HP (+11 HP)

5000 RPM: "151" cam = 337 Torq., 323 HP (Max HP)
5000 RPM: Crane 272 = 337 Torq., 321 HP (-2 HP)

5500 RPM: "151" cam = 306 Torq., 320 HP
5500 RPM: Crane 272 = 320 Torq., 335 HP (Max HP)(+15 HP)

Bottom line is that the Crane beat the "151" @ most RPM.

As an exercise, I am going to "reverse" engineer these 2 cams (using the EA sim program), and see how close the program comes to these actual dyno results. It ought to be interesting (and hopefully tell me if the simulator is even close). I will have to take a few "guesses" (like comp. ratio!), but still should be a good test.

One other point I'd like to make about the LT-1 cam: On the Z-28 (with the stock LT-1 cam and with the original GM exhaust system components), the exhaust sound is the best I have ever heard from a small block Chevy.

Plasticman

 

Look at the exhaust opening point of the LT-1 cam compared to the others. There's your answer to the reason why, if you wanted to know.

I expect that dyno test was done with open exhaust and maybe headers. Given that most aftermarket cams of similar duration have more overlap than OE cams, when you put it in a car with manifolds and an exhaust system, it's going to be a different story.

That's one reason why I like EA (and what a lot of guys just don't get). I can simulate the "as installed" configuration, not just predict SAE gross power on a lab dyno.

The bottom line is the torque power curve as installed in the car, not SAE gross numbers on a lab dyno.

Duke