I'm in the process of rebuilding the motor on my 1967 SB 350hp. My current CAM has some wear and I'm looking into replacement options. My only concern with the stock L79 cam is low RPM performance; a friend with a 300hp engine is faster off the line. My research has yielded three options at this point:

1) L79 Stock CAM
2) LT-1
3) Competition CAM - Model 234-2 (recommended by summitracing.com)

Here are specs. on the CAM options I've looked into:

CAM Name, LIFT Intake, LIFT Exhaust, Duration

L79, .447, .447, 342
LT1, .458, .485, 317
234-2, .447, .454, 268
Base 300hp, .398, .398, 258

I've been told that a lower duration will give you more power at lower RPMs. Therefore, I'm thinking that the 234-2 offers the best blend at this point.

Can anyone provide more information on the specs, or give recommendations?

 

Those cam specs are all measured using different contexts, so comparing them is misleading and meaningless, and without point of maximum lift indexing there is insufficient data to compare even if the duration numbers were all listed in the same context.

I recommend that most L-79 owners rebuilt their engines to OE spec or install a LT-1 cam if they want a bit more top end power and the extra 500 revs at a slight loss in low end torque.

The 300 HP cam is stronger up to about 3000-3500, so "detuning" a L-79 with the 300 HP cam is an option if you rarely rev the engine over 3500. I only recommend OE cams made by reputable manufacturers such as Federal Mogul.

Whichever can you use, pocket porting, port matching the heads will improve top end power 5-10 percent without changing the low end torque characteristics.

All this has been extensively discussed. Suggest you do an archive search.

Duke

 

Duke, On the subject of cams, talk a bit about big blocks. Can you tell me about the characteristics of the L78 cam in a 396? What is the rpm range when it should really come on?

 

The L-78/72/71 cams all use the same lobe on both the inlet and exhaust although there are two different camshaft part numbers because the rear journal groove was eliminated in 1967.

The basic specs for these cams are as follows:

Duration (.050" lobe lift above the top of the base circle): 231 inlet and exhaust (This can be compared directly with typical hydraulic cam .050" specs)
Points of max lift: 108 ATDC/120 BTDC
Gross lobe lift: .30572" inlet and exhaust
Top of clearance ramp, above base circle: .012" inlet and exhaust

Since the lobe is asymmetrical, the point of max lift is not coincident with the "centerline".

This lobe was also used on the LT-1 cam inlet side, indexed at 110 ATDC POML. The LT-1 cam used the 30-30 lobe on the exhaust side, indexed four degrees earlier at 122 BTDC POML.

Due to the longer stroke, this lobe is somwhat "milder" in a BB than SB, but it is still definitely a SHP cam. In a BB it should show peak torque at around 4000 and may show a little weakness down low, especially compared to the 390/400 HP cam, with a surge of torque in the mid 3000 range. With massaged OE heads it should be very strong from 4500-6500.

Duke

 

Duke
sorry if this is a dumb question but I know nothing about camshafts. I know from a lot of previous posts you recommend the LT-1 cam on motors like my '65 L76 over the stock 30-30 cam for a bit more low rpm range torque. Based on that I assumed the LT-1 cam was a solid lifter cam but in this thread you are recommending using either the LT-1 or the stock cam.
Does that mean that the same cam can be used on either solid lifter or hydraulic motors or would putting an LT-1 cam into a L79 also require changing the lifters to solids?

sorry to sidetrack your thread Dusseaud.

 

This is probably the best street driven small block cam I ever used. GM Hydraulic #3896962 Works great with 9 - 10.5 compression.

good luck

 

3000 to 6200

 

You say your friends car is faster off the line with the 300 engine. I don't think I'd buy that if everything else is equal, meaning the gearing and tires are the same and the engines are in good tune. The 300 will pull slightly better below 2500 or so than a 350. In a drag race, you're never UNDER 2500. You may have a higher overall gear than your buddy. Higher rear gear or close ratio transmission. If that's the case, you're gonna' get beat from a dead stop regardless of what cam you put in it. On the top end, you'll pull it back but it's easier to get it to start with.

The 300 cam is a rather unexciting cam, pulls good from 700 rpm up in high gear but runs out of breath pretty quick. Keep the 350 cam and make sure it can stay at least high 2000's for plenty of kick.

I wouldn't use the LT-1 cam in anything it didn't come in from the factory for several reasons. And then I still might not use it.

 

I used the 962 cam in my 327/300hp with good results. After about 5000 revs the power band lost some steam but overall performance was still good. This cam will easily rev to 6K. The stock 929 cam will outpull the 962 in the lower rev range, no question.

 

Camshafts are specifically designed for either mechanical or hydraulic lifters. The clearance ramp designs for the two are completely different.

The LT-1 and 30-30 cams are mechanical lifter, L-79 is hydraulic.

Whenever a new camshaft is installed it should be accompanied by NEW lifters of the proper type. A used camshaft in good conditions should be installed with the same lifters each lobe mated with (MARK them) or new lifters should be used.

Duke

 

I am a new member (today) and this format is totally strange to me, so I hope I can get someone to get me headed in the right direction.

I am a G.O.F. (genuine old fart). I bought a brand new 327, 360 hp short block in the crate from Chevrolet about 1964/5. I had a friend who worked for the dealer in Glendale California, and I remember that I paid about $250 for the short block (dream on). I know I paid about $25 bucks more for the new Muncie 2.54? first gear four speed.

The engine was installed in a 1956 Arnolt Bristol, and at 2400 pounds wet, was a terror on the street. (where else??)

I am in the process of restoring this little life long project and have quite a few questions that I hope this club can answer. One of the first is the actual specs for the :"30/30" Duntov cam, so I can compare it with modern camshafts. Since the car is light, even with an 11 pound pie plate for a flywheel, I never had problems with low end torque.

At some point in time, I bought a pair of 261X(?) 2.02 heads, which along with the flip top fuel injection (which I still have) made it a factory 375 HP. I eventually pulled the F.I. due to bad carbon bearings in the high pressure pump. I replaced it with a stock factory 302 Z28 highrise and 780 Holly duel feed, with all the trick stuff I could figure out. The combination must be close to right because I used to be able to nail the throttle at about 1500 and pull steady in fourth gear until I ran out of guts or road. The engine was limited to 6800 due to either valve float or point bounce. (Mallory high spring rate single points.)

My best guess is that the engine has less than 35K on it. I am hoping to get away with keeping the stock Corvette forged domed pistons. When I put it back together, I obviously have to do something with the 11.5 compression and non lead free heads. I am looking at aluminum heads with about 70, vs 64 cc chambers. I have always been happy with the Duntov cam but wonder if sometime in the past 40 years something CONSIDERABLY better hasn't come along. This will be strictly a fun to drive hot rod, with no intention of trying to qualify for some class of racing. (on the other hand, I like to go fast!!!!!)

If I am totally lost, as far as your protocols go, someone can E mail me at Thumpermcq@aol.com.

Thanks, Jim McQuay/ Arnolt57

 

thank you Duke. That confirmed my initial thoughts on the camshafts that they were designed for one or the other lifter types.
so, if the poster of this thread ended up going with the LT-1 cam he would have to swap out to solid lifters also, in affect converting his motor into an "upgraded" L76 as I believe the only other significant different between the L79 and the L76 besides cam and lifters was the larger oilpan?
Thanks for the above answer Duke.

 

Due to the longer stroke, this lobe is somwhat "milder" in a BB than SB, but it is still definitely a SHP cam. In a BB it should show peak torque at around 4000 and may show a little weakness down low, especially compared to the 390/400 HP cam, with a surge of torque in the mid 3000 range. With massaged OE heads it should be very strong from 4500-6500.

Duke[/QUOTE]
Thanks Duke, You have answered my question. The previous owner of my L78 rebuilt the engine in 1987 and he told me it is completely stock other then improved valve springs and teflon seals. Pistons and cam are original. I noticed immediately that the car below 3000-3500 didn't have as much as my 67 427/390, but it pulls very strong above 4500 all the way up. One thing I did find that was an issue was the wrong springs were in the Holley and the secondaries were not opening all the way nor as quickly as they should. After replacing the springs, response to WOT was much quicker, and the engine winds up faster.

 

The 30-30 cam (it is NOT the "Duntov 30-30") is 239/239 110/118, .323", .017" It's really too big for a good street cam, but it's a good vintage racing cam. In a light car the relative paucity of low end torque may not be as big an issue. With pocket ported heads, the LT-1 cam (231/239. 110/122, .306/.323. .012/.017) makes nearly the same top end power, with better low end torque, which is why I recommend it to replace the 30-30. The Duntov cam is obsolete.

Typical OE machined blocks with the forged domed pistons will come in at about 10.5:1 with a typical composition head gasket. Don't install big chamber heads, but make all the MEASUREMENTS to compute actual CR.

The best modification you can make is to pocket port/port match the heads.

The early 327 rods are WEAK and should be replaced with higher quality rods. I recommend Crower Sportsman.

All these issues have been extensively discussed. Search the archives. Also specifically search for threads started by "Dave McDufford" to see dyno results for a LT-1 cammed 327. With a better 180 degree inlet manifold Dave's engine would have pulled about 375-380 and close to 400 with FI.

Duke

 

Correct. Search for threads started by "Dave McDufford". That's what he did.

Duke

 

A good combination in a street engine is to use the stock 350HP cam but have it advanced 4 degrees at installation. This will give you greater torque at lower RPM and will only hurt top end power slightly.

 

Duke, thanks for the reply. I wonder if I have a misunderstanding on which cams we are talking about. Back in the dark ages, the later cam, in the 360 to 375 HP 327's were referred to on the street as a 30/30 Duntov. This was because the cam had quieting ramps and called for 30 thousands valve lash, cold. If you got much tighter than 28 thousands, the low end went to hell. Is this the cam you are refering to as the 30/30 cam, or am I lost in space. Mine certainly worked ok on the street, even pulling 3:23 rear end gears. Of course, the 2.54(2.53?) first gear Muncie and 2400 pounds helped.
thanks, Jim.

 

In the early/mid 1960's in Eugene, Oregon we called the cam that came in 360 hp 327 engines the 30/30 cam. We call an earlier cam that came stock in 270hp 283 engines the Duntov cam.

Maybe there were regional differences?

 

Thanks, I think at the time, all high performance corvette's were considered "duntov" cammed by the local hot rodders hanging around Bob's Big Boy in Glendale, Pasadena, Taluka Lake. It's a hoot that you were in Eugene. I grew up in the Glendale California area but am now in West Linn, Or, and have been since the late 60's.

Jim.

 

As Duke mentioned the Duntov is not the 30-30 cam. The 30-30 is a beast of it's own. I think the 30-30 was used to replace the Duntov, and first showed up in 1964.

The 30-30, (from the AIM) is lashed at .030, but Duke and JohnZ did a total reverse engineering project and posted there finding some time ago, along with a cold lash procedure that works great. .026" on both the intake and exhaust works just fine, and contributes to a smother idle, and less "clacking". New data Duke brought forth shows that .023" would be just fine as well, and I used that on my last adjustment.