Dan H.

Several folks have given me recommendations on a stock cam replacement for my LT-1. I have a couple questions about the differences (subtle I think) but the devil is in the details.

Here are the cam specs from part number 3972178
FRom GM partsdirect
This mechanical flat tappet is used on the 70-71 Corvette and Camaro LT-1. It is a good all around street mechanical cam (ID#3972182). The duration at lash point in degrees (intake/exhaust) is 300/312; duration at .050" tappet lift (intake/exhaust) is 242/254; and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 435/455. Valve lash is 024/030 and lobe centerline is 116 degrees.

Here is the Crane Cams version
Brand Crane Cams
Manufacturer's Part Number 110951
Part Type Camshafts
Product Line Crane Mechanical Flat Tappet Camshafts
Summit Racing Part Number CRN-110951
UPC 02117404495

Cam Style Mechanical flat tappet
Basic Operating RPM Range 2,800-6,600
Intake Duration at 050 inch Lift 242
Exhaust Duration at 050 inch Lift 251
Duration at 050 inch Lift 242 int./251 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.459 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.485 in.
Valve Lift with Factory Rocker Arm Ratio 0.459 int./0.485 exh.
Lobe Separation (degrees) 116
Camshaft Gear Attachment 3-bolt
Intake Valve Lash 0.020 in.
Exhaust Valve Lash 0.025 in.
Computer-Controlled Compatible No
Grind Number 3972182
Valve Springs Required Yes
Quantity Sold individually.
Notes Replacement for factory 330 hp, 350 cu. in. camshaft. Must machine cylinder head for required larger valve springs.


My questions
There is a difference in valve lash
.020/.025 Crane vs. .024/.030 GM

Difference in Valve lift
.459/.485 Crane vs. .435/.455 GM

Duration at .050 lift
242/251 Crane vs. 242/254 GM

These differences are small fractions of an inch. My goal is to be as close to stock as the marketplace allows. Do these subtle differences present issues anywhere else? I have purchased the Comp Cams lifters with the EDM oiling holes. GM no longer sells 3972178.

I understand there is modern technology and better cams to use. Please understand, I'm not interested in those. I want to use the original stuff.

cv67

Valve timing events are probably where the real changes are. The .050 lift duration dont tell the whole story.

DRIVESHAFT

You might try sending an e-mail to Chase Knight at Crane Cams. cknight@cranecams.com

He's been with Crane for 40+ years & can probably tell you anything that you want to know about their LT-1 grind.

ezobens

Just to add to the confusion, Elgin also makes an LT-1 cam:
http://catalog.elginind.com/app/Engi...gh+Performance

Les

The Crane lift specs are a match for the original factory cam. The lash specs for the GM cam are a match for the original factory cam. The duration specs for the Elgin cam appear to be a match for the original factory cam, although they don't list if they're at .050. I'm pretty sure the lobe separation of the Crane cam is a match for the factory cam, if memory serves.

Bottom line, they would all perform in a very similar way. If I had to choose one, I'd go with the Crane cam because the specs are most correct but it has a tighter lash design and I happen to prefer that.

What compression do you plan to run?

Dan H.

9.5:1

Already got a response from Chase at Crane Cams. This was very helpful and provided the answers I was looking for. I'm posting it because it may help others understand that may have the same question.

***Email below from Chase***
Hello Dan,
There were indeed two Chevrolet camshafts, the original 3972178 (correct for your car) and the superseded version 3972182. The 182 having a slightly different lobe ramp design, therefore the different valve lash.
There’s a lot of different information out there on the cam specs. For example, I found one early Chevrolet manual listing the 3972178 as 229 and 237 at .050”, while the 1994 GM Performance manual lists it as 242 and 254.
The valve lift that we list is the gross valve lift, which is the cam lobe lift times 1.5 (your rocker arm ratio). The GM specs represent the net valve lift, which is the gross lift minus the valve lash.
We do sell a BluePrinted 3972178 cam also, with the .024” and .030” lash. This is our part number 11-3972178. Although it’s a special order item, it’s the same price as the 110951. Both of our part numbers check 242 and 254 at .050”, not sure where you obtained the 251 exhaust for the 110951 (Summit misprint?). These profiles are based on GM prints that we computer smoothed for better valve train stability, but would not affect the performance characteristics of the engine. Idle quality, vacuum, and power levels would be virtually identical to stock, while the RPM potential of our version may be slightly higher than the factory piece.
Lifters must be replaced, but the rest of your valve train will accommodate either of these grinds.
It would be very difficult to notice any difference in drivability and performance between either grind. If you want the 3972178 with the .024/.030” lash, as would be factory correct, the 11-3972178 would be the way to go.
Please let me know if you have any other questions.

Regards, Chase

63mako

I would lean toward the Crane 110951. It is a tighter lash cam with the same characteristics as your factory cam. Better valvetrain stability and tighter lash specs will lead to less wear, better long term dependability and less frequent valve adjustments. I think the differences you are seeing in some of the specs especially the duration @ .050 are the difference between the lash being taken into account and not. In other words the true duration at actual .050 lift and the duration at actual .050 lift minus the lash.

Belgian1979vette

Mayor intensity of the crane cam is higher, meaning it will have more area under the curve and produce more power and torque. The 116 lc is prohibitive of higher rpm's and power.

Solid LT1

Same cam profile just GM lists "Net Lift" taking into account lash settings where Crane has "Gross Lift" if you subtract the lash setting, from the Crane figures you will see what I mean. Melling also has this grind in their catalog, and probably provides it to GM as an OEM replacement. The quality of the Crane cam would probably be better than other grinders. I have not used a Crane cam in may years but, Crane always had decent quality.

Dan H.

Thank you all. I ordered the Crane 110951.

Radiator and shroud are out. This weekend I'm going to tackle the water pump, radiator frame, and pick up a harmonic balancer puller. I know the support doesn't have to be removed, but its one of the few parts on the car that has any rust. So I'll get it sand blasted and paint it up while its all apart.

I will also take a look at whats needed to get the oil pan off. My father seemed to think the pitman arm has to be disconnected to get the pan off.

Solid LT1

Unbolt the Idler Arm on the passenger side of the frame then you should be able to pull down the steering center link and remove your oil pan without damaging any suspension seals.