350 HP/327 vs 350 HP/350

[Loren L.]

Gary B's recent post about the cam found in a '58 turned over a few loose rocks in the memory zone that I need to ask about:

1. Am I correct when I remember that the 350/327 camshaft is a different grind than the 350/350?

2. That at some date (early 70's?) Chevrolet supplied the 350/350 cam for ALL 350 HP engines?

[William C.]

Re: 350 HP/327 vs 350 HP/350

No the 300/350 and 270/350 used the "base" cam, but there was a change to the 350/350 cam from the 327/350 version, the duration was reduced about 4 degrees on the intake and 2 degrees on the exhaust, 327 part number 3863151, later part number 3896962 I think Duke had a discussion in the archives about how the changes helped the 350 engine because of the different bore/stroke relationship than the 327.

[Duke W.]

Re: 350 HP/327 vs 350 HP/350

The two camshaft assemblies are very close. The 350/350 cam (3896962) has about 2 degrees more .050" lifter rise duration than the 350/327 (3862151) - 224 versus 222, and though the ...962 inlet and exhaust durations are the same, the actual lobes are different, where the ...151 cam uses the same lobe on both sides.

Both have 114 degrees LSA. The biggest difference between the two is the indexing with the ...962 having a inlet POML of 114 deg. ATDC, while the ...151 is 110.

If you installed the ...962 advanced four degrees it would likely be indistinguishable from the ...151 on a dyno, and likewise if you installed the ...151 retarded four degrees its test results would be within typical dyno repeatabililty (1-2 percent) of the ...962.

Both cams were available through service parts for a long time, and I'm not aware that the ...962 ever replaced the ...151 in service or vice versa.

I suspect the lobes were designed based on what GM had learned about valve train dynamics in the early/mid sixties. Also of note is the that part number is very close to the 3896929 camshaft assembly that when into production on base engines in '67, yet the ...962 didn't show up on a production engine until 1969. It could be that the engineers' intent was to replace the ...151 with the ...962, but tests showed too much low end torque loss on the short stroke 327, and not enough rev potential to take advantage of the higher top end power/revs when you retard a cam.

But the later indexing would work better in a longer stroke engine.

In my simluation work the ...962 yields virtually the same torque curve as the LT-1 cam (all other things equal), but about 500 RPM less valve train limiting speed.

IMO the primary reason for the LT-1's greater power is the higher flowing manifold. The L-46 has the same cast iron manifold as the base engine.

The ...962 cam disappeared from production engines in 1971, but reappeared from '73-'79 in the L-82 engine option.

Duke

[Joe L.]

Re: 350 HP/327 vs 350 HP/350

The two camshaft assemblies are very close. The 350/350 cam (3896962) has about 2 degrees more .050" lifter rise duration than the 350/327 (3862151) - 224 versus 222, and though the ...962 inlet and exhaust durations are the same, the actual lobes are different, where the ...151 cam uses the same lobe on both sides.

Both have 114 degrees LSA. The biggest difference between the two is the indexing with the ...962 having a inlet POML of 114 deg. ATDC, while the ...151 is 110.

If you installed the ...962 advanced four degrees it would likely be indistinguishable from the ...151 on a dyno, and likewise if you installed the ...151 retarded four degrees its test results would be within typical dyno repeatabililty (1-2 percent) of the ...962.

Both cams were available through service parts for a long time, and I'm not aware that the ...962 ever replaced the ...151 in service or vice versa.

I suspect the lobes were designed based on what GM had learned about valve train dynamics in the early/mid sixties. Also of note is the that part number is very close to the 3896929 camshaft assembly that when into production on base engines in '67, yet the ...962 didn't show up on a production engine until 1969. It could be that the engineers' intent was to replace the ...151 with the ...962, but tests showed too much low end torque loss on the short stroke 327, and not enough rev potential to take advantage of the higher top end power/revs when you retard a cam.

But the later indexing would work better in a longer stroke engine.

In my simluation work the ...962 yields virtually the same torque curve as the LT-1 cam (all other things equal), but about 500 RPM less valve train limiting speed.

IMO the primary reason for the LT-1's greater power is the higher flowing manifold. The L-46 has the same cast iron manifold as the base engine.

The ...962 cam disappeared from production engines in 1971, but reappeared from '73-'79 in the L-82 engine option.

Duke

Duke-----


The GM #3863151 was discontinued without supercession about 5 years ago. The GM #3896962 remains available to this day. In fact, it is the cam supplied with several GM SERVICE 350 cid engine assemblies.

By the way, I believe the 3896962 is the oldest cam part number still available from GM. In addition, it must hold the record for longevity in the GM parts system for ANY camshaft under the original part number----over 40 years now. I don't think that any GM cam has ever been available in SERVICE under the original part number for that long------or, anywhere even near that long.

[Duke W.]

Re: 350 HP/327 vs 350 HP/350

That's interesting! They're probably still buying this camshaft assembly from Federal Mogul or Dana. The Speed Pro number is CS1095R and the Clevite number is 229-1615.

It's an excellent cam that incorporates everything GM learned about valve train dynamics in the early to mid-sixties. The difference between the two cams is very subtle and appears to be primarily milder dynamics on the closing flanks of the ...962, which likely reduces the incidence of valve bounce on closing at very high revs.

For a L-79 restoration I would prefer this cam installed with 4 degrees advance to the ...151. With the 3911068 or equivalent valve springs set up properly it should rev to at least 6500, and make a very similar torque curve to the LT-1 cam. The biggest advantage of the LT-1 cam is another 500-700 revs added to the valvetrain limiting speed, and if the heads are properly prepared a 327 will make useable power to 7000+.

Duke

[Steven B.]

Re: 350 HP/327 vs 350 HP/350

That's interesting! They're probably still buying this camshaft assembly from Federal Mogul or Dana. The Speed Pro number is CS1095R and the Clevite number is 229-1615.

It's an excellent cam that incorporates everything GM learned about valve train dynamics in the early to mid-sixties. The difference between the two cams is very subtle and appears to be primarily milder dynamics on the closing flanks of the ...962, which likely reduces the incidence of valve bounce on closing at very high revs.

For a L-79 restoration I would prefer this cam installed with 4 degrees advance to the ...151. With the 3911068 or equivalent valve springs set up properly it should rev to at least 6500, and make a very similar torque curve to the LT-1 cam. The biggest advantage of the LT-1 cam is another 500-700 revs added to the valvetrain limiting speed, and if the heads are properly prepared a 327 will make useable power to 7000+.

Duke

Agree with that. I put together a street/autocross 350 about 30 years ago with that cam and tried 6 degrees and 4 degrees advance. I settled on the 4 degrees and it ran great with no problems.

Steve

[Todd L.]

Re: 350 HP/327 vs 350 HP/350

It never ceases to amaze me the knowledge that is available on this forum. Having access to this forum is well worth my dues.

You guys probably forgot more than I will ever know.

Todd