1992 LT1 Camshaft

[Joe L.]

Most folks don't know this but the 1992 Corvette LT1 used a unique camshaft that was not used for any later LT1. This camshaft was GM #10168506. Here's what happened: 1992 Corvette LT1's had excessive engine noise and many complaints were received over it. The noise made the engine sound like it was equipped with mechanical lifters. Of course, by 1992 virtually no US engines were equipped with mechanical lifters and had not been so-equipped for MANY years (the last GM PRODUCTION engine so-equipped was the 1972 LT-1). So, the mechanical lifter-like sound of the 1992 LT1 was only appreciated by the few and not the many.

It tuned out that the noise was mostly created by the lobe ramp profile of the 10168506 camshaft. So, for the 1993 model year GM did at least 2 things to quell it. First, they slightly revised the camshaft lobe ramp profiles. This helped "quiet down" the engine without having any reported effect on power output. Second, they eliminated the magnesium valve covers used for 1992 and, instead, used new design composite valve covers. The new composite valve covers would also help attenuate any remaining noise.

The GM #10168506 camshaft was discontinued from SERVICE in July, 1997, most likely when GMSPO inventory was exhausted, and and replaced by GM #10224241, the 93-94 LT1 camshaft.

[Clem Z.]

Re: 1992 LT1 Camshaft

Most folks don't know this but the 1992 Corvette LT1 used a unique camshaft that was not used for any later LT1. This camshaft was GM #10168506. Here's what happened: 1992 Corvette LT1's had excessive engine noise and many complaints were received over it. The noise made the engine sound like it was equipped with mechanical lifters. Of course, by 1992 virtually no US engines were equipped with mechanical lifters and had not been so-equipped for MANY years (the last GM PRODUCTION engine so-equipped was the 1972 LT-1). So, the mechanical lifter-like sound of the 1992 LT1 was only appreciated by the few and not the many.

It tuned out that the noise was mostly created by the lobe ramp profile of the 10168506 camshaft. So, for the 1993 model year GM did at least 2 things to quell it. First, they slightly revised the camshaft lobe ramp profiles. This helped "quiet down" the engine without having any reported effect on power output. Second, they eliminated the magnesium valve covers used for 1992 and, instead, used new design composite valve covers. The new composite valve covers would also help attenuate any remaining noise.

The GM #10168506 camshaft was discontinued from SERVICE in July, 1997, most likely when GMSPO inventory was exhausted, and and replaced by GM #10224241, the 93-94 LT1 camshaft.

i am not familiar with that year corvette but did it have roller rockers as i know some corvettes did and they are noisier than the stamped steel rockers in any chevy engine

[Pat M.]

Re: 1992 LT1 Camshaft

Joe, the 96 LT4 cam was completely different from the last LT1 cam, right?

[Duke W.]

Re: 1992 LT1 Camshaft

Valvetrain noise is highly affected by jerk - the rate of change of acceleration, which is associated with shock loading - like hitting something with a hammer.

Sixties cam designs have lower peak jerk than fifties designs. This reduced valvetrain loading and noise. The 30-30 and LT-1 cams are quieter than the Duntov because the Duntov lobes show peak jerk just a couple of thousandths above the tops of the clearance ramps. The '67-'74 base engine's cam has only half the peak jerk of its '57-'66 antecedent.

Roller cams typically have higher jerk, so they can end up being noisy.

The LS valvetrain is considerably stiffer than the Gen I valvetrain, so it can handle higher jerk, but it's noisier.

...ever heard a classic luxury car from the thirties idle? Most have mechanical lifters, but the engines are virtually silent at idle because the valve train dynamics are so mild. For this and other reasons, they didn't have high specific output, but their large displacements yielded high torque, which was more than adequate when "highways" were what we now call two-lane country roads, and speed limits were 55 MPH.

Duke

[Joe L.]

Re: 1992 LT1 Camshaft

i am not familiar with that year corvette but did it have roller rockers as i know some corvettes did and they are noisier than the stamped steel rockers in any chevy engine

clem------


All 1992-96 LT1 engines used conventional stamped steel rockers, all of the guided type. The 1996 LT4 was the first "modern day" Chevrolet engine to use roller fulcrum and roller tip rocker arms. After that, of course, Gen III and IV series engines all used roller fulcrum rocker arms (but not roller tips).

[Joe L.]

Re: 1992 LT1 Camshaft

Joe, the 96 LT4 cam was completely different from the last LT1 cam, right?

Pat------


Yes, it was. It was GM #12551142.

[Bill M.]

Re: 1992 LT1 Camshaft

It tuned out that the noise was mostly created by the lobe ramp profile of the 10168506 camshaft. So, for the 1993 model year GM did at least 2 things to quell it. First, they slightly revised the camshaft lobe ramp profiles. This helped "quiet down" the engine without having any reported effect on power output. Second, they eliminated the magnesium valve covers used for 1992 and, instead, used new design composite valve covers. The new composite valve covers would also help attenuate any remaining noise.

No difference in power, but torque was 330 lb-ft for '92 and 340 lb-ft for 93-96...

Joe, have you seen comments by Dave McLellan on the comparison of the solid-lifter LT-1 lash "music" to the '92 LT1? I can't find it. I remember he drove an LT-1 convertible through Yosemite? It's possible that I remember it from a talk he gave to the Michigan Chapter.

[Joe L.]

Re: 1992 LT1 Camshaft

No difference in power, but torque was 330 lb-ft for '92 and 340 lb-ft for 93-96...

Joe, have you seen comments by Dave McLellan on the comparison of the solid-lifter LT-1 lash "music" to the '92 LT1? I can't find it. I remember he drove an LT-1 convertible through Yosemite? It's possible that I remember it from a talk he gave to the Michigan Chapter.

Bill------


I have not seen or read those comments.