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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I have been out of the 3rd gen circle for awhile as I sold my 87 IROC back in 2018. I have since picked up a 92 TPI B4C L98 project this past year and am back here seeking advice. Thank you for taking a look!
Recently I picked up a camshaft very inexpensively and I believe it to be a GM 94666492. Online searching hits primarily that this is a Crane Camshaft 2032 grind part#104224, however there is also some folks who believe it can also be the Howards 180225-12 cam. Both are similar but the Crane cam is slightly bigger. My concern is that I have attempted to measure gross valve lift and also duration at .50 with a makeshift bench tool and Harbor Freight dial indicator to see which of the two grinds this cam more closely matches, and my readings are much different than either option. Could it be that my measurements are simply very inaccurate with the tools I'm utilizing, I am missing a piece of the mathematical puzzle, or that this cam is neither of the two mentioned and is completely different? Here are my measurements and also specs of what the Crane & Howards Cams are:
Crane Cam Duration at 050 inch Lift: 214 int./220 exh. Valve Lift with Factory 1.5 Rocker Arm Ratio: 0.452 int./0.465 exh. Lobe Separation (degrees): 112
Howards Cam Duration at 050 inch Lift: 207 int./213 exh. Valve Lift with Factory 1.5 Rocker Arm Ratio: 0.450 int./0.465 exh. Lobe Separation (degrees): 112
My Readings taking measurements from camshaft Cylinder 3 int/exh & Cylinder 4 int/exh back from the front of the camshaft as follows:
Front of camshaft position in order- 1e, 2e, 1i, 2i, 3i, 4i, 3e, 4e, 5e, 6e, 5i, 6i, 7i, 8i, 7e, 8e,
Cyl. 4 Intake duration 94 deg cam x2 crank = 188 degrees, .305 lift x1.5 rocker ratio = .457
Cyl. 4 Exhaust duration 99 deg cam x2 crank = 1198 degrees, .313 lift x1.5 rocker ratio = .469
Cyl. 4 ICLexh. - ICLint. = 110 deg (however I believe this measurement to be wholly unreliable with my instrumentation, could be 112 degrees also)
There is a lot of indication that my 6492 camshaft could be an OEM Mercruiser marine camshaft 431-866022T takeout. Any thoughts on what I have and the numbers listed above? Could it be another GM takeout grind perhaps? Could I expect this camshaft to provide any better performance in an otherwise stock 92 L98 engine with 083 heads and standard TPI intake, assuming a spring upgrade? 92 L98 cam specs I believe are GM#10111773, 202/207 .413/.428 114.5, 90-92 350,305
Thank you
87 SLEEPER
Last edited by 87SLEEPER; Dec 8, 2025 at 11:04 PM.
Re: Picked up a Mystery GM 6492 Camshaft. My measurments don't add up. HELP
Wanted to update that new information since original post leads me to believe I was mistakenly measuring the bare cam for lift at .050 when in fact it needs to be measured at .0333 when the cam is on the bench rather than in the block. At this new measurement my duration is roughly 208/216 and this checks out with what many have indicated is close to the Howard's mentioned above.
Re: Picked up a Mystery GM 6492 Camshaft. My measurments don't add up. HELP
Stop stressing over it, throwing it in, fire it up, may need a little VE tuning if it is a speed density setup but I bet even then it runs pretty decently and enjoy the added power. That cam really likes 10-10.3:1 compression, a 2,500 rpm converter and good exhaust flow from headers and a decent exhaust. A 1.6 rocker will pull some more lift and duration through the curve as the ramp rates are milder which is great for cam/lifter life and low noise to keep the knock sensor happy. It also enjoys better head flow but will work well even with the stock heads.
My 10.25:1 L31 with that cam, 1.6 full roller rockers, aftermarket 185cc intake runner 2.02/1.60 Vortecs and a dual plane MPFI intake manifold with a 1,000 cfm 4150 TB made 348 rwhp @ 5,300 and 387 rwtq @ 3,100 rpm through a TH400 in 2nd gear with the clutch fan screaming on the dyno in a 100F heat.
The 6492 cam works extremely well in a 350 where the TPI setup wants to make power RPM wise. I have also tuned a TBI 350 truck with this same cam used as a roller cam upgrade and it too ran extremely well especially compared to the 194/203 @ 0.050 flat tappet stock TBI truck cam. It had the stock swirl ports, stock TBI manifold, stock TBI unit, shorty headers, Y-pipe into a single 3" cat and still made ~260 whp and ~330 wtq.
In for what for all practical purposes is a factory L31 truck engine the 6492 cam makes 300-340 hp under 5,000 rpm and 380-400 tq in the various boats it came in. That was using the Mexican Vortecs that flow terribly with GMs crappy 12cc dished pistons at 9.1:1 compression with 0.053" thick marine stainless head gaskets.
Re: Picked up a Mystery GM 6492 Camshaft. My measurments don't add up. HELP
Originally Posted by Fast355
Stop stressing over it, throwing it in, fire it up, may need a little VE tuning if it is a speed density setup but I bet even then it runs pretty decently and enjoy the added power. That cam really likes 10-10.3:1 compression, a 2,500 rpm converter and good exhaust flow from headers and a decent exhaust. A 1.6 rocker will pull some more lift and duration through the curve as the ramp rates are milder which is great for cam/lifter life and low noise to keep the knock sensor happy. It also enjoys better head flow but will work well even with the stock heads.
My 10.25:1 L31 with that cam, 1.6 full roller rockers, aftermarket 185cc intake runner 2.02/1.60 Vortecs and a dual plane MPFI intake manifold with a 1,000 cfm 4150 TB made 348 rwhp @ 5,300 and 387 rwtq @ 3,100 rpm through a TH400 in 2nd gear with the clutch fan screaming on the dyno in a 100F heat.
The 6492 cam works extremely well in a 350 where the TPI setup wants to make power RPM wise. I have also tuned a TBI 350 truck with this same cam used as a roller cam upgrade and it too ran extremely well especially compared to the 194/203 @ 0.050 flat tappet stock TBI truck cam. It had the stock swirl ports, stock TBI manifold, stock TBI unit, shorty headers, Y-pipe into a single 3" cat and still made ~260 whp and ~330 wtq.
In for what for all practical purposes is a factory L31 truck engine the 6492 cam makes 300-340 hp under 5,000 rpm and 380-400 tq in the various boats it came in. That was using the Mexican Vortecs that flow terribly with GMs crappy 12cc dished pistons at 9.1:1 compression with 0.053" thick marine stainless head gaskets.
This is basically my plan. Install and send it. Most any consensus is that it's an improvement over the stock cam, even if no one truly knows it's specs. Fortunately, I was able to get my hands on some better test instruments through a buddy of mine and will post those readings later when I can for comparison. See if this harbor freight dial tool is worth a damn.
Here is with another set of instruments. I'm still not confident on the LSA, but keep coming up with 110 or 111. Could it really be that a stock GM cam has such a tight LSA? Assuming this is an OEM marine takeout application.
Exhaust Duration. 216 Exhaust Duration Intake Duration 206 Intake Duration Exhaust Base Exhaust Lift. .459 Intake Base Intake Lift. .453 ELC Lift ILC Lift LSA. 110 or 111
Last edited by 87SLEEPER; Dec 12, 2025 at 06:34 PM.
Here is with another set of instruments. I'm still not confident on the LSA, but keep coming up with 110 or 111. Could it really be that a stock GM cam has such a tight LSA? Assuming this is an OEM marine takeout application.
Exhaust Duration. 216 Exhaust Duration Intake Duration 206 Intake Duration Exhaust Base Exhaust Lift. .459 Intake Base Intake Lift. .453 ELC Lift ILC Lift LSA. 110 or 111
In the engine block I measured 111 ICL and 120 ECL on my later 6492 cam purchased from GM in like 2017. This was with my dial indicator directly on the lifter body with the heads off. Lift measurements are lobe lift. Mine idles with 20 in/hg vacuum at 625 rpm in the 350 it is in with 1.6 rockers on it so I feel the 115.5 LSA is correct atleast for my cam. I have idled it down as low as 450 rpm and it was still making 17.5 in/hg idle vacuum and still running smoothly. It is very smooth running at low rpm because marine engines rely on very low idle speed to engage the dog clutches to go into gear however it does have a bit of an exhaust note to it from the larger exhaust lobe similar to the ZZ4 208/221 cams.
I had the crank, #1 rod and piston without the rings and the cam with the factory Vortec single roller chain when I measured mine. I first verified exactly where TDC was with the piston then moved to the cam.
