Cam Motion 6.2L Stage 2 feedback
Sep 17, 2021 | 07:26 PM
#21
I was pretty sure the only difference between the L92 and LS3 heads is a lighter valvetrain. Maybe someone else has better info.
Every bench is going to be a little different, the bore size, and the adapter entry plays a factor. Plus we don't know for sure what pressure drop they used (28"H2O? 25"H2O?), as not everyone uses the same standard. I assumed given the healthy numbers, the LS1Tech was @ 28". I've also noticed a some of the Motortrend numbers being a bit more pessimistic on different heads.
The other factor could be interpolation. For late GM heads, there's typically a bigger delta going from .500" lift and .550" versus between .550" and .600" lift. So if you only have the .500" and .600" and the program interpolates linearly, it's going to predict low. I try to find data with the .550" lift point whenever possible to better understand where flow curve.
The spotty information I've found on GM cam data has intensities going from as low as 63 to as high as 77 (even varies intake vs exhaust on the same cam sometimes). Don't have it for this one.
Every bench is going to be a little different, the bore size, and the adapter entry plays a factor. Plus we don't know for sure what pressure drop they used (28"H2O? 25"H2O?), as not everyone uses the same standard. I assumed given the healthy numbers, the LS1Tech was @ 28". I've also noticed a some of the Motortrend numbers being a bit more pessimistic on different heads.
The other factor could be interpolation. For late GM heads, there's typically a bigger delta going from .500" lift and .550" versus between .550" and .600" lift. So if you only have the .500" and .600" and the program interpolates linearly, it's going to predict low. I try to find data with the .550" lift point whenever possible to better understand where flow curve.
The spotty information I've found on GM cam data has intensities going from as low as 63 to as high as 77 (even varies intake vs exhaust on the same cam sometimes). Don't have it for this one.
Sep 17, 2021 | 07:53 PM
#22
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Thanks Formula, would you think it would be normal for the stock cam to beat "truck" cams below about 4000rpms? Also given that most truck cams are decently light on the LSA so to not cause rough idle, so they have to push their valve events out away from each other rather than a rough idle cam with more overlap?
Sep 20, 2021 | 11:52 AM
#23
Thread Starter
Teching In
Joined: Sep 2021
Posts: 34
Likes: 9
From: Richmond, VA
Thanks for all of the feedback so far. Just remembered that I still have a set of Vinci high tensile chrome-silicon steel dual valve springs that were run for only a few hundred miles. Since I have some time to spare while my cam is made, I'm thinking of swapping out the BTR beehives for these duals. I also have a set of new Fel-Pro seals to go with them. Would these be a good match for this cam and a worthwhile "upgrade"? I'm using factory rockers with a BTR trunnion upgrade, BTR chromoly pushrods and new Chevrolet Performance lifters. Thanks for any thoughts.
Specs:
155 lbs @ 1.780"
360 lbs @ 1.230"
380 lbs @ 1.180"
400 lbs @ 1.130 "
coil bind @ 1.070"
od; 1.300
id: .509
Max lift: .660
Specs:
155 lbs @ 1.780"
360 lbs @ 1.230"
380 lbs @ 1.180"
400 lbs @ 1.130 "
coil bind @ 1.070"
od; 1.300
id: .509
Max lift: .660
Sep 20, 2021 | 02:56 PM
#24
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One argument for the dual valve springs is, if the o.d. breaks, the inner spring may keep the valve closed so you don't have to worry about damage (although even during a break with a mild camshaft does that happen). At least that's the theory.
Overall, you want just enough force to keep the valve from lifting off the nose under high rpm (creating valve float and valvetrain damage). But too much increases hertzian stresses on the cam lobe and lifter, plus more stress on the rocker arm, and increases parasitic torque loss. So you don't really want to go too far in the other direction on a vehicle that will see a ton of miles.
Given this is a daily driven truck that rarely see high rpm, and a mild cam, the dual springs would be overkill. The beehive should be plenty.
Overall, you want just enough force to keep the valve from lifting off the nose under high rpm (creating valve float and valvetrain damage). But too much increases hertzian stresses on the cam lobe and lifter, plus more stress on the rocker arm, and increases parasitic torque loss. So you don't really want to go too far in the other direction on a vehicle that will see a ton of miles.
Given this is a daily driven truck that rarely see high rpm, and a mild cam, the dual springs would be overkill. The beehive should be plenty.
Sep 20, 2021 | 08:00 PM
#25
One argument for the dual valve springs is, if the o.d. breaks, the inner spring may keep the valve closed so you don't have to worry about damage (although even during a break with a mild camshaft does that happen). At least that's the theory.
Overall, you want just enough force to keep the valve from lifting off the nose under high rpm (creating valve float and valvetrain damage). But too much increases hertzian stresses on the cam lobe and lifter, plus more stress on the rocker arm, and increases parasitic torque loss. So you don't really want to go too far in the other direction on a vehicle that will see a ton of miles.
Given this is a daily driven truck that rarely see high rpm, and a mild cam, the dual springs would be overkill. The beehive should be plenty.
Overall, you want just enough force to keep the valve from lifting off the nose under high rpm (creating valve float and valvetrain damage). But too much increases hertzian stresses on the cam lobe and lifter, plus more stress on the rocker arm, and increases parasitic torque loss. So you don't really want to go too far in the other direction on a vehicle that will see a ton of miles.
Given this is a daily driven truck that rarely see high rpm, and a mild cam, the dual springs would be overkill. The beehive should be plenty.
Any idea why 68Formula? You hear the only place for a reverse split cam in the usual 2 valve large intake smaller exhaust valve type engines is with turbos, but then you hear any cam is a "turbo cam". As with the cam above, obviously no one would probably use it as a "truck cam", especially since I optimized it starting at 2000 rpms. Also that's where the stock converter will stall up to at full torque but not if the converter is locked. In reality if towing you would be in tow haul and the engine probably would always be above about 2500rpms if towing a lot, so not sure there is a point trying to optimize torque that low.
The cam above would have 7 degrees of overlap @ 0.050 and I wouldn't' think it would idle that good which wouldn't be a very good "truck cam".
Sep 20, 2021 | 08:54 PM
#26
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While trying to iterate through cam profiles while maximizing the torque area under the curve between 2000-6500, then moving towards 2000-6000, I find it starts to reverse split the cam:
Any idea why 68Formula? You hear the only place for a reverse split cam in the usual 2 valve large intake smaller exhaust valve type engines is with turbos, but then you hear any cam is a "turbo cam". As with the cam above, obviously no one would probably use it as a "truck cam", especially since I optimized it starting at 2000 rpms. Also that's where the stock converter will stall up to at full torque but not if the converter is locked. In reality if towing you would be in tow haul and the engine probably would always be above about 2500rpms if towing a lot, so not sure there is a point trying to optimize torque that low.
The cam above would have 7 degrees of overlap @ 0.050 and I wouldn't' think it would idle that good which wouldn't be a very good "truck cam".
Any idea why 68Formula? You hear the only place for a reverse split cam in the usual 2 valve large intake smaller exhaust valve type engines is with turbos, but then you hear any cam is a "turbo cam". As with the cam above, obviously no one would probably use it as a "truck cam", especially since I optimized it starting at 2000 rpms. Also that's where the stock converter will stall up to at full torque but not if the converter is locked. In reality if towing you would be in tow haul and the engine probably would always be above about 2500rpms if towing a lot, so not sure there is a point trying to optimize torque that low.
The cam above would have 7 degrees of overlap @ 0.050 and I wouldn't' think it would idle that good which wouldn't be a very good "truck cam".
Sep 20, 2021 | 09:20 PM
#27
Having the overlap split biased BTDC as you have, will increase low end WOT torque. However, that really doesn't reflect part load conditions. The IVC isn't bad for a 6.2L truck, but overlap as you mentioned would be very mismatched. Not only would the overlap cause low vacuum, but it, in combination with very early EVO; would make throttle response and part load soggy until your foot is virtually fully in it.
I feel like there is a lot more "optimization" to be had, especially making a cam optimized for cam phasing. Of course I don't have any way to prove it or data to back it up, I just feel like all these "custom" cams are for is just to make you feel a little more special about your build but in reality the cam is basically the same one off the shelf that's the same "stage 1" or "stage whatever" you can get from the other guys.
Sep 20, 2021 | 10:01 PM
#28
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To their credit, it's a lot of variables to cover. Engine displacement, naturally aspirated, turbo, positive displacement supercharger, centrifugal supercharger, cylinder head flow, intake manifold design, throttle body size, rocker arm ratio, header type, exhaust, static compression ratio, fuel type, weight, torque convertor, rear gearing, operating rpm, intended use, and driving characteristics. Heck even the cam ramps themselves can be a factor. And I probably missed a couple. Nice thing is there are enough vendors out there offering dozens of cams each, that you can often find a shelf cam that's reasonably close. If not, you can always call a company like Cam Motion and have a custom one ground for you.
I hear you though. My biggest pet peeve are cam sellers that list an "operating range" and then claim it applies to a 4.8L up to 6.2L.
I hear you though. My biggest pet peeve are cam sellers that list an "operating range" and then claim it applies to a 4.8L up to 6.2L.
Last edited by 68Formula; Sep 20, 2021 at 10:11 PM.
Sep 21, 2021 | 09:26 AM
#29
To their credit, it's a lot of variables to cover. Engine displacement, naturally aspirated, turbo, positive displacement supercharger, centrifugal supercharger, cylinder head flow, intake manifold design, throttle body size, rocker arm ratio, header type, exhaust, static compression ratio, fuel type, weight, torque convertor, rear gearing, operating rpm, intended use, and driving characteristics. Heck even the cam ramps themselves can be a factor. And I probably missed a couple. Nice thing is there are enough vendors out there offering dozens of cams each, that you can often find a shelf cam that's reasonably close. If not, you can always call a company like Cam Motion and have a custom one ground for you.
I hear you though. My biggest pet peeve are cam sellers that list an "operating range" and then claim it applies to a 4.8L up to 6.2L.
I hear you though. My biggest pet peeve are cam sellers that list an "operating range" and then claim it applies to a 4.8L up to 6.2L.
Sep 21, 2021 | 09:59 AM
#30
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I wish I could quantify the "range" where the idle gets unstable and you start to be able to feel the engine shake. I know the engineering way of doing this is using statistical covariance but without at least pressure transducer data or something like that you don't know. Or at least some reliable data that would correlate an overlap number to the rpm you start to get instability based on a 2 valve LS combustion chamber.