Was it the checking at exactly 3 and one half thousandths of an inch?
'77 mopar 400 cam swap
- Thread starter casey henson
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rumblefish360
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Come on now…. Spill da beans!
gtxrt
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checked at .0035 or closes at -5
PRHeads
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On both of those cards, the theoretical lobe C/L for the advertised duration lift point, and the .050” duration lift point are quite different from each other.
The C/L’s for the advertised duration of first cam are 112/112, while the .050” C/L’s are 107/117.
The second cam is 111/113 advertised, and the .050 numbers are also 107/117.
The very ends of the ramps must be quite different on the two sides to show a 4 and 5 degree difference in C/L going from the seat checking point, to .050” lift.
I usually use my measurements to arrive at the “advertised” timing figures and the .050” numbers.
I just don’t recall ever seeing the calculated C/L change that much between those two checking points.
The C/L’s for the advertised duration of first cam are 112/112, while the .050” C/L’s are 107/117.
The second cam is 111/113 advertised, and the .050 numbers are also 107/117.
The very ends of the ramps must be quite different on the two sides to show a 4 and 5 degree difference in C/L going from the seat checking point, to .050” lift.
I usually use my measurements to arrive at the “advertised” timing figures and the .050” numbers.
I just don’t recall ever seeing the calculated C/L change that much between those two checking points.
Geoff 2
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Some comments about the cam cards shown in posts 57 & 58.
- both are Crane cams
- post 57 cam: [1] The adv duration is 300* [2] The 297* is at 000 tappet lift, so duration cannot be greater than 297? [2] The timing #s to install the cam are at 0.0035" tappet lift.
post 58: [1] 320* duration at 000 tappet lift [2] 'Advertised' duration is 284* @ 004" tappet lift
The difference in C/Ls at the adv duration & 050 duration is because the lobes are asymmetrical.
Somebody mentioned the high lift of stock Mopar cams. That is likely because the cam was ground for the Mopar 904 lifter, which can take more lift than the Chebby & Ferds lifters.
Big adv #s are pretty useless/meaningless. Pumped up to make the cam look big. How does 400* sound? Not a misprint. Bigger is better, right? A Herbert #70 grind.
Ch was sensible & conservative with it's cam specs, including the adv duration #s. The Pontiac Ram 3 cam & a Ch 440 cam are 224 & 225 respectively @ 050. The adv duration of the P cam is 301*, 284* for the 440. At the lowest measured lobe lift of 0.008", both cams were 276*!!
- both are Crane cams
- post 57 cam: [1] The adv duration is 300* [2] The 297* is at 000 tappet lift, so duration cannot be greater than 297? [2] The timing #s to install the cam are at 0.0035" tappet lift.
post 58: [1] 320* duration at 000 tappet lift [2] 'Advertised' duration is 284* @ 004" tappet lift
The difference in C/Ls at the adv duration & 050 duration is because the lobes are asymmetrical.
Somebody mentioned the high lift of stock Mopar cams. That is likely because the cam was ground for the Mopar 904 lifter, which can take more lift than the Chebby & Ferds lifters.
Big adv #s are pretty useless/meaningless. Pumped up to make the cam look big. How does 400* sound? Not a misprint. Bigger is better, right? A Herbert #70 grind.
Ch was sensible & conservative with it's cam specs, including the adv duration #s. The Pontiac Ram 3 cam & a Ch 440 cam are 224 & 225 respectively @ 050. The adv duration of the P cam is 301*, 284* for the 440. At the lowest measured lobe lift of 0.008", both cams were 276*!!
Dodge Bros
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To bad companies didn’t follow Crane lead on those old cam cards…you can see the assymetric’s in the cam design. Everyone went to the averages instead of what the cams actually are at different lift points. The 300/300 cam (post 43) was showing 5* of assymetric’s, (opening rate of the profile 5* faster than the closing from .050” to .004” tappet. The 284/284 PR heads mentioned on #57 is showing 4*. The HMV Crane grinds that were mentioned either in the thread had 5*. The SUMMIT grinds have NONE, they are symmetrical cams. Compared to a symmetrical ground cam, an Asymmetrical grind can run more duration at .050”, and/or narrow the LSA up and not loose any idle quality. The LSA acts wider on the cams like those cranes, it moves the intake closing later and adds some top end, but the more aggressive opening ramp on the intake pulls harder on the intake earlier, retaining low end manors fairly well.
On a low compression 400 with really tall highway gears the Isky and the 262H comp were good choices. With better gears and converter in the future the summit 6400 would be ok. With the gears it has now though it will probably be slower than the stock factory cam.
Compcams XE, hi energy and magnum grind are assymetric by 6-7* from .004” to .050. Lunati voodoo and Ultradyne grind are 7-8. Combining that with a more aggressive grinds you can run a pretty good side cam over a symmetrical comparing at .050” numbers, and not loose much idle quality or low end.
On a low compression 400 with really tall highway gears the Isky and the 262H comp were good choices. With better gears and converter in the future the summit 6400 would be ok. With the gears it has now though it will probably be slower than the stock factory cam.
Compcams XE, hi energy and magnum grind are assymetric by 6-7* from .004” to .050. Lunati voodoo and Ultradyne grind are 7-8. Combining that with a more aggressive grinds you can run a pretty good side cam over a symmetrical comparing at .050” numbers, and not loose much idle quality or low end.
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.297 lobe lift x 1.5 = .4455 (.446)
.320 lobe lift x 1.5= .480
PRHeads
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Exactly.
That’s why the box those figures are listed in is labeled “lift”.
The timing events are clearly marked on those Crane cam cards, and at what lift they are taken at.
The first card shows the intake event at .0035 to be 38/82, plus the 180 = 300*
The second card shows the intake event at .0040 to be 31/73, plus the 180 = 284*
Nothing on those cards denotes the duration at “zero” lift.
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PRHeads
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As for the OP’s combo, if the stock converter and 2.45 gears will remain in the car, I’d run a pretty small cam.
The comp 260H or an Isky 262 Super Cam.
Either of those would work with replacement 440HP valve springs, which will be compatible with the factory retainers and installed height.
The comp 260H or an Isky 262 Super Cam.
Either of those would work with replacement 440HP valve springs, which will be compatible with the factory retainers and installed height.
Geoff 2
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I made a mistake in post 66. I thought the '297' was duration; it isn't, it is lobe lift.
Asymmetric lobes are not new or 'modern', as some cam grinders would have you believe. Isky referred to asymmetric lobes in the 1974 catalog I have; & who knows, it might have been in earlier catalogs.
Asymmetric lobes are not new or 'modern', as some cam grinders would have you believe. Isky referred to asymmetric lobes in the 1974 catalog I have; & who knows, it might have been in earlier catalogs.
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