[GtoFM]

I have 2 1970s cams that I want to have reground. An Isky 280HYD and an unknown brand T257. Both core castings are 524 886. I do not know the profiles.

I'm trying to keep the stock appearance. '64 healthy stock build, .030 (at least) over, 716 heads, 10.5:1, Tri-power, MT, 3.23:1, ethanol-free pump gas.

The 068 seems to be the popular choice for this build however, the specs vary slightly between manufacturers. Even the OEM specs differ on lift. Some literature shows OEM .414 while others show .407 lift with 1.5 rockers.

Do the aftermarket mfgs. differ to be unique or to improve performance? Since I will give the profile which spec should I follow?

Bullet Cams in Mississippi will use a Cam Doctor to see what I have then go from there.

Hart's Machine Shop in Cecil, OH needs to know the desired profile to see if they have the 'template' to amtch.

TIA

[Kenth]

From the 1970 Pontiac Service Manual:

[steve25]

The slight discrepancy you mention in valve lift is really irrelevant if your running stock rockers.

The I have seen the stock stamped steel factory rockers veri from a ratio of 1.46 up to 1.52.

With 068 Cams lobe lift of like .276"if a recall right then the lift seen at the valve could veri from 402" up to 419"

[glhs#116]

The 041 numbers looked way off to me and then I remembered a factory 041 would be on factory 1.65 rockers, right?

Sam

[P@blo]

Originally Posted by Kenth

From the 1970 Pontiac Service Manual:

Are these measurements taken at 0.02" or 0.006"? The picture you posted is missing information in this regard. Looks like there is also some confusion in LSA and ICL/ECL as well which is not helping.

The Melling SPC-7 is the exact copy of the factory 068 cam. Also, the SPC-8 is the exact copy of the 041cam. Pay me now or pay me later, I'm still getting paid.

[Stan Weiss]

Ken / H-O has said Pontiac measured some wheres around 0.004" - 0.0045"

All the specs I have seen say the 041 cam is 308 degrees intake.

The crane cam is suppose to be the close copy. See Chart below.

Stan

[steve25]

The 1968 1/2 400 raII motor used the 041 Cam, but only with 1.5 rockers so about .470" lift.

[GtoFM]

Thanks for the info! I figured the differences would not impact a stock build.

Anyone know of the 2 shops I listed or additional shops?

[Jay S]

Camcraft cams in North Carolina does a lot of regrinds for factory performance cams. I recall they have some Pontiac copies on the 744 and 041. I don’t recall if they have the 068.

https://www.camcraftcams.com/

Crane had some very good factory cam copies. 96878 was the 068 blueprint replacement.

[KEN CROCIE]

Pontiac cams are measured at .002" on the opening side and .008" on the closing side. However, when setting up the camdoc to give me the duration @ .004" lift, the duration is very close to factory adv. duration.
The .414 lift shown from the factory manual is the max allowable spec. Kinda like 72 cc heads(adv.) usually check out @ 76-78 cc. .407" lift is what the cams will usually deliver.
If you're looking for a smallish cam similar to the 068, the Comp Cams 260AH-10 is virtually identical to the 068 but with .444 lift. A step up would be the CC 268AH-10 with 222/226 @.050 and .463" lift. Disclaimer: I have not personally used either of the cams.

[P@blo]

Originally Posted by b-man

Intake lobe.



Exhaust lobe.

My SPC-7 has the same flats over the nose as the post from B-man's 068 thread.

Ken kind of prooved the 068 cam specs are just a target not what is in the box. I bet if you degreed a Crane blueprinted, Warrior Racing, SPC-7, and a 068 they would all come out the same. Even the stock class racing guys used the Melling SPC-7/8 cams and were not buying up all the NOS factory cams.

Any difference in numbers are probably there so you don't get sued for stealing a GM cam. Stan gets 308* duration at 0.004-0.0045 on the 041 intake and the Melling comes in at 304* @ 0.006. Am I missing something here?

I see why they used the 0.50 numbers...

[P@blo]

Originally Posted by KEN CROCIE

Pontiac cams are measured at .002" on the opening side and .008" on the closing side. However, when setting up the camdoc to give me the duration @ .004" lift, the duration is very close to factory adv. duration.
The .414 lift shown from the factory manual is the max allowable spec. Kinda like 72 cc heads(adv.) usually check out @ 76-78 cc. .407" lift is what the cams will usually deliver.
If you're looking for a smallish cam similar to the 068, the Comp Cams 260AH-10 is virtually identical to the 068 but with .444 lift. A step up would be the CC 268AH-10 with 222/226 @.050 and .463" lift. Disclaimer: I have not personally used either of the cams.

Thanks for posting Ken. Are the 260AH-10 and 268AH-10 the same as the Summit 2801 and 2802 cams? Betting same guy in different clothes and another example or moving numbers around on the box but not the bumpstick itself.

[Stan Weiss]

Originally Posted by P@blo

QUOTE=b-man;5314122]
My SPC-7 has the same flats over the nose as the post from B-man's 068 thread.

Ken kind of prooved the 068 cam specs are just a target not what is in the box. I bet if you degreed a Crane blueprinted, Warrior Racing, SPC-7, and a 068 they would all come out the same. Even the stock class racing guys used the Melling SPC-7/8 cams and were not buying up all the NOS factory cams.

Any difference in numbers are probably there so you don't get sued for stealing a GM cam. Stan gets 308* duration at 0.004-0.0045 on the 041 intake and the Melling comes in at 304* @ 0.006. Am I missing something here?

I see why they used the 0.50 numbers...

The 308 number is from H-O and many other say the same thing about what the 041 has.

The chart I posted above and those numbers below are from a Cam Dr file of the Crane 969681 cam that was measured many years ago by H-O and sent to me by Ken Crocie.

_______I__N__T__A__K__E
Rocker_Arm_Ratio_=_1.650_________Valve_Lash_=_0.00 000________Valve_Angle_=_14.0

CAM_______Lift______Opens___Closes__Duration
_________________Deg_BTDC__Deg_ABDC_______Area____ ICL
_________0.00400____31.90_|__98.86_|_310.76_|__26. 04_|_123.48
_________0.00450____30.68_|__96.59_|_307.26_|__26. 03_|_122.96
_________0.00500____29.66_|__94.41_|_304.07_|__26. 02_|_122.38
_________0.00600____27.83_|__90.08_|_297.90_|__26. 00_|_121.13
_________0.01000____22.59_|___77.14_|_279.73_|__25 .93_|_117.28
_________0.02000____14.84_|__65.34_|_260.18_|__25. 78_|_115.25
_________0.04000_____5.27_|__54.22_|_239.49_|__25. 46_|_114.47
_________0.05000______1.51_|___50.12_|_231.64_|__2 5.27_|_114.31
_________0.10000____-14.12_|___33.66_|_199.54_|__24.05_|_113.89
_________0.15000____-28.35_|___19.09_|_170.75_|__22.12_|_113.72
_________0.20000___-43.43_|____3.95_|_140.51_|__19.43_|_113.69
_________0.25000____-61.22_|__-13.98_|_104.80_|__15.29_|_113.62
_________0.30000___-89.25_|__-41.90_|__48.86_|___7.44_|_113.68

_________Max_Lobe_Lift_0.31374

Stan

[Jay S]

For all Melling cams the seat timing ratings are by SAE standards. The standard modern OEM rating system for seat timing is duration at .006” valve lift (not tappet lift). A SAE rating will change depending on the rocker arm used. A 1.6 rocker are grows the seat timing 2* at the same SAE rating. A 1.72 (Ford) usually grows it 3*.

Melling’s SPC-8 is rated for the 68 RA 2 rating with 1.5 rockers arms, not the later RA4. 304* is the SAE rating for SPC-8 with 1.5 rockers intake duration. It is closer to 302 * at .004” tappet (versus SAE at the valve) and 292* at .006” tappet (modern aftermarket rating). Most times if the cam is a copy the aftermarket will use the original MFG rating no matter how it was originally rated. Crane never offered a seat timing rating for their blueprint cams, only part numbers it replaced. The bigger difference between cam copies is the changes to dwell over the nose of the cam versus the seat timing variations.

The Compcams AH series are more aggressive Asymmetric profiles from Compcams Magnum line.

[KEN CROCIE]

The 260 ah 10 and 268 ah 10 are not generic cams and as Jay S pointed out they are more aggressive than GM lobes (Magnum lobes.) I usually use 8 degrees to guesstimate a CC seat duration vs Crane seat duration. in other words, a 280 degree (adv. @ .006) CC would be an estimated 288 deg. (adv. @.004} from Crane.
Crocie Jr.s 64 GTO (389+060, H-O H-C 01 cam (222/[email protected] 465/494lift. 716 heads, 8.8:1 CR. Tri power, 3.23 gears. TH 350, Headers. Ran consistent 12.80s @102mph Idle was good @ 750 RPM 15 " vac. nice performance type idle.
The AH 268-10 has approx. 10-20 deg LESS seat dur. than the 068 which results in good idle characteristics. BTW 268 is the CC adv. dur. as opposed to 288 for the 068
I would definitely not have a cam reground. Buy new.

[Dragncar]

Originally Posted by Jay S

Camcraft cams in North Carolina does a lot of regrinds for factory performance cams. I recall they have some Pontiac copies on the 744 and 041. I don’t recall if they have the 068.

https://www.camcraftcams.com/

Crane had some very good factory cam copies. 96878 was the 068 blueprint replacement.

There is some good info on that site.
https://www.camcraftcams.com/selecting-a-cam/

[P@blo]

Stan, Jay, Ken, and Dragncar. You guys are something else. Thanks for posting your information. It helps me learn and it was funny because I had to draw a diagram of the cam/lobe/base circle withe the tappet/pushrod/rocker/valve 90* apart to get the visual on the dwell aspect.

So the ramps cause the fastest tappet movement, the base circle the lowest, and the dwell (tappet stationary) on the nose which is pronounced on the factory cams. I might not be understanding this correctly but I think I get it now.

Stockish heads want to reach max lift as quickly as possible, which is modest and then hold it as long as possible. Any additional lift is pointless. Modified heads do not need to hold the valve open at a lower lift and can reduce dwell and make better use of the higher lift flow which is why Ken mentioned the higher lift less dwell cams.

Am I on the right track?

[Jay S]

Most D ports don’t go turbulent until about .5” lift, especially when you bolt the intake to the heads. While it is true a stock D port doesn’t gain a lot of flow after .4”, most all Pontiac’s respond positively to more lift than .407”.

Extra dwell on a cam that has the same low lift durations as another cam is the result of trying to get more area and limiting the cams lift. There is a point where the cam profile has better harmonics with more lift and less dwell.

Some cams have .2” tappet lift duration ratings. Generally if 2 cams have equal lift and durations at .050”, the cam with the larger .2” duration will make more power. Unfortunately that is pretty unknown on most stock cams. That file Stan had of a Crane 041 Blueprint was showing 140*. A Crower RA4 60919 has around 134* @.2”. I don’t recall exactly what a Melling SPC-8 has @.2”, but I think I recall it’s .2” duration it is closer to the Crower version of the 041 than the Crane.

The 068 variations may not vary as much as the 744 and 041 in how they are ground. Would be interesting to compare some cam DR files for the various 068 copies.

[P@blo]

So the lobe area would be the area of the lift ramp pictured?

I'm just thinking out loud but the area seems like a better way to compare measurements instead of valve events at x.xxx. Sorry guys I have to close the loop on this for my brain...

[Jay S]

Originally Posted by P@blo

So the lobe area would be the area of the lift ramp pictured?

I'm just thinking out loud but the area seems like a better way to compare measurements instead of valve events at x.xxx. Sorry guys I have to close the loop on this for my brain...

You have the right idea, where the profile holds the tappet open is the area. Area can also be measured out at valve for more accuracy.

Area isn’t very easy to use comparing cams for several reasons. Lift changes area, area over the nose of the cam effects the engine different than it does when the area is changed at the cams overlap. Cams have different seat timing adding area at low lifts instead of over the nose. Profiles can be Assymetrical, and shift more area on the closing side of the ramp from the opening side.. A Crane 041 blueprint cam is an example of those things, it more duration and area above .2” than a Melling SPC-8. The Melling SPC-8 is basically symmetrical, the Crane is very Assymetrical at lower lifts.