Valve spring advice for 097 cam/1.6 rockers
05-31-2019, 07:39 PM
#1
Valve spring advice for 097 cam/1.6 rockers
All - I’m installing the correct 097 cam in my 57 dual quad motor and need some advice on valve springs. The heads are 997s, the only mod being screw-in rocker studs. I would like to use 1.6 rockers given the low lift of the Duntov cam. Can someone knowledgeable on this configuration recommend appropriate valve springs? Thx!
Last edited by mtbengel; 05-31-2019 at 07:40 PM.
05-31-2019, 07:49 PM
#2
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All - I’m installing the correct 097 cam in my 57 dual quad motor and need some advice on valve springs. The heads are 997s, the only mod being screw-in rocker studs. I would like to use 1.6 rockers given the low lift of the Duntov cam. Can someone knowledgeable on this configuration recommend appropriate valve springs? Thx!
That cam was designed to use in the engine/head combination as is. Why are you trying to re-engineer?
06-01-2019, 07:29 AM
#4
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ALL small blocks for any given model year used the SAME valve spring for ALL camshafts. There was a new design spring that went into production for the '67 model year that is slightly stiffer than the previous spring... about 80 pounds on the seat, 267 lb/in rate for about 200 pounds full open depending on lift. This spring is Sealed Power VS677, and you should be able to buy a set for about 25 bucks.
Keep in mind that NO rocker arm has a constant ratio. The OE "1.5:1" rockers start out at about 1.37 at low lift and achieve about 1.44 at maximum lift. I don't know the behavior of so-called 1.6 rockers, but you should measure. It's easy to do with a couple of dial indicators, one on the rocker pushrod socket in line with the pushrod and the other on the retainer. Zero the indicators on the base circle and then take measurements about every ten degrees of rotation. You don't need to use a degree wheel, just rotate the crank an estimated ten degrees for each measurement. Then compute the ratio at each data point.
You'll have to compute proper valve clearances because of what might be a slightly higher rocker ratio at low lift. The Duntov cam top of the constant velocity clearance ramps are .008/.012" above the base circle, so multiply these numbers by the measured low lift rocker ratio and those are the cold clearances you set. Search this site or the Web for the Hinckley Williams valve adjustment, paper, Sept/08 revision, to learn the indexing scheme to be sure each lifter is on the base circle when you set the clearance. For the rocker ratio measurement set the valve clearance at close to zero.
For maximum valve train limiting speed, multiply maximum lobe lift times the measured rocker ratio at maximum lift. Add this to the VS677 coil bind height. which is 1.15" plus .090/.100" coil bind margin. This should yield at least 7200 before incipient valve float sets in. When setting the valve spring height this tight I recommend you actually measure coil clearance with feeler gages after each valve spring is shimmed, just to be sure there is no binding. It should be at least .015"
If you don't plan to rev it this high you can increase the coil bind margin to .120".
Also carefully inspect pushrod clearance to the heads. You may have to open them up to provide adequate clearance with higher ratio rockers.
Duke
Keep in mind that NO rocker arm has a constant ratio. The OE "1.5:1" rockers start out at about 1.37 at low lift and achieve about 1.44 at maximum lift. I don't know the behavior of so-called 1.6 rockers, but you should measure. It's easy to do with a couple of dial indicators, one on the rocker pushrod socket in line with the pushrod and the other on the retainer. Zero the indicators on the base circle and then take measurements about every ten degrees of rotation. You don't need to use a degree wheel, just rotate the crank an estimated ten degrees for each measurement. Then compute the ratio at each data point.
You'll have to compute proper valve clearances because of what might be a slightly higher rocker ratio at low lift. The Duntov cam top of the constant velocity clearance ramps are .008/.012" above the base circle, so multiply these numbers by the measured low lift rocker ratio and those are the cold clearances you set. Search this site or the Web for the Hinckley Williams valve adjustment, paper, Sept/08 revision, to learn the indexing scheme to be sure each lifter is on the base circle when you set the clearance. For the rocker ratio measurement set the valve clearance at close to zero.
For maximum valve train limiting speed, multiply maximum lobe lift times the measured rocker ratio at maximum lift. Add this to the VS677 coil bind height. which is 1.15" plus .090/.100" coil bind margin. This should yield at least 7200 before incipient valve float sets in. When setting the valve spring height this tight I recommend you actually measure coil clearance with feeler gages after each valve spring is shimmed, just to be sure there is no binding. It should be at least .015"
If you don't plan to rev it this high you can increase the coil bind margin to .120".
Also carefully inspect pushrod clearance to the heads. You may have to open them up to provide adequate clearance with higher ratio rockers.
Duke
Last edited by SWCDuke; 06-01-2019 at 07:43 AM.
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mtbengel (06-01-2019)
06-01-2019, 08:20 AM
#5
ALL small blocks for any given model year used the SAME valve spring for ALL camshafts. There was a new design spring that went into production for the '67 model year that is slightly stiffer than the previous spring... about 80 pounds on the seat, 267 lb/in rate for about 200 pounds full open depending on lift. This spring is Sealed Power VS677, and you should be able to buy a set for about 25 bucks.
Keep in mind that NO rocker arm has a constant ratio. The OE "1.5:1" rockers start out at about 1.37 at low lift and achieve about 1.44 at maximum lift. I don't know the behavior of so-called 1.6 rockers, but you should measure. It's easy to do with a couple of dial indicators, one on the rocker pushrod socket in line with the pushrod and the other on the retainer. Zero the indicators on the base circle and then take measurements about every ten degrees of rotation. You don't need to use a degree wheel, just rotate the crank an estimated ten degrees for each measurement. Then compute the ratio at each data point.
You'll have to compute proper valve clearances because of what might be a slightly higher rocker ratio at low lift. The Duntov cam top of the constant velocity clearance ramps are .008/.012" above the base circle, so multiply these numbers by the measured low lift rocker ratio and those are the cold clearances you set. Search this site or the Web for the Hinckley Williams valve adjustment, paper, Sept/08 revision, to learn the indexing scheme to be sure each lifter is on the base circle when you set the clearance. For the rocker ratio measurement set the valve clearance at close to zero.
For maximum valve train limiting speed, multiply maximum lobe lift times the measured rocker ratio at maximum lift. Add this to the VS677 coil bind height. which is 1.15" plus .090/.100" coil bind margin. This should yield at least 7200 before incipient valve float sets in. When setting the valve spring height this tight I recommend you actually measure coil clearance with feeler gages after each valve spring is shimmed, just to be sure there is no binding. It should be at least .015"
If you don't plan to rev it this high you can increase the coil bind margin to .120".
Also carefully inspect pushrod clearance to the heads. You may have to open them up to provide adequate clearance with higher ratio rockers.
Duke
Keep in mind that NO rocker arm has a constant ratio. The OE "1.5:1" rockers start out at about 1.37 at low lift and achieve about 1.44 at maximum lift. I don't know the behavior of so-called 1.6 rockers, but you should measure. It's easy to do with a couple of dial indicators, one on the rocker pushrod socket in line with the pushrod and the other on the retainer. Zero the indicators on the base circle and then take measurements about every ten degrees of rotation. You don't need to use a degree wheel, just rotate the crank an estimated ten degrees for each measurement. Then compute the ratio at each data point.
You'll have to compute proper valve clearances because of what might be a slightly higher rocker ratio at low lift. The Duntov cam top of the constant velocity clearance ramps are .008/.012" above the base circle, so multiply these numbers by the measured low lift rocker ratio and those are the cold clearances you set. Search this site or the Web for the Hinckley Williams valve adjustment, paper, Sept/08 revision, to learn the indexing scheme to be sure each lifter is on the base circle when you set the clearance. For the rocker ratio measurement set the valve clearance at close to zero.
For maximum valve train limiting speed, multiply maximum lobe lift times the measured rocker ratio at maximum lift. Add this to the VS677 coil bind height. which is 1.15" plus .090/.100" coil bind margin. This should yield at least 7200 before incipient valve float sets in. When setting the valve spring height this tight I recommend you actually measure coil clearance with feeler gages after each valve spring is shimmed, just to be sure there is no binding. It should be at least .015"
If you don't plan to rev it this high you can increase the coil bind margin to .120".
Also carefully inspect pushrod clearance to the heads. You may have to open them up to provide adequate clearance with higher ratio rockers.
Duke
Last edited by mtbengel; 06-01-2019 at 08:23 AM.
06-01-2019, 08:42 AM
#6
Safety Car
A Comp Cams 981 or Elgin VS 943x will give you about 20 more lbs on the seat around 30-40 more open pressure. When you install 1.6 rockers you move the push rod towards the stud. The push rod slot in the head is NOT long enough for 1.6 so you MUST lengthen this slot. You can do it with a hand grinder or you can buy the Louis tool from Comp Cams. If you are going to grind it just move the radius towards the stud maybe .100". Be very not to widen the existing slot. If they installed guide plates when they did the screw in studs the slots should have been drilled out and this is not an issue.
Last edited by Robert61; 06-01-2019 at 08:42 AM.
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mtbengel (06-01-2019)
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Robert61 (06-01-2019)
06-01-2019, 09:09 AM
#8
I have made a number of fairly innocuous and easily reversible modifications to my car that have made it much more pleasant to drive. This would include polyurethane bushings in the rear suspension, 3.31 differential, vacuum advance pointless distributor, retro-design radial tires, and heat isolation of carburetors to allow it to run on pump gas. Without these modifications I would not drive and enjoy the car near as often as I do (which is my reason for owning it!). Ultimately, my mother would say it’s because I can never leave “good-enough” alone.
Last edited by mtbengel; 06-01-2019 at 03:58 PM.
06-01-2019, 03:05 PM
#9
Team Owner
I would just throw old single coil 142 springs on it! The step up for solid lifters! The diameter will fit all of those early heads! I just don’t know if any are around cheap for sale! The GM performance parts supply has severely dried up! I think I have the most NOS GM Bow tie stuff of anyone! All of my engines minimum have the 585 duals!
Elongating the slots, doesn’t take much cut to get the clearance! I did that in my 20s, but roller rockers of better quality can be bought for cheap!
Elongating the slots, doesn’t take much cut to get the clearance! I did that in my 20s, but roller rockers of better quality can be bought for cheap!
06-01-2019, 03:52 PM
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The real question is, what do you really gain/sacrifice with all that whizz bang stuff?
06-01-2019, 05:00 PM
#11
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I ran 1.6 rocker arms in my 340hp 327 for over a decade with no spring or head modifications, and no problems.
The stock GM valve springs for the SHP engine worked with no problems, and I would rev to 7000 on occasion (beyond the cam's best power range).
The pushrod slots in the heads required no modification (461/462 castings). Test by setting near zero lash and turn the engine two revolutions while spinning and rocking the pushrod back and forth with your fingers. If there is head contact you can feel it and it can score the pushrod coating. My pushrods were visibly clear of the head throughout the engine cycles and I never had a problem.
Valve lash is subjective. I tried everything from the 63' spec 0.008/0.018, to the prior years spec at 0.012/0.018, to 0.018/.0.018 and as wide as 0.024/0.024. The tight 63' spec lash is quieter but gives away off-idle torque and around town drive ability suffers. The more loose lash settings improved the idle and off-idle response. I noticed no high rpm issues with any of the lash settings. I ended up running 0.012/0.018 on track days (tight 0.008 intake lash slowed down the 60' times). I usually ran 0.014/0.020 around town for the best balance of off-idle ease and low noise.
Wider lash can add valvetrain stress and more lobe impact force, but I experienced no cam or lifter damage and witnessed no damage on tear down. The 097 cam is very forgiving and lash is just another tuning variable.
The stock GM valve springs for the SHP engine worked with no problems, and I would rev to 7000 on occasion (beyond the cam's best power range).
The pushrod slots in the heads required no modification (461/462 castings). Test by setting near zero lash and turn the engine two revolutions while spinning and rocking the pushrod back and forth with your fingers. If there is head contact you can feel it and it can score the pushrod coating. My pushrods were visibly clear of the head throughout the engine cycles and I never had a problem.
Valve lash is subjective. I tried everything from the 63' spec 0.008/0.018, to the prior years spec at 0.012/0.018, to 0.018/.0.018 and as wide as 0.024/0.024. The tight 63' spec lash is quieter but gives away off-idle torque and around town drive ability suffers. The more loose lash settings improved the idle and off-idle response. I noticed no high rpm issues with any of the lash settings. I ended up running 0.012/0.018 on track days (tight 0.008 intake lash slowed down the 60' times). I usually ran 0.014/0.020 around town for the best balance of off-idle ease and low noise.
Wider lash can add valvetrain stress and more lobe impact force, but I experienced no cam or lifter damage and witnessed no damage on tear down. The 097 cam is very forgiving and lash is just another tuning variable.
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mtbengel (06-01-2019)
06-01-2019, 05:49 PM
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It helped mid-range torque, 2500-5000 rpm, and 50-80 mph passing time. The 1/4 mile ET dropped a 10th, from 14.0 to 13.90, with the same 100-102 mph trap speed.