John's right about Bobby-boo. He's definitely an Indian Freak. But, I'd have to have the heads too, and of course we all know the factory F codes ran ported (by Geoff Mummert) heads and roller rockers. What, you didn't know that? Well it's like all '57 Scrubs came with four speeds!

Frank/Rebop

Bristol, In ( by Elkhart) 

Frank: Your remark about the 4 spd 57 Ch-v-s, reminds me that was one of the reasons that they got an undeserved big reputation in racing. As alluded to, "no" 57 Ch-v-s came factory acquipped with 4 spd transmissions! They were automatics or 3 spd close ratio transmissions. It didn't take long for some racers to aquire Corvette transmissions used or over the counter. At first they were illegal in stock classes.. then certain people who were close with G.M and in at least one case, a high ranking official in the NHRA, managed to weasel them in at some point as legal. Which was just dandy, cause neither Ford nor Chryler were supplying 4 speeds for their cars until later dates..

Paul

You got it Paul. Don't forget the Sedan Deliveries with 4 speed Hydro's, not SlushGlides. After all the deliveries were trucks right? And the Trucks were built with Hydromatics! Besides, Ford had a three speed automatic so Chevy should have more than the PowerGlide for the automatic classes.
NHRA might have been a bit partial to the General! (Sarcasm)

Frank/Rebop

Bristol, In ( by Elkhart) 

Back to the rockers, as you move the ratio higher the shaft gets closer to the pushrod end and further from the roller tip. The question is when doing this it multiplies the pressures on the lifters so when the ratio is increased do you use softer valve springs? If not I would think lifter and lobe wear would be drastically accelerated.

55 Vicky & customline

58 Rack Dump, 55 F350 yard truck, 57 F100

59 & 61 P 400's, 58 F100 custom cab, 69 F100, 79 F150, 82 F600 ramp truck, 90 mustang conv 7 up, 94 Mustang, Should I continue?

Pressure at the tappet increases in a linear fashion and is directly related to the increase in valve lift that’s accomplished by increasing the rocker ratio.

Lorena, Texas (South of Waco)

Hi Ted,

I'm sure that what you just said is correct, but I'm scratching my head. -No, I did not have a wild weekend!

Is there any type of a numerical example that you might give to help me with my learning curve? I'm 'lost' on this one.

Thanks for your patience!

Regards,

NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

If the spring is 200 lbs. at a given point, the pressure on the lifter is multiplied by the rocker ratio. So 200 X 1.54 = 308 #. If you'd run a 1.70 rocker then the pressure would be 340#s. Actually that's only part of the issue because the velocity of the valve, rocker , and pushrod AND the lifter all contribute to the forces the cam/ lifter interface sees.

Frank/Rebop

Bristol, In ( by Elkhart) 

Frank has pretty much nailed how to calculate the actual load on the lifter based on the spring pressure. As a short cut and while not absolutely accurate, the valve spring over the nose pressures are typically used as a guide of what’s permissible for tappet loading. As a general rule, the valve spring pressure at 330-350 lbs is the limit for flat tappet camshafts. That would equate to 528-560 lbs actual pressure at the tappet using 1.6:1 rockers. But you’ll not hear the 560 lb value being used, only the 350 lb value. This is just a matter of semantics and the average person just needs to be aware of what the numbers actually represent so those numbers can be kept in their proper perspective.

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Valve springs have a rate per inch value that can be used to calculate the amount of valve spring pressure at a given valve opening. It’s this value that can also be used to calculate ‘over the nose’ or lobe/tappet pressures. If the rate per inch isn’t known, it can be calculated from any two known compressed points on the spring. The linearity of the valve spring pressure rate makes this possible.

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For a performance Y, the Isky p/n 165-A beehive valve springs are a popular choice so I’ll use it in this example. This spring is rated at 130lbs. @ 1.800” and 320 lbs. at 1.200. This is a 190 lb increase in pressure with a .600” lift. Doing the math for a 1.000” valve lift knowing these two values, the rate per inch would be 316.67 lbs. Going to the catalogue and looking up this spring shows its rate per inch listed at 310 lbs. While slightly different, it’s close enoughto be comfortable with using the catalogue value.

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Knowing that particular rate per inch allows other valve spring compression values to be calculated. If the net valve lift is 0.531”, then the ‘over the nose’ pressure will be 130+ (.531 X 310) or 295 lbs. This is of course assuming the closed pressure is being set at the recommended 130 lb level. Likewise, if the net valve lift is 0.650”, then the ‘over the nose’ pressure will be 130+ (.650 X 310) or 332 lbs. If using my calculated value of 316.67, then the ‘over the nose’ pressure for the 0.650” lift cam will be 336 lbs. We’ll not quibble over 4 lbs. When in doubt, the valve spring pressures should always be checked with a valve spring tester at both the intended closed installed height and at the maximum valve opening.

Lorena, Texas (South of Waco)

Frank and Ted,

Thanks for the information. Truth be told I'm still absorbing what you've both shared.

GooD GrieF! The more I learn, the more I realize that I don't know!

Regards,

NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

One thing that should be added to the good info given is that the rocker arm is a tool. One might argue that the spring pressure would increase on a given lobe. But!! One must be looking at Pounds per square inch. A low ratio rocker forces you to go in all the wrong directions with the lobe. Because the bearing journals are a given dimension the lobe height cannot exceed this height. Resulting in reducing basecircle size for each thousandth of lift desired. Seeing that the lobe you are trying to grind on the core is a fixed shape every thousandth you reduce the basecircle the nose radius decreases right along with it. To understand how much stress is really on the nose of a lobe you calculate how much square area is contacting the lifter, figure out what percent of a square inch it is then divide your total spring pressure x rocker ratio by that. As an example 340 open lbs. x 1.54/ by .1" = 5236 lbs/in.. Now if you choose a lobe that has the same valve events with your new ratio the the lift can drop by 10% meaning the basecircle can increase by 20% 340 open lbs. x 1.7/ by .12"= 4816.66 lbs/in..
The other thing that should be looked at is where the load is applied to the lifter. Running more lift on a lobe of a given duration increases the lobes velocity there by placing the load farther out from the centerline of the lifter increasing the shear stresses on the stem and lifter bore. A higher ratio rocker increase valve lift without imposing this additional stress.
Please remember that these are for example figures. The simple point trying to be established is that fastest way to decrease lifter pressure is to increase the area of the wear face and keep it closer to the center of the lifter.
This new rocker arm set up is a tool. Allowing for greater selection of lobes to be used for street or racing use.. We believe this motor needs more options on the table.
Putting things into perspective Winston Cup or whatever its called today is still forced to run flat tappets and wear/ slash cam life is something they have been dealing with.. Bigger cam bearings allowing for bigger basecircles, high rocker ratios, high grade oils, etc. etc. are all part of their solutions.
As was mentioned before Ford Engineers shot up over 1.7 ratio by 1958 and rarely looked back..
FE, MEL, 385 Series(429-460), Cleveland, M Series, 3.8-4.2 V6, Boss 302 all used 1.7 or higher ratio from the factory.





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