Camshaft/Custom pushrod question

[asylummotorsports]

After looking at all the lobe options and the fact they are basically negative ground, in that for the most part they are taking material off the base circle, are the "custom" pushrods cam-specific?

[robertisaar]

it seems that would be necessary for proper geometry...

[AaronGTR]

I think it depends on the cam profile you order. The way it was explained to me... the cam bearings are a certain size and in order to get a lobe with a certain amount of lift, but still have it fit through the cam bearings when installing, they have to grind the base circle smaller and then you need longer pushrods or you will lose preload and lift. If the lobe lift is under a certain amount then they don't need to grind the base circle. I don't recall what the cutoff is. I had to get custom pushrods for mine because of my lift and the rockers I was using.

[asylummotorsports]

I understand the whole concept of these cams and the fact negating base circle material is what is done to increase lift.

But that would dictate that every cam profile would need a cam-specific pushrod to do this properly? NO??

WOW! What a PITA that situation becomes!

But I guess when there is nothing else you live with the premium, HUH?

[IsaacHayes]

Ben measures and sends you the correct pushrods if you order through him I believe.

[ghrarhg]

If in doubt you should definitely measure, but the varying amounts of preload will account for small changes in base circle. IIRC I believe someone found out that factory we run around 0.080" of preload. I shot for 0.020-0.040 when I ordered mine. So if the diameter of your base circle didn't change by more than 0.100 (0.050 off both sides), you'd be right where I am with the same pushrods. The hydraulic lifters give a little room for error as far as needing cam-specific pushrods

[SappySE107]

You want .073" preload optimally. .050-.090 is a good range to be in. .020-.040 is not enough when you have .146" plunger travel. The same pushrods will work with a number of lobe grinds but without having the cam to measure, I couldn't tell you what lengths are needed. I figure them out as they are ordered and I receive the new cams.

[3400-95-Modified]

Eric, until we have the option of adjustable rockers, then yeah we are stuck with almost cam specific pushrods...

Most custom 350's and such have cam specific pushrods as well... but sometimes they are longer or shorter because of the way the rocker mounts, not necessarily the lobe, so how is that any different than what we have?

You have to adjust somewhere and that's the place to do it if you want to keep the rocker point on the same area of the valve stem

[AaronGTR]

Even with adjustable rockers you may still need custom length pushrods in order to keep the rocker tip in the right area on the valve stem. Plus you need heat treated pushrods to work with the guide plates needed for adjustable rockers, so you are still required to get custom pushrods anyway.

[dskopek]

You want .073" preload optimally. .050-.090 is a good range to be in. .020-.040 is not enough when you have .146" plunger travel. The same pushrods will work with a number of lobe grinds but without having the cam to measure, I couldn't tell you what lengths are needed. I figure them out as they are ordered and I receive the new cams.

On the note of preload, we shim the hyd lifter plunger for a max of .030 travel to allow much higher engine speed with the hyd lifters, We will spin about 7700 rpm with no valve float in 302 CI Ford V-8's all day long at the track. I would think with some testing you can get the same from these

[SappySE107]

We get 7k with the stock lifters but its all about the ramp up rate and the valve springs. So far our lighter valvetrain has helped quite a bit for max RPMs. We are in the 7000s on regrinds.

[Lilchief]

Is the optimum preload for an iron head 3.4 lifter also .073? When I originally done mine I used a dial indicator and set them at .050 which was about 1/4 turn.

[SappySE107]

I am not sure. You need to measure the total plunger travel and divide by 2 to find optimal preload.