Does this seem logical?

[DarkKnight]

I forgot to add, duration is the measurement of the points where the basecircle becomes elliptical. If they only took material from the base then duration would not be affected. I was wrong on that part, but I am 100% sure on the rest. Nevermind what I said in my first post. I knew what I was thinking, but I explained it all wrong. The one above this is much clearer.

Found this on the net too

Think of the regrind as thus...you are changing events, whether it is lift, duration, ramp speed or whatever. You merely decrease the cam circle profile to achieve this. The cams are on a smaller circle than the factory grind. To compensate for this smaller circle, longer pushrods have to be used to get the desired valve lift. Just adding adjustible rocker arms will not correct the new geometry introduced. They are only good for maintaing proper lash in a solid setup or plunger travel in a hydraulic setup.

Rocker Arm Geometry;

[Guest]

No, no, no.....

Pushrod length has NO effect on overall lift, none, nada.

Think of connecting rods a longer rod does not increses stroke, but changes teh geometry, same thing with cam grinds. Just because his push rod was not changed with the new cam, does not mean that overall lift was not changed, but preload and geometry was not optimized.

By decreasing the base circle and leaving the peak of the of the lobe the same the overall lift is increased, yes a regrind will generally lose some duration, but they are at low lift points anyway, and the ramp will be increased making the valve actually open faster, possibly providing more "area under the curve", it would depend on what shape the lobe is after the regrind, how it will affect duration.

Again, it is the difference between the base circle and the lobe tip that determines overall lift.

Even with the shorter pushrod, overall lift was increased, but may affect the opening rate of the valve, it will still open the valve as far, but may be slower to open.

I think I know what you are trying to get at, but it would be extreme cases of pushrod length being incorrect that might effect overall valve lift, basically enough so that the pushrod is loose and would fall out.

You can think of it this way, in relation to stroke of a crank, just because the connecting rod length may be changed does not mean that the stroke changes.

[DarkKnight]

Ok, I understand what you are saying. Perhaps I am assuming that there is too much of a difference. When I imagined the model of the valvetrain operating, I assumed that enough material had been removed as to make the lifters nearly unloaded. If we forget lift completly, and just take into consideration the position of the lifter (on the base circle), material *was* removed. That would make the lifter sit lower in it's bore, closer to the centerline of the camshaft. So, what takes up the slack that is created by the lower lifter? With your crank example, there is something I don't understand. The stroke of a crank is determined by the offset of a journal when compared to the centerline. When you increase that offset (to increase stroke) often you end up using shorter rods, like 5.7" vs. 6" as in a SBC. This is to compensate for the rod being moved further from the centerline. With a cam there is no offset, only differences in the surface radius. When you shrink that radius (by a regrind) you set the minimum value of the base cricle below what is to be expected by the lifter. The lifter in turn, moves closer to the centerline of the camshaft. What happens when that lifter moves in to the lower point? Also, why doesn't someone just put in a call to compcams or crane and see what they have to say?

[v6h.o.]

With your crank example, there is something I don't understand. The stroke of a crank is determined by the offset of a journal when compared to the centerline. When you increase that offset (to increase stroke) often you end up using shorter rods, like 5.7" vs. 6" as in a SBC.

no not nessesarilly, depending you can still use the long rod or a longer rod with a stroked crank but you have the pin height for the piston higher up on the piston. but there is limitations to this as always. but its not to say it cant be done, GM retained the stock Rod lenth from the 2.8L (5.7inch rod)when it "stroked" the 2.8L to 3.1L, the rod stayed the same lenth. (i know this is not a High performance extreme stroke combo comparision but still the same none the less)

his example was refering to you can change the rod lenth, but this will not change the engines stroke,
lets say you wanted to put in a set of 6"rods, due to you wanted the benefits from a longer rod compared to your 5.7" rods.

to do this you need a new set of pistons that have the Piston Pin bore higher on the piston, to fit the longer rod in the same lenth of stroke.
therefore the lenth of the rod does not change or alter the stroke of the engine, it is still the same actual stroke, but the rod lenth has changed.

If we forget lift completly, and just take into consideration the position of the lifter (on the base circle), material *was* removed. That would make the lifter sit lower in it's bore, closer to the centerline of the camshaft. So, what takes up the slack that is created by the lower lifter?

yes the lifter would sit lower in the bore due to the reduced base circle material. which is why technically to take up the slack now induced into the valvetrain system from this removal of material, he needs a new set of custom lenth pushrods that will be the proper lenth for the new reground cam and have the correct lenth for the proper lifter preload.

[DarkKnight]

yes the lifter would sit lower in the bore due to the reduced base circle material. which is why technically to take up the slack now induced into the valvetrain system from this removal of material, he needs a new set of custom lenth pushrods that will be the proper lenth for the new reground cam and have the correct lenth for the proper lifter preload.

And with the proper preload, he should achieve a higher lift right?