Does this seem logical?

[bszopi]

Ok, for those that know my car and myself, you know that my car is far from what it should be performance wise with the mods I have. One thing I know I need to do is get custom pushrods for my cam. But with some recent discussions on regrinds here and on other sites, I started really thinking about this more....

Stock lift is 0.273" (@lobe) / 0.415" (w/1.52 rockers).
My regrind is 0.302" (@lobe) / 0.459" (w/1.52 rockers).

In order to get the increased lift, they removed material from the backside (basecircle). If you look at the numbers, it would make sense that they removed 0.029" (0.044" at the rockers). With that said, since I am still using the stock pushrods, would this then cause my lift to actually decrease? Now that I think about it more, probably not. What it would cause though is the valve being opened for a shorter amount of time (due to the backside being less than stock, therefore the duration would have to go down). Is this making sense? I am almost positive that if I get new pushrods that my performance would increase do to this.

I know the truly best way to go about getting custom length pushrods is to get the test pushrod. But, could I just add the amount of material removed (0.029") to the lengths of the pushrods to get it back to normal?

[customandsound]

who did the regrind?

[bszopi]

Crower

[GPXSS]

dont ever assume when it comes to pushrods.. especially when you are gonna blow $70 for a non-returnable set. I say you need to measure to be sure.

Did you measure those cam specs or is that what they gave you? Sometimes there can be a variance between what they advertise and actual. They also "could" have taken material off the lobe peak to flatten the lobe out, giving you more duration.

[bszopi]

Hmm, that makes sense. Ok, so I decided to buy a checking pushrod cause I am too lazy to make one myself. Started to do some searching, and Crower is the only company that makes one short enough for these engines. $33. Oh well, as long as it works. So hopefully I will know what length pushrods I will need within the next few weeks.

[wiccanferret]

Hmm, that makes sense. Ok, so I decided to buy a checking pushrod cause I am too lazy to make one myself. Started to do some searching, and Crower is the only company that makes one short enough for these engines. $33. Oh well, as long as it works. So hopefully I will know what length pushrods I will need within the next few weeks.

Once you know, I would like to know the exact specs on the cam and exact specs on the pushrods so I can make a DIY page for my site. Seems this is the only way we're gonna get a cam, so once you pioneer the correct way, we'll all want to copy.

[v6h.o.]

i have one from Comp Cams Brad. it was 23 bucks from summit racing.

part number #7701, 5.8-6.8 inch lenth.

oh crap, wait, yeah you guys and your roller lifters.. need 5.75inch or so.. nevermind.

[bszopi]

Yeah, I need ~5.68". The one I ordered was $34 from Summit, with free shipping. From Crower directly, it was $23.50, plus $9.14 for shipping (are you kidding me?!?!?). Needless to say, it was cheaper and quicker to get it from Crower (Summit was backordered). It's also the high tech one (Ooooo...), which is nice, but did I need it? Obviously, since it was the only one that went to the length I needed....

BTW, after I use it, I'll be willing to rent it out to others for a small fee. Hey, might as well try to get some of the money back and save you guys money at the same time!

[Chris88CL]

What was the part number from summit if you dont mind me asking?

[ikessky]

Sitting here thinking about it, it does seem logical. But then again, wouldn't that mean you can simply replace your pushrods to increase lift without getting a different cam?????

[v6h.o.]

its more that your lifter preload has been decreased more than anything.

you need to restore the proper preload, which may or may not have an affect on the performance of the car.

[GPXSS]

http://www.cranecams.com/hydlfaq.htm

[DarkKnight]

How can you "remove" material and achieve a higher lift? It's almost like I can see it somehow, but it's just not making sense at the moment. The lifter would ride lower on the basecircle, so you could use a larger pushrod to make the valves open more, but if you tried to use a stock pushrod that wouldn't change anything, right? Stock, it would just make the valve train a little more sloppy, because the springs and lifter would have to take up the slack on the close points. Does that make any sense at all?

Edit: I want to add to this
The way I see it, the whole point of a regrind is to use custom length pushrods to replace the missing material on the grind, and attain a new profile. If you stuck with the stock rods, with a new profile, both your lift and duration would suffer. If they *only* removed material from the base, then your overall duration would be less, and the ramp would be more aggressive, but stock max lift. If you used a longer pushrod on a stock cam the lift would increase, but the valve would never close. You solve this by shaving material off the basecircle to allow full closeure of the valve and attain the higher lift of the longer pushrod! Ha, I solved it.

[Guest]

No, that is not correct....

"Lift" is a difference of distance between one point to another, in this case the base and the lobe peak. By removing material from the base circle, but leaving the peak of the lobe at the same point, the over difference is increased, increasing lift. This can be thought of in relation to a center point in the midle of the cam and the difference of the distance between that and the base and the lobe peak.

Changing pushrod length will not change anything with lift or duration, pushrod length is important for valve train geometry.

[DarkKnight]

No, that is not correct....

"Lift" is a difference of distance between one point to another, in this case the base and the lobe peak. By removing material from the base circle, but leaving the peak of the lobe at the same point, the over difference is increased, increasing lift. This can be thought of in relation to a center point in the midle of the cam and the difference of the distance between that and the base and the lobe peak.

Changing pushrod length will not change anything with lift or duration, pushrod length is important for valve train geometry.

Yes, the max difference is increased, but the diameter of the elliptical is decreased. You only increase Valve life when either the lobe lifts higher, or the base closes lower and you use a longer pushrod shifting the geometry to not bind. In this case the lift stays completly the same, because actual lift height is based on a the radius of the eccentric (lobe). So a stock push rod depends on a stock radius, if the lobe stays the same, but the base radius is decreased, then you only take advantage of a higher lift when using a longer pushrod. Think of it like this, with a stock setup, the spring (working through the rocker and pushrod) force the lifter against the base and the valve is closed. Now if you move the base circle closer to centerline by removing metal, that only allows the lifter to move down further, not up. The valve was already closed at a further distance from the centerline with the stock grind. So you have to take up that slack with a longer pushrod. He still only has a stock lift, because he never compensated for the smaller diameter by using a larger pushrod. If he were to install a longer rod on a stock setup, he could achieve a higher max, but it would bind when the valve closes. So they take away some matieral from the base circle, and this allows the higher max lift of a longer pushrod, but the closeure of a stock setup.