maxeffect

iTrader: (1)

Stage 2 heads milled .060 / Cam 02-03 LS6 cam.

Can I get away with stock length poshrods?

Thanks

Jason99T/A

iTrader: (21)

I used 7.35" with heads milled .050" and the TR230/224 cam. The basecircle on that cam is slightly smaller than that of the '02 LS6 cam.

Greg_E

iTrader: (4)

I don't know if you can "get away with" the stock length pushrods, But I was told by LPE that I would need the 7.35" pushrods with the GM Performance Parts Z06 heads, milled .060" and the Z06 cam.

maxeffect

iTrader: (1)

I got 7.250 pushrods with the cam and heads. But I think that they would be too short.

Greg_E

iTrader: (4)

I'm not the guy that can answer that question, but it sounds like that's a little short. It is important to maintain the proper geometry between the lifter, pushrod and rocker. I have read that the lifter can compensate for some variation to the optimum length, but I don't know how much. Any experts out there that can answer this?

maxeffect

iTrader: (1)

????

PacerX

iTrader: (4)

TO WHOMEVER MAY READ THIS THREAD:

See, this is what I was talking about when I said there ought to be a standard chart here on the website that shows what the ideal pushrod length is for a given combination.

.030 milled heads + .010 smaller base circle cam = X.XXX length pushrods

This isn't rocket science as far as general information this site should have. Hell, somebody give me the geometry and I can calculate it.


TO THE AUTHOR:

If you really want to be safe you can purchase an adjustable single pushrod that will tell you the proper length. I think Comp sells them, as do a few of the other large houses.

Follow the instructions on how to install it and measure it.

JimMueller

iTrader: (9)

Doesn't lifter preload play a part in this equation also? I read that Comp R lifters might need to be shimmed thus needing a slightly longer pushrod.

Tin Indian

Ditto with what Jason recommended. You will need 7.35" hardened Thunder pushrods with the LS6 cam and the heads milled .060"
That's a lot to be removed from your heads!
__________________________________________________ _____

Quote from Jim: "Doesn't lifter preload play a part in this equation also? I read that Comp R lifters might need to be shimmed thus needing a slightly longer pushrod".

I don't think "maxeffect" has Comp R lifters. Anyway, Comp R lifters do like less preload. That is why they need the shims installed under the rocker arms. This has the same effect as using shorter rods. You don't want to install longer rods if you use the Comp R lifter [and] the shims. Installing longer rods would just cancel out the reduction in lifter preload that the shims gave you.

Ron,

Tin Indian

Lets do the math on "maxeffect"s engine:

Stock GM pushrods are 7.385" long (not 7.40"). This 7.385" rod gives the correct lifter preload on a stock cam and head engine.

With that info in mind, lets see how you have changed things:
__________________________________________________ ___

Your stock LS1 cam had a cam centerline to lobe heal distance of .775"

The 2002 LS6 cam has a cam centerline to lobe heal distance of .748"

This means the LS6 cam has a .027" smaller cam centerline to lobe heal distance which would require a pushrod that is exactly .027" longer than the stock 7.385" It would need a new rod that is in fact 7.412" long.

Now, you milled .060" off the head. That will now reduce the rod length .060" from the new dimension of 7.412"

The rod length now becomes 7.352" (7.412 minus .060)

Thats only .002" (2 thousands) in difference from a set of 7.350" Thunder hardened rods.

Again..... Use 7.35" rods and no spacers.

Ron,

4thGENRETARD

nice one Ron, that's why I looove this forum

Joe Kizzire

What you're asking for could be done but it would not be accurate. As lift and duration change so does the base circle of the cam. As the base circle changes so does the pushrod length change in order to keep preload and valve train geometry correct. Cams that have the same lift and duration numbers but come from different companys will have different base circles. The base circle and how much the head is cut is the key. This is the reason so much time is spent on valvetrain geometry when building high rpm race engines.

There's just too many varibles to have a set rule for pushrod length.

Tin Indian

Thank You

Tin Indian

Joe just used the term "Base Circle". You may have noticed that I did not use the term "base circle" above. Base circle is actually the distance across the lobe (90 degrees from the highest point of the lobe). This can be measured with a set of calipers or a mic.

You need to know the base circle distance in order to get the cam centerline to lobe heal distance. In fact, the centerline to lobe heal distance is exactly 1/2 of the cam's base circle.

The cam centerline to lobe heal distance is the distance from the centerline of the cam out to the back of the lobe (opposite of the highest point on the lobe)

The cam centerline to lobe heal distance is what is important to know when you pick pushrod length, as this is where the lifter is riding when the cam is at it's lowest lift point (valve closed).



Ron,

How ya doing Joe? Haven't talked to you in a long time.......

annil8r

Hes right, u know whats going to happen if u put stock length push rods in there. ur going to put every thing together, sit in ur garage and crank ur car, its going to turn over very free and its not going to start then ur going to wonder why its not starting. I will tell u why no compression, and that comes from the pushrods being to long and holding the valves open about .060s of an inch so take the tin indians advice use the 7.35 tr or comp push rods.

Tin Indian

I included a little diagram that just shows where on the cam you would see the base circle and the centerline to lobe heal distance. As you can see, it is very easy to measure the base circle. Then just cut that number in half to get the cam's centerline to lobe heal distance.

JimMueller

iTrader: (9)

Do you need physical access to the cam to measure the centerline to lobe heal distance? Can it be determined by other specs? Most of our aftermarket cams use smaller base circles, right? Are they a common size?

Tin Indian

You need the cam out of the car in order to measure it.

(Stock LS1)
Base Circle = 1.552"
Centerline to Lobe Heal Distance = 0.776"

(TR220)
Base Circle = 1.502”
Centerline to Lobe Heal Distance = 0.751” (.025” less than stock)

CAT3

iTrader: (9)

ok, if you have the TR224, and its CtoH D of .751, and you use .030 milled heads, you come out with a 7.380 pushrod. Now with the lifter providing some cushion, is it better to use a 7.4 or 7.35? The .4 might hang the valves open, or the lifter might take up the diff, and the .35 wont open the valves all the way reducing your effective lift.

Tin Indian

As long as the hyd lifter has [some] preload, it won't reduce the lift on the valves.

I would go with 7.35" rods. A little less preload is better than a little too much.

Too much preload will cause the lifters to pump-up at high revs.