I'm trying to figure out what pushrod length is best here. Hopefully some of you more experienced guys can help.

First a little about the set up. 355, Cam motion SR (263/270@.050, .686"/.678lift"). Heads are TFS LT1 set up with longer valves, springs are 1.550 dia., 225lbs seat pressure, installed at 1.950". Comp +.050 10* locks and comp 11/32" x .080 lash caps. Comp endurex SR lifters, Comp 1.6 rockers, ARP studs, TFS 5/16" guideplates. Block is decked to 9.015, Felpro 1074 gasket. (12.4:1 comp with domed pistons)

I am trying to measure for proper pushrod length. I have been doing alot of reading on this subject and maybe I have read too much and I am now not sure.

Here is what I have done, adjustable pushrod wth a jam nut and a set of 12" calipers.

7.950" pushrod length. to me its clearly too short. The rocker starts way on the intake side and shoots across to the exhaust side.


8.000" pushrod length. Better but the total sweep is big compared to the others


8.050" pushrod length. I think this is good. The rocker tip starts on the intake side, goes to the exhaust side at full lift and is centered fairly well... a little generous to the exhaust side but thats good from what I have read in searches.


8.100" pushrod length. I'm torn between this and the 8.050". This is very similar but the sweep is tighter. It looks like its shifting a bit over center to the exhaust side also.


8.150 pushrod length. clearly moving to the exhaust side and not centered anymore.



Now I have read that the rocker tip is supposed to start on the intake side, reach its furthest point to the exhaust side at mid lift and come back to center ar full lift. I can tell you thats not going to happen with this set up. The tip starts on the intake side and at full lift its on the exhaust side. Most of the movement(from intake side over center to exhaust side) is during the first 1/3 of the lift. I measured the sweep with a set of calipers so they are pretty close but I am going to say they are probably not dead on. I'll say the margin of error on them would be +/- .003".

So what do you think I should go with? I think I should go with the 8.050"... seems pretty centers and the sweep is still on the lower side.

I'm going to get the 5/16 comp hi-tech chromoly pushrods. I belive they will be up to the task of opening my valves.

 

If it was my motor, there would be no question in my mind about running shaft mount rockers, the SBC rocker system is not conducive to power, it creates a lot of rotational friction if you measure it at the crank as compared to a BBC rocker setup that has a better pivot point and stud location. You should see a good power increase and much better guide and valve stem longevity with a shaft mount system, not to mention doing away with weight.

The 8.050" looks best to me.

 

I'm planning on switching to shaft rocker in the near future. I just dont have the cash for them right now. I've dropped alot of money into this motor as it is. I do realize that the shaft rockers are better. I just dont have the budget for them. I'm tapped out.

The rocker set up I think will be ok. I am running comp 1.6 rockers and a girdle... I already have them so its helping keep the budget in check.


Shaft rockers are definatley on the horizon though... I have a newborn on the way that is going to require some cash before I can go for shaft rockers.


I think the 8.050 looks the best too.

 

Or unless I stumble across a set used that I could trade up on. I have $500 in my rocker/girdle/cast aluminum valve cover set up.

 

Your cam is very similar to mine. You want the tip of the rocker to operate in the center of the valve, don't worry too much about the size of the sweep. I used this same method 6 years ago. My car was a daily driver for about 4 years and my cam is 264/274 @ .050" with .630" lift using 1.5 ratio rockers.

I freshened up the motor last year after 5 years of driving and racing. There was zero wear on the valve guides.

 

I like the 8.000" a tad more travel but it's centered better.

If it's a SR and you have shafts don't **** with the 5/16 do a 3/8th's pushrod

Comp 7983-16

Bret

 

Ok, so here is my next question. Since I have asked this I have had several people tell me to run shaft rockers. I have even has someone PM me about this. Can I really see upwards of a 25hp difference in steppin up to shaft mounts? Also I have never messed with Shaft mount rockers... Will they bolt straight on with no modifications to the heads? I do not want to pull the heads back off this thing.

what brand is good but reasonably priced if i go new? Anyone know anybody selling a set used? Do I need a set for a standard 23* SBC? or are they special for an LT1?

I'm going to give it a try and see if I can sell my stuff first. I have to get at least $550 for my stuff for me to even consider this but I guess its worth a shot. In order for me to run a 3/8 pushrod i would have to get new guideplates anyway.

 

If ya run shaft rockers no guideplates are necessary.
The 8.000 looks the best as long as the starting point is correct.

 

the starting point is on the intake side... basically where the mark starts is it. It starts there and at full lift its at the end of the marking on the exhaust side. Most of the movement is at the first 1/3 of lift. the least 2/3's of lift the movement across the valve is minimal.

I should have said if I stick with the stud mount I will need new guideplates to run a 3/8 pr.

I'm going to research the shaft mount, but I just dont know if I can afford it right now.

 

The Jesel sportsman series stuff is affordable.

 

Hmmmm, that sounds like the Comp Cams method of selecting the proper pushrod length. Start at intake side of the valve stem and at full lift wind up on the exhaust side of the valve stem.

Two other methods I'm aware of. One is the Miller mid lift principle. The begining of the sweep starts at the intake side goes across the center as shown with say mid-lift at the exhaust side of the valve and then as the valve is raised further the roller comes back across the center and at full lift is on the intake side at the same spot where it started. When the valve is released the reverse is true.

I did that on my recent installation with only .570" lift and got a .030" sweep. Pushrod would have been 7.485" long plus .015" for the preload. By the way I used a dial indicator and was able to get the sweep dead nuts. Problem is the center of the sweep most likely will not be in the center of the valve. Mine favored the exhaust side by quite abit.

The next method is a variation of the Miller method. With this method you try to center the sweep on the valve or get close to it but you will have an increase of the sweep area. This is what I did and wound up with a sweep of slightly over .040". Pushrod turned out to be 7.350" long plus .015" for the preload. Again this is with a lift of .570"

There are people on this board that are light years ahead of me regarding engine rebuilds so I would follow their advice. Just reporting what I did and what I have read and FWIW.

 

Yeah I tried to follow the miller mid lift but there is no way this setup is going to do that. I starts on one side and ends up on the other with just under .700 lift.

I have read several discussions about it here but not to many discusions with actual pictures and results.

I'm going to try and sell my stuff. It looks like jesel makes a sportsman series for the LT1/4 head. But from the pics it looks like its a solid shaft the length of the valves. That would cover the center bolt holes for any valve cover to possibly fit. I'm going to have to call them to find out more details.

Somehow this thread went from a tech question to a sales meeting.. sorry bout that but I want to do this right the first time. I too am far from a a SBC expert here so I am trusting the vast knowlege of people who have responded.

Hopefully I can make this switch for a reasonable price. If not I'll have to go with my current stud mount (which is top of the line, but still not shaft mount)

 

They should work... Looking at a set of heads, the valve cover bolts are closer to the valves than the stud holes for the shaft mounts. You may need slightly taller valve covers to make them work, but I don't think center bolt will be a problem.

 

I've done it the "Comp Cams" way, I saw WJ do it once on TV and he did it the same way as I do.

It also ends up with the shortest pushrod most times which is always a good thing.

Bret

 

ok next question... I am going to go with 8.000" if I keep the stud mount rockers.

Now will the shaft rockers require me to measure again and if I go that route? How do you know what length PR to use with shaft rockers if I do pull off this upgrade?