I'm in the process of ordering some new springs for an LS6. While emailing back and forth with a certain company, a gentleman points out to me that pushrod flex is an issue on the stock valvetrain and that if I'm considering going the 1.8 RR route I should upgrade pushrods as well. On their website they say it isn't necessary. But the tech is telling me otherwise He even mentioned pulling the heads to clearance the holes to run larger pushrods if I can.


Am I going overboard for a bolt on application??

 

Deflection is pretty common with the stock stuff. I'd upgrade while your in there anyway. It's easy and cheap insurance, although not really deemed necessary with stock springs.

 

To me it comes down to insurance and peace of mind. While there have been plenty pushrods that have caused failures, my argument with a lot of those cases is that they were the wrong size to begin with (and sometimes you just get a bad rod). Staying away from the rev limiter helps we well. Ultimately, it's an extremely cheap modification. Upgrading pushrods is never a BAD investment, but calling it a necessity is a stretch for your application. Aside from internal diagnostics, the only time I'd pull the heads is if you're replacing/porting them.

 

I would throw in a good 5/16 .80 wall and call it good. They are cheap and will not bend like stockers if you hit the rev limiter.

 

I've seen some weird looking dyno graphs on here before. Is that an example of flex?

If its such an issue I think I would have known about it lol

 

There's a video out there of some aftermarket pushrods that look like spaghetti noodles at 7k rpms. It does happen. Even with aftermarket stuff.

 

The tech I spoke to gave me some really good info.

With valve springs and pushrods you always shoot for the safe side. As far as I’m concerned the stock spring pressures are marginal and the stock pushrods cause a lot of stability and power loss issues. To make a point on pushrod stiffness, years back doing Spintron testing on an LS1 with moderate springs there was a 400 rpm gain and an increase of 6 degrees in valve duration just by swapping a 5/16 .080 pushrod for a 3/8 .080 pushrod.
I don’t have any testing information for spring load recommendations but those loads are what is commonly used with the factory rev limit.


The issue is not the spring pressure making the rocker fail, the problem is inadequate spring pressure and pushrod flex causing lifter pump up and shock loading that causes the rocker to fail. When you use a higher ratio rocker it not only gives you more lift, it speeds up the valve and loads the pushrod more. So a higher load spring is needed and a more rigid pushrod . When customers think it’s a “bolt-on” the lifter may pump up premature (sometimes earlier than the factory redline) and parts start to break. If you do the math from a lifter pump up situation it’s lifter preload times the rocker ratio equals momentary added valve lift, ex. .050 x 1.8 = .090. It that case there would not be enough added travel in the valvetrain and there would be momentary mechanical lockup which breaks parts.
The other issue with the 1.8’s is pushrod to head clearance. With higher ratio rockers (all engines) the pushrod comes thru the head on more of an angle so the clearance will have to be checked and it is an issue with some of the LS6 heads. I don’t normally recommend purchasing 1.8’s unless the heads are coming off.
As far as the pushrods, in 5/16 diameter minimum wall thickness .110” (all LS even stock ratio) and if the heads are being removed open up the holes in the heads for 3/8” pushrods and use .080 to .120 wall.

 

It happens a lot. Get the biggest pushrod that will fit.

 

This. ^^^^

No reason not to. The tech you spoke to is right. I know that Manton makes an 11/32" pushrod that will fit with no grinding on the heads. If you can fit a 3/8" all the better.

 

That's my plan. He mentioned that pushrod clearance varies on the LS stock castings. Opening up the hole for the pushrod is common. Especially when you run higher ratio rockers due the angle change. I guess this is news to me.

 

Any issues drilling the PR holes? Can this be done at home with a drill press and angle jig?

 

11/32 will fit.

3/8 usually fits.

Anything beyond that requires clearancing.

 

I ran slp 1.85 rockers with 918 springs, ti retainers, stock push rods. The car trapped 115-116 FBO and beat a couple 12.1 cars from a dig and roll. Never had any problems and it pulled hard up to 63-6400rpm. I ran 12.0 on the street according to my g-tech meter.

Bigger diameter pushrods definitely have their place. I am considering going with trend dual taper on my current setup, but I have a hard time believing you need anything more then a good 5/16 for a stock cam car. I could be wrong but when I tore my car down for the H/C/I install @ 17,000miles, Everything looked brand new. Fwiw the 1.85 rocker setup was installed around 3,000mi. So roughly 14,000mi with the 1.85 setup and the cam, lifters, and pushrods( again looked brand new).

My current setup I am shifting between 68-7000rpm and it just rips up to that rpm. I am running a Manley heavy wall 5/16. I need to get it on a dyno and see what it looks like, but it feels great.

 

I hear ya man. That was all news to me. I'm running the same pushrods on my camaro as you that I'm selling and I run it to the same rpm with no problems. Curve looks great on the dyno.

 

One thing that stood out was when he said he was able to get an extra 400 rpm out of the pull. That's huge at the drag strip. Just from a push rod change. I've seen dyno graphs fall off a cliff so to speak. But what I'm confused about is, did they end the dyno pull or is the are the push rods failing? When I spoke to the tech on the phone he said on a dyno, when the power drops off dramatically its the push rods failing...

 

Here is something to read. OD is what will make the pushrods stiffer, wall thickness has a less significant affect on the stiffness. Many are running the Manton 11/32" in their stock setups. I went with the 3/8" double taper in my AFR heads and yes it did change the upper RPM and smooth out the curve.

Pushrod Stiffness

 

Thanks for that link. Just the info I was hoping to read.

 

Any recommendations on preload for stock lifters on an LS6?

 

buy stock length push rods, torque to 22ftlbs, and call it good.

 

I'm changing the rocker ratio. If I need to shim them for the wipe pattern that could change pushrod length.