A fellow Q-16 racer leaked out that the new trick deal this year, for max effort race engines, is just the opposite that I have ever heard. Now using the spin-tron sp, they have figured that a super heavy wall CM push rod is the way to go. The weight is not near as important as the flex I guess. Also he has a hot new Comp cam with LS of 106 and way more duration on exhaust than intake. Like 180 intake and 207 exhaust. He's running a 555 like me in a way lighter shorter older dragster and runs 7.3's on a single gas Dominator with the old stuff last year. That's HP no adder. Will be interesting to see what happens at our 1st race Sunday after next... hey... can you boys melt the snow off the track with a jet blower and race. :D Can one of our resident cam SME's validate any of this new stuff??? graemlins/waving.gif

The pushrod issue he talking about has been around for a while.... the huge rocker ratios with .800 + lifts with valve springs strong enough to use on the front suspension of your car....( J/K ) seem to want to make things deflect and move around.... I have heard of some people expirmenting with 1/2 in dia pushrods...


A 555 with a 106 LSA .... hmmm..... like to see the results of that one....

The pushrod deal is correct,GM Pro Stock boys are using 9/16 Ø that neck down to fit the lifter.

Paul,

If you call LSM or Manton they will tell you how much deflection/lost lift you will get with different pushrods. I use the LSM double taper wall pushrods and they are super fat in the middle - I'm sure they don't deflect much even with my 900lb open pressure.

They are about 11" long (big chief) and are suprisingly light but not light on the wallet.

If you think about it, it makes sense to not worry so much about the weight of the pushrod for we have other places(Titanium valves,retainers) to loose weight but rather to concentrate on knowing where the valve is going to be in relationship to the piston. If you look closely there is a move to running the piston to valve clearance alot closer.There have been some improvements in HP by doing this. We just have to make sure things are where they need to be.I use 1/2 moly pushrods in my stuff as we have surpassed the .860 range in lift. They are pretty light for the size, but I was always more concerned that they did thier job more than how much they weighed.

I use a jessel shaft rockers. It has way better control compared to a stud rocker. With the shaft rocker I don't see how push rod deflection could be an issue unless it was so bad that it fell out. Correct me if I missed something on that point. My friend still uses a stud rocker system... it's money thing for him. After my 2nd nasty failure using hi end rockers, in which it's never clear what failed 1st, I poneyed up for the jessel shaft rockers. Other than the custom length push rods and the trimmed studs or bolts... I went to bolts.. I no longer have those nasty failures in that area.. this is me knocking on wood....>>>> graemlins/clonk.gif I saw a year back Jessel now sells one for BBC that is for weaker springs and for less money. Think they said 750lb max.

Jesel would be one of the first that recommends big pushrods for a BBC race engine.

Pushrod flex is not only caused by poor geometry. It also has everything to do with spring pressure and lobe profiles loading the snot out of the pushrod. Even my small blocks had about 300 on the seat and over 800 open. I ran into the 7.30's back in '92 with a carbureted gas 572" using only Brodix 2 heads which started life as a pretty small port volume but were well ported, and used Jesel stuff as well. It is all in the combination, and you obviously have got it if you have gone 20's yourself. ;) I have used Jesel rockers on big and small blocks and they work great. I would probably not go with the lesser-expensive variety for an all-out race motor though. The valvetrain is one place to not save a nickel, it can have dire consequences.

Originally posted by pcs0snq:
I use a jessel shaft rockers. It has way better control compared to a stud rocker. With the shaft rocker I don't see how push rod deflection could be an issue unless it was so bad that it fell out. Correct me if I missed something on that point. My friend still uses a stud rocker system... it's money thing for him. After my 2nd nasty failure using hi end rockers, in which it's never clear what failed 1st, I poneyed up for the jessel shaft rockers. Other than the custom length push rods and the trimmed studs or bolts... I went to bolts.. I no longer have those nasty failures in that area.. this is me knocking on wood....>>>> graemlins/clonk.gif I saw a year back Jessel now sells one for BBC that is for weaker springs and for less money. Think they said 750lb max. ==
Paul,
Consider the pushrod as a piece of spring steel complete with harmonics & resonant frequencies for a moment instead of a nice stiff rod.
Now consider what happens when your spring goes through it's harmonics & dances clear off the head & retainer.
And at some point in your rpm range I can just about guarantee it does.
An 800lb spring has about 1400 lbs on that little piece of spring steel with a 1.7 rocker.
And this doesn't even take into consideration the acceleration loads of the cam.
All pushrods deflect & rats are one of the worst offenders with their goofy angles.
A pushrod cannot be to stiff to control valve movement.
If you consider it as a piece of spring steel you can see why the thick double taper ones are the pushrods of choice in most professional hi rpm applications now.
Once you see a spintron test & what springs & pushrods do you may never want to build another engine :eek:
I do a 330" sb engine for a customer that sees about 9300 pretty regularly & it picked up about 10hp just going from a very good .080x5/16 pushrod to a set of the double taper ones. This was with 1.65 Jesels.

Anyone been brave enough to try the carbon fiber pushrods yet? I have wondered myself if that would be beneficial to use from the harmonic standpoint. Carbon fiber is a pretty 'dead' material, I have carbon fiber seatposts on my mountain and road bicycles along with a carbon fiber fork on the road bike just for that purpose; to dampen and absorb vibration. And it works wonderful. I have a very stiff aluminum frame on the road bike to make it more responsive to steering input and for feel, but the post and fork make the ride tolerable. Same reason riders rave about the smooth ride of steel since it flexes and eats up road shocks. I have seen some of the ads a while ago for the pushrods and was tempted to call and get some info on them, so I wondered if anyone else had heard good or bad feedback? The only thing I would worry about is that from what I have seen carbon fiber gives nearly no warning of impending failure like steel does but rather will usually have a catastrophic failure. You would have to be very careful with them too as any scratches on the tube would generate stress risers for the material to begin to delaminate and fail.

Hey Mike, Thanks for the insight. I use the Crane 99735 3/8 tube 5/16" ball push rods 8.550" intake and 9.30" exhaust. They call them heavy wall .080" 4130 chromemoly. Should I change to a 7/16"-3/8" double tapered? I'd have to look at the cylinder head penetrations. The side clearance on a few are close now as I recall no interference just close. Nothing that could not be drilled out, just was thinking if this was a easy swap, I'd get them and report back the on the track gains... Racing tonight for me. Bracket racing HP only. Thanks graemlins/waving.gif