Im not going to repost again on this. The only thing that is affected by the different length pushrod is how far the plunger of the lifter is pushed. Its called preload. Longer pushrods push the plunger lower and the net lift is set to what the lobe lift is and you multiply that by the rocker ratio. Its not a simple fact as you say. You are wrong and need to investigate why or post on LS1 tech for others to show you why.

I am not going to debate physics with a common fact like that. I took the time to answer your questions which very few people would do let alone tuners and you are fighting the answers and not looking into the issues. If you had a sold roller motor and there was no plunger to move, the valve would be hanging open all the time off the seat. There is only one length of pushrod that is correct. All other will cause incorrect preload and do not affect lift.

Call thunder racing or texas speed and inquire as to which pushrods you could use to increase lift. Perhaps they can get you an answer that helps or at least satisfies you more. You have made statements such as shims being not safe and this pushrod length/lift issue which make me think I'm wasting time here, but youre a nice guy so I'm still trying.

 

well, thanks... to be honest, i wasn't trying to get under your skin or anything like that.

i was simply stating what i knew.

http://www.compcams.com/information/Products/Pushrods/

http://www.cranecams.com/?show=techarticle&id=2

 

I read both articles and dont see where you are saying longer pushrods increase lift.

There is only one correct length pushrod that you can use. There is only one correct preload amount you can use. if you have too short a pushrod you can loose lift but that doesnt make the reverse is true. The plunger not going in all the way has a gap, and you loose lift from the amount of gap. Its not an engine building variable the builder uses to get a custom lift. It is a msitake.

I read your articles but now are you going to call an engine builder...thunder racing or texas speed???

EDIT: the article also describes increased lift from what is called lifter pump up. In that case you have valve float from the valve hanging open when it is supposed to be on the seat and not an adjusted increase in lift for running the engine. The range of lift is the same, you increaed peak lift by not allowing the valve to be on the seat.

"Therefore with excessive preload, as the engine RPM and oil pressure increases, the hydraulic mechanism will pump-up the pushrod seat. This will cause the valve to be open longer and the lift to be higher. This will decrease the cylinder pressure, lowering the performance of the engine. If the preload is excessive it may cause "backfiring" from the engine."

You totally misunderstood that statement in the article. The valve is off the seat and hanging open. You cant run the engine that way thinking you increase usable lift.

One correct length of pushrod is used with one correct preload. Its not an optional variable. Anything else is a mistake.

You stated: "using the same ratio rocker, the one with the longer pushrod will result in more lift, it's a simple fact. " Totally incorrect; the one with the longer pushrod has a valve off the seat and will backfire as per your article.
It has higher lift at the expense of not being on the seat. The travel distance of the lift is eactly the same: it simply goes from where it is (off the seat) to the lobe height times the rocker arm ratio. If the pushrod is way too short, the pushrod doesnt make contact with the plungerand you lose lift because the pushrod must be moved the distance to the lifter befroe it can start moveing the valve. Again not a usable set-up.

 

do i have too ?? can't i just find something that actually talks about pushrod length and total lift from the seat ?

agreed, the article's really didn't say much about using length. they just reminded us to make sure we get the proper length.

 

I just showed it to you in your own article. That red typing is from the article you just sent. You can't vary lifter preload. There is only one correct amount of it. No if, ands, or butts. The length of pusrod is set since the amount of preload is set. If you increase preload, you increase peak lift causing backfiring...it says that!!! If you have too little preload from a pushrod that is too short it has insufficient preload ad may not make contact with the lifter. This looses lift since you are slamming the pushrod into the seat every time the valve opens. Neither situation is acceptable to running an engine.

Your article was talking about the fact that you have to have the correct preload and how to get it. It was saying there are losses in performance when you vary from it.

Asking an engine builder would be the best way to learn since articles you read can, and apparently have, been misunderstood.

Pushrod length is not a variable unless you have adjustable rockers to set preload by first finding zero lash.

 

There's really nothing to explain, pushrod length has no bearing on valve lift in our engines with stock rockers, it only effects lifter preload. If you're making a connection between PR length and valve or cam lift, you're making a mistake.

You're a saint for lasting as long as you did.

 

i guess we just ran past each other...i'm simply saying that when you start swapping out heads, cams, rockers, etc. you will need to make sure the pushrods are the proper length. 'stock' length may not be the correct length for the combination. anything longer than 'stock' is considered 'longer', in my book.

i believe the proper length is with the valves fully seated but on the 'cusp' of opening.

 

I have that exact cam!

 

Spin, your are WAY more patient than me. I've had similar conversations with Zig on a variety of subjects. Always starts with Zig posting an excerpt from somebody's website or from a Google search, followed by an explanation that is not fully understood, followed by more explanations that are also not understood, ad infinitum. Always ends with a "clarification" that he didn't really mean what he said.

You can lead a horse to the font of knowledge, but you can't make him think.

 

so what did i say ??

didn't spin say that pushrod length has nothing to do with lift.

i said a longer pushrod will give more lift.

what's wrong with that.

initially, i asked what his pushrod length turned out to be after he installed his heads, cam, and rockers.

http://forums.corvetteforum.com/show...2&postcount=13

edit: remember, everyone has a reason why they believe such. if you can get them to explain their reason and you know yours, then you are twice as knowledgeable.

 

Duh.......

 

<unsubscribes>

 

technically speaking, both spin and i were wrong when we spoke about pushrod length. spin said pushrod length had nothing to to with lift, i said longer pushrods give more lift.

technically, only the proper length works correctly . spin is right, a proper length will not add anymore lift. i was right, a stock length will not work properly when heads, cam, rockers are replaced, but you would not use a longer than required rod just to get extra lift. i think it was some assumptions on both of our parts that lead us to believe we were each idiots. oh, well...

is this the lift you ended up with including the 1.7 rockers ?

.588/.595

 

Pushrods dont increase lift. If you change the length of a pushrod, lift is exactly the same. Increased peak lift that occurs at high rpm comes from lifter pump up and not the length of the pushrod. At lower rpm's even by your articles, the lift is exactly the same even with the wrong pushrods.

Just give it up already.

Im unsubscribing.

 

i'm already past it i simply wanted to know what parts you used and how everything turned out.

wasn't the cam being used .588/.595 lift @ 50 ? is that with or without the 1.7 rockers ?

i had always thought the rockers would change the total lift and that's what i had originally asked about. we then got off on a pushrod tangent, which basically ended up a discussion about using the proper length pushrod for your/or anyone's combination. maybe some folks learned some stuff maybe some didnt', who cares.

i'd be really suprised if you are using the 'stock' pushrods, that came installed in your c6, but i'm past that.

what type of vacuum are you getting at idle ?

 

Sheesh. Folks will argue an untenable position to the death.

Just look at Dubya...

Rick

 

Camn specs dont work that way. Duration is usually given as advertised duration @.006 or @.050. Lift is advertised as what the peak lift is and not .588/.595 @ a lift number. How can you have .588 lift at .050 lift?? Check your terminology.

I think what you are asking is what the cam lift is and what it is with a certain set of rockers. Cam lobe lift is .346" and .350". With 1.7 rockers...that is stock, crane, jessel, whatever is still the same for all 1.7 rockers and its .588/.595. To get the lift from 1.8's you multiply the lobe lift by the rocker ratio 1.8.

Lift for piston valve interference occurs during the overlap period off peak so you have to check your set-up by claying it or using a feeler guage method once it is assembled. You arent going to check P/V clearance reliably by doing the math on paper. Crane eat up some differnece by virtue of having some aditional lift at differnet points on the lobe. I dont know what these are. I checked clearance with a clay method.

As I said earlier I used Crane rockers which are adjustable and come with their own pushrods. The pushrod length is a non issue with adjustable rckers for most changes. The crane pushrods are shorter.

I didnt check vacuum but since all accessories like brakes work fine with any cam, I doubt there is an issue with anything that fits this motor. Checking vacuum isnt needed.

 

quote.

"STOP! Before you order custom length pushrods for your new camshaft, please read this important information.

A large number of variables are involved in determining the correct length pushrod for your application. Pushrod length is affected by any one or all of the following:

• block deck height
• head deck height
• head stud boss height
• rocker arm brand/design
• cam base circle size
• lifter design/brand/pushrod seat height
• valve stem length

Don’t assume anything in determining the right pushrod for your new engine. A pushrod that fits one engine may not necessarily work in another. Any number of items can be different on your engine, requiring you to use a different pushrod length. Following the steps below will streamline the pushrod selection process, ensuring that you get the right parts the first time."

http://www.compcams.com/information/Products/Pushrods/

quote:

"What is the difference in the design of a Hydraulic and Mechanical Lifter?

Basically, the hydraulic lifter pushrod seat is moveable, the mechanical lifter seat is not. Both lifter types look the same from the outside, with both having pushrod seats held in by a retaining lock. The pushrod seat in a mechanical lifter usually registers upon an internal step inside the lifter body preventing it from moving (thus it gets the nickname "Solid Lifter").

What's below the pushrod seat in the hydraulic lifter is a different story. Its pushrod seat is not restricted by a step, but instead sits on top of a moveable hydraulic mechanism which acts like a tiny hydraulic pump. Below this mechanism is valving and a spring to produce an upward force, moving the pushrod seat upward against the retaining lock. "

"What is Hydraulic Lifter Preload?

Mechanical cam designs require a running clearance or valve lash, while hydraulic lifters are just the opposite. When the rocker arm assembly is properly torqued down into position, the pushrod must take up all the clearance and descend into the hydraulic lifter, causing the pushrod seat to move down by .020" to .060". The distance that the pushrod seat moves down away from the retaining lock is the "Lifter Preload". The hydraulic mechanism requires this precise amount of "preload" for it to do its job properly. See figure below."

....

"What happens if the amount of Hydraulic Lifter Preload is wrong?

[i]If clearance exists between the pushrod and the seat in the hydraulic lifter, after the rocker arm assembly has been torqued down, you will have no lifter preload.[i]'

ie. rod too short

'In this case the valve train will be noisy when the engine is running. All of the hydraulic force produced by the lifter will be exerted against the lifter's retaining lock, and this could cause the lock to fail. If the opposite occurs and the pushrod descends too far (more than .060"), then you have excessive lifter preload."

rod too long

"In theory, a hydraulic lifter can pump up whatever preload you put into it.

Therefore with excessive preload, as the engine RPM and oil pressure increases, the hydraulic mechanism will pump-up the pushrod seat. This will cause the valve to be open longer and the lift to be higher. This will decrease the cylinder pressure, lowering the performance of the engine. If the preload is excessive it may cause "backfiring" from the engine. How to correct this situation will be explained in the next sections. "

"Fast and Easy Way to Check Hydraulic Lifter Preload when using Non-Adjustable Rocker Arms

With the cam, hydraulic lifters and pushrods in place, install your rocker arm assembly. Use the prescribed method in your repair manual and torque down all the valve train bolts in the proper sequence. Pick a cylinder that you are going to check. Hand rotate the engine in its normal direction of rotation until both valves are closed. You are on the compression cycle for that cylinder. (At this position the valve springs are at their least amount of tension making the job a little easier to do.)

Wait a few minutes, allowing the lifters to bleed down. Now, lay a rigid straightedge across the cylinder head, supporting it on the surface of the head where the valve cover gasket would go. Using a metal scribe and the straightedge, carefully scribe a line on both pushrods. Now carefully remove the torque from all valve train bolts, removing any pressure from the pushrods. Wait a few minutes for the pushrod seat in the hydraulic lifter to move back to the neutral position. Carefully scribe a new line on both pushrods.

Measure the distance between the two scribe marks, it represents the amount of lifter preload. If the lines are .020" to .060" apart you have proper lifter preload. If the lines are the same or less than .020" apart you have no, or insufficient, preload. If the lines are further apart than .060", you have excessive lifter preload. To bring your preload into tolerance, use one of the methods described in the next section if necessary, or call the Crane Tech Line for assistance (904/258-6174).

Methods to Adjust for Proper Hydraulic Lifter Preload

There are several different methods for increasing or decreasing the amount of lifter preload, depending on valve train design and how the rocker arm is held onto the cylinder head. Keep in mind that the automotive manufacturers have made changes to the valve train over the years. What may work on one year's engine may not work for another, even though they are basically the same engine. There is one method that universally works on all these engines, change the pushrod length!

Use a longer pushrod to increase preload, a shorter to reduce preload. Crane offers various length pushrods, and offers custom length pushrods."

i didn't say it crane did. hhmmm...

blah blah blah...

http://www.cranecams.com/?show=techarticle&id=2

 

thanks.. i had to say something to get you back.. all i had was the specs. that were posted earlier and went back and grabbed them, i didn't even bother to check.

 

None of the above long winded article applies to the adjustable rockers I was talking about. The preload isnt set with adjustables by varying pushrod length, you adjust preload with adjustables by turning the lock nut untill the desired prelaod is acheived. I have no idea what you were trying to say with the long article.