Hydraulic Lifter Power - lashing for max rpm!

[Dusty]

‘Lifter pump up’ – who, among hydraulic cam users, hasn’t heard of it? There is certainly no mystery here - and the answer is just about everybody. What is surprising though is how much about hydraulic lifters, there use and function, is misunderstood and surprisingly a lot of pro engine builders are certainly not out of the loop here. While only OHC motors figured in my life I had not given too much thought to hydraulic lifters as used in a typical domestic V8 engine. Becoming part of a Late Model Stocker team employing crate motor power and building my first few small and big block V8’s changed all that. It quickly became evident that unless I had some understanding of hydraulic lifters my motors were going to be both short of power and rpm capability. Here from racing, testing valve trains and getting valuable info direct from the valve train dynamics guru’s at both Comp and Crane, is what I have learned over the last 3 years or so.

First let’s understand that, even though they essentially have the same hydraulic innards, there is a big difference between the performance of a flat and roller lifter. I don’t want to duplicate efforts here so, to understand why flat and roller hydraulic lifters have such differing characteristics, I suggest you read the ‘Hydraulic Roller Race Oil – what’s it worth’ story posted back in 09-07. Here the effects of side load on a roller are explained as well as the consequences. What I want to do here is answer a question that crops up regularly - namely how to decide on the type of adjustment to use for a hydraulic lifter. Should they be adjusted deep into the travel or shallow or even lashed like a regular solid lifter?Here’s a short and to the point way of looking at maximizing rpm and function from a hydraulic system which, as I heard, got me a 10 out of 10 score for being succinct and to the point with Billy Godbold, Comps profile mathematician. It goes like this:-

1) If the lifter is good and the valve train bad (or even not so good) adjust the system with a very small amount of lash (as per a solid).

2) If the valve train is good but the lifter is bad adjust the lifter deep or even just shy of bottoming out.

Why Would Anything be Bad?

The question that immediately pops to mind here is why would anything in the valve train be ‘bad’. Well that could be a word that is a bit harsh but the truth is a valve train can never be perfect. The difference here is between an average one (which does not service the racers needs to well) and a good one (one that allows race winning performance).


Let’s start with situation #1 – good lifter - bad valve train. Let us assume a lifter that is always up to the job in as much as it near instantly takes up lash and has a minimal bleed down rate such that the lift envelope, during the opening cycle, is virtually uncompromised. If this lifter is used with a valve train that has undamped harmonics we are in trouble. Harmonics are vibration frequencies at, or multiples of, the valve trains natural harmonic frequency. Vibrations of the pushrod, rocker and valve spring can cause separation of the components which, as far as a good lifter is concerned, looks like valve lash. The whole point of a hydraulic lifter is to take up valve lash. When valve train component separation occurs the lifter takes up the clearance and ends up holding the valve a few thousandths (and sometimes a lot more) off the seat. This is called ‘lifter pump up’. It is not a lifter problem. The lifter is doing exactly what it was designed to do – that is take all the lash out of the valve train.

Also another misconception is that a high oil pressure will cause lifter pump up. No it won’t. What a higher oil pressure does is to cause the lifter to pump up quicker and to a greater extent when any valve train component separation occurs. In other words it just makes the problem worse but it does not actually cause the problem in the first place. The proper fix for lifter pump up is to re-evaluate your engines valve train. But hold on a moment - what about anti pump up lifters? Aren’t they supposed to fix this problem? Make no mistake about it - anti pump up lifters are a band aid fix for a poor valve train. An anti pump up lifter is just a regular lifter with a lot of leakage usually at a certain point in the lifters plunger travel range!

Both Comp Cams and Crane are striving for hydraulic roller lifters that will turn more rpm before crashing. This is achieved mostly by building the lifters to far closer tolerances internally.

If the valve train you have must be used then, adjusting the lifter with just a minute amount of lash means that it cannot pump up and hold the valve train open. This exercise needs to be tackled with a degree of caution though. If the both the lifter and valve train are not so good we find, though it seems rare, that the plunger can beat the commonly used round wire retaining clip out of it’s groove. When that happens the engine ends up with a lifter valley with the guts of a lifter in it and a pushrod possibly wrapped around the camshaft. If sustained high rpm at the ragged edge of the valve trains crash speed are involved the best bet is to replace the round wire clip with a snap ring of a size that only just compresses enough to be installable.

Reworking the lifter and setting it up with one or two thousandths of lash is only a partial fix for an otherwise less than desirable valve train. What we rally need to do is fix the valve train. The #1 most important component in the valve train is the valve spring. It is not enough to choose a spring based solely on the load it delivers to the valve when seated and at full lift. Sure these are considerations but at least as important is the springs Natural Resonant Frequency (NRF). And, you ask, where on earth do I find that number? Good question as no spring catalog to my knowledge gives this number. But all is not lost.

Take note, the beehive spring is not just here to stay but will, in the next ten years, be used in 90% of all applications. Whatever application you may have just check to see if there is a beehive suitable to replace what you might otherwise have used.

What we are looking for here is a spring with as high a NRF as possible. The stiffer the spring is in relation to it’s weight the higher this number will be. When selecting a spring go for the one that is the smallest and has the least mass possible for the seat and full open loads required. Finding such a spring can actually mean that less seat and wide open forces are needed to get the job done. This is one of the reasons why a beehive spring works so well. It has low mass for the forces delivered and the way it is wound means it has no clear cut resonant frequency so it’s far less sensitive to being excited by valve train harmonics.

Situation #2 Good Valve Train – Bad Lifter

It is far from obvious but over the last ten to 15 years the springs available to the performance enthusiast and racer alike have become significantly better. This is a very real factor toward getting the best out of a valve train. The bottom line is the spring actually dictated just how good the overall valve train will be. Install a cheap and heavy (high mass) spring and the result will be a valve train with less rpm capability, less high lift and less high acceleration capability. All three of these factors are what is need to make more hp. The availability of superior springs means valve trains capable of greater opening areas and higher rpm limits.

A good way to get high valve lift is through the use of higher ratio rocker. But the extra lift comes at a price – it reduces the rpm to valve train crash. This makes the hydraulic roller valve train all the more sensitive to best preparation and adjustment.

However if the lifter collapses (and this applies mostly to roller lifters) the whole valve train goes to pot. If the lifter has a propensity to collapse then we need to tackle the situation by limiting just how much it can collapse. The extreme case here is to adjust the lifter all the way to the bottom of it’s travel so there is no further travel for it to collapse into. The down side of this is that we now have, in effect, a solid lifter and no lash clearance. By adjusting the lifter to within say ten thousandths of the bottom of the travel we are getting back the hydraulic action require but limiting any collapse to just ten thousandths. In practice most rollers will collapse this amount and recover during the closed part of the cycle so that lash continues to be taken up as intended.

Here is how we deal with hydraulic roller collapse. This 5.0 small block Ford lifter has had two washers (of about 0.090 thickness) installed at the point arrowed. The spring is removed and the round wire clip is replaced with a stout snap ring. (circlip)

The same effect can be achieved by installing washers or a travel stop of some sort into the lifters innards. This means the lifter may only have ten thousandths of hydraulic travel. Going this route compensates for a poor lifter and the limits of a less than perfect valve train. This, for a high performance application is my choice.

This Rev-Kit if from Comp Cams. Although originally intended for use with solid roller lifters it non-the-less works well with hydraulics.

It’s worth noting that as the amount of plunger travel into the lifter is increased so there is usually an increase in rpm to the crash point. For instance a roller valve train that crashes at say 5800 rpm with a quarter turn into the body when adjusting at the rocker stud may run to 6000 when adjusted three quarters of a turn in. the reason for this is the reduced volume when adjusted deep, recovers quicker while the valve is closed. Also if the lifter is bottoming out it takes a lot less to refill to the lash point.

Here is an AFR rev kit just going into one of our small block Chevy test engines. We found a solid 500 rpm increase with this!

Well that’s all I have to say on this subject so hopefully it is of help to those of you wondering what sort of lash choice you should apply to your valve train.

Dusty Kennett

[DAWG]

rev kits are a engine life saver
I would have blown a motor years ago if i didnt have it installed.
push rod broke-revkit kept lifter in the bore so i didnt lose oil pressure.

[boss68]

Thanks Dusty,very interesting and informative.
I would like to ask the reason for removing the spring when modifying hydraulic lifters and is it correct that this would also work with a flat tappet lifter?
Would this change be acceptable on a street driven vehicle?
How large is the contribution of push rod design to the stability of the valve train?
I would like to say i have been looking for a tech forum such as this one for quite some time. I am very interested in achieving one hundred percent from each piece and little info exists on getting that last one percent. My library consists of many of David Vizard's books as well as many others and i have found the information extremely valuable.
Many thanks to everyone who makes this information available. It is very much appreciated.
John

[old blue 75]

Originally Posted by boss68

Thanks Dusty,very interesting and informative.
I would like to ask the reason for removing the spring when modifying hydraulic lifters and is it correct that this would also work with a flat tappet lifter?
Would this change be acceptable on a street driven vehicle?
How large is the contribution of push rod design to the stability of the valve train?
I would like to say i have been looking for a tech forum such as this one for quite some time. I am very interested in achieving one hundred percent from each piece and little info exists on getting that last one percent. My library consists of many of David Vizard's books as well as many others and i have found the information extremely valuable.
Many thanks to everyone who makes this information available. It is very much appreciated.
John

Dusty I have the same ?s as boss.

Thanks old blue 75

[old blue 75]

Originally Posted by boss68

Thanks Dusty,very interesting and informative.
I would like to ask the reason for removing the spring when modifying hydraulic lifters and is it correct that this would also work with a flat tappet lifter?
Would this change be acceptable on a street driven vehicle?
How large is the contribution of push rod design to the stability of the valve train?
I would like to say i have been looking for a tech forum such as this one for quite some time. I am very interested in achieving one hundred percent from each piece and little info exists on getting that last one percent. My library consists of many of David Vizard's books as well as many others and i have found the information extremely valuable.
Many thanks to everyone who makes this information available. It is very much appreciated.
John

Dusty I have the same ?s as boss.

Thanks old blue 75

[Dusty]

well the spring really has no place left to go with the washers in there. Pushrods have everything to do with valvetrain stability. Your goal it for the valve to mimic the cam lobe x the rocker. With flimsy pushrods all those hours spent on cam dynamic go out the window as the pushrods will act as spring and accelerate and decelerate the valve not as intended. This also wreaks havoc on the valve springs capabilities. You fight twang by increasing the diameter and tapers effects harmonics in a positive way. Any time you plan on spending time above 7k rpm plan on spending the extra money on some 3/8 tapered pushrods. I might be able to dig up some dyno numbers on a crate motor that we switched to 3/8 pushrods on and motor was only run to 6300 with a mild roller (that move was deamed legal by a particulair track)

[paulo]

Dusty

About 15 years ago when I was living in NJ,I adjusted the lash to zero on a stock Ford 302.It was in a Maverick I drove on the street and did some Time-Trials with.It took only one event at Pocono Raceway to fall into a low oil pressure situation,that I later found to be the wear of the small washer-valve to push rod support piece.I was amazed at how the combination of 16 small leaks droped pressure so much and I never used zero lash again.After this experience,on an engine that reved only 5000 rpm on a stock camshaft,I wonder what would have happened if I had tried small amount lashs,as I was planning.From that point on I usually adjust a full turn in on hydraulic engines I build,small or big camshafts.Comments?

Thanks Paulo