HataErasa

iTrader: (1)

Okay , I would like to better understand the theory behind spring selection.

How do you guys trade off between seat pressure and stability in a high lift situation ?

At what point is there a diminishing return?

How much does RPM affect this?


Are the drawbacks of valvetrain harmonics of concern and what are the greatest contributing factors to this condition?
should one go for the largest spring available ?

Please Educate me

many thanks

Old SStroker

It's a lot like choosing a girlfriend.

You need a spring which will control the valve throughout the engine rpm range, minimize seat bounce, and not exert excessive loads on the valvetrain. That's the thin, rich, beautiful nymphomaniac analogy.

Ideally you would run your particular valvetrain on a Spintron and select the spring which did the best job. Few of us can have that done, so using data from similar Spintron-tested combinations is a good first step. Experience the valvetrain designer has with certain combinations is a big factor. In many cases the spring supplier (cam company) will have fairly good recommendations.

Just as you wouldn't go for the largest duration/lift cam you could cram into the engine (would you?), you don't need to go to the strongest springs available.

Yes, spring harmonics are a very important issue, and developments like beehive springs and knowing how close to run to coil bind have gone a long way toward valvetrain stability, as have lighter valvetrain parts.

RPM is always an issue, but not just max rpm. If you reach a particularly evil harmonic say around 5700-6000 your engine may never get past that to a more stable rpm where hp might be peaking.

My observation is that guys have at least as much trouble choosing a girlfriend as they do choosing valvesprings. Maybe we should have a www.eHARMONICS.com website.

HataErasa

iTrader: (1)

In my situation I am looking at spinnning the motor to 7500 rpm. Right now I am using stock stroke and a mild cam 233-239 which combined with my 1.8 shaft rockers will yield about 630 lift. I am going solid roller with my lifters.


My concern is that the behive design will not hold up to the lift therefore I will have to switch at least to a dual spring design.

My eventual goal will be to use a cam in the 250 range and to stroke the motor to 383.

I do not want to continually beat the seats out of this thing as it still is technically my street car.

I am wanting to understand the theory behind the different spring rates because I am looking to find a proper balance between seat longevity and valve float

Old SStroker

Your valvetrain designer needs to know valve mass, retainers, rockers, lifters, pushrods, etc. before a spring is chosen. I hope the valvetrain guy gets to specify all those parts. The type of lobe also plays into spring choice: some of the lobes are aggressive near the nose which springs don't like @ 7500.

I'm not sure what you mean about a spring "not holding up to .630 lift". It either has enough capacity to control your valvetrain at that lift and rpm or it doesn't. As you get heavier springs (more mass) and larger diameter retainers you need more spring load to control things, which means heavier springs, etc. Are you certain you need to go to 7500? I haven't see a lot of 350 SBCs getting max power above 7000 with 23x duration lobes. What is the rest of the engine?

High seated load doesn't mean the valves will beat on the seats; it could be just the opposite. As far as "beating the seats out", you'll need enough seated load to keep the bounce to a minimum. Two or three bounces up to .015-.020 every time the valve closes does bad things to power as well as the valves and seats. The closing ramps on the lobes and the correct lash will help out a lot. Again, your valvetrain designer should be taking all this into consideration. If you are the valvetrain designer, this isn't the engine to learn on, IMO.

racer7088

IS this an LS7? Without Ti valves you are not going to 7500 in any hydraulic roller deal I can see.

SStrokerAce

iTrader: (2)

I don't know if i would say that Erik. You definatley have to watch the mass but with the right parts i've done 7500rpm stable with SS valves.

Bret

PAC Racing Springs

There are many factors that affect spring selection. To put it in real basic terms, you can use the old F=ma equation. As the "m" or mass get larger as with bigger valves, retainers, rockers, etc and as the "a" acceleration gets faster then you need more "F"or force. Most of this is common sense but what gets complicated is when harmonics of the cam and components come into play.

The springs coils surge and are very active even at low speeds. As the coils surge, the loads in spring vary. This varying load can come and go as engine speeds change and that can make the valve bounce at certain speeds and then get better at higher speeds. This is pretty complicated and if you look at the high speed video in our website then you might get a better idea of how much stuff is moving at speed. Generally if you can get a spring that has high frequencies, which are never listed, then you can have better RPM potential. Generally with everything esle being equal a lighter weight spring with a higher rate has a high frequency. Unfortunately, they are higher stressed too but that is another story. Beehive springs are unigue in that the coil configuration allows for many frequencies as the springs are compressed.

I design many springs for many applications and getting the right spring for a given camshaft/valvetrain is complicated compromiae of load, rate, wire size, OD, material type, processing, torsional stress and as with everything money.

racer7088

Yes you can get the rpm if you lame out the lobe or if you use special parts but with normal valvetrain it will not happen. We've turned 8500 with hydraulic roller with tricks and lame lobes but it wasn't a true street engine.

This topic does really interest me however as I just had an engine not go as far in rpm as I thought and I am rarely surprised like this. It wasn't an LS1 and it did have steel valves and pretty nice parts. I wish I had my own spintron!

Old SStroker

Sounds like a worthy purchase for SAM...or get a few Cup teams to pool their resources and donate a used one as they upgrade.

HataErasa

iTrader: (1)

So how can you force the negative harmonics out of the frequencies generated by the operable RPM range 0-7500?


what size material would you be looking at?

what kind of ratio are you looking to maintain between the size of the spring and the overall mass of the valvetrain?

surely there is a general methodology to follow.

In my own situation I am not creating a cup car that goes to 10,000rpm and has absolutely insane lift numbers, but I am attempting to generate something a little above average, and I very much do not follow a "throw any combination of parts together and expect them to work harmoniously" approach to building a car.

bluecamaroz28

Here is some additional information on valve springs for hydraulic roller engines (obtained from a cam grinder, not a sponser here or I will mention the name):

Hydraulic roller cams present a unique problem for higher rpm use, especially above 6000-6500. The heavy lifters and relatively fast acting profiles (which is what makes real power) require lots of spring pressure to get that heavy tappet back on the base circle of the lobe and hold the valve closed. However, virtually all springs you can find from other sources that do have enough seat pressure, also give very high open pressures. This sucks, since open pressures over 340-350 will squeeze the oil out of the lifter, and making the profile "look" smaller to the engine. (If you have difficulty with this one, contact the actual lifter manufacturers). It's as if a slice of the backside of the lobe was removed, as far as the breathing part of the engine is concerned. Therefore, the rpm ability given by the higher seat pressure is taken away by the heavy open pressure reducing the duration seen by the engine. Without that duration, the engine will not rev as well or make as much high end power.

SStrokerAce

iTrader: (2)

Erik,

In one case I'm thinking of the lobes were not lame at all, the valves were solid SS 11/32nd valves and the motor was a street/strip motor. It suprised me because it made 500rpm more than I thought it would. Don't say things will not happen, certain things definately help or not help but the reality of the results is always there.

I was just reading Race Tech on the can and a good article in there about Race Design Engineers was in there.... one of the good quotes was:

"Perhaps one of the key ingredients in being successful is not being fullly aware of what you can't do"

Bret

PS I hear SAM is in the EMC, good luck you guys should do well!

SStrokerAce

iTrader: (2)

Well I don't agree with the heavy lifters part, BUT the rest of that quote has a lot of info in it that I think people don't get about hyd rollers.

Bret

HataErasa

iTrader: (1)

Just to be clear I am asking about a mechanical roller not a hydraulic roller

thanks for the info I greatly appreciate garnering a greater understanding of how these pieces interact

Old SStroker

Probably not a simple one unfortunately. Think of a pushrod valve train as 10 or more "springs" in series (cam, lifter, pushrod, rocker arm, rockerarm mount, valvestem, valve head, valve seat, valve spring(s), retainers, locks) all with their own rates, natural frequencies and harmonics. Now cycle them from say 1000-7500 rpm and look at the interactions. It boggles my mind.

For some help you might try software called 4stHEAD from www.profblairandassociates.com. Look at "Valve Train Analysis". If you have to ask the price, it's probably not for you.

PAC Racing Springs had some excellent points. Listen to him.

My original suggestion still applies: go to someone who has successful experience in this type of valvetrain and use the parts they recommend. There are not always simple answers to complex mechanical problems even if we'd like it to be that way.

gollum

iTrader: (1)

So using the lower harmonic beehive valve springs (915's,918's) with a slower "hydraulic" valve lift of maybe .570 or less is the best combination for the everyday driven LS1 motor. Higher valve rates/lifts and spring pressures must use solid roller design lifters/cam to prevent lifter bleed down.

racer7088

Well a Mechanical roller can turn the rpm you want to with the right parts very easily.

racer7088

Yes that would be really nice! I know people that run these all year long and you also need some experience to fully interpret the results but it sure would be nice. Anyone getting one of these could probably make money leasing it out just like a dyno anyway.

gun5l1ng3r

Aren't they still quite a bit heavier than equivelant solid lifters?

HataErasa

iTrader: (1)

That is what I am getting at. I know I can do it with the right parts, I am trying to figure out how to make a relatively educated selection of those parts.

I am not trying to build a cup car or a pro mod, just a very agressive street car.