Alu push rods vs spring preassure

[Elnef]

Hi

How much valve spring preassure on a alu push rods is it possible to run with

(dual tappered 7075 alu)

John

[BeetleBug]

Hi

How much valve spring preassure on a alu push rods is it possible to run with

(dual tappered 7075 alu)

John

You`re asking the wrong question John. What you should ask is how LITTLE spring pressure you can run. I went down from K800 to a so called Chevy spring then to a single Chevy spring on my 2332 with a FK87. No problems at all. Revs to 8700 rpms.

[Jesse/DVK]

What else did you change BB? Also looking into getting my valve train light already got 55 grams lifters.

[Elnef]

Hi

How much valve spring preassure on a alu push rods is it possible to run with

(dual tappered 7075 alu)

John

You`re asking the wrong question John. What you should ask is how LITTLE spring pressure you can run. I went down from K800 to a so called Chevy spring then to a single Chevy spring on my 2332 with a FK87. No problems at all. Revs to 8700 rpms.

Hi Kalle

I belive I ask the right question I would like to know what people run with with "a lot" of cam and big valve 53/42 titanium

Do you know the weight on youre parts valve and lifter and maybe what spring preassure

John

[BeetleBug]

What else did you change BB? Also looking into getting my valve train light already got 55 grams lifters.

Nothing. What happened was that I bent a Manton Pushrod at high rpm going of the throttle at high boost (on dyna packs) I changed the pushrods (and tubes) to the JPM alu ones and started out with the same K800 springs. After a little while I changed to the Chevy ones (if I remember correctly I had 390lbs at max lift with them compared to 420lbs with the K800`s) and later the same season I removed the inner chevy spring. Cam is a FK87 matched with 94g UDO lifters. Comp Eliminator heads with big, heavy valves.

-BB-

[Elnef]

Thanks Kalle 

[Tekken]

Kalle, what type of Manton pushrod did you bend-dual tapered?

[richie]

What else did you change BB? Also looking into getting my valve train light already got 55 grams lifters.

Nothing. What happened was that I bent a Manton Pushrod at high rpm going of the throttle at high boost (on dyna packs) I changed the pushrods (and tubes) to the JPM alu ones and started out with the same K800 springs. After a little while I changed to the Chevy ones (if I remember correctly I had 390lbs at max lift with them compared to 420lbs with the K800`s) and later the same season I removed the inner chevy spring. Cam is a FK87 matched with 94g UDO lifters. Comp Eliminator heads with big, heavy valves.

-BB-

So what you are really saying is you spent all your money on really expensive pushrods so couldn't afford new valve springs and just used what you had already lying around

Does amaze me that the weight saving of an ally pushrod makes that much difference to allow so much lighter spring pressure, I really need to try some myself and gain those benifits,I have not had a flat tappet VW engine that would spin that high rpm

cheers richie

[BeetleBug]

Kalle, what type of Manton pushrod did you bend-dual tapered?

No, I used the HD straight ones: Manton 3/8" Chromoly Pushrods, Straight, .058" Wall Thickness.

So what you are really saying is you spent all your money on really expensive pushrods so couldn't afford new valve springs and just used what you had already lying around

cheers richie

At that time I attended classes at a old school. The teachers told me that it was better with too much spring pressure than not enough. I tried several times to ask what was considered enough but could never get a straight answer.

I changed school and will never go back.

[Udo]

It is a question of what you have , FK 87 does not need that much spring pressure . i think elnef needs K800 with Jay Cee chrom molly pushrods

Udo

[John Maher]

The valve spring and pushrod combo that works in one engine might not work in another, even if the cams have similar duration and lift.
Cams that take up initial lash more gently are kinder to the valvetrain - if you're not hitting the valve hard to lift it off the seat and then place it back on the seat in a more controlled manner, you can generally get away with less spring pressure.

Engine expansion plays a big part in the equation. If lash is set to zero when cold, what is it when the engine is at operating temperature? In many instances lash increases beyond the point at which the cam manufacturers designed in take-up ramp is intended to work i.e. the valve takes a hard hit on initial opening.

It isn't the lighter weight of an aluminium pushrod that allows you to run less spring pressure.... it's more related to the fact aluminium pushrods have a greater rate of expansion than chromoly, therefore valve clearances on a hot motor are smaller, which in turn makes the initial take up ramp on the cam work more effectively, resulting in a less stressed valvetrain.

[Jesse/DVK]

Than there is the next questions for a newbie like me. Is it possible to calculate the pressure needed? Or is it trial and error? Possible to hear valves float?

[BeetleBug]

Is it Possible to hear valves float?

Yes indeed, you will notice valve float but then it is of course too late.

On a sidenote; next time you`re at a VW meeting I advice you to listen carefully to all the cars arriving and ask yourselves why they all have such a noisy valve train. Then read the post again from John Maher.

If you buy a camshaft from a serious company they will give you all the info needed.

-BB-

[Udo]

If you messure the cam on a cam doctor for example and have all the weights of the valve train you can calculate it . but it is better  you have one that can tell you the experiance ...

Udo

[John Maher]

Than there is the next questions for a newbie like me. Is it possible to calculate the pressure needed? Or is it trial and error? Possible to hear valves float?

Some of the better quality (ie expensive!) engine simulation software programmes will calculate spring rate and pressures if you've input complete cam data but you still have to test it on a real engine to see if the predicted results work in the real world.

There are things about your engine you may consider as not being directly related to the valvetrain but can still play a part in whether you float the valves or not.........

Regarding engine expansion (as mentioned in my previous post when talking about aluminium pushrods), an interesting point came up in conversation with Johannes from JPM the other day.... aluminium cylinders expand approx twice as much as cast iron. Zero cold lash becomes as much as 1mm (.040") when the engine is hot. All camshafts feature relatively gentle opening and closing ramps, designed to smoothly take up slack in the valvetrain (valve lash) before applying rapid acceleration to lift the valve off the seat. Most aftermarket cams feature an opening ramp on the assumption hot lash is approx .006" to .008". But with 1mm (.040") hot lash, the cam is well into its acceleration phase while the valve is still on the seat. WHACK!!

Same thing happens on valve closing.... instead of being decelerated in a controlled manner, the valve smacks into the seat before the lifter has made it on to the closing ramp of the cam. In this situation, regardless of what valve springs you're using, the valvetrain can never work as intended, except for the first few seconds after you set valve lash.

Just another example of how seemingly unrelated components can affect the end result and why it's often impossible to make a specific recommendation without taking a whole lot of stuff into account.

[jaqo]

That's interesting. So what should be done when you're building an engine with aluminium cylinders and steel pushrods?

[Fiatdude]

That's interesting. So what should be done when you're building an engine with aluminium cylinders and steel pushrods?

Get dual taper aluminum ones -- my 2919 blows up, size wise, as it heats up -- and I just hated my steel PR

[John Maher]

That's interesting. So what should be done when you're building an engine with aluminium cylinders and steel pushrods?

Lower your rpm expectations.

[jaqo]

Can't be done in this combo,i guess we'll have to buy some pushrods;)

[andy198712]

this all begs the question, is there a better way to set lash, ie when warm/hot?

[viNce]

If you set your valve lash hot with steel pushrods, you may have tight valves when cold

With Alu pushrods, setting lash to 0 when engine is hot could be a great solution, then you let the engine cool down and you look at the lash when cold. Now you know how to set your lash when cold for future settings.

[ALB]

There are things about your engine you may consider as not being directly related to the valvetrain but can still play a part in whether you float the valves or not.........

Regarding engine expansion (as mentioned in my previous post when talking about aluminium pushrods), an interesting point came up in conversation with Johannes from JPM the other day.... aluminium cylinders expand approx twice as much as cast iron. Zero cold lash becomes as much as 1mm (.040") when the engine is hot. All camshafts feature relatively gentle opening and closing ramps, designed to smoothly take up slack in the valvetrain (valve lash) before applying rapid acceleration to lift the valve off the seat. Most aftermarket cams feature an opening ramp on the assumption hot lash is approx .006" to .008". But with 1mm (.040") hot lash, the cam is well into its acceleration phase while the valve is still on the seat. WHACK!!

Same thing happens on valve closing.... instead of being decelerated in a controlled manner, the valve smacks into the seat before the lifter has made it on to the closing ramp of the cam. In this situation, regardless of what valve springs you're using, the valvetrain can never work as intended, except for the first few seconds after you set valve lash.

Just another example of how seemingly unrelated components can affect the end result and why it's often impossible to make a specific recommendation without taking a whole lot of stuff into account.

Does any one make cams with really soft initial ramps that would work better with aluminum cylinders? I'm thinking something that goes to 6500...

[reijo5]

I ve been thinking of switching to aluminium push rods , whos do you guys uses/ recomend ?

cheers

Jamie

[Fiatdude]

aircooled.net -- dual tapper

[dangerous]

These are some interesting experiences.

The only experience I have, is with an engine I built using the LN cylinders,
and despite expecting to have to use aluminium PR due to expansion,
we tried some light cromoly ones set at zero lash, and it is very quiet.

Mind you the oil temp never goes over 100C, which would help.

I am "all for" aluminium pushrods if the flex can be reduced to acceptable levels,
but this would be a balancing act with the spring load, pushrod design and material(7075 or 2024),
and of course the ramp rate and other numerous details of the profile used.

For my own engine with a roller cam profile that has a fast ramp rate, but stable profile,
titanium valve, retainer and collet,
I have not found, or made an aluminium pushrod,(3/4"!) that does not lose lift through flex,
unless I get below about 400 nose pressure.

I think that it CAN be made to work, but will require a lot of spintron time.

At this stage, I think I can make it work with some of the large base(1.58") beehives, but these are not rated to .800", only .750"

To respond to the fellow's original question,
I would imagine the JPM taper deals made from 7075 should work ok
if using less than 450lbs and 1.5 rocker,
provided the lobe profile is not some wierd spring killer profile.
..which should be more than just about any flat tappet profile should ever need.

But as others have suggested, a simple question does not mean a simple answer, especially when it comes to valve train!

[Jyrki]

At that time I attended classes at a old school. The teachers told me that it was better with too much spring pressure than not enough. I tried several times to ask what was considered enough but could never get a straight answer.

I changed school and will never go back.

 
BR,
'one of the teachers?'
ps. still running 700lbs at full lift

[Udo]

Alu pushrods on a race engine is more like female 

Udo

[Elnef]

Alu pushrods on a race engine is more like female 

Udo

Hmm At least its not a type1 engine I am building 

[Udo]

You are right , it is a bus engine which is built for no high rpms ...
I would look for the fast engines ... this is what i do since 30 years now and still it is ok . the us guys are the fastest and they will continue like that .

Udo

[Fiatdude]

a aluminum push rodded engine just won the unlimited street event at Las Vegas