Upgraded Valve Springs?

[mmt 15]

Hi,

 

I´m running a 8 valve 1,9 on 45mm webers with a full race spec. cam. No rev limiter. (Race car only)

 

The valves starts to "sing"/"float" over 7.000 revs. (I run it up to 7800 rpm)

 

Is there any way to a cheap upgrade to avoid the "singing"floating"?

 

Found some aftermarked 240Lb springs. Is that ok for 8000 rpm? What´s the standard spring rate?

 

Thanks

/Martin

[Cameron 16]

I don't know if anyone's tried this already, but GTI6s have some nice double valve springs. If they fit it could help.

[petert 591]

I found that Datsun L4 double springs to be the best upgrade, without spending heaps of dollars. Just do a search of the major spring manufacturers. The retainer will take the inner spring with only minor modification, although you'll need spring bases for the bottom of the spring. Like any spring upgrade, to do it properly, you need to measure the installed height and shim accordingly. It's not something that can be done easily on the car.

 

eg

http://store.datsunspirit.com/index.asp?Pa...D&ProdID=57

 

http://www.crowcams.com.au/media/catalogue...ication%201.pdf Part #5480 AUS$79.20

Edited January 23, 2009 by petert

[edbar 6]

Like peter says double springs are the way but need alot of machining to do it. I have the kent vs52's in my 8v and you have to machine the original platform out, then i had platform shims made to suit and the retainer needs the inside machining also.That route is expensive due to the time it takes and complexity of the work involved. piper and kent told me that upto a 280 deg cam, good standard springs should be fine though.

[mmt 15]

Thanks guys,

 

Seems like it´s not that easy gooing for double springs.

A set of brand new standard springs might be the way for me to go.

 

And keep the revs down:-(

 

/Martin

[James_R 3]

Puma Racing sells a set up good for 8200rpm I believe for sensible money

[tony perks 1]

I use th4e std green valve springs with 2 shims under on mine and rev to 8000 with no float, but if you get wheel spin as well the valves do occasionally brush the pistons, as witnessed by slight shadows on the top of the piston, not very healthy!!

[omega 82]

I don't know if anyone's tried this already, but GTI6s have some nice double valve springs. If they fit it could help.

 

this seams 2 be the best option if it works

[petert 591]

16V springs are nothing like the required physical size and/or properties. The valves in an 8V are much larger and heavier, thus requiring more seat pressure.

[Owain1602 0]

It is not possible for anyone to make a statement that a certain spring rate will work with a certain cam duration.

 

Required spring rate is not a product of camshaft duration, it is dictated by the section of the cam that has negative acceleration which is around the peak of the cam. You could have a very short duration cam but it the negative acceleration is large around the peak then you can experience float at lower engine speeds if the spring force is not large enough to deliver the required force.

 

Also double valve springs are not usually used for increasing valve spring forces, the main reason is to alter the frequency of the valvetrain assembly and avoid the assembly frequency operating within the resonance frequency of the springs. I must admit that they do increase spring force but this could also be done by increasing the rate of a single spring.

 

Basically the spring required is dependent on the masses of the components, the camshaft profile and the engine speed operating range.

 

This is hardly scratching the surface of an incredibly deep subject. You could adopt the approach of measuring the current springs and their respective rates and it could be possible for you to shim the bottom of the spring so the pre-load on the spring is greater but you must make sure there is enough movement left in the spring.

 

Without knowing exact detail it is strange the valves float at 7000rpm, depending on the standard rev limit, Peugeot would put quite a considerable safety margin on this before they experienced float. If they are infact floating, the cam negative acceleration must have increased too much compared to the std profile or the valve-springs have weakened over time.

[James_R 3]

I use th4e std green valve springs with 2 shims under on mine and rev to 8000 with no float, but if you get wheel spin as well the valves do occasionally brush the pistons, as witnessed by slight shadows on the top of the piston, not very healthy!!

 

Stupid question tony but where did you get the shims from (or do you mean the std seats under the stem seals?? and what is the cam's max lift you're running with that set up?

 

thanks

 

james

[Guest 99hjhm]

The cam company should be able to supply/advise a set of springs suitable for the cam you have..... I don't know if it will be the cheap option, but it's a race engine revving near 8K!!

 

Any valve spring on a race engine should be shimmed to the correct fitted height..... Can't comment on the Pug set-up, but this can often be done with thin flat washers.

[monty69 6]

Be prepared to change the timing belt earlier, look at all the gti6 belt snapers out there due to the double valve springs. Turning one over by hand is like turning a 2.5 diesel!

[petert 591]

Monty69. Not sure how you deduced that! The spring rates won't be any stiffer than single springs, within a reasonable tolerance. If they were power would be wasted.

 

What 99hjhm said is correct. You just can't shim up the standard springs without doing some measurements. How do you know it won't coil bind and wipe the top of the lobes off?

 

You need to:

 

1. Measure the installed spring height

 

2. Measure the fully compressed spring height

 

3. Subtract maximum valve lift from point 1, and add 0.035" (ensures there is space between each coil at full lift).

 

If Point 3 is more than Point 2, you've got issues!

Edited February 25, 2009 by petert