ALFAGTV6.COM

[jema]

Hello!

I'm wondering how stiff valvesprings that will be optimal for my GTV6 2.5 engine.

I'm having 282-degree duration cams with 11,4mm lift, thinking of reving max 8500rpm.

Can I have different stiffness on exhaust/intake? (the camlift is different, of course)

Does anyone have any good formula to calculate spring stiffness in Nm?

If I got it right, what would happen with too "unstiff" springs is that the springs will start to "float" and with too stiff springs the camshaft wear will be uneccessarily high. Or..?
But rather too stiff then...

Does anyone know how much stiffer the IA performance valvesprings are?

//Kind Regards - Mattias

[jema]

none!?

Not even tested the IA springs?

[tectoteam]

hello.

about the ia spring....did you ask them ? perhaps they know the stifness of the stuff they sell, unless DONT buy it...
im not a ultra specialist, but something like 85 lbs on seat pressure and 185 at full lift seems to be a good starting point for a 8000 rpm and 12v engine


the better....is to measure weigth of different components, 'digitalize' the cam profile and do a cad program bench.
i did it for my regrinded cams (290° 10.1mm)on a 24v engine, and it sounds that, i need a few very little more pressure at full lift...a very little, then a washer did the job.
speaking in kg...oem is70kg at full lift, seller of cam says "~" to fit 83kg, i found in solid works(motion) 72kg is enough sufficient.....then i fit 75 (70 for exhaut).
dont blow the engine until today... , then calculation is the better solution...and no need to be THE engineer to do that. good sense , good measures, and patience.

[Jim K]

Mattias, have a look here, exactly a year ago and it may answer part of your question:
http://www.alfagtv6.com/bb/viewtopic.php?p=14258#14258

Jim K.

[jema]

IA told me their springs are approx. 30% stiffer to originals...

tecto, your free to make a new calculation for me I guess you'll need the cams though...

thanks Jim, I'm seeing forward to your book release...

//M.

[tectoteam]

IA told me their springs are approx. 30% stiffer to originals...

tecto, your free to make a new calculation for me I guess you'll need the cams though...

thanks Jim, I'm seeing forward to your book release...

//M.

yes. but dont know about the original 2.5 springs...
this 30% seems to be a little bit big, but i'm not a cam specialist at all.
this should work with those new cams.

IMO :saying 30%...is a quite strange way for speaking...not to much technical...
this sounds like a commercial kinda words to make you decide to buy these springs whitout any other important values.

after all that it is very depending about the springs: must take a look about their free length/compressed height/stiffness to see if they can work on your engine.
in most common of time this cannot be achevied whitout opening and measure the parts and the clearances.

about this, sorry, i do not have any info about 12v springs length and else.

i just had a few experience in my only case regarding about oem q4 cams from a 3.0L 24v and a set of regrind ones i get from kent cams with some specs, like (if i remenber well) i ask for 10mm lift with ~290° duration and 12000mPer sec² of max acceleration and 5.800 m*Sec of max linear speed for a 4 valve head. only value i had to exploit.

can follow this topic, but exact minimum requierement can be achivied only with the exact 'lift law' and some cad test ( to make things faster).
about springs, about some value at seat pressure 380N and at max lift about 820Newtons. sounds good for a 12v and 10.5-11mm lift cam...but depending again about ramp design...
and also harmonic vibrate of the spring (im not familiar at all with this)

mesurement and checkings are the key.
then you must dismantle everything before to change anything.