valve springs

1st November 2012, 21:27

what springs would you recommend for a boosted 8v'r?
im currently rebuilding the engine i have bought and im going to buy uprated springs, just need a point in the right direction i suppose

thanks

1st November 2012, 21:41

Standard. Springs are springs.

1st November 2012, 21:48

if you are using a standard camshaft then use standard springs. Only upgrade if you need to as stiffer springs increase the engines parasitic losses.

1st November 2012, 22:13

Argue elsewhere. Topic cleaned.

2nd November 2012, 08:07

Depends how much boost you are running,

I've seen the valves take a hit due to boost forcing them open.

2nd November 2012, 08:13

i am planning on running the standard camshaft, but will the standard valve springs be ok for boost application ?

planning on running @10psi to start with

2nd November 2012, 08:23

Quote:

Originally Posted by vtr91

i am planning on running the standard camshaft, but will the standard valve springs be ok for boost application ?

You should change springs ideally, however some will say they have been fine with standard springs. The maths will tell you otherwise however.

I would always change springs for uprated items on a boosted engine, and the spring rate would be dependent on several factors, including boost pressure and maximum rpm, and camshaft profile.

However, even with a standard camshaft, I would highly recommend changing springs.

2nd November 2012, 08:29

Wats up ross... Touve been far too serious...

2nd November 2012, 08:30

this is what i was wanting to do, ive read a few progress threads and it seems sooner or later a valve will drop.
what would you recommend ross?

2nd November 2012, 08:59

Quote:

Originally Posted by greyjasper51

Wats up ross... Touve been far too serious...

Genchat is the place for bullshit - the specific forum areas are there to assist others with genuine, useful information. If people want to argue over something off-topic, take it to an off topic forum area

Quote:

Originally Posted by vtr91

this is what i was wanting to do, ive read a few progress threads and it seems sooner or later a valve will drop.
what would you recommend ross?

Lets say you end up running 15psi (because realistically, you'll want more and more...)

TU5JP engines run a 40mm inlet valve, which has a surface area of approx 1250mm² or 1.9in². Standard valve spring force in the region of 90psi. With an additional 15psi of boost on each square inch of surface area, your valves now have 28.5psi just in air pressure trying to force them open, reducing the effective force of the standard valve spring by 30%, increasing the chances of seat bounce significantly.

This needs to be compensated for. The larger the valves, and the more boost you run, the stronger valve springs you need. It's not linear (IE, you don't need to run 30% stiffer springs in my example) because it's more complex than that - very high RPM and the transient stage between on/off throttle at high rpm play havoc with the drivetrain.

Conversely don't forget that too much valve spring pressure is as bad as too little. You really need to talk to an experienced engine builder about what they recommend, and use quality components in your build, if you want your project to last.

Edit: Just had a quick chat to my engine builder. Calculate the additional force generated, add around 2/3rds of that figure to the standard camshaft spring requirement for the same engine when NA, and there's a rough guide figure.

2nd November 2012, 09:03

hi

from personal point of view, we have never yet had a problem, certainly on stock cam//low boost set ups.

we have spent numerous years building competition engines from the 8v TU engines, some of which are formulas where rules state stock valve springs must remain, yet camshaft is free (providing it fits without modification) so of course, valve spring free length, compressed height, seat pressure etc are all vital. these engines regularly run to over 8000rpm (naturally aspirated mind) no problems. valve length and collet height must also remain stock.

however there are ways to improve things, and also methods to prevent the tops breaking off the valves, even when using standard retainers. this of course is information you only gain from experience.

however, you are not limited by any rules, so apart from defecit of increaded losses in the valvetrain / valvetrain wear, wont do no harm.. but there are other methods that do not require use of competition springs.

hope thats helpful

regards

colin.

2nd November 2012, 09:26

Now that's proper engine maths

2nd November 2012, 09:45

If you run a blacktop you'll be fine

If your run a silver top then source some blacktop springs and caps or buy some uprated items

I've dropped a valve on standard silver top springs on standard rev limit on a boosted engine, it ran fine for a while and then got valve bounce and dropped no 3 inlet, snapped my rocker arms aswel!!

The silver top springs are well known for being shit.. Just have to put them next to a standard blacktop set to see the difference

Can pick the revs up much quicker with boost then you could on a standard vtr engine

2nd November 2012, 09:53

blackie is correct --If you are running a silver top engine(white) going beyond 6500rpm can cause spring s to float --use blck top springs(green) + caps (different dia) and they are good to 7500rpm all day
this on the presumption that you are not running a silly cam that has lots more lift than std --which on a turbo car is not what you want anyway
if the engine has done alot of mileage or is old --which it will have ,the new springs are not a bad idea +change valve stem seals at same time --they get hard with age

2nd November 2012, 09:56

I'm might even have a set of blacktop springs you can buy mate, ill have a look tonight

2nd November 2012, 11:04

Quote:

Originally Posted by Ross

Lets say you end up running 15psi (because realistically, you'll want more and more...)

i know this will end up happening, im going to give myself some scope for improvements

Quote:

Originally Posted by axsaxoman

this on the presumption that you are not running a silly cam that has lots more lift than std --which on a turbo car is not what you want anyway
if the engine has done alot of mileage or is old --which it will have ,the new springs are not a bad idea +change valve stem seals at same time --they get hard with age

no wild cams, going to use the stock cam

changed the valve stel oil seals already

Quote:

Originally Posted by blackie_2k5

I'm might even have a set of blacktop springs you can buy mate, ill have a look tonight

if you do have them, ill buy them from you

3rd November 2012, 19:01

Quote:

Originally Posted by gazza808

Depends how much boost you are running,

I've seen the valves take a hit due to boost forcing them open.

If that really happens, then you should increase the pre-load on the spring by machining a thicker bottom spring platform, not increase the spring stiffness. You must then check the spring does not go coil bound.

You can measure the increased force on the back of the valve using f=p.A and increase the spring pre-load by that amount.

5th November 2012, 08:47

I think you are getting a bit technical for this man ,as i doubt he will have any way of measuring compressed load value or have the ability to check if coils are touching on full cam lift -
-just fit black top or single uorated springs if you have any worries

5th November 2012, 18:54

Quote:

Originally Posted by axsaxoman

I think you are getting a bit technical for this man ,as i doubt he will have any way of measuring compressed load value or have the ability to check if coils are touching on full cam lift -
-just fit black top or single uorated springs if you have any worries

indeed. going to ring citroen tomorrow to get a price on a few bits so see what they come up with or possibly buy some piper springs.

6th November 2012, 01:56

i have blacktop springs..just not caps