Valve Springs

[swordfish210 20]

Hi. i'm rebuilding a TU3-A engine for my XT at the moment and i read somwhere that if you run over a 270 cam (i'll be using a Dr Schrick 284 cam) the standard valve springs will bounce horribly at high RPM. Is this true?

[RossD 43]

The springs from the 106 XSi (TU5J2 and TU3J2) are suitably "uprated" over the standard TU3 models. Saying that a new set from CatCams works out cheaper than buying from pug.....

[christopher 5 1 Cars]

The springs from the 106 XSi (TU5J2 and TU3J2) are suitably "uprated" over the standard TU3 models. Saying that a new set from CatCams works out cheaper than buying from pug.....

 

Strings are dependant on lift and acceleration. This cam lifts a massive 11.4mm.

 

I'm using standard TU24 springs with a lift of 10.7 mm which is fine. Since the XS springs will be much softer then I would think you need to upgrade yours.

 

Schrick do not sell springs to match and piper & kent cams only lift to around 10.4mm.

 

Catcams are the only other manufacturer that I know of that sells cams that lift this high so they should have springs to suit.

 

At what lift does flow tail off is the golden question........ I've always wondered why catcams make cams that lift that high..

 

I think Stu and the guy from portugal are running this cam. So you might want to ask them

Edited January 22, 2008 by christopher

[swordfish210 20]

Thanks guy's. BTW this is Stu's old cam, i traded it for a Kent 310

[christopher 5 1 Cars]

Thanks guy's. BTW this is Stu's old cam, i traded it for a Kent 310

 

How did the 310 run actaully?

[swordfish210 20]

I'v no idea because i never ran it. I bought a TU3.2 engine sometime last year for £70 because it had that cam and a vernier pulley on it so i stripped the engine and a mate of mine ported the head and i rebuilt it then i decided that the 310 would be far too much for everyday use and probably would be a bit too much on track as well so i traded it for stu's 284 because it would be a bit milder and easier to use every day

[stu_woac 1]

I used pipers single springs for the cam work fine as they are the same springs they use for the one of the vtr cams witch is a 10.9 lift never had any probs

[Mattsav 1]

At what lift does flow tail off is the golden question........ I've always wondered why catcams make cams that lift that high..

 

Because even if you lift higher than the peak head flow, the valve has to accelerate faster to get to the higher lift so passes though the low lift/flow region faster. This gives you more area under the lift curve which gives more torque.

[Sandy 189]

Catcams TU profiles certainly seem to be ahead of the Piper/Kent TU profiles, which appear to me to be generic carry overs that don't really suit the engine. (Just an opinion obviously!)

[bren_1.3 1]

Because even if you lift higher than the peak head flow, the valve has to accelerate faster to get to the higher lift so passes though the low lift/flow region faster. This gives you more area under the lift curve which gives more torque.

 

agreed. im sure dave baker used to say something similair..

 

EDIT: my TU24 engine is on PTS double valve springs. not sure that info is of any use, but you could go to that extreme if necessary. it would require machining new seats for the springs though.

Edited January 22, 2008 by brens_1.9_wide_arch

[swordfish210 20]

I'll probably give Piper a ring tomorrow to see about getting a set of springs then. Thanks guys, at leastt his saved me learning the hard way and having to take the head off again

[christopher 5 1 Cars]

agreed. im sure dave baker used to say something similair..

 

EDIT: my TU24 engine is on PTS double valve springs. not sure that info is of any use, but you could go to that extreme if necessary. it would require machining new seats for the springs though.

 

 

The ones from kent are double..

[bren_1.3 1]

The ones from kent are double..

 

ahh ok, wont they require machining new seats aswell?

[swordfish210 20]

i rang piper today and the can sell me a set of single springs for £50 +vat and they dont require new neats or caps so i'll probably just get them. thanks for the replies

[christopher 5 1 Cars]

ahh ok, wont they require machining new seats aswell?

 

It is a while ago since I spoke to them. If I remember rightly no...But I would check again to make sure. Ive seen a pic once with shiny titanium caps..

[Owain1602 0]

I think this is an unnecessary ammount of lift for a standard sized valve/port. The point about area under the curve increasing if you accelerate the valve quicker is true but this can also be achieved without increasing maximum lift. For L/D>0.25 the valve lift stops being the determining factor in flow, at this stage the minimum flow area is a factor of the port diameter and stem diameter.

[Mattsav 1]

I think this is an unnecessary ammount of lift for a standard sized valve/port. The point about area under the curve increasing if you accelerate the valve quicker is true but this can also be achieved without increasing maximum lift. For L/D>0.25 the valve lift stops being the determining factor in flow, at this stage the minimum flow area is a factor of the port diameter and stem diameter.

 

To increase the acceleration you have to increase the lift, the cam needs time to accelerate and then slow down at peak lift.

The maximum acceleration is determined by a lot of factors including the follower design, the rigidty of the valvetrain, maintaining the required oil film etc.

 

You can increase the duration to get more air flow but then the engine gets more cammy.

 

Short duration, high lift agressive cams give better power curves at the end of the day.

 

Look for the required duration @1.0mm and then pick the cam witht he highest lift.

 

The 0.25 ratio is gained from having the perfect port shape on a flat plate. Ie no chamber or bore walls influencing the flow.

 

At high lift the air can't make the short side turn so flows across the back of the valve. This isn't accounted for in the 0.25D ideal

 

In reality it doesn't often apply. In fact I dont think I've come across a head where it does apply (unless the port/throat diameter is restrictive for the valve size.

 

A 43mm XU 8v inlet should stop flowing at 10.75mm but peak flow is usually around 12.5mm

 

The mi16 34.6mm valve should have peak flow at 8.65mm but in reality the low/midrange is poor and peak flow is somewhere near 15mm (I've never actually bothered measuring it as the valve will never open that far. Its definatley over 13.25mm)

[christopher 5 1 Cars]

A 43mm XU 8v inlet should stop flowing at 10.75mm but peak flow is usually around 12.5mm

 

The mi16 34.6mm valve should have peak flow at 8.65mm but in reality the low/midrange is poor and peak flow is somewhere near 15mm (I've never actually bothered measuring it as the valve will never open that far. Its definatley over 13.25mm)

 

Matt where is peak flow on the TU heads you have tested actually?

 

I'm actually considering another cam (pehaps catcam) so could do with some words of wisdom on those..I'll send you a PM if you have time..