Standard 4AGE Valve Springs and 18+psi???

[Duk]

I'm slowly but surely putting my twincharged 4AGZE back together and that icludes an overhauled 4AGE head and standard (GE) cams.
The question is, will standard GE valve springs seat properly at high revs with 18+psi worth of boost pressure pushing on the back of them???

[beerhead]

If they're new they'll be fine for ages.

2nd hand - the easiest way to find out is to take the complete head to the machine shop an get the valve seat tension measured. They should be able to make sure you're on the right track.

[dangdang]

Short answer, no.

Long short answer, not worth not upgrading to find out.

I'd spend the little extra whilst having the head done.

[fixeruperer]

^ exactly, your there, you may aswell just put aftermarket ones in.

[beerhead]

I've seen a bigport race motor revving to over 8500 rpm on brand new stock valve springs with big cams - this motor went for years. HD Valve springs will just loose power if you don't need them - go to an experienced engine builder who will have some decent information charts - based on the valve surface area and the required rev range of the motor they will be able to tell you if you "really" need heavy duty springs.

Springs you can do at any time without pulling down the motor. If the machine shops say's that the springs are within spec I'd run with them, no questions asked.

Asking here you'll only get answers from people who've built a handful of heads in there life - unlike a good machine shop that built a handful this afternoon, and have just about seen it all.

20psi on an untouched GZE has been done more times than I can remember now - unless you're talking over 8000 rpm and monster cam's I really can't see how you can go wrong of your engine builder say's they're fine.

[dangdang]

New build, new gear, for the small monetary push, assurance

[beerhead]

You obviously didn't read what I said... The only advice I gave was to see someone who really knows about this stuff - I said to take the head to someone who can measure the spring tension of the springs, they can tell you the largest diam valve at a certain RPM that it can seal based on the seat pressure - nothing more, if the car was nanna driven under 4000rpm they will probably test like brand new springs, probably as good as half the aftermarkets out there.

None of my 4AGE's have ever valve bounced, all were 180,000km+. As you said most of them can bounce on the rev limiter all day long with 200,000km's on them, doesn't really sound like a weak point of the motor to me.

It's just a waste of energy to put valve springs that have the tension to close a valve at 12,000rpm on a car that will probably see 8000rpm max.

If it's bad advice to get your spring tension measured by your machinist and upgrade them if needed shoot me please

[dangdang]

It's just a waste of energy to put valve springs that have the tension to close a valve at 12,000rpm on a car that will probably see 8000rpm max

Its not valve bounce from excessive rpm that will be the problem!

Its valve float that becomes the issue, the springs have trouble seating the valves with high boost pressures behind them.

[oldcorollas]

during intake stroke the valves are open anyway
during compression, there is no way the valve will open
during power stroke... LOL
during exhaust, probably not, since there is still high cylinder pressure

is probably only end of intake stroke that it could be an issue.. (start of intake stroke maybe.. but still some cylinder pressure)
intake valve is ~1.13sq inches (30.5mm valve). 18psi = 20lb force...

BUT, gotta remember the air is at high velocity and stopping and starting all the time. and do you really have 18psi in the port above the valve, just as it closes? or is it lower? or is it higher?

please remember that at the end of the intake stroke.. the cylinder will be full of air... if you have done your intake correctly, the pressure in the cylinder just before the valve closes will be HIGHER than the manifold pressure ( good VE, piston on it's way up)....
that will force the valve closed even more than an NA setup......

when you go way up in rpm.. and the VE of the motor starts to go down, then you might have an issue, with less air getting into the clyinder to force the valve closed, compared to the build up of pressure (from heat too.. sinceSC) in the intake..

TRD springs are 20kg on seat = 44lb
factory seat pressure = 33lb?

[oldcorollas]

oh, and also remember that when you are at high rpm with CLOSED throttle, you will get decent vacuum.. maybe 10-12psi vacuum (on both NA or SC.. doesn't matter)...
this vacuum in the cylinder will have a greater effect opening the valves, since it acts on the whole valve, whereas boost onyl acts on the diameter of the seat (ie the valve it can see)

so the effect of vacuum or boost in the cylinder is greater than in the port.. so you are probably more likely to float at high rpm on decel, than at high rpm on boost..

ps, i'm happy to be proven wrong

[banana_socks]

^^ I would tend to agree. At no point should there be a greater manifold pressure than cylinder pressure whilst the valve is trying to close. The amount of boost should be negligible as there will be an increase on both sides of the valve.

Also its not like other areas where going overkill is better, as stiffer springs will rob you of power which is no good. Finally as they're relatively easy to change, I'd probably stick with the stock and see how it goes.

[dangdang]

Hmm I had a think about it and that makes a lot of sense oldcorollas.

Only time it could induce float is on the overlap perhaps?

I know the xr6 turbo's supposedly suffer from valve float at higher boost levels.

[oldcorollas]

slightly heavier springs can be good, but not to the extent of the whole amount of boost x valve seat area

peak power on an XR6T motor is at 5250rpm, but modded/boosted ones rev much higher...

say they rev to 7000rpm, it would need 70% heavier valve springs to achieve the same amount of control compared to 5250rpm...

from nizpro..
http://www.nizpro.com.au/valve_springs.html

Cobra Valve Springs
Following months of design, development and engine dyno testing, Cobra has created a special heavy-duty valve spring to suit the BA XR6 Turbo engine. Cobra valve springs cope with high lift camshafts, but without radically heavy spring rates often associated with high performance engines.

As a consequence, whether you are using a stock or modified camshaft, the Cobra valve spring will not reduce the life span of the valve train (camshaft, valve etc).

The Cobra valve spring is designed to work in almost every application with engines ranging from mildly modified to radical 800kW applications. They are also recommended for all 'boosted' engines whereby the factory intercooler results in significant backpressure on the back of the valve (a problem not associated with Cobra's Stage 2 kit due to the incredibly free intake design).

interesting... a more free flowing intake design... which would result in MORE air gettin gto the valve.. does NOT have a problem of the valves blowing open??
and these springs, will be ok for an 800kw motor, but without radically heavy rates? (thats a big range of boost...)
hmmmmmmm isn't that a bit contradictory?

(all that said, i'd be getting slightly uprated springs, but not 60lb seat pressures on a 4A )

[dangdang]

So the whole boost pressure causing valve float is probably a misnomer.

My Performance springs are 48lb from memory. http://www.performancesprings.com.au...ngssingle.html

[fixeruperer]

i wouldnt say, it doesnt happen.