MTBDOC

iTrader: (1)

I have also posted this on the FI board: I am ready to tune my LS2 GTO w/ STS. No internal engine mods, but I am seriously considering dropping in a set of 918's and hardened pushrods tomorrow [dyno tune Monday]. BUT: are these the LS1 springs, or are they LS6 springs? If they are LS6, are they up to 10+ psi boost? Do I need to swap in some better springs?

Thanks for the input!!!

MTBDOC

iTrader: (1)

Anybody have ANY thoughts about the springs in the LS2 motor?

Grimes

iTrader: (3)

the 918s will work on ls1 or ls6 heads. But if you are planning for that much boost, i'd upgrade to a dual package.

MTBDOC

iTrader: (1)

What I'm trying to sort out is whether or not the STOCK LS2 springs are up to handling some boost. I realize that the LS1 springs aren't...

Down the road, I may pick up some heads to lower CR and improve flow. Obviously at that point will come better springs. Just trying to figure out if I need to do so now or not.

Gary Z

Valve spring requirements are determined by cam profile and maximum engine speed; they have little or no direct relation to boost. Supercharging an engine may lessen the need for high-performance valve springs because increased power at lower engine speeds makes extreme high revs unnecessary.

MTBDOC

iTrader: (1)

except that boost pressure [psi] x valve size [in^2] = pressure from the intake side that decreases the effective spring rate. With the tendency to float that the LS1's have, boost effectively weakens the spring pressure and increases that potential to float. This is independent of lobe profile or rpm.

Gary Z

I don't know enough to say that your concern is baseless but I would be amazed by evidence of boost-induced valve float. The effect you mention is only significant when the valve is very near its seat.

MTBDOC

iTrader: (1)

"float" on down to the FI forum and poke around...seems to REALLY be an issue on the LS1 cars, hence my questions. I'd never have worried about it until I read about it [repeatedly] there. Didn't mean to come off as adversarial about it [which I am sometimes RIGHTLY accused of!]...

And, I didn't spend the $165 on the springs...so, I'll see what happens. If I need a valvespring upgrade, I'll just get the pre-installed valvespings [you know, they are already attached to VALVES...and some other chunks of aluminum I think ] Told my wife that those are EXPENSIVE springs...heard about AFR springs...

Gary Z

As I said, I don’t know for certain, but my suspicion is that this issue, while somewhat plausible, is mostly myth. I can believe it is a concern with something like a Formula One engine but I doubt it applies to an LSN. Obviously very fancy equipment and facilities would be required to investigate this question. In any case, I’ll take your advice and search the FI forum for evidence.

ChucksZ06

iTrader: (9)

It is not a myth. I have a cobra with 15 psi bell blower. I am sure it would not be a huge factor unless springs were marginal. It also has a big effect on the amount of fuel an injector will flow ( you have to subtract the psi from the rating of the injector.

Grimes

iTrader: (3)

Oh, sorry. Well to answer your question, I don't think the stock ls2 springs will be too good at 10+ lbs of boost. You should upgrade to a dual spring package to prevent valve float.

BlueSix

You'll be fine with 918's.

GTO122

How did you get a STS turbo kit for the 05 GTO, i have a 05 GTO and STS told me they were still developing the kit ( that was a week ago ) Its going to be a twin turbo set up.

slt200mph

iTrader: (42)

The LS2 engine has the 2001 Z06 heads and cam in it a long with the 2001 Z06 valve springs..boost has no effect on the springs it is the profile of the camshaft that determines the springs that are required..

robertbartsch

I have had REV double springs with titianium keepers on LS6 heads for 2 years. Althoguh my cam lift is mild at 560, I have had no issues so far....

As I can remember, the spring pressure for doubles is typically is a bunch higher than stock ls6 (your factory setup) springs which fights valve float. On the negative side, behive springs have less harmonics, can rev higher and their keepers are smaller and lighter making for less valve train weight.

There was an article in GM High Performance that listed the many advantages of behives... really a no brainer...

I think it is fair to say that the technology is moving toward behives and away from doubles and straght profile single springs. I only bought REV doubles since, at the time, the 918s were busting like pop corn as a result of bad heat treating from the factory.

Currently, there are a number of behives on the market. I would consider getting a more stout spring then the 918, however, if you are FI. Also consider getting the titanium keepers - very expensive at $175 or so - but worth the extra dough...

MTBDOC

iTrader: (1)

I am not trying to argue, but this is NOT correct. Increased intake manifold pressure produces a force on the backside of the valve that tries to compress the spring. PSI x valve size [sq in]. For example, 10 psi x 3.2 sq in = 32 pounds force LOST in the spring.

MTBDOC

iTrader: (1)

As a follow up, my gto ran out of fuel pump on the dyno...so we didn't really run past 5000 rpm [was leaning out] and only 5.5 psi...so no valve float yet.

Installed a Walbro 340 on Tues...have a few other issues to sort out.

And HPTuners 2.0 is NOT complete at this point. There is stuff missing that the tuners need!

All that said, the car is still a blast with short bursts to 5000 rpm. Was producing over 450ft-lbs even w/ such low boost. Further results pending...

slt200mph

iTrader: (42)

Grimes

iTrader: (3)

Doc is correct - you are increasing manifold pressure, thus the forces on the valve that is trying to keep shut, and thus on the spring. Boost wont "change" the spring, but the forces acting against it. go to the forced induction forum, and many people have solved high rpm problems by switching to stiffer springs.

96 Comp T/A

iTrader: (8)

Not trying to start a flame war but has anyone forgotten about the anywhere from several hundred to a couple thousand pounds of pressure in the combustion chamber holding the intake valve shut when the valve is closed.
Valve float by definition is when the valve stops following the profile of provided by the camshaft + whatever physical geometry in the valvetrain. This generally occurs after the cam has already moved the valve close to max lift. I know there are cams that are designed to specifically do this (known as slapper cams, cheater cams, etc etc) but that is a topic for another discussion. So back to your original statement. If I am understanding what you have said is that @ 10 PSI of intake tract pressure you leffectively lose 32 lbs of spring pressure. If the valve is on the seat that's still around 100 lbs holding the valve shut with no motion being provided by the cam If there was in fact no other forces acting on the valve which we know is not true. It's not going to float there. So I am guessing that you must be referring to the valve being "hung" open by the force of the pressure in the intake as the valve begins to close. Well with the Intake valve already open the pressure has equalized between the intake runner and the cylinder so no float or loss of spring pressure there. As the intake valve is closing, the piston has already moved almost halfway up the bore and is compressing the charge. The instant the valve shuts compression begins generating a huge pressure differential between the intake tract and the combustion chamber. You couldn't open the valve now if you wanted too for the very same reason you can pump compressed air in to the combustion chamber and change valve springs. So unless someone can come up with some real science as to what is going on, i.e back to back tests on a spintron I am calling on this.