Some parts too look at (Valvetrain)

[geoffinbc]

Took some weight meaurements

Comp Retainer : 11.3g
LS6 Retainer : 11.5g
Comp Spring : 73.7g
LS6 Spring : 76.1g

Comp Combo : 85.0g
LS6 Combo : 87.5g

Might be of some use to someone.

[AaronGTR]

Yeah, shouldn't be a problem with a complete roller valve train (much like I equipped my engine with ). I just know I got good results from switching springs even before the cam switch. With stock cam and heads my power peak was 5600rpm on the dyno, and after adding LS1 springs and porting (mild port job, stock valves) it shifted to 5900-6100 before drop off. That may or may not be the point at which the stock cam becomes the limiting factor. All those dyno's were with headers too... otherwise the power peak might not have shifted any higher since the stock 3400 exhaust manifolds are the most restrictive thing on the engine. lol

[torq455]

They did mention the roller lifters, but nothing on the flat tappets. Maybe no loss on the roller lifters but some on the flat tappets. Understandable, the rollers don't rely on an oil film, so they can have all the psi they can handle.

[SappySE107]

I remember reading about the spring pushing on one part when its compressing another which "balances it all out'. Forgot about that but also, though I have also read that using a stiffer spring than is needed wastes power through frictional losses and also causes more wear on the cam lobes.

I will let lorenzo post his dyno sheets if he wants, but I can say that the power was building well past 5600. He is running the green LS6 springs and with .5xx lift, there is no valve float.

[smilinguy99]

Found this on Comp Cams web site: Common Misconception:
Many people mistakenly think that using higher seat pressures causes a reduction in the horsepower delivered to the flywheel because...

Thank you for posting that. I was in a discussion on this board some time ago about spring pressures and I don't know who it was, but they were deathly afraid high pressures were going to do very bad things.

It has been my experience that high pressures are a good thing for roller tappet engines. I could not convince them of that. Oh well.

In fact LOW spring pressures do very bad things and are the cause of more damage and power loss than too much pressure. This I have experienced first hand.

Yeah the valvetrain is quite a recumbant device. There is actually very little power being robbed by the valve train, most of it comes from just the weight of the components (rotating/reciprocation mass).

[Mars]

Never looked at it that way. cool.

[torq455]

LS1 isn't much stiffer. LS6/LS2 on the other hand are a lot stiffer. I wouldn't use the LS2/6 springs on a stock cam, just no reason for it. No harm to the valvetrain that I have seen reported but more pumping loss on the engine equals less power. Valve float wouldn't be an issue though:P

Found this on Comp Cams web site: Common Misconception:
Many people mistakenly think that using higher seat pressures causes a reduction in the horsepower delivered to the flywheel because higher seat pressures (and also higher spring rates required for high performance) require horsepower to compress the springs. This thinking is simply incomplete! For every valve that is opening and its valve spring being compressed, another valve is closing and its valve spring is expanding. This expansion returns the energy to the valve train and the engine. This results in a net power loss of "0" hp. Many engineering texts refer to this as the "regenerative characteristic" of the valve train. Recent tests at Crane have shown no horsepower loss on a hydraulic roller equipped engine when changing the seat pressure from 135# to 165#. Power actually improved significantly at top end, probably due to better control of the relatively heavy valves in the engine.

[torq455]

Strange. GM advertises that the power peak is at 5600 RPM. Can't imagine why it would loose power after that. Might have something to do with the cam unable to make power higher than that. Don't think GM would want to sacrifice bottom power for a little more power at a higher RPM.

[AaronGTR]

How is stock too weak for the stock cam?! It dosen't have any valve float up to it's fuel cut off.???? If it was too weak, I'd have float up there somewhere.

Stock redline (on a 99+ n-body anyway) is 6000rpm. It can in fact have valve float before that. It's been observed by many different people on their dyno chart where power drops off after 5600rpm, even if they have headers and ported heads. I saw it happen with my own car and it had less than 50k miles on the engine. As soon as the engine gets some miles on it and the springs start to get some fatigue and settle, it can happen. This was also confirmed by a GM engineer I talked to at the grandamgt.com picnic several years ago. Even he said the stock spring were weak and have been known to float anywhere after 5k rpm when they start to fatigue.

[torq455]

They fit pre 2000 heads. they are copper coloured.



Assembled.



required no mods at all on my 1999 3400 heads.

those seats.....are they for an LS6 head?

[torq455]

[quote="AaronGTR"]Because the stock springs are too weak, even for the stock cam, and shimming them won't do much. You really need a stiffer spring, especially if you go to a bigger cam.
How is stock too weak for the stock cam?! It dosen't have any valve float up to it's fuel cut off.???? If it was too weak, I'd have float up there somewhere.

[tejohnson]

Yup... Called up Pace this afternoon, the made an order this evening once I was "comfortable". It also helped to run int the thread Jordie posted a while back:

http://www.grandamgt.com/forum/showthread.php?t=51512&highlight=12565118

[AaronGTR]

Because the stock springs are too weak, even for the stock cam, and shimming them won't do much. You really need a stiffer spring, especially if you go to a bigger cam. You don't really need .550" of lift... the only reason that was brought up was from discussing how much lift you can run with an LS6 spring just so we know if we needed to worry about spring bind. Seems like we have to worry about the retainer hitting the valve seal before that happens.



Todd, Your car is a '99 right? If your heads are still from a '99 then stock LS1 copper shims will work fine. They changed the valve guide diameter in mid-2000 so later heads require the different shims and seals.

[torq455]

Why can't we just shim our stock 3400 springs? Will we really need lift of .550?