Some parts too look at (Valvetrain)

[SappySE107]

That says .580 lift which would be .480 lift on our setup.

[tejohnson]

Shop I am workin with feels up to .475 would be safe...

[Mars]

I can confirm the valve float at high RPM with stock Gen III springs. With a centrifugal blower, it is even more noticeable beause the higher the revs get, the more boost is produced, consequently, the more valve float you get.

Just to compare, the LS6 style is quite a steup up from the stock 3X00 spring...

[SappySE107]

Do those gold seats work? They dont fit any of the heads I have tried them on so im wondering if you have had any luck with them.

[Mars]

They fit pre 2000 heads. they are copper coloured.



Assembled.



required no mods at all on my 1999 3400 heads.

[tejohnson]

They fit pre 2000 heads. they are copper coloured.
required no mods at all on my 1999 3400 heads.

Do they fit the valve guides snug? What is the ID? Part number please?

I bought a set of Comp, but they are .570 ID (worried about chatter against the valve guide), so I am dumping them cheap.

BTW, if anyone is interested in Comp ID locators (4785-16):

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=8020241123

[Mars]

Do they fit the valve guides snug? What is the ID? Part number please?

I brought the valves, seals, seats, everything to my machine shop. He threw them together for me. Reputable shop, they know their stuff, and didn't have any trouble with anything fitting. Stock GM parts.

(12) LS1 spring shim (seat) 12565118

Keep in mind I also used :

(6) 1991 3.1L valve stem seals (exhaust)
(6) 1991 3.1L vavle stem seals (intake)

[torq455]

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

[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.

[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

[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.

[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?

[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]

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.

[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.