I'm currently replacing head gaskets on my 1996 LT1 and am having the heads done as well. Testing some of the valve springs, the machine shop says a few are weak.

I found some specs online and it says they should have a closed position pressure of 76-84 psi. However, other info says that they should have at least 100 psi. The shop is measuring says they're measuring around 80 on some. These might be okay, but a set of springs are cheap. They offer a set with 76-84 psi and another set at 104-116 psi. I don't know which set to get. Does anyone have info on factory specs? The car is bone stock.

Thanks very much in advance!

 

GM PN 12495494.

101lbs@1.780"

http://www.jegs.com/i/Chevrolet-Perf...rentProductId=

Will

 

Thanks Will! Thanks also for the link to the Jegs page. Those say they're for an LT4. Are they going to be the same for an LT1?

 

The LT4 springs will go right on the 96 LT1. Same retainer and everything starting in 1994. The LT4 spring has a slightly higher seat load and rate. It's also made from ovate sectional wire. It's a better spring all around than the LT1 spring and cheap insurance if you want to put new springs on it.

FYI the 1992-1997 LT1 spring has an advertised seat load of 85lbs@1.780 but I can't find them for sale anywhere.... the "LT1 valve springs" you commonly find are the old 1970-72 1.260 OD solid lifter flat tappet spring and no good for use on a hyd roller.
Will

 

Sorry if i disagree but the old LT4 "Hot Cam" springs while have more close pressure dont have as much full open press as the stock LT1 vlv springs. The LT4 springs were designed for the light hollow vlvs in the LT4 heads and can float withe the heavier solid vlvs of the LT1 at high rpm. Better choice is the new GM LS6 beehive vlv spring #12499224. Cheap but u need the beehive retainers also.

 

There seems to be some confusion about the specs on the LT4 springs with people mistaking the open pressure with the rate. Pace perf clearly states 332 is the open pressure.

To figure out the rate you need to do a little math. You need to subtract seat height from the open height and the seat pressure from the open pressure.... then divide the sum of the heights from the sum of the pressures.

332lbs@1.220 is the open pressure. With an install height of 1.780 and 101lbs this gives you a rate of 413lbs per inch. So 332-101=231 & 1.780-1.22=.558 Then 231÷.558=413

Now GM makes it easy for us by publishing the rate of the LT1 spring pn 10206040 as 373lbs per inch but not the open pressure.... Great, I get to do some more math...

85lbs@1.780 and ???@1.260

1.780-1.260=.520 So we take the rate and multiply it by the sum of the heights 373x.520=193 (the sum of the pressures) now we can take the sum of the pressures and add it to the seat pressure to determine the open pressure of the LT1 spring. 193+85=278.... so 278lbs@1.260

As you can see the LT4 spring is stronger all around with more pressure all around.

Will

 

The spring rate times the amount of lift is added to the close press for total press at max lift. Well those are the numbers i use. Take it or leave it. The spring numbers i have are from GM parts direct performance parts.

LT1 #10206040 - Valve Spring
This single valve spring is use on LT1 Production Corvettes.
Technical Notes: Single spring with 1.30" O.D. and 1.26" solid height. The pressure at installed height is 85# @ 1.78" with 373# the average rate of pounds per inch.

And my calcutations. LT1 vlv springs: 85# @ 1.78", solid @ 1.26", 373lbs/in
1.78" - 1.26" = 0.520", 0.520" - 0.060" (safety margin) = 0.460" max lift
0.460" x 373#/" = 171.6#, 171.6# + 85# closed = 256.6# open press (@ 0.460" max lift)


Next the LT4 "hot cam" spring #12551483 - Valve Spring "LT4-ZZ4"



This single valve spring is use on 1996 LT4 Production Corvettes and ZZ4 crate engines.
Technical Notes: Single spring with 1.32" O.D. and 1.22" solid height. The pressure at installed height IS 101# @ 1.78" with 332# the average rate of pounds per inch. Use with retainer P/N 10168424.

My calculations. Hot Cam vlv springs: 101# @ 1.780", solid, 1.220", 332lbs/in
1.780" - 1.220" = 0.560", 0.560" - 0.060" (safety margin) = 0.500" max lift
0.500" x 332#/" = 166#, 166# = 101# closed = 267# open press (@ 0.500" max lift)
but at the LT1 cam lift of 0.460", 0.460" x 332# = only 152#, 152# + 101# = only 253#


Just for comparision the LS6 beehive springs #12625033: 90# @ 1.800", solid @ 1.25" = 295#
295# open - 90# = 205#, 1.800" open - 1.250" closed = 0.550", 205# / 0.550" = 373lbs/in
1.800" - 1.780" (installed height) = .020", 0.020" x 373#/" = 7.45lbs
7.45# + 90# = 97.45# closed press
1.780" - 1.250" = 0.530" lift, 0.530" lift - 0.060" (safety margin) = 0.47" max lift
0.470" x 373#/" = 175#, 175# + 97.45# = 272.6# open press (@ 0.470" max lift)

 

Again 332 is not the rate of the LT4 spring. Thats a typo by GM.
Will

 

Ya know the GMPP (cataloge) does have plenty of numerical errors. The listed specs for the LS6 beehive springs listed in the sbc section was actually the LT4 "hot cam" springs specs for a couple of years. And the LS6 springs specs in the LSX sections didnt seem correct either.

I will have to look into this more. I have read of reduced performance using the LT4 springs on an LT1 head though. Thats the reason im using a low lift cam in my 4th gen LT1 now - so i could use the stock LT1 springs. Hey it works if u keep rpm <6,000rpm.

Thx Will.

 

FWIW, I have the LT4 springs in my stock LT1 and it makes stock HP on a Mustang dyno. (246RWHP, 304RWTQ) I don't think minor differences in spring pressure are going to affect much at all. This isn't NASCAR or a LeMans, folks.

LT1 springs are harder to find and more expensive than a set of LT4 springs which are about $60 or so.

 

I use LT4 spring package since 1998 on all LT1s and L98s even some with mild cams like ZZ4 on L98s. They work well and are reasonably priced with retainers,locks etc. If you can swing it use the GMPP 1.6 rockers too for some extra power and lower oil temps. Springs will work well with them.

 

While I don't think that there is any doubt that the LT4 springs are decent - relatively inexpensive springs - I know of two motors that have had one of them fail (both used at HPDE events). Generally speaking having a valve spring fail is NOT GOOD !!!! Personally - I've gone to aftermarket springs and retainers.

Yes - the aftermarket springs are a bit pricier, but the GM Springs were speced by engineers that had very rigid price points - which is not true with springs used by the aftermarket cam companies. Spend a little bit of time on line looking at springs by Comp Cams, Manley, Crane, PAC, etc. etc. etc. You want something that has comparable seat load, and comparable load at max lift, and that won't be within 0.080" of coil bind at max lift. There are LOTS of options out there - don't limit yourself to only the factory stuff !!!

 

Thanks for the help and all of the info everyone! I'm learning a lot about these valve springs and the differences!

 

Ya know the only real way to verify springs is w/spring tester. ProForm has a entry level tester for $80 u need to place in a vise. It even has scaled case so u can set the compressed height.

And I think u will find springs will vary enough within a batch u will need assorted shims for the installed height. U also need a spring height mic for that. Sorry another $50.

So let me share what race teams will do. They buy several sets/batches of vlv springs and sort them out. They throw out quite a few to.

Good luck and please post what u find. It helps us all.