[Tim M]

I've got 20,000 miles on my SS 1LE LT1.

I just added an LT4 supercharger at 9.5 psi. The car pulls much more strongly to and thru the 6500 rpm redline.

I'm a bit concerned at high rpm reliability due to valve springs with a few miles and more specifically, 9.5 psi deceasing the effective pressures.

Fortunately, there have only been a few lost LT1's...mostly appeared to be valvetrain issues (possibly driver induced).

This car will spend a bit of time at high rpm - road course/autobahn speed.

2 questions:

-What is difference between LT4 and LT1 valve springs?

-Will the factory installed AFM lifters take a 'light' aftermarket valve spring upgrade (ie. will additional pressure cause issues)?

Thanks!

[oldman]

They are the same spring, GM reduced the weight of the LT4's intake valve to make-up for boost. There are some mild pressure beehive springs that should work, several of my posts about AFM compatible cams talk about valve spring and approximate seat and open pressure. From memory, I think BTR and Cam Motion have something that should work. I think most can be shimmed in to work with factory lifts..

Also IMO and as a complete aside, I don't like a hollow intake valve with boost and sustained RPM. I like a solid preferably titanium (what GM did), or quality slightly reduced stem (Manley Proflow valve) but this adds weight and that is "bad" on an AFM setup. GM thought about it and their elegant solution was to go titanium. I would have gone that route too if I was still on AFM compatible cam.

[Tim M]

oldman: Thanks. I've read many of your posts - appreciate the detail. I'm leaning toward replacing the lifters next season to remove the AFM pieces, if forced. However, I would prefer some safety buffer with the valve springs currently. Something compatible with existing pieces.

I did notice the BTR .660 lift LT1 replacements and have a note into them on few specifics. They did say they recommend the LT1 package rather than the LT4 package - no reasons why though.

A quick look at Google returns different part numbers between LT1 (12678635) and LT4 (12691120) springs - unsure what/how they are different...or if they are now interchangeable.

Of course, they just implemented stop movement here in Stuttgart other than critical functions so won't be getting any miles for a spell!

[oldman]

2016 SS blue top spring 12691120
Other Names: Engine Valve Spring,
Description:
Escalade ESV. Corvette. Yukon XL. Suburban. Camaro. CTS-v. 6.2l. Sierra, silverado.

Applications: 6.2L W/ZR1. 5.3L, 6.2L. 6.2L W/O ZR1.
Replaces: 12629515, 12661339, 12678635

2019 ZL1 shows same spring.

Assume this is an updated version, the look the same with blue top.

I like the
https://cammotion.com/valve-springs/...ve-spring-set/
Check the install height and the 1.260 OD to make sure it is close enough. I got the stock stuff somewhere I could mic. I can't tell install height on stock LT1, somebody else chime in, Since you shim from the bottom, it should not matter. coil bing is at 1.150 so 650" lift is bind, .590 we are at 270 lbs open. 104 seat at 1.8" seems about right
The GM performance blue spring is 90 lbs seat at 1.8" and 295 lbs open at .550. So it is a stiff spring with less seat. The CM is a less stiff spring but with more seat and more max lift.

Pac makes a nice LS spring as long as you check OD / ID top and bottom this should work
https://www.racingsprings.com/index....ing-11211.html
105 seat 300 open, they have a pretty good reputation.

[oldman]

https://www.briantooleyracing.com/bt...pring-kit.html

Spring specs are PSI 1511ML .625" Lift Beehive Springs. 130 lbs @ 1.800", 370 lbs @ 1.175", Coil Bind 1.100", 1.290" OD, .630" ID

That is a thick spring seat. It seems a little stiff for an AFM lifter IMO of course. BTR knows way more than me.

[oldman]

https://www.compcams.com/600-lift-be...retainers.html
Comp Cams LT4 beehive has 125 seat 372 lbs / in rate so seat + (.570x 372) = 337 this is more in my line of thinking.
The LT4 has a special retainer/seat stock so I assume the LT4 kit has a different intake retainer to make up for the different groove height of the LT4 intake valve.

So if I'm comfortable with this setup if they make a LT1 version.

[Tim M]

oldman: More options than I realized - Thanks!

Further correspondence with BTR resulted in confirmation of compatibility with their SK013 with no other changes to an LT1. They did state the difference between LT4 and LT1 packages they offer is installed spring height - believe you hinted at that.

I may give it a try since we've got some downtime.

Do you have experience with a suitable valve spring compressor?

[KingLT1]

Imo the AFM lifters are the weak link in the LT1 valve train not the valve springs. If you are worried about the springs then I would install a small supercharger cam, dod/afm delete, and then upgrade the valve springs. Which adds a lot of cost to fix something that isn't broke.

That are plenty of supercharged LT1's at your boost level and mileage that have not had any valve float issues. The factory spring is pretty decent. jm2c

[ssmofo]

Plus with 9.5 psi of boost on the LT1, do you really need to jam it up past 6500? Prolly not. If you're using the stock cam, your not going to make more power past 6500 anyway.
https://www.texas-speed.com/p-5440-t...-seatseal.aspx

[Tim M]

I agree the AFM lifters are not ideal. May consider swapping them next year as another big project, but not over the driving months. No interest in a cam change.

But check my math...

LT1 intake valve diameter: 2.126 inches
Area of intake valve: 3.55
Boost impact to valve: 3.55 * 10.3 = ~36 psi decrement to valve spring pressure due to boost. (40 degree day today resulted in higher than 9.5 psi > 10.3)

Seems like one should offset this in either higher spring pressure and/or lighter valve weight (Chevy did both).

Admittedly, my interest is two fold - ensuring reliability and there is a bit of interest to see 200 mph with this car on the autobahn - again math says 6800 rpm in 5th should equal that number.

Besides the rpms sure sound nice!

[oldman]

Originally Posted by ssmofo

Plus with 9.5 psi of boost on the LT1, do you really need to jam it up past 6500? Prolly not. If you're using the stock cam, your not going to make more power past 6500 anyway.
https://www.texas-speed.com/p-5440-t...-seatseal.aspx

I run this spring on my ride, it would kill the AFM though.

[oldman]

The car could use a thin wall molly pushrod for weight, comp cams already list tool steel retainers for the LT1. I don't like titanium for this application because it can cause wear. Of course, GM just said screw it, we run titanium intake valves.

[DorkMissile]

Originally Posted by oldman

The car could use a thin wall molly pushrod for weight, comp cams already list tool steel retainers for the LT1. I don't like titanium for this application because it can cause wear. Of course, GM just said screw it, we run titanium intake valves.

IMO the pushrod weight is significantly less important than valve weight, I actually went with 3/8" push rods in my build.

Ti on the retainers IMO is fine, the geometry is what holds it all together, not the material

[oldman]

titanium can wear both the spring, the spring seat and the retainer itself, now granted modern springs have much better and fatter seats, so maybe no issue at all. My 4V engines has a much slimmer inner spring seat, same as "damper" springs used in single spring setups. But long lived paranoia keeps me into tool steel. For pushrods, I was with the stock spring, with aftermarket springs there is a need to go with a thicker wall and thicker pushrod.