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LT1 Valve Spring Kit, Moderate to Hot Cam Profiles, 135 Lbs Seat Pressure, Vsk4J21-Q5

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Product Description

For moderate to Hot HP cam applications

High Performance Valve Spring Kit for SBC LT1 w/ Aluminum Heads, 135 Lbs Seat

Fits: SBC LT1 aluminum heads as well as 80's L98 aluminum heads w/ single groove valves.

For Hydraulic Roller Cams up to .570" Lift.

L98 applications: See Notes at bottom of page.


This is version III of our popular High Performance valve spring kit # Vsk4J21-Q5.

Starting in March of 2018, all kits will be version III which includes our new custom "tall centering wall" locators. The new locator features an enhanced lower support system which provides improved spring stability over common short wall designs. Another proprietary design from Alex's Parts.

The new locator is counter bored on the top for additional seal to locator clearance. Most engines don't need the counterbore but it's there if required.

With 135 Lb seat pressure, Vsk4j21-Q5 is very popular for use with moderate to large HP cams.

Keep in mind, we offer three different LT1 kits, customers can select the best version for their specific application.


  • Vsk4j21-P, 140 Lbs Seat <--- Not this listing
  • Vsk4j21-Q5, 135 Lbs Seat <--- Yes, this listing
  • Vsk4h21-R, 120 Lbs Seat <---- Not this listing



Definitely one of the best ways to set up your LT1 valve train for increased RPM power and you won't find springs, retainers, locks and locators for this price anywhere else!


      This Kit comes with:

  • High Output 1.268" OD Single Coil Valve Springs
  • Chrome Moly Steel Retainers, 7 degree
  • 7 Degree Hardened Valve Locks
  • Chrome Moly Valve Spring Locators, our own "Tall centering wall" design.

Use to replace the stock springs and hardware to help your engine make the best of your new HP cam installation.


Can be used with high ratio rockers as long as the lift does not exceed .570" lift @ the valve.


  • Outside Diameter- 1.268"
  • Inside Diameter- .880"
  • 135 Lbs @ 1.775" - Seat Pressure (use installed height spec included with your kit)
  • 318 Lbs @ .500" Lift
  • 337 Lbs @ .550" Lift
  • 345 Lbs @ .570" Lift
  • Rate- 366#
  • Average Coil Bind- 1.150"


Suitable for most hyd roller cams up to the around 244 degrees duration @ .050" on the intake. Additional duration on the exhaust is OK.


Requirement- Valve Seal replacement is required when installing this kit. The valve seals must be removed in order to replace the stock spring base with the locators included in this kit. The stock spring bases cannot be re-used, they must be replaced so you will need new valve seals to complete the installation.

The stock guides for LT1 & L98 heads use 11/32" X .558" valve seals. For the best seal life, always replace with good quality viton seals like available by using the check box towards the top of this page.

Not for Iron LT1 heads. If you have a pair of mid 90's Impala iron LT1 heads, use one of our vortec spring kits. Select from part # Vsk4h52 and Vsk4h53 which both will fit iron LT1 used in mid 90's Impala engines.

Note 1. Since these kits are custom built, please allow around 7 days for shipment from order date. Additional time may be required during peak season. It's always best to plan ahead and order in advance.

Note 2. When using self aligning rockers and aftermarket valves, the valves must have the stock tip lengths of .260"/.289", not .250"/.250" as commonly used on aftermarket valves. Anyone interested in replacing valves should check out our 1.94"/1.50" stainless valves w/ .260"/.289" tip lengths.

Note 3. Most installed height micrometers will not clear tall centering wall locators. What happens is the inside of the mic will contact the top of the locator instead of sitting down on the intended locator surface below. Our solution is to include one extra locator which has been machined down to clear all the various installed height mics out there. Using your installed height mic, this modified locator can be used as a tool to aid in verifying all the installed heights. Once each installed height has been established, replace the modified locator with one of the sixteen tall wall locators. Next install the valve seal and spring/retainer assembly. Do this in each position until finished. The modified locator is easy to identify visually. Save the modified locator for future possible use.

Note 4. Valve seals must be installed after all the locators are in place.

Worth mentioning- when we build these LT1 kits, we install one retainer and lock combination onto an unmolested LT1 aluminum head which we use to verify that the installed height is close. If your heads have never been apart and are like our test head, the installed height should be close and can be installed without measuring. Do we guarantee your installed height will be correct on your heads without measuring? Absolutely not as this is out of our control but if your heads have never been apart, chances are, they'll be close. If your heads have been apart, had valves changed or had a valve job, you will most likely need to add shim(s) to get the installed height correct. LT1 heads use the following shims underneath the locators. 1.250" X .570" which we normally carry in: .060", .030" and .015" thick.



Alex's Parts- Excellent quality and performance at an attractive price.

Warranty Information

All components guaranteed against breakage for 6 months from purchase date.

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