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C4 86-91 L98 Corvette Header Installation

 

1986-1991 Corvette Header
Installation Instructions


  

  1. Raise car and support well on jack stands.
 
 
  2. Disconnect battery.
 
 
  3. Remove front center inner fender shields to allow better access to exhaust manifolds.
 
 
  4. Disconnect AIR fittings at top of manifolds.  Requires a 1” and 7/8” wrench.  In most cases you can avoid removing hose from fitting by loosening hose clamp to allow fitting to turn in hose.
 
 
  5. Disconnect passenger side EGR fitting and retain gasket if possible (1986-1991 vehicles only).
 
 
  6. Remove spark plug wires and spark plugs, (driver side plug removal optional, header will go in with plugs in motor).
 
 
  7. If convertible remove X-brace under car.
 
 
  8. Disconnect o2 sensor and smog line at catalytic converter and remove exhaust from car.
 
 
  9. Remove PS fuel filter shield.
 
 
  10. Disconnect metal smog line bracket attached to lower front of RH exhaust manifold.
 
 
  11. Loosen two starter bolts.  Remove outer bolt towards PS of car allowing starter to pivot out of the way enough to remove manifold. 
 
 
  12. Remove oil dipstick.
 
 
  13. Install DS header from under car.  Insert new header gasket*. Start all header bolts before tightening. Second bolt back from front requires 3/8”x 2 ¼” Allen cap and spacer to properly space alternator bracket support. Tighten header bolts; last bolt near firewall can be tightened easiest with Allen wrench from under car. Connect AIR fitting and tighten hose clamp.
 
 
  14. Install driver side o2 sensor and secure wire away from header.
 
 
  15. Install PS header from under car.  PS frame support bracket from engine cross member to right front frame rail may have to be loosened for clearance.  Be patient- a second person up top to assist guiding the header into place and around smog lines will help.  Knock sensor tab may have to be bent a minor bit to clear header flange.
 
 
  16. Insert new header gasket and start all header bolts before tightening.  Third hole back from front requires 3/8”x 2 ¼” Allen cap and spacer to properly space A/C pump mounting bracket.  Fourth hole back also requires 3/8”x 2 ¼” Allen cap for oil dipstick.  The mounting tab on oil dipstick may have to be ground for proper fit and clearance.  To make installation of rear bolt easier we have included another 3/8”x 2 ¼” Allen cap and spacer.  Tip:  To tighten this bolt cut off  ¾” of your 5/16” Allen wrench and insert into head of bolt, then use a 5/16” wrench on that piece to tighten bolt.  Tighten header bolts.   Connect AIR fitting and tighten hose clamp.  Connect EGR tube*
 
 
  17. Pre ’92 Corvettes had only one o2 sensor.  Enclosed is an Allen plug for the passenger side header o2 sensor location. 
 
 
  18. Recheck all bolts, plugs, wire clearances, and fittings.
 
 
C4 Corvette Exhaust Header & Exhaust Systemsc4headersad-copy.jpg

*Fel Pro exhaust manifold gasket #1406 is most commonly stocked at your local parts store, and will work for L98, LT1, and LT4.

*1986 vehicles had a stand-alone crimp on style EGR tube that tended to leak once removed.  1986 vehicles may use Melrose SF86-91 headers but require ’87-’89 EGR valve pipe (GM# 10055728) to replace the ’86 crimp on style.

 

Packing List:


  • Eight - 3/8”x1” Allen cap
  • Four- 3/8”x2 ¼” Allen cap with spacers
  • Four- 3” strap clamps
  • Four- 3” step clamps
  • Two- 2 ½” muffler clamps
  • One o2 bung plug (for 1984-1991 L98 cars only)