Reinforced exhaust valves Opel C20XE C20LET

Opel engines covered

The C20XE is the 2 litre 16-valve twin-cam engine of the Opel Kadett E GSI, Astra F, Vectra A and Calibra; the C20LET is its turbo version, fitted to the four-wheel drive Calibra and Vectra A.

Both engines carry 8 exhaust valves, two per cylinder, Opel part 90322697 (6 42 858): 29.0 mm head, 7.0 mm stem and 105.0 mm length. On the C20LET they run in hotter burnt gases, especially when boost is raised.

SUPERTECH reinforced exhaust valves

The metal of an exhaust valve head reaches 760 to 870 °C on the naturally aspirated C20XE and goes beyond 1,000 °C on the turbocharged C20LET. About 75 % of that heat leaves through the seat and 20 % through the guide. An EV8 family steel keeps 550 MPa at 600 °C but offers only 300 MPa at 800 °C: the head sags, fatigues and the seat seal deteriorates.

SUPERTECH makes this valve in Inconel, a nickel-based superalloy that keeps 860 MPa at 730 °C and 554 MPa at 815 °C, about 85 % more than the reference steel near 800 °C, with a 3 groove stem like the original.

Its 30 mm head is 1 mm larger than standard: burnt gases leave the cylinder more easily, with 10 to 12 cfm more flow per millimetre of head, provided the 8 exhaust seats are machined to that diameter.

Exhaust valve technical specifications

GEVI-3303F-8 has a 30 mm flat head, a 6.95 mm stem and 3 grooves.

Valve fitting

The 3 groove collets refit on the GEVI-3303F stem; replace any that are worn or marked.

The 30 mm head, 1 mm larger than standard, requires the 8 exhaust seats to be machined by the workshop.

C20XE and C20LET cylinder heads do not all share the same guide outside diameter: have the head identified before choosing the spring seats.

Technical guide

Our brand

SUPERTECH Performance, a Californian maker of competition valves for more than thirty years, offers one Inconel exhaust valve at +1 mm with 3 grooves for the C20XE and C20LET.

How to choose

A single version is offered for these engines:

When reinforced valves become necessary

• C20LET with raised boost (Inconel version)
• Higher lift camshafts on the C20XE
• Rally, track or hill climb
• Cylinder head rebuild with burnt or distorted exhaust valves

Vehicle compatibility

OEM part number (exhaust valve): 90322697 (6 42 858)

Don't forget the inlet valves

A C20XE or C20LET cylinder head on the bench is the moment to renew the inlet valves and the valve stem seals as well.