Reinforced exhaust valves VW Golf 2 Corrado Scirocco 1.8 16V KR 2.0 16V 9A

VW engines covered

Volkswagen first fitted the 1.8 16V KR to the Scirocco II, the Golf II GTI 16V and the Corrado, with 136 to 139 hp depending on the version, then the 136 hp 2.0 16V 9A to the Corrado from 1991 to 1995. Both naturally aspirated four-cylinders have four valves per cylinder.

Each one therefore has 8 exhaust valves. SUPERTECH gives a 28.0 mm standard head for the KR and the 9A, with a 7 mm stem and a 98.2 mm length. These are the valves that take the extra heat when the engine is tuned.

SUPERTECH reinforced exhaust valves

Without forced induction, the head metal of an exhaust valve works between 760 and 870 °C; with a turbo or a supercharger it goes past 1,000 °C. The head only cools by contact, about 75 % through the seat and 20 % through the guide. For the original steel, the reference used is the EV8 family, which falls from 550 MPa at 600 °C to 300 MPa at 800 °C. Beyond what it can take, the head fatigues, warps and then loses its seal on the seat.

The SUPERTECH range for these engines brings together black nitrided stainless steel (VWEVN-1034), EV16 stainless steel (VWEVN-1035), Inconel (VWEVI-1034F, VWEVI-1035, VWEVI-1037) and Nimonic with a hollow stem filled with sodium (VWEVI-1035-HS). Inconel, a nickel based superalloy, keeps 860 MPa at 732 °C and 554 MPa at 816 °C, nearly 85 % more than EV8 steel around 800 °C; sodium, liquid above 97.8 °C, moves heat from the head up into the stem.

The VWEVN-1035, VWEVI-1035 and VWEVI-1035-HS take the head to 28.5 mm (+0.5 mm) and the VWEVI-1037 to 29.5 mm (+1.5 mm). Burnt gases leave the cylinder more easily, the next fill improves and power increases; in return the exhaust seats must be machined to that diameter.

Exhaust valve technical specifications

SUPERTECH note: the VWEVN-1034 and VWEVI-1034F are listed as the KR and 9A standard size (28.00 mm).

Valve fitting

The collets must match the groove of the chosen valve: check that the profiles agree at assembly.

The VWEVN-1034 and VWEVI-1034F fit seats as they are; with a 28.5 or 29.5 mm head, the 8 exhaust seats are recut to size.

Their 7 mm stem diameter is common to the six part numbers on this page.

Technical guide

Our brand

SUPERTECH Performance, based in California, has been developing racing valves and valvetrain parts for more than thirty years. On the KR and the 9A it offers nitrided stainless steel, EV16 stainless steel, Inconel and sodium filled Nimonic, in standard size, +0.5 mm and +1.5 mm.

How to choose

First choose the size, which decides the seat machining, then the material:

When reinforced valves become necessary

• Turbo or supercharger added (Inconel version recommended)
• Camshafts or valve springs changed
• Frequent track use
• Cylinder head rebuild with tired exhaust valves
• Enlarged seats to improve flow

Vehicle compatibility

OEM part number (exhaust valve):

Don't forget the inlet valves

For a KR or 9A with a rebuilt cylinder head, also think of the inlet valves: