Hello.

First excuse me for my bad english, im from Switzerland.
I have a golf Mk4 AGU. Pistons and Rods changed, big trubo, JBS and 3" exhaust. ECU was changed from M 3.8.3 to Me 7.5 (29f800). No DTC when i read the ecu, VVT  offset. Runs Lambda 0.8, IAT is about 30 degres celsius ingniton angle is fine, but the EGT is too high. Exhaust starts to glow at WOT, has anybody an idea why? Thanks for inputs.

In a what I would think to be is a high horsepower engine,
a visibly glowing manifold wouldn't be uncommon.

Internal combustion gasoline engine are only roughly around 30% thermally efficient.
so when you make for example 250 kw of power output,
you generate 500 kw of waste energy in heat.
Roughly.

That's why people wrap their exhausts and heat shield in all kinds of ways I high performance cars

But a EGT gauge would be a good idea so you can actually tell if it's too hot

Install an EGT gauge. If you do 10-12 WOT pulls it is normal to glow if you stop and check less than 1 minute from stopping.