Ah, race gas. The pink stuff is leaded alright, 118 must be about $9 a gallon right now. Your problem maybe a 914 with 400HP..... Are you sure the radiator is big enough and is getting enough air? Any tiny production cars you see with massive power usually have to go through some drastic measures to configure the radiator to properly bleed off heat. Are you using an electric fan? Do you know the compression ratio of the engine? Do you have pictures of how the radiator is positioned?

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Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320