With a grille block and removing the cover from the air cleaner box I hit up to 170F in my truck, and that's with no ducting from the exhaust manifold. I've been tempted to put some ducting in to help with short trip and warmup IAT's, but been to busy to get it done.
I have heard that the magic number is between 180 and 200 degrees.
I would be cautious experimenting this time of the year. come spring and summer, you may forget that you had modified it and go way over that 200 mark. I don't really know what happens at those temps because I like to be cautious and I like for my car to stay in working order.
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