The insulation is there primarily for noise reduction. Having it in place or not will have little if any impact on average underhood temps. It might help underhood temps stay warm a bit longer after you stop the car. It might also somewhat reduce paint oxidation on the hood by reducing hood surface temps.
From what I've heard its good to keep it on because it keeps the motor from cooling to fast if its very cold and it keeps the hood from getting very hot which could over time mess the paint up.
As stated all ready the main purpose is noise reduction. Removing one will not effect the exterior paint on the hood although it possibly could effect the paint underneath. My opinion is it's not really nesesary and is any easy way to get rid of weight by removing the insulation. That stuff is actually quite heavy.
Shon.
Hey.... It All Add's Up!!! Remove one thing then another and another thing before you know it you just shedded 30Ibs off your car! That Insulation is definetly heavier then that.
Somebody go to the the dump and weigh that thing I did take mine off for a while trying to save weight but I put it back on because all the dirt and dust that was on the hood and I didn't wanna clean and wax the underside all the time....yes I waxed it
The one guy I was talking to at Ford claims it is also there for use as a fireblanket. He said if an engine was to catch fire, the material would put it out. I don't know sounds like a bunch of crap, but just another thought. I have a cervini's cowl now, so apparently that didn't stop me haha.
Matt
Works primarily as a fire blanket and noise supressor.
I've talked to a few 5.0 mechanics and they've seen a few burnout 5.0's and the "blanket" never worked. The plastic retainer clips are to melt as soon as fire breaks out and the insulator is to drop smothering the fire. Never works though.
I leave mine in just for the purpose of keeping heat from affecting my exterior paintjob.
Be carefull of them sagging though. Mine did over the fan and caught the blades cracking them. Ended up having to replace the fan and cutting out the saging material from the path of the blades.
Definitely not a fire blanket -- that's an old rumor. If it was, I can assure you it would be there to protect people in SSP cars -- which it is not. This is in addition to other cars and trucks that do not come with it.
It also has no effect on exterior paint -- same reason.