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Discussion Starter #1 (Edited)
Dash Shaking!! MYSTERY SOLVED!!

Up until today, my car would go up to 120mph Before the Carbon fiber hood would start shaking.
I haven't been in a major hurry to get it straightened out because I don't do 120 a lot.
So today a friend and I changed the idler pulley the supercharger pulley and put a Steeda cold air intake on my 2008 4.6 L Stage 3 Roush.
I bought the kit from Brenspeed.
Everything came off and everything went on fine no problems.
After I loaded the tune, started it up everything ran fine looks fine etc.
I get it out on the road after it's warmed up I bring it up to 90 miles an hour my whole dash mainly the top starts shaking like crazy!! Every single time, it starts very mildly a little over 80 by the time you hit 90 it's shaking really good and the faster you go the faster it shakes, vibrates like crazy.
My friend left before I thought to have him rev the car while I looked at the motor and the pulleys. but I never thought it could possibly be the new pulleys because just looking at them at an idle they're spinning fine and true.
The steering wheel feels fine, and I have not hit any potholes or anything since the other day of going 120 miles an hour and everything is fine except for the hood.
Anybody else ever have this problem?

UPDATE, The cause of the dash vibration was caused by a loose chin spoiler, quite interesting to me at least how things can transfer through a car from one spot to another.
 

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That's your car telling you it doesn't want to go that fast.
 

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That's your car telling you it doesn't want to go that fast.
Yeah OK. If you're gonna have a car that you can't drive over 90mph, you might as well trade in the Stang and buy a Smart(ass). ;)
If the pulleys were out of true, you'd feel some vibration from the engine at idle. Could the CAI heatshield be fouling on the hood and not allowing it to close properly?
 

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Yeah OK. If you're gonna have a car that you can't drive over 90mph, you might as well trade in the Stang and buy a Smart(ass). ;)
If the pulleys were out of true, you'd feel some vibration from the engine at idle. Could the CAI heatshield be fouling on the hood and not allowing it to close properly?
No, those are governed to 84 mph. You can't go 90 in those either.

The vibration is not rpm related so I would rule out the motor. It's gotta to be something speed related like wheel balance, driveshaft, suspension, etc. Could be the hood vibration is transferring to the firewall and your dash. Could just be your dash is getting tired and starting to rattle. Throw some hood pins in there or raise the stops so it don't shake and then see if the rattle persists. At least rule it out.
 

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I had a vibration at 100-120 at the track and it came from one of the weights (peal and stick) came off one of my rear rims, it was a string of 4 of them but 3 were still there and one square of stickys had a weight missing after putting the street tires back on I had no vibration.

Over the years the front vibration is something you notice early through the steering wheel at slower speeds (below 40 mph) while the rear shows up around 50 mph depending on just how bad the problem is. The higher the speed before you feel it the smaller the imbalance is. As for the hood problem you could put tape over the gaps on the sides to the fenders where the hood seems loose normally between the adjustable front alignment bumpers and the rubber hood guides about mid fender for a test to see if it is the hood transferring it's vibrations to the dash or check to see of hinge points on the hood are tight and put tape over that area too if you think that part might be a cause. Just be careful pulling the tape off after the test.

I'd look for a missing weight first.
 

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Discussion Starter #6
UPDATE.... The cause of the dash vibration was caused by a loose chin spoiler, quite interesting to me at least how things can transfer through a car from one spot to another.
 
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