I'm looking for input. My car is a 95' Miata with approx 93,000 miles on it. Suspension is stock except for Flyin Miata sway bars front and rear and Advanti storm 15x8 rims with Yokahoma S drives. The car makes a thumping noise that can be felt in the floor when taking a hard decelerating, downhill right hand turn. Driving the car in a less spirited fashion does not cause this condition. I jacked the car up and checked for play in the wheel bearings and found none. I can see no signs of the tire contacting anything. Taking a pry bar to the suspension bushings on that side doesn't seem to reveal any unusual wear but it's hard to tell for sure. Has anyone else here experienced this?

 

Have you checked your alignment? More grip+fatter sways can cause old, tired eccentric bolts to elongate and the adjustment plates to slip. Make sure one side up front isn't in a vastly different position than the other.

 

Check if your exhaust hits something under the car. Could be that with the extra grip you can now force the exhaust against a subframe piece. I had a hanger that was hitting the subframe. It sounded like it was coming from the front wheels. Had me searching for weeks to finally fix that.

 

You mentioned your suspension was stock, but I had a similar condition only when hard cornering recently. Take a look at the shock top hats and all the nuts. I had the shaft nuts loosen slightly and when cornering the shock was loose and would bounce/thump around. Should be an easy thing to look at.

 

Thank you gentlemen for your knowledgeable feedback. I will get into the car this weekend and check the eccentric adjuster bolts, exhaust system and top hats and nuts. I will report back with what I find. Thanks again.

 

I think I may have found the source of the noise up front.

I checked the items suggested in the above reply's and while checking for exhaust to body contact up front noticed marks on the turbo housing suggesting it is contacting the frame. My theory is, the combination of hard deceleration, turning right and being pitched down hill all the while, is causing the motor to pitch to the left and make contact with the frame. This is the Flyin Miata FM II system that required cutting the frame lip and bending it down to have clearance for the unit. There is still only about 1/4", or less, clearance between the frame and the housing.

I have installed new motor mounts shortly after the turbo install a couple of years ago. I need to come up with a solution for this issue now. I don't really want to have to cut a notch and weld the frame rail. Because of where the contact is, I don't think rotating the compressor housing will gain anymore additional clearance. I am thinking of shimming the motor mount, on the driver side, slightly to increase the clearance. Hmmm.

 

What mounts are you using

 

I don't recall the brand but they are OEM type (or OEM spec) mounts.

I sense this might have been a mistake?

 

With the greater power/torque produced, you really need something more stiff than OEM or even Mazda comp mounts. I can get about 6 good months out the comp mounts before shifting gets sloppy. I'd recommend Blackbird Fabworx Street mounts.

Also, give the upper ball joints a look for axial bearing play to see if they make any popping noise. I've encounter the same symptoms you've described and isolated down to those before.

 

I would stick something under there as a wear indicator and go for a test drive to make sure that's the actual issue, just to confirm its not scuff marks from installation/handling.