Q45 "Tuning" posibilities

[landtodd]

Q45 "Tuning" posibilities

Hey, this is fun! Like many Q45s, my car has a vibration peak at 1900 rpm. What appears to be an inertial damper is bolted to the the exhaust system. Its presence suggests that Infiniti has looked at exhaust-vibration resonance before. When Infiniti engineered their solution, the small damper, their engineering mule (or their computer simulation) had all-new rubber exhaust hangers, so conditions, under my car at least, have changed. Changing the mass of the damper could change the vibration resonance characteristics of the exhaust. I wondered if the change would be noticable.

I bought a medium-sized pair of locking pliers and clamped them to the "ear" of the damper. The locking pliers are up close to the body so that they're not the lowest part of the undercarriage. I've driven only a couple of miles since doing this at lunch, so the following are initial impressions.

The vibration peak at 1900 rpm appears to be sharply reduced. Vibrations related to engine rpm have changed. There seems to be a new, very narrow vibration band at an indicated 900 rpm, which I now feel briefly as the motor returns to idle. There may be a new one at 3000, too, but I wasn't able to explore it. I used up all my time hunting for the missing 1900, wondering if I was crazy or what.

Of course, what this really means is that I need to replace all my exhaust hangers so that they damp vibration instead of serving either as nodes around which vibration occurs or as vibration transmitters to the body. I think I'll leave the locking pliers where they are for now, just until I start on my rubber-replacement program.

[AZhitman]

You're my hero Todd.

Hope they don't fall off at 140 mph.

[Q45tech]

I bid on a $25,000 [brand new price] acoustic/vibration spectrum anaylser on ebay but it got too rich for me.

You have to have an accelorameter and anaysler to see the Zero to 40 Hertz vibrations and measure the exact levels - seat of the pants/ human body measurements are near worthless as you cannot remember from test to test.

http://www.lordcorp.com/news/2...u.htmh ... amics.com/

Fundamentals of Vehicle Dynamics (R114) by Thomas D. Gillespie (Hardcover)