Strengthening floor pan around gearbox mount - too much flex

[RB30X]

I took my LS1 240Z out to mine and its first track day recently (its actually a large go kart track so its tight and you dont go very fast) and I had a camera record in car footage from the rear strut brace. I noticed something scary after viewing the footage about how much my passenger seat was flexing around during acceleration. Watch the video below and look at how the passenger moves against the LH quarter glass. I spoke to a racing guru and he referred to it as 'oil caning' where the floor is flexing around where the gearbox is mounted due to the torque that these brilliant engine put out.

 

 

Now my car has coil overs with stiff springs and I run the stickiest street tyres available. The only real chassis strengthening I have done is the rear strut brace. I do have an old front strut brace which I have to modify to fit over the LS inlet manifold. My mate recommends strengthening using an X type pattern across the floor, with braces across the trans tunnel to keep the floor ridgid. I would encorporate the transmission mount into these braces but I'd have to work the exhaust around all this and I already think it hangs too low. I may even put some supports inside the cabin and foot well, along the floor around where the seat rails are.

 

I'd like to see what others have done to strengthen the undersides of their cars to prevent the floor flexing around as mine does. Below is pics of how my trans mount bolts to the floor.

 

 

 

 

 

[getoffmyinternet]

The pressure the tranny puts on the floor could be greatly reduced by simply making the crossmember inline with the mounting point so that the entire engine doesn't leverage against that fulcrum as it tilts back under acceleration.

 

Also is it possible to use the original posts that are inside the tunnel or did you cut them off already? They are made for this purpose and should be much more solid than just the flat skin made to keep your feet from dragging. I made a bar that goes straight across the tranny mount to the floor but also goes up to the original posts to make it structurally sound. It doesn't look pretty but four points get the job done better than two.

 

Edited April 30, 2011 by getoffmyinternet

[RB30X]

The pressure the tranny puts on the floor could be greatly reduced by simply making the crossmember inline with the mounting point so that the entire engine doesn't leverage against that fulcrum as it tilts back under acceleration.

 

I would have thought the engine and driveline would twist across rather than tilting back, so the LH side of the cross member is trying to flex the floor into the cabin where as the RH side is trying to pull the floor downwards.

 

Also is it possible to use the original posts that are inside the tunnel or did you cut them off already? They are made for this purpose and should be much more solid than just the flat skin made to keep your feet from dragging. I made a bar that goes straight across the tranny mount to the floor but also goes up to the original posts to make it structurally sound. It doesn't look pretty but four points get the job done better than two.

 

 

I'm pretty sure the PO already removed at least one of the original posts to fit the T56. I'm thinking I might remove the gearbox cross member and weld some pieces onto it to spread the load over the floor more. Something like the attached pic. Ideally it would be nice to encorporate it into some new chassis rails.

[RB30X]

The Drivers side mount inside the tunnel was there but unused and the passenger side one got ground away a bit to fit the fatty boomba T56. My 'new and improved' cross member has spread the load over more of the floor and also uses the original drivers mount inside the tunnel. Plus I get more clearance for the exhaust.