Frame Stiffening

[BillR1212]

Hi Team,

I just upgraded my drive shaft and u joints. My slicks and front runners have arrived, and planning on giving her hell at the drag strip (Also went the extra mile and picked up drag insurance, as we're not covered at the track in any way shape or form without it, just a public service announcement for anyone thinking of hitting a test and tune). Anyways, at what point should I look into stiffening the frame? 475 rear wheel HP/TQ. Not sure if thats enough to cause any damage, but better to ask now. If she grips, it should cook to the 60ft pretty quick.

Currently my Drag Radials just spin and I'm hovering between 2.0 and 1.8 in the 60ft. I've added double adjustable QA1's to the rear, and have singles up front, so I"m hoping between the better weight transfer, and better tire it should improve greatly.

73 Cuda with a 505CI btw.

[303 Mopar]

Subframe connectors are a good addition, and make sure you have a snubber or cal-tracs.  You could also add radiator support stiffening, box the LCA and k-member and inner front fender support too. Do you have a driveshaft loop?

[GoodysGotaCuda]

I feel that all of these cars should have had more stiffening leaving the factory, time hasn't helped that.

Trying to tune a suspension around a floppy chassis is going to be a no-win situation.

[jimynick]

I don't know what your car is nor it's weight, but with 475RWH, I suspect it'll go into the 11's and at 11.49 it requires a cage, let alone a driveshaft loop. The factory had body flex issues with the 425 HP rated hemi and I can't see your car being any better flex-wise. 

[Chryco Psycho]

I agree with both above !
Driveshaft loop is a must , the 1/8 mile pole vault is bad !!
Subframes for sure also , I assume you must have a roll bar at this point , if not your time slips will likely dictate it  & it will also help stiffness .
To increase traction you need to make the front section of the leaf springs as stiff as possible adding extra 1/2 leafs & clamping then together with a U bolt will help , take the straps off of the rear section of the springs to allow them to separate more easily , or
If you really want traction , add a set of ladder bars with floaters , nothing seems to hook harder in my experience , my street legal Duster was doing 1.40 in 60' pulling the front wheels .
What do you think Alan ? 

[RUNCHARGER]

Yes: 475 RWHP with sticky tires means you pretty much need subframe connectors and a driveshaft loop. If you don't want the subframe connectors then don't run the sticky tires. The DS loop is a good addition for any HP car.

[BillR1212]

Hi Team - Thanks for replies. I'll hold off on the slicks until I get some sub frame connectors. Sounds like a good idea. I was also going to fabricate a DS loop. Being that when I took the front yolk out of the trans, and rear, there was absolutely no way I could get that thing past the mufflers without unbolting them from the headers and lowing them. Seemed like a safety loop in of itself? I tried for a half hour to get that out with two of us pulling from different angles.

I have traction bars today? They don't look like anything special. is that same as ladder bars? I'll have to do some research. 1.4 60ft would be amazing. They say it takes .2 off the big end. my best 60 is a 1.85 right now and a 11.7 quarter.

Any subframe connectors you recommend that weld right in? Also thanks for the traction tips. I'll reference this late in the year when I have the rest of the car right.

[bluespruce]

Traction bars on a Mopar don't do much but bend the spring, a pinion snubber works a lot better, ladder bars better yet.

[303 Mopar]

Any subframe connectors you recommend that weld right in? Also thanks for the traction tips. I'll reference this late in the year when I have the rest of the car right.

I like the 2" square steel tubing inserted into the front and rear subframes and welded up.

[BillR1212]

Has anyone used US Car Tools before? They're local to me and seem to specialize in mopar frame stiffening. They're saying I'd have to drop gas tank and pull carpet to install their stage 1 kit. I didn't think it was that involved. Did you guys remove carpet and fuel tank to weld in your set ups? I suppose you don't want sparks near the fuel tank, but I'd like to not get that involved into a project.

[HP2]

Anyways, at what point should I look into stiffening the frame?

Ohhh, at about the 90 horsepower level additional frame reinforcement is necessary.

Seriously. HP aside, chassis stiffening makes panel gaps more consistent, allows window seals to be more effective, stops rattles and squeaks, and give the suspension a more stable platform to work from. Throw 400+ horsepower on it, and it is a must.

[Chryco Psycho]

I use 1x2" .125 wall tubing , put a notch in the middle to clear the floor pan & reweld the notch then you can weld both ends without pulling the carpet & interior apart .
Traction bars do very little on a Mopar & look ugly , Ladder bars are far better & work perfectly with a floater & leaf springs , the springs only hold the body up , all of the power is transferred through the ladder bar which can be tied onto the subframes .
If you are running 11.7 with a 1.85 60' you definatly need frame stiffening & Nhra will demand a roll bar under 11.99

[BillR1212]

Thanks for the reply Chryco - I'll research that route, and keep the drag slicks off until I make some more enhancements. Any ladder bars that you recommend? Roll cage was on the list just for pure safety. Didn't know it was a requirement below 12.0 Heck the three tracks I went to for test and tune don't even make me wear a helmet, although I decided to start just incase.

Also pictures of your set up would be good. I'll get the car on the lift soon and see if we can fabricate something. Thanks for the tip.

[Chryco Psycho]

Chris Alston is the first name that comes to mind for ladderbars  & floaters .
http://www.jegs.com/webapp/wcs/stores/servlet/SearchResultsPageCmd?Ntt=32+%27+ladder+bars&requestYear=&storeId=10001&catalogId=10002&langId=-1&year=&make=&model=&submodel=&engine=&Nrpp=&No=&persistYmm=false
The floaters are need to allow the diff & springs to move in different arcs as the front mounting points are at different distance from the diff  .
32 " works , make sure everything is square & level when you weld it , square it measuring an x , measure lots & weld last !!
This way the car will go straight when the front tires are not on the ground , I did not even realize my car was lifting the tires for a while !!
I have no pix handy as my car is 5000 miles away but it is simple , line up a piece of 1x2" tube [1" vertical] run it straight forward to the trans cross member  , taper the rear to meet up with the rear subframe , run it straight forward , you will see where you need to put a slice into the tube to follow the contour of the floor , I generally weld a plate onto the crossmember at the front & weld the subframe to the plate to give it more strength you can then tie the ladderbar crossmember to the subframes &  square everything up .
the 60' times will plummet & the view of the grandstands may disappear ! 

[HP2]

I'd encourage you into doing an NHRA rule book research on roll bars and cages before you start welding stuff in. IIRC, I believe  there is  an exception that allows roll bars instead of roll cages so long as there is less than x amount of modified floor pan and the original firewall is intact, and I believe the roll bar  must be a 6 point minimum. If these variables aren't true, then a cage is required. I believe you can get down to the 11 second flat range with this arrangement, but it has been a few years since I  looked it up. At 10.90 everything changes dramatically as this is the  first level for Super classes.