Factory Cross Frame improvement?
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 800
Likes: 3
From: Port Orange FL
Factory Cross Frame improvement?
I have the cross frame brace off of my 94 Vert and to be quite honest it seems kind of uh....Flimsy.
I was wondering if there would be any benefit to bracing it up while I had it off? My thoughts ran from boxing in the front section where it doesnt bolt to the floor to welding the center together where they meet to possibly running a straight brace from piece to piece to triangulate it.
I guess I am not entirely certain of the forces at work on this piece so I am not clear on exactly how it flexes under stress.
Input welcome.
Thanks
Roy
I was wondering if there would be any benefit to bracing it up while I had it off? My thoughts ran from boxing in the front section where it doesnt bolt to the floor to welding the center together where they meet to possibly running a straight brace from piece to piece to triangulate it.
I guess I am not entirely certain of the forces at work on this piece so I am not clear on exactly how it flexes under stress.
Input welcome.
Thanks
Roy
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
I have mine off right now too and I was considering boxing it. Not only would it strengthen it but it would give it a skid plate effect so it wouldn't get all banged up going over bumps.
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
A cable can be quite strong in tension, yet seem flimsy in compression.
I have the R-D Crossframe on my coupe and it uses rectangular tube
for the cross sectional pieces. However, it is a two-piece unit and
one of the braces is notched for a cut-out that the other brace fits
into. The R-D piece makes a worthy improvement to a car that has
no brace. (I'd caution that my car has a stock ride height and suggest
that people with lowered cars make enquiries about ground clearance.)
CFI-EFI, Bogus or one of the other grey beards here has boxed their
OEM brace. Perhaps you could search in the archives to see whether
you can find their remarks about the effort/reward trade-offs for
cars that already have the factory brace.
.
I have the R-D Crossframe on my coupe and it uses rectangular tube
for the cross sectional pieces. However, it is a two-piece unit and
one of the braces is notched for a cut-out that the other brace fits
into. The R-D piece makes a worthy improvement to a car that has
no brace. (I'd caution that my car has a stock ride height and suggest
that people with lowered cars make enquiries about ground clearance.)
CFI-EFI, Bogus or one of the other grey beards here has boxed their
OEM brace. Perhaps you could search in the archives to see whether
you can find their remarks about the effort/reward trade-offs for
cars that already have the factory brace.
.
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 800
Likes: 3
From: Port Orange FL
Cross Frame improvement
Slalom, I tried searching and came up empty. I am very aware of how a structure can be weak in one plane and nearly indestructible in another. I am trying to picture exactly how the car flexes and what this brace does so that I dont go adding a bunch of metal for nothing and missing a small lightwieght improvement that would make a big difference. The way it seems in my brain however, the braces job would be to keep the structure of the car from twisting (IE LF up while RR goes down) and this brace would seem to be very ineffective at that. If however the forces applied to it keep the LF and RR wheels from moving closer together or further apart then it is already fairly effective. Any chassis engineers out there?
Roy
Roy
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
I don't know if you are interested in trying some modeling
but if you are, then a little time with styrene sections like
you can get from hobby shops (or even cardboard strips cut
out of cereal box) can be fruitful.
Diagonals across a rectangular shape help to keep the corners
from moving in relation to one another.
The weak point I see with the braces is that these need to
have Z-shaped steps or jogs at the ends to accomodate the floor
pan.
.
but if you are, then a little time with styrene sections like
you can get from hobby shops (or even cardboard strips cut
out of cereal box) can be fruitful.
Diagonals across a rectangular shape help to keep the corners
from moving in relation to one another.
The weak point I see with the braces is that these need to
have Z-shaped steps or jogs at the ends to accomodate the floor
pan.
.
Race Director
Joined: Feb 2003
Posts: 11,672
Likes: 20
From: Lake Wylie SC
I boxed my X-frame for 2 reasons. I thought it would strengthen the undercarrage and it gave me extra places where I can jack the car up. And it does a good job of protecting the frame. I can't find the pictures I took of it after it was finished, but I'll keep looking.
Drifting
Joined: May 2003
Posts: 1,979
Likes: 48
From: Lakeport CA
Check the wrecking yards... including the used parts vendors that are forum supporters. I got my stock one that way for my coupe & like it. Didn't box it, yet, but I did notch it for my 3" tpis front Y pipe that I thought was rattling... someday I'll find what is resonating... 
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Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 800
Likes: 3
From: Port Orange FL
Done
Well I went and did it. I decided to box the whole thing as the metal added less than 5 lbs total. It is substantially stronger than it was before. Before I could easily twist it with one hand. It is now completely immobile even with both hands. The boxing made for a much much stiffer structure. The degree of handling improvement from the boxing is going to be hard for me to quantify as I am putting a camber brace on at the same time however.
Total cost $5 and added less than 5 lbs. I have nowhere to post a pic but if someone does let me know and I will send you the pic to post.
Roy
Total cost $5 and added less than 5 lbs. I have nowhere to post a pic but if someone does let me know and I will send you the pic to post.
Roy
Race Director
Joined: Jan 2005
Posts: 10,641
Likes: 13
From: Slidell Louisiana
Originally Posted by Fastmax32168
Well I went and did it. I decided to box the whole thing as the metal added less than 5 lbs total. It is substantially stronger than it was before. Before I could easily twist it with one hand. It is now completely immobile even with both hands. The boxing made for a much much stiffer structure. The degree of handling improvement from the boxing is going to be hard for me to quantify as I am putting a camber brace on at the same time however.
Total cost $5 and added less than 5 lbs. I have nowhere to post a pic but if someone does let me know and I will send you the pic to post.
Roy
Total cost $5 and added less than 5 lbs. I have nowhere to post a pic but if someone does let me know and I will send you the pic to post.
Roy
Mike
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
I also went ahead and boxed mine too. May I ask a question, I can't see where you left access to the fasteners at the center or where it bolts to the floor. Did you weld the flat stock in? I left the center of mine and the area that bolts to the floorboard open for access.
Safety Car
Joined: Apr 2003
Posts: 3,793
Likes: 9
From: VA
Originally Posted by reidry
Any chance one of you guys wants to upgrade to the RD Cross Frame? I need a stock cross brace for my '85 coupe for autocross.
Safety Car
Joined: Apr 2003
Posts: 3,793
Likes: 9
From: VA
My intuition is that most of what the boxing will do is stiffen the x-brace itself, but not contribute much to the job of stiffening the chassis. I think you might get a small improvement in chassis stiffness, but you've added a lot of weight to get it.
Just a WAG.
[edit]I just noticed one of the above posters said it was only 5 lb. In that case, what the heck go for it.[/edit]
Just a WAG.
[edit]I just noticed one of the above posters said it was only 5 lb. In that case, what the heck go for it.[/edit]
Last edited by VenkmanP; Nov 15, 2005 at 12:55 PM.
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 800
Likes: 3
From: Port Orange FL
Boxing
Midnight, There are two holes in the boxing where you bolt the unit to the floor. They are about 1" in diameter so there is easy access to the nuts. I boxed the center part in, eliminating the ability to ever take it apart. IMHO that center on the one piece is easily the weakest spot in the brace. The shape pressed into the metal is obviously to keep it from flexing in that plane. Yet in the middle where they join you essentially have a piece of flat stock with no ribbing that was easily flexible. I had considered only boxing that area and after lifting up the metal and seeing the small amount of weight I just did the whole thing.
I also considered cross bracing it but decided it was stiff enough after the boxing. I may yet do that in the future.
Roy
I also considered cross bracing it but decided it was stiff enough after the boxing. I may yet do that in the future.
Roy
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Okay, thanks, I just left a small opening at the floorboard holes but left about 6-8 inches open at the center. My car is lowered and I have had to straighten the brace twice already, that's why I left the center open. Your way is probably a bit stronger. I can't wait to see what kind of difference it made in the car.