RD Racing cross frame modification
Thread Starter
Le Mans Master
Joined: Jun 2005
Posts: 5,037
Likes: 520
From: Texas
RD Racing cross frame modification
A couple of questions for those of you who own and have installed the RD Racing cross frame (the one that goes under the car) and have a 3" exhaust.
Currently, I have spacers on the car to clear the exhaust. I spoke with Dave about smashing the center portion of the cross frame to make more room where my 3" Y-pipe is. So, I am wondering where the lesser evil lies: having spacers where the cross frame mounts to the frame (1/2" if I remember correctly) which means using longer bolts or smash the center down to clearance the Y-pipe (going to have to crush it pretty much all the way down).
This car is strictly for autocrossing and road course racing. Having longer bolts makes me uncomfortable since there is more of a chance of it breaking. Dave says that the cross frame stretches rather than compresses, so crushing the center will not cause it to fold or collapse. Still, the idea of smashing the center down does not sit well with me (sorry Dave).
Dave also said that there are quite a few guys who installed these on their cars and had 3" exhausts already installed. He advised them the same way he advised me: crush it. Anyone have an RD Racing cross frame with a 3" exhaust (L98 or LT1)? How many of you autocross/road race with it?
Currently, I have spacers on the car to clear the exhaust. I spoke with Dave about smashing the center portion of the cross frame to make more room where my 3" Y-pipe is. So, I am wondering where the lesser evil lies: having spacers where the cross frame mounts to the frame (1/2" if I remember correctly) which means using longer bolts or smash the center down to clearance the Y-pipe (going to have to crush it pretty much all the way down).
This car is strictly for autocrossing and road course racing. Having longer bolts makes me uncomfortable since there is more of a chance of it breaking. Dave says that the cross frame stretches rather than compresses, so crushing the center will not cause it to fold or collapse. Still, the idea of smashing the center down does not sit well with me (sorry Dave).
Dave also said that there are quite a few guys who installed these on their cars and had 3" exhausts already installed. He advised them the same way he advised me: crush it. Anyone have an RD Racing cross frame with a 3" exhaust (L98 or LT1)? How many of you autocross/road race with it?
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
I have the R-D brace but not the 3" exhaust.
The factory brace on the convertibles is stamped strip rather than
rectangular tube. Customizing your's in the R-D approved manner
would seem to be a valid approach.
Or.
How much length of the exhaust is affected? Do the pipes interfere,
or is it the increased cross section of the crossover pipe (Magnaflow?).
How much clearance needs to be created, including extra for engine
movement and chassis flex?
My view is that performance would not be significantly affected by a
massage of a short section on a 3" exhaust.
.
The factory brace on the convertibles is stamped strip rather than
rectangular tube. Customizing your's in the R-D approved manner
would seem to be a valid approach.
Or.
How much length of the exhaust is affected? Do the pipes interfere,
or is it the increased cross section of the crossover pipe (Magnaflow?).
How much clearance needs to be created, including extra for engine
movement and chassis flex?
My view is that performance would not be significantly affected by a
massage of a short section on a 3" exhaust.
.
Thread Starter
Le Mans Master
Joined: Jun 2005
Posts: 5,037
Likes: 520
From: Texas
Originally Posted by Slalom4me
I have the R-D brace but not the 3" exhaust.
The factory brace on the convertibles is stamped strip rather than
rectangular tube. Customizing your's in the R-D approved manner
would seem to be a valid approach.
Or.
How much length of the exhaust is affected? Do the pipes interfere,
or is it the increased cross section of the crossover pipe (Magnaflow?).
How much clearance needs to be created, including extra for engine
movement and chassis flex?
My view is that performance would not be significantly affected by a
massage of a short section on a 3" exhaust.
.
The factory brace on the convertibles is stamped strip rather than
rectangular tube. Customizing your's in the R-D approved manner
would seem to be a valid approach.
Or.
How much length of the exhaust is affected? Do the pipes interfere,
or is it the increased cross section of the crossover pipe (Magnaflow?).
How much clearance needs to be created, including extra for engine
movement and chassis flex?
My view is that performance would not be significantly affected by a
massage of a short section on a 3" exhaust.
.
It sounds like you are on board with Dave's solution (correct me if I am wrong). I generally dont like permanently modifying something unless I know someone else has done it and it works as good if not better than the way it is originally. I would hate to bend the cross frame and find out that I solved one problem only to cause another.
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Originally Posted by Performance nut
It sounds like you are on board with Dave's solution (correct me if I
am wrong). I generally don't like permanently modifying something
unless I know someone else has done it and it works as good, if not
better than the way it is originally. I would hate to bend the cross
frame and find out that I solved one problem only to cause another.
am wrong). I generally don't like permanently modifying something
unless I know someone else has done it and it works as good, if not
better than the way it is originally. I would hate to bend the cross
frame and find out that I solved one problem only to cause another.
However, IIRC, the brace tubing is 1" on the short side, relieving this
for 1/2" clearance would seem likely lead to some dimensional changes
along the 'X' legs. If the rear holes and Riv-Nuts have not been
installed yet, then a dimensional change may be trivial.
If Riv-Nuts HAVE been installed and the hammering tweaks the brace
into new dimensions, I imagine that reinstalling the modified brace will
cause it to be preloaded if it has to be 'encouraged' in order to get the
bolts back in.
Is some revision to fitment truly important in the big picture?
I don't know.
If the exhaust interferes at the 2-1 collector segment on the front
'Y'-pipe, is there room for this to move upward? There is a good length
of pipe forward to the collectors. It is a short distance back to the
joint for the cat/test pipe where there was a hanger on the OEM
system. A capable exhaust shop might be able to persuade the
pipes into a more favorable position.
I also wondered about localized flattening. Again the exhaust shop
might be able to to do this with the system on the car. I've also
thought about C-clamps and bar or angle stock to rig up a way to
swage the pipe at home but I'm unsure whether this would be able to
exert enough clamping force.
Pulling the exhaust and massaging it in a hydraulic press would let you
change the cross-section.
The work would change the exhaust dimensions, too. But the hangers
have more take-up. The openings can be restored with an expander.
My 2-1/2" exhaust and brace coexist. I have not had to resort to
any of the approaches above, so the usual caveat applies.
I'll close by suggesting a visit to a few muffler shops in search of
someone you can talk to and someone whom seems to have the right
answers for your questions. An hour on the rack and $100 might
result in a happy outcome.
.
Thread Starter
Le Mans Master
Joined: Jun 2005
Posts: 5,037
Likes: 520
From: Texas
Originally Posted by Slalom4me
On board? I'd rather say that I am supporting his rationale.
However, IIRC, the brace tubing is 1" on the short side, relieving this
for 1/2" clearance would seem likely lead to some dimensional changes
along the 'X' legs. If the rear holes and Riv-Nuts have not been
installed yet, then a dimensional change may be trivial.
If Riv-Nuts HAVE been installed and the hammering tweaks the brace
into new dimensions, I imagine that reinstalling the modified brace will
cause it to be preloaded if it has to be 'encouraged' in order to get the
bolts back in.
Is some revision to fitment truly important in the big picture?
I don't know.
If the exhaust interferes at the 2-1 collector segment on the front
'Y'-pipe, is there room for this to move upward? There is a good length
of pipe forward to the collectors. It is a short distance back to the
joint for the cat/test pipe where there was a hanger on the OEM
system. A capable exhaust shop might be able to persuade the
pipes into a more favorable position.
I also wondered about localized flattening. Again the exhaust shop
might be able to to do this with the system on the car. I've also
thought about C-clamps and bar or angle stock to rig up a way to
swage the pipe at home but I'm unsure whether this would be able to
exert enough clamping force.
Pulling the exhaust and massaging it in a hydraulic press would let you
change the cross-section.
The work would change the exhaust dimensions, too. But the hangers
have more take-up. The openings can be restored with an expander.
My 2-1/2" exhaust and brace coexist. I have not had to resort to
any of the approaches above, so the usual caveat applies.
I'll close by suggesting a visit to a few muffler shops in search of
someone you can talk to and someone whom seems to have the right
answers for your questions. An hour on the rack and $100 might
result in a happy outcome.
.
However, IIRC, the brace tubing is 1" on the short side, relieving this
for 1/2" clearance would seem likely lead to some dimensional changes
along the 'X' legs. If the rear holes and Riv-Nuts have not been
installed yet, then a dimensional change may be trivial.
If Riv-Nuts HAVE been installed and the hammering tweaks the brace
into new dimensions, I imagine that reinstalling the modified brace will
cause it to be preloaded if it has to be 'encouraged' in order to get the
bolts back in.
Is some revision to fitment truly important in the big picture?
I don't know.
If the exhaust interferes at the 2-1 collector segment on the front
'Y'-pipe, is there room for this to move upward? There is a good length
of pipe forward to the collectors. It is a short distance back to the
joint for the cat/test pipe where there was a hanger on the OEM
system. A capable exhaust shop might be able to persuade the
pipes into a more favorable position.
I also wondered about localized flattening. Again the exhaust shop
might be able to to do this with the system on the car. I've also
thought about C-clamps and bar or angle stock to rig up a way to
swage the pipe at home but I'm unsure whether this would be able to
exert enough clamping force.
Pulling the exhaust and massaging it in a hydraulic press would let you
change the cross-section.
The work would change the exhaust dimensions, too. But the hangers
have more take-up. The openings can be restored with an expander.
My 2-1/2" exhaust and brace coexist. I have not had to resort to
any of the approaches above, so the usual caveat applies.
I'll close by suggesting a visit to a few muffler shops in search of
someone you can talk to and someone whom seems to have the right
answers for your questions. An hour on the rack and $100 might
result in a happy outcome.
.
The nutserts are already installed. The Y-pipe doesnt have a whole lot of clearance on top. I guesstimate about 3/8" - 1/2" between the pipe and the vehicle at most. I thought about nudging the Ypipe up a little and maybe a bit of massaging might get some if not most of what I need and still give a little clearance on top of the Y-pipe.
The exhaust shop solution might of been feasible if 1) my car was street legal and 2) I had a good exhaust shop in the area (which I dont since most dont do custom exhausts, mainly converter and muffler changes with the occasional catback).
At this point, I am exploring my options. If people have crushed these and raced on them with no issues at all, this might the route I may take. You brought up a good point about the preloading though. Didnt take that into consideration.
