Remove radiator crossmember, relocate to here?

[zxgtr]

Working on a 83 zxt, there are holes on either side of the engine bay right before the headlights, the area is flat and is basically the end of the car (at that point).

 

 

What I want to do is remove the radiators cross member, ive already cut out the spot welded trim around it and was going to weld a 1 1/4" square bar under the stock cross member, this works and looks ok but looks like the other location is much better.

 

My main goal is to move the rad and ic up more, bend the cross member part out around the engine and then weld it in place with another cross member right below it on the frame.

 

 

 

The hole is right in the middle, this is in the same location on the other side and is only 1" away from the end, before the headlight bracket.

 

Seems to me this would be stronger, instead of going out even more then going across with sheet metal it would be going straight across with thick square tubing further in at a better point, making it stronger.

 

Any thoughts on this?

 

[Nismo280zEd]

I'm confused on what your doing... you cutn' out the crossmember for the radiator.. then welding it back in with square tubing?

-Ed

[blueovalz]

I'm a bit confused as well, but would like to help you out if you'd provide more information or photos.

[zxgtr]

Yes, weld it back to the other location with 1.25" square tubing then another 1.25" square tubing going closer to the frame rails.

[zxgtr]

 

Remove the radiator cross member then stick the new cross member a little lower and to the right of it, its the only flat spot in that area and holds the pipe I cut just for pics very tight, no screws, weld or anything..

 

 

With the current configuartion there is no need to bend the pipe around the engine, my plan is to be able to do that in the future, need to relocate the radiator + fan and i/c before the new bar and I'm set, basically sticks the radiator where the old crossmember is.

 

 

Drives side inside:

 

Pass side inside:

 

This location gives me exactly what I need, add another bar below it on the frame rail (top of it) and id belive it would be much stronger then factory, in a whole new location.

 

Let me know if this makes sence

[zxgtr]

Here is basically what I am after..

 

I want to locate the square tube at the best location, I saw your pics blueovalz using 3/4 stock, is that structural on your car? (looking at the radiator pics).

 

 

 

I can move it up to the top more but it would require me leveling out the top area more, its at a big of an angle, could cut the bar to fit but making it flat sounds a little better to me.

 

Theres now 4" of clearance from the fan and engine, before was less then 1" (even with overall width of 5.25" radiator + fan).

[240hoke]

I would like to see the use of bigger tubing, and that weld in the middle I wouldnt trust.

 

I think another important thing is to have a seal between the radiator and the hood, to force all the air through the radiator. This would mean you need a bar up top with some type of seal on it. I thought about doign the same thing you are doing but decided against it, i think the s30 is simpler though. My idea would be to reinforce the top area nd put it there. But ive never messsed wit ha 280zx.

 

Good luck, hope to see how it turns out

 

-Austin

[zxgtr]

Thanks 240hoke.

 

I was looking more last night and if I stick a cross member on the very top (out a little more) then on the very bottom (below where it is now a little) then I think it will be super stiff in that area.

 

I think ill up it to a 2" square tube.

 

This whole area is already pretty strong (afaik) adding a strut tower bar on the front will make it even more stiff.

 

I want to go a little overboard, make it really strong.

[blueovalz]

I do not consider anything forward of the strut towers as "structural". This opinion is based on the following argument specific to what I’ve done on my car: The strut tower location is where the suspension forces are impressed into the unibody (the sway bar is another location for impressed stresses, but it is in close proximity to the tower’s base, on a boxed steel support, and considered to impart negligible forces forward to the core support), and if these points are reinforced directly (as they are with the multi-point strut tower bracing I use), then there should be no movement forward of these points (core support area), because there is nothing forward of these points placing significant stresses onto the unibody. If the unibody IS flexing at points this far forward (at the core support area), then using the engine bay’s side sheet metal shape to counter these forces is, in my opinion, an ineffective use of the bracing you want to use. In essence, the bars you are placing across the sides of the front bay area will flex at the point of the welds (OEM sheet metal in particular) and no matter how big a tube you use, the flex area will not change or diminish. This is why the OEM core support used sheet steel (in the same plane as the support to distribute this loading along its entire height) on both sides of the radiator to provide a rigid box (gusseted for lack of a better term).

 

One might argue that engine torque is another source of concern in distorting the (un-reinforced) core support area, and this is a viable argument (even with a simple single strut bar support), which is another reason why I chose to solidly mount the motor to the unibody using multiple points of attachment as well as tubes attaching the motor to the strut towers. BUT, again, simply attaching a bar(s) between the sides of the front bay (as I have done on my car as well) will not keep this core support’s “rectangle†from flexing at it’s corners. My success in using the small ¾†tubing to support my radiator is only because of the bracing done further back at the towers. Too many horror stories of cracked radiators due to weak core supports affected my modifications further back toward the strut towers.

 

From what I can see from you photos, I would say you've got some room to triangulate the tubes behind the IC. One tube would be good, two tubes (an X connecting the two cross-tubes) would be great. Doing this would allow smaller (lighter) tubes because you'd now be dealing with tension/compression forces on these tubes instead of shear forces at the welds at the ends where they meet the OEM sheet metal.

[zxgtr]

Thank you blueovalz! Youve cleard up some of my thoughts.

 

 

Here is a sad attempt and photoshoping wht im after.

 

 

I would put 2 cross members in the front, about 4" before the stock radiator support, the top cross member will be attached (at some point) to the strut tower bar, idealy not on the bar but on the plate itself (that bolts to the strut).

 

I dont really think adding the 2 extra cross member to strut tower bar will add a ton of extra support but its gotta be atleast somewhat stronger, help prevent some flex as well.

 

 

Looks like I am hopefully on the right track, I want to free up the room I need and at the same time make it stronger then factory, with the strut bar and the new cross members do you think its as strong as it was before?

 

I can mount the top cross member closer to the ends of the top 'frame' (more like the hidden box for wires), I have room to clear the engine but doing that wont let me move the engine fwd more, so id rather not.

 

Thanks! Any other tips or suggestions? I will start to look at a better way to mount it and see where that goes

[zxgtr]

Going over what you said again (and again)..

 

From what I can see from you photos, I would say you've got some room to triangulate the tubes behind the IC. One tube would be good, two tubes (an X connecting the two cross-tubes) would be great. Doing this would allow smaller (lighter) tubes because you'd now be dealing with tension/compression forces on these tubes instead of shear forces at the welds at the ends where they meet the OEM sheet metal.

 

Seems to be a good option, reinforcing the 2 new cross members with a x piece then attaching it all to the strut tower seems to be like it would be really really strong.

[blueovalz]

In reference to your photoshoped photo, will you have any room to bring the two "side bars" (that connect to the towers) inward as they go forward, so that they can create a triangle over the front of the engine (or would this cause problems with access to parts and pieces?)? For example:

______

__/__

[zxgtr]

As long as the new cross member is up at the top I dont think it will cause any clearance issues, ill look at putting the 'side bars' in the middle going out when I get the new bar welded in place.

 

Ive just cleaned up the driveside, filled the holes ground it down and put some primer on it, looks pretty good and I am ready to move to the other side to take it apart

 

I was looking at the stock L bracket (that connects the side to the radiator cross member) and it looks like I can re-use it with some minor modifications, would it be better to weld that to the top and the side of the car then weld the cross member to that and the side of the car? Would give the cross member more 'contact surface'? keeping in with the way nissan did it in 83.

 

 

Do you recommend sticking with the 1.25" square tubing? Its perfect size for me, your using 3/4" and 240hoke says go bigger, based on what you seem to be saying 1.25" is a little overkill as you seem to say 3/4" is plenty.

 

 

Thanks again blueovalz, youve been a lot of help.. Wonder how many people have done something like this, doesnt seem very many, if any at all with 280zx's.

[zxgtr]

The side bars would have clearance being set about 1 foot in from either side, leaving about a 1' space in-between the bars (in the middle).

[blueovalz]

bar size is a function of what kind of stress you'll put on the bar. A 1/2" tube can hold a ton of weight if it were strictly compressive forces. A flexible cable could do the same for tension loads. Get my point? Properly triangulated structures rely on this principal, and this is why I rely on it as well. It allows lightweight aluminum tubing when no shear loading is present. In your case, if you evaluate what you've done, and see no significant shearing, then it won't make any real difference on the size of the tubing. A string quite a while back (and it was quite an argument on this point) about a "bent" strut tower tube brace brought up this point that a structure of straight tubes connected at common points, will be very strong, AND light in relation to the small size tubing used. Look at the Birdcage Masarati for example. Yes, it was a complicated structure, but it was very rigid.

 

In regards to recommending a size for you tubing? I'd rather not go there being I cannot see the car and what you are planning to do. Any time the "connections" (the points of the various triangles in the structure) of the tubes start getting separated, it's wise to up the size of the tube. This is because the forces of tension and compression start becoming lost in the other forces of shear and twist as the points become more and more distant.

[Nismo280zEd]

No offense but the design looks really weak. There are no structural shapes in your braces. Your forgetting a key part of engineering... the strength is in the shapes. Equilateral triangles will be the stongest shape you can make in your bracing. From what it looks like your tying the strut bar into the radiator support which I dont' think is such a hot idea. Strength in the Z is from the sheetmetal as blueovalZ mentioned. but the suspension is tied to our frame rails. If your going to use tubing to weld up a radiator support... you need to extend the frame rails forward and box them closer like the factory did. Then use that as a base to tie all your bracing into. The use of the X cross bracing would be very strong, but prolly interfere with cooling fans or airflow depending on which side you put it. Furthermore, you can't just weld square tubing to the sheetmetal with out some problems... your goign to have to weld a flange to the sheetmetal for more surface area for the load to disperse, then weld up your "rectangle" with tubing... on each corner weld in a cross brace... so you have your corner that meets... say go back from the corner 4" on each bar... and weld in a diagnol. That forms your triangle... Weld those in all corners and that should keep it from "flexing" out of shape. Also the radiator does not need to be mounted so rigidly that horizontal forces cause the core to shear.

 

But hey it's your car...

-Ed

[zxgtr]

Heres what we came up with, doesnt come across well in the image but I will try to explain.

 

 

Basically there will be 2 front cross members, one where the hole is, sorta middle out, the other will be at the very top where the top frame rails end, about 3-4" before the lower cross member.

 

Those 2 bars will go left-right across the car, they will be welded together with cross members inside those, the number of cross members there will depend on the final outcome, for now lets just say it will be 4.

 

From there the top bar will attach to the strut tower or the strut tower brace.

 

I will work on trying to duplicate the factory corner brace that I removed, the idea with that is to have the top cross member welded to the sides of the car the mimic the factory brace design where the cross member will be welded to the brace that will be welded along the top rails.

 

Seems looking at the car that this is about the best way I can do it, with the proper mounting design It looks like it would be very strong, never really know till you go out and thrash on it I guess.

 

 

Thanks for your insight Nismo280zEd, the top bar will be tied into the frame rails and everything basically going from there, luckly with the way its setup there are no clearance issues at all, all the i/c pipe can be bent around any support and both the radiator and i/c are angled with the top out, adding a ton more clearance then factory.

 

 

Thanks guys, let me know if the above pic is more on track, seems like it to me, lmk what you think

[Nismo280zEd]

I'm a very visual person, but I think I get the jist of your diagramn with your explanation. Being tired doesn't really help either, but from your diagramn.. It looks like your weak link is still gonna be the bars coming from the sturts.. they just weld up in teh middle of the brace.. any force get's put on them.. they are going to want to break taht weld. Is there a reason why the can't meet up in the center of the horizontal brace? is that allowing room for the radiator to drop in.. or? I'm still confused one why you are even tying the strut bars to the radiator support. I'd keep them seperater personally.

 

Keep in mind how everything is going to go in and out of your car as you add all this bracing.. Make some of bolt together, so you can remove the engine later, etc.

 

Good luck, post pics of the progress.

-Ed

[zxgtr]

Thanks Nismo280zEd.

 

 

I wanted to weld the cross bars to the strut tower bar, not on the bar itself but on the flange that it attaches to, that bolts to the struts themselfs, so it wouldnt flex the strut tower bar itself.

 

If I welded them in the middle they would have to go to the front inside of the strut tower, maybe not a bad location but havent given it much thought yet, I dont think they are required just wanted some extra support on that axis? if it matters at all..

 

I think building new corner pieces is the best option, would give me what I want from attaching it to the strut tower.

 

I had a idea last night (based on the input here), basically make the ends of the new cross members attach to decent sized steel plates that would simply bolt to the car, one bolt could go through the top frame rail into the pipe itself then 2 bolts on the inside holding the plate to the car (excessive?), that way nothing is really welded to the car, 1 bolt on the outside 2 on the inside insure the bar and plate would be held very securly, I like how open the whole front end is now, makes removing the engine or anything at that very very easy, if its a bolt up type system then removing everything could take 5-10mins instead of (with oem) a hour or so.

 

The way its looking now allows plenty of room to remove anything and taking out the engine (will find that out shortly).. The radiator sits on the bumpers side of the cross member at an angle so it slides right out the front nice and easily, along with the i/c .

 

So many options Thanks again everyone for your input, trying to do something a bit diffrent here, hopefully it will pay off in the long run making my life easier Its sort of nice not needing the oem items (headlights included), just get to start fresh with a nice base to go from. I love these cars

[ZROSSA]

Howdy,

You have still ignored what the lads have been saying. If you want this to be strong then you will need to get some triangles in there. I would do the radiator suport like a small space frame. I still dont see much of a benifit in joining the struts to the radiator support. I would drop them down to the front suspensiom mounts. Try not to join any tubes to the middle of another tube. It just creates a place for that tube to bend.

 

Douglas