I am working on the 69 Corvette frame, doing many of the Chevy Power Book mods simply to make the frame stiffer. But I have a question about boxing in the front frame horns......to better support the front sway bar. I have done many forum and internet searches on this, and most show the front frames boxed either completely, or simply a brace near the front of the frame horn to bridge the top and bottom of the C channel. But, there is one thread that shows that the right side horn gusset has to be somewhat modified i.e. caved in on the inside, to theoretically provide room for the lower radiator hose. I could use some pictures of this area, with radiator installed, to see why this is required. It seems to me that if the outermost edge of the radiator clears the frame horn,........would the hose connection NOT be also clear of the frame horn, i.e NOT requirring any room inside the C section of the horn. This mod suggests that somehow the radiator hose travels "inside" the C section of the right front frame horn. What do you all think? Pictures would be helpful.

FYI.....car will have big block radiator....most likely Dewitts aluminum.

 

I guess nobody knows.

 

Well, just hold on there....

I read your post yesterday and went home last night to search my picture archives to see if I could post something to help you.

I did the same chevy power book mods to my 78 frame when I had the body off. I fully boxed the front horns on both sides. Unfortunately, I am in the middle of another project on the car and the radiator is out (it's a DeWitts aluminum like you) so I could not snap a picture for you with the hose and radiator. What I can say is that it fits, but it is super tight. I believe I had to remove the radiator hold downs up top and shimmy the radiator over to get enough clearance to grab the hose to remove it. My boxing has no indentations.

 

So without pictures, I have more questions. If I were to only gusset the area directly above the sway bar bushing mount (app.two inches wide)..rather than the whole way back to the crossmember.....

1.....Would it achieve the purpose of strengthening this area?
2.....Would it provide more clearance for the radiator hose?

Frankly, when I look at this reinforcement, I lack the understanding of what it is trying to do. The frame horns are further strengthened with the radiator support extensions, AND the front bumper extensions.....so the concept these are "twisting" under load is hard to believe. OR.....is it simply that the lower flange of the C section is deflecting under load, rather than the entire frame horn twisting. If this is the case a two inch bridge between the two flat sections of the C section, right at the bushing mount, should help. What is it?

 

Let me snap a few pictures of my car with radiator out so you can see my setup and will post them in a follow up.

I think the rationale behind boxing that area is that it will reduce the flex, both in general by increasing the amount of the frame that is boxed, and also due to the stress at that point from the stabilizer bar. Those mount points are under load when the stabilizer bar needs to twist so there is definitely a force there. Boxing just the mount portion would strengthen that area, but would leave an open C area between it and the rest of the frame (rearward side). In effect, the stronger part would move in unison, and twist in the open C.

The power book mods need to be looked at in context IMO. They were going racing and wanted every bit of stiffness they could get with what is there. Personally, I think the most improvement comes from the completion of the stitch welding and the gusseting of the lower A-Arm mounts (these things rip off on street vettes ).

Will post some pics later so you can see what I have done.

 

what if you just add a piece of flat stock on the bottom of the frame horn from the sway bar mount back to the crossmember?

 

I have seen one restorer install a triangular gusset that lays horizontal from the crossmember to the bottom flange of the frame horn C section. There appears to be no reason, or interference with doing so. I am no engineer,...but it seems that triangular gusset in the location would help stiffen it. I think fully boxing would really reinforce the frame horn from twisting, if looking straight back from front of car. But I really am doubting that those horns would twist much......given that I do not see how the sway bar would impart a twisting force upon the frame horn. I can see a force straight up and down, but not twisting. Plus, the radiator support is connected across the front of the car to the two radiator support brackets that bolt flush up against the frame horn....AND the fender brackets do the same. I will accept an engineer disagreeing with me.....but, until then, I will use my own mind to decide.

In reality....I am not racing the car.....its all probably nonsense to even bother with it.....but I have a bare frame, a welder and so.....

 

i bought my 75 with a nose hit. it took a LOT to straighten the 2 frame horns. another car hitting them will twist them. i doubt the sway bar will...

 

Here are the pics of my setup as an example. Images are big. I had to add the aluminum spacer to the sway bar to clear the radiator hose (on the bottom). Not quite sure why this was needed as I had the same radiator in the car before I did the frame-off, but the clearances were just too tight without it.

 

Well....with that gusset in place, I assume you have mounted the radiator, and the radiator hose does not interfere with the gusset....correct? That answers that.....as long as I put a gusset in the same place, I should be able to install a big block radiator and there will be no interference.

I guess the only other thing to ask is ......does the radiator hose connect exactly in the same place on a small block radiator as it does a big block radiator????

 

Yes, I have had the car fully assembled with the radiator and the hose without interfering with the gusset. If you look at the product pages on the DeWitts site, you will see that the radiators are almost identical. The site does not list the dimensions for the big block radiator for a 69, but it does for the small block for my year. Advise you to give them a call.

 

Thank you very much for the pictures and the help.

 

Found this kit from Ciro Racing in California that provides gussets for C3 Corvettes that make up the majority of what the Chevy Power Book recommends. The pieces are thick, like 1/8 inch steel, and look to be machine or waterjet cut. They fit pretty well on my 69 frame, and I will be welding these in. As you can see, the two pieces for the front frame horns does NOT full box in the horns as the Power Book describes, and is why I started this thread. Ciro believes that their gusset will support the lower C section well enough. They are racing a 68. You can find them on Facebook.

 

.....From a physics standpoint it seems like the lower a-arm mounts are the weakest link in the entire frame. They tear loose on street vettes, and that spot handles near 80-90% of the cornering loads. The entire frame is only 1/8" thick sheet metal. Honestly a much thicker mounting plate/reinforcement or internal vertical supports there would be an improvement. Haven't seen that done yet.
.....My 2nd concern would be the parallelogram twisting of the upper & lower a-arm mounting structure "box". Solid engine mounts and the upper a-arm strut bar should help significantly here. I saw one guy who added a vertical side to side support inside the lower frame under the engine. Welded it in in real well. That was genius and he reported it really stiffened the front end. It should. But not sure it would be significantly stronger than just the upper strut bar, which is waaay easier.
.....My third concern would be torsional or twist or vertical flex in the s-bend sections. Very little can be done about this short of adding an upper engine compartment frame "cage" like they do on the race cars. Chevy added two vertical supports internally in this area to decrease the torsional twisting. It could use still more, but how would you add them internally?
.....Other frame mods would be far behind these in effectiveness. Aka the sway bar area.

.....Chevy tested a significantly thicker frame that seriously reduced twisting forces. However that idea was discarded because the car rode "worse". How little they understood handling in the early 60s. They were inadvertantly using frame flex as a "spring". Today's cars have somewhere from 2-4 times more torsional stiffness than these old cars. There is little you can do to change this without adding a full roll cage.

My advice: Just make the normal frame "powerbook" mods, especially fully welding the frame. That will help the most. And the strut bar. Then just enjoy it.

I guess am going to have to engineer an upper strut bar for my BBC with my mechanical fan. Most people say it won't fit. I don't agree. But I can be more persistant than most! LOL

 

Thanks Leigh for responding. I am fully welding the frame, between the stitch welding. Already started that. My post above shows the gussets I bought from Ciro Racing to fully gusset the lower control arm mounts and the engine mount. I have also fabricated and welded in a gusset inside the engine mounts on both sides to better secure them.

As for the sway bar reinforcement, I think I am going to use the Ciro gussets as close to the sway bar mount point as I can.....little fitment problem there because the 68 they made these for has slightly different profile at the sway bar location.

As for the comment on reinforcing the crossmember, the fix I did is same as I did on my 77. I purchased a replacement lower crossmember plate from Zip. It is made to exact specification to replace the entire lower plate, from spring hole to spring hole. I cut it into THREE pieces, and added it as a doubler to the lower side of the crossmember. THAT fixes the ugly dented lower crossmember, and makes that piece 1/8 thicker, now with THREE layers of metal versus TWO. I would think it has some effect on strength, but mostly its a fix for the dented center portion of the crossmember. Win Win.

I have seen on this forum the guy who cut a slot across the lower crossmember, and added a 1/4 inch thick vertical plate from top to bottom of crossmember......great idea....I am just not doing it.

Lastly, I totally agree about the spreader bar.......we both are installing big blocks, and I would like to stick with mechanical clutch fan and factory shroud.....NOBODY is making that now. One forum member did it by adding a spacer between the clutch fan and water pump....providing the necessary clearance for the spreader bar. That may be the fix we are looking for, but I want to make sure it is not adding too much load to the water pump bearings. I don't think it takes much spacing.....but that is my plan to work on. I should have the frame on wheels with the VortecPro big block installed by end of year.....and then I can start working on the spreader bar.

With electric fans, like Dewitts dual Spall fans......a spreader bar is easy....and the only real reason I would consider electric fans.

 

I sent a PM to Tom Dewitt to see what he thinks.

 

My 79 frame developed cracks where the lower A-Arm attaches. 700# coil overs and 295 width front slicks are brutal on these frames when they are rust free. I bought the gusset kit years ago. But it didn't include anything up by the front sway bar. It was steering box, rear kickup, and front A-arm areas plates.

 

Anyone have anything further to add to my question. I would like to fully box in the front frame horns forward of the crossmember.

 

I think you ought to go for it. Don't forget to report back and let us know how it goes.

 

Here is the problem I need confirmation on....and first......we have to have the right information. This will be a big block radiator....which is different than a small block radiator.. Cold Case has dimensions on their website, Dewitts does not. Is the lower radiator hose neck on a big block radiator INSIDE the front frame horn C-section? If it is, I cannot have a welded in gusset in the way.

The pictures above clearly show that whatever radiator this is....the lower hose fitting is INSIDE the frame horn C-section, and there would no way to box that horn completely. But that lower frame support looks alot like my 77......so this would be a small block radiator. That does not help. I appreciate the pictures though. Also, the radiator hose fitting on the big block is up higher on the radiator than this.....or the radiator is taller and extends lower.

In any case, what I need is to see pictures, just like above, of a factory big block radiator (or direct fit radiator like Cold Case or Dewitts) on a 69-72 Corvette......does anyone have these needed pictures?