C4 Frame Project

[Custer55]

I started my project about 3 years ago when I found the C4 parts I needed at the Iola car show swap meet. I started thinking about doing a frame several years before that. My wife has a 90 Corvette and after taking some measurements on her Corvette and my 55 it seemed to be something that would work well as the track width is almost identical. My 55 is about 190 pounds heavier than the Corvette so there pretty close. The front to rear weight balance is also very close.
The first step in the project was to set my 55 on blocks at the desired ride height and take a few pictures.
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I cut an old tire from the Corvette in half so I could put it in the wheel wells and made cardboard wheels to get an idea what it would look like.

The next step was to build a frame table from 3 x 3 square tube to mount the frame on. I drilled and tapped the top and both sides of all the tubing so I can bolt fixtures in place on the table as needed. Needless to say this took quite a while. I don't have any pictures of just the table but you should be able to see it some of the pictures to follow.

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I started with mounting the rear end as I figured it would be easier the the front stub. Just some tabs under the frame, a cross member for the upper shock mounts and pinion mount and the dog bones. I still need to figure out how I want to mount the rear sway bar. It doesn't look like it will work above the frame to the rear because of gas tank and body clearance, so I may try putting it forward of the rear end at the bottom of the frame. I still need to check on muffler and exhaust clearance before I decide on that though.


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Next up was to cut out the original cross member and position the Corvette cross member on axle and chassis center lines and at ride height.


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The next step was to fabricate the new frame rail sections from 1/8" steel plate.


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Here is the radiator saddle cross member welded in place. I made this from four pieces in the same manner as the front frame rail sections.

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Here is where I'm at now. Bracing plates between the original frame and the new frame rails tacked and plug welded in place. Next up is the transmission cross member / x member. I'll add some more pictures when I get started on that.

Brian.

[NickP]

Looks like some fun. Did you rotate the rear batwing mounts for the 4 degrees of pinion angle to match the engine? Chevynut will appreciate your efforts too. Keep the pics and updates coming.

[carls 56 (RIP 11/24/2021)]

nice, your way beyond what I could ever do. ...... so what you do after lunch?

[chevynut]

I started my project about 3 years ago when I found the C4 parts I needed at the Iola car show swap meet. I started thinking about doing a frame several years before that.

Only 3 years? When my brainstorm hit me was when I was at a car show at a local Chevy dealer several years ago. There was a blue C4 vette there with the hood flipped up and I was looking at the suspension pieces....it amazed me that they were all aluminum. I thought it would be great to use the a-arms and whatever else I could use on my Nomad. At the time I didn't even know anyone was already doing these conversions, but I searched the internet and found a Roush Engineering website and they were doing one for a tri5 using the 4 plate method you are using. Not long after that I got a Super Chevy or CHP magazine and there was a red C4 conversion frame on the cover. It was Roush's. That's when I decided to move forward with my Nomad. I spent weeks laying it all out to make sure everything fit, after I bought the suspensions and took measurements. Today it seems like such a simple thing.

My wife has a 90 Corvette and ... the track width is almost identical.

If by track width you're referring to the tire centerlines, they're kinda close. The tri5 track width is 58" in front and 58.9" in the rear. The late C4 is 59.6" in front and 60.4" in the rear. However, the wheel mounting surface is quite a bit wider on the C4 than the tri5 as you probably know.

My 55 is about 190 pounds heavier than the Corvette so there pretty close.

Everyone thinks the tri5s are such heavy cars, but they're not. They're just roomy.

A '90 vette coupe is 3255 pounds and a convertible is 3301 pounds curb weight. The ZR1 was 3479 pounds. A stock 55 Chevy 2-door BelAir sedan is 3285 curb weight with a 3-speed. A C4 suspension will knock 150 pounds or so off of that.

Looks like you're planning to use the stock C4 springs. It should be fine in the rear since they height is adjustable, but the front is sometimes tricky to set up at the right ride height. Some of it depends on the engine you use. Front ride height isn't very adjustable on these suspensions unless you use coilovers.

I still need to figure out how I want to mount the rear sway bar. It doesn't look like it will work above the frame to the rear because of gas tank and body clearance, so I may try putting it forward of the rear end at the bottom of the frame. I still need to check on muffler and exhaust clearance before I decide on that though.

I have done it both ways. Newman puts it in front, but it's visible from the side of the car. In the rear it interferes with the stock gas tank. I've looked at solutions and there are a couple I came up with. One is to use a swaybar that has shorter arms, or shorten the C4 swaybar arms. That will make the swaybar stiffer so I'd use one of the smaller diameter ones. Another solution is to use a different gas tank. I've done that and mounted it to the frame instead of the body. If you need a new tank anyhow, it's a good solution.

Keep up the good work and keep us posted on progress.

[Custer55]

I had the brackets attached when I set the rear end in place and I also have spacers between the brackets and the rear end so there will be some adjustment if needed.
Brian

[Custer55]

nice, your way beyond what I could ever do. ...... so what you do after lunch?

Thanks, It sure keeps me busy.
I started out with some smaller projects like the my custom made exhaust tips (Oval shaped kind of like the Cup Cars)

[Custer55]

Only 3 years? When my brainstorm hit me was when I was at a car show at a local Chevy dealer several years ago. There was a blue C4 vette there with the hood flipped up and I was looking at the suspension pieces....it amazed me that they were all aluminum. I thought it would be great to use the a-arms and whatever else I could use on my Nomad. At the time I didn't even know anyone was already doing these conversions, but I searched the internet and found a Roush Engineering website and they were doing one for a tri5 using the 4 plate method you are using. Not long after that I got a Super Chevy or CHP magazine and there was a red C4 conversion frame on the cover. It was Roush's. That's when I decided to move forward with my Nomad. I spent weeks laying it all out to make sure everything fit, after I bought the suspensions and took measurements. Today it seems like such a simple thing.



If by track width you're referring to the tire centerlines, they're kinda close. The tri5 track width is 58" in front and 58.9" in the rear. The late C4 is 59.6" in front and 60.4" in the rear. However, the wheel mounting surface is quite a bit wider on the C4 than the tri5 as you probably know.

I took my measurements on the outside of the tires front and rear. I have aftermarket wheels and tires and dropped spindles in the front so mine is already wider than stock. Our 90 Vette is the same in the rear and just a tiny bit narrower in the front.



just roomy.

A '90 vette coupe is 3255 pounds and a convertible is 3301 pounds curb weight. The ZR1 was 3479 pounds. A stock 55 Chevy 2-door BelAir sedan is 3285 curb weight with a 3-speed. A C4 suspension will knock 150 pounds or so off of that.

I weighed both cars at the local race track (Paved stock cars) where I work part time. I don't remember the exact weight but my 55 was about 190 lbs heavier. Should be pretty close with the weight savings the C4 suspension has. The weight at each wheel is very close also so the front to rear balance is very close also (Stock cars are weighed on a separate scale for each wheel)

I do plan to use the Corvette springs, but have the upper shock mounts set up so I can convert to coilovers if needed.

[ATTACH=CONFIG]4176[/ATTACH] [ATTACH=CONFIG]4177[/ATTACH]






a swaybar that has shorter arms, or shorten the C4 swaybar arms. That will make the swaybar stiffer so I'd use one of the smaller diameter ones. Another solution is to use a different gas tank. I've done that and mounted it to the frame instead of the body. If you need a new tank anyhow, it's a good solution.

Keep up the good work and keep us posted on progress.

I post more pictures as I go.
Brian

[Custer55]

This weeks update

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This week I started on mounting the rear sway bar. I decided to put it in front of the rear axle down low on the frame.
The top of the bar in middle will sit at the bottom of the frame, and the bottom of the bar will be 7/8 to 1" below the frame. The sway bar mount brackets will be about a half inch below the frame. This will allow enough room for exhaust system etc. without causing a huge ground clearance problem. I may need to make a slight notch on the outside of the frame rail to clear the bar on up travel. Next will be to fab the mounting tabs for the lower end of the links. This will go between the lower shock bracket and the original shock mount tab.
That's it for now, I'll update my progress in a week or so.
Brian

[chevynut]

Looks to me like you might avoid interference with the frame if you turn the swaybar over or shorten your link. This is the only one I ever did that way....

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[Justin@ECP]

Killer work both ways!

How do they drive with the C4 stuff on there?

[rockytopper R.I.P 5-13-2017]

Very Nice!!

[chevynut]

How do they drive with the C4 stuff on there?

The guys who have driven their cars with Newman's or my frames say they drive like a modern car, like a Corvette, and "like it's on rails" or "like a slot car". The power rack is 2.36 turns lock to lock (high perf ones are 1.96 turns) and caster is 6 degrees for stability on the highway. You get 4-wheel discs (11.5" or 12" OEM standard) and all C4 rears are POSI. I figure the setup takes 150 pounds or more off the stock frame.

[Custer55]

Good to know. Makes me want to keep working on mine.
I'll post a progress udate in a few days.
Brian

[Justin@ECP]

Awesome!

The guys who have driven their cars with Newman's or my frames say they drive like a modern car, like a Corvette, and "like it's on rails" or "like a slot car". The power rack is 2.36 turns lock to lock (high perf ones are 1.96 turns) and caster is 6 degrees for stability on the highway. You get 4-wheel discs (11.5" or 12" OEM standard) and all C4 rears are POSI. I figure the setup takes 150 pounds or more off the stock frame.

Takes all the floatiness(yep, that's a word) out of the OE setup. They are great cruisers, but I bet it's a lot of fun to do some carving with one on C4 suspension!

[Custer55]

Progress Update

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I took some time off from the frame project to do a side project last week. I built this bending brake to bend 1/8" up to 6" wide. I did do a test bend on a piece of 2" wide 3/16" that worked pretty well also. I made it out of 1 1/2 x 2 rectangular tubing (1/8" wall). I used this because I had a bunch of 2 foot pieces from the local steel suppliers surplus stock. You can make one with flat stock or angle iron as well, you just have to make sure the center of the pivot point is right where the top corner of stationary bed meets the top corner of the bending bed. I made 2 different hold down pieces, 1 from the rectangular tubing that puts a nice radius on the bends but you can't quite get a full 90 degree bend, or do a tight u-bend. The second hold down is just a piece of 3/8 x 4" flat stock I had laying around which works well for finishing the 90 degree bends and the tight u-bends. in the last 2 pics you cans see the spacer (made from 5/8 dom tubing drilled to 3/8 in the center) to let the handle pivot freely and a couple of test pieces I bent up. Of course this led to some shop reorganization and a new workbench to mount the brake to. I should have built one of these years ago though, It sure beats the heck out using the bench vise and a hammer!

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Up next on the frame is the center cross member. I'll finish up on the rear sway bar later. I am building the cross member similar to the Art Morrison frames. So far I have the rear bulkhead built. I am using 3/4" x 1 1/2" .080 wall rectangular tubing and 1/8 x 3 flat stock to form an I beam. The exhaust holes are 4" x 1/8" wall round tubing, I used a 4" hole saw to make the holes for tubing to slip into. The center hoop I built a form and bent the tubing around it with the help of the acetylene torch. I'll probably add a piece of 1/8 flat in the lower part of the center hoop once I mock up the engine, trans and drive shaft so I know how much clearance is needed. The plan for the rest is to make another bulkhead like the rear one about 2' in front of it, and tie the 2 together with I beams parallel to the drive shaft tunnel and then angling out to just behind where the original rear motor mount were. The trans cross member will be bolted in where needed. This should make the frame quite a bit stiffer in the middle without added a bunch of weight.
Slow but sure I keep making progress.
Brian