1973 240z Chassis Strengthening

[jacob80]

Hello!

 

I have a 1973 Datsun 240z that I plan on putting an 800hp 2JZ in but obviously need to work on some chassis strengthening before I rip the thing apart with that much power.

 

Here is a short list of items I found posted by the late John Coffey himself for a streetable car:

 

1. Seam Weld (every sheet metal seam overlap.)
2. Bad Dog Subframe Connectors
3. Weld-In Roll Bar.
4. Welded In Rear STB.
5. Triangulated Front STB.
6. Radiator Core Support Reinforcement.
7. Transverse Link Bracing Reinforcement.
8. RT Diff Mount.
9. Tubular Seat Mounts.
10. Box Upper Frame Horns to Firewall/Cowl.
11. Reinforce Pedal Box/Brake MC Mount.
12. Reinforce Front ARB Mount.
13. Reinforce Front Strut Tower to Frame Rail Junction.

 

I plan on doing some competitive drag racing, roll racing, track days, and driving the car around just about everywhere!

 

I have a very clean paint job on the car and the body is nearly perfect, so repainting the car/pulling out glass isn't really something I'd like to do. However, I think pulling everything else off the car and putting it on a rotisserie would make the seam welding much easier as well as the frame rails and such and I can live with that. I would LOVE to hear from you guys that have done this and if you were able to preserve the paint and glass on the car. This is a pretty big undertaking so I'd like to prepare myself as much as possible before jumping into this huge project.

[Nelsonian]

I have seen a friends L28et swapped 280Z start to crack under the newly painted car in the leaded joints above the C pillars close to the top of the hatch. His car was only in the 300+ hp range with very little chassis strengthening.

Edited May 7, 2016 by Nelsonian

[rturbo 930]

If you're planning on having 800hp, and launching it, I think you're gonna need more than what's on John's list for a street car.

[jacob80]

Car is going to be a 6 speed stick shift car. When you say "more"...are you suggesting a fully tubular front and back half?

Edited May 9, 2016 by jacob80

[rturbo 930]

Lol no, that's overkill. But I would say some kind of structure that goes from the front strut towers to the rear strut towers. Mind you, I am not any kind of expert, mostly going with my gut based on all that I've read here over the years. Look into what 74 5.0L Z did on his tube frame. Again, I'm not saying you need a tube frame, but his design goes from the rear strut towers all the way to the front, but doesn't have an A pillar or roof bar, so it's still reasonably safe on the street. 800HP is a lot of power, and when unleashed all at once, that's going to really stress the chassis.

 

Also, another thought... I'm betting you're going to need to reinforce the front diff mount, and surrounding area.

Edited May 9, 2016 by rturbo 930

[240zdan]

Seam welding the car on a rotissire would be iffy n my book. You may warp some of the unibody, especially when the car is on its side. Most people stitch weld the chassis while its resting on the suspension points, staggering the welds to avoid warping. I stitch welded mine and would say its a waste of time. Most of your reinforcments should be tubular as the 240z is made of such thin metal. It may help, but probably not worth your time.

 

Main thing I would focus on are full length frame rails and a well built cage that ties into the suspension points. Let the tubes do the work. Reinforcing the TC rod area will give you piece of mind when slamming on the brakes. The front diff mount is always problematic, I tied mine into the rear subframe by building a cradle after tearing the welds off the original mounts.

 

Integrating your strut bar races into the cage would help alot. Running tubes from the cage to the engine bay would be killer.

 

 

If youre main question is can it be done without damaging the paint, I would say no. When I did my car I stripped it down to the shell. With all that cutting grinding and welding itll be hard not to scratch the paint. I would probably go as far as soda blasting the entire shell to have nice clean surfaces to weld to, then after all the mods are complete get everything painted nicely.

Edited May 10, 2016 by 240zdan

[jacob80]

Seam welding the car on a rotissire would be iffy n my book. You may warp some of the unibody, especially when the car is on its side. Most people stitch weld the chassis while its resting on the suspension points, staggering the welds to avoid warping. I stitch welded mine and would say its a waste of time. Most of your reinforcments should be tubular as the 240z is made of such thin metal. It may help, but probably not worth your time.

 

Main thing I would focus on are full length frame rails and a well built cage that ties into the suspension points. Let the tubes do the work. Reinforcing the TC rod area will give you piece of mind when slamming on the brakes. The front diff mount is always problematic, I tied mine into the rear subframe by building a cradle after tearing the welds off the original mounts.

 

All the other things you have planned are good. If I were to take on a project like that I'd be definetley stripping the car down to the shell.

 

Tearing the car down to a shell is a pretty intimidating thought to be honest, considering I'm doing all the work myself. I'm not opposed to it, but at that stage it starts to get *really* intense and it starts to sound like a 2-3 year project. I'd be a lot more open to something like this if it were a battered old example that needed work anyway, but this is a pretty clean example of the 240z that I'd like to preserve as much as possible.

 

At this point, it sounds like I should probably tone down the HP goal I want to something a little more reasonable (3-500hp, which is still a lot in this chassis but much less than 800hp) to take stress off the chassis since I won't be seam welding or tearing it down to a shell. I will do all the bracing John C. recommends, but I need to preserve the exterior paint, glass, and body on this particular car to complete the project in a reasonable time frame and keep labor/cost down.

[240zdan]

I ran 500whp, I turned down my power to a more reasonable 350-400 depending on my mood. Much happier with how the car behaves. 800hp is awd territory, good for scaring passengers and yourself but a bit pointless if you ask me. Its nice to know you have the power but honestley 300-400 is so much more enjoyable, the car will feel balanced and this allows you to run a smaller turbo for nice engine response.

Edited May 10, 2016 by 240zdan

[Bzltyr]

What is a STB?

[jhm]

I'm assuming he meant strut tower bar.

[Bzltyr]

Thanks.  Just a bar going from left to right in the back and triangulate the front.

[Michael]

It's been a little over 3 years.  Has anything happened to this car?  Has the goal of 800 hp been achieved, and if so, what has been the owner's experience with driveability?