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Old 07-29-2015, 04:01 PM   #1
Straight Success
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Technical Documentation For Building A RWD CB7!

This topic has been brought up in many conversations over the past decade or so. There is evidence that these cars can be turned into RWD, and attempts by members who have poured many man hours into trying to build the next great RWD CB7 are currently being developed.

This thread will serve the purpose of engineering the CB7 platform to function as a RWD car. Tons of R&D will be documented here to blueprint/map out what's needed to embark on building one. A few years back I stated that I would be attempting to build one. Well, here's the beginning of that process. Also, I will be performing this with the intent of making the RWD CB chassis drivable and comfortable on a daily basis.

Quick background about me. I graduated from Temple University with a degree in mechanical engineering in 2013. I have been focusing my efforts over the past 3 years in becoming the best design/mechanical engineer I can be as this is always what I wanted to do. I also like to take what I design and actually build/manufacture it. To say in the least, I love doing this as a hobby and a career.

Advice is always welcome. Please post in the thread as a good engineer listens to all advice and evaluates it to see how feasible an idea is.

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First and foremost, with any project, the very first thing to consider is... can I afford to embark on this journey? If the answer is NO, keep reading. If the answer is YES, keep reading.

BUDGET

To begin, I will be documenting this from the point of a person who has the capabilities and resources to perform a full automotive restoration job in the comfort of their own home garage. So, if you are reading this thread, more than likely you immediately know that this will single handedly be the most EXPENSIVE modification that can be done to this platform (with the exception of going AWD, but it's in the same realm).

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

:::SPECS:::

ENGINE
TRANSMISSION

REAR
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Old 07-29-2015, 04:01 PM   #2
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Chassis Evaluation

To begin, out of the options for the CB chassis (coupe, sedan, and wagon), I'm not sure at this point which one is the easiest to start with. However, they all will follow the same format as far as fabrication. In the world of handling performance and stability, well, I'm only going to perform the necessary calculations for the coupe (the dimensions are somewhat very similar). The concepts used for the front of the vehicle will be the same for all chassis. It's only in the rear where it'll differ. However, I'm sure anyone attempting this will be able to find solutions to the changes in the rear.

In reality, a 50/50 weight distribution is optimal. Being honest, we're taking a FWD car and adding weight to the middle and back (transmission, drive shaft, and rear differential) of it that was never present before. The weight distribution, at this point, I have no idea where it'll end up.

Furthermore, we're going to try and avoid any unnecessary cutting to the chassis if possible. This means using as much of Honda chassis engineering team's (circa 1986) creation as possible. Ideally if we can use existing suspension mounting points (a stretch, but it maybe possible) the car may be just a tad bit more rigid when we finish. We have to do some evaluation to see if this will be the case though. Also, chassis stiffening for torsion is a must. This car was never engineered to twist in the longitudinal direction. Also, trying to keep the original front spindle setup minus the drive shafts is an idea that seems like it'll help in the time department. Using the existing rack or some custom rack would be great. These are all things that need to be evaluated.

- Coupe

- Sedan

- Wagon
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Old 07-29-2015, 04:02 PM   #3
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Engine Selection / Rear Differential

This should not have to be mentioned, but I will try not to leave any aspects unaddressed. When choosing an engine for this project, it is best to choose an engine out a car that was originally RWD. Can you use an engine that was never design for a RWD application? Yes, but it would make the project that much more difficult, expensive, and time consuming. The engine/transmission options for a project of this magnitude vary greatly, so it is wise to plan and choose Accordingly! , Sorry I had to. Realistic options range from inline 4s, 5s, and 6s, to V6s and 8's. .

It should be clear to see that the smaller inline options, at least at first glance, may be an easier option to swap in simply attributable to spatial constraints. However, the planning here will be done from one of the most extreme cases; a V8. This will also allow to engineer the most extreme case which, in theory, should work without additional evaluation in the less extreme cases.

Rear Subframe Options To Investigate:

- Corvette (C4/C5/C6) - by popular demand.
- Mazda Miata
- Nissan 240SX/300Z/300ZX
- Honda S2000
- BMW E30/E36
- Mercedes Benz C Class
- Lexus IS250
- Toyota SC300
- Audi A4/TT
- Other
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Old 07-29-2015, 04:02 PM   #4
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Chassis Strengthening / Engineering Analysis

Initial Known Variables ('92-'93) [using unverified data for now]:

Length (Coupe/Sedan) : 4704 mm (185.2 in.)
.... ......(Wagon) : 4745 mm (186.6 in.)

Width (Coupe/Sedan) : 1704 mm (67.1 in.)
.... ......(Wagon) : 1714 mm (67.5 in.)

Height (Coupe/Sedan) : 1326 mm (52.2 in.)
.... ......(Wagon) : 1351 mm (53.2 in.)

Wheelbase (All models) : 2720 mm (107.1 in.)

Curb Weight (All models) : 1237 kg (2728 lbs.)

Fluid Capacities

I need the naked sprung and unsprung weight.

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I'm thinking once I get the car completely stripped, I can evaluate it better. Esentially, I will design the entire interior space in Catia V5 and apply various loasd to the structure in the form of real world predictability. It will not be certain, but it will give me a good idea where the weak points would be to inform me of where to properly brace. I'm thinking going with a tube structure that would transfer the various forces evenly throughout the tube structure. I also would like to incorporate the tube structure so that the original interior pieces can go back together without noticing the additions.
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Old 07-29-2015, 04:03 PM   #5
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Sourcing

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Old 07-29-2015, 04:03 PM   #6
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Fabrication

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Old 07-29-2015, 07:07 PM   #7
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I would imagine the wagon may be the easiest just because of the space that you have to work with.

I REALLY like the Corvette Transaxle configuration. We may be able to avoid as much cutting for the transmission tunnel. The CB and the Vette's wheel base is very close. We can make a simple adapter to mount to the torque tube and use any engine that will fit and spin the correct direction as the clutch is no longer directly attached to the transaxle. The tube can also be used for bracing and stiffening.
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Old 07-29-2015, 07:36 PM   #8
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Quote:
Originally Posted by sonikaccord View Post
I would imagine the wagon may be the easiest just because of the space that you have to work with.

I REALLY like the Corvette Transaxle configuration. We may be able to avoid as much cutting for the transmission tunnel. The CB and the Vette's wheel base is very close. We can make a simple adapter to mount to the torque tube and use any engine that will fit and spin the correct direction as the clutch is no longer directly attached to the transaxle. The tube can also be used for bracing and stiffening.
The wagon does give tons of room with the hatch which is probably the most easiest. I am in agreement.

However, I think (an Anthony opinion) for a first solid RWD CB, the coupe would probably be the most appealing to enthusiast.

As far as the Vette goes, which year/chassis, C5/C6/C7?

I haven't had the privilege of seeing the intricacies of one up close and personal to evaluate the frame/chassis layout. I'll be frequenting a few junk yards this week, and I'll be taking my digital camera and tape measure. I'll try to find one.

The trans/drive shaft tunnel is a huge aspect of this build. The rear too! Actually, they just may be the most important aspects along with making the car structurally sound.
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Old 07-29-2015, 07:48 PM   #9
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The most logical sense to me would be to buy a smashed up s2000 and just transfer everything to the cb chassis. This is something I would love to do but , I am not an engineer and I have no welding or fabrication experience. If you have the techical knowledge go for it , that way you can somewhat keep costs down.

I looked into it once , me and a good friend measured up the rear end and it fits the cb pretty good. When measuring suspension travel we figured out that we would have to cut into the rear bottom seat area for the s2000 differential. That's when I just backed out and said that its just way to much work for my liking, plus I couldn't trust someone else with the fabrication.
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Old 07-29-2015, 07:51 PM   #10
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Also you are going to have to cut a tunnel area under the dash, s2000 setup sits to low if you don't modify that area. You would have to raise the car to stock height for ground clearance of the transmission and oil pan.
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Old 07-29-2015, 08:18 PM   #11
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Quote:
Originally Posted by laz93se View Post
The most logical sense to me would be to buy a smashed up s2000 and just transfer everything to the cb chassis. This is something I would love to do but , I am not an engineer and I have no welding or fabrication experience. If you have the techical knowledge go for it , that way you can somewhat keep costs down.

I looked into it once , me and a good friend measured up the rear end and it fits the cb pretty good. When measuring suspension travel we figured out that we would have to cut into the rear bottom seat area for the s2000 differential. That's when I just backed out and said that its just way to much work for my liking, plus I couldn't trust someone else with the fabrication.
Quote:
Originally Posted by laz93se View Post
Also you are going to have to cut a tunnel area under the dash, s2000 setup sits to low if you don't modify that area. You would have to raise the car to stock height for ground clearance of the transmission and oil pan.
Under Consideration
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Old 07-29-2015, 08:24 PM   #12
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I agree about the ground clearance. It seems like that the would have to be mounted extremely high in the cabin to allow space for the exhaust too. C6 seems to be cost effective and closer to our wheelbase.
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Old 07-29-2015, 08:45 PM   #13
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Rear Options

Solid rear or independent multi-link?
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Old 07-30-2015, 05:07 PM   #14
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I vote independent multi-link.

I really need a stripped down booty butt naked to the bare bones Accord to really get serious. I guess I'll be on the hunt soon for a CB coupe with an okay body to embark on this journey.
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Old 07-30-2015, 06:44 PM   #15
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Both? One document for solid and the other for multi.

Honestly, I think the diff that you end up choosing will determine that.
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Old 07-31-2015, 08:17 AM   #16
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Both? One document for solid and the other for multi.

Honestly, I think the diff that you end up choosing will determine that.
That would be nice.

I'm thinking that a solid rear axle would be the easier swap of the two which would require less chopping in the rear of the CB chassis. Further more, I'm learning towards the multi-link set-up offering better performance and stability due to many factors. Time to compare rear suspension layouts.
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Old 08-17-2015, 04:43 PM   #17
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I can't help but imagine the process would be just as hard, if not easier, to go mid engine rwd. Civics, integras, del sols, and crxs all have been converted to rwd with a mid engine setup. Get a front clip from another accord, cut out the rear, strip down the front clip to subframes, and weld it in. You'd keep front fabrication down to a minimum and the chassis would be more in tune with the torsion forces encountered, reducing the bracing needed to a minimum. And then, you could grab it from a 3.0cl and have the ability to mount a v6
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Old 08-17-2015, 05:10 PM   #18
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I can't help but imagine the process would be just as hard, if not easier, to go mid engine rwd. Civics, integras, del sols, and crxs all have been converted to rwd with a mid engine setup. Get a front clip from another accord, cut out the rear, strip down the front clip to subframes, and weld it in. You'd keep front fabrication down to a minimum and the chassis would be more in tune with the torsion forces encountered, reducing the bracing needed to a minimum. And then, you could grab it from a 3.0cl and have the ability to mount a v6
That's also an option.
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Old 08-17-2015, 05:28 PM   #19
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This is definitely a project that I'm trying to see through to the end.
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Old 08-17-2015, 06:33 PM   #20
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This is definitely a project that I'm trying to see through to the end.
You better, I'm tired of seeing all these projects go to the wind and not a single person actually have a running RWD CB7
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