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Old 12-14-2004, 01:16 PM
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Your thoughts on a project I'm pondering

Been away from the board from awhile. Last time I was here I was seeking advice on rebuilding my Allante.

Anyhow, been thinking of where to take the project next. This is long-term, thinking-out-loud stuff.

I would like to convert the current transverse fwd drivetrain to longitudinal RWD or AWD. For the purpose of discussion, lets assume that the powertrain would physically fit in the space available.

The current set up is a strut-based unibody.

Front-end: engine cradle (similar to an Astro's) bolts up to the unibody at six points and holds the lower control arm mounting. The strut mounts are located in the strut towers of the unibody. The unibody extends forward from the firewall, incorporating the strut towers and "frame rails" that extend forward for mounting the fenders, radiator, etc. These rails aren't especially sturdy for powertrain mounting purposes, but they do provide a significant amount of crash protection for the occupants.

Rear-end: also strut-based. The entire (independent) rear end bolts into the unibody as an assembly. Consists of a transverse plastic leaf spring (like C4 vettes, IIRC) and formed metal "strut towers" that are part of the overall assembly.

My goal is to make a very streetable vehicle, with improved handling, a much stiffer chassis, and capable of a more powerful powertrain.

My first thoughts were to try and use the existing mount points for the front and rear suspension members. While that might work up front, the rear was never designed to take the forces RWD would exert. This wouldn't help the overall chassis structure either. I've done some research on stiffening 80's mustangs, and some guys are apparently using weld-in frame members that run over the top of the floorpan, and mount to rear suspension mounting points. I'm thinking that something like this is the way to go - build a frame over/under the floorpan that extens fore/aft to include the suspension mounting points. Extend this upward to include the upper fore/aft mount points. Leave as much of the unitized body in place, but essentially reinforce it everywhere.

What do you guys think? Am I on the right track? Has anyone ever attempted something like this?

Just as an aside, I would probably obtain another Allante unibody (less fenders, doors and interior) and build as much as possible off that before tearing down my current car and transferring the body parts.

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Old 12-14-2004, 06:09 PM
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I would think building a full frame would be much easier. Use Corvette suspensions front and rear. I don't think there is much of a difference in the wheel bases or track widths between the Allante and the 'Vette so getting a frame built would be your biggest hurdle. You could possibly even re-use the Allante front suspension if you tied the current cradle into a "back half" frame with vette rear suspension.
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Old 12-14-2004, 09:25 PM
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You would probably have an easier time of just moving the drivetrain to the back wheels. Its an automatic, so no worries on being able to shift - you can just get a longer shifter cable. That at least limits your worries for fishing details like a driveshaft down the middle of the car. You would also already have most everything you needed. If I were tackling the project, I would be inclined to cut away everything in the rear that was in my way as far as fitting the drivetrain/cradle in place, purchase another front suspension setup and see about making it bolt in the rear with toe arms attaching to where the steering tie rods used to go. I would also recomend Googling "Bill Strong Northstar" just to give a little better idea (and pictures) on some tricks for making things fit that weren't intended.

Not to mention that a mid engined rear drive Allante would be much more bad A than just a rear drive one. It would also be the platform that would offer the least amount of weight addition and greatest handling benefits.


btw- as I recall, Hot Rod magazine had a write up on a guy who put a Northstar in the back of his Eldorado. Didn't replace the one up front...just added another in back. He described the sound of the two engines revving independently of each other as pretty wild. Obviously, that would add weight but at least you know its been done before.
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Old 12-15-2004, 02:31 AM
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I'm with the original poster -- use the front suspension by modifying the original engine cradle. For the rear I'd pick up a Jag rear axle assembly. They are fully self contained in a sheet metal "cage" assembly that mounts to the body via four rubber mounts and two trailing arms. They can be expensive -- I bought a core unit for $100 then spent $800 refurbing it. But I had to change gears (bought a used set of 3.55 gears with posi chunk off e-bay for $300, paid $150 for a pro to set them up), replace rotors, one caliper (rebuilt the other -- one was rusted firm!), of course pads, all seals, and outer wheel bearings. I used a crossmember instead of the original cage, but the cage might work for you. It isn't hard to narrow one either. Any good welder can do it easily since you basically have two drive shafts instead of a solid axle. Well, the original Jag units are solid, but they can be cut and welded with a sleeve over them or two short tubular driveshafts can be made like the older Corvette IRS (I'm not familiar with the later model 'vettes). It uses standard Chevy size u-joints.

You might look at a late model T-bird IRS also. It has a subframe that could be adapted, but might be to wide for the Allante. Another that comes to mind is a 280Z IRS, but not sure that will handle more than 350 hp or so. The Jag will handle 500 hp easy.
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Old 12-15-2004, 06:53 AM
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dmc12mk3:

I had thought about a mid-engined setup. There would be plenty of room back there if I relocated the gas tank to the front and used a Fiero-style radiator setup. I could even use a 500CID and drivetrain out of one of those giant Eldorados and keep it all Cadillac.

However, I'm still faced with the problem of the rear end of the car not being designed to take any sort of torque. As it is, it just trails the rest of the car, so I'd have to build a frame.



Don't know if you guys have seen this thread http://hotrodders.com/showthread.php...77#post384477, but the idea of AWD is sounding very doable with a frame.


astroracer, farna:

After thinking more about this last night, I think a full frame is the way to go. I liked the idea of integrating the frame into the unibody, until I thought about the level of noise and harshness that would transfer to the passenger compartment. The best solution is probably going to be channeling the unibody over a frame so I can isolate the two. Part of the problem with a unibody car is that the isolation between the suspension and the unibody has to do double-duty - provide link mounting points, but also isolate noise. With a frame, the mount points are largely (although not completely) designed for maximum handling, and the frame/body mounts handle most of the noise reduction.

I would have a lot of extra weight to haul around with a full unibody and a frame. With a low center of gravity, that might not be a huge problem. I suspect I could do some trimming. I bet it would be a solid-riding machine.



I'm not sure where to go with the frame. Getting a Corvette frame would be the most straightforward and you can pick up a C4 basket case for around $1500 with a good frame. If I went strictly with RWD, that would be comparatively easy and parts are available. I'd probably be able to swing a lot of the drivetrain too, though it would need rebuilding.

I also have to consider passing emissions. My Allante is an '89. If I use later-model driveline parts, I have a better chance of getting through the complicated process of getting permission from the state. I've looked into the process and its not insurmountable, but it is complicated. As long as the drivetrain is from a newer model, you're half of the way there.

I like LT1's, but I'd prefer to go with something a little more in keeping with the Allante, like a N*. Although to be honest, the 4.5 in the Allante is no slouch and is comparitively light (aluminum block), and can be easily enlarged all the way up to 4.9. No hop-up parts available though for the 4.x series. That's all a subject for another thread ...

The Jag rear sounds good too. They're also pretty plentiful here in the NorthEast because Jags don't seem to do well on salted roads. Is the rear of the XJ the same as that of the XKS?

OTOH, perhaps the best way to go would be a fabricated frame that mounted the vette or jag rear and either vette or AWD front.
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Old 12-17-2004, 08:45 AM
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Well, some more thoughts...

I was reading a Chassis Engineering book last night - the one by Herb Adams.

Anyhow, if I read the book right, the setup he recommends for a street/strip Cobra is essentially is a unitized-looking frame (a combination of tubes and sheet-metal panels) with the fiberglass body hung over it. IIRC, his seats mount directly to his unitized frame and he recommends nylon bushings and heim joints on all suspension mounts, which would pretty much not isolate the suspension from the passenger compartment.

I can't help wonder how "bad" it would be, comfort wise, to not isolate the passenger compartment from the chassis. The engine, trans and exhaust would still have isolating mounts.

Thinking about the precision and chassis stiffness that would be posssible makes me drool. OTOH, no one's going to want to ride with me if their fillings rattle out.

Maybe I'll start a new thread specifically on the topic of unisolated passenger compartments.
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Old 12-17-2004, 10:25 AM
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"his seats mount directly to his unitized frame and he recommends nylon bushings and heim joints on all suspension mounts, which would pretty much not isolate the suspension from the passenger compartment"
You really want to stay away from this type of car if you plan on driving it on the street. A race car (which is what Herbs car is) is driven on smooth tracks and driver/passenger comfort is not even a consideration. Rock hard suspensions are not only hard on the occupants but they are hard on every other component in the car also. Nylon bushings and heim ends have their places in race conditions but, when you put them in a real world environment and throw in a little water and dirt, they become self destructive. Driving a car like this on the street is no fun when you cringe at every expansion joint and have the back swing out on you in every bumpy corner...
The final decision is yours of course but, like you said, what's the point if no one will ride with you...
This is just my experience and opinion though so call me stupid if you want to...
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Old 12-17-2004, 02:53 PM
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Astroracer:

I appreciate your opinion.

What I'm contemplating would primarily be a daily driver outside of winter. I'm willing to trade a certain amount of ride quality for more precise handling, although to be honest, a FWD unibody convertible isn't exactly the most rigid structure - just about anything I could come up with would be better.

I guess one avenue I could pursue would be to start off using as many stock parts as possible for the suspension, and build the frame to be as rigid as frames can be by their nature. Then I can replace suspension mounting points with harder materials with the ability to always go back to the stock rubber.

I still have the problem of what to do with the unibody - make it part of the frame, or channel it over a frame. Without the strut towers, the rest of the body isn't that much different from any other framed vehicle body, except there's no place for a frame or driveshaft. I suspect its a little on the heavy side too, but in a driver that's not necessarily a problem.

The thing is, without a top, there's not much to stiffen the area between the front and rear suspensions. Although the more I think about it, the more I think I could do:

The Allante doesn't have a back seat, but there's a substantial cargo area. If I sacrificed some of that, I could triangulate the top of the rear suspension with the frame just aft of the seats, and do the same thing up from the trans tunnel to the front suspension points. Depending on the space, I might be able to build a tubed "backbone" along the driveshaft and then mount the body above all that. The console would have to be enlarged, but I could live with that - maybe I'd lose the glovebox.

Luckily, the ragtop "pancakes" into a fairly shallow well behind and above the cargo area, so I could probably do a lot and still preserve the appealing aspects of the car while simultaneously vastly improving the chassis rigidity.
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Old 12-30-2004, 08:56 AM
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More help

I've been doing some research and talked to a couple of you off-forum.

I think I've settled on the idea of a Corvette C4 as the basis for the rear end. The track width is exactly the same as the Allante in the rear, so other than tubbing for the wider wheels, I should be pretty well set.

The shortest way to go would also be to use the C4 for the front end and the entire frame. The C4 front end is .8" narrower than the rear, where the Allante is the same - I think that's pretty darn close. The wheelbase of the vette is 3.2" shorter, but I can work around that pretty easily.

However, I'm still trying to make the AWD thing work.

So here are some questions:

Can any "modern" front suspension handle the 40% torque split of AWD? At first I thought this would be "no", but then I thought about how the front brakes are the primaries for stopping the car. If the front suspension can take the force of stopping, then shouldn't it be able to take part of the force of driving, especially with some harder control arm bushings?

The reason for the above Q is that, althought the S-10 front chassis clip sounds pretty good, I think its a little bit narrow. I'd like to use a mix of OEM parts as much as possible, so I was thinking that perhaps a vehicle with a wider front track (maybe a G-body? or even the Vette) could be adopted with S-10 spindles and possibly lower control arms (with torsion bars) easier than trying to widen an S-10 front clip and maintain the geometry, or trying to get around it with large spacers on the wheels.

An alternate question might be, is there any significant difference between the S-10 2wd front suspension and the S-10 4wd front suspension, other than the torsion bars and lower control arms?
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