twin engine AWD car

[Andy Dorsett]

I posted this on another page and didn't get much response. I am interested in building a car with twin FWD drivetrains. I have seen the Mosler caddy, the Tibron in Sport Compact, and the A class. I need some opinions on what car to use. The focus will be on acceleration and the ability to drive around. I doesn't need to be a handling car. I am thinking Grand Prix GTP right now and tha DSM has been sugested but my knowledge of most front drive cars is limited. In my opinion modding a FWD car is a complete waste of time therefore I don't have the years of reading experience with them as I do others. Here are my requirements and initial thoughts but I will listen to differing opinions.
1. Must be an auto. Manual linkages seems too difficult to implement.
2. Must be the car that came with the drivetrain. Only want to have to perform performance enhancements to the front drivetrain.
3. Rear drivetrain must be the same as front or at least before mods.
4. Must be a popular car for modding.
5. Must be a fairly common car or car that is easy to get parts for.
6. Don't want to spend more than about $10k for the first car. First car being the one that gets the second drivetrain.
7. Want to retain airconditioning and stuff like that.

I want to go 9's and have a somewhat reliable car. Right now I have a tubocharged 93 Cobra that you can drive everyday, will go high 10s, gets 19mpg on the highway, and I don't have to do anything but change the oil. I am trying to decide between the twin engine car and taking my current drivetrain and putting it in a Shelby Cobra kit. I know I can get in the 9s that way but something intriges me about the concect of a car with independant drivetrains.

[curtis73]

Originally Posted by Andy Dorsett

2. Must be the car that came with the drivetrain. Only want to have to perform performance enhancements to the front drivetrain.
3. Rear drivetrain must be the same as front or at least before mods.
4. Must be a popular car for modding.
5. Must be a fairly common car or car that is easy to get parts for.
6. Don't want to spend more than about $10k for the first car. First car being the one that gets the second drivetrain.
7. Want to retain airconditioning and stuff like that.

So you want to take a front drive car, and buy another drivetrain to put in the trunk, right? Not like putting a 3.8L in the bed of an S10? Won't you run into serious problems with the unibody? The amount of cutting you will have to do to the main car support (the rear seat bulkhead and shock towers) might leave you bent in half (literally).

I've seen this done several times with unibody cars, but it came with million$ of R&D based on the original computer designs of the car.

You might want to consider a Toronado or Eldorado from the V8 era. If you have an eldo, you would have one of the greatest V8s of all time ( the 500 ) which has incredible aftermarket support and makes brutal torque. Super simple to make 1hp/ci Plus, you'll have a TH425 (the transverse TH400) that will take tons of power. All of it will go into a body-on-frame design that doesn't really matter if you cut the body up.

I can see it now; an AWD 1000 ci, 1000 hp, 1200 ft-lb beast. I'll bet you'd do better than 9's

Not really a popular car to mod, but maybe a better choice without the benefit of a CAD unibody design.

[Andy Dorsett]

yes, no and no. I will not have cad design. My co-worker with a copy of ProE will probably not be willing to model an entire car "on the side" for me. I will use the brute force put way to much tubing in meathod. It has been done many times before by backyard mechanics and I'm sure I can handle it.

What year cars are you talking about. I had no idea there was a transverse version of the 400. Two 500's would be flat awsome.

[MagicRat]

This has been done before, by none other than the folks at Car and Driver, about 15 years ago.
In their article, they explored all the options available to them at the time, and asked the same engineering questions you have.
They built a Honda CRX, and left the front driveline stock. They installed a second stock driveline in the rear and ended up with (I think) a 13 sec quarter mile AWD car that worked very well.
Given all the performance parts available, a 10 sec twin engine Honda should be attainable.
If you can, look up their back issues. The article was a bit light on the exact engineering details but they had many photos and a very interesting article.

BTW I think curtis is referring to the '66 to 78 Olds Toronado and the '67 to 78 Eldorado. (GM made similar downsized models through '85)
Neither used a transverse V8 engine; the engines were longitudinal, with a 3 spd auto trans mounted beside it, driving the front wheels through a conventional ring and pinion gear through two half-shafts.
I believe Hurst performance products built a twin engine '66 Toronado show/drag car called the Hurst Hairy Olds (I think). It could smoke all 4 tires through most of the quarter mile.

[curtis73]

Originally Posted by Andy Dorsett

yes, no and no. I will not have cad design. My co-worker with a copy of ProE will probably not be willing to model an entire car "on the side" for me. I will use the brute force put way to much tubing in meathod. It has been done many times before by backyard mechanics and I'm sure I can handle it.

I love how you think !!! Anything fits anything with a sawzall and a welder

What year cars are you talking about. I had no idea there was a transverse version of the 400. Two 500's would be flat awsome.

Ummm.... I'm guessing on this since I'm away from my Standard Catalog, but 67 through 77. I know they went at least that long, no sooner, but maybe as late as 78? The transverse 425 accepts many of the TH400 upgrades and can also be found in some obscure places like the mid 70s GMC front-drive motorhomes.

Here's a 67 Eldorado...



Here's a 76.....



And a 67 Toronado.......



If ever in doubt, you can usually tell from the wheels. They have the positive offset on the order of +38mm. The later caddys had a wider body and they could run a minimal +14mm that looked a little more "normal" as you can see in the pic of the 76

The Olds obviously had the 455, and although it had big displacement, it is handicapped by small bores and a long stroke. Although it has a good aftermarket support, it will always be hindered by breathing. Great torque, but if you're shooting for a 9 second car it might be of concern. The early caddys had the 472. Starting later, all caddys came with the 500. I don't have the numbers infront of me, but the 472 and 500 are externally indistinguishable. Even casting numbers don't always tell you, so pick up a book that will tell you the history. The 455 is also considerably heavier than the 500. The 500 with an aluminum intake weighs the same as a small block chevy with an iron intake.

[Andy Dorsett]

By the looks of those pictures it would have to end up a much quicker car than 9s for me to be able to drive it.

I will start researching the CRX. MagicRat I can't imagine a car magazine not having much engineering detail in thier article.

Keep the good input coming guys!

[Reed]

i would also suggest the crx. i saw on tv some guy who had a dodge I4 turbo motor in the back. might also want to try a mini, vw golf, any hatchback like that. i just think it would be easiest to get a motor in the back of one of those and fab up the mounts and whatnot. i dont know much about auto trannys but i would think that to get them to shift at the right time it would be best to go with manual trannys. im guessing that its not a great idea to have your front and rear wheels turning at different speeds while going about 200 mph even for a fraction of a second.

[Andy Dorsett]

It doesn't make any difference if the trannys shift together. You could have different engines with different trannys with different final drive gears and it won't matter. One just may end up pushing harder and doing more work than the other. If at 100mph if one engine is at 5000rpm and the other at 6000 it doesn't matter.

What range of years for the CRX? I know nothing about these cars.

[curtis73]

Originally Posted by Andy Dorsett

It doesn't make any difference if the trannys shift together. You could have different engines with different trannys with different final drive gears and it won't matter. One just may end up pushing harder and doing more work than the other. If at 100mph if one engine is at 5000rpm and the other at 6000 it doesn't matter.
.

Quite true, in fact when dealing with the Cad 500s and TH425s, its often preferable to have them shift differently. A guy in Clymer, PA put two Cad 500s in an S-10. The front engine was near stock with just an Edelbrock intake, 204 cam, and 2.93 final drive. The rear engine was similar but had a shift kit, 220-ish cam, 10:1 compression, and 3.23 gears. They complimented each other nicely since while one was shifting, the other was in a sweet part of the torque curve. It felt like a six speed. For daily cruising he was trying to find a way to let the rear free-wheel without damaging the tranny. He was going to try to adapt 4x4-style hubs that could be disengaged, or use those wimpy shaft locks like RVers use on FWD dinghy towed cars. On demand double displacement Gotta love it. It was in the mid 10s which was pretty good for a 5500-lb truck.

[MagicRat]

Originally Posted by Andy Dorsett

I will start researching the CRX. MagicRat I can't imagine a car magazine not having much engineering detail in thier article.

What I meant is that the article is not a step-by step instruction manual on how to build the car. Some details, especially about the structural reinforcement to the rear and not discussed much.

A few things here folks,
Yes, andy and curtis are correct, with auto trans, the shift points don't matter, but the folks at Car and Driver wanted both auto trans to shift together to manitain equal drive forces on all wheels.
Their concern is that if you were doing some hard cornering, and the thrust at either the front or back end changed due to a transmission shift that was NOT coordinated with the other end would upset the cornering balance.
For example, more thrust at the rear wheels would produce more oversteer, more at the front only would produce understeer.
At best this would produce spooky, unpredictable handling when driving fast, at worst it would spit you into a ditch.
Different final drive ratios would do the same thing, as would having one engine produce significantly more power than another.

However, in a straight line, it would not matter much.

[Andy Dorsett]

MagicRat I was joking. I hope I didn't offend you. It is my experience that magazine articles almost never give enough detail and that is from the fact that they are not engineers they are journalists.

My setup will be for straitline performance and will almost definitley have a more powerful rear engine and more rear gear if possible. The reason why is the same reason it is a waste of time to make a powerful FWD car. The faster you accelerate the more weight is transfered to the rear wheels. A fast enough 60' time and you will have no weight on the front wheels which is why you have wheely bars. My initail calculations assuming a static weight distribution of about 55/45 (what I calculated a typical 65/35 FWD car with another drivetrain in the back to be) accelerating at about a G show the dynamic weight distribution to be about 33/67. The rear wheels need to have about twice the torque applied to them to fully utilize the traction available. This is where it becomes hard to get enough power to weight ratio to go 9s without being able to fully utilize the front drivetrain.

[Andy Dorsett]

I'm researching the civic. I can't find anything for an automatic tranny. I simulated it with two manual trannys but by the time you get to the high 10s you are shifting from first to second less than a second into the run. This means it would be very difficult car to drive and again I don't see getting the one stick to flawlessly operate two gearboxes or at least I don't think I have what it takes to do it. Same thing with the DSM, no auto tranny support. I'm back to the Grand Prix GTP again.

[MagicRat]

Originally Posted by Andy Dorsett

MagicRat I was joking. I hope I didn't offend you. It is my experience that magazine articles almost never give enough detail and that is from the fact that they are not engineers they are journalists.

hahaha, use these guys next time!!

yes the best way to become disillusioned or ticked off at a journalist is to read about something you know a lot about, then find all the flaws.
Car and Driver (or as my wife says Car and Drivel) is a bit better than most because some of the scribes (including the person who wrote the CRX article) are former auto engineers.
This begs the question though, if they were any good at engineering, why are they journalists now??