mid-engine sunfire?
 

I have been thinking about my sunfire project while I do all sorts of other projects. How do you folks think a mid/rear-engine setup would turn out?

I'm still going with the 3800 and 4t60E. Go ahead and brainstorm. Throw down some ideas and beat them to death. I want to see how this could turn out. It would give the engine more room. The car would be cooler in the summer time because the heat maker would be behind you. It would be easier to steer, but how light would the front end be? Will a front hub fit on the rear?

Jump in guys, lets have fun with this.

I can't really see the benefits of moving the engine to the rear for fuel economy reasons. Any potential benefits are not going to be worth the fabrication, time, and money invested in such a project.

The benefits of RWD and MR configurations is in handling, specifically weight transfer and center of gravity. Traction is also improved in some cases (Porsche rear engine).

I think Corv8s are the schnizz... this could be sorta like that. But mainly as a toy. The layout pretty much destroys a lot of the utility and comfort of a vehicle.

do you need seating for 4 people?

might be cheaper just to pick up a fiero and do the swap to it.

either way it'll be a 2 seater.

Would get without the rear seat, but at least there would have 2 trunks :D

Anyway, eventually transfering the engine to the rear wouldn't be the worst thing ever, altough it would still be quite an odd project. And if you did a power-steering delete, the weight transfered from the nose to the rear would reduce the effort required to steer.

The easiest way to do this is to buy another Sunfire, so you can pull all the hardware out of the front of that car (including the mounting points for the engine, transmission and suspension) and transplant it into the rear... include the full front suspension and brakes. The transmission will be the tricky part. Lots of welding.

Leave the battery and as many ancilliaries as you can up front, to balance the car out a bit. You'll need a fuel cell, too.

After that, your biggest problem will likely be tuning the suspension so it doesn't understeer like a pig when you enter a turn or hit the brakes (a brake bias controller would be nice). You'll need to install an aftermarket suspension or stiffen up the rear end a bit to balance the car out.

A more interesting proposition is a twin-engine set-up, which is twice as impractical, but twice as crazy.

There it is, the answer you are looking for Fiero.

Or a sandrail which needs an engine. Do your own aero-body over it.

I'm just playing with the idea right now. I want to throw ideas around and see what we come up with.

I am going to measure a few things just to satisfy my curiosity.:D I was planning on putting air springs in the rear anyway, so maybe that would work if everything measures out ok. My truck has almost NO body roll with air springs. I can take a corner at 60 and the truck will skid before it leans. Of course the air springs in the truck are independent so the air cannot transfer between sides.

"The mid-engine layout is typically chosen for its relatively favorable weight distribution. The heaviest component is nearer to the center of the vehicle, reducing the vehicle's moment of inertia and making it easier and faster to turn the vehicle to a new direction. Also the engine weight is more evenly carried by all the wheels with this layout. As a result, vehicle stability, traction, and ride quality are naturally improved when turning, braking, and accelerating.
Mounting the engine in the middle instead of the front of the vehicle puts more weight over the rear tires so they have more traction and provide more assistance to the front tires in braking the vehicle, with less chance of rear wheel lockup and less chance of a skid or spin out. If the mid-engine vehicle is also rear-drive (as almost all of them are) the added weight on the rear tires can also improve acceleration on slippery surfaces, providing much of the benefit of all wheel drive without the added weight and expense of all wheel drive components. The mid-engine layout makes ABS brakes and traction control systems work better, by providing them more traction to control. The mid-engine layout may make a vehicle safer, since an accident can occur if a vehicle cannot stay in its own lane around a curve or is unable to stop quickly enough. Mid-engine design is also a way to provide additional empty crush space in the front of the automobile between the bumper and the windshield, which can then be used in a frontal collision to absorb more of the impact force to minimize penetration into the passenger compartment of the vehicle.
In most automobiles, and in sports cars especially, ideal car handling requires balanced traction between the front and rear wheels when cornering in order to maximize the possible speed around curves without sliding out. This balance is harder to achieve when the heavy weight of the engine is located far to the front or far to the rear of the vehicle. Some automobile designs strive to balance the fore and aft weight distribution by other means such as putting the engine in the front and the transmission and battery in the rear of the vehicle. Some of the same benefits are gained, but at the cost of greater moment of inertia compared to the mid-engine layout, making it harder and less responsive to turn the vehicle to a new direction.
Another benefit comes when the heavy mass of the engine is located close to the back of the seats. It makes it easier for the suspension to absorb the force of bumps so the riders feel a smoother ride. But in sports cars the engine position is once again utilized to increase performance and the potentially smoother ride is usually more than offset by stiffer shock absorbers.
This layout also allows the transmission and motor to be directly bolted to each other—with independent suspension on the driven wheels this removes the need for the chassis to transfer engine torque reaction."

Why do things have to fit so good? The engine only needs 36" of room sideways and 28" front to back. It would sit directly under the rear window, which slopes down smoothly and would give a very good view of the engine.:D The rear struts could be moved to the rear of the trailing arms and would likely have close to the right rate at that point, if I chose not to use air springs.

The front end would house the battery and fuel tank, possibly the radiator, but I don't know if I want to run plumbing that far. It would be easier to use ducts to cool the radiator at the rear. That would allow me to use the bigger olds radiator.:thumbup: It will be manual steering either way, so the weight shift would be a plus. I will be using the steering from the olds because it has a better ratio.

I could weld the cradle from the olds directly to the bottom of the sunfire with the mid engine idea. That would save me some fab time on the mounting. The engine would stick past the current back seat by about 8 inches. I have been thinking about moving the rear wheels back to make up for it.:rolleyes:

I don't mind the fabrication. I have been doing that for a long time. I can't get this idea out of my head. I have been googling all day and have used up a good portion of my day doing research. It looks easier as I find more info.:rolleyes:

I hate to lose the back seat, but if I could move the rear axle back 8-10 inches, that would let me keep it.

Don't let this thread die in vain. If you have anything to say, say it. Good or bad....

I would ONLY consider it for a DD type vehicle if lack of traction and/or severe understeer were insurmountable problems with FWD.

I am considering it because the rear end is way too light. My brother and I picked it up to swing it into place in the shed. The rear end will be, comparatively, even lighter with the new motor/tranny in there. I was thinking a mid engine design would fix the problem of the rear end wanting to fly out/ come round all the time. It was horrible in the winter because there was no traction back there. We almost sailed off a cliff one time because of that light rear end. I can't seem to find any negatives to doing the conversion except for possibly losing the back seat, which isn't even that big of a deal. I would feel a lot safer with a mid engine and I would not worry about my wife driving in the winter time.

That much oversteer is odd... isn't it?

It scared us pretty bad the first time it happened. It was winter and we were going around a corner at a reasonable and prudent speed and the back end came right around on us. It took a few wags of the tail to get it corrected and when we came to a stop, we were looking down a 30 foot cliff, 4 feet from the edge. It was not too bad in the summer, but winter was terrible. It put me in the ditch twice. Don't even think of swerving in it, because the back end will surely jump in front.:( It is a 2 door coupe. No sway bar on the front, yet.

I had forgotten about the tail swing until last week. Then I remembered the thread about the mystery car and I decided it might be a good idea to try a mid engine design. It would make everything easier to work on, instead of trying to get fingers down in the engine bay.

I think that's atypical. Perhaps your car has a suspension flaw.

Given the amount of work required to move the driveline, trying an anti-roll bar on the front, maybe trying a few different sizes if they're readily available, would be much easier if the only issue is handling balance.

What is the rear suspension design? H-beam? If so, that will have an anti-roll bar inside the cross bar of the 'H'. You might find a thinner/softer replacement for that.

It's a J-car isn't it? There's got to be a heap of models that use very similar chassis. Worth a wander around the junkyard?

Good catch- no front sway bar on a fwd is bad juju. WTH? :confused:

Plus if the front end is heavier with the big engine, a/c delete and battery relocate to the trunk may be all the weight xfer measures needed to settle 'er down.

Moving the engine midship isn't the greatest way to cure snap oversteer. It will just add some nasty understeer before the weight-related oversteer occurs.

If you're getting snap, that's all down to the suspension and tires. A stiffer front bar or a softer rear bar... change the alignment... change the tires...

If you really want to do the mid-engined thing, you'll still have to fix the suspension, anyway, because you're opening up a whole can of worms. Guys who've done this project have had issues on track. The mid-engined Integra that entered the SCC Ultimate Street Car competition suffered from poor braking (incorrect bias) and lateral grip (needed suspension tuning). There was a feature in Auto Italia a few years ago of another mid-engined build, full tube-frame, engine moved rearward... similar issues with balance... massive understeer on corner entry.

Mid- would be fun to do, but if you're doing it to cure a handling issue... no.

I just want to know why you thought it would be prudent to make a mid-engine Sunfire. If you want to move the engine, there are tons of better cars to do this with. If you want better handling, why not rebuild the suspension? You could surely make a Z24 coilover kit fit, along with new poly pushings all around. It would sure be cheaper than moving the engine.

I had a car that would do that, it actually felt worse than it was. I got to the point where I knew how to induce it. Lift suddenly while cornering quickly, weight transfers to the front and around comes the rear. I had a buddy film it for me once, what felt like a huge drift was hard to even see on film. My suggestion is to find a nice open area and practice inducing the rear to slide and practice the recovery. Ff cars are great for therecovery end, you just give it more gas and she will straighten her self out. Oh yeah 1997 Nissan Maxima, 3.0 V6 w a 5spd mt.
You can soften the onset of the oversteer with a tire pressure adjustment, bump up the psi a couple lbs in the rear and ,Iirc will reduce oversteer.

If just one of your tires is a little off, lets say one worn more than the others, or one tire is under-inflated on a FWD car, especially if that is a rear tire - then handling disasters are sure to happen.

It doesn't take much.

If you were lurking around a mid-engine layout for fun, that would be prefectly understandable. But if you wanna improve the handling, there are other options that would be easier and more cost-effective.

It is not oversteer exactly, it is more of a really light rear end not having enough traction to hold the road. Like I said earlier, My brother and I picked it up and swung it around to get it where it is now. The front end is much heavier. It doesn't help that the engine weight is semi-cantilevered. It has always been light in the rear.

I thought it would be fun to have a mid engine car since it is under construction already. I love the feel of a rear wheel drive compared to front wheel drive. It would be partly for fun.

I was thinking of keeping putting front hubs on the rear beam and extending the beams past the hub so there is about a foot sticking out toward the rear and putting air springs on them. That would support the extra weight and would reduce roll. I could also put air on the front end. I have some rear air shocks from the caddy that I could fab in. If those won't work, I could always put air springs in the front. I have them in the truck and they work wonders.

https://encrypted-tbn3.gstatic.com/i...UgghnrOSw20xl-

You can conjure up many reasons to support the middie idea but fixing your car's weird handling isn't one of them.

Hey Frank, what should I do? I know I need a front sway bar. I would like the car to handle well so I can have some fun when I want to. I am still looking for good mileage, so don't think I am going on a "fun run" brain trip.:p

I think it would handle better as a mid engine car vs fwd, but I need to make sure the suspension is working correctly first.

First, why is there no front sway bar?

Second, get to a scale and tell us how much weight is on the front axle and rear axle.

I don't know why there is no sway bar.


I can't really get it to a scale because it is taken apart in the shed. A sunfire is supposed to weigh about 2650 lbs. The published weight split is 63/37.

This puts the weights as follows:

Front: 1670 lbs

Rear: 980 lbs

It came with a sway bar. :confused:

I know that 65/35 results in good daily driver handling.

There is no evidence whatsoever of any front sway bar. The parts store lists a regular control arm and a sport control arm. Maybe the sway bar was on the sport version.:confused:

I have some time to think it over. I would really like to make it a mid engine, as you can tell. I have measured things out and it would fit perfectly. All I would have to do is cut the bottom out and attach the sub frame and struts. I need to remove some surface rust under the car anyway, so it would be a good opportunity to take care of anything that needs attention. My mother in law drove it for a while and she is murder on cars. She said, that before she got her van, she ran over a tree that was laying in the road!!!!!!:mad: That explains the control arm bushings that were ripped out of their sockets.:( Don't worry, I fixed those already. She also backed her caddy into my wood pile, then I hear VROOM, and she is ON my wood pile.......

Anyway, I am going to hash this over and see what happens. I may end up putting the motor up front for now, with a sway bar, and see how it handles.

There has to be. FWD cars simply are not sold without them.

http://www.youtube.com/watch?v=MfVU3m-Ayj8

Here's what it looks like ( I only watched the first 40 secs).

it should have an 18mm dia anti-roll(sway) bar on it(unless it had a 2.2ohv, that's weird); i'm more wondering what his tires are like 3/32" of tread is classified as bald. what was the air pressure at the time the more air pressure in the tire the smaller the contact patch.

It had a 2.2 ohv in it.

Come to think of it, it had almost bald michelins on it when we got it and cornered ok. The new tires were goodyear eagle h2's and it was horrible. I tried pressures from 30 psi to 45 psi and it was still bad. My mother in law wore those tires out and put goodyear viva 2's on it, I think. Maybe the goodyears are garbage.

I have talked it over with my wife and we are both split on the idea of a mid engine conversion. It would be nice to get everybody in the car, but it would balance out better and be more fun with a mid engine.:rolleyes: She asked if it would be able to pick the front end up with the mid engine.:D She is so much fun!

There's no doubt a mid-engine conversion, properly done, would be very cool but it's not a trivial undertaking to do it. It's more than just moving the engine from the front to between the rear wheels. You will essentially be designing a whole car from scratch.

Mid-engine and front engine, especially with FWD, require very different suspensions, because of the different weight distributions and forces on the tires. FWD steering and suspension is affected by the wheels being driven rather than being dragged (pushed), with the suspension geometry set up to compensate. Both ends of the car's suspension system have to be redesigned.

Like niky and Frank Lee, I think it likely to make the thing handle worse rather than better by moving the driveline.

Because it's J-body there's got to be a heap of different anti-roll bars that will bolt on or can be made to do so. Even if it didn't come with one from the factory, different models that share fundamentally the same chassis did. There will also be some available from the aftermarket as upgrades.

You can get scientific about the size(s) to try but empirically maybe a good start would be to find out what was used in V6 versions of the J-body (18mm ^?) and try some of those. They're going to be really inexpensive to buy because they don't wear out.

Without checking the full back story on the car, it originally had a 2.2ohv in it and now has a 3800, correct? Did it get stiffer front springs, to compensate for the extra weight, at the same time as the engine swap? The springs will also contribute to the roll stiffness of the car and its handling balance. As a simplification, the end of the car (pair of wheels) with the greater roll stiffness will lose grip faster than the softer end (pair of wheels).

One thing that may be happening to cause snap oversteer with a soft front end is for the rear suspension to run out of travel in droop while there is still load on the inside rear wheel. That will result in the immediately transfer of all the rear cornering force onto the outside rear wheel and a net reduction of rear grip - oversteer.

As an aside when Nader vilified the Corvair, in part by levelling the accusation that the 'dangerous handling' was due to the engine location and resulting rearward weight distribution, GM conducted some testing with vehicles of various configurations. The conclusion was that, in a four wheeled vehicle, the handling can be balanced, largely by altering the differential in roll stiffness at each end of the car, regardless of the static weight distribution.

Swapping an engine without the suspension to go with it will do that. A 3.8? The car will plow like a tractor with that much weight on a stock suspension!

I've seen some crazy swaps that I'd like to have tried... the kookiest have to be the Altima-engined Sentras... imagine a 2,000 pound B13 with a 3.5 liter Altima motor up front... 13 second quarters and no balance at all... :p

Not know the specifics of the suspension, but suspecting it's a rear H-Beam... no. You will be swapping the entire front suspension, with subframe, into the rear. The rear H-Beam is not built with drive-axles in mind. You'll be looking at some expensive machine shop work. Been there, done that (with a previous engine swap... I wouldn't wish custom CV Joints and drive axles on anybody. They're bad business. Especially if the car is being built to drive hard.

Using a front suspension out back means that your suspension is properly tuned for the weight that's put on it. This gives you beefier shocks and springs under the motor, to boot.

Yep, I thought of that after I posted about the h-beam. I am looking for a donor car for a front end and then weld that into the rear end of the sunfire.

Sounds like a neat project, but as others have said, I don't see the eco gain.
With that trans axle your basically rear engine. You'll need to tweak the braking proportion, re tune the suspension, maybe add some rear roll control. Are you going to keep the radiator up front? your adding how much weight with long rad hoses/pipes, plus how to run them where they wont get damaged and how many more gals of coolant, water weighs 8+ lbs a gallon. You'll need to tweak the braking proportion.

But it does still sound like a neat project.

Keep in mind, the 3800 has NOT been installed in the car at all yet.

The transmission puts the engine well ahead of the rear axle, so the weight would be distributed much better.

The rear brakes would be replaced with front brakes so the braking would be fairly even front to back. I could then install a brake proportioner as needed.

The radiator can go in the rear. That would free up more room up front for trunk space.

The fuel tank would get put up front.

Both front and rear would get sway bars.

The engine and transmission add about 150 lbs to the car. The suspension would get tweaked as necessary. The balance of the car would be roughly 45/55 instead of 63/37. What I have read on the subject indicates that the car should handle well and will have good traction.

I am not building this car for the track. I am replacing a problem ridden "beater" motor with a bigger reliable motor. The new motor has never given us any trouble in 186,000 miles. It has started every time and has provided good mileage in a heavy car.

The sunfire will be roughly 800-1,000 lbs lighter than the donor car and should therefore get much better mileage, especially in town and hills. The sunfire also has a lot of aero potential that I plan to take advantage of. The front end can be closed up and smoothed over and the rear of the hood can be raised a few inches. The lack of hot plumbing under most of the car will allow me to install a full belly pan. The mirrors will be replaced with convex 3" dots to reduce drag. The rear of the car can easily be modified to help airflow to stay attached. The spoiler can be re-purposed as a partial boat tail.

The rear window has a very shallow angle and the air sticks to it well. This will give me an extra boost in the aero dept.

The only down side I see is losing the back seat. My wife and I are still trying to figure this out. If we are going to get the sunfire going, we want to get the most for our effort. Like I said, this is not final, just ideas.

Sounds an awful lot like you are trying to re-engineer a heavy, oversized Fiero.

-soD

Re-engineer is right. I just found the SHOgun! Pretty much what I have in mind.:D

Ah, OK. I didn't realise that.

Re. mid-engine conversion. A couple of things that I can think of off the top of my head:

A simple transfer of the front end of a FWD car to the rear will mean that any anti-dive in the (former-front-now-rear) suspension geometry will result in a very odd virtual centre for the anti-dive/anti-squat. It will probably be below ground and rearward of the rear wheels.

If you can't or don't want to design a suspension system from scratch, maybe match, as close as is possible, the geometry from another car with similar dimensions, weight, tire size, weight distribution and suspension design. Without checking (or knowing what the Sunfire will end up with) the exact specifications, one car that comes to mind is the mid-90's Toyota MR2. Those have struts front and rear, derived from FWD chassis.

That is one of only two professional attempts at converting a FWD chassis to a road going mid-engine RWD that I can think of atm. The other one is the Giocattolo. (There are numerous more home built one offs.)

Have you found the forum thread on the guy who did the mid-engine conversion on the Integra?