mid-engine sunfire?

[baldlobo]

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.

[IsaacCarlson]

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. She asked if it would be able to pick the front end up with the mid engine. She is so much fun!

[Occasionally6]

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.

[niky]

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...

Originally Posted by IsaacCarlson

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.

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.

[IsaacCarlson]

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.

[Jasen]

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.

[IsaacCarlson]

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.

[some_other_dave]

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

-soD

[IsaacCarlson]

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

[Occasionally6]

Originally Posted by IsaacCarlson

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

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.

Originally Posted by IsaacCarlson

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

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?