Motor Migration - Vision Test

[Jack Olsen]

Along the lines of Jocke's 'What's Changed?' photo comparison, I saw two pictures of my car today which demonstrate how much Tyson at TRE was able to move my motor and transaxle forward when building BB2 from the pieces of BB1.

Note the position of the exhaust tip relative to the bumperette in the picture of BB1 and the one, below it, of BB2.



How much it helped the car's weight distribution is impossible to say, since so much else was changed at the same time. Still, it's a fair amount of movement.

And since I'm going through pictures tonight, here's one of my dog, Lefty:



(Click on the picture to see a bigger version of the dog.)

I post the picture of the dog because he might not be with us much longer. You see, he's recently learned to climb up on top of the 911, like a goat, when there's a car cover on it. He's jealous, maybe? Who cares. If it continues, he may 'get sent to a farm, out in the country, where he can play with other dogs.'

[KTL]

I'd have to guess that the drivetrain relocation makes a sizeable difference. Many say that removing weight from the extremities of the car (battery relocation, fiberglass bumper replacement, sunroof removal, etc.) make a noticeable difference in how the car feels. I know the entire drivetrain is not necessarily at the extreme rear of the car. But moving such a large amount of weight that small amount certainly has to amount to something!

Too bad the dog's so fast. Hard to reprimand him if you can't catch him. I have a dog similar to yours in that she's got some cat/mountain goat in her. Big fat fluffy thing that likes to sit atop the back of a chair near a window. She's no whippet though.........

[Bob's Flat-Six]

Jack,
Can you feel the weight transfer to the front wheels?

And why the higher ride height?

Nice dog. He's got a nice goatee

[speeder]

I will come over and talk to Lefty tomorrow.

[Jack Olsen]

It's hard to say how the car 'feels' different, relative to the motor's movement, since so much was changed between the two cars. The new version is definitely better balanced, but there are a lot of factors contributing to that.

It's also hard to say if the ride height is higher, since the flares were custom-fitted to the body -- not at any standard height relative to the wheel center or the suspension.

From other angles, the rear looks pretty low.

[Bob's Flat-Six]

Does it go around in Squiggly circles faster, Thats all that matters

[Chuck Moreland]

Interesting how the flares can't really be seen in your first post. I had to look twice, then a third time to be sure both pics aren't BB1.

I think the relocation had to make a substantial difference. Even though it only moved a couple inches, that is a lot of weigth that is nearly all behind the axle.

So let's make up a few crude approximations and see how much impact it has on polar moment:

- Weight of engine + trans = 500 lbs
- Distance between center of mass of the car and center of mass for the engine + trans starting = 36 inches
- Distance between center of mass of the car and center of mass for the engine + trans ending = 34 inches
- Distance between center of mass of the car and the rear bumper = 48 inches

PM1 = Polar moment starting
PM2 = Polar moment after relation

PM1 = 500lbs x 36 inches = 18000 in/lbs
PM2 = 500lbs x 34 inches = 17000 in/lbs

delta = 1000 in/lbs = 83.3 ft / lbs

Okay, lets turn that into real terms I can relate to:

How much weight would I have to take off the rear bumper to get the same reduction in polar moment?

1000 in/lbs / 48 in = 20.8 lbs

So for polar moment, that mod is like taking 21 lbs off the rear bumper. I think my fiberglass RS bumper saved less than that.

Yes, that is substantial.

[lateapex911]

Cool stuff. I'd ask how it was done, but I don't want to know badly enough to have a contract out on me! Trade secret?

[Tyson Schmidt]

No secret, just switch to coil-overs in the rear, notch the center tunnel and remove the torsion bar anchors, and reinforce everything. Then modify the trans crossmember and trans mounts. The rear engine crossmount just needed to be bent back straight, since it was modified to fit the 3.6 into an early car, so I just put it back to where it was, and reinforced it.

Then there's shortening the shift rod.

Modifying the engine sheetmetal.

Cutting some of the clutch cable protrusion from the center tunnel in the rear.

Shortening the clutch cable itsself.

Shortening the throttle rod.

Am I forgetting anything?

[bell]

Originally posted by Tyson Schmidt


Am I forgetting anything?

the couple cases of beer

[HawgRyder]

Jack....if you send the dog to a farm...(not the dog buying the farm)...he will be happier for it...probably.
And to Tyson....I saw a pic of a neat suspension here on the board a while ago....a-arms at the rear....with coil-overs I think.
It got me thinking (read..spend money)...maybe...mine...hmmmm.
No...got to get it on the road first....driveable...then worry about improvements.
Bob

[Por_sha911]

If a dog is climbing on top of my car, he'd be at (or buying) the farm fast. Nice ride.

[Tyson Schmidt]

I knew I forgot something:

Remove part of the trans crossmember to clear swaybar.

There, I think that's it.

[Randy Webb]

What is the wt. distribution of the finished car?

And your 3.6 has the stock induction/exhaust, right?

[Tyson Schmidt]

BB1 was around 37/63.

Despite using the same drivetrain, and now having f-glass doors and fenders, the weight distr. on BB2 is now 39.5/60.5

Moving the drivetrain forward also puts more of it within the wheelbase, so the front wheels share more of the load, and don't lose as much grip from weight transfer.

[Randy Webb]

Zehr gut! -- too bad that wasn't in the Excl. article.

[lateapex911]

Veeeery interesting.....I've looked back there with that thought in mind, but I had presumed that as the relationship between the engine and the axle outputs was a fixed dimension, and that you wouldn't want to increase the 'resting' CV joint angle. But I'm guessing that you think the amount of forward movement isn't too much for the CV joints. Cool!

I'm also surprised that there is enough real estate for the forward migration.

[speeder]

Jake, I think that he had to remove some real estate that was in the way, (torsion tubes), and the CV angle is inconsequential with this amount of movement.

[scca_ita]

I now have coilovers. What would the weight savings be for just removing the torsion bar anchors? Any pictures of this and how to re enforce once they are removed?

[lateapex911]

Originally posted by speeder
Jake, I think that he had to remove some real estate that was in the way, (torsion tubes), and the CV angle is inconsequential with this amount of movement.

Of course...

\

Thanks, Denis.