Motor Migration - Vision Test
 

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.

http://forums.pelicanparts.com/uploa...1070694510.jpg

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:

http://forums.pelicanparts.com/uploa...1070694564.jpg

(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.' ;)

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. :D 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.........

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 :D

I will come over and talk to Lefty tomorrow. :cool:

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.

http://forums.pelicanparts.com/uploa...1070701481.jpg

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

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.

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?

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?

the couple cases of beer :D

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

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

I knew I forgot something:

Remove part of the trans crossmember to clear swaybar.

There, I think that's it.

What is the wt. distribution of the finished car?

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

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.

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

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.

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. :cool:

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?

Of course...
http://www.pelicanparts.com/support/...s/a_frusty.gif
\

Thanks, Denis.

The back seat was sacrificed as well. Not that it was going to be used AT ALL in this car. When I rode in it I was really impressed with how comfortable the ride was. While taking hard corners, I did not feel as if I were being flung about. That had a LOT to do with the seats, too.

Jack, put some rosebush clippings on a piece of corragated cardborad and lay that on top your car. Rosebush clippings work wonders in flower beds to keep cats out.

I remember it being about 4 pounds. (But how much I added back with reinforcements??????)

I took a lot of pictures with Dave's (TRE owner) digital camera, but I'm not sure what happened to those pic's. Maybe he deleted them for secrecy?????

Jack may still have the pictures he took while I was doing it, but those don't show the process or the detail.

I cut open the rear seat area to gain access for reinforcement when I tied the center tunnel in with the front of the torque tube. And due to the significant space required by the Smart racing inner camber boxes, it made sense to just remove the whole rear seat area since the roll cage made the jumpseats useless anyway.

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.
----------------------------------------
Evil
I would be interested to see these corner weights and #'s. Maybe your total wt is high??? This does not reflect what we see when we set up these 911's for the track due to the fact that the engine and Gbx represent such a large portion of the total weight, and ther are perched so far rearward of the rear axle, atleast on a light say 2000-23000 lb race car, that one cannot improve the frt rear percentage that great. Maybe 63/37 is the best we ever see with a bunch200-300lbs) of lead doing the ballasting up to class weight. Unless, the car is say 2700 lb ish, and full gas say 22 gallons at 6.2 lbs per gallon way forward. The heavier the car becomes and the more petro, the smaller the % of the total wt the engine/gbx represents. Fiddle with the numbers alittle by adding weight forward in 50 lbs increments to one end vs the other and you'll see not much happens %-wise.

Kevin Roush
GAS Motorsport
Performance Porsche

_________________
"Evil

Well, he has an underbelly condensor, A/C evaporator, dual oil coolers up front, front condensor, fire-safe bottle up front, full cage, and we took a lot of weight out of the back compared to the old car as well. Lexan rear window, 911R taillights, fiberglass quarters, 72 oil tank location versus '73. I'm sure there are other factors.

It showed 2389 on the corner scales (with no driver), and that was with 1/2 tank of gas. The F/R distribution figure is with me in the driver's seat. (#175)

I don't know about the weight savings, but the weight of the torsion bar anchor is kind of wasted when you're not using torsion bars. I think the total weight change could have been a wash, with the reinforcements, but the benefits are clear -- engine forward about an inch, and diagonal reinforcements imroving rigidity. Here are some pictures:

http://forums.pelicanparts.com/uploa...ndWhistles.jpg

http://forums.pelicanparts.com/uploa...orcement02.jpg

http://forums.pelicanparts.com/uploa...orcement01.jpg

http://forums.pelicanparts.com/uploads/99RearSeat.jpg

It's actually closer to 1 1/2". There's room for more movement as well, with some more tweaks to the trans cross member. But why get greedy.

Axle life has been fine. Still feel great after a lot of serious track work.

Tyson, great job on this car!

Since the backseat sheetmetal has been replaced, what did you hook the tranny mounts to? Also, is the replacement panel in the backseat area welded, screwed, or riveted in place? Is there a significant benefit or risk of welding diagonal supports to the tortion tube in a car that is not going to use a coil over suspension?

Thanks!

Thank you!

The trans. actually mounts to the torque tube, so no issue there.

The only thing I had to work around were the tabs for the brake hoses. They normally attach on the bottom side of the the rear seat tubs. I welded tabs off of the control arm pick-up points instead.

Any bracing is going to help, but I don't think it's necessary if the torque tube is still completely intact. Especially if you aren't tracking the car with huge slicks, or have lots of HP.

Wow, I guess that is a little beyond my skills. Are these the type of mods needed for a G50 tans install too?

Thanks for the help. I had to go back outside and look at my engine and trans on the dolly, but I see what you are saying. Dumb question, sorry about that :)

You don't have to do this to fit a G50, but if you don't, it puts the engine back in the chassis nearly an inch. Not exactly a good trade-off just for a little better shifting, especially since the G50 is so damn heavy to begin with.

Tyson, wow it sounds so easy I think that I might just head out to the garage right now!!!! Just kidding! I recently read about the work in Excellence and it sounds truly amazing. Nice job.

Jeff

The numbers then are(roughly) 775# across the back, and 506 #across the front, with you in the car(175#) at a total weight of 2564 with 1/2 tank of gas? I will check my notebook manana but from memory I have serious doubts whether this is possible and have had many discussions about it with the rulemakers in the POC regarding older cars putting in later motors and updating to later specs and total weight , but having a percieved weight distribution advantage. I have notes on atleast 10 cars in this weight range.
Bottom line is the weight comes very easilly off the frt of the car but the rear is a fixed quantity, even moving the engine as you did you only gained about 45lbs of weight distribution change(assuming the gents math was correct regarding the polar moment-which feels correct from previous calculations I have done).

Well, he has an underbelly condensor, A/C evaporator, dual oil coolers up front, front condensor, fire-safe bottle up front, full cage, and we took a lot of weight out of the back compared to the old car as well. Lexan rear window, 911R taillights, fiberglass quarters, 72 oil tank location versus '73. I'm sure there are other factors.

I have added 300 lbs of lead to cars forward of the frt seats in a 2450# car and cannot get where you claim to be on a 2564 lb car? Those little factors like lexan, taillights, light rear bumpers, are a given on most of the track cars. The oil tank movement is a help though.

Kevin Roush
GAS Motorsport
Performance Porsche
--------------------------------------------

It showed 2389 on the corner scales (with no driver), and that was with 1/2 tank of gas. The F/R distribution figure is with me in the driver's seat. (#175)


__________________
"Evil" Gruppe member #001

I'm going from memory on this Kevin, so I may be remembering it incorrectly. I'll try and find the sheet. It was done at Marty Mehterian's shop on his scales. (Maybe they aren't that accurate???) And it was about a year ago, so maybe my memory isn't what it used to be.

Jack's car still uses a magnesium trans. also, FWIW.

We just recieved our new scales and platforms at TRE, so I'll be rechecking it soon enough anyway. I'll let you know what it comes out to.

Do you mean the trans is an early 901?

What did you do to hook up the CV joints to the trans?

Randy, 915 trans were magnesium up until '75(?). :cool:

1977 was the last year of the mag-case 915, I think. Mine is a 77, although it also has the billet side plate and a heavy cooling pump and cooler just ahead of the rear axle.

QUOTE:
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.


I have a question, as I don't think mine was changed at all...so is it different in a middle year car?

No, they are all the same. I would bet that they just didn't worry about it. The rear mount will flex forward and backward quite a bit. It is designed to be very stiff in relation to the engine twisting, but allows a lot of fore-aft movement. The trans mount takes care of the fore-aft movement.