Reducing rear weight / improving weight distribution

[Series8217]

The aim of this thread is to improve weight distribution, in the interest of maximizing the amount of useful tire that will fit on a stock body. This relates to the discussion here: http://realfierotech.com/phpBB/viewtopi ... =3&t=17389

I added a bunch of weight to the rear by putting in the overweight pig that is the LQ1 3.4 DOHC V6, so my car needs to lose a lot of weight to get it to 45/55 or better.

A 45/55 weight distribution allows a tire stagger of 225/275, or 235/285 if you can fit a 285 in the back. I'm not sure if a 245 can fit up front, but if it can then a 46/54 or 47/53 weight distribution would also be workable, without reducing the rear tire size.

Anyway, back to the weight, since there's already another thread about wheels and tires.

At 2800 lbs and 45/55, relocating ~30 pounds of weight from rear to front improves the weight distribution by 1%. Likewise, removing 50 lbs from the rear altogether improves the weight distribution by 1%.

So far I have done the following:
* Lightweight starter from a late-model 60-degree V6: saved 7 lbs
* Lightweight flywheel: saved 8 lbs
* Short-runner intake manifold: (?) 4 lbs (estimated)
* Relocated battery to just behind the front crossmember
* Removed spring perches from the struts while doing the coilover conversion: ~ 1 lb
* Removed screens from the decklid vents: < 1 lb
* Removed firewall insulation: < 1 lb
* Removed all unnecessary brackets, intake silencer, etc: ~ 1 lb

Total weight removed from the rear: 21 lbs + battery relocation (my battery weighs 23 lbs).

I know the trunk metal weighs quite a bit (I removed it from my previous car) but I don't want to cut out the trunk on this one. I also don't want to remove crash structure (rear bumper beam).

A thinwall stainles steel exhaust with a small straight-through muffler and a single tip would minimize exhaust system weight but remain reasonably durable.

Is there anything more than a pound in weight that I've missed besides the trunk metal and exhaust system?

My car didn't come with a wing so I left that one out.

The only other idea I have left is a carbon fiber decklid shell. I ought to weight my spare decklid to see how much it would be worth to make lighter.

For reference the corner weights of my previous DOHC V6 88 coupe are here: http://realfierotech.com/phpBB/viewtopi ... 12&start=0

[Series8217]

Also, who has some race scales in SoCal that I can borrow or rent? I haven't weighed my red car.. it would be nice to get a new baseline.

[CincinnatiFiero]

Have you seen the guy who, my defender 90 friends call it "bobtailed," his notchback? He shortened the back of his car by like 6 inches to remove weight off the back end? Thats a bit extreme but he's local, I actually sold him some panels for the bodywork. He said it made a significant difference at autocross

[Shaun41178(2)]

you could remove the eggshell behind the rear bumper but not the crash impact beam. Thats worth about 5 lbs or so. and honestly that crash impact beam is a flimsy pile of metal. Its not as thick or strong as you might think. someone said thats worth 10 lbs. But the eggcrate crap could go if you want while still leaving the impact beam in place.

Not having a full exhaust like you said will save some weight. I think a simple dump down where the factory cat converter would be would save an easy 20 lbs or so. Maybe a simple design that you can unbolt the stock exhaust and reattach it after the autocross for street driving?

Do all body panels have to be on while autocrossing? If not, then leave the decklid off the rear. Your aerodynamics won't be that affected because you probably won't be reaching the speeds to make a difference.

to get the proper percentage for your target F/R weight bias, you might have to add more weight to the front. Put a normal weight battery back up front will help get you there. They are close to 40 lbs which is more than your current one.

[Series8217]

you could remove the eggshell behind the rear bumper but not the crash impact beam. Thats worth about 5 lbs or so. and honestly that crash impact beam is a flimsy pile of metal. Its not as thick or strong as you might think. someone said thats worth 10 lbs. But the eggcrate crap could go if you want while still leaving the impact beam in place.

The rear end crash structure does a great job of absorbing energy in a strong rear-end collision. As far as autocross goes, I'm not sure which classes allow it to be removed. It would be a useful method of weight reduction for any classes that allow it, but it might be limited to Prepared and Modified.

Not having a full exhaust like you said will save some weight. I think a simple dump down where the factory cat converter would be would save an easy 20 lbs or so. Maybe a simple design that you can unbolt the stock exhaust and reattach it after the autocross for street driving?

Oh yeah, I wasn't even thinking about a stock-style Fiero exhaust. For a stock-style routing the race pipe would save even more weight than it does for me (my exhaust system dumps off the back so its already has a lot less piping).

Do all body panels have to be on while autocrossing? If not, then leave the decklid off the rear. Your aerodynamics won't be that affected because you probably won't be reaching the speeds to make a difference.

Good idea. I think you can only remove exterior body panels in Prepared and Modified, and even then I think it's just bumpers. However, I usually run in the regional class we have for any California street legal vehicle -- if the vehicle code doesn't prohibit the removal of the decklid, I can do it. I wouldn't expect to be competitive in that class though.

With more power (and preferably a lighter drivetrain like a turbo Ecotec) it might be possible to make a Fiero competitive in SSM, at least at a regional level if the competition isn't too fierce. 400+ whp Miatas on slicks dominate that class locally.

to get the proper percentage for your target F/R weight bias, you might have to add more weight to the front. Put a normal weight battery back up front will help get you there. They are close to 40 lbs which is more than your current one.

I'd rather just add ballast than switch to a heavier battery. The ballast could be placed low, in line with the front axle (my battery is behind the front axle).

That said, I think it's more productive to consider relocation and reduction of weight rather than just adding ballast.

[Series8217]

Have you seen the guy who, my defender 90 friends call it "bobtailed," his notchback? He shortened the back of his car by like 6 inches to remove weight off the back end? Thats a bit extreme but he's local, I actually sold him some panels for the bodywork. He said it made a significant difference at autocross

He must run in Prepared or Modified. Those cars are far from street cars.

[fieroguru]

I am planning to take a hole saw to the backside of the notchie panel It is double walled for the majority of the structure and quite a bit of the inside panel can be removed without being visible. Same could be done for the underside of the rear deck lid, but those would be visible when the decklid is open. The rear window could be replaced with lexan.

Here is an over the top thread on lightening the Fiero. Its not the most refined craftsmanship, but the thread has lots of information about the weights of the various parts and how much he saved with his modifications to the parts.
http://www.fiero.com/forum/Forum2/HTML/112942.html

[CincinnatiFiero]

Have you seen the guy who, my defender 90 friends call it "bobtailed," his notchback? He shortened the back of his car by like 6 inches to remove weight off the back end? Thats a bit extreme but he's local, I actually sold him some panels for the bodywork. He said it made a significant difference at autocross

He must run in Prepared or Modified. Those cars are far from street cars.

As Ohio doesn't do inspection they are all "street" cars lol. But I forgot about the classes for autocross and that you need to stay in a street class.

[The Dark Side of Will]

and honestly that crash impact beam is a flimsy pile of metal. Its not as thick or strong as you might think.

It doesn't have to be heavy to be strong. The configuration of the beam is extremely optimized for the job it has to do.

There are aluminum impact beams used in the bumpers of modern cars. Because of how light and optimized the stock impact beam is, the aluminum ones won't save any weight, but they can give better protection. The same goes for the door impact beams.

Steven, you've run into the problem that it's pretty tough to remove weight from a Fiero without seriously compromising its utility as a street car.

[Series8217]

Looks like the next step is to get some scales again and see where I'm at.

[Shaun41178(2)]

it won't be weight from the rear but you can remove the passenger seat. Going to a sparco or Corbeau seat would save about 15 lbs per seat.

[Series8217]

it won't be weight from the rear but you can remove the passenger seat. Going to a sparco or Corbeau seat would save about 15 lbs per seat.

I have Corbeau A4s.

You can get an idea of how seat weight affects front to rear balance by looking at my old car's specs, since it has weights with driver and without. The weight distribution shifted forward by 0.4% with me in the car (120 lbs at the time) vs without.

[eHoward]

Depending on how crazy you are you could start replacing old bolts with new Ti aerospace ones.

[The Dark Side of Will]

Burns has Titanium tubing... that could cut a pound or two out of your exhaust.

[Series8217]

I forgot about the manifolds... replacing the cast iron ones with some thin-wall stainless logs would save quite a bit (10 lbs is my guess).

[CincinnatiFiero]

Pick up some power too!

What are the limitations in terms of SCCA rules for what you are allowed to alter?

[Series8217]

Pick up some power too!

What are the limitations in terms of SCCA rules for what you are allowed to alter?

Depends on class. Keeping with the streetable theme in mind, SSM (Super Street Modified) makes the most sense for this discussion.

The rules are here: http://www.scca.com/assets/2012_Solo_Ru ... educed.pdf

AFAIK, any frame modifications would be prohibited in SSM, except for minor clearancing and holes to accomodate allowed modifications like engine swaps, rollcage, etc.

[Shaun41178(2)]

When you cut the trunk out was it that bottom half that most cut out? I would guess yes. Idea on how much it weighed or have an exact weight?

I know you said you weren't going to do it to this car, I was just curious to the weight. I would guess 20 lbs but not sure

[Series8217]

When you cut the trunk out was it that bottom half that most cut out? I would guess yes. Idea on how much it weighed or have an exact weight?

I know you said you weren't going to do it to this car, I was just curious to the weight. I would guess 20 lbs but not sure

It weighed 18.6 lbs. Here's my old thread about it: phpBB/viewtopic.php?f=3&t=2288

The pics seem to be missing from that thread, but here's one: http://www.pbase.com/series8217/image/66338646/large

A fiberglass or carbon fiber trunk replacement would kick ass.

[Shaun41178(2)]

I am curious as to how this affects airflow under the car, and how it exits out the rear. I wonder how much the air would catch the bumper and find its way into the rear bumper creating a parachute affect or sorts.