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Discussion about car weight, weight distribution and turning


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Having so many brilliant minds here I wanted to open the floor for discussion on the topic of weight distribution.

  • First of all, what is the approximate weight distribution of our cars? Whatever it is, it is probably far from 50/50.
  • In theory the lighter the car the fastest it would be able to change directions, thus turn faster.
  • Although a very generic statement, a 50/50 bias is a "good" goal, maybe a little more rear bias is better, but at least close to 50/50. I understand there are many variables involved here.

The above aspects brings me to a thought. Assuming I can't change weight bias by removing weight, as in our cars unless you change to aluminum block or make some more drastic changes in the front, it would be hard to move the bias to the rear. If you add weight to the rear you can probably come closer to 50/50, but you will be adding weight to the car, which will make it harder to change directions. So the question would be, what is the balance between increasing weight, and changing bias when you can only add weight? As you can see, it is an interesting conundrum so I want to hear your thoughts.

 

PS: I also understand that there are other options to lighten the front beyond an aluminum block, but I expect the changes would need to be dramatic to make a significant difference in the bias. Yes, you can go to an aluminum intake, remove the A/C compressor and some small change here/and there, but that probably will make too little of an impact, or maybe I am wrong and it would be more important.

20160929_171923_edit2_small.jpg

 

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump

Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes

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According to this vintage road test, weight distribution of a Boss 351 is listed as 57.1 / 42.9

https://www.curbsideclassic.com/blog/vintage-reviews/vintage-reviews-1971-ford-mustang-boss-351-its-possible-that-stylist-cant-work-in-a-sporty-medium/

If I'm remembering my vehicle dynamics classes (argh memory test), the feeling of crisp response and nimble handling comes from having a low CG and keeping all of the heavy parts as close to that CG as possible.

As far as the traditional muscle car front weight bias issue is concerned,  battery relocation is your best bang for buck. Weight reduction in front of the CG (aluminum engine parts etc.) will shift the bias rearward.

Edited by mjlan
Spelin
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Using the 1971 AMA Specifications I came up with this:

Coupe with 302 and automatic 57.0%/43.0% front/rear

Mach I with 302 and automatic 57.2%/42.8% front/rear

Mach I with 351 Cleveland 4V and 4-speed - 58.0%/42.0% front/rear

Mach I with 429SCJ and 4-speed - 60.1%/39.9% front/rear

I'm out of space, so couldn't post the chart.

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“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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36 minutes ago, Don C said:

Using the 1971 AMA Specifications I came up with this:

Coupe with 302 and automatic 57.0%/43.0% front/rear

Mach I with 302 and automatic 57.2%/42.8% front/rear

Mach I with 351 Cleveland 4V and 4-speed - 58.0%/42.0% front/rear

Mach I with 429SCJ and 4-speed - 60.1%/39.9% front/rear

I'm out of space, so couldn't post the chart.

Thanks. Depending of the configuration, it is a little better than 60/40. With some of the aluminum part replacements and mods I may be close to 57.5/43.5 - I still have the battery on front, which in should be about 40lbs. The Boss has the battery in the back so it looks like it is close to 57/43.

I agree that a low CG is critical, but would a car with a light rear tend to oversteer? Traction aside we would need wider tires in the front than the rear, but that's silly because we need wider rear tires to transfer that V8 power to the ground.

I am just wondering if you add a ballast to the rear end of the car, would that improve cornering ability, or not really because now the car is much heavier.

20160929_171923_edit2_small.jpg

 

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump

Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes

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As far as front weight bias, you can replace the Mach 1 urethane bumper with a chrome, or even fiberglass, version and save at least 100 lbs. What worked for me way back when, was lowering the car 1" in front, 1/2" in back, using stiffer springs and shocks and larger sway bars front and rear. This lowered the center of gravity and reduced body roll. While it may sound cliche', the car handled like it was on rails, and felt every bit as nimble as the TR6 I also had at the time.

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As mentioned above, a battery relocation to the rear passenger side makes a difference. I also lowered the car 1" all around, aluminum intake, removed AC, larger front sway bar (1 1/8"), all new stock style suspension components (I boxed in the LCA's to stiffen them), 12.7:1 steering conversion, 17x8 in front 17x9 in rear, KYB Gas-A-Just shocks all around (kind of stiff). These mods made a complete night and day difference in how the car handles in the corners. So I reduced weight in front by removing or lightening items and relocated some of that to the rear to help weight distribution (getting closer to that 50/50 mark), this along with the lowered center of gravity and stiffening of the LCA's and larger sway bar all work together to improve handling. While just doing a weight distribution change will help some it is a combination of several things to really see and notice a difference. Hope this helps. 

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73 Grande H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

 

- Jason

 

 

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1 hour ago, rvrtrash said:

As far as front weight bias, you can replace the Mach 1 urethane bumper with a chrome, or even fiberglass, version and save at least 100 lbs. What worked for me way back when, was lowering the car 1" in front, 1/2" in back, using stiffer springs and shocks and larger sway bars front and rear. This lowered the center of gravity and reduced body roll. While it may sound cliche', the car handled like it was on rails, and felt every bit as nimble as the TR6 I also had at the time.

Wow. I never though that the urethane bumper was that heavy. Good to know.

20160929_171923_edit2_small.jpg

 

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump

Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes

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Yea, the 73 front bumper I have is heavy as hell, especially when it has the mounting brackets on it. I will be going with a chrome front bumper, already have the 71-72 front bumper mounts installed.

Tom

 

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Wow. I really can't see myself running so close to the edge to really notice a difference in front bumper weight.

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I can only say that I did not regret removing the heavy 73 bumper on my grandé and relocate the battery in trunk above rear axle. The heavy Intake, waterpump, fan etc.. replaced by aluminium ones, these without GC in mind, but combined all together it gave a massive difference in handling, especially on the highway exits we have here, where the car would plunge on the front under hard braking and loose grip on the rear while in the curve. Unless you go for originality, these easy changes do really make a difference. Reminds me I should be enjoying all this very soon again! Yeah!

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73 modified Grande 351C. Almost done. 

71 429CJ. In progress

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I can only say that I did not regret removing the heavy 73 bumper on my grandé and relocate the battery in trunk above rear axle. The heavy Intake, waterpump, fan etc.. replaced by aluminium ones, these without GC in mind, but combined all together it gave a massive difference in handling, especially on the highway exits we have here, where the car would plunge on the front under hard braking and loose grip on the rear while in the curve. Unless you go for originality, these easy changes do really make a difference. Reminds me I should be enjoying all this very soon again! Yeah!
Did you replace the urethane bumber for the chrome?

Sent from my SAMSUNG-SM-G930A using Tapatalk

20160929_171923_edit2_small.jpg

 

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump

Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes

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Ounces add up to pounds.

Aluminum Intake manifold.

Headers instead of cast exhaust manifolds.

Aluminum heads.

Fiberglass hood (with or without hinges).

Remove AC.

Aluminum accessory drive kit for alternator etc.

Fiberglass front bumper.

Aluminum water pump.

Fiberglass fenders.

Battery relocate.

All that adds up to quite a bit.  

 

Have you exhausted all of the "tuning" options to make your car handle?  What is it doing?  Oversteer?  Understeer?  What are your alignment numbers?

 

 

 

 

 

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This old post may be helpful. 

 

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1 hour ago, Bentworker said:

 

Have you exhausted all of the "tuning" options to make your car handle?  What is it doing?  Oversteer?  Understeer?  What are your alignment numbers?

 

I don't have an specific issue with the car handling at this time, but there is always part of me looking for more performance if there is. I am brain storming at this time.

20160929_171923_edit2_small.jpg

 

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump

Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes

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47 minutes ago, c9zx said:

This old post may be helpful. 

 

Thank you. Great link. So what I gathered is that I can make the car lighter if I have an empty gas tank, empty oils and empty engine water:biggrin:

20160929_171923_edit2_small.jpg

 

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump

Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes

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Don't forget the driver, wonder how much a remote control system would weigh? :classic_biggrin:

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“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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Posted (edited)

Doing some math based on Chuck's car weight results.

Total: 3,583 lb (58.25/41.75 F/R%)

Front: 2,087 lb; Rear: 1,497 lb

Let's make a couple approximations (simplified not taking into account the weight distance from the CG)

Assuming a battery weight of 40 lbs, but adding 20 lbs of wiring equally rear/front:

Weight: 2,047/1,537 (57.18/42.89 F/R%)

Assuming the front bumper is 100 lbs, and adding a 20 lb bumper (??) - these may be amplified in real life due to how far is forward.

Weight: 1,967/1,537 (56.14/43.86 F/R%)

 

EDIT PS: in summary, approximating:

-by shifting ~35 lbs from front to rear will shift the weight by 1%.

-by removing ~70 lbs of front weight will shift the weight by 1%.

Edited by tony-muscle

20160929_171923_edit2_small.jpg

 

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump

Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes

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I dig you breaking out the math!

With 3500 pound car if you moved 35 pounds from the front to the back you would reduce your front by one full percent and raise the rear one full percent.  A 57/43% car would become a 56/44% car for example.  I follow that math, seems like a good reason to move the battery, or at least go with one of the lightweight lithium ones up front.  

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Don't forget that controlling the weight transfer (fore and aft, side to side) is a big piece of the puzzle. Even if you get 50/50 distribution, weight transfer can still cause you problems. Especially if your weight balance requires moving things further from the cg...the longer the pendulum, the more it takes to control it.

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On 7/13/2020 at 2:43 PM, Don C said:

Using the 1971 AMA Specifications I came up with this:

Coupe with 302 and automatic 57.0%/43.0% front/rear

Mach I with 302 and automatic 57.2%/42.8% front/rear

Mach I with 351 Cleveland 4V and 4-speed - 58.0%/42.0% front/rear

Mach I with 429SCJ and 4-speed - 60.1%/39.9% front/rear

I'm out of space, so couldn't post the chart.

Any figures for sportsroof with a 460 - C6

Kilgon

 

 

"The only dumb question is the one not asked"

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It looks like it would add 7 pounds to the front and 1 pound to the rear. Not a lot of difference.

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“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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  • 2 weeks later...

When I got my 73 Mach 1 new I did a lot of autocross runs. What I had to do to improve the handling was to actually raise the rear by putting the helper springs on the shocks. The cars have horrible push in the turns. I tried radial tires a couple brands, B.F. Goodrich and Dunlop but neither worked on the car. Did better with bias plys. I actually almost rolled the car first time I ran the radials. We ran in the same parking lot was actually where I worked so I knew speed to run for the turns. Went into a turn and the car did not turn it just broke loose and slid sideways into concrete curb and people said they could see the whole bottom of the car. 

When I worked in the race shop and we built a car for circle track the boss would take all the weight off components that were not carried by the springs or un sprung weight. We got every I think Buick aluminum brake drum that showed up at junk yard. 

We also had to cut every scrap of metal we could out of the top and then sand the top with a side grinder until it was like tinfoil. We eliminated the rubber bushing in the leaf spring eyes and put in aluminum with a thin nylon bushing in the center for the bolt. 

The front end got the A frames boxed up to strengthen them.

If you are road racing you want all the weight you can take out of the rotating parts in the drive train. Aluminum flywheel, drive shaft. the lightest axles you can get by with. Light wheels and brake rotors or drums. Why you say when road racing you are constantly on the brakes or going wide open on the gas. If you have a heavy cast iron flywheel, steel drive shaft and other heavy components they store energy and act like a flywheel and increase your braking distance. Also when accelerating you need less torque to rotate the lighter part. You have to have a good balance of torque and rpm. Lots of rpm on a road coarse is good. Not so good on a circle track you want more torque there. 

Saw this video on facebook the other day love the sound of that Ford 289 winding out. It sounds like he runs out of gear on the long stretch. Second gear goes fast also.

 

When a man is in the woods and talks and no women are there is he still wrong??:P

David

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