Confirm understanding of lightweight mods

[SuperTom]

Originally Posted by 86TOYO2k17

I did edit my last post in the time you where still replying it looks like lol...

Still fun to play around with weight/hp to see different guestimated results.

Do you happen to remember the weight of stock full header back? And the stock air intake noise generator and all?

If you would like its in my build thread somewhere. I took pictures of everything on the scale to verify throughout my build
http://www.ft86club.com/forums/showthread.php?t=118243


Edit looks like around post 36 I started weighing and changing exhaust stuff

[SuperTom]

Originally Posted by gtengr

US curb weight is 100% full tank per the NHTSA.

That's good information thanks. driving with a half a tank (Stock tank 13.2G) should shave another ~40lbs off (6.6G x 6lbs)

[86TOYO2k17]

Originally Posted by SuperTom

If you would like its in my build thread somewhere. I took pictures of everything on the scale to verify throughout my build
http://www.ft86club.com/forums/showthread.php?t=118243


Edit looks like around post 36 I started weighing and changing exhaust stuff

Just read entire build thread. Pretty nice! A little more extreme then I’m willing though. And looks like my headerback is a lot less loss then I thought about 10lbs, you didn’t seem to change our air intake just the tube getting rid of sound generator and that side resonator but no weights , so maybe I’m just at about -20ish lbs

Didn’t realize how much weight loss could be had in the brakes though, and your battery setup I may have to do, although a DD that needs to be reliable in 30 degree weather I’ll have to look into that more. And possibly the DSS CF DS. That could get me about another 50lbs. For a solid 70+lbs weight loss more then making up for a full tank of gas.

Still have spare tire to, may look into some alternatives still want something just Incase.

[gtengr]

Originally Posted by 86TOYO2k17

That is interesting. I could see that. So it would make less difference for street pulls and 40 rolls etc... I wonder then if there is any quantitative data / mathematical calculations for splitters/diffusers and aerodynamic reductions on say a 60-115mph pull?

What I did was set up a spreadsheet that compares speed vs. drag vs. horsepower required in 5 mph increments (and put rolling resistance and associated power required on the same sheet), then looked at the Cd of other production cars to make inferences about what aggressive aero might do on the BRZ. For example, the Cd difference between a stock Viper and the Viper ACR is 0.37 vs. 0.54, an increase of 0.17. Knowing how aggressive the aero is on an ACR, I estimated that a BRZ with a big wing + splitter might be around 0.27+0.17 = 0.44. Plug that into the spreadsheet to observe the difference in horsepower required vs. stock, and usually that ballpark answer is enough to satisfy my curiosity. There are more caveats than this, since Cd isn't the same at all speeds, ride height, etc, but those are the basics.

If you prefer a road test, you could install the aero mods and then re-measure the top speed with a precise instrument (not the speedo). If you know the new drag limited top speed, have a dyno graph of your rwhp, and have checked your spreadsheet with the stock top speed to ensure your rolling resistance power estimate is close, then you can back-calculate how much power was lost to aero at this new top speed, and from that back-calculate the associated Cd with the aero on.

[bfrank1972]

Originally Posted by gtengr

What I did was set up a spreadsheet that compares speed vs. drag vs. horsepower required in 5 mph increments (and put rolling resistance and associated power required on the same sheet), then looked at the Cd of other production cars to make inferences about what aggressive aero might do on the BRZ. For example, the Cd difference between a stock Viper and the Viper ACR is 0.37 vs. 0.54, an increase of 0.17. Knowing how aggressive the aero is on an ACR, I estimated that a BRZ with a big wing + splitter might be around 0.27+0.17 = 0.44. Plug that into the spreadsheet to observe the difference in horsepower required vs. stock, and usually that ballpark answer is enough to satisfy my curiosity. There are more caveats than this, since Cd isn't the same at all speeds, ride height, etc, but those are the basics.

If you prefer a road test, you could install the aero mods and then re-measure the top speed with a precise instrument (not the speedo). If you know the new drag limited top speed, have a dyno graph of your rwhp, and have checked your spreadsheet with the stock top speed to ensure your rolling resistance power estimate is close, then you can back-calculate how much power was lost to aero at this new top speed, and from that back-calculate the associated Cd with the aero on.

Or you could download this

http://www.cartestsoftware.com/

[SuperTom]

Originally Posted by 86TOYO2k17

Just read entire build thread. Pretty nice! A little more extreme then I’m willing though. And looks like my headerback is a lot less loss then I thought about 10lbs, you didn’t seem to change our air intake just the tube getting rid of sound generator and that side resonator but no weights , so maybe I’m just at about -20ish lbs

Didn’t realize how much weight loss could be had in the brakes though, and your battery setup I may have to do, although a DD that needs to be reliable in 30 degree weather I’ll have to look into that more. And possibly the DSS CF DS. That could get me about another 50lbs. For a solid 70+lbs weight loss more then making up for a full tank of gas.

Still have spare tire to, may look into some alternatives still want something just Incase.

My bad some of the weights were taken from other people that have weighted things on the forum. Intake sound tube crap is 2lbs.

Yeah I keep the stock battery on a charger a change out in the winter.

In place of the spare I keep a Slime kit its around 2.5lbs
https://www.amazon.com/Slime-70005-S...dp/B001DZFZPG/

Here is my weight loss file. Doesn't count Sparco bucket seats with buddy club sliders which will get me to 2500 haven't completed that yet.

[SuperTom]

This SportCompactCar article from like 15 years ago what really inspired my obsession with weight reduction. Also good for a funny laugh
http://www.rcramer.com/fun/econobox/

[86TOYO2k17]

Originally Posted by SuperTom

This SportCompactCar article from like 15 years ago what really inspired my obsession with weight reduction. Also good for a funny laugh
http://www.rcramer.com/fun/econobox/

Interesting article about 1,000lbs reduction shaved almost 3sec off 0-60.

Just ordered the slime kit, free 1 day on amazon ftw. Spare and jack solid 30lb reduction.

Got to get that battery setup, maybe a slightly bigger one then yours could run fine all year. I try not to take short trips anyways. Maybe a 10lbs battery setup would be fine for another 20lbs getting me that 70lbs total. Then someday I may DSS CF DS for another 14lbs

[SuperTom]

Originally Posted by 86TOYO2k17

Interesting article about 1,000lbs reduction shaved almost 3sec off 0-60.

Just ordered the slime kit, free 1 day on amazon ftw. Spare and jack solid 30lb reduction.

Got to get that battery setup, maybe a slightly bigger one then yours could run fine all year. I try not to take short trips anyways. Maybe a 10lbs battery setup would be fine for another 20lbs getting me that 70lbs total. Then someday I may DSS CF DS for another 14lbs

well that is one of the largest shorai batteries I am using. I have no problems taking short trips at all in a heat wave. It may be good for the winter but I felt better with a stock battery in the winter. I didn't want to risk not making it to work one cold snowy morning but I'm not saying it won't work.
I also keep a cellphone sized jumper in my glovebox which is less than 2lbs
https://www.amazon.com/Portable-Ultr...ds=mini+jumper

[nikitopo]

Originally Posted by mrg666

And it is not all about weight. There is vibration to consider as well. Reciprocating and rotating masses contribute to vibration differently. That is why race engines require a certain mass on the crank pulley. Because, while lighter crank pulleys improve throttle response, they cause vibrational power loss at high rpm. This has been discussed so many times but anyway. If I change my crank pulley, it will be Fluidamper which is not light but designed for damping of vibration at higher revs.

Originally Posted by SuperTom

Looks like it mainly better for motors that stay in high RPM's all the time. The stock & Lightweight pulleys had better #'s in the torque dip range where the Fluidampr picked up top. It looks we are only talking about 2hp either way which could be influenced by other factors such as where the IAM is at 1 or lower during the run.


The one thing for sure is that weight is easy and accurate to measure and I know with my pulleys I saved 5lbs off the front of the car.

Depends how you want to present the data and the kind of the racing application. If you do a 5th gear dyno, then Fluidampr might give the theoretical 2hp top gain cause of the less vibration. However, on small race tracks or mountain roads you rarelly work on high gears. You are interested much more on corner exit speed acceleration mainly on 2nd or 3rd gear. Over there a lightweight pulley will have the advantage cause of the less rotational inertia. On 5th gear this advantage is lost and it doesn't show on a dyno because the RPMs are rising much slower. Additionally, as very well pointed by SuperTom in most racing applications you don't stay all time in high RPMs. Maybe NASCAR might be an exception, but these cars are not relevant with this area if you don't swap a motor.

[Tcoat]

Originally Posted by nikitopo

Depends how you want to present the data and the kind of the racing application. If you do a 5th gear dyno, then Fluidampr might give the theoretical 2hp top gain cause of the less vibration. However, on small race tracks or mountain roads you rarelly work on high gears. You are interested much more on corner exit speed acceleration mainly on 2nd or 3rd gear. Over there a lightweight pulley will have the advantage cause of the less rotational inertia. On 5th gear this advantage is lost and it doesn't show on a dyno because the RPMs are rising much slower. Additionally, as very well pointed by SuperTom in most racing applications you don't stay all time in high RPMs. Maybe NASCAR might be an exception, but these cars are not relevant with this area if you don't swap a motor.

The minuscule advantage that a light weight pulley offers is lost the second the car is put in gear. Any gear. As soon as the engine has to rotate a flywheel, clutch disc, transmission gears, drive shaft, differential, axles, wheels and all the shafts, joints and other moving parts involved the fact that you saved a pound in rotating mass in a pulley isn't even noise much less measurable.

[Spuds]

... thread deja vu...

[humfrz]

Originally Posted by Spuds

... thread deja vu...

[Tcoat]

Originally Posted by Spuds

... thread deja vu...

Yep. Same old bullshit.