Hi,
driving a lightweight sportscar, I know the better way to get a faster car is less weight instead of more power.

The question is:

How can we put the RX-8 ona diet?

My ideas for weight savings are:

Remove the plastic cover from the engine -1kg
removing the trunk carpets -2kgs
Sport exhaust -10kgs
K&N air filter system -2kgs
Carbeau or Sparco front seats -30kgs
OZ Superleggera wheels -20kgs
alloy tank -5kgs


Total weight savings: = 70kgs


My target is getting 140kgs off which means a dry weight of 1.200kgs...

Any ideas???


Stefan Janssen
Germany

 

Alu brake calipers all round should reduce the weight.

Also, maybe smaller items like the steering wheel and electric window motors will aid the weight reduction.

Of course if you want to go to extremes, then take out the air con and the rear seats! Should save you some weight

Otherwise, there maybe some sound deadening which you could remove.

Of course, some of these will effect the driving quality of the car, so it depends on how much you are willing to sacrifice to get a light car.

 

precisely. sound deadening material, interior panels, spare tyre (if your geographic region includes one), lighter rear-door glass (get non-moving light-weight plastic), DEFINITELY things like the electric motors for all the automatic flibbity-jibbets... i wonder if you could just get crank windows (i would even if i was gonna get this car)...??

big things: AC, the HOOD (i know it's "ricey" to have carbon fibre, but paint it), the boot lid, exterior panels/plastic/cladding/add-on styling stuff, the whole sound system (amps and speakers are DENSE)... i dunno, it's hard to think of stuff to rip out when i'm not sitting in the car

REDUCING UNSPRUNG WEIGHT IS A BEAUTIFUL IDEA!! if you can afford stuff like ultra light-weight rims and brake calipers, maybe even light alloy/ceramic rotors... brilliant stuff.

 

Go on a diet.

 

Stefan,

Your goal of putting the RX-8 on a diet is smart but your weight reduction estimates are off.

To save 10 kgs (22 lbs) by changing the exhaust you are gonna have to use Titanium.

The OEM fuel tank is plastic so an aluminum alloy tank will be heavier.

I calculate that same sized one piece forged aluminum wheels will save about 11 kgs (24 lbs) not the 20 kgs (44 lbs) you predict. My estimate is based off of my experience with OEM Mazda wheels for the Miata and RX-7. Mazda always seems to have cast wheels lighter than its competitors.

The K&N filter system probably will not work well with the RX-8 since the high power version comes with a dual inlet intake system wherby one of the inlets is servo controlled.

Enough of being negative. A few ideas I have and to reinforce some already said:

1. Usually you will recieve the car with transporter tie down hooks (some think they are tow hooks) still attached to the car. They serve no function once the car is unloaded from the transporter since they are not strong enough to tow the car. On a Miata these weight about 3 kgs (6.6 lbs) and are easily removed. The front hooks can be unscrewed and the rear hooks cut off. Fifteen minutes of work. A bonus is these items are on the ends of the car so the weight reduction has a significant effect on the polar moment of inertia (PMI).

2. The engine will usually have a couple of brackets attached for installation purposes. Remove them and save them in case you ever have to yank the engine.

3. Light weight batteries are available. These can save 5-7 kgs (11-14lbs). The battery on the RX-8 is quite far forward so this change will also improve PMI significantly.

4. Forged aluminum wheels are a must.

5. Aluminum brake calipers would be sweet since in the pics I have seen it appears the OEM calipers are cast iron. Savings of maybe 5 kgs (11 lbs). Remember all this weight is unsprung.

6. A fabricated exhaust manifold will probably save 1-2 kgs (2-4 lbs) because the OEM manifold id dual wall. Of course this modification will increase emissions on start up.

7. Run the washer fluid level at 50% instead of 100%. This is free and will save 1 kg (2 lbs).

8. Read the owners manual and then leave it at home. Maybe 1/2 kg (1 lb).

9. Do not get a car with a sunroof. Someone estimated this is a 18 kg (40 lb) hit. There is a thread on Edmunds about this where I posted some calcs on the effect upon the CG. The effect was significant.

10. Skip the navigation system, fog lights, etc. These items will end up adding another 20 kgs (44 lbs) of pork.

I will think about this some more and review what I have done to my Miatae and post some more ideas.

 

A few more:

A. Yes a carbon fiber composite hood will save some fat but not much because the OEM hood is aluminum. Savings my be only 1-2 kgs (2-4 lbs).

B. Since the car is going on such an extreme diet it may be wise to revert to the smaller front brake rotors on the base model. I calculate this will save 1.4 kgs (3 lbs). Rotating unsprung weight at the ends of the car here. By far the biggest performance multiplier effect here.

C. Titanium lug nuts. I have seen them but do not remember where. Maybe save 1 kg (2 lbs).

D. I have found that aftermarket seats are not lighter than OEM Mazda unless the aftermarket seats are non-adjustable racing type seats. When going to the racing seats one can save up to 10 kgs (22 lbs) per seat.

E. Lightened flywheels can save 3-6 kgs (7-13 lbs) but there are driveability issues to deal with.

 

I hope this is the direction Mazda is taking with the MPS Rx-8. No big wing, ground effects or big amp, but about 100-150 lbs of weight reduction. Add the engine from the next Rx-7 (if there is one) and they will sell like hot cakes.

elisemk1, what part of Germany are you from? I was in Ramstein couple of years ago and I missed it dearly, some of the best times I've ever had.

 

Amen to that. I think that the MPS RX-8 should be pretty standard looking like the RX-8 is... the option is ALWAYS there to add the body kits, wings, stickers etc.. later on..

But they are impossible to take off when you get the car.

 

I definetly think there should be an appearance difference in the MazdaSpeed compared to regular 8. I really like the look of the MazdaSpeed and hope that they have that bodykit available to buy if I end up with a regular 8.

 

I think that the differences between the RX-8 and the MPS cosmetically should be fairly obvious, similarly to the E46 3 Series and the E46 M3, same chassis but not one shared body panel. I think the '8 can be more aggresively styled without adding a full on body kit.

 

So True. The most overlook yet beneficial mod.

 

This is so trite! It seems to be the first response to a weight reduction post, no matter the forum. Some of us aren't fatties.

 

I was wondering if Buger would be so kind to run that program to see what kind of performance we might be expecting for the MPS Rx-8. You know, 300 hp, less weight, may be a little shorter gearing?

 

since there are no hard numbers, or even a confirmed MPS RX-8, it really doesn't matter what those numbers are, right?? it's pretty safe to say it'll be faster (if)... how much?? no one can say for sure yet... and even if we did have some numbers, the sim program isn't infallible...

to guess, let's say 5.5s to 60mph. sound okay to you?? i think that'd be quick enough.

 

Yeah of course that's fast enough for me, in fact looking at the c&d video, I think even the regular Rx-8 might be beyond my current ability. The limit is certainly beyond any street condition.


However, it doesn't hurt to dream :o

 

I like this thread alot... the weight aspect of performance is sorely underrated. Is there any way to find out exact weights of rx8 components?


Also,

1. Do the leather seats weight more than cloth seats? To see what I mean, observe pictures of the two. The cloth seats don't have that metal-looking shell on the back. Also, how much does a the leather on a leather seat add to the weight of the seat?

2. Will taking fog lights off affect functionality/safety in any tangible manner? Does rx8 have daytime running lights?

3. For whomever posted on edmunds' with the demonstration that the moonroof significantly changes Cg height, can you link it or repeat it here?

4. How much does the intake system weigh? The variable piping actually looks somewhat complicated to me, and for the purposes of this discussion, complicated = weight. Might putting a turbocharger in place of the intake system actually save weight? Is this how modding w/ a turbo normally works (replacing intake box w/ pipe to turbo to filter)?

5. Does the US-spec RX-8 not have that rotary triangle-shaped light between exhaust tips? How much does this weigh? Will the wiring and bracket stuff still be back there?

6. How much more will the 3-coat mica paint weigh vs other paints?

 

Let's answer them one at a time ...

1. The leather seats weigh more not only because of the leather being a weightier material than cloth, but also because leather seats have a driver's side electronic control pod standard.

2. The fog lights being removed should have minimal impact on safety.. The design of the headlights looks good and I think without the fogs you'd be hard pressed to get that much more light, especially if you opt for the Xenons

3.

4. I think that a turbo on this engine is very difficult given how compacted the engine is, there's nearly no room for it. The intake and exhaust system however look like they could definately use lighter materials but that as you know, comes at a cost. Mazda had to make the cuts where they felt would keep the price low and I'm happy they did.

5. The US spec RX-8 as far as we know, does not have that rotor light in the back (fog light) standard. It's an option. I'd imagine it's about 2 or 3lbs.

6. Negligible I think. Maybe a pound.

 

Hey I've just thought of something. Doesn't the Rx-8 uses run-flat tires? If so there should be a little weight saving by going to a regular tire. Of course you would have to keep your cell phone handy in case of a blowout.

 

the intake is mostly plastic, not a cast iron piece like the huge exhaust manifold on the 13BREW... i really don't know how much you could save there, at what cost, and keep the variability...

anyhoo, you might find a few pounds, maybe maybe maybe, in the exhaust header... double walled, and steel, i think...

 

I am too stupid to know how to post a link to a response on a thread on another forum or even this forum. I just got a push button telephone a few years ago. Damn 1970's era AT&T phones never die.

Anyways my calculation of the effect of the sunroof was it raised Cg by 3.2%. This was calculated from a poster stating that a sunroof that they removed weighed near 50 lbs. I then subtracted the weight of the hole made in the roof and headliner (~8 lbs). I then factored this weight into the published RX-8 weight and the published Cg height (RX-8 media kit) and came up with my 3.2%.

No way a turn]bo system will weigh less than the OEM intake setup. Don't forget about the required intercooler and big daddy exhaust a turbo needs.

Surprisingly paint weighs a ton. I was told a large passenger jet has some 5000 lbs of paint! Doesn't a car use a couple of gallons of paint. If so this would be maybe 20 lbs. What about the weight after the solvent evaporates? I guess I dunno the answer to this one. Sorry.:headsmack

 

Well like I promisesd three months ago I have thought about weight reduction some more. Here is a review with some new ideas and some more accurate wieght reductions. I do not neccessarily endorse all of these areas I am simply posting them to spread ideas.

1. Wheels - Another thread mentioned that Mazda told them the OEM 18"x8" wheels weigh 20 lbs each. This is quite good for the size. However, there are several forged wheels available that save significant weight. Centerline RPM 18"x8.5" wheels weigh 15.0 lbs each. Weight savings ~ 20 lbs.

2. Kyokugen closed end heptagonal lug nuts weigh 27 g each versus 60 g each for a stock lug nut. Weight savings ~ 1.44 lbs.

3. Go with the non-sport front brake rotors. Weight savings ~ 3 lbs.

4. Use cool looking cross drilled, stock sized brake rotors with aluminum hats. Weight savings ~ 3 lbs.

5. From pictures it seems the RX-8 uses the same iron calipers as the Miata. If so, use aluminum 4 piston front brake calipers and aluminum 2 piston rear calipers. Hi Spec Motorsport offers these with dust seals (a must for a street car) and soon will offer the two piston calipers with a cable actuated parking brake mechanism. Custom mounts required. Based on Miata weights the weight savings ~ 19.0 lbs

6. I believe the OEM battery is a 24F lead acid type. If so an Odyssey 680 can be substituted. Weight savings ~ 22.7 - 27.7 lbs.

7. An OEM 2001 and newer Miata seat weighs 24.5 lbs without the rails. Since the RX-8 seat is larger I estimate a weight of 30 lbs. Nex Racing Recliner seats are the only light reclining seat I know of and weigh 16.5 lbs each. Weight savings ~ 27 lbs.

8. AEM says they will offer a complete aluminum pulley set (crank, H2O pump and alternator). Based on the FD RX-7 weight savings ~ 2.0 lbs.

9. Many guys will offer lightweight flywheels. A steel flywheel will save ~ 6 lbs.

10. Based on a Miata a full sized titanium muffler (are you listening Arvin Meritor?) that is still quiet will save ~ 9.5 lbs.

11. A fabricated exhaust manifold will save ~ 4 lbs.

12. A fabricated titanium exhaust manifold will save an additional ~ 4 lbs.

13. Advanced Design makes aluminum shock absorbers with titanium guts for the Miata. If made for the RX-8 weight savings ~ 9 lbs.

14. Titanium coil springs can be wound by Renton Coil Spring if someone supplied them with a set of stockers or aftermarket units to match or the engineering specs they want. Weight savings ~ 9 lbs.

15. And to repaeat a few; remove engine lift hooks, tie down hooks, plastic engine cover, trunk carpet, owner's manual and 50% of washer fluid. Weight savings ~12 lbs.

16. (Added May 10th) Aluminum side housings, if possible and RB makes some for the Renesis. Gonna be expensive! Weight savings ~40 lbs.

Total weight savings ~ 194 lbs. Not bad considering basically neglible reduction in functionality that comes from mods like stereo removal, HVAC removal, etc. The ~194 lb reduction includes ~ 51 lbs of unsprung weight and ~ 27 lbs of rotating weight. I calculate if we apply some of the simple multipliers bandied about on the net regarding the effect of reduced rotating by ~27 lbs that the lightened RX-8 will now have a relative weight of -140,000 lbs compared to a stock RX-8. Estimated 0-60 time of 3 milliseconds.:D

Edit note: I have added #16 on May 10 and will keep adding to the same post to keep it all in one place.

 

That is, if lesser reliability and voiding the warranty on the engine are worth a mere 2 lbs.

---jps

 

I am no rotary expert but I looked closely at the pictures of the e-shaft (~crank) pulley on the Renesis in the RX-8 pess kit. It appears this pulley has no dampening system whatsoever. I don't see a problem here like we would see with the Miata setup causing oil pump failures.

 

Strip the inside OUT completely that **** weights so much all together...i remember someone stipped the bmw inside a wile ago around here and the car dropped 250lb's...i thnk thats like 160kilo

 

the hoods made of aluminum you can't make it any lighter