Weight Saving

[Ilogik]

As I have been quite inspired  by the techno pro spirit MR-S and how light weight it is, the plan for the gt300 is to try and make it as fast as possibly by making it as light weight as possible.

Soft top is being removed 20kg if I remember rightly
the monocraft kit reduced weight by about 5kg over stock
17 inch wheels with mumma sized tyres will add weight but I couldn't part with those.
CF wing is being removed

Whilst the engine is out, do you think it would be worthwhile removing the AC, for the amount of good weather we have im wondering if its worth it. If it is how much weight do you save?

[mrzwei]

Google something like Colin Chapman or Lotus; as I'm sure you know it's all about power to weight ratio so the cheapest route is to get rid of excess weight.

[Anonymous]

You're starting in the wrong place for weight saving. The best kind of weight to lose is unsprung, and if you're not going to get rid of those wheels then it's not worth the effort trying to save a few kilos on aircon removal.

[markiii]

Dan has a point

first thing is find out how much of weight penalty you have with those wheels

[Ilogik]

Just checked wheel weights

19.0 for the fronts without tyre

weight for 17x9 is 20.5 but im pretty sure I got 17x10 on the rears.

[markiii]

so thats how much total unsprung weight increase?

[Ilogik]

Trying to find out how heavy the stock wheels are, but not having much luck, compared to my advan 16,s which were either 12.5 or 14.5 kg each fair amount of extra weight.

[Anonymous]

I shipped 2x stock 16" recently and I'm pretty sure they were 17.5kg without tyres.

[markiii]

its in the library

[Anonymous]

Weight is missing from the 16"s in the library.

[Ilogik]

Be nice to find the complete spec list to the spirit mr-s

 m http://www.youtube.com/watch?v=6MgN_vvneOk m

I know it never be like it, but i can pretend   s:lol: :lol: s:lol:

[Rowland]

Much of the weight is with the interior, and of course the battery.
It depends on how much you wish to comprimise your daily driver by ripping the weight out.
You only have to look at my race car to see what's achievable.
For the record that weighed 900kgs with hardcore roll cage installed.

Goodbye air-conditioning system
Goodbye interior
Goodbye fat ass battery

Trust me, removing the weight on a MR2 Roadster makes a big big difference!

  s:D s:D

[Ilogik]

haha i was curious to try a scoop ontop of the hardtop, with the softtop remove and ac removed. Something like this

[Rowland]

haha i was curious to try a scoop ontop of the hardtop, with the softtop remove and ac removed.

Lotus got that right with the Exige IMO

[kentsmudger]

Much of the weight is with the interior, and of course the battery.
It depends on how much you wish to comprimise your daily driver by ripping the weight out.
You only have to look at my race car to see what's achievable.

Rowland's interior last year - Bigger

[uktotty]

anyone wanna retro fit Logics aircon into my car?

[davidarden]

Depends how uncomfortable you want to make your road car, and also if you want it to be turned back to stock before you sell it in future.

If you do, light weight battery and some kevlar bucket seats would be a good start   s:D s:D

[StuM]

Lotus got that right with the Exige IMO

Although, the Exige one feeds air into the intercooler, rather than venting the cabin - which I presume is what the one above does?

[northernalex]

Ive got a lightweight battery. Butt dyno says it made a difference.  Cant start on cold mornings without a jumpstarter though.

Alex

[ChrisGB]

The effects of losing weight from the car are dependent on where you lose it from. For straight performance gains, the MR2 with a driver on board, makes around 0.125bhp/Kg. What this means is that in terms of sprung mass off the bodyshell, every 10Kg you remove will give you the same performance boost as having an extra 1.25bhp. Given that a completely stripped out car may only get down to 900Kg, you can expect a total gain in acceleration equivalent to 12.5bhp. This means one very light seat with EVERYTHING else gone. No carpets, no sound system, no airbags, no dash, no door cards, no carbon trim, marginal battery (which would be best placed where the spare wheel will no longer be).

Of course this is a lot of compromise for a road car and only relevant if you are chasing that last few tenths per lap in competition.

Lets look at what else we can do to get the car going faster and handling better. In straight line speed terms, you have those big alloys. These are bad for straight line performance for two reasons. First, they weigh more than the stock, wheels, so more weight to lug, but more importantly, that weight is further away from the centre of the wheel than the stock wheels and this means more polar inertia (they take more power to increase their turning speed). This is very relevant. I noticed a butt dyno improvement going from Hankook RS2 to Toyo R888 and I think this was down to weight of the tyres. While we are talking polar inertia, a light weight flywheel will produce gains far greater than the weight difference would suggest. Of course we also need to look at the wider tyres other issues: Rolling resistance and air resistance. Wider tyres will create more drag as they roll along and this can knock significant amounts off the performance. As an example, a car fitted with 205 section tyres may use up to 10% more fuel than one on 185 section tyres in my experience. So with your wheels, that is your 12.5bhp just about used up before polar inertia does its thing. The other problem with the big wheels is the big wheel arches. These add significantly to air drag, as do the larger deeper front air dam and rear air scoops. Lots of lost performance there at higher speeds for sure, maybe losing another 10% acceleration once into 3 figure speeds, not to mention a fair chunk off top speed.

Losing weight out of the shell is also going to have a different effect on dynamics depending on where it is removed from. Weight high up is always a good place to start. Next is to get rid of weight that is a long way from the axis of rotation of the car. The deep front air dam and bulky front end are a long way forward of the rotational axis (in the MR2 this is roughly where the engine is) and so these make for more inertia for the fronts tyres to overcome when turning in. Losing weight out the rear end is a good thing in my experience. I went with a PPE manifold and decat pipe feeding a carbon fibre exhaust system weighing 4.5Kg. Net result is probably 10 - 20Kg less weight behind the engine and the benefits in handling are really tangible, particularly in fast transitions.

But the big loser here is the gain over stock in unsprung mass. Heavy wheels and tyres really burden the way the MR2 moves and handles. On heavier wider wheels, the car feels more planted for sure, but to take advantage of it you need to add proper amounts of power. I had the pleasure of driving Liz's TTE turbo on SP17s and the ratio of grip to grunt was nicely judged, but those wheels would IMO be a liability with a non turbo car.

I would say that if you want to make it as fast as possible, either add a whole lot of power to make use of the wider wheels or sell it on and get a stock roadster.

Chris

[Ilogik]

I like the looks too much, Im happy with a bit more grunt, It is a bit of a project so will see where the wind takes me   s:lol: :lol: s:lol:  

I have managed to source a 2zz with 6 speed box, so have bit more go go

[markiii]

I have managed to source a 2zz with 6 speed box, so have bit more go go

unfortunately not where it counts

extra weight requires extra tprque

[ChrisGB]

I have managed to source a 2zz with 6 speed box, so have bit more go go

unfortunately not where it counts

extra weight requires extra tprque

At least it has the right gearing to get the plot moving. One of my pet gripes about the MR2 is the silly tall gearing.

The extra go from the 2zz will help offset some of the extra weight, inertia, rolling resistance and air drag. Cant help thinking it would go better in a stock MR2 though.

Chris

[mrzwei]

When you say tall gearing, my interpretation is that in top, the engine may not quite reach maximum speed in relation to maximum revs. My 5 speed pre face lift is screeming for another gear on the motorway. Or have I got this the wrong way around?

[ChrisGB]

When you say tall gearing, my interpretation is that in top, the engine may not quite reach maximum speed in relation to maximum revs. My 5 speed pre face lift is screeming for another gear on the motorway. Or have I got this the wrong way around?

I was referring to the lower gears. First and second and third are way too tall for optimum acceleration IMO and then there is a yawning chasm to fourth as well. Sixth is just nice on the motorway though.

Chris