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I've seen various comments regarding weight reduction and HP on various threads, so I've read across some basic power to weight theory to the Mk3 RS, happy to stand corrected if there are any errors.

(Admin, please move to technical section, if it ought to be posted there).

Info read from http://www.tuneruniv...o-weight-ratio/

Theory on weight loss and equivalent gains in hp, power to weight ratio, gives:

View attachment RS P to W ratio.pdf

RS%20MK3%20PtoW_zps4tdhgys8.jpg

Factory RS MK3

Kerb weight (inc 75Kg driver) = 1599 Kg

Horse Power = 345 HP

Power to weight ratio = 0.2158 HP/Kg

Therefore:

weight reduction = 10 Kg

new weight = 1589 Kg

Power to weight = 0.2171 HP/Kg

Equivalent HP = 347.17 HP

HP increase of = 2.17 HP

So the first reduction of 10Kg is equivalent to a 2.17HP increase.

It is not quite a linear relationship but as a rule of thumb each 10Kg improvement (from 10Kg to 150Kg) is equivalent to 2.4HP on average. In fact the HP equivalent increases slightly for every 10Kg weight reduction, so for example removing 10Kg weight from 140Kg to 150Kg gives an equivalent of 2.61HP

I tried to attach my Excel file showing the workings out but the file type is not allowed.

The question is, what's the best HP increase per £ spent ? Tuning or weight reduction ? It'll be both aspects, particularly in the basic early stages when costs are relatively low.

Hope it's a clear as mud ;)
 

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Interesting Sunday stuff..............

So to muddy said waters some more:

Going the custard route I can reduce my car to 1585.6 kgs. Happy days :) But that will cost me £3305 :(

Or - put another way - £264.64 per kg of weight lost.

Ouch!

Oh, nearly forgot - I do gain about 2.4 bhp at the same time.

Regards
 

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IMHO if we put aside handling improvements with a lower weight you can not beat price/performance ratio of the tuning.
+50hp remaps are available or will be available soon and that would be equivalent to 200kg weight reduction which is very, very hard to achieve.
 

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Discussion Starter · #6 ·
There are no big gains from any single source, apart from software. Granted, it is does cost, take effort and most likely not or everyone, myself included. Something I keep in the back of my mind.
 

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Discussion Starter · #9 ·
Interesting Sunday stuff..............

So to muddy said waters some more:

Going the custard route I can reduce my car to 1585.6 kgs. Happy days :) But that will cost me £3305 :(

Or - put another way - £264.64 per kg of weight lost.

Ouch!

Oh, nearly forgot - I do gain about 2.4 bhp at the same time.

Regards
What's "Going the custard route..." ?
 

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I'm going to cut my left leg off
15kg hence 3 more BHP
Just not sure how I'm going to manage the gear changes 😂😂😂
 

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Weight reduction on a daily driver is pretty much not possible without either removing things you need or replacing things with a lighter version which is excessively expensive. Aftermarket bits like wheels, brakes etc, plastic windows, aluminium body panels and chassis parts. If you have to go to those lengths, just get a lighter car in the first place.
 

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Well, a full tank petrol (50L) weighs around 37kg, which according to your figures is sapping 8.029 hp so I'd say only put £5 in at time. :bleh:
That's actually not as silly as it sounds.

I remember reading a test a couple of years ago, think it may have been in Auto express or a similar sad mag where they worked out the saving if you did a tank of fuel every week and instead of filling up with 60 litres you did 3 lots of 20 over the same period, the saving over a year was over a £100

s'pose it's ok if you want to spend half your life in a petrol station
 

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Interesting. Must have been a tricky thing to measure (20 litre fill ups), not filling the tank means you can only go by the onboard fuel computer.

Also depending upon how out of your way the petrol station is then you spend a larger proportion of the fuel burnt driving to / from the petrol station which is probably largely insignificant for town dwellers.
 

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Drain the air con.

Back when i could afford to race my car weighed only 740kg. And i found myself modelling spreadsheets of power gain by MY weight loss.

And losing 1-2 stone was not insigificant with that low a base weight.

Trimming weight from the car isnt cheap. But its a bit of fun exercise to strip a little fat here and there if you can afford to. Get 100kg or more out of the RS and you'd notice differences.
 
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