I have a question after reading about lightened pulleys:

Let's say you took your average impreza, with standard spec.

Then removed all unnecessary weight, swapped every part you could for magnesium/titanium/forged/fancymetalium in order to save weight and increase efficiency. I mean everything, suspension, brakes, wheels, the lot.

Having left out the power mods and just focused on the rest, would you end up with a quick car? I like the idea, but think costs would be prohibitive, so this is purely for discussion really

In theory, it would be completely reliable as its running standard power with better internals. Much quicker due to weight reduction and also far more economic.

 

In theory yes as you change the power to weight ratio, in practice not sure how much you would notice.

 

Well, what if you had lightweight pulleys/pistons/valves and whatever else makes an engine work... I get the power to weight, but due to requiring less effort, would one see the engine behave differently, or better?

 

Does reducing weight make your car faster? Yes. Of course it does - basic physics. There are several other advantages to having a lighter car in terms of handling, braking and so on - but I'm not sure it'd be possible to replace the internals for lighter components without increasing the power output, unless you had a restrictive map put on the car... which would be a pretty pointless way to spend a lot of money.

 

Well yes, perhaps I have been too specific. If I replace parts, by their nature, this might increase the engine output. I am not suggesting we restrict it. But I wouldn't be looking to change turbos, air filters, fuel pumps etc to gain power. I guess I'm looking to avoid bolt on engine mods, and simply upgrade the OEM spec to run as best it can.

I'm not sure I know how to word what I mean...

 

I think I see what you're getting at - a 200BHP engine from a 2000kg car would still make 200BHP in a 1500kg car, but it wouldn't have to work as hard to achieve it so would be running more efficiently. The car would be faster due to the reduced weight.

 

Thanks mate you are right of course.

Lets focus just on the engine. If I take a 200bhp engine, fit lightened parts (lighter, but same spec, so not designed to increase power, just be a lighter version of the OEM part)

Does it remain at 200bhp? I am assuming so, as I am not adding anything. Just saving weight and increasing efficiency.

 

How much can be saved has been detailed by owners in the past, such as below (taken from another forum):

http://www.iwsti.com/forums/gd-membe...bs-2598-a.html

Saving weight makes the car so much more responsive and allows the revs to build more quickly - I notice a huge difference between having my mate (100kgs) and not in the car. 100kgs is the sort of weight saving Ferrari and Porsche achieve in their special edition lightweight vehicles!

 

And in response to your question, if you made the car properly light then yes, it would be quick.

 

With lighter internals the engine would be capable of making more power, but unless you remapped the ECU to take advantage of the increased efficiency it'd theoretically still make 200BHP. I say theoretically because I'm not sure how a unmapped engine with lightened internals would run - I suspect badly!

 

This is so true. I remember when I first got my car I took my mate out in it full of gusto about how quick it accelerated... Suddenly it felt increadibly slow with him in it compared to not having him in!

 

Let's assume its mapped and running fine

Stock internals on engine of 200bhp vs upgraded internals on engine of 200bhp. Surely the latter leads to a faster car? Same power output. Better efficiency. faster.

 

Weight makes a huge difference.
Look at motorbikes for instance, they only need to put out about 150bhp to destroy most production cars.

 

Yes. My wording may be terrible, but It's not vehicle weight that I'm questioning.
I understand lighter vehicles can be faster. I'm not that retarded

Can engine output be increased via saving weight on components and improving engine efficiency. Ie, if it has to work less, surely it can use the power "saved" to propel the car.

 

Would that then be, but on a much smaller scale obviously, similar to the effect of using air con etc. anything that drains fuel economy due to making the engine work harder?

 

Yes I suppose it would be a similar theory.

 

"Sort of" is the answer.

Lighter engine components allow the car to rev faster and higher, and there is a correlation between revs and power, however as the revs build there becomes a greater demand on other components and auxiliaries being able to satisfy the engines requirements.

In your example question it would only be the moving parts that would make a difference, having a lighter block/manifold etc etc wouldn't change the output. So you would need lighter cranks and pistons etc, however changing these would only make a minimal difference on performance, and changing the minor moving components such as pulleys for lightweight versions would have almost no impact on their own.

If you changed everything in the engine bay for a lightweight equivalent you may start to get a real difference, but we aren't talking about a big jump in power, maybe an extra 10 or 20 bhp max. Nonetheless there would be an increase in power that would be unavoidable purely because, as you originally thought, the engine is working more efficiently.

However, the cost of gaining this extra power would be significant (read cost more than the car) and completely pointless, having about the same impact as removing the spare wheel and installing light weight seats.

 

Ah. Thanks man. Good reply. That's exactly what I was thinking, lighter cranks and what not. But I had no idea what the end result might be.
10-20bhp gain, sure, that's not a lot, and definitely not worth it from a cost point of view. It'd be a great engine though

 

I don't know if any one actually makes parts light enough for an Impreza though!

It is essentially along the basis that a lighter engine can rev more quickly and get to peak revs sooner, allowing for more explosions per minute, hence more power.

That is why we see amazing naturally aspirated engines with huge rev limits like on the Ferrari 458 Italia and the old M5 V10.

 

If you want to start saving weight, then start with unsprung weight ie. wheels. I think every 1kg unsprung is worth 4kg of sprung weight. So in theory saving 25kg on a set of wheels would make up for giving a fat mate a lift. Then just tune your engine using upgraded lightweight parts as you go.

What's the idea behind not upgrading the power anyway? Or is it just purely hypothetical? Surely when modifying a car power is normally top of the list. Even if it's just a safe minor power hike to get the most out of your engine.

 

I've no idea either

 

All hypothetical mate. But I do believe power isn't everything.