Safe Speed Forums

Yes you are.

You are thinking of 'fly-by-wire' throttles, which are becoming far more common. My 1991 TVR has an ecu, the throttle cable directly opens a butterfly in the intake, the ecu can 'see' this throttle opening, the amount of air flowing into the engine and the timing of the ignition, it uses this input to set the timing and duration of the fuel injection. It is quite possible to change the 'chip' in this ecu and reprogram it to give a better fuelling curve.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

Ok, I see, the ECU in that case controls the injection and not the throttle opening. Well I learnt something...

Is the opposite to what I said true though? That is, if the accelerator pedal is NOT connected directly to the engine (eg. it has wires coming straight out of it or has a cable going to a box with wires coming out) then there has to be an ECU in there somewhere?

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Andrew.

I would suspect that is the case, there is definitely going to be at least some electronics involved though there could be some unusual setup that just has remote actuation of a throttle I suppose.

In the case of the TVR the system is called efi - electronic fuel injection, it all depends on how you define an ecu. Efi controls the fuelling using inputs from sensors, electronic ignition can control the timing and duration of the spark but whether you could call that an ecu?

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

Surely the acceleration isn't an issue for brakes. It's the speed you are travelling that's important. As soon as you take your foot off the accelerator the car will begin to slow down. It will not keep accelerating so I don't see the corellation.

More acceleration means you can reach higher speeds so you need better brakes. This is most likely to occur on roads with short straights between bends where you can now achieve higher speeds before slowing to the same speed you always used for the next bend.

Example

If you exit a bend at and can now accelerate to 44mph rather than 40mph before braking to 30mph for the next bend you dump 48% more energy to do so, the majority of which ends up as heat in your brakes.

Assuming I got the maths right

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

Which are points I accept, but are purely academic. The brakes need not slow any greater mass, and are designed to work at the full range of forseeable road-speeds as stock. As a safe driver you are going to be braking earlier for the same corner at a higher speed anyway.

I did the sums when I was considering putting a 3l aluminium V8 into my Triumph Spitfire, a mod that actually reduced weight ever so slightly over the stock 1300 cast iron lump, and unless you plan on using the extra performance to hoon around like a maniac (braking late, cornering 'on the limit', etc.) then the brakes and suspension need no modification. Of course the drivetrain would have in my case, unless I wanted drive shafts that resembled barbers' poles, but perhaps even that wouldn't be a problem with a relatively small jump in engine size, particularly on a modern mass-produced car, when a lot of the parts are likely to be common across the range.

You are saying that better brakes slow you down better. That is true but isn't the point as I see it. In your wexample above, a smaller engined car could achieve 44mph on a slighter longer straight. So you have the same speed at the bend with a smaller engine. The speed you enter the bend is down to the driver not the engine size.

You might be quite surprised at the difference between the brakes fitted to a BMW 318 and those on the 330.

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Malcolm W.
The views expressed in this post are personal opinions and do not represent the views of Safespeed.

I might be, but I was talking about the drivetrain.

Better brakes can slow you down better but only if the original brakes were not capable of overcoming tyre grip. What better brakes do in this case is slow you down more times or from higher speeds before they overheat and fade.

On a slightly longer straight the more powerful car will still be going slightly faster still so dump more energy into the brakes. That you enter the bend at the same speed is exactly the point I am making, it is the speed from which you decelerate that is important.

The idea is that whatever the length of the straight providing it is not long enough to reach a terminal speed and stop accelerating then the more powerful car is going to be going faster before it brakes so dumps more energy into the braking system. If you go to the effort and expense of tuning up your car then it is highly likely that you will use that extra performance or why bother in the first place.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

I see your point now.

Which is amazing given the lack of punctuation in my sentence.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

I thought you must be a lawyer for a moment.

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Malcolm W.
The views expressed in this post are personal opinions and do not represent the views of Safespeed.

how old is the car, did you buy it new from a dealer? They might give you a good upgrade deal after 12 months for a sportier model.

Like said, modding is a labour of love and a money drain, usually more economical to go for the sporty version in the first place, especially once you take into account resale values, insurance costs etc.




I'm pondering a re-chip for my imminent new van, a merc vito 3.0 V6 (diesel). as this "new" engine is in fact hoiked from the outgoing E-class, the german tuning houses already have an enticing range of off-the-shelf options for it, a re-chip will take it from 200 to 270 bhp for starters. But then, do I really need that in a van thats already the quickest on the market (8 sec 0-60), will spend most of it's life bumbling round london at sub 20, and do I really wanna invalidate the warrenty?

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Fear is a weapon of mass distraction

I'm not sure that's quite the case to be honest! My first car was a Reliant with drum brakes all round. It could lock it's wheels, no problem, but was truly AWFUL at slowing down! Originally it had Reliant's own 700cc engine and I put the 850cc engine in it before finally going to a Ford 1600 crossflow - at which point it would have been utterly suicidal to keep those drums (although they could still lock the wheels)! I went for Triumph Vitesse front discs and that made things much better.

Good brakes will convert the cars kinetic energy into heat AND THEN GET RID OF IT. It's quite remarkable how much difference a decent set of "anchors" makes - even long before the point where wheel lock occurs!

On a more general note, I agree with the Prof. You'll not easily make much difference to a normally aspirated car simply by making changes to its chip. To answer your earlier question, pretty much all passenger cars for the last 15 years have had an "ECU" - in which there is a "chip".

I'm not familiar with the Clio but generally, these days, the ECU controls fuel injection and ignition timing. The "chip" they refer to stores a "map" of data points. Depending on what the various sensors (airflow, engine speed, throttle position, crankshaft position etc) tell the ECU, the processor inside it looks in the "chip" to see how much fuel and ignition advance to give the engine. In other words, it "looks" at the sensors and sees (for example) "3000 RPM, half throttle, "x" litres per minute of air going in to the intake". It then goes off to the "map" stored in the chip and finds the appropriate value that corresponds to those engine conditions and then gives the engine "y" dose of fuel and "z" degrees of ignition advance. By changing the "chip", you can make it give more fuel and / or more ignition advance but that may or may not make the car go any faster.

People who sell chips will tell you that the manufacturer can't give you as much power as the engine could potentially manage because they are constrained by emissions laws, fuel consumption expectations, warranty considerations and countries where fuel quality might be low. In reality, however, the major manufacturers don't "give away" power unless they really have to! I've tried "chipping" my own normally aspirated car and could fell very little difference. The car just used a lot more fuel!

Cars with turbos though, are a completely different kettle of fish! Here, in cases where the "chip" also contains settings for the turbo wastegate, you can pretty much get as much power as you like out of the engine by altering the chip settings! - obviously with a corresponding increase in fuel consumption and reduction in component life!

My Missus has had two 1.2 Clio Dynamiques prior to her present 1.4 Expression. The 1.4 is still virtually torque-free but, in the power-band, it has pretty zippy acceleration.
All Clios after 'Y' plate are fly-by-wire and the ECU sits on the firewall next to the EFI distributor. The 1.2 engine is very exhaust-sensitive and already more-or-less tuned to destruction, so mapping or chipping is out. Also, if you try and fit an induction kit, the temperature sensor in the inlet gets affected by the cryogenic effect of the filter and runs the EFI too rich all the time, so you just end up putting more fuel in the damned thing!
Sorry to p!ss on your parade, matey.

It is, however, very reassuring to know that young people are still interested in getting a bit more grunt out of their cars - I can't remember the last 'tuning' thread we had on here - this is very refreshing! Thanks and welcome to the fold.

BTW, if you want to get into modding cars, I suggest that, once you have paid for this one, get rid of it and find yourself a classic to play with. A MkI Fiesta XR2 is a good start. For not much money you get a car that gets to 60 in 9 seconds and 115mph flat out. Mine left me able to reach 60 in 7 seconds and 130mph and all for less than a grand outlay. It also stopped well and stuck to the road like cat-sh!t to a carpet!

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Aquila



Licat volare si super tergum aquila volat...

I agree, "Old" cars are much more fun to mod, you have a lot more flexability with what you can do and the absence of bothersome electronics means that it is much easier for a competant DIYer to do so.

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"The road to a police state is paved with public safety legislation"

I'd love an old XR2.... not many decent ones left mind you, and spares were a hassle for my 1300S ten years ago, so God knows what it's like these days.

Sorry for not replying earlier been a little busy over the weekend, fencing competition and a track day.

I have never driven a car with drums on the front but if I ever do I will bear in mind your experience and comments, thanks. As for getting rid of the heat that was exactly the point I was making about better brakes, I perhaps did not state it clearly enough.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May