Crippling a Supra on purpose

[RedM]

Hi,

 

I've had a look for an answer but can't find one on here so.....

 

Is it possible to set an ECU or whatever to run with selectable modes? I'm thinking of a normal one for nice, speedy driving and another that would give great MPG but cripple a Supras performance to something like a 1.3! Prevent the turbos from kicking or something?

 

Is that possible? When I get my Supra it will be my only car and as I spend most of my daily journey time doing under 40 and crawling I thought this might be a way to save money. Then, when the roads are clearer, press a button and hare off down the road.

 

Good idea or load of bozwellox?

[Whitesupraboy2]

i suspect somehow it be possible, but if your going below 40, you should be able to drive without the turbos coming online...i would of thought (dont have a TT just a thought)

 

i think carl0s asked this when he joined have a search

[Ian C]

Your non-turbo button is the accelerator The great thing about turbo engines is, if you are off-boost you are NA. I can get 26+mpg even when using mild boost now and again.

 

And anyway, no, you can't switch off the turbos They are permanently plumbed in.

 

-Ian

[LeeT]

you could always do the ETTC mod and keep the revs below 3.5k

[Aerotop Dave]

I can do my entire journey to work below 2000rpm. It just takes practice

[JamesG]

My boost controller has a peak boost display, and once I managed an entire journey without making +ve boost. Was quite pleased with myself Okay, so it was only a mile and it was in traffic...

[tbourner]

Turbos have better fuel economy than NAs anyway (if you drive them nicely obviously).

[Aerotop Dave]

Really? How's that work then?

 

Without using the turbos it's acting like an N/A, so I would have expected the same mpg. When using the turbos, you have more air going in and thus more fuel going in to even up the mix, so the mpg would be higher.

 

Confused!

[tbourner]

Really? How's that work then?

 

Without using the turbos it's acting like an N/A, so I would have expected the same mpg. When using the turbos, you have more air going in and thus more fuel going in to even up the mix, so the mpg would be higher.

 

Confused!

 

 

Basically..........

 

 

I don't know much about the ECU/fuelling in the Supra, so it might be slightly different, but I doubt it.

 

In general a Tubro'd engine will be more fuel economical than it's NA equivalent.

 

It's easier to explain in terms of a 4 cylinder engine. The 4 stroke cycle consists of Induction stroke, Compression stroke, Power stroke and Exhaust stroke.

 

1. During induction the piston moves down the cylinder, creating an air pressure that is lower than that of the atmospheric pressure in the inlet manifold. This causes the air (and vaporised fuel) in the inlet manifold to enter the combustion chamber. This vacuum is created because the piston is moving down the cylinder, which is caused by the rotation of the crank. Therefore an ammount of energy in the crank is taken to perform this action (not a lot I'll admit - see number 5).

 

2. The piston moves up the cylinder, compressing the air and fuel in the combustion chamber causing a temperature rise, hence when the spark is shown to the mixture it ignites (there's a hell of a lot can be written about this as well - compression ratios and pre-ignition/detonation etc.). Again an ammount of energy from the crank is taken to compress this air/fuel mixture, and it's more than is required for the induction stroke (again see number 5).

 

3. The ignition causes a rapid expansion of the air/fuel, which propogates through the combustion chamber until (ideally) all the mixture is burnt. This rapid expansion creates a much higher pressure in the chamber, which forces the piston to move down the cylinder. This is the power stroke and is the only stroke in the cycle that actually gives energy to the engine!

 

4. The exhaust valve opens as the piston moves up the cylinder, and the burnt mixture in the combustion chamber is forced out of the outlet to the exhaust manifold. Similarly but opposite to the induction stroke the gas in the combustion chamber is higher pressure than the gas in the exhaust manifold, and so it flows out with ease as the pressures equalise, and therefore creates very little pull on the energy from the crank.

 

5. The 4 points above are happening all the time, and only 1 cylinder is on it's power stroke! So the other 3 are either relatively idle (power-wise) or are actually taking power from the system!! There are then various designs to talk about with manifold design on both inlet and exhaust, because the opening and closing of the valves creates 'pulses' of air in the manifolds, and if they happen to be going the wrong way when the next cylinder's valve opens (i.e.: one section of a 4-2-1 exhaust manifold joins to 2 cylinders that run opposite each other) then it will push air into the exhaust valve (or pull out of the inlet) meaning there will be an incorrect charge in the combustion chamber for the next power stroke! The system is usually designed for optimum pulsing at a particular rev range (usually quite high), and the pulses actually aid in drawing gas from the chamber or pushing charge into it. Wich is why putting a big exhaust on a NA engine will mean there is less back pressure in the exhaust system, and therefore the higher power at higher revs will decrease!!

 

 

Anyway, a turbo will negate all of these problems because the exhaust gas is kept at a more constant flow rate with no 'pulsing', and the inlet is also at a more constant pressure. And so up to a certain point of throttle you aren't losing any power that you would have lost in the equivalent NA. Of course when you floor it the ECU poors in fuel and the shoes on the other foot!!

 

Any comments welcome, including reasons why I'm totally wrong!!