Acceleration pedal

[emil_t]

Is it just me or (i'm talking about a 105hp renault engine here) at more than a quarter throttle there is next to no diffrence if i press it to the floor or not, acceleration wise

[the Interceptor]

Maybe. Given it's an electronically operated pedal, Renault might have programmed it to do that. Some manufacturers go down this path to make their cars appear "meatier", since even a bit of pedal action will give you quite a surge. I know Opel did that with the Astra, the OPC at least.

[epp_b]

On a 105hp engine? You bet it'll make no difference

[narf]

It's similar in our Astras, both non-OPC (1.4 and 1.6).

Some motivation may be to artificially increase the felt power, but I'd say fuel economy plays a bigger role. We all know engines are more efficient at higher load levels, the engine management thinks "you want to accelerate, let me help you be economical". If you want less acceleration you can always shift up

[LeVeL]

From my experience WRXs are like that too. In the ones I've driven, 1/2 throttle is almost the same exact thing as WOT.

[Nabster]

Not the case with either of my cars. Pretty noticeable differences in both feel and sound between heavy and light throttle.

[brydiem]

My 65 bhp car has a definite difference between 1/4 pedal and full pedal. I daresay it would be a programmed thing (the no difference thing in the Renault), given my car is 15 years old.

[bone]

i think that's normal to butterfly throttlevalves. 3/4 or full open doesn't give that much difference in flow.
i think that's also why sportier engines have double valves, the second one only opens when passing 3/4 throttle

[rowd22]

^Yep, definitely normal for butterflies.

Thats why good race engines have a butterfly per cylinder - it makes the engine more responsive across the rpm range

[bone]

Originally Posted by rowd22

Thats why good race engines have a butterfly per cylinder - it makes the engine more responsive across the rpm range

nope, that's to keep the distance between the throttle valve and the cylinder valves as short as possible. the shorter this distance, the responsier and revier the engine will be...results in less torque though

[Spectre]

Sportier engines do not have two throttle butterflies (with the second opening after the first) unless they've got one of the various "variable length intake tract" schemes.

[emil_t]

i drove a car with the BMW-PSA engine 1.6 variable valve timing, and that is even worse, it feels to be at full power sooner that the renault engine does, though i haven't had time to check it properly, but it does have some wizardry, at full thorttle it has a button (i belive it's called kick-down,but i thought they were only for automatics), i didn't go past 4000 rpm (engine revs to 6000) at wide open thorttle , but really haven't felt hardly any diffrence.

[rowd22]

Originally Posted by bone

nope, that's to keep the distance between the throttle valve and the cylinder valves as short as possible. the shorter this distance, the responsier and revier the engine will be...results in less torque though

Torque has a lot to do with the airbox (plenum) size as well, not to mention the runner length.

[bone]

Originally Posted by Spectre

Sportier engines do not have two throttle butterflies (with the second opening after the first) unless they've got one of the various "variable length intake tract" schemes.

GTI throttle body:


and a GTI doesn't have variable length intake

[rowd22]

Cool, interesting feature it has then

So by the looks of it, the smaller one opens first, then the bigger one at 3/4 throttle?? (correct me if im wrong )

[bone]

^you are correct

alows you to have the power, but still have good mileage when cruising along

[Spectre]

That partially explains why the GTIs have so many fuelling problems.

This also means that for the given external size of the throttle body, it's actually a restrictor and hurts maximum power. This would have been more easily resolved with a big throttle blade and throttle by wire.

[bone]

Originally Posted by Spectre

That partially explains why the GTIs have so many fuelling problems.

This also means that for the given external size of the throttle body, it's actually a restrictor and hurts maximum power. This would have been more easily resolved with a big throttle blade and throttle by wire.

true, but won't the engine be less responsive in low revs with a single big throttle blade?

and what has throttly by wire to do with it? i've always been told to stay away as far as possible from those...

[Spectre]

Originally Posted by bone

true, but won't the engine be less responsive in low revs with a single big throttle blade?

and what has throttly by wire to do with it? i've always been told to stay away as far as possible from those...

That depends on the engine displacement and how the bellcrank that opens the the throttle blade is arranged. You can design a bellcrank so that the throttle pedal travel isn't linear, such that small inputs at low speed don't open the throttle blade much. Such things are easier to fine-tune in software than with mechanical engineering like a non-linear bellcrank.

If anything, the only thing you lose at lower RPM with a single large throttle blade is low rpm low throttle precision. Since this is unimportant to most people, it's not exactly a problem. A system like what you pictured has some severe drawbacks at mid and high RPM, too; especially when you consider that fitting a larger throttle body and blade (within certain limits) will improve throttle response, not damage it.

[matt2000]

Some trivia for you from my new Land Rover magazine issue. On normal petrol engined cars with carbs, the throttle pedal is connected to the carb and controls the fuel/air flow, as we all know. On the governed 2.25 Land Rover diesel, however it controls the RPM, and the governor on the engine controls the fuel to maintain the revs, and speed.

This is actually designed to use with PTO farm equipment to maintain RPM if the load increases. On a normal road though, it would allow you to drive up to a hill and not move your foot on the pedal, because the governor will give it more fuel.

/I did not know that.