Throttle Response

[KOY 23]

I have read of many instances where a new carb has been fitted and the comment made that the car feels much more responsive and faster, inferring that the engine power has been increased, possibly but without before and after rolling road runs, unprovable.


However the comment that it is more responsive may well be true. It depends on the throttle set up, most systems tend to be progressive in that 10% of throttle movement gives 10% of throttle opening, throughout the range. Aftermarket systems may not be compatible with the accelerator pedal travel and small throttle movements giving larger throttle openings and the greater initial response that many see.

My Son has a Boxter which he ran on the rolling road, then fitted a well known tuning box, he said the car felt much faster and more responsive and put it on the same rollers again, expecting to see a good increase in power/torque. The results were identical, all the tuning box did was alter the throttle response.

Recently I drove another car which has a slow initial response to the throttle, it needed a much larger initial throttle movement than I’m used to to get the car moving, which made it feel initially sluggish, probably a good feature on a car with 500bhp.

[Ian F]

This is so, so true and no more evident than with a modern vehicle that has “Economy/Normal/Sport” settings that change the throttle maps.
My other half has just got rid of a Nissan Juke 1.5dci diesel that had precisely this feature; in Economy the throttle was sluggish, felt Rev limited but covered circa 54 mpg, in Normal, it felt more lively and you could “nip out” into traffic something that was dangerous in Economy. In Sport it was even more reactive, jerky even, so this was hardly ever used but it felt like a different car. Same engine, no more power - all down to throttle mapping though - not the linkage!

Mercedes usually have long throttle actions for that reason - mete the power gradually!,

ian F

[KOY 23]

Spot on Ian , it was a SL55.

[Stagdad]

Even a weak throttle return spring can have the same effect. The throttle bodies I have on my efi set up has a special linkage building in exponetial, it's really quite clever how they have done it. It's of a Vauxhall omega and gives nice feathered throttle in low openings and opens up fast in the second 2/3rds of the moment which means you do have to push hard when you want to give it some.

[Matt Cook]

I also read somewhere that large throttle openings at low revs give rise to the largest cylinder pressures and stress on the bottom end of the engine......

[STypeR]

I ditched a non standard carby set up at the last moment but I must admit that I never thought of throttle response being a possible perception factor. It begs further analysis of the question.
Is HP the be all and end all? I would have thought that 400 HP would be enough for any man as in my daily driver but there are many in that club that constantly tinker with some smart ideas and have spent thousands with some reasonable results but ultimately worth the effort?
I couldn't find the energy to go there on my Stag whilst on a full car restoration and the hassle of getting effective cold air into the thing really put me off. I must say I didn't really see too much convincing evidence on the gain after the cost, time and effort were taken into account.
One must ask in the absence of multiple examples of hard and thorough supporting evidence for the Stag if we are seeing throttle response fooling us as in the case of the Boxter example above as a major factor of such conversions?

[Hettiherald]

I really do think that the point is being missed here and talk of extra power etc etc is muddying the water. There are those of us that are happy with a modified set up, Webber , holly, or injection which give the car that little bit of reliability over worn strombergs. I personally don’t use my car as a sports car, but a comfortable tourer, and am happy with any mod that gives me a bit more confidence in everyday use. If Somone ever produces new strombergs at an affordable price, I will be in the que, but until then .........
dave.

[flying farmer]

Back in the days of Ford Cortinas with Pinto engines a common go faster mod was to fit the 3 litre Weber car. Made them seem much faster as both throttles opened simultaneously rather than sequentially. Didn't actually make any more power- just felt like it did!

At the other end of the scale my sister had a Talbot Samba, can't remember the capacity but about 1 litre. I was amazed how quick it felt until I used it on a motorway journey, half throttle gave about 80mph, full throttle gave about 83! The throttle was geared to open very quickly which was what made it feel so lively.

A classic example of huge throttles making an engine feel rapid is my Toledo with its twin plenum Rover V8. This has twin 65mm throttle discs, and still has its original cam arrangement throttle linkage which opens the throttles relatively slowly. Despite this I can exceed the legal limit with a mere 7% throttle opening according to the megasquirt data logging.

This makes mapping interesting as nearly everything has to be packed into the first 50% of throttle opening, as except at the upper end of the rev range there is no difference between 50% and 100% .
With only 3528cc capacity and the crap volumetric efficiency that comes as standard with Rover V8s, the engine cannot draw anywhere near enough air to even justify one throttle disc of 65mm.

Eventually I am going to replace the factory cam with something more lively and see if I can make the twin plenum actually work for its living!

Neil

[Guest]

This is so, so true and no more evident than with a modern vehicle that has “Economy/Normal/Sport” settings that change the throttle maps.
My other half has just got rid of a Nissan Juke 1.5dci diesel that had precisely this feature; in Economy the throttle was sluggish, felt Rev limited but covered circa 54 mpg, in Normal, it felt more lively and you could “nip out” into traffic something that was dangerous in Economy. In Sport it was even more reactive, jerky even, so this was hardly ever used but it felt like a different car. Same engine, no more power - all down to throttle mapping though - not the linkage!

Mercedes usually have long throttle actions for that reason - mete the power gradually!,

ian F

Yay, she’s got rid of the Puke!!!!!!

[Ian F]

Yup, she’s got Nigel now, a Fiesta Viagra (sorry Vignale) Automatic and NO I didn’t choose the colour.

Had it early October, drove it twice and had her other knee replacement, hadn’t driven it since, for 6 weeks, until Thursday and now has to get used to it again. For a 999cc 100 ps triple petrol auto. it goes like stink