This engine's throttle response

[Peter Carmichael]

I have ftp'd up a log of my new engine running to the Sevens list site. An upchange at 4000rpm is overlaid on a similar upchange on the old Supersport engine and shows the difference in throttle response.

 

it is here

 

The highlighted area shows the comparison. The red line is the trace of the

revs of the new engine. The grey line in the background is the trace of the

Supersport engine. The rate that the revs drop away on the new engine is as

astonishing as it looks and they pick up as fast.

 

These are both fluffed casual changes, with the revs being allowed to fall

too far before the new gear is selected. The way it feels to drive, there

seems to be no speed limit on gearchanges with the new set up.

 

Edited by - Peter Carmichael on 6 Oct 2000 23:58:15

 

Edited by - Peter Carmichael on 8 Oct 2000 11:59:44

[Glen]

Peter

 

Is this maily due to the special clutch and flywheel? Or does the engine management play just as big a part?

 

I have heard that modern engine management maps are designed to deter very quick changes in engine rpm, as a deliberate design feature to smooth out the delivery and improve emissions and fuel efficiency. In other words these off the shelf systems (the standard Caterham/Rover fitment for example) are very much for every day cars and pretty badly designed from a pure driving enjoyment point of view - the total power potential is, I guess, unaffected by these tweaks, they just knackers the nice crisp delivery which you seem to have succeeded in capturing.

[Roger King]

Glen,

 

You're right on both counts - Peter's flywheel might best be described as a 'clutch mounting bracket', i.e. there's precious little of it. The clutch is pretty impressive too.

 

And yes, modern engine management is often very poor on throttle response. In an ideal world, the fuel/air ratio will be richened quite a bit during 'transients'. This is a posh word for the act of opening the throttle. A pair of DCOE carbs have little internal pumps to put this extra fuel in when needed, resulting in great response (if calibrated correctly).

 

Unfortunately, the side effect of this is to worsen emissions drastically, particularly on the hydrocarbon front. This is unburnt fuel that comes out of the exhaust. Therefore, in this emission conscious age, transient enrichment is kept to the miminum possible.

 

I have a Ford Ka, which apparently is much better than average on emissions. It's a great car in many respects, but the throttle response feels like there is a piece of elastic between the pedal and the engine - it's so bad that you have to try it to believe it.

 

Peter's engine has not yet had the mapping optimised, but it seems that his transient enrichment is not too far out.

[Peter Carmichael]

The transient I have plotted is on a trailing throttle, so I don't think the injection management makes much difference.

 

Throttle bodies vs. plenum makes a difference because there are a few gulps of air available for the engine left in the plenum, however I think almost all the effect you are seeing is down to the flywheel and clutch.

[Mike Bees]

I think the management does make a difference. The GEMS box has allows you to set 'deceleration fuelling' as well as acceleration fuelling. I also suspect that road car systems use the IACV to bring the rpm 'in to land' slowly at the lower end of the rev range.

 

Mike

[Peter Carmichael]

Mike,

 

I don't think that is what the graph shows. You can kill the ignition on the Supersport and the rev drop is the same. It is a factor of four faster, which either means that the Supersport MEMS is keeping the engine firing effectively, producing power equivalent to three quarters of the pumping losses on a closed throttle, or I have one quarter the inertia.

 

If getting it off the line is anything to go by, I have one quarter the inertia.

[Matt Prior]

Roger,

 

If you think the Ka is bad (which it undoubtedly is), have you tried the Skoda Fabia 1.4?

 

The elastic band attached to the throttle, I'm told, threads around the rear suspension before heading down to the engine...

 

[Mike Bees]

"I don't think that is what the graph shows" - fair enough. Mine was more of a general comment on the state of play.

 

Mike

[Roger King]

Peter,

 

My comment about engine management was made without reference to your graph, because when I wrote the reply I hadn't looked at it! Only got around to it since you made it more easily accessible.

 

Matt,

 

I've heard this about the Fabia 1.4; apparently, it ruins an otherwise great little car.

[Tony Martyr]

Peter,

Thanks for posting this detail of your project I am following with interest as it parallels work I witness in new test cells that are all emissions driven. Your curve shows the effect of low inertia to a degree that the normal driver would find difficult to handle. What is the idle speed set at?

 

[Peter Carmichael]

Idle is regulated by the ECU to a very steady 1200rpm. It gives the cam lobe noses an easier time of it.

[Peter Carmichael]

>>Your curve shows the effect of low inertia to a degree that the normal driver would find difficult to handle.<<

 

The ridiculous thing is that it makes the car easier to drive accurately and smoothly than all the combined fudging that happens in modern cars. Yes, there is an issue getting away from the line, but I think a more moderate clutch with some sort of shock absorption would cure that. Once on the move it is utter bliss to use, although at the moment I have to remember to move fast.

 

I think trends in car design have bred ignorance into drivers and that every safety advance will be nullified in the medium term by the dumbing down of the act of driving. In the long term, obviously driving will not exist.

[Glen]

If called upon, and trained, to do it the human brain is easily capable of using the throttle carefully to maintain a smooth drive. I totally agree that it's overkill to have so many facets of engine behaviour (or other elements of car handling) taken care of by a computer. This is easy for me to say of course because mine's a standard 1.8k and I don't have to worry!

[Tony Martyr]

Peter wrote "I think trends in car design have bred ignorance into drivers and that every safety advance will be nullified in the medium term by the dumbing down of the act of driving"

How true. 7 months of driving in Detroit, where 99% of the cars only have two pedals and multiple airbags, has taught me that most of the drivers including engineers working in the auto industry have had all 'feel' for the vehicle removed. They redress the balance of risk by driving at 75mph in all weathers inches from each other. I predict that the general conversion to automatic gearboxes is a sign of social and moral decline :-)

I still think driving around Milton Keynes in your car in heavy traffic Peter would be a nightmare.

 

[Mick Day]

Tony wrote: "I predict that the general conversion to automatic gearboxes is a sign of social and moral decline"

I disagree. A good auto gearbox allows a road driver in heavy traffic, ie SE UK, to concentrate on the road with both hands on the steering wheel. Ideally a button gearchange on the steering wheel is the way to go if you want to swap cogs.

[AshJackson]

I had a go in an Alfa which had buttons on the steering wheel and I found that they were too far into the wheel and sometimes (especially in corners) I had to really reach in to press them.

 

Of course, an F1-Style paddle shift would be quite nice smile.gif

 

 

 

 

..... Ash.

+++ Honestly, it was like that when I got here.