Let's see, when in my 72 911 cruising in 2nd gear at 2000 rpm, and I nail it, it gets up and goes. When I'm doing the same in my 88 saab spg turbo, it does not. It takes about 2 seconds before the train leaves the station in the saab. So, my porsche has great throttle response, my turbo does not. How's that for laymen turns.:)

I go for the more specific meaning, like Bill's; the time from moving the pedal to getting force from the engine.

I normally nod my head yes on Magilla's posts, but in this case I wouldn't use RPMs as a direct indication. Even in the case of comparing different flywheel weights when not in gear, I'd call that rev-response instead of throttle. Throttle response to me would be reflected in the immediate torque, that's the first thing you're getting with MFI or carb spitters and it's what you are waiting for while the turbo spools up.

What if you were pulling a 30ft boat ( spank yourself if you've done this with your 911 ) and stepped on it. Would you say your throttle response was bad because the RPMs didn't climb fast or would you say it good because you could feel the engine pulling right away.

Hey blu! Good example, but there are siimilar delays in worst-case examples in the normally-aspirated spectrum, too! I used to say that in driving a friend's '84 Bronco II ... all you were doing by nailing the throttle ... <b>was putting a request for power in the queue of the Ford EEC IV processor instruction stream, and it wasn't a very fast processor!</b> Similar resulting delays to your Saab example, though completely different technologies involved!

That's what I'm getting at. My old Honda 125cc dirt bike had great throttle response, it just didn't respond very much.

I recall reading a review of the new Boxster S in Excellence. The author talked about the new "e-gas" technology and how he thought there was a very slight lag from pedal input to throttle response vs. a more direct feel with the old cable system. :(

Markus

Excellent Throttle Response: John Force's Funny car


Poor Throttle Response: Geo Metro pulling a boat

Hmm, my son's Pontiac Grand Am. Hit the gas, that sends a request to a committee, once they are done discussing, studying, and voting on the request the car goes. That would be poor throttle response. My '88 3.2 in any gear above 2K rpm good throttle response. Michael Schumacher's Ferrari F1 unbelievable throttle response.

Just wanted to comment on JPIII's post. Actually it's the MFI that out "responses" the carbs as it is more than just dumping fuel. I believe the more critical factor is the atomization of the fuel (think hairspray vs. garden hose). The "atomized particles" condition is more desirable for the combustion process.

Yikes! This is one of those topics which elicit a lot of "soft" responses as opposed to any facts. I guess I'll throw a couple more cents in...

"Can a dyno measure throttle response?" -- Yes. If it is a transient dyno. These are fairly new and as of a few years ago I had not heard of many of them. I do know that Mercedes has one in Stuttgart, but I don't know how wide spread they have become. This is a dyno that can be programmed to measure part throttle conditions or programmed to run a complete race simulation. The other alternative would be to compare track data from a Pi-System or something similar.
-- Incorrect port size can cause poor throttle response as a result of the excess air mass in the ports. Ports which are too small can choke off a motor so you might have an instant response but no HP. But how could you tell???
-- Intake runner length affects where the Torque peak will occur as a result of tuning the harmonics. This is the same principle the a flute operates under. Shorter runners have a higher frequency and as a result aligns with higher harmonics and higher rev's. Longer ports have a lower frequency and so are tuned to lower rev's. There is a formula, but I haven't been able to find it recently. In order to increase the torque band, F1 and F3000 engines have been using variable length intake trumpets for a number of years depending on the rules. Another way to do this is to run two different length intake horns. I've saw these on a IMSA 240Z years ago and this is what they claimed. I don't know how it worked, but I haven't seen a lot of them set up like that lately.
-- I agree with that was said earlier, I believe the primary issue to improving throttle response is to get the corrected mixture into the cylinders as quickly as possible after the throttle has been moved. I've heard that it is one of the two big advantages of the Direct Injection Audi's racing last year in PSR and Le Mans. In their case the fuel is injected directly into the cylinders just like a diesel. The other big improvement apparently was mpg. MFI's do this well because of the improved atomization from the high pressure injectors, the prefigured fuel amount and the small volume of air between the throttles and the valves. As others have said, other systems suffer in one or more of those areas. But the actual affect is most likely fractions of a second until you are talking about Turbos.

Reducing the rotating mass (ie lightweight flywheels and wheels) helps reduce the resistance to the acceleration. But testing throttle response in a drive way is most likely not valid since there is little if any load being placed on the motor. Gas motors really run best while under load. Having a light car helps to mask the other factors mentioned above also. The thing is that FC cars (as well as FF's, S2's etc) corner so fast that they really don't have to accelerate near as fast as a big heavy sedan. This is why the 150 HP (from a 2bbl 32/36 carb on an unequal length intake manifold) in a FC or S2 is enough to go so fast, because the cars only weigh 1100 lbs +/-.

Very interesting. I do not believe this term is something that you would hear race engineers refer to because it is essentially meaningless. What it boils down to is:

Good throttle response: Lots of power.
Poor throttle response: Not so much power.

I think this is more of a layman's term for someone like me to abuse.

Hmmm, I see two camps forming:

Engineer-types: how quickly the air/fuel system couples a pedal movement to the cylinder.

Horsepower-types: push pedal, go faster.

My brain is in the former, my batteries prefer getting charged in the latter. Yah-hoo!

There is a lot to agree with here and I do agree. Interesting that only John mentions racing with the post on the Mercedes dyno. My idea of throttle response is if you can drive the car in a corner with the throttle. A turbo, or turbine for that matter, comes on too late to use the throttle positions to turn the car. Of course this all depends on how the car is set up and if it responds well to the gas-o-meter. Think of a dirt oval racer. Driven with right foot and two hands. Poor throttle response would make the dirt car undriveable. IMO, response is how quickly the car reacts to the input.

Now driving a 911 in a corner with the throttle? Just let off real fast and see the world turn around. That, folks, is throttle response.

Zeke, I agree with your practical, real world definition of throttle response. In a 911, it is while throttle steering in a corner under load where great throttle response becomes most valuable in real life. Driveway testing and straight line performance may favor carbs, but MFI will beat carbs all day long under high G loads.

I am fortunate to have two 911s, one with MFI ('72S w/ 2.7RS spec engine) and another with programmable engine management ('72T/RS with 3.2L Motec and Varioram). In a corner under load, the MFI is better at producing the quality of throttle response that you most need when coaxing out the last degree of traction that borders on tail out oversteer - but not by much. Riding this rail is the best part of owning a 911. Porsche was right - there is no substitute

Got to disagree, Orb! Maybe not these days, because 'racing engineers' thse days are nothing but analysts, and they NEVER drive the cars! They look at computer-collected telemetry, and go look up an answer based on previous trends and data ...

But, the 'real' racing engineer/drivers in the past like Dan Gurney, Jim Hall, Bruce McLaren, and specifically, Mark Donohue, DID worry about such phenomenon! I cite the example of the 'Happy Cam' story during the development of the 917/10 engine from <b><i>The Unfair Advantage,</b></i> and it involved Mssr's Flegl, the Can-Am project engineer, and Donohue, a 'racing enginee/driver' of the type the Black Forest gentlemen had never encountered before!

Yikes is right!
 

2 pages! I suppose this is what we get when we mix vague terminology with a dash of nonlinearity, and stir. :D
I was thinking jluetjen's first post seemed quite adequate. Apparently not. (BTW; Excellent follow thru on the second post, jluetjen. )
Certainly Throttle Response Time can be measured by more accurate means than a calibrated pair of Levi's.
If one means Throttle Power Response, that can be measured as well.
How quickly you get throttle and how much you get are two different (sometimes related) things. That's my 2¢ worth.

I just figured out how to solve the problem of throttle response with the cis systems. Run a horizontal rod from the throttle body plate shaft to the body of the sensor plate.

On the end of the shaft of at the sensor plate, install a arm 90 degrees to the horizontal rod. From this arm, install a vertical rod down to the underside of the sensor plate.

Now, with cams and gears and a little bit of know how, adjust the rod at the sensor plate to lift the sensor plate up when the the throttle is opened.

The amont of sensor plate lift (fuel going to the engine) would have to be adjusted so that the fuel to air ratio going to the engine would be correct regardless where the throttle body plate was.

Now if you wanted to do a little fuel enrichment, add a micro switch so that when the throttle was mashed open, a circuit would close and energize the cold start selenoid. (more gas, more air, quicker response, faster rpm's

How does that sound for a quick fix?

Alwright, maybe it does sound a little far fetched, but what the heck, anything is worth a try to get more response out of a CIS system.

Just a thought.

Steve

Randy:
God willin' and the creek don't rise, I'll get up to Bremerton this summer. I'm willing to be educated. ;)

I'm working on the throttle steering. The car/motor is more than willing (none of the dreaded lean/flood nastys). The driver sux, however. Maybe I ain't going fast enough.:confused:

A couple more thoughts....

stormcrow: Good idea. What you just described is essentially an MFI system with an air flow sensor. If you just ditched the air flow sensor entirely, you'd have most of an MFI system. If you replaced all of the levers and rods with electronics, you'd have most of a DME system and if you kept the electronics and pitched the sensor you'd have something similar to what Motec sells!

Warren: Are you just going to bait us with the Mark Donohue reference or are you going to share the story for those of us who do not yet have "The Unfair Advantage". (BTW: It is on my B-Day list!)

Zeke914: It's funny that you of all people describe the 911 as spinning fast from TTO. Wait until you race the 914!!!:eek: The shorter polar moment resulting from the mid-engine design will really get your attention. Think of Sarah Hughes spinning with her arms outstretched (911) and then pulling them in (914). Can you say reduction in rotating inertia???

orbmedia; You said "I do not believe this term is something that you would hear race engineers refer to because it is essentially meaningless." That's half the fun of racing (to me at least!). Just because race engineers don't discuss it a lot does not mean that it is meaningless -- it just means that the engineers don't want to discuss it ;) ;) ;) . Given that HP really is kind of finite in an non-turbo internal combustion engine (Check out the recent thread referencing a UK engine builder), it all comes down to intake valve area. After that it just comes down to spinning the engine as fast as possible to generate the most HP. So how does a Race Engine Engineer build a world beating motor? The devil is in the unglamorous details: low center of gravity (AP clutches and Renault 119 degree V10's), Low weight (Cosworth's linerless V10 and beryllium anything), more rev's (Cosworth's HB V8 with it's short stroke and big valves, Nascar engines with their light weight valve trains), fuel milage (Audi's direct injection V8) and throttle response (Audi's direct injection again). A lot of this stuff only comes out after the rules have been changed and the motors are obsolete.

If you check out the old R&T track test of a 917-10 (October '72), the writer did a pretty good job of reporting the intake configuration and guessing at how it all worked. In hindsight it has all since been explained, but at that time Mark Donohue was pretty silent. In fact he actually does a clever job of diverting the attention to the frame being made of "Unobtainium". While the frame's material (Titanium) is important, the secret to the 917-10/30's success was the managing the Turbo which was done by the intake system. It wouldn't be the first time that a Race Engineer has thrown out a "red herring". Now what was Audi saying about the improved MPG of the Direct Injection being the competative advantage? The car's sure seemed to be running well out front even prior to their pit stops....:rolleyes: