Chipping a normal motor will make no difference...

[h100vw 0]

If carbs were so good, would they not be used and F1.

Gavin

[Kevin Bacon 5]

Yeah that makes sense mate..... like the 'splatoosh' word too. I think that needs to go in the Oxford Dictionary...."The noise emitted by spark plugs in internal combustion engines" :lol: I think splatoosh is also the sound bullets make as they rip your innards to pieces..... and there's a pleasant thought for Christmas week :)

[Neil VR6 0]

I would imagine that fuel injection can meter fuel more effectively which is so vital for forced induced cars. Only if the fuel pressure and injectors are correct for the given state of tune though. Having injectors running at 90% duty cycle is too much for instance as there is less control seeing at the injector is "open" for 90% of the time. Set up correctly, surely fuel injection will always win and prove more reliable?

[coolrado 0]

If carbs were so good, would they not be used and F1.

Gavin

 

with the fine tolerences and mega high rev's in f1 cars, carbs just aren't up to the job they do provide plenty of power but at the expense of fuel economy and reliabillity

[dr_mat 0]

And fuel economy is actually important in F1, believe it or not, given the weight and performance penalty of an extra 10 litres of fuel.

Carbs overfuel like mad, which covers your arse if the mix isn't quite right, but to get absolutely everything it's possible to get out of the fuel it has to be carefully metered. Also, the injectors can provide a finer mist of fuel in the air, promoting a better burn, and can do so right at the entrance to the cylinder (or IN the cylinder with the direct injection engines they're working on now).

[Joe M 0]

I think theres a bit more to f1 engines and its not worth making a comparison.

Check out this vid: http://www.renaultf1.com/php/vidpopup2. ... 24_220.wmv

[coolrado 0]

my mates westfield with a 1.8l ford engine and weber twin 40's would be lucky to get more than 20mpg and had to be re-tuned twice a year with the changes in temperature,

it also had a nasty habit of firing back out of the carbs and blowing the foam filters off the carb trumpets :lol:

 

carbs are just a crude way of getting plenty of ponies out of your engine and are better suited to track cars but can be quite reliable if well set up

[Kevin Bacon 5]

Injectors can also be sequentially fired, which is far more efficient than one carb sharing the atomised mixture out 4 ways.

Plus obviously you get one injector per cylinder, which again is more efficient and closer to the combusion chamber.

[dr_mat 0]

Why do most fuel injectors run at 1.5ms pulses at idle no matter how big the cubic capacity of the engine?

What is the point of the variable inlet plenums on the new VW engines?

Why can you sometimes get more torque by delaying the ignition timing?

 

Perhaps most engine designers choose injectors (or FPRs) with the right capacity/flow rate to allow a 1.5ms injector opening at idle? Perhaps all cylinder sizes require around the same amount of fuel to maintain tickover? Who knows? Who cares? Anyway, mine runs at 3.5ms at idle, according to VAGCOM. It'll drop to 1.5ms on overrun program. But maybe the engine wasn't fully warmed up yet?

 

Variable inlet - well it's like the schrick for the VR6 innit. I refer you to the great docs about how that works elsewhere.

 

More torque from delayed ignition timing only works when your ignition timing is too conservative. Most modern cars run pretty close to pinking, so fiddling with the ignition timing isn't going to help too much.

 

:lol:

-frank

 

Or were you actually taking the piss..? ;)

[Joe M 0]

Why do most fuel injectors run at 1.5ms pulses at idle no matter how big the cubic capacity of the engine?

 

Perhaps most engine designers choose injectors (or FPRs) with the right capacity/flow rate to allow a 1.5ms injector opening at idle? Perhaps all cylinder sizes require around the same amount of fuel to maintain tickover? Who knows? Who cares? Anyway, mine runs at 3.5ms at idle, according to VAGCOM. It'll drop to 1.5ms on overrun program. But maybe the engine wasn't fully warmed up yet?

 

 

It might be more simple than that. Maybe its the quickest the injectors can open and close and its not possible to get the time below that.

[Kevin Bacon 5]

It might be more simple than that. Maybe its the quickest the injectors can open and close and its not possible to get the time below that.

 

Sounds feasible....

[davidwort 0]

...direct injection engines they're working on now).

 

Just been reading about the FSI engines, blimey!, that's a lot more complicated than I thought :? , not just squirting straight into the combustion chamber. Only problem is these things are going to cost a fortune to diagnose and fix if they ever go wrong.

 

David.

[dr_mat 0]

Tell me about it. My father's got one. New Mondeo 1.8 SCi (or whatever ford call them). He's been getting check engine lights pretty much since new, and they've just recently managed to do a firmware update that they *think* might have fixed it.

These things are clever. The direct injection means they can actually perform a controlled burn in just a small PART of the cylinder. The remainder of the cylinder is filled with exhaust gases via the recirc valves. That way they can run with insanely small fuel amounts without causing pinking. (The small part of the cylinder that *has* fuel when the spark fires is at a normal fuel/air ratio.) Part load economy is extraordinary on these things... Of course, they feel a little weird to drive, the switchover between insano-lean-burn and normal-burn seems to effect the way the engine pulls.

But as you say, come 10 years time and 100k miles + these things are going to have dodgy engine sensors and all kinds of BAD, EXPENSIVE things will be happening!

[Scott 0]

Injectors can also be sequentially fired, which is far more efficient than one carb sharing the atomised mixture out 4 ways.

Plus obviously you get one injector per cylinder, which again is more efficient and closer to the combusion chamber.

 

Unless the car is single point injected :wink:

[chubbybrown 0]

Carbs pump in more fuel, end of story. That's why the increase in power. Another reason is an engine on carbs is generally running without catalysts, so the exhaust is more free flowing. Well, with all that overfuelling going on, the cat would die pretty quick anyway. It's no mistake that every car ever built with a catalyst has electronic fuel injection.

 

I had a nissan with a carb and a cat

 

no end of problems as the carb would cut the fuel as it would knacker the cat and create what started to be a 'twin choke effect' that over time turned into 'kangaroo juice' at every road junction,Honda had carbs n cats but they had it sussed

compared to the nissan '£500 to replace it Mr' effect,they tried timing and alsorts

thankgod she worked at a nissan dealers and got the warranty man in the office and stood at the door until he let her get a free new carb without admitting liability

Crazy world we live in.....

[CoxyLaad 0]

Yeah that makes sense mate..... like the 'splatoosh' word too. I think that needs to go in the Oxford Dictionary...."The noise emitted by spark plugs in internal combustion engines" :lol:

Yes....just happened to be thinking of saturday morning TV when Ant and Dec used to play that game called Splatoon.......Saturday morning telly has not been the same since they left, its more kids stuff now...... :cry:

 

I think splatoosh is also the sound bullets make as they rip your innards to pieces..... and there's a pleasant thought for Christmas week :)

 

Loverly :)

[dr_mat 0]

.. an engine on carbs is generally running without catalysts... no mistake that every car ever built with a catalyst has electronic fuel injection.

 

I had a nissan with a carb and a cat

 

no end of problems as the carb would cut the fuel as it would knacker the cat and create what started to be a 'twin choke effect' that over time turned into 'kangaroo juice' at every road junction,

 

Ah, the exception that proves the rule I think! ;)

[davidwort 0]

.. an engine on carbs is generally running without catalysts... no mistake that every car ever built with a catalyst has electronic fuel injection.

 

I had a nissan with a carb and a cat

 

no end of problems as the carb would cut the fuel as it would knacker the cat and create what started to be a 'twin choke effect' that over time turned into 'kangaroo juice' at every road junction,

 

Ah, the exception that proves the rule I think! ;)[/quote:ebfb4]

 

and some of the small Seat's, I remember seeing and article about how they had developed a system that enabled accurate enough fuelling to run a cat on some of those awful panda clones, Marbella I think (I'd rather walk.)

 

David.

[G100extreme 0]

Here are the answers you've been waiting for... Yes most people got them right! There must be some professionals on this board as one or two of those questions are not generally things that people will discover without a real engine dyno system, and experience in design engine/fuel management systems. I think we can all go out and buy ourselves a beer! 8)

 

Answers after each question...

 

Time to ask some basic questions to gauge the level of knowledge here. I just had to add some logs to the fire... :wink:

 

Why are there different ratings for fuel octane?

Ok, so this question is badly worded...Should be "why are there different fuels of varying octane". Octane rating of fuel however you want to rate it with whatever standard (SAE, RON, DIN) is to do with the speed the flame front burns in the mixture. It also partly indicates available power, and has an effect on the timing and compression ratios. For more info on the subject look up keyword knock testing engines. Basically single cylinder steam type engines where it is possible vary the compression ratio of the engine while it is running. Everybody should have a play with one- it really shows how timing, mixture and compression are the most critical things that affect power. Ideally a fuel would explode very slowly. Low octane fuels burn fast because they generally have shorter hydo-carbon chains. High, burn slow.

 

What effect does changing the compression ratio have?

The maximum push from an expanding gaseous explosion in a crank driven engine is when the crank is at 90 degrees to the axis. Think of a person standing on a bicycle pedal. Max push is when the pedal is horizontal... but in an engine you start pushing before top deal centre... By increasing the comprssion ratio, it is possible to delay the ignition point, by increasing the flame speed (the flame travels faster when the mixture is denser) so that the gasses have their maximum pressure (or push) further round in the cycle, ideally at 90 degrees to the axis. This is never actually possible, but ends up being a compromise varying constantly between 75 and 120. This is partly also why diesel engines are so torquey, because the fuel charge can be injected later... Obviously if the compression is too high the flame front will always travel faster than the descending piston and will collide or "knock" with it. For very high RPM engines, you can get away with it to a point, but then you are limited by a sonic wave. Flames cant burn faster than the speed of sound. So your piston descent speed is limited by that. (most engines redline at about 6 for that reason)

 

What effect does increasing cam dwell and overlap have?

This is what I call the hose pipe effect... Get a long hose of water, with water flowing quite slowly through it supply from a bucket with low supply pressure. If suddenly you block the end of the hose where the water flows out, the weight of all that water will keep trying to move down the pipe like it was before- the inertia. Suddenly there will be a huge pressure buildup at the end of the pipe.

Cam dwell uses the same principles, but with air. If the inlet ducts are long (they often wrap over the top of an engine) the weight of that high speed air in the duct from the plenum, causes a pressure rush. If the length is right, it appears just when the valve opens. This effect is useful allowing just a fraction more inlet charge at high revs, giving more power. (take a look at the lobe profile of a motor bike engine camshaft). Too much dwell and overlap can actually mean that unburnt mixture goes straight through the inlet and out of the exhaust valves, giving flames emerging out of the tail pipe (many racing cars). The disadvantages are obviously lost fuel, but it also means that each cycle you get a full charge giving a bigger bang, = lots more power...

 

Why do you need to advance the ignition as the RPM increases?

This is all to do with octane. The flame front travels at a fixed speed. So to get the most push out of the fuel at just the right time, you need to start it burning a bit earlier as the revs go up. The lower the compression ratio of the engine, the more advance you need usually. (for normally aspirated, non variable compression engines)

 

Why is it that longer exhaust manifolds/headers/extractors (or whatever you want to call them) increase power?

Already kind of answered this question- Hose pipe effect again. The manifold will always be longer than the inlet ducts as there is now a different mixture of gases. The chemical reaction of the fuel has created more gases, so the waste leaving the cylinder will have a bigger volume (as well as being hot = more expansion). So to get a suction effect this time using the inertia of the exhaust gases, the tube has to be longer. Different lengths give different performance at different RPMs. You could say that they are tuned to operate at one particular RPM. By having 4 into 2 into 1, the lengths of the two second stage tubes spread the effect to a lower RPM. Short tubes give more 'boost' at higher RPMs. Long tubes have more of effect at low RPMs. The pressure at the back of the exhaust valves varies from sucking (slight vacuum) to pushing (slight pressure) throughout the cycle, and through out the rev range. An ideal scenario would be to have variable length header tubes, set to just the right length for the actual RPM.

 

Why does water/steam injection help generate up to 20% more power?

In a nutshell, it slows down the expansion rate of the flame front during the explosion process, because of its quenching (or cooling) properties. Water on fire slows down its burning. The same effect can be partly found from throwing in too much fuel, as the excess fuel will tend to quench the burn. That is why most normal systems dump in huge amounts of fuel at WOT and high RPMs, to help reduce knock.

 

Why do most fuel injectors run at 1.5ms pulses at idle no matter how big the cubic capacity of the engine?

This has all to do with control. In a 4 stroke engine, the inlet valve is open once only for a few degrees in each two rev cycle. So at idle for example, the piston takes a certain time to descend from TDC to BDC, sucking in charge ,when the inlet valve is open. The descent time obviously depends on RPM. So for say 1000 crank RevsPerMinute which is 16.7 per second which is 60ms to do one rev. Divide by two to get the suction descent time which is 30ms where the crank big end pulls the con rod down. So at idle in a textbook scenario, with valves opening and closing at exactly TDC and BDC, there is lots of time to inject a small 1.5ms amount of fuel as the charge is being sucked in. The problem arises at high RPM and at WOT. To keep the mixture right, lots more fuel is needed for each bang. The trouble is, there isn't much time to dump all the required fuel in. In fact at 6000, only about 10ms. In 10ms, it isn't possible to inject the right amount of fuel, so the injectors have to stay on almost continuously, blasting away their little sprays this time against the back of a closed inlet valve for 40ms. So what happens to all that puddle of fuel? Some of it gets burned... the rest just leaves as partly burned fuel, because the droplets are so big. So the answer to the question is it comes down to the amount of fuel that the injectors can supply at WOT and max RPM. Increments of 1ms at idle on an injector open for 1.5 would make an engine idle really roughly, if at all...

 

Why do carburettors generate more power than injectors?

Smaller droplets of atomised fuel. Unburnt fuel simply makes your engine oil black. Engines that run on Propane (or LPG) can go over 20,000miles before needing an oil change; and when they do, the oil is still almost clear. Fuel evaporating off a venturi generates a much finer mist of fuel than an injector. It comes down to the size of the surface area of the chemicals reacting. We all know that a sugar cube disolves slower in a cup of tea than a teaspoon of icing sugar for example. More reactive surface area means bigger bang, and more power...

 

What is the point of the variable inlet plenums on the new VW engines?

Its the hose pipe effect... but now variable to suit different RPMS. All we need now is variable exhaust tubes.

 

Why can you sometimes get more torque by delaying the ignition timing?

Combined with a slower burning fuel (or steam injection) and high compression ratio, the push on the piston crown will happen at closer to 90 degrees...

 

:lol:

 

-frank

[dr_mat 0]

I knew he was taking the piss! :)

Did we pass the test, frank? Do we get certificates?

[exturbo2003 0]

Carbs pump in more fuel, end of story. That's why the increase in power. Another reason is an engine on carbs is generally running without catalysts, so the exhaust is more free flowing. Well, with all that overfuelling going on, the cat would die pretty quick anyway. It's no mistake that every car ever built with a catalyst has electronic fuel injection.

sorry mate but there are nissan primera's with a carb on and a catalyst on a 'n' reg

also i think there were a few skoda's

[G100extreme 0]

Yeah ok, (writing with a grin...)

 

Back to the main subject again... so now you all understand why chipping a normal unmodified engine wont make any difference... :)

 

Anyone from AMD like to comment? :wink:

 

-frank

(So I must be an engineer...)

 

I knew he was taking the p***! :)

Did we pass the test, frank? Do we get certificates?

[monVR6 0]

So here's a question - I have the AMD remap and a K&N panel filter (95 VR6). AMD printout showed 213bhp - (hmm) !! Seemed smoother after this, but I did not have a hugely noticeable difference in performance. The filter - (which was done later) did though with much better throttle response.

 

So - if I now add a larger throttle body - will the benefits of the remap have a bigger effect???

[dr_mat 0]

sorry mate but there are nissan primera's with a carb on and a catalyst on a 'n' reg

also i think there were a few skoda's

 

Already discussed.. :)

 

Anyway, the scarcity of such cars really does point out that it was never a good idea, on the whole.. :)

[Kevin Bacon 5]

AMD printout showed 213bhp - (hmm) !!

 

Exactly.... glad you're not suckered in by their BS figures!

 

Seemed smoother after this, but I did not have a hugely noticeable difference in performance. The filter - (which was done later) did though with much better throttle response.

 

That's usually what most people find after a rechip - smoother running but no real extra urge to write home about.

 

So - if I now add a larger throttle body - will the benefits of the remap have a bigger effect???

 

Not really. The bigger TB is another one of AmD's horse sh1t "gives you 10% more power" modifications. I really wouldn't bother on a standard + chipped engine. It does make a difference when used with what I call the "Big three" - Schrick VGI, 268 cams and the bored out throttle. It comes alive in the mid to top end 8)