26 replies to this topic

[Ali_G]

I remember that McLaren ran trumpets which used to go up and down depending on which cylenders were firing. The hope was that when one cylender was firing that a trumpet would move up and hopefully get better airflow into the cylender.

Just wondering but are any Engines today using this same system.

Niall

[Matt Davis]

At a guess it is banned. Or at least I know varying the length of the exaust is banned.

[Bluehair]

The intake trumpets are designed to move up and down in relation to rpm. They are shorter at high rpm and longer at low rpm. This gives a more optimum intake velocity over a broader range. I don't think the trumpets were ever meant to move up and down depending on which cylinder was firing. Last year's Peugot used this system and it is thought that several others are also using variable lenth intake runners of some sort.

[Timm]

I think it was Honda in the early '90's that introduced it to F1. The theory is that longer trumpets equals more torque because as the pressure waves of the airflow reach the open end of the trumpet, a supercharging effect is set up. The downside is that engine response isn't so good.

Different inlet tract lengths are common on road cars. The Opel Carlton has dual intakes seperated by a butterfly valve.

In US racing, a lot of discussion revolves around the use of single or twin plane intakes. It's basically the same idea.

On the other hand, I'm probably completely wrong.

[Jaxs]

The vauxhall Carlton uses a twin choke throttle housing, the best example of a built in plenum chamber with secondary throttle is the 2 litre twin cam toyota corolla, complex for what is designed for but works relative well in traffic conditions.

[Top Fuel F1]

I believe I counted up to at least 4 F1 teams in 99 using variable trumpets. The variability has to do with the extension or retraction of the intake tube only and is primarily based on a function of RPM. However I don't know how instataneous the change in the tube's length is or if and other conditions or functions are factored in to the equation for changing the length.

There is a previous Tech. Forum Thread on this subject. However it vectored off into a discussion on variable exhaust pipes which of course don't exist in F1 to my knowledge.

[Jaxs]

The idea behind the variable trumpet design is a better control of the air mass moving into the engine, both the speed and amount of air is critical in F1 engines.

[desmo]

Just to put a finer point on it, the purpose of variable legth intakes is to use standing wave resonances inside the intake columns to achieve a mild supercharging effect. The ideal length/volume is a function of revs so to keep it near optimal it is neccessary to change the length/volume in response to rising or falling revs. This will have less effect on HP which is a steady state measurement, than on the ability of the engine to recover revs after an upshift which is more germane to actual on-track performance. This also affords the engineer another tuning parameter. F1 cars corner in a sub-band below the peakier part of the power band used for acceleration. This is important as the balance of the car while cornering is very sensitive to throttle inputs otherwise. The transition from this sub-band to the steeper part of the power curve used for full-power acceleration is critical to achieving a good drive out of corners.

[Jaxs]

Ther seems to be a funny smell, is it chickens?, no is it pigs?, No...

Desmo, sub band, do you really believe all that..... tell me what does effect HP, and I sincerely hope that means Horse Power, then think and tell me what effects Brake Horse Power.

We could be talking about two different things here Horse power is a set measurement ... brake horse power is a variable Now if you are talking about BHP, I would appreciate the your input on torque and the control of same with variable trumpet design, and not all that bit about cornering over and above the power band.. why do they fit gear boxes .. to allow the driver to select the optimum ratio to maintain the engine rpm within its specific power band........the varience achieved with tuned lenght exhaust and variable inlet trumpets does have a direct effect on the torque and bhp.

and standing wave resonance..... let's consider the layer of still air within the inlet manifold design. the Harmonics of valve springs.... Venturi create air speed, ram effect of road speed will give forced induction but supercharged???

Jack

[PDA]

jaxs - it has been known for more years than even I can remember that inlet lengths tuned to the harmonic length of the resonance in that inlet can enhance cylinder filling. It is also a fact that the harmonics change with revs, so a variable length inlet tract can be advantageous by smoothing out the power band. I understand that all F1 engines have variable length inlets to take advantage of this.
BTW - hp = horse power, a measure of the power generated by an engine. BHP - brake horse power - the measured horse power - measured on a dynamomenter rather than in the car. The two expressions are more or less interchangable in this context.

[Ray Bell]

To my knowledge, the first F1 engines built with this feature were the M196 Mercedes-Benz straight eights being prepared for the 1956 season.

[Jaxs]

Horse power and brake horse power are more or less interchangable in this context. really, and in what context would they not be 'more or less interchangable'?

[PDA]

One H.P equals 55 fot lb per second of work.
B.H.P is the horse power of an engine measured on a dynamometer.

In this context, H.P and B.H.P are not interchangable.

On the other hand, whjen we say the Ilmor engine in the Mac produces 820 h.p. we are not making a distinction between installed h.p or b.h.p.

[Top Fuel F1]

Originally posted by PDA
I understand that all F1 engines have variable length inlets to take advantage of this.

At least in the 1999 season the engines with moving trumpets were:

1. Ilmore/Mercedes
2. Ferrari
3. Supertec
4. Petronas
5. Arrows

In that the Ferrari and Mclaren teams use them there must be a good reason. Why everyone in F1 was not using them in 99 is a good question. Maybe they are by now.

Rgds;

[Jaxs]

and we both know that the 820 refers to BHP , I'm not sure when I last saw it expressed as just HP.

re tuned length..... isn't that what I said.

[Ray Bell]

I'm at a loss to understand this discussion about bhp & hp, for they are one and the same thing... except for rated hp, which is extinct, anyway, isn't it?

Whether the engine is in the car or on the test bench, what it produced on the dyno is brake horsepower, 'brake' referring to the test brake that is the dyno that measured that power (although, strictly speaking, those terms may now be out of date).

Sure, the horsepower availability as installed may differ, but it can't be measured once it's installed (except by inefficient means) anyway.

Anyone care to enlighten me what this is really about?

[PDA]

Good question Ray. Not sure why we got down that blind alley.

Re measurement installed. I believe that nowadays, they attach strain gauges on drive shafts etc. and can obtain realtime measurements of torque, and hence calculate real installed h.p.

[desmo]

Just one more thing here. It has been brought to my attention that the relationship between intake length and rpm may not be a strictly linear one in F1, and that the intake length may in fact cycle through a number of times in the working rev range. I don't really understnd why this would be done, but a little birdie pointed it out.

[blkirk]

I can answer that in one word. Octaves. If a given length is optimal at 5k rpm, it will also be good at 10k and 20k. Note that I said good, not optimal. Some other length would be truly optimal at the higher revs, but the one that worked at 5k would still be better at 10k and 20k than the length that is optimal at say 5.5k.

You can use this to your advantage by picking the range you want truly optimal power and limiting motion to the intake lengths that work best over that range. The further you decide to move the trumpets (i.e. greater intake length variability), the bigger and heavier all the parts get.

Say you pick 10k-18k as the range for optimal tuning. You get to re-use all those same lengths at 5k-9k. The effect won't be as strong at the lower revs, but it'll help more than a fixed length intake tuned for one frequency. (It'll also work from 2.5k-4.5k, but when was the last time you saw/heard an F1 engine running that slow .)

OK, that was a lot more than one word. So shoot me.

[desmo]

I should have known that. My father has written a book on the physics of musical sound and the similarities between the intake/exhaust systems in F1 and horns are surprising. The intake trumpets on an engine and the bell on a trumpet are both similar shapes for the same reasons!

[Top Fuel F1]

What kind of mechanism extends and retracts the trumpets? For instance hyraulic, pneumatic, or even elec. motor driven.

Rgds;

[Ray Bell]

Or a mechanical link from the tacho needle?

[PDA]

The inlet tracts are extended/contracted by use of a hydraulic motor. The hydraulic system comes under great stress at teh start line, as the engines are being blipped, activating the inlet system, the gear change is used, as is the clutch. The hydraulic system is driven by the smallest motor they can get away with, whihc really means that the resevoir is too small for the activity at the start, and the pump is sized for when running at high revs. hence the occassional goofs by otherwise very good drivers (MS, Suzuka, DC Montreal) on the start line.

[Powersteer]

[QUOTE]intake length may in fact cycle through a number of times in the working rev range. - desmo



During the lower rp/m's the trumpet will tune itself for reflecting pulse number 4, meaning the sound waves has reflected 4 times inside the inlet. As rpm go much higher it wont have time to 'catch' the 4th reflecting pulse so it lengthens itself to create a distance for the wave to travel buying time and catching the earlier 3rd wave. This is just an example though, i dont know how many times the sound waves relflect inside the intake.

[davo]

Catching an earlier snippet in this thread...
Didn't Ferrari run variable exhaust length (head to first merge) some years ago? The system was complex even by the standards of F1 but this was at a time when Ferrari were spending more and achieving less than anyone else

[desmo]

I seem to have a dim recollection of Ferrari indeed trying such an idea in F1, a V-12 I think. Anyone else remember?

[Powersteer]

It would be a nightmare to seal the variable exaust.