23 replies to this topic

[Canuck]

When looking at an F1 engine exhaust it is of course of fixed geometry, and does not appear to have a megaphonestyle tip to it. In reading a couple of SAE papers from Honda and Scientific Design of Exhaust and Intake systems, all sources put forth the idea that a megaphone on the exhaust will broaden the RPM where maximum Ve is obtained. That said, neither F1 nor any of the high-performance cars or motorcycles I can think of off the top of my head use megaphones today.

That leads to me to ask 2 questions - a) is the megaphone theory full of baloney and b) are F1 engines tuned for maximum peak power or for a broader power band at the expense of peak power?

[Stian1979]

If it give anny benefitt it's baned.

Variable lenght inlet manifoils are baned because it give both top end and low end power witch is no no

[cosworth bdg]

Originally posted by Canuck
When looking at an F1 engine exhaust it is of course of fixed geometry, and does not appear to have a megaphonestyle tip to it. In reading a couple of SAE papers from Honda and Scientific Design of Exhaust and Intake systems, all sources put forth the idea that a megaphone on the exhaust will broaden the RPM where maximum Ve is obtained. That said, neither F1 nor any of the high-performance cars or motorcycles I can think of off the top of my head use megaphones today.

That leads to me to ask 2 questions - a) is the megaphone theory full of baloney and b) are F1 engines tuned for maximum peak power or for a broader power band at the expense of peak power?

Neither, the engine electronics control every function................

[jimclark]

cosworth bdg - "Neither, the engine electronics control every function................"

How, pray tell, do electronics control the flow of exhaust???

[Stefan_VTi]

(Honda) HTEV

ontopic: there are more ways to rome, it could be the F1 engine builders found that shifting optimum points (eg, intake optimum rpm, exhaust optimum rpm) around resulted in more usable power in the range they required than topping off (and broadening) the optimum rpm of (for instance) the exhaust.

[Kimi on nopein]

Originally posted by Canuck
b) are F1 engines tuned for maximum peak power or for a broader power band at the expense of peak power?

My guess would be that they're tuned for max area under the power curve across the rev range used.

[J. Edlund]

Originally posted by Kimi on nopein


My guess would be that they're tuned for max area under the power curve across the rev range used.

They are probably a bit more advanced than that. I think they simulate and test the performance of the car, and maximize that rather than the output of the engine.

[rhm]

I can't tell you why they didn't flare exhaust tips in the past when they exited at the back of the car in amongst the 'junk', but there's no way they'd do it now with the pipes exiting directly into a crucial part of the airflow over the rear bodywork. It would increase drag due to increased frontal area and also there's the issue of: do they really want to slow that exhaust down as it leaves the pipe from an aero point of view?

[Kimi on nopein]

Originally posted by J. Edlund


They are probably a bit more advanced than that. I think they simulate and test the performance of the car, and maximize that rather than the output of the engine.

Sure they do. Everything effects everything and so on. They may be designed for a lot of things, effiency, packaging, power,.. But saying they're tuned for max area under the power curve over the used rev range can't be far off.

[12.9:1]

Canuck - "neither F1 nor any of the high-performance cars or motorcycles I can think of off the top of my head use megaphones today"



Here the current points leader in MotoGP riding a Honda 990cc V5 - other pipes under seat. More over the exhaust tapers gently all the way back to head. Fully tapered exhaust systems are common in SupperBike as well as GP, have a look in the back of a sport bike magazine to purchase a set!

[Canuck]

Originally posted by cosworth bdg
Neither, the engine electronics control every function................

Forgive my ignorance here...If there are no variable exhausts and no variable intakes, that leaves fuel and ignition control only (assuming no cam timing) does it not (with respect to the engine, not the car of course). So how then can they broaden the power band using only that?

Exhaust tapered all the way to the port 'eh? Interesting. Amazing now some ideas come in, go out then come back again. I mean, it would seem that if real-world testing showed that a megaphone of appropriate divergent angle and L/D ratio improved the width of the Ve curve, that it would be always be the case and thus always be used. Rarely a straight answer out there. I assumed either it's been a) tossed in the 'old tech' bin, b) proved to be wrong, misleading or effective in only narrow use or c) shown to be incompatible with a 'better' idea.

[J. Edlund]

Originally posted by Canuck

Forgive my ignorance here...If there are no variable exhausts and no variable intakes, that leaves fuel and ignition control only (assuming no cam timing) does it not (with respect to the engine, not the car of course). So how then can they broaden the power band using only that?

It's quite simple. To make an example, optimize exhaust pipe length for 19,000 rpm, then you optimize inlet lengths for 16,000 rpm and so on until you achieve a rather flat torque curve for the rpm range you had in mind. If you were to design a peakier engine, like an ILR engine, you gather all these "positive effects" for a single or a narrow rpm range instead.

[Canuck]

While that is an answer that I was looking for, it doesn't at all address Cosworth BDG's post - which was the gist of my 'ignorance' question - which perhaps wasn't clear in itself. What I'd intended to say ask was in reference to Cosworth's response on electronics - if nothing is mechanically variable, how can fuel and spark broaden the power band. On the other hand, you've given me the answer the underlying (and unasked) question which was, how best to tune for a broad power curve. Thanks.

[jo-briggs]

A parallel piped exhaust can be seen as a variation of an organ pipe, having one resonant frequency with 2nd, 3rd and 4th harmonics all reducing in amplitude, additionally confused by having several headers exiting into one tail pipe, so being discontinuous in its operation. When the revs and the exhaust flow rate harmonise with the pipe length it works more efficiently, hence the convolutions in the headers in an attempt to make them all of the same length. A megaphone confuses this by trying to spread the available harmonic range by acting as a straight sided trumpet bell (a proper flared horn would be too long and of too large a diameter). Formula One engines have variable valve timing, variable valve lift; being pneumatically operated; variable ignition, and variable anything else that can be electronically controlled on an engine, so the effect of a single length exhaust can be ameliorated by controlling the exhaust flow by means of ignition and valve timing, dwell and lift.

On the illustration of the MotoGP Honda it should be noted that it is a partially closed cone with its exit diameter being smaller than its major diameter, so not a true megaphone - that doesn't stop it working exceedingly well though!

[Canuck]

Originally posted by jo-briggs
Formula One engines have ... variable valve lift; being pneumatically operated;

Come again? I'm certainly not the most up to date but it is my understanding that F1 valvetrains are still operated via camshaft(s). Pneumatics have replaced the valve spring but how can they alter lift?

[desmo]

Don't believe VVT has ever been in common use in F1 either.

[rhm]

That's a fairly common misconception among non-technical fans it has to be said. It's down to people talking about "pneumatic valves" when they really should say "pneumatic valve springs" or "pneumatic valve return systems".

The only variable valve system in F1 is, AFAIK, Honda's VTec and that was outlawed in the early 90s because apparently fuel ecconomy hasn't always been as popular with the FIA

[jo-briggs]

Well there you go, I don't know everything after all.

I had assumed that if one was using air pressure instead of valve "springs" it would only be sensible to have a double acting cylinder and by pressurising each side of the piston in turn you could have, in effect, a pneumatic version of a desmdromic valve system with positive opening and closing; timing, dwell and lift would all be controllable by software - maybe I've just invented my 4th method of variable valve timing!

[Pioneer]

You could but I don't think you can make the pneumatics operate fast enough to run the RPM's that current F1 engines run.


I could be wrong.

[Stoatspeed]

Originally posted by Pioneer
You could but I don't think you can make the pneumatics operate fast enough to run the RPM's that current F1 engines run.

Most certainly true ... in fact the whole history of so-called "active" valve actuation is plagued by system response. There have been electromagnetic and electrohydraulic systems built and tested with some success on road car engines and truck engines (Lotus, Sturman, Navistar/International, Caterpillar to name a few ... Google will give details), but the upper speed limit is going to be well below F1 speeds unless you have enormous power available to power the system with extremely high hydraulic pressures or very large EM actuators ....
Pneumatic valve springs are a great idea, though, and not really speed dependent.

[jo-briggs]

But are they not affected by adiabatic expansion, and all the thermodynamic consequences of Boyle's Law?

[J. Edlund]

Originally posted by jo-briggs
But are they not affected by adiabatic expansion, and all the thermodynamic consequences of Boyle's Law?

Some systems use nitrogen from a bottle, others use air from a compressor. In F1 nitrogen from a bottle is the typical approach. The bottle is around .7 liters and pressurized to about 200 bar. Each pneumatic spring, essentially a cylinder and piston attached to the valve, has one in and one outlet for gas. The outlet is design in such a way that it removes oil that over time gets into the cylinder. With the use of valves on the inlet and outlet ports the pressure in the pneumatic valve system can be controlled, typically the pressure is about 15 bar.

A description of a PVRS can be found in the following patent
http://patft.uspto.g...RS=PN/6,083,140

Camless valve systems, in addition to the lack of high speed precision, also consume much more power than what ordinary cams take in friction. To reduce the power consumed by the system, it must be able to get energy back when the valve is closing. Weight is also a problem.

Camless system by Renault
http://patft.uspto.g...RS=PN/6,871,618

[Stoatspeed]

Originally posted by J. Edlund

Camless valve systems, in addition to the lack of high speed precision, also consume much more power than what ordinary cams take in friction. To reduce the power consumed by the system, it must be able to get energy back when the valve is closing.

Thanks for the info, J! I didn't know the details of F1 pneumatics, so most enlightening.

The point about cam friction loss versus power to drive a camless system is well made, and is a big part of the development compromise. Camless systems CAN deliver net improvements in fuel economy, but they do it by their ability to radically alter valve timing in response to operating conditions in a way that no conventional VVT can achieve - basically a fully-mapped or even adaptive system. By using this variability range (lift amount, timing, lift profile), the thermodynamic performance of the engine can be improved by more than the mechanical performance is degraded, especially if energy recovery methods are used to get back some of the valve opening energy. On the topic of accuracy, I have seen some response plots from a camless hydraulic system running at 5500 rpm which actually showed better dynamic control than a conventional system, so it can be done. It took a major "brains trust" working for about 5 years to get there, though .... :

Interesting thread, keep it up, guys!

[jo-briggs]

In that case I'll give myself a pat on the back for working that one out all on my tod; not having worked in the business since 1965!