Question on LeMans rule requirement for GTS Class

[ViperACR]

I am a bit perplexed on something which hopefully someone can answer for me. I was going through the rulebook from the ACO in regards to Le-Mans and the GTS class. Unless I read it wrong it seemed to me that it stated that the cars with the bigger engines had smaller restictor diameters. This is surprising as we all know that the bigger the engine the more power it will make. It also did not matter if the car had 2 valves or 5 valves. All that mattered was how big the engine was. But again I am surprised that it seemed the bigger engines had the smaller restrictors. Can someone explain to me why this is. Here is the link to the Le-Mans rulebook from the ACO. It is on the last page which is page 18, appendix 1.

http://www.lemans.org/univers_sport/...ts_2004_gb.pdf

Thanks

[Fogelhund]

Bigger engines make bigger power, and therefore need to be restricted more then smaller engines. To restrict more, you need a smaller sized restrictor.

[hotgemini]

In terms of 'area under the curve' power and torque figures, a big engine through a specific restrictor will be a better option than a small engine through the same restrictor. Hence smaller restrictors for bigger engines. The total peak airflow possible before going supersonic will be about the same with the same size restrictor so *peak* power output would be similar (ignoring volumetric efficency variation).

[Pilgrimage]

That's all clear then

[paul-collins]

Originally posted by ViperACR
It also did not matter if the car had 2 valves or 5 valves. All that mattered was how big the engine was.

If you were to read a little closer:

2 valve engines :
For two valves per cylinder engines, the following restrictors diameter must be corrected according to the formula:

D = {[D-1] x 1,034} + 1.

The result will be rounded up to the nearest decimal.

It's the first line in Appendix 1.

[JAG]

ACR, the Viper is not competitive as it is a car that has come to the end of its development life, not because of the size of its restrictors.

Get ORECA to develop the new car, and it will be a different matter.

Just reading through the orignial post again, is there some confusion about the 'smaller' restrictor on the bigger engines?

The smaller the restrictor, the less power the engine can produce. Not vice versa.

[ViperACR]

JAG the vipers are doing very well with their Racing Coupe. The Larbre Viper did very well in LeMans considering it does not have the budget of the other factory cars. But yes I agree that the Viper would do better with Oreca at the helm.

But I still am confused with the size of restrictors. If you have a bigger diameter restrictor that allows less air to pas through then how can that make more power than a smaller restrictor. The secret to making power is to get airflow. If you have a big restriction in the way then how can you make more power than a small restriction.

Thanks

[hotgemini]

Viper: The diameter of the restrictor is in inside diameter. The restrictor is a section of pipe of a specified minimum length at a set diameter. The larger the pipe, the more air that can go through. The smaller the pipe, the less air that can go through.

[JAG]

The idea is that a 4l V8 can produce the same (600-650BHP) as an 8l V10.

The restrictors balance the 2 engines to produce the same BHP.

BTW, the bigger the restrictor, the MORE air gets to the engine.

Therefore bigger restrictors are fitted to the smaller engines. While the Viper 8l V10 gets a smaller restrictor.

I think you are getting the terms mixed up.

Bigger restricor = more BHP (e.g.4l V8)

Smaller restrictor = less BHP (e.g. 8l V10)

[hotgemini]

The reason air restrictors are so effective is that they can the maximum volume of air available and therefore the horsepower proportionally to their size. At a given air velocity (and thus at a given rate of flow) the restrictor will cause the air velocity to reach supersonic levels and the engine will effectively cavitate.

So an 8 litre motor breathing through a single 30mm inlet restrictor (barring variations in VE) should make the same *peak* horsepower as a 4 litre motor. The 4 litre motor will make it at higher RPM and will have a less usable torque curve but should make very similar horsepower.

In a class with a single set limiter size to be competitive you'd chose the motor of the largest capacity available within the normal reasonable constraints (weight, packaging etc). The race car would be easier to drive, the motor less stressed and quicker in lap times.

[paul-collins]

Perhaps a better term than "restrictor" (what it does) would be "orifice" (what it is).

[ViperACR]

Thanks guys now I understand that it is the inside diameter of the air flow pipe and the not the inside diamter restriction. I thought I was losing my mind because everyone knows that the more air and fuel you can get into an engine the more power it will make. The smaller engines can compensate for their lack of engine capacity with higher revving engines, but that is only to a point. Formula 1 cars have small strokes and a lot of high tech valve train to make them rev to 19,000rpm.

But I dont understand why a racing sanctioning body will not let a less competitive engine have a bigger restrictor if it is not competitive. If the prodrive ferraris and the Corvettes are ahead of a less funded Larbre Viper then why not level the playing field and give them a bigger restrictor. Unless they are all supposed to be at a given horsepower for a given weight. Does anyone know what is the horsepower limit in LeMans and the ALMS as I did not see any horsepower restriction limit in the Lemnas rulebook

Thanks

[JAG]

There is no limit as such, just restrictor sizes that the ACO/FIA believe will give a car a particular amount of power.

In the case of GTS it is between 600-650BHP.

As we have seen in LMP1 there is still a lot of scope for engine devleopmnet, even with the restrictors. For example the well developed Audi V8 turbo engine was produceing 600+BHP, while the Pescarolos Peugeot V6 produced 550BHP, or less.

As for changing restrictors to balance the field, I think the FIA did give the Vipers a restrictor break a few years back to give them a helping hand. However this was at a time when the series was struggling for new GTS cars, so the Viper teams needed to be kept in the series.

Nowadays I could not see the FIA giving a particular car a restrictor break, to boost power. They will peg a winning car back with ballast penalties however.

In ACO races, it is the survival of the fittest, with no restrictor brakes/penalties for any car.

In national series such as French/British GT it is a different matter however.

[ViperACR]

I dont know what formula they use as to how big or small a restrictor must be for a particular engine size but it is obvious that it is not the best way to make things fair. The way they should do it is to give the cars a horsepower number and let the teams decide how they get to it and what size of restictors they should use. If they go over the horsepower limit they can add more weight or get a smaller restrictor and vice versa. The way they have it now is not right with their own formulas because certan engines do not react as positively as another car with a different size engine and configuration. Let the teams decide what they want to do and forget about the sanctioning racing bodys unfair formulas.

[hotgemini]

That strikes me as a tremendously naive suggestion... So, give the teams free reign and expect them all to make sensible, rational and cost-effective choices... Australian Porsche Cup racing used to have a similar system, with just a given power:weight to be acheived more or less with a free reign. To say it was open to some fairly interesting interpretations would be an understatement and to say that it lent itself to abuse and misuse would be a fairly accurate reflection.

[Cadete]

Originally posted by ViperACR


But I dont understand why a racing sanctioning body will not let a less competitive engine have a bigger restrictor if it is not competitive. If the prodrive ferraris and the Corvettes are ahead of a less funded Larbre Viper then why not level the playing field and give them a bigger restrictor. Unless they are all supposed to be at a given horsepower for a given weight. Does anyone know what is the horsepower limit in LeMans and the ALMS as I did not see any horsepower restriction limit in the Lemnas rulebook

Thanks

That's something which I would not like to see. It would mean that no matter how competitive you were, you would be set on the same pace as the other teams.

In my opinion, air restrictors should be used the weights were used in the past. The bigger the displacement, the bigger the weight, to keep the big engines and the small ones somewhat equal chances. The advantage for the ACO and FIA of the restrictors is that it helps them keep that equality of chances AND helps them keep speeds in check.
Still in the "keeping speeds in check" thing, the restrictors should not be adjusted every year to keep the power allways the same. Get a formula, stick with it for a few years and act if things go out of control.

However, to go using "personalized" restrictors, with different sizes for the same displacment and weight, punishing sucess, is not the way racing should be. You should have the same rules for everyone, not create special cases to "keep the interest high". I for one prefer to see a team winning because they can than see a team winning because they were helped.

[paul-collins]

Originally posted by ViperACR
I dont know what formula they use as to how big or small a restrictor must be for a particular engine size but it is obvious that it is not the best way to make things fair.

Not obvious at all. You have to give teams areas to do their development on, otherwise why bother? Are they to just show up at the track and get a turnkey solution?

The same restrictor rules (more or less) have been in place for years, and teams who want to push the envelope have developed more horses from the same size over that period. It's not up to the sanction to ensure that teams who aren't prepared to spend money on testing and development can still compete on raceday.

[ViperACR]

The problem with the way it is now is that the formula to determine what size restrictor an engine gets which is dependant on engine size is flawed. The teams should be allowed to be innovative because certain restrictor sizes will hurt one engine more than another. It is not right because a 4 valve engine can breath better with a smaller restrictor than a 2 valve engine. This formula is a joke. keep them to a certain horsepower and then addweight if they go over. This allows the teams to be innovative

[ViperACR]

If you want to really keep it fair then let every car and manufacturer have the same size restrictor and weight.

[paul-collins]

Originally posted by ViperACR
The teams should be allowed to be innovative because certain restrictor sizes will hurt one engine more than another. It is not right because a 4 valve engine can breath better with a smaller restrictor than a 2 valve engine.

Well, that's not a problem from a sanction's point of view. Look, if (say) Ford's cammer is a crappy race engine, why should it get special breaks just to become competitive? Why not just tell the manufacturer "come back when you've designed a proper up-to-date race engine?" If a manufacturer is wedded to an obsolete or bad idea, then why reward them on the track and (by extension) at the sales office? Surely we as consumers are better served by the manufacturers being challenged to improve their product?

I've already shown you that 2-valve engines get restrictor breaks. So that's a non-issue.

[Hauptmann6]

ViperARC you must be younger as you haven't seemed to learn an importaint lesson in life and raceing; IT ISN'T FAIR! Nor is it meant to be other than some specfic guidlines.

[MulsanneMike]

"It is not right because a 4 valve engine can breath better with a smaller restrictor than a 2 valve engine"

The regulations actually take that into effect. For equal displacement, a 2-valve engine is allowed a larger diameter restrictor than a 4-valve engine. An 8 liter multi-valver engine running at 1150 kgs has a 43.2 mm diameter restrictor while a 8 liter 2-valver can run a 44.6 mm.

Personally I think the regulations are working very well. That the Viper GTS isn't competitive is completely in the hands of Dodge and that the car's development stopped in '00 or thereabouts.

[Asa]

I still think the FIA and ACO should restrict the prices of the racing cars they sell to the privateer teams.

FIA already state in their rules that any car that enter the GT C'ship must be available to privateers, so why not make sure it is available at a price no more than X dollars/euros?

That way if the Maserati MC12 proves to be exceptionally quick, still many privateers can get the car and be competitive.

[Asa]

Also if the sale price is restricted, then the manufacturers will not be so keen to make a car so high-tech that they will make a loss everytime they sell one.

It will limit the technology and it is in effect a budget cap, the manufacturer who spends wisely will win.

[ViperACR]

I will say it again. If they want to keep it fair and see what engine is the best and what manufacturer is best and the most innovative then the restrictors and the weight shouyld be the same for every team. This way it is a ridiculous formula that determines who wins and loses. Let the teams and their cars decide. The rules are flawed and favour smaller engines.