Turbos vs Atmo Engines

[EspritS3]

Following the last few years dominance of prototype racing by the Audis (and Bentleys) and their turbo V8s, where does this leave other LMP1 teams/manufacturers for engine choice?

Not only are the Audis powerful enough to be fastest (with so far only LMP675 derived cars able to match them for pace), but their fuel economy sees them pull out more laps than everyone else between pit stops (except for Frank Biela!) - again with only the fragile LMP675 cars able to match them (if they would hold together long enough).

Apart from the BMW V12LMR (which was not the fastest car) we have not had an atmo-engined car win Le Mans since Group C days (the GT McLaren F1 excepted). Can normally aspirated engines be competitive (over 24 hours) with the current rules?

How would the Rollcentre Dallara/Pescarolo Courages fair with an Audi engine instead of the Judd?

Your thoughts please...

[BSchneiderFan]

The Judd GV4 and GV5 seem to be pretty competitive in terms of power; it's just a reliability issue. The truth is that no major manufacturer has tried a normally-aspirated engine for a while. Bear in mind, though, that Porsche were due to switch from turbocharged to normally-aspirated in 2000, and had withdrawn from the GT Championship at the end of 1998 largely because their blown engines were not competitive.

[paul-collins]

I would think the question is better phrased "Can non-Audi engines be competitive (over 24 hours) with the current rules?" Cadillac's turbo Northstar wasn't powerful enough, and I doubt it was any more efficient.

Remember that Audi has direct injection, which was good for about a 5% increase over regular EFI.

My guess is that restrictor rules, as currently envisioned, are perhaps a bit generous on the turbo front. In order to generate similar power in a NA engine, I think they're having to enrich the mixture, whereas running with a little more air might provide them with more efficiency.

I've heard that the Judd GV4 made enough power in qualifying at the expense of efficiency, and that the engine was always dialled back for the race. Perhaps the GV5 had resolved this? Since it was only installed in the Rollcentre Dallara and the Pescarolos (which were never fully sorted according to Seb Bourdais), we never saw their true capabilities.

[jhansen]

I don't understand why the NA engines are restricted so much. But the ACO's restriction rules have always baffled me.

I don't see why they have to hold the Saleen back either. With the smaller rear wing in ACO spec it is already at a disadvantage. The BMW-LMR and Ferrari 333SP both ended up down on power due to restrictions if I recall. The BMW should have had a longer racing life and Ferrari teams resorted to the Judd.

Seeing the dominance of the Audis in both fuel mileage and power (even the little MG-Lola gets good mileage), why not give the NA engines a bit of a power boost?

[paul-collins]

BMW's racing life was curtailed by aero rule changes, I thought.

Ferrari never developed their engine to the changes in restrictors.

I guess the question is, are turbos more thermally efficient? ie do they extract more motive power out of each litre of fuel? If so, a power break won't do much for NA engines except get them to the next pit stop that much more quickly. And LM is won by staying out of the pits!

[Danske]

I'd think that a larger restrictor would reduce the work needed to draw in the air making the engine more efficient.

[Félix]

What's killing everybody is the Audi's torque. The advanced electronics controlling the boost and the FSI direct injection give it almost twice as much maximum torque as a Judd, and this torque is available all the way through the rev-range. What the air intake restrictions do is only strangling the engine when its rpm is high enough that it would need more air. An unrestricted Audi would have the same torque up to 5000 revs, but would make a power in the top revs in a more peaky way using the extra air available. The Judd barely enter its sweet spot when the air restriction is beginning to be felt.

[EspritS3]

Thanks for your thoughts guys.

Its a good point about the extra torque from the Audi compared to the atmo engines - again isn't much increased torque a characteristic of turbocharging?

The proof should be in what Porsche do should they return - use the V10 from the Carrera, a V8 turbo derivative from the Cayenne, or the turbo-six from the 911. Lets hope we have an annoucement before too long!

[billnchristy]

Well, in the GT1 times Mercedes complained that the Porsches and other turbos were given a better deal because of the restrictor placement.

If there is an advantage for turbo cars, Porsche will use it.

[JAG]

Originally posted by billnchristy
Well, in the GT1 times Mercedes complained that the Porsches and other turbos were given a better deal because of the restrictor placement.

If there is an advantage for turbo cars, Porsche will use it.

As I recall it was the complete opposite.

When Porsche raced the 911 GT1 in 1996, it was so dominant that the FIA banned ABS brakes and reduced the restrictor size for turbo engines for the 1997 season.

The FIA failed to realise that the following season, all of the respective manufactuers would have their homologation specials ready to race.

The 911 GT1's performance advantage, in 1996, was its advanced chassis/aero not the power it produced.

When the CLK-GTR, F1 GTR Long Tail arrived, the 911 GT1's chassis/aero advantage was no more, plus the car was saddled with an underpowered turbo engine.

Apparently, the Porsche falt six only put out around 580BHP, while the CLK-GTR and F1 GTR had around 640-650 BHP.

[jhansen]

I thought I recall the Porsche 911-GT1 EVO being penalized in 1998 part way into the championship. The car was on the front row the first two races and then was hard pressed on pace after.

[JAG]

The 911 GT1 was penalized at the end of the 1996 season. The car struggled in 1997.

In 1998 the 911 GT1 98 was the pace setter for the first few races, until the CLK-LM hit the tracks!

[MulsanneMike]

Originally posted by paul-collins
I would think the question is better phrased "Can non-Audi engines be competitive (over 24 hours) with the current rules?" Cadillac's turbo Northstar wasn't powerful enough, and I doubt it was any more efficient.

Remember that Audi has direct injection, which was good for about a 5% increase over regular EFI.

My guess is that restrictor rules, as currently envisioned, are perhaps a bit generous on the turbo front. In order to generate similar power in a NA engine, I think they're having to enrich the mixture, whereas running with a little more air might provide them with more efficiency.

I've heard that the Judd GV4 made enough power in qualifying at the expense of efficiency, and that the engine was always dialled back for the race. Perhaps the GV5 had resolved this? Since it was only installed in the Rollcentre Dallara and the Pescarolos (which were never fully sorted according to Seb Bourdais), we never saw their true capabilities.

I don't think there is much to choose hp-wise between the best turbo powerplants and the best NA powerplants. The big difference is torque, economy, and adustability. A tubo allows for consessions to be made if track conditions are less than ideal. On a NA engine all you can do is cut revs (and power and torque). Certainly a turbo is more complex and more than likely why there isn't a customer turbo engine. It would be nice if Audi let some of those FSI engines out into the market...

[JAG]

What about sticking a turbo on the new Judd V8, for LMP1 use?

I did read somewhere that Pescarolo could run the Judd GV5 during the race (LM24), in the same spec as in qualifying, which you, apparently, cannot do with the GV4.

[billnchristy]

Maybe I did have it backwards, round about point was, Porsche knows turbos and if theres any advantage to it, they will use it...IF they return

[cybersdorf]

It all depends on the way the regulations are written. Some favour turbo engines, some favour N/A engines - which ideally shouldn't happen.

Right now, the FIA and ACO GT regs are not turbo friendly (air restriction, boost) so there aren't any turbo cars out there.

As for Merc vs. Porsche in GT1, this was not so much technical as political. Don't forget that when Merc entered the then-new FIA GT series, they had just killed the original DTM, and wanted to turn GT racing into an ersatz DTM, with equal engines for everyone (6l atmo), and sprint races. Also, don't forget that Merc itself used turbocharged engines to good effect in the Gp.C cars.

The Gp.C engine regulations were the best engine rules ever i.m.h.o. - you could do whatever you liked to achieve the task in hand - complete the race distance with a given amount of fuel, and be faster than the others in the process. In prototype racing at least, it should be like this today.

[Nordic]

The Gp.C engine regulations were the best engine rules ever i.m.h.o. - you could do whatever you liked to achieve the task in hand - complete the race distance with a given amount of fuel, and be faster than the others in the process. In prototype racing at least, it should be like this today.

That is right, a very simple but effective soloution that gave a range of differnt options, with the plus of valauble research into MPG that could be passed onto road cars.

[BSchneiderFan]

Originally posted by cybersdorf
Don't forget that when Merc entered the then-new FIA GT series, they had just killed the original DTM

Hardly. Mercedes-Benz was the only company to commit to the ITC for 1997. It was Alfa Romeo and Opel who withdrew.

[JAG]

Originally posted by BSchneiderFan
Hardly. Mercedes-Benz was the only company to commit to the ITC for 1997. It was Alfa Romeo and Opel who withdrew.

They tried to turn the DTM/ITC into the touring car equivalent of F1, which other manufactuers could not afford.

[cybersdorf]

Originally posted by BSchneiderFan
Hardly. Mercedes-Benz was the only company to commit to the ITC for 1997.

...having corrupted the series format into the lunacy that was Class 1.

It was Alfa Romeo and Opel who withdrew.

...not being prepared to perpetuate this lunacy.

[Bob Riebe]

Originally posted by cybersdorf
It all depends on the way the regulations are written. Some favour turbo engines, some favour N/A engines - which ideally shouldn't happen.

The Gp.C engine regulations were the best engine rules ever i.m.h.o. - you could do whatever you liked to achieve the task in hand - complete the race distance with a given amount of fuel, and be faster than the others in the process. In prototype racing at least, it should be like this today.

The original IMSA AAGT formula favored neither, and it was not the formula that kept US cars from winning. It was US manufacturers sitting with their thumbs up their butts.
In Chevys case it was week trannies, and not supporting the Chevy die-hards.

The best formula ever is simple weight to displacement or a single displacement and weight rule.(In the IMSA and Trans-Am turbos were treated as a larger displacement engine and had to meet said same weight.)
The latter made the Trans-Am, the success it was, in the US, and the former took-over when the latter was replaced.
We don't need no stinkin economy runs.

What is needed is to get rid of artificial under-car aero aids (requiring wings or spoilers to be factory stock also would be nice)and artificial intake obstructions to do what weight to displacement does best.

It is only when NASCAR type air restrictors are used that an advantage can be given to either NA or blown engines.
Mathematical formulas deriving engine equivalents to NA four-strokes work well, plus adding or removing weight to make up for any errors does not cost any team tens of thousands of dollars to try to make an engine do what is was not designed to do, i.e. breathe while being strangled.

[pounetbf]

Originally posted by Bob Riebe

The best formula ever is simple weight to displacement or a single displacement and weight rule.(In the IMSA and Trans-Am turbos were treated as a larger displacement engine and had to meet said same weight.)

"turbos were treated as a larger displacement engine" what will be our equivalence ? if the maximum atmo size is 6 liters, what would be your maximum displacement for a turbo engine ?

this coeffiecient has varied in the history from 1.4 to 3.


All the motorsport history shows that you cannot have in the same time atmo and turbo engine with just a displacement equivalence coeffcient for turbo engine.


because if the performances are equivalent between atmo and turbo, you just have to increase the turbo boost to increase the power.
Turbo engine will always win

To let the choice you need something else than just a displacement rule.

[MulsanneMike]

Originally posted by pounetbf
"turbos were treated as a larger displacement engine" what will be our equivalence ? if the maximum atmo size is 6 liters, what would be your maximum displacement for a turbo engine ?

this coeffiecient has varied in the history from 1.4 to 3.


All the motorsport history shows that you cannot have in the same time atmo and turbo engine with just a displacement equivalence coeffcient for turbo engine.


because if the performances are equivalent between atmo and turbo, you just have to increase the turbo boost to increase the power.
Turbo engine will always win

To let the choice you need something else than just a displacement rule.

I agree. Its my opinion the IMSA GTP weight to displacement formula was a failure. So many times did the turbo engined cars simply walk away into the distance. And how IMSA GTP Championships were won by normally aspirated engines? Hell, how many raceswere won by normally aspirated engines during the GTP days?

Yes, the ALMS championship is no better when you compare turbo to normally aspirated and I can't say the ACO formula is perfect. But in one respects it is in that across the board you can't say anyone has a power advantage. Where advantage lies is the area in the power curve before the restrictor takes effect and that is where the turbo cars do have an advantage.

Again, doing away with aero is dangerous. Why? Never push designers into a corner where by they can gain a serious advantage by taking drag off the car (and downforce). Regulations should never be written that encourage that direction and put the limiting factor not on downforce, but on drag. Taking away underbody devices would do just that as they encourage further limiting downforce by the designers as a way of reducing drag to make the car go faster. Given a track like Le Mans I'm taking drag out of the car to go fast (lap time) if I don't have much downforce to start with within the regulations.

Sure at a slow speed track the aerodynamacist will find ways to make the cars work by implementing gurneys and spoilers and making the car produce draggy downforce. But at the high speed tracks the cars are in their element and the direction is to then take drag off the car and the low downforce (by design) cars become even lower downforce, and, in my opinion, very dangerous.

But if the regulations mandate a set amount of downforce by the implementation of underbody and wing induced downforce there will be a safety buffer of downforce (and drag) and speeds in the straights will be self limiting and the amount of downforce will be useful in keeping the cars on the ground.

[Dauntless]

We've been over this territory before, and it still boils down to the fact that current technology and rules limit atmo engines to about 125 hp/liter for 24 hour races. That simply leaves too much torque under the curve for them to make up over the turbo engines.

[Dauntless]

Originally posted by Bob Riebe
The best formula ever is simple weight to displacement or a single displacement and weight rule.(In the IMSA and Trans-Am turbos were treated as a larger displacement engine and had to meet said same weight.)
...
We don't need no stinkin economy runs.

Simple weight-to-displacement rules don't work because they ignore the impact of inertia. Assuming the lighter car has enough hp to reach terminal velocity on the longest straight it always has the advantage.

However, I agree that economy runs are bad rules. They drove engine costs through the roof and were a major factor in the demise of that era.