Air Restrictors In Wrc

[Robin Plummer]

Over the last ten years or so Air Restrictor sizes have come down from 40mm-38mm-36mm and now 34mm in Group A/WRC turbo class. Everyone claims to have "only" 300bhp a worded limit set in 1987 by the FIA. What do these current car's really produce after 16 years of development at this rule? And can you tell me how much in power output each reduction in restrictor size will affect the engine?

For example how much more power would the engine have with a 38mm or 40mm Restrictor than the current 34mm one?

[avsfan733]

i think that everyone is maxed out at about 300-320. i have read that subaru once maxed an engine at 340 on an engine dyno but to quote the article "that particular engine didn't have the most desirable torque curve"
obviously it affects the way it works not qute sure how much though

[Robin Plummer]

I notice that in the FIA European Rallycross championship there are some ex WRC cars like the Escort WRC they run with an slight overbore from 1993cc to 2058cc and run a 45mm air restrictor on the same type of engine as used in the 1998 championship they produce 450-500bhp. I got chatting to a bloke work worked for Mountune in 2000 and he said the Hyundai Accent unit produced about 325bhp with 34mm restrictor in the WRC.

[Robin Plummer]

I forgot to say I read a report once that said in 1992 with the 38mm restrictor the Lancia Delta Integrale 16v Evo unoffically produced 370bhp not sure about the torque.

[boyracer]

Read article last year (2002) that had ford the highest at a claimed 380, and hyundai and subaru pretty close to the bottom on about 320-340. Most teams (I think anyway) are injecting water after the restrictor. The main components of water being hydrogen (big bang gas) and oxygen (does that help fuel burn ?). The high temperatures/pressures of combustion break the water into it's elements and you get a bigger bang. Also the world rally fuel (I thinks it's a form of ELF) is an oxygenated fuel anyway (contains oxygen).

[mixxer]

Originally posted by boyracer
Read article last year (2002) that had ford the highest at a claimed 380, and hyundai and subaru pretty close to the bottom on about 320-340. Most teams (I think anyway) are injecting water after the restrictor. The main components of water being hydrogen (big bang gas) and oxygen (does that help fuel burn ?). The high temperatures/pressures of combustion break the water into it's elements and you get a bigger bang. Also the world rally fuel (I thinks it's a form of ELF) is an oxygenated fuel anyway (contains oxygen).

By injecting water you decrease the Air Temp which will increase the density of the Air then you have to increase the amount of fuel being injected to stop it Leaning out to far and all of a sudden you have more horsepower

[boyracer]

Yes, they also spray water over the intercooler which lowers the air temp of the boosted air going into the engine (because of course by compressing the air you add heat to it) but the water into the engine is for the extra oxygen. It has been used on road cars to prevent pinging on cr#p fuel (such as we get here in australia), and sometimes mixed with enthanol to increase the bange and the latent heat capacity of the liquid.

[alfasud]

I seem to recall that when Possum Bourne ran his Group A Subaru WRX in a hillclimb event in New Zealand, he ran without the restrictor, but otherwise standard turbo and remapped Group A engine. I think the power output was in the 400-450bhp region.

The fastest Pikes Peak hillclimb vehicals are in the region of 800bhp (or more?).

Not sure if I follow boyracers "The main components of water being hydrogen (big bang gas) and oxygen (does that help fuel burn ?)" theory.

To split water into hydrogen and oxygen, requires the same sort of energy to split those molecular bonds as is realised when hydrogen and oxygen is burnt (to make water vapour). The only way I know to split those bonds is electrical current or some sort of chemical reaction to release the hydrogen.

Water is injected and energy (heat) is removed by evaporation of the water, but the hydrogen and oxygen components don't come into it..... you certainly don't get to burn them in combustion.

I suspect the prevention of pinging is due to the lowering of temperatures in the combustion chamber.

[avsfan733]

it is its not like boyracer has it written although that would be nice, think about a water powered car
It functions the somewhat differently as alcohol injection.. Alcohol injection cools the combustion chamber because it burns and evaporates at a much lower temperature. The alcohol is injected and immediately evaporates cooling the intake charge (works the same way on your skin)tehn it burns in the combustion chamber andding power but burning cooler than fuel.

Water injection works much the same way but doesn't burn so it doesn't give u any power.

Both of these work to lessen pinging, also known as detonation, by preventing the hotspots on the piston or on the cylinder from forming and then preigniting the air/fuel mixture

[boyracer]

OK, so if you're adding water into the airstream, you are decreasing the amount of fuel that the air can support then where is the advantage ? Sure the combustion chamber may run a little cooler, but given the huge temperatures (thus heat energy) and the miniscule amount of water that is being added I can't see the point ? Even given that as the water changes from liquid to gas there is a huge heat capacity, I can't see it being enough to warrant the hassle. And I know for sure that WR cars run water injection, and they're on this control fuel. And I know from personal experience that the amount of ignition timing that the fuel can take is ridiculous ! Why persue water injection ? The intake charge is already being cooled by the intercooler (which is being water sprayed at the same time). So in short, Y?

[Marsh]

Originally posted by boyracer
OK, so if you're adding water into the airstream, you are decreasing the amount of fuel that the air can support then where is the advantage ? Sure the combustion chamber may run a little cooler, but given the huge temperatures (thus heat energy) and the miniscule amount of water that is being added I can't see the point ? Even given that as the water changes from liquid to gas there is a huge heat capacity, I can't see it being enough to warrant the hassle. And I know for sure that WR cars run water injection, and they're on this control fuel. And I know from personal experience that the amount of ignition timing that the fuel can take is ridiculous ! Why persue water injection ? The intake charge is already being cooled by the intercooler (which is being water sprayed at the same time). So in short, Y?

The expansion ratio of water as it turns to steam is actually greater than that of combusting air/fuel. The more water the better, until you either break a connecting rod during the compression stroke, or inhibit combustion. Don't forget that the intercooler is used to cool the charge because the turbo heats it up a great deal. It is impossible to make the air coming out of the intercooler any cooler than the ambient air, it would violate the second law of thermodynamics. Spraying water gives an evaporative cooling effect that, theoretically, could cool the intake charge to below ambiant.

[avsfan733]

like Marsh said it does more than you think, and it allows the engine to run leaner and with more advanced ignition timing which counter this by developing more power and running in the engines "sweet spot" longer without overheating and burning a piston

[Speck]

boyracer: The water injection system used in turbocharged cars acts as knock-retardent, i.e it delays the onset of pinging. This is useful if you had a maxed out type tuning done during a cold day, but is competing on a hot day, for example.

[boyracer]

Speck, if your engine management system is worth using it should allow you to add air temperature compensations. If not, not even injecting water will save the engine from melt down.

Thanks everyone, your insights into the water injection scenario have been quite enlightening.