Turbo cars staging
Discussion
A free reving motor doesn't make enough gasses/heat to spin the turbo quick enough to make boost, a loaded motor makes more gasses/heat in the exhaust system, pulling timing will effectively fire unburned fuel into the exhaust creating more gasses/heat.
(ISH) roughly speaking!
It's one of the main reasons my new motor is blown!
(ISH) roughly speaking!
It's one of the main reasons my new motor is blown!
Edited by AutoManics on Friday 25th April 14:56
It makes sense if you think about it. It doesnt take a lot of fuel/air to make an engine rev when theres no load on it - you can see that in your road car. If you sit with it in neutral and give it a little throttle it will shoot through the revs alot faster than if you have it in gear and give it the same amount of throttle. If you sit there with the throttle buried with it in neutral you'll either be into a rev limiter (if your lucky) or youll find a pile of bits that used to be in your engine sitting on the floor after your engine has blown up. So you actually need that load to give your engine some work to do - some resistance. Then you can burn more fuel with more air and make more exhaust gas.
I wonder if compressed air could be pushed into the exhaust to spool the turbo instead? Im sure its been tried and either wasnt viable or is actually in use in some circumstances. Maybe you'd just need soo much compressed air that it just doesnt work.
I wonder if compressed air could be pushed into the exhaust to spool the turbo instead? Im sure its been tried and either wasnt viable or is actually in use in some circumstances. Maybe you'd just need soo much compressed air that it just doesnt work.
Nitrous is used quite commonly in "small tyre" classes and Pro Extreme type cars like the El General Camaro etc to aid the spool process. Adding a few horsepower of nitrous at low RPM creates a massive increase in cylinder and exhaust pressure which gets 'em spinning no problem. Such practice is banned in legal pro mod classes though.
Foot activated transbrakes are used in pro mod to theoretically cancel out any RT advantage over the clutch cars. So to stage an auto you activate the transbrake, build up the RPM and then "bump" in to stage once you've achieved your desired startline boost. There's usually a button on the steering wheel attached to a device that either pulses or momentarily interrupts the transbrake operation, the tricky part is setting it up so it doesn't bump you through and over the startline altogether.
With a clutch, the process is similar, but because there's no converter to "load" the engine up against, you have to use a much more aggressive anti-lag system that retards the timing more and at a higher RPM to create enough energy in the exhaust. This involves a foot on the throttle (usually with a switch halfway to activate the spool up RPM, boost controller and initiate the anti-lag), and a thumb on the line-lock to prevent the centrifugal pressure on the clutch pulling the car through stage as the revs increase. Once the turbos are spooled up to the right pressure (usually by knowing how long you need to be on the 2 step for), you let the clutch out slightly to roll through in to full stage and then mash the throttle to the floor. This now contacts another switch that enables a higher launch RPM and also arms the boost controller for it's run sequence. It's quite a busy situation!
Foot activated transbrakes are used in pro mod to theoretically cancel out any RT advantage over the clutch cars. So to stage an auto you activate the transbrake, build up the RPM and then "bump" in to stage once you've achieved your desired startline boost. There's usually a button on the steering wheel attached to a device that either pulses or momentarily interrupts the transbrake operation, the tricky part is setting it up so it doesn't bump you through and over the startline altogether.
With a clutch, the process is similar, but because there's no converter to "load" the engine up against, you have to use a much more aggressive anti-lag system that retards the timing more and at a higher RPM to create enough energy in the exhaust. This involves a foot on the throttle (usually with a switch halfway to activate the spool up RPM, boost controller and initiate the anti-lag), and a thumb on the line-lock to prevent the centrifugal pressure on the clutch pulling the car through stage as the revs increase. Once the turbos are spooled up to the right pressure (usually by knowing how long you need to be on the 2 step for), you let the clutch out slightly to roll through in to full stage and then mash the throttle to the floor. This now contacts another switch that enables a higher launch RPM and also arms the boost controller for it's run sequence. It's quite a busy situation!
AutoManics said:
We load ours up on the trans brake once in full stage and fire a small shot of Nitrous in to get it up on the chip quickly, without the nitrous it takes an age to come up.
Just what you need to be doing at the very time you're supposed to be concentrating on the tree. We had too much carb/inlet volume on our super-pro car which made it bog if you floored it too quickly. We fitted an auto pump-shot device (rev related) to get it up on the chip ASAP. We were using a sportsman tree of course and that didn't leave much time to be fiddling about, it must be one hell of a problem on a pro tree, especially if you're second into stage. Turn7 said:
Thanks Lee. Im digeyou need lng all of that - slowly.
What does the anti lag actually achieve ?
Also, I still dont quite get why you need load. Turbos spin faster according to exhaust speed not temp is my understanding ?
Yours - a PM turbo numpty...
The anti lag retards the ignition on random cylinders so that the fuel is igniting as the exhaust valve opens. This causes "explosions" in the exhaust and this energy is used to spool up the turbine wheel of the turbo.What does the anti lag actually achieve ?
Also, I still dont quite get why you need load. Turbos spin faster according to exhaust speed not temp is my understanding ?
Yours - a PM turbo numpty...
The easiest way to describe why you need load is to think of the engine as an air pump, and how fast the turbo spins is down to the volume and velocity of air being expelled. Without load on the engine, maximum RPM can be achieved at quite a small throttle opening, which means that the volume of air coming out isn't large or fast enough to effectively act on the turbo. Now place a load on the engine and you have to open the throttle much wider to achieve the same RPM, this means much more air is entering the combustiom chamber...so in turn, much more air is coming out, and to empty the cylinder at the same speed as before despite the increased volume means that the expelled air must also be travelling much faster. So you now have a bunch more air travelling at a much greater speed...hence you're now spinning the turbo harder and consequently making boost. Also remember that the wastegates will be manipulated by the boost controller or ecu too, which will monitor engine load via manifold vacuum and in most cases won't close the wastegates unless the engine actually requires boost in the first place.
Flying Phil said:
Thanks to the posters in this thread - the technology involved in top class drag racing is awesome and little appreciated by the vast majority of fans - let alone the general public.
Whole heartedly agree Phil. The science, or is it art?, of racing to an index is another area which is poorly understood in general. All that stuff about staging techniques, performance management, down track tactics... are a black art to many in the grandstands... maybe to some racers too! Turn7 said:
Thanks Lee. Im digesting all of that - slowly.
What does the anti lag actually achieve ?
Also, I still dont quite get why you need load. Turbos spin faster according to exhaust speed not temp is my understanding ?
Yours - a PM turbo numpty...
It's all down to exhaust gas expansion, which is what drives an internal combustion engine. The more resistance against the expanding gas you provide, the more complete the mixture burns, the hotter the burn temperature gets and the larger the pressure/volume of gas produced in the cylinder.What does the anti lag actually achieve ?
Also, I still dont quite get why you need load. Turbos spin faster according to exhaust speed not temp is my understanding ?
Yours - a PM turbo numpty...
This is why nitro is such a powerful fuel in an internal combustion engine. The more you compress/resist it, the more aggressively it burns and expands, thus making more power. It's why we run large barge-boards in front of the rear wheels, and why we use such a large two-piece rear wing flap (the upper flap curves to vertical) - aerodynamic drag (load).
With turbo cars, without enough loading on the engine, you cannot create enough exhaust gas expansion/pressure/volume to drive the turbo exhaust turbine hard enough to in turn produce enough inlet boost for the best launch engine power. Anti-lag, nitrous injection, they all seek to increase the volume and pressure of exhaust gas produced to better drive the turbo exhaust turbine.
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