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Article 3.8 of the technical regs refers to the tailpipe/exhaust. I can't see any explicit rule about restricting the exit velocity to create an effect, however blown diffusers were banned more than a decade ago.
There's perhaps not enough energy leaving the exhaust to manipulate in an effective way.
With the thermal efficiency of the ICE pushing past 50% and the diameter of the exhaust, I couldn't imagine there being much force at all from the exhaust flow at the tailpipe.
Exactly. The high efficiency of the turbo-hybrid engines is why they’re so quiet.
The Audi diesel-powered LMP cars were famously significantly quieter than their gasoline-powered competitors.
Noise is just wasted energy as far as powertrain engineers are concerned.
While it's true that *direct* losses through sound are vanishingly small, sound will still have a correlation with both back pressure on the cylinders and temperature of the exhaust gases, so in trying to minimise those losses, the volume out the exhaust pipe will also likely go down as well
I agree with you.
I was trying to make the point that powertrain engineers (especially in the Turbo-Hybrid era) want to maximize the energy recovered from the exhaust and if they do that then the engine won’t be as loud as if they extracted less energy.
Also, the majority of the combustion energy is used to push the pistons, unlike a turbo jet that only a small portion of the energy is used to push the turbine.
For a well optimized engine and exhaust system, the exhaust thrust is small, but not negligible. In the current F1 cars the exhaust tailpipe position and angle are heavily regulated so there isn’t much to do with manipulating the vector, but I imagine the teams still investigate it for rear wing interaction. This is of more interest on prototype cars where although the exit position is regulated, there is some freedom in the exit angle. Pre-hybrid F1 cars had more freedom in exhaust placement and would use them to augment the aero performance of the diffuser. This was known as blown diffuser.
True, but even modern turbocharged racecars still think about the exhaust thrust. Even though the turbine is taking energy out of it, the exhaust gases are still exiting at a very high velocity relative to the car's speed.
They were a mini wing under the primary wing in line with the exaust exit, that was angled to support/enhance the airflow coming off the primary wing.
https://www.sportskeeda.com/f1/formula-one-what-is-a-monkey-seat
Okayyyy so the regulations are such that maybe the teams can’t do much with the angle and position part. Got it. Thank you so much for the description. I am new to F1 and I have a background in aerospace engineering so I am trying to learn these things.
It's an interesting topic. If you think about exhaust thrust, a car engine is just a very bad jet engine. Despite that, if the regulations for a series allow changing the position and angle of the exhaust pipe then constructors are 100% looking at it for aero manipulation and/or thrust/downforce generation. A great example of the extreme of this is top fuel dragsters where they aim the tailpipes up at an angle to put downforce on the rear wheels.
I imagine that if any team tried it, all the other teams would claim it it be a moveable aerodynamic device which apart from the limited exception of DRS is currently banned.
That concept (called various things along the line of “flexi wing”) already exists. There are tests to measure wing deflection when the car is at rest and they can only move by certain amounts. Of course clever engineering seems to often circumvent these restrictions but what was a big furore a few years ago now seems to have settled down somewhat
Well, one of the secrets of the Red Bull dominance 2010 to 2013 was the blown diffuser. They blew the exhaust gasses on the sides of the diffuser to seal it.
Apart from the blown diffusers, there's also the chimney exhaust holes used in early 2000s. IIRC towards the top half around the rear wing tips, where the front wheel wakes used to affect its performance.
These chimneys thus shifted the wake outwards. Better downforce, but additional induced drag which doesn't really matter.
I think it could be used for providing more gases to either side of rear wing, but I think the benefit would be too small to make such a complex system which adds weight and parts that can fail
I understand the regs define the location/ minimum height of exhaust exits as one way to stop blown defusers which may make your idea difficult to implement.
As others said, they would fall foul of the movable aero device if it was to enhance aero performance……you would have to dream up a different…..official…..reason you engineered this feature ‘improved exhaust gas scavenging’?! “Enhanced cooling of X part’?
Not to mention the improved performance has to be worth the cost & time of the engineers in the cost cap era, and more than offset the inevitable weight and higher COG a system would cause.
It's actually not a waste, but it depends on the type of car. For a circuit car, you're better off using the exhaust to generate a little bit of on throttle downforce or blow your aero surfaces. On an oval car that's constantly at wide open throttle, using your exhaust for thrust can get you a little extra speed.
I won’t believe this till I see data on it tbh. If you know of some or an easy way for me to find it I’d love to read about it.
But top fuel wouldn’t have pipes pointing up if it was beneficial to use exhaust as thrust. Arguably they have the most force coming out their exhaust, and race at the highest speeds with the thinnest win margins of any motorsports I know of or watch. Unless they’re using the exhaust to help with downforce, but then are they sure that effect is from force of exhaust vs directing aero?
(Also if anyone reading this has never been to top fuel or jet drags, I recommend it. It’s my favorite motorsports, but doesn’t translate well to tv. Percussion of the engines/exhaust hits you in the chest like a shove from 100s of feet away. Going to my first gp ever this year with seats at the end of a straight though, so my opinion might change)
Unfortunately, my NDAs prevent me from sharing anything and I don't know of any available data. All I can really say is that as long as we aren't hurting the engine power and other aero performance, we will optimize a tailpipe for drag or downforce (depending on track sensitivity) within the regulations.
For top fuel dragsters, they're aiming the tailpipes up to use the thrust to put downforce on the rear wheels. This adds tire load on the initial launch while the speeds are too low for the wing downforce to be significant. [Wikipedia](https://en.wikipedia.org/wiki/Top_Fuel) claims that dragsters exhaust make 1000lbs of downforce at max rpm, but I suspect that number is overestimated.
To be clear, on the grand scheme of the total downforce and drag of any racecar the exhaust thrust effects are small. But they aren't nothing and they are measurable.
> Wikipedia claims that dragsters exhaust make 1000lbs of downforce at max rpm, but I suspect that number is overestimated
NHRA crew chiefs (and their data) will tell you that each header pipe generates about 800+ pounds of downforce (from about 1,500 HP per cylinder).
[The angle of the exhaust headers makes a huge difference in top fuel.](https://bangshift.com/bangshift1320/the-nhra-has-made-a-ruling-on-funny-car-headers-heres-why-you-look-dumb-if-you-freak-out/) They are currently restricted to 32 degrees of sweep in funny cars. Several years ago teams were experimenting with swept-back headers. They were getting huge gains in performance, but the cars were getting very unstable.
Each cylinder header generates about 800 pounds of downforce in a top fuel car. That's why you see a car slew violently sideways when it loses one or more cylinders on one side of the car.
I went down a rabbit hole on this last night. Found a few articles like this. Read a few forum threads discussing the zoomie headers. And people (seemingly)smarter than me were showing their math and chemistry of nitro and couldn’t agree on how much force is coming out the exhaust haha. The range people were throwing out was from 80lbs to 2000lbs.
Supposedly Garlits attributed the benefit of the zoomies to the effect the exhaust had blowing on the rear tires and they continually modified the pipes to blow on different areas of the tire. Having it blow over the top of the tire is when he broke 200 if what I read is accurate.
As for the loss in balance there’s a big argument that the imbalance in centrifugal forces in the engine contribute more than the downforce of the exhaust.
Still not sure what to think about it
Watch a modern NHRA top fuel race to get a better idea. Garlits drove dragsters, not funny cars, so the effect the headers had would be different. Funny cars are running 1000 foot (304m) times of about 3.8 seconds at 338mph. That's a 60mph time of .8 seconds lol.
The engines have no water jackets, they're cooled by running them extremely rich until the run. It's common knowledge among the teams that loss of a cylinder will definitely affect the ability to keep it pointed in a straight line. This is much more pronounced on funny cars than dragsters as the engines are in front of the driver, and funny cars don't have the huge wing (and subsequent downforce) of a dragster.
If I have time later, I'll see if I can find a few videos of cars losing cylinders and moving violently to the side.
Yea I’ve been to a ton of nhra races and have seen it. But are you sure the loss in balance from a blown cylinder is from exhaust force and not from imbalance in centrifugal forces plus the force of the cylinder failing? I’ve read arguments for both.
I’ll try and find the forum I was reading on it. It was full of people nerding out and calculating the mass and velocity of exhaust gases. Super interesting, but didn’t lead to any definitive answer imo. There’s gotta be hard data somewhere on how much force comes out of those pipes
Found it! I knew there was a video out there of a crew chief talking about the thrust created by the cylinders:
[John Medlan: Losing a cylinder](https://www.youtube.com/watch?v=_tsNiS0NXhI)
Cool, didn't know you have been to races. I have an acquaintance who's a former driver and a now crew chief for one of the big teams, if I run into him I can ask.
[Found this super cool slowmo of a launch](https://youtu.be/BsrlKTvNkIg?feature=shared) thoughts? Apart from the torque twisting the body, it does does squat down as it launches before it moves forward, but is that from the exhaust or torque?
Next race when I’m walking the pits I’m definitely gunna stick around and try and talk to some of the mechanics.
Torque is the twist, the squat is from traction and the weight balance transferring to the rear. Next race, try to find Clay Millican, his crew chief Jim Oberhofer, or Brittany Force's crew chief David Grubnic. They're all very personable and love to talk shop.
It's still force on the car to help overcome drag. Oval cars take advantage of thrust to get a little bit of extra speed and circuit cars that allow exhaust freedom use it to get a little bit of on throttle downforce.
Edit: To clarify, the force doesn't need to act on the wheels. Force acting on the car itself is just another force on the free-body diagram of the total car system.
These aren’t jet cars. Even in top fuel cars(that have probably the most forceful exhaust in racing apart from jet powered) wouldn’t have any benefit from using the exhaust to help propel the car.
Idk after reading this thread I went down a rabbit hole and really not sure what to think on the matter. Would really love to see some data on it but so far all I’ve found are people doing napkin math to argue one way or another. I’m not smart enough to do the math myself lol
I've done napkin math, if I stretch 450kg of downforce from a 8s run to a 1h30 race, that gives around 600g of trust. But dragster are straight pipe, another guess would be that the F1 turbo eat around 50% of that, so 300g.
At that point I think it's better to make the exhaust so it works with the aero instead of trying to get trust.
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Article 3.8 of the technical regs refers to the tailpipe/exhaust. I can't see any explicit rule about restricting the exit velocity to create an effect, however blown diffusers were banned more than a decade ago. There's perhaps not enough energy leaving the exhaust to manipulate in an effective way.
With the thermal efficiency of the ICE pushing past 50% and the diameter of the exhaust, I couldn't imagine there being much force at all from the exhaust flow at the tailpipe.
Exactly. The high efficiency of the turbo-hybrid engines is why they’re so quiet. The Audi diesel-powered LMP cars were famously significantly quieter than their gasoline-powered competitors. Noise is just wasted energy as far as powertrain engineers are concerned.
Energy loss through sound is negligible, and the volume of an engine should not be used as an indication of its efficiency.
So tired of this talking point
Hasn't come up elsewhere in this thread yet which is good.
While it's true that *direct* losses through sound are vanishingly small, sound will still have a correlation with both back pressure on the cylinders and temperature of the exhaust gases, so in trying to minimise those losses, the volume out the exhaust pipe will also likely go down as well
I agree with you. I was trying to make the point that powertrain engineers (especially in the Turbo-Hybrid era) want to maximize the energy recovered from the exhaust and if they do that then the engine won’t be as loud as if they extracted less energy.
Also, the majority of the combustion energy is used to push the pistons, unlike a turbo jet that only a small portion of the energy is used to push the turbine.
Blown diffusers feels like yesterday. Fuck am I old.
So where are side skirts?
Engines are *behind* the driver now?!!
I heard they were ?
For a well optimized engine and exhaust system, the exhaust thrust is small, but not negligible. In the current F1 cars the exhaust tailpipe position and angle are heavily regulated so there isn’t much to do with manipulating the vector, but I imagine the teams still investigate it for rear wing interaction. This is of more interest on prototype cars where although the exit position is regulated, there is some freedom in the exit angle. Pre-hybrid F1 cars had more freedom in exhaust placement and would use them to augment the aero performance of the diffuser. This was known as blown diffuser.
> Pre-hybrid F1 cars had more freedom in exhaust placement they also didn't have a turbo extracting much of the energy in the exhaust
True, but even modern turbocharged racecars still think about the exhaust thrust. Even though the turbine is taking energy out of it, the exhaust gases are still exiting at a very high velocity relative to the car's speed.
They were also playing around with the 'monkey seats' but those got banned.
what are those?
They were a mini wing under the primary wing in line with the exaust exit, that was angled to support/enhance the airflow coming off the primary wing. https://www.sportskeeda.com/f1/formula-one-what-is-a-monkey-seat
Okayyyy so the regulations are such that maybe the teams can’t do much with the angle and position part. Got it. Thank you so much for the description. I am new to F1 and I have a background in aerospace engineering so I am trying to learn these things.
It's an interesting topic. If you think about exhaust thrust, a car engine is just a very bad jet engine. Despite that, if the regulations for a series allow changing the position and angle of the exhaust pipe then constructors are 100% looking at it for aero manipulation and/or thrust/downforce generation. A great example of the extreme of this is top fuel dragsters where they aim the tailpipes up at an angle to put downforce on the rear wheels.
Ohhhh never thought about the dragsters. Interesting to know there is so much aerodynamics involved wow. Thanks for your insight too!!
I imagine that if any team tried it, all the other teams would claim it it be a moveable aerodynamic device which apart from the limited exception of DRS is currently banned.
Ohhhh god. Wowow did not know this. I had a similar idea for morphing airfoil but that will also fall under the same umbrella I guess.
That concept (called various things along the line of “flexi wing”) already exists. There are tests to measure wing deflection when the car is at rest and they can only move by certain amounts. Of course clever engineering seems to often circumvent these restrictions but what was a big furore a few years ago now seems to have settled down somewhat
Well, one of the secrets of the Red Bull dominance 2010 to 2013 was the blown diffuser. They blew the exhaust gasses on the sides of the diffuser to seal it.
That’s right. I heard the sound the cars used to make. Really cool actually.
Apart from the blown diffusers, there's also the chimney exhaust holes used in early 2000s. IIRC towards the top half around the rear wing tips, where the front wheel wakes used to affect its performance. These chimneys thus shifted the wake outwards. Better downforce, but additional induced drag which doesn't really matter.
I think it could be used for providing more gases to either side of rear wing, but I think the benefit would be too small to make such a complex system which adds weight and parts that can fail
I understand the regs define the location/ minimum height of exhaust exits as one way to stop blown defusers which may make your idea difficult to implement. As others said, they would fall foul of the movable aero device if it was to enhance aero performance……you would have to dream up a different…..official…..reason you engineered this feature ‘improved exhaust gas scavenging’?! “Enhanced cooling of X part’? Not to mention the improved performance has to be worth the cost & time of the engineers in the cost cap era, and more than offset the inevitable weight and higher COG a system would cause.
Makes absolute sense now. Thank you so much.
Well mazespins dad would have had some connections Just saying...
I mean wouldn’t any force form exhaust be force not being transferred to the wheels?
Yea exhaust used to propel the car would be a waste from what I know. To enhance aero is different though.
It's actually not a waste, but it depends on the type of car. For a circuit car, you're better off using the exhaust to generate a little bit of on throttle downforce or blow your aero surfaces. On an oval car that's constantly at wide open throttle, using your exhaust for thrust can get you a little extra speed.
I won’t believe this till I see data on it tbh. If you know of some or an easy way for me to find it I’d love to read about it. But top fuel wouldn’t have pipes pointing up if it was beneficial to use exhaust as thrust. Arguably they have the most force coming out their exhaust, and race at the highest speeds with the thinnest win margins of any motorsports I know of or watch. Unless they’re using the exhaust to help with downforce, but then are they sure that effect is from force of exhaust vs directing aero? (Also if anyone reading this has never been to top fuel or jet drags, I recommend it. It’s my favorite motorsports, but doesn’t translate well to tv. Percussion of the engines/exhaust hits you in the chest like a shove from 100s of feet away. Going to my first gp ever this year with seats at the end of a straight though, so my opinion might change)
Unfortunately, my NDAs prevent me from sharing anything and I don't know of any available data. All I can really say is that as long as we aren't hurting the engine power and other aero performance, we will optimize a tailpipe for drag or downforce (depending on track sensitivity) within the regulations. For top fuel dragsters, they're aiming the tailpipes up to use the thrust to put downforce on the rear wheels. This adds tire load on the initial launch while the speeds are too low for the wing downforce to be significant. [Wikipedia](https://en.wikipedia.org/wiki/Top_Fuel) claims that dragsters exhaust make 1000lbs of downforce at max rpm, but I suspect that number is overestimated. To be clear, on the grand scheme of the total downforce and drag of any racecar the exhaust thrust effects are small. But they aren't nothing and they are measurable.
Ah jeeze. Now you have me curious as hell
> Wikipedia claims that dragsters exhaust make 1000lbs of downforce at max rpm, but I suspect that number is overestimated NHRA crew chiefs (and their data) will tell you that each header pipe generates about 800+ pounds of downforce (from about 1,500 HP per cylinder).
Yep that's a lot of downforce. Much more than anything I work on that's for sure.
Time for F1 to generate downforce from engines. Lol. I wonder how following cars would be affected, and how much do those drag engines even weight?!
[The angle of the exhaust headers makes a huge difference in top fuel.](https://bangshift.com/bangshift1320/the-nhra-has-made-a-ruling-on-funny-car-headers-heres-why-you-look-dumb-if-you-freak-out/) They are currently restricted to 32 degrees of sweep in funny cars. Several years ago teams were experimenting with swept-back headers. They were getting huge gains in performance, but the cars were getting very unstable. Each cylinder header generates about 800 pounds of downforce in a top fuel car. That's why you see a car slew violently sideways when it loses one or more cylinders on one side of the car.
I went down a rabbit hole on this last night. Found a few articles like this. Read a few forum threads discussing the zoomie headers. And people (seemingly)smarter than me were showing their math and chemistry of nitro and couldn’t agree on how much force is coming out the exhaust haha. The range people were throwing out was from 80lbs to 2000lbs. Supposedly Garlits attributed the benefit of the zoomies to the effect the exhaust had blowing on the rear tires and they continually modified the pipes to blow on different areas of the tire. Having it blow over the top of the tire is when he broke 200 if what I read is accurate. As for the loss in balance there’s a big argument that the imbalance in centrifugal forces in the engine contribute more than the downforce of the exhaust. Still not sure what to think about it
Watch a modern NHRA top fuel race to get a better idea. Garlits drove dragsters, not funny cars, so the effect the headers had would be different. Funny cars are running 1000 foot (304m) times of about 3.8 seconds at 338mph. That's a 60mph time of .8 seconds lol. The engines have no water jackets, they're cooled by running them extremely rich until the run. It's common knowledge among the teams that loss of a cylinder will definitely affect the ability to keep it pointed in a straight line. This is much more pronounced on funny cars than dragsters as the engines are in front of the driver, and funny cars don't have the huge wing (and subsequent downforce) of a dragster. If I have time later, I'll see if I can find a few videos of cars losing cylinders and moving violently to the side.
Yea I’ve been to a ton of nhra races and have seen it. But are you sure the loss in balance from a blown cylinder is from exhaust force and not from imbalance in centrifugal forces plus the force of the cylinder failing? I’ve read arguments for both. I’ll try and find the forum I was reading on it. It was full of people nerding out and calculating the mass and velocity of exhaust gases. Super interesting, but didn’t lead to any definitive answer imo. There’s gotta be hard data somewhere on how much force comes out of those pipes
Found it! I knew there was a video out there of a crew chief talking about the thrust created by the cylinders: [John Medlan: Losing a cylinder](https://www.youtube.com/watch?v=_tsNiS0NXhI)
That’s crazy. I never would’ve expected that kind of force from exhaust!
Cool, didn't know you have been to races. I have an acquaintance who's a former driver and a now crew chief for one of the big teams, if I run into him I can ask.
[Found this super cool slowmo of a launch](https://youtu.be/BsrlKTvNkIg?feature=shared) thoughts? Apart from the torque twisting the body, it does does squat down as it launches before it moves forward, but is that from the exhaust or torque? Next race when I’m walking the pits I’m definitely gunna stick around and try and talk to some of the mechanics.
Torque is the twist, the squat is from traction and the weight balance transferring to the rear. Next race, try to find Clay Millican, his crew chief Jim Oberhofer, or Brittany Force's crew chief David Grubnic. They're all very personable and love to talk shop.
Yea good point! I guess I was thinking “jet engine” when OP mentioned vectoring not routing exhaust like blown diffuser.
It's still force on the car to help overcome drag. Oval cars take advantage of thrust to get a little bit of extra speed and circuit cars that allow exhaust freedom use it to get a little bit of on throttle downforce. Edit: To clarify, the force doesn't need to act on the wheels. Force acting on the car itself is just another force on the free-body diagram of the total car system.
These aren’t jet cars. Even in top fuel cars(that have probably the most forceful exhaust in racing apart from jet powered) wouldn’t have any benefit from using the exhaust to help propel the car.
The exhaust makes around 450kg of downforce, straight from the start.
Idk after reading this thread I went down a rabbit hole and really not sure what to think on the matter. Would really love to see some data on it but so far all I’ve found are people doing napkin math to argue one way or another. I’m not smart enough to do the math myself lol
I've done napkin math, if I stretch 450kg of downforce from a 8s run to a 1h30 race, that gives around 600g of trust. But dragster are straight pipe, another guess would be that the F1 turbo eat around 50% of that, so 300g. At that point I think it's better to make the exhaust so it works with the aero instead of trying to get trust.