Hi.
Respect Scawen Victor and Eric.
You seem the only people in this brunch who understand car physics. Congrats on the tires improvement, it's a really a major change. Having raced on S1 and S2 (unfortunatelly only demo as far) for some years now and beeing a driver in reality i'd have one suggestion regarding the car reaction when stepping off the gas pedal. Real race-tuned car will brake with the engine then. S2 lacks that. I understand that strong braking after taking the foot off the throttle could be a nightmare for mouse racers when going trough corners as the RWD cars would most likely loose grip of the rear wheels then. That's why i'd suggest an additonal engine-braking bar setup with which everyone could set as they find suitable(basically in real race cars that can be regulated). Engine braking is very important for the car dynamics. After engine braking, engine regains underpressure in the inake manifolds which makes it release more torque after stepping on the throttle again afterwards. Also higher engine rpm in rwd cars with the engine placed lenghtways stabilises it on the corners which is qiute hard to prove but can be easily felt when driving a real vehicle.
Pour some life in the engine reactions and the driving expirience will be even more enjoyable.
Congrats once again.
(im reeling from shock that these days someone aims not only for money and remains so devoted to the customes relasing so many good impovements)

LFS cars do implement Engine braking, but you wouldn't be able to tell, since the best example of this is the BF1.

I have on many occasions slid the rear tires of the XRT on approach to T1 on Blackwood due to the engine braking being more then the tires have grip to handle. Its there, its noticable but with out the seat of your pants g-forces you just can not sence it well.

I don't even want to get in to the mistakes and assumptions you make reguarding how engine braking works and how you think its adjustable.

This also depends on setup as its possible to make this effect the car more/less by playing with the diff.

What in the.....

"engine braking bar"?

"more torque following a closed throttle -> open throttle transition" .. why? Some kind of breif transient of airflow because of it's inertia lasting 1/10,000th of a second? Seems bizarre.

LFS does not model engine mounts (the actual physical component I mean, the engine orientation is of course modeled) to my knowledge, so any "stablization" due to a longitudinal engine orientation would not be noticed in LFS.... If that's what you were getting at

Giving you the benefit of the doubt for now; turn on the F9 display and observe the G meters at the bottom centre area of the screen. You will note how much engine braking there is for a given speed & given gear, and note that it's dyanmically calculated (obviously). There's a number of people in this forum with exceptional physics and vehicle dyanmics knowledge, and experience so if I was you I might not shoot my mouth off regarding physics subsequent to a post like that....

What do you race IRL?

I think he was suggesting an "engine brake reduction" bar, like the BF1 has, which is controlled via the electronics. basicly it applies a little throttle to keep the car from swapping ends any time you let off the gas

Quote from Gimpster :

I have on many occasions slid the rear tires of the XRT on approach to T1 on Blackwood due to the engine braking being more then the tires have grip to handle. Its there, its noticable but with out the seat of your pants g-forces you just can not sence it well.

I don't even want to get in to the mistakes and assumptions you make reguarding how engine braking works and how you think its adjustable.

Easy now. See people beeing quite agressive off the track as well
The example that you gave make me think you did not exacly understand my idea. I'm not talking about engine braking due to gear reduction. That of cours is noticable and works quite relisitc, but I meant engine braking abilities whenever you step off the gas pedal within the same gear. I only compare LFS car reaction to a real car ( not Punto, not Focus, not even bloody R-type or other pseudo sports puschairs openly sold to the mass) but a car that is meant to be used for racing. Had you taken your foot of the throttle too fast in such car and not prepare yourself well enough you'r nose would be in danger of beeing smashed agains the steering wheel. (example taken from life actually). XRT does not brake that strong. You say i'm beeing wrong it's adjustable? Darn than, what's that vehicle standing in my garage. An exeption? People refer engine braking to only what's happening after they switch to a lower gear, that is caused by simply the difference between the engine RPM and what the wheels trought increased cluch transmision ration are forcing it to go. The braking i meant has different reason and is applied by the change in ignition timing phase as soon as you stop pushing gas pedal (the phase of ingintion is then acutally so much shifted back that the pistons are beeing pushed back down yet before they reach their higher point) . Actually the whole process takes a bit of additional fuel (that's why "city cars" wont react like that- economy.

Quote from Ball Bearing Turbo :

What in the.....

"engine braking bar"?

"more torque following a closed throttle -> open throttle transition" .. why? Some kind of breif transient of airflow because of it's inertia lasting 1/10,000th of a second? Seems bizarre.

LFS does not model engine mounts (the actual physical component I mean, the engine orientation is of course modeled) to my knowledge, so any "stablization" due to a longitudinal engine orientation would not be noticed in LFS.... If that's what you were getting at

Giving you the benefit of the doubt for now; turn on the F9 display and observe the G meters at the bottom centre area of the screen. You will note how much engine braking there is for a given speed & given gear, and note that it's dyanmically calculated (obviously). There's a number of people in this forum with exceptional physics and vehicle dyanmics knowledge, and experience so if I was you I might not shoot my mouth off regarding physics subsequent to a post like that....

What do you race IRL?

more torque following a closed throttle -> open throttle transition- exactly. Why?.. as far as i know it's linked with the fact that sports cars air intake systems are based on a system of eghmm throttles :} (sic. the thigie that cuts off the the air) but that for sure you know. You also are aware of the fact that there is underpressure building up behind them (inside the engine) whenever the engine is braking. Now as soon as you open the throttles the air will be sucked in way faster which will cause a higher compression ratio in the cylinders for the very first moments when you want to start aceelerating. That also means you get more air to be sucked in for the first compression cycles, more air means you can melt more fuel with it.(just to keep the lambda coefficent at its best for the engine performance). This mixture is enough more explosive to be noticed in a faster and stronger car reaction. Inertia, probably adds a bit to it too. Filling in even only 1l of engine capacity (lets say two of four cilinders of our XRT 2l engine are beeing filled at a time) at 5000RPM means that 1l of air has to be sucked in 2500times per minute wich is est. 40 times a SECOND. This has to meet with air resistance. Now imagine it's decreased to almost 0 shorlty after each closed throttle -> open throttle transition, due to under pressure.

I did made use of the G-force indicators before posting and did compared the braking abilities with a real car with an enigne of same capacity and close power. XRT almost does not brake at all compare to that. (real life example. 4th gear 140km/h to 100km/h in about 4sec after just taking my foot off).

The engine orientation is indeed modeled as even after pressing F and observing the vectors of pressure of wheels against the track you can see that when agresively adding RPM when declutched the vectors react accordingly to the In line engine mount for XRT and crosswise mount for XFG due to engine torque. I may be wrong but i think i can tell already the little difference between entering a corner at 5000rpm in XRT and entering it same speed but when declutched. Still that could be felt a bit stronger.

"There's a number of people in this forum with exceptional physics and vehicle dyanmics knowledge, and experience" - you say. I'd like to meet them and have an intereting conversation. Basically that's why i wrote my suggestion. Suggesting is far from shooting ones mouth off in my understanding.

Quote from KeiichiRX7 :

I think he was suggesting an "engine brake reduction" bar, like the BF1 has, which is controlled via the electronics. basicly it applies a little throttle to keep the car from swapping ends any time you let off the gas

So it's used in other cars? (please remember my suggestion is regarding the behavour of demo version vehicles only). So i guess that wold be it, with the only diffrence that it could not only decrease but also add to engine braking ability.

Quote from Woz :

This also depends on setup as its possible to make this effect the car more/less by playing with the diff.

Yes i think i'v noticed

Quote from wheel4hummer :

LFS cars do implement Engine braking, but you wouldn't be able to tell, since the best example of this is the BF1.

Well that i find very true ... eghm. Time to get a license :}

Engine braking is most certainly modelled, is amplified by the gearing reduction, is present at all rpm, and there is also the additional braking effect generated from rotational intertia when you increase the rotational velocities of the engine parts upon changing down a gear (if you don't blip the throttle).

The diff does not change the engine braking forces, only their distribution among the driven wheels.

You realise most that most of the braking at high speeds will be aero drag, not engine braking? So you can't easily use such methods to compare cars. Engines also vary a lot, I'm not mechnically knowledgable enough to go into further details on what bits of an engine affect engine braking. The engine simulation inside LFS is known to be not finished (like most of the program, really) so until that work is finished, small effects like this are likely to change.

Easy proof - use the XRT, and drive at a medium speed in a low ish gear, at high revs. Switch to extenal camera, use forces view, and let go of the throttle. Watch the longitudinal forces on the tyre as the car coasts to a halt. Play with the clutch and watch the size of the bar decrease when the clutch is depressed.

I'm not that knowledgable in automotive engines, so excuse me if I spout off stupidity.

Aside from gear ratios, isn't it engine compression that gives you the most engine braking? Judging by danowat's "I'm running out of petrol!!!!" thread, it seems that you all normally have a higher compression ratio than we do over here in the states. I see alot of talk about 92-97 octane fuel in that thread (didn't read it all that closely) which would just be a waste of money over here using it in the majority of cars we have. Our cars generally run 87 octane and they usually have a compression ratio of 8.5 or 9.0:1. Folks building high performance musclecars and stuff usually build for higher compression like 11:1 (just guessing at all the numbers here) and they would take a higher octane gasoline. Using a higher octane fuel in a stock road vehicle is only a waste of money (unless the car you bought is the high performance package and is designed for higher octane, ie, higher compression ratio).

Now, back to engine braking. It feels to me like both the road cars and the race car counterparts in LFS have generally the same compression ratio. If over in UK/Europe, you guys have higher ratios in your normal road cars, then I guess this is fine. But, normally here, the road cars would have the said 9.0:1 compression where race cars would be more like 11.0:1 or higher. Thus (in my guestimation) race cars would have more engine braking due to the higher compression ratios. In LFS, it just feels to me like there isn't any difference between say, the FZ50 and the FZR, or the XFG and the XFR.

Quote from DaDriver :

XRT does not brake that strong. You say i'm beeing wrong it's adjustable? Darn than, what's that vehicle standing in my garage. An exeption?

Well, since I don't have a race car of my own, I can only compare road cars - in which case the road cars in LFS seem appropriate in this area. I have never smashed my nose on the steering wheel in any car by suddenly decelerating (using only the engine) in any given gear... What kind of car do you have? I asked the first time because I am interested

Quote :

People refer engine braking to only what's happening after they switch to a lower gear, that is caused by simply the difference between the engine RPM and what the wheels trought increased cluch transmision ration are forcing it to go.

Whether shifting down or not; the principle is the same and the phenomenon occurs for the same reasons. Clearly; forcing an engine to increase in revs will eat more energy than "only" using it to slow down in the current gear.

Quote :

The braking i meant has different reason and is applied by the change in ignition timing phase as soon as you stop pushing gas pedal (the phase of ingintion is then acutally so much shifted back that the pistons are beeing pushed back down yet before they reach their higher point) . Actually the whole process takes a bit of additional fuel (that's why "city cars" wont react like that- economy.

Some spark advance is necessary for efficiency on the throttle, but what you're describing is either REALLY severe spark retardation (in which case you would be firing buring fuel/air out of the exhaust valve) or slightly too much advance (I think that's what you mean by "shifting back") Usually that's called pre-ignition and would probably cause your head to lift eventually. Imagine what the cylinder pressure would be at TDC with a rapidly expanding charge that just lit off.

It appears you're also saying more fuel is burnt during that odd occurance, which makes no sense unless you're trying to lower mean effective pressure by running rich to compensate for so much advance. The whole thing sounds sketchy to me so far; perhaps you or someone else could explain it a bit better.

Quote :

Now as soon as you open the throttles the air will be sucked in way faster which will cause a higher compression ratio in the cylinders for the very first moments when you want to start aceelerating. That also means you get more air to be sucked in for the first compression cycles, more air means you can melt more fuel with it.(just to keep the lambda coefficent at its best for the engine performance). This mixture is enough more explosive to be noticed in a faster and stronger car reaction. Inertia, probably adds a bit to it too. Filling in even only 1l of engine capacity (lets say two of four cilinders of our XRT 2l engine are beeing filled at a time)

Yes, the engine is under vacuum with a closed throttle under deceleration. As soon as you open the throttle, the pressure will attempt to equalize as much as it can. How fast depends on the flow characteristics of the engine (volume, manifold design etc). I have a hard time thinking that any pressure above the engines normal operating pressure (for given RPM / throttle position) will occur for any measurable amount of time, especially for long enough that the ECU would pick up lean conditions (greater than approx 14:1). The XRT is a forced induction car, so even if this was true (which I'm still not convinced it is, but I'm still open to a good explanation of it) the effect would probably be nullified.

Quote :

at 5000RPM means that 1l of air has to be sucked in 2500times per minute wich is est. 40 times a SECOND. This has to meet with air resistance. Now imagine it's decreased to almost 0 shorlty after each closed throttle -> open throttle transition, due to under pressure.

Actually, at 5000 RPM:
Since one cylinder is 500cc, and every 1/2 revolution one cylinder is on it's intake cycle, that's 1000cc per complete revolution which is 1L 5000 times per minute, assuming 100% theoretical volumetric efficiency. Of course, this doesn't happen because of pumping losses etc but we'll ignore that. So, 83.3 times per second there demand for 1L of air, that's fine. It still does not explain anything about what happens in a closed to open throttle transition; especially & specifically why there would be a notable transient of pressure above normal for given RPM & throttle position. Don't forget how much demand there is for the air; even when the throttle is opened back up. The only thing I can see happening is the vacuum decreasing to it's normal amount; hence no more fuel would need to be added to maintain your lambda.

Quote :

So it's used in other cars? (please remember my suggestion is regarding the behavour of demo version vehicles only). So i guess that wold be it, with the only diffrence that it could not only decrease but also add to engine braking ability.

Well, I thought you were saying this should apply to race vehicles only (since you said that IRL it was not done on road cars for efficiency reasons), but then you said you decelerate from 140k to 100k in 4 seconds in a road car. Is that into a 80km/h head wind? You said that was in 4th gear, which on most 5 speeds is a 1:1 ratio, so you could test it with a 1:1 ratio in LFS also, assuming the same differential ratio and tire size. I'm tempted to go try it, but I think I'll wait until morning just to see. Of course, drag coefficients make a big difference in this situation. I beleive the XRT is a 0.4, so you might want to keep that in mind too. Nonetheless, as Bob stated wind resistance plays a large role at higher speeds.

@Mike - octane is measured differently (not R+m/2) IIRC overseas. (RON / MON)
Mine is stock 10.5:1....

I think there are a lot of topics getting confused in this thread. I have now seen references to engine braking, scavenging (Only happens in N/A engines) and some other oddly related topics.

As others have said until we get a more complex engine physics model some of these thiong are just not possible to add in to the simulation yet and things like scavenging, electromicly controled engne braking reduction, and the like are just not likely to happen as the physics they need to work are not in the physics model yet or are just placeholder pieces.

Some how I do not see LFS becoming so compled as to accualy model the physics of how an engine works, how the transmission, shifting and clutch work and some of the other rather complex componantes of the cars. Even though we would love to see such complecity.

Personaly I would love to see LFS become a truely complex vehicle simulation which works as closely to how reality does as can be done on a modern PC. But then it may detract for what makes LFS as great as it is, which is being a very fun, accesable and fairly realistic racing simulation.

There are other projects that are striving for more extreme accutacy of vehicle physics. They are targeting a different crowd then LFS is though. If LFS can get the vehicles behaving a little more like real cars, get the tire feel closer and build the damage system in to a nice complex componant then I think LFS will have achieved its intended and correct level of realisim and retain it fun factor.

nKPro, i-Racing and Drivers Republic are all trying to more accurate vehicle simulations, but none will be as accessable or easy to use and the racing will not be as fun for the casual racers like LFS is. LFS will always be the sim of choice for me when I just want to have fun and a good race. I will look elseware when I want a real experance.

mrodgers - the US and EU ways of measuring octane differ. The same fuel will get a lower octane rating in the US, I doubt your fuel is really that different to ours.

Quote from Bob Smith :

mrodgers - the US and EU ways of measuring octane differ. The same fuel will get a lower octane rating in the US, I doubt your fuel is really that different to ours.

US tends to use MON (Motor Octane Number), whereas the EU tends to use RON (Research Octane Number). Just a different way of testing the fuel, although MON is arguably a better indicator of full load performance.

Usually it's averaged over here (RON + MON / 2), and labelled PON. That could just be Canada, not sure though.

One evening I did notice that road cars do have bit weak engine braking, but then again I'm used to pretty strong engine braking of my own car, when I did drove 98 Focus it felt like engine would have no compression at all, it was so weak this engine braking and very similar it is in LFS.


I have locked rears with engine braking at 4th gear, granter there was ice but I had also winter tires with studs, I can get tail out easily on gravel at 2nd gear with lifting off throttle completely at corner.

BTW sorry for being a tad cranky in my first post

Well, just had a little outing tonight so I tried your experiment:

1:1 transmission gear ratio with a 3.65:1 differential.
140km/h -> 100km/h
calm conditions
flat road
10.3:1 compression 1975cc inline 4 (listed as a 2L). 140hp @ 6000RPM.
car weighs 2635lbs dry

It took ~12s to coast from 140km/h to 100km/h under those conditions.

I realise each ECU will handle things a bit differently due to emissions controls and so forth; but this is one example anyway. This is obviously a road car.

Don't you need to perform that coast down test with and without the clutch so you can see the difference engine braking makes?

Quote from Bob Smith :

Don't you need to perform that coast down test with and without the clutch so you can see the difference engine braking makes?

Yes, specially in those speeds air resistance is already quite big part.

Imo, only small gears I have found out LFS engine braking be bit less, but then again there are cars that have rather poor engine braking, like Focus.

In heavier cars it does not feel so well either. I would say that in LFS engine braking is very possible for some cars to have such low engine braking at low gears and lower rpm.

From racer.nl

Quote :

Engine braking When the engine is spinning, it has the tendency to slow down, mostly because of the compression effects in the cylinders. A coefficient is used which generates a negative torque; its value is in engine.braking_coeff and it is used as braking_torque=braking_coeff*rps. Note the rps, which is rotations per second. So an F1 car doing 14,500 rpm would mean rps=14500/60 = 241, so the negative torque with a coefficient of 0.74 would be 07.4*241=180 Nm of engine braking torque.
This effect helps a lot in braking for F1 cars, and most other cars. You can feel the effect by driving and letting go of the throttle and feeling how fast the engine tries to brake the car (the rolling resistance of the tires will generally be a secondary effect).
Note that this coefficient and the engine inertia decides on how fast the engine will rev down when the clutch is fully disengaged (after all, F=m*a, as is T=I*w, so 'w', the angular acceleration of the engine, is dependent on torque and inertia). It is upto this point (v0.5) not yet known whether a street car has a lower or higher engine braking coefficient w.r.t. an F1 car.

I've noticed quite large variation in engine braking between different typres and sizes of cars.

Alot of road legal cars inhibit engine braking to help maintain good imission control as far as I know

All road legal cars that I've worked on have a solinoid/damper or similar device to artificially hold engine RPM up momentarily after you relase the throttle, so you wouldn't feel the true engine brake effect in most road going cars...

The best case of engine braking in a road car that I can recall is a m8's worked 327 chev, it was quite easy to get compression lock in it when changing down gears

Quote from Glenn67 :

All road legal cars that I've worked on have a solinoid/damper or similar device to artificially hold engine RPM up momentarily after you relase the throttle, so you wouldn't feel the true engine brake effect in most road going cars...

I hate that - makes modern cars unsafe and difficult to drive totally smoothly... The Earth can die from smoke inhalation, but I demand cars that drive sensibly!

Quote from Bob Smith :

Don't you need to perform that coast down test with and without the clutch so you can see the difference engine braking makes?

Yes.

Should've though of that :ashamed:

Unfortunately the earliest I could do that is Thursday, but I will commit to doing it on Thursday.

Quote from Glenn67 :

I've noticed quite large variation in engine braking between different typres and sizes of cars.

Alot of road legal cars inhibit engine braking to help maintain good imission control as far as I know

All road legal cars that I've worked on have a solinoid/damper or similar device to artificially hold engine RPM up momentarily after you relase the throttle, so you wouldn't feel the true engine brake effect in most road going cars...

Yeah I've noticed a lot of variation as well. It seems that some modern cars attempt to discern when you are "trying" to engine brake and release whatever mechanism is inhibiting it. In my car even in neutral, if the car is not stopped the engine does not sit at it's 600RPM idle, closer to 900RPM until the car stops (or the speedo stops registering at least) and then it sinks to 600RPM. Emissions controls are poo!

I guess I could turn my car right off and repeat that test to avoid the emissions controls....

This is why I buy older cars with simplistic computers. No OBDII for me.

Scavenging/pulse tuning work exactly the same on an F/I car. All F/I does is emulate a higher ambient air pressure. Just as a car operating at or below sea level will make more power than one above it. What works for N/A works for F/I.
The theory he mentions on the first application of throttle after it being closed filling the cylinder more makes sense too as the air will be equalising with a higher momentum than before, as there is a greater pressure difference.

Quote from tristancliffe :

I hate that - makes modern cars unsafe and difficult to drive totally smoothly... The Earth can die from smoke inhalation, but I demand cars that drive sensibly!

+1 for that

I had advanced engine management where I had possibility to control everything with lap top, had also some engine braking as there was no silly bypasses at engine braking, there was fuel cut that I did use and it did make engine braking even stronger, when driving normally it did not even cross my mind to lift off throttle completely above 2000rpm, because in some other cars it would mean hitting brakes harder than normal gently braking that you do, that was level of engine braking

2nd gear was good to 90kph @ 6200revs

I have driven diesels and those have usually bit better engine braking, but certainly haven't driven any other car that would have had as strong engine braking as this that I did build. Throttle were completely closed when pedal was not pressed, there was idle bypass and it let just so little air go trough that engine braking was quite impressive.

Now back to shitty carb again because stupid laws and I would sell my mother if that would help to get injection back, well not that anyone would buy as she is small and makes really bad noise