Rank: Driver's Permit
#1 Posted : Monday, May 25, 2015 11:06:05 AM(UTC)
What do people think about engine restrictors on road cars?

There are many cars within Forza that have great top end speed stock and are penalised in PI for a grip tune.

To take the BMW F10 M5 as an example. It has excellent top speed standard and it is difficult as a handling car because it has little PI to play with. So restricting the engine to gain Performance Index can help this.
Rank: On the Podium
#2 Posted : Monday, May 25, 2015 3:18:19 PM(UTC)
The introduction of performance restrictors would be nice; not just engine-based, but also weight-based with the installation of a ballast.
Rank: A-Class Racing License
#3 Posted : Monday, May 25, 2015 4:03:23 PM(UTC)
I'm all for it; anything to allow more parity (as you noted in the PI changes thread) in Forza Motorsport is welcome.

Coming from someone who enjoys hosting race series, I'd have to say air restrictors, along with the above mentioned ballast, make it a lot easier for race stewards to balance a field of cars. If it can be done in the real world, I'm all for it being included.
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#4 Posted : Monday, May 25, 2015 8:16:15 PM(UTC)
Originally Posted by: The Shadow Edge Go to Quoted Post
The introduction of performance restrictors would be nice; not just engine-based, but also weight-based with the installation of a ballast.


This would be well appreciated.
Rank: On the Podium
#5 Posted : Tuesday, May 26, 2015 6:10:33 AM(UTC)
Or just redo how PI is calculated. The car is already penalized for having a good top speed. The stock PI should be lower.

Restrictor plates would just be a bandaid to fix one problem but would likely open the flood gates for other problems.

I personally would build a grip tune, use the restrictor to drop PI and then add further upgrades to make the car even faster lap time wise. Who cars if I can't go over 140 mph (for example) if I can get to that speed at a faster rate and/or be able to hold a higher average speed around corners.

It would just bring back the beloved FM4 rev-bangers.
Rank: A-Class Racing License
#6 Posted : Tuesday, May 26, 2015 2:36:58 PM(UTC)
Search for restrictor plates
Wikipedia on the subject
Raetech on the subject (Interesting graphs on their page).

Restrictor plates in the real world aren't a band-aid fix. They are used to balance a field of cars by reducing the amount of air available to "x" engine. An engine is after all, nothing more than a fancy air pump.

"A single inlet restrictor will put a definite limit on peak power, but a well-designed restrictor will not greatly affect your power and torque below this limit." -from the Raetech page.

So, a well-designed restrictor only reduces an engine's top end power because power is dependent upon the quantity and quality (temperature, thickness, etc.) of available air. Low RPM power is made when the engine isn't sucking a whole lot of air, so power at and below (Ex: 2750 RPM) doesn't care if the intake opening is reduced from 77 mm to 68 mm, it can still make the same power through the smaller opening. Mid-range RPM power is going to be slightly affected. It's the upper RPM power band which will be hugely affected if that intake opening is reduced said 9 mm, and even more affected if the intake opening becomes smaller still. Summarized: an air restrictor doesn't (y - z% power) throughout an engine's RPM band, it's more complex than that.

Will people use restrictors in their builds to do what you've exemplified? Yes.
Will stewards who host online race series (Ex: NASA American Iron) be able to balance their field with many different types of cars? Yes.

Maybe then air restrictors can be brought in with a tweak to the performance index? Maybe Turn 10 needs to incorporate a calculation for the area under the curve so all power is taken into account? If that were to be done, a car with an air restrictor equipped would decrease performance index points, but not by an overcompensated number. Its low range power wouldn't be affected and its mid-range power would only be minimally affected while the high end faced the chopping block.

Edited by user Tuesday, May 26, 2015 2:43:38 PM(UTC)  | Reason: Forums automatically stop useage of ori - fice. It's only a synonym for opening.

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#7 Posted : Tuesday, May 26, 2015 9:14:38 PM(UTC)
Originally Posted by: RPM Swerve Go to Quoted Post
Or just redo how PI is calculated. The car is already penalized for having a good top speed. The stock PI should be lower.


I don't agree with that at all. PI represents all aspects of performance, not just the ones that are relevant to the race you're doing. A high top speed is part of that performance. If you're on a high-speed circuit, that will matter a great deal. If you take a 220-MPH car to a circuit where it will rarely exceed 150 MPH, you brought the wrong tool. They can't say, "Well, on this particular circuit, top speed isn't as useful, so we'll just give it less credit." If you do that, you have to credit acceleration less because if you're on a superspeedway it doesn't matter so much if it takes me a bit longer to get up to top speed if I'm pretty much always going fast. If I'm on a track where high downforce and grip are of limited value but my car has F1 downforce, the PI rating will need restructured because it's giving too much weight to attributes I don't really need.

If you have a Veyron at Tsukuba, you picked the wrong tool for the job. I don't care that you have 500 more horsepower than you need and your car's PI comes largely from an attribute you don't need at Tsukuba. We can't look at that and slash your Veyron's PI rating to compensate because if you then take it to Talladega suddenly that thousand horsepower and high top speed will be everything.
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Rank: Racing Legend
#8 Posted : Tuesday, May 26, 2015 9:37:18 PM(UTC)
Originally Posted by: IceMan PJN Go to Quoted Post
Originally Posted by: RPM Swerve Go to Quoted Post
Or just redo how PI is calculated. The car is already penalized for having a good top speed. The stock PI should be lower.


I don't agree with that at all. PI represents all aspects of performance, not just the ones that are relevant to the race you're doing. A high top speed is part of that performance. If you're on a high-speed circuit, that will matter a great deal. If you take a 220-MPH car to a circuit where it will rarely exceed 150 MPH, you brought the wrong tool. They can't say, "Well, on this particular circuit, top speed isn't as useful, so we'll just give it less credit." If you do that, you have to credit acceleration less because if you're on a superspeedway it doesn't matter so much if it takes me a bit longer to get up to top speed if I'm pretty much always going fast. If I'm on a track where high downforce and grip are of limited value but my car has F1 downforce, the PI rating will need restructured because it's giving too much weight to attributes I don't really need.

If you have a Veyron at Tsukuba, you picked the wrong tool for the job. I don't care that you have 500 more horsepower than you need and your car's PI comes largely from an attribute you don't need at Tsukuba. We can't look at that and slash your Veyron's PI rating to compensate because if you then take it to Talladega suddenly that thousand horsepower and high top speed will be everything.


I think you misunderstand Swerve's point.

He is saying that increases in top speed increase PI too much in the current model.

A sound model takes account of all aspects of performance (you are correct in saying that) but a sound model takes account of them in correct proportions.

There is a belief by various people that either improving speed increases pi too much and / or decreasing weight does not increase pi enough.
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#9 Posted : Wednesday, May 27, 2015 6:23:16 AM(UTC)
Originally Posted by: SatNiteEduardo Go to Quoted Post
Originally Posted by: IceMan PJN Go to Quoted Post
Originally Posted by: RPM Swerve Go to Quoted Post
Or just redo how PI is calculated. The car is already penalized for having a good top speed. The stock PI should be lower.


I don't agree with that at all. PI represents all aspects of performance, not just the ones that are relevant to the race you're doing. A high top speed is part of that performance. If you're on a high-speed circuit, that will matter a great deal. If you take a 220-MPH car to a circuit where it will rarely exceed 150 MPH, you brought the wrong tool. They can't say, "Well, on this particular circuit, top speed isn't as useful, so we'll just give it less credit." If you do that, you have to credit acceleration less because if you're on a superspeedway it doesn't matter so much if it takes me a bit longer to get up to top speed if I'm pretty much always going fast. If I'm on a track where high downforce and grip are of limited value but my car has F1 downforce, the PI rating will need restructured because it's giving too much weight to attributes I don't really need.

If you have a Veyron at Tsukuba, you picked the wrong tool for the job. I don't care that you have 500 more horsepower than you need and your car's PI comes largely from an attribute you don't need at Tsukuba. We can't look at that and slash your Veyron's PI rating to compensate because if you then take it to Talladega suddenly that thousand horsepower and high top speed will be everything.


I think you misunderstand Swerve's point.

He is saying that increases in top speed increase PI too much in the current model.

A sound model takes account of all aspects of performance (you are correct in saying that) but a sound model takes account of them in correct proportions.

There is a belief by various people that either improving speed increases pi too much and / or decreasing weight does not increase pi enough.


Yep. Top speed is important to a degree but not as important as PI implies. There is only one track where top speed matters in forza. All other tracks is a combo of acceleration and/or grip.
Rank: A-Class Racing License
#10 Posted : Wednesday, May 27, 2015 8:18:01 AM(UTC)
Restrictors aren't the answer. Every engine has a different air volume requirement at peek power and as you can change aspiration on most cars it would become an unnessecary complicated mess. I don't see the problem with PI. If you can't get a tune you like on one car then just choose another car, there are plenty of them. The PI in its current form is the same for everyone so whilst it may not appear accurate to some at least it's fair.

If anything I'd prefer a limit on what you can do with a car. For example you can currently run a Civic in just about every class. It's not very realistic to see a little hatchback on track with super cars. Perhaps each car should be limited to compete in its starting class and one class above. This would iron out some of the disparities and may result in a more mixed LB in terms of cars. It's no mystery why racing in the low classes is generally a lot more competitive.
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#11 Posted : Wednesday, May 27, 2015 12:35:12 PM(UTC)
Originally Posted by: Dadiodude Go to Quoted Post
Restrictors aren't the answer. Every engine has a different air volume requirement at peek power and as you can change aspiration on most cars it would become an unnessecary complicated mess. I don't see the problem with PI. If you can't get a tune you like on one car then just choose another car, there are plenty of them. The PI in its current form is the same for everyone so whilst it may not appear accurate to some at least it's fair.

If anything I'd prefer a limit on what you can do with a car. For example you can currently run a Civic in just about every class. It's not very realistic to see a little hatchback on track with super cars. Perhaps each car should be limited to compete in its starting class and one class above. This would iron out some of the disparities and may result in a more mixed LB in terms of cars. It's no mystery why racing in the low classes is generally a lot more competitive.


The quirks in the pi calculation affect cars in stock form as well though.

There are cars with the same pi in stock form yet 1 car dominates the other on every type of track.

I would like a PI system that as far as possible allows every car to compete. Some cars at the moment are nothing more than a handicap within whatever class they are in.
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#12 Posted : Wednesday, May 27, 2015 12:48:52 PM(UTC)
You're right, restrictors aren't the answer to fix the performance index, as suggested by the initial poster. They are however a welcome option were Turn 10 so inclined to program them for us. Trust me, stewards would love to have their availability just for the reason of creating parity.
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#13 Posted : Wednesday, May 27, 2015 11:17:12 PM(UTC)
On FM4 under online lobby settings you can reduce power and grip by 5% increments, all the way down to -75%. Instead of going through a bunch of math equations for every car to get hyper realistic restrictor plates, I suggest just doing it in a percentage based reduction format. Say I equip a restrictor plate to my car in FM6: I can then go into tuning and lower engine power output by a specific percentage, all the way down to -99% of the car's original power output. This would also affect performance index. Suddenly (in terms of FM4) I could restrict a Hennessey Venom GT down to around 650HP and run it in s-class. Plus it'd be an extremely useful tool for those that run online racing leagues where car balancing is needed.

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Rank: A-Class Racing License
#14 Posted : Thursday, May 28, 2015 12:52:06 AM(UTC)
Can somebody please verify for me: I believe personal best lap times set while in a power reduction bucket are ineligible for the leaderboards. If that is true that's one possible solution Turn 10 can use to deter people from purposefully decreasing power to race in lower classes. It might be possible to allow cars to set times one class less than stock but not two or more classes less than stock.

The programming math for restrictors (such as Raetech's restrictors) might be complicated to figure out at first, though just like with many things, once it's found it's only a matter of applying the same formula to a variety of parts.

Edited by user Thursday, May 28, 2015 12:00:29 PM(UTC)  | Reason: Changed punctuation.

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