Aces High Bulletin Board
General Forums => The O' Club => Topic started by: SFRT - Frenchy on June 17, 2005, 03:59:37 PM
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I'm trying to maximize acceleration in those racing video games, what should I do?
Shift at the peack HP, and set the next gear to start at peack Tq?
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Gotta say... I had my misgivings when I saw the title.
In regards to the question, which games specifically? Depending on the realism, the max torque might be elsewhere, and waiting until the redline might not get you the best acceleration.
If, on the other hand, it's like 'Pole Position' by Atari from the 80s, then redline that sucka.
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Forza Motorsport for Xbox, fairly realistic. Peack HP is not the redline.
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don't know about games but...
allways shift at peak hp or a little above so long as HP doesn't drop off too radicaly or you induce something like valve float.
lazs
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It all depends on the powerband of the engine. You want to shift at the max of the powerband.
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uh.. define "powerband" and "peak" for me rpm.
lazs
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It would rather depend on what type of racing. In the 1/4 mile, typcially you want to keep the engine at its peak power output for every shift.
In a road race, you want to make sure each shift does not result in a power loss when the engine shifts RPM's. In other words, you might push the RMP higher and allow the horsepower to drop off, if it means the next shift will come in at the same of higher horsepower than the last gear.
This is a way over simplistic perspective as there are hundreds of variables involved in real life. Dunt know about the game though.
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Rule of thumb I'd say is to shift as soon as there's more power in the next gear. Allowing for any additional variables like Skuzzy says, e.g. clutchtime or road slope or sideways Gs at shifttime, etc.
Simplest way is to graph power/rpm, memorize that, then draw rpm/roadspeed, and draw your ratios as you best guess they should be.
e.g. if you have an engine with a perfectly flat peak of power from 5 to 10krpm, there'd be 1st gear from 0 to 10krpm, then each consequent ratio just a tad more vertical than the previous, altogether covering the ideal low and top speed of the circuit.
Then adjust for useable grip, etc
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why would you ever want to shift at a point lower than what would leave you at peak hp for the next gear? Unless we are talking about pulling trailers or trying to move a buncha crates of eggs or sumthin.
lazs
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Just estimating by instinct.
You'd want the gears to stretch from 1st to last (say 6th), with the ratios set to have as much power as possible from lowest to highest speed expected on the circuit.
(http://taenia.homestead.com/files/power1.gif)
(http://taenia.homestead.com/files/power2.gif)
I figure the best acceleration is found with the ratios yeilding the most thrust, most thrust is from most power, most power in a given time lapse is with any given ratio that sits with the most surface between it and the power curve above it.
(http://taenia.homestead.com/files/singleratio.gif)
This is where I imagine an ideal ratio should be if the gearbox is linear and sequential.
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Yep, looks about right for a wide ratio tranny, and assuming the ratios are the same increment from shift to shift.
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I see what you're saying lazs, I guess it depends how much you want to squeeze the ratios together.
All things being equal, with a 4-ratio gearbox on a stretched out track, you'd have long ratios and be forced to land the next gear before peak power, like the third pic above, but on a short track with a 6-gear, you'd be able to squeeze em together enough to shift at the moment that lands you on the next gear's peak.
(http://taenia.homestead.com/files/singleratio2.gif)
Not sure which is right. Instinctively it still makes more sense to me that the ratio'd include more total power sitting with the peak above its middle rather than at one end.
(http://taenia.homestead.com/files/singleratio3.gif)
That's assuming a regularly shaped peak, and ignoring resistance increasing with speed (wind, tranny friction etc).
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Dang, I thought this was a thread about RL.
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That's what I came up with. I have have my virtual engine at 430 HP @ 5700RPM. I have the best results by shifting setting up gears 2 to 5 to shift at 6,500 (400HP), and they grab the next gear at 5,000 (400HP).
So I always have from 400 to 430HP. After 6,500RPm, the HPs take a nose dive, it's not worth pushing to 7500.
If I set the gears to start right at peack of Hp (5,700 @430HP), it's not good because I spend my time shifting. I loose time for shifting, and it's not offset by riding the peack of the power curve more tightly.
Seems like the Tq doesn't have anything with setting up your trany. What is Tq curve usable for?
BTW, driving sims are good enought, that like in real life, setting you trany according to ur engine output, and camber/springs/rebound/damper matter if you want to drop lap seconds.
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It ain't rocket science guys... I got no fancy charts but...
you have 3 to six gears of whatever ratios... makes no friggin difference.. you will drop, depending on ratio and how you shift (full power, speed shift ham fisted brit tranny shift, whatever) you will drop from 400 to 1000 rpms or more by the time you are in the next gear... if you get peak HP at 5700-6,000 rpm and drop 500 hp every shift you might want to carry the shift point up to 6200-6400...
depending on how bad the power.... HP, drops off after 6000 and below 5700..
In practice... it is simple as ****.... you hold in gear, pedal to the metal till the damn thing quits pullin and then bang off a gear. All the charts in the world ain't gonna matter if you can't feel it and if you don't know how to shift tho.
unless you have an automatic in which case it makes no friggin difference... have the "guy" set it up for you and go join the "what's your favorite tea?" thread.
lazs
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It's not just bangin gears Lazs, I got the impression he wants to optimize the ratios as best as he can.
What he said about shifting at peak HP into next gear's peak torque made sense, all I thought was fishy was shifting into the next gear's peak.
Used charts to avoid written math. Integrals give you the ideal ratio for most power.
Unless the power peak is more than a little asymetrical, it seems best to shift before the next gear's peak.
(http://taenia.homestead.com/files/Untitled-01.gif)
What I'd like to know is what Frenchy asked about torque.
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Optimize the ratios? unless you have a dead flat powerband like a diesel... there is only one way to "optimize the ratios"
you get as tall as you can stand in first so that you have the least amount of room between 1'st and whatever is top and you space em out evenly... you shift a bit higher than peak Hp but... not so much that the HP drops off and the car quits pulling... you want to end up in the best place in the next gear you possibly can HP wise and you ignore torque.. unless...
you are delivering eggs or sumthin.
Torque curve is built on the bench along with HP and will be what it will be but... you can't shift for torque... if the torque band is so narrow and low that it is way below the HP peak then you will simply drop a few more RPMs between shifts cause the motor won't pull the gearing.... This would be a very badly set up engine tho and not at all like frechys example.
I guess what I am saying is that "short shifting" (shifting below HP peak) is never a good plan... you are not gonna gain rpm in the shift... you will allways lose rpm.
lazs
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Laz, sorry I didn't reply to your question sooner, but I haven't looked at this thread in a while.
An engine does not nessessarily produce max HP at max RPM's, as Moot's chart illustrates. Unless you have a gas turbine. Most drop off in HP when they get close to max RPM.
While it's true higher RPM's in top gear produce higher speed, it's not so in the lower gears. There is a point where the next gear's ratio and the engine's max HP overlap. That would be the optimum point to shift to gain maximum accelleration.
That's why road racer's tend to do better than guys who run superspeedway's when NASCAR runs at Infinion and Watkin's Glen. They have more experience using the tranny for more than flat out top speed in high gear.
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rpm... you are simply repeating what I said... I never said max RPMs are where you shift. RPMs and torque are both meaningless numbers for acceleration.. just look at HP numbers.
Take my Healey for instance... it is a light car with a close ratio 4 speed.. It is capable of running up to 7000 or more if I want to risk the lower end but... peak hp is about 6200.. It quits pulling hard at about 6600 (hp drops off a lot).. Being a light car I can shift at 6500.. even if I drop below 6200 it is making better HP than spending time above 6500. I can make up the time (acceleration) by coming from somewhere below 6200 easier than I can make up the time stretching to say 7000 and ending up at the absolute peak in the next gear.
moots numbers on the chart he shows don't make any sense to me but... depending on the tranny/rear ratios and weight of the car.. you would want to shift between 12 and 14 (whatevers) on his chart.
In the lower gears you don't have to stretch as much as the higher gears due to wind resistance tho.. You will lose more RPM in the higher gears between shifts typicaly.
lazs
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Originally posted by lazs2
rpm... you are simply repeating what I said... I never said max RPMs are where you shift.
My initial post was directed towards Frenchy's post about when to shift. I was talking to him, not you. You asked me to explain powerband and peak HP. I wasn't trying to disagree or argue with you.
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Well, since I don't have Forza yet... and I'm bored... here's how to drive the NASCAR sim you'll find in malls (it'll have its own store). You can't miss them, there's usually 12-16 simulators on 3dof motion platforms and 3-screen projector setups. The interior looks convincing enough so it's pretty cool.
Once the 10 second countdown starts, hold the clutch down and flip the start switch. Tap the gas to make sure the engine is on and your tach works. Now, you should have a good 8 seconds left before the start. Make sure you're in first gear. Put the gas pedal to the floor and hold it (pretty much for the next 7 minutes depending on the track). You can't blow the engine, so let it sit at 9500rpm. You should rapidly be approaching the start. When it says go, slide your left foot to the left and dump the clutch. Don't let off easy, don't even pick your foot off, just slide to the left and dump it. Be ready to shove your way past newbies as you lurch ahead. The 1-2 shift comes quick, but don't shift when the light comes on (8k), go alittle past it to 8500rpm, don't bother with the clutch, and slam the shifter into second. It may get alittle squirrely but with practice smoothes out. Same for 2-3 & 3-4. Now, slalom newbies that are bouncing off the wall and race the good drivers to victory. Be careful, when pulling 225 in the draft on Daytona (extreme mode w/o restrictors), the 90mph drivers become a major obstacle, spot them far off, plan accordingly, and pray they don't swerve.
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We're saying the same thing, lazs. I'm just being overmeticulate.
Thanks for answering.
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Lazs its one of the rare times I agree with you. You don't need charts you should be able to feel whats going on.
Tall first gear then evenly spaced ratios is whats fitted to old road burners like BSA gold stars and I believe some of the more rev happy japanese stuff ( I know bugger all about cars so Ill stick with bikes )
The only reason to short shift is if yiou want a relaxing ride and the engine makes more Torque than a tractor. Something like a big Harley or Victory. Short shifting a revvy little Jap motor is a recipie for going nowhere fast.
In essence if the torque curve is fat and flat then short shifting shouldn't be too nuch iof a problem but if its steep and rises like the HP then short shifting will as you say just result in dropping revs dropping out of the power and going nowhere fast.
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Rule of thumb I use is I set the tranny for the max top speed for the longest straight away. A short track where I might see a speed of say 120. So my final gear would be adjusted so I see 120mph in 5th or 6th. I set gearing so that I stay with in peak RPM at slower speeds. And on a longer track say Road America I pull the gears out so that I can run a higher top speed.
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another thing.. setting up the transmission is not done in a vacuum... you need to consider tires diameter and final drive ration... simply put.. you need to know your final drive ratio.
In a six speed for instance.. you might have a 1.0 or a 0.76 or even higher sixth
My richmond gear 6 speed has a 0.76 6th... my muncie four speed is 1.0 in 4th.
lazs
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i thought you guys were going to be talking about something else in here.
phew. thank god i was wrong.
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Ok... so one has to ask... If yu thought it was about transmissions.... why would you look since you know nothing and care nothing about cars?
since you thought it was about something else.... why would you look unless it was a subject that interested you?
lazs
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oops :rofl JB88!