Author Topic: Setting your trany up (Read 663 times)

moot · « **Reply #15 on:** June 19, 2005, 07:36:03 PM »

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.

What I'd like to know is what Frenchy asked about torque.

lazs2 · « **Reply #16 on:** June 19, 2005, 07:52:07 PM »

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

rpm · « **Reply #17 on:** June 19, 2005, 08:28:42 PM »

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.

lazs2 · « **Reply #18 on:** June 20, 2005, 08:39:48 AM »

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

rpm · « **Reply #19 on:** June 20, 2005, 12:41:32 PM »

Quote

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.

indy007 · « **Reply #20 on:** June 20, 2005, 03:13:58 PM »

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.

moot · « **Reply #21 on:** June 20, 2005, 07:33:14 PM »

We're saying the same thing, lazs. I'm just being overmeticulate.
Thanks for answering.

Skydancer · « **Reply #22 on:** June 21, 2005, 05:53:09 AM »

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.

nuchpatrick · « **Reply #23 on:** June 21, 2005, 07:42:27 AM »

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.

lazs2 · « **Reply #24 on:** June 21, 2005, 07:55:03 AM »

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

JB88 · « **Reply #25 on:** June 21, 2005, 11:40:59 AM »

i thought you guys were going to be talking about something else in here.

phew. thank god i was wrong.

lazs2 · « **Reply #26 on:** June 21, 2005, 02:11:21 PM »

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

Skydancer · « **Reply #27 on:** June 21, 2005, 02:42:05 PM »

oops

JB88!