Shifting At Right Time

[EclipseDriver95]

I have a 95 eclipse gs, with just a cold air intake and a pipe tip, and i am just now starting to race with various people, u know drag race, and i was reading up on my car, and i was seeing my car creates like a peak hp of 140hp, at 5,000 rpms, does that mean i should shift at 5,000 rpms, or should i still red line it at 7grand, witch would give me the most power through my gears, were should i shift??????

1 more question, what and how exactly is double clutching, and should i do it, does it help!!!!

PLEASE HELP WITH ALL THE INFO U CAN!!!!

[Mediocrity]

a 95 eclipse GS...with an intake... and a tip... and you want to race people with that thing?

[kjewer1]

You can do a search on double clutching and get all the info you need. 90% of it will be wrong though I think www.howstuffworks.com has a writeup on it from some autocrossing sites archives...

The other question I cant answer with specific rpms, but I can explain to you how to figure it out for yourself. Ask 10 people that question and you will get 10 different answers. Here is the math/physics version.

A couple little tidbits first. Max torque will occur where the motors Volumetric Efficiency peaks (VE). People with dSMlink can read Airflow/Rev. Thats what this is. MAximum HP will typically coincide with your peak airflow (mass) over time, like lbs/min, grams/sec, etc.

The proper point to shift is when you would be making more wheel torque in the next gear than you are currently making in this gear. Seems to simple almost... But the complication comes in when you consider that wheel torque is different in every gear. If you are handy with Excel, you can make up a quick spreadsheet that has your wheel torque in 250 rpm intervals (look for a chassis dyno chart for stock car, or modded similar to yours), and each of your gear ratios (can be found in the vfaqs). Have it show your wheel torque (motor TQ times gear ratio) at each 250 rpm interval, for each gear. Then you can spot the best shift point easily. I have a spreadsheet made up for a AWD car, but I dont remember if I finished it or not. I would attach it, but that doesnt seem to be an option here. Maybe I'll clean it up and host it on the posr site in the coming week if i have time.

So if your TQ peaks at 500 rpm, its probably safe to say you dont want to be shifting any higher than 7k, but it depends on the curve, and the gear ratio spread from gear to gear. It almost always makes sense to redline 1st, then shift a little lower in each successive gear on mosly stock cars. An example is my car on the stock turbo. I was shifting at ~7000 in every gear and running 15 flat. By dropping 2nd and 3rd shift point to 6k, I went a half second faster, consistently.

Hope that helps.

[EclipseDriver95]

thanx man, that helps alot, i appreciate it, but i mean i dont get the math part! But i will try, umm.... i am gonna search the internet for sum stuff, if u could i dont understand the spread sheet excel thing, but i mean if u would could u try and make me one, and send it to me, i would appreciate it!

[JoeWagon]

Visual Way to Understand Shifting (scroll down for the math/truth):

Ok, we see here an extremely accurate powerband (found using a torquometer)

The pink segment represents shifting to stay in the circle above the horizontal red line. this is the POWER BAND

When you reach the RIGHT pink X, you are going to want to shift. The reason is this: If you continue in that gear, you will be at a lesser torque than if you shift.

The pink line determines when you shift. It is affected solely by the gear ratio.



Note: there are some other things to note.
1. this is very very crude. you may or may not understand it based on your understanding of a few things:
a. gear ratios
b. math
2. the horizontal line doesn't mean anything, except the pink line extended to let you visually see the points of shifting.
3. This entire discussion is a lie so far. It is to point out why shift? This graph is simple. It is based on a gear ratio that is equal in 2 gears of upshifting (note: THAT CANNOT HAPPEN. If you upshift to a gear that has the same ratio, you will be at the same rpm.)

This is the REAL deal:

The factors that are included here, and not above, are gear ratios. 5000rpm in 3rd gear produces MORE wheel torque than 5000rpm in 4th gear.

In words:
Base your shift points on one reason: My wheel torque will be greater if I shift to the next gear, than if I continue accelerating in my current gear.

In numbers:

Anything before shift time
in 3rd gear. Gear ratio is 1.10. Your engine torque is 100 at 5000rpm's.
in 4th gear. Gear ratio is 0.80 Your engine torque is 90 at 3636rpm's (0.80/1.10 * 5000rpm).
5000rpm / 3rd gear / wtq= 110 (100 x 1.10)
4000pm / 4th gear / wtq= 72 (90 x 0.80)
Don't shift, too early

Shift point
in 3rd gear. Gear ratio is 1.10. Your engine torque is 150 at 7000rpm's
in 4th gear. Gear ratio is 0.80. Your engine torque is 208* at 5090rpm's (0.80/1.10 * 7000rpm's).
7000rpm / 3rd gear / wtq= 165
5090rpm / 4th gear / wtq= 166.4
Shift. Power in next gear is greater.
*why is power greater at 5090rpm than 7000rpm? because as rpm increases, power (efficiency) drops off on a dyno curve

If you continue to 8000rpm in 3rd gear, you will find that you are producing significantly less power than if you were to shift to 4th. THIS IS WHY SHIFTING IS NECESSARY. If an engine could produce a linear power curve (dyno curve), shifting would not be necessary, however, it drops off.
Also note that power drops off at higher rpm for various reasons, but it's safer not to be accelerating past 12,000rpm (if the power held out that long) for the engines.

[kjewer1]

Originally Posted by JoeWagon

The factors that are included here, and not above, are gear ratios. 5000rpm in 3rd gear produces MORE power than 5000rpm in 4th gear.

The only issue I have is this statement. Wheel power will always be the same in every gear. Torque will change, but because the wheel rpm also changes is each gear HP is maintained. This is why it doesnt really matter whatgear you dyno in, aside from making sure you can load hte motor enough to build full boost (typially third gear). Jsut a technicality though.

[JoeWagon]

I see what you're saying perfectly, but what should I change the sentence to read, or should I eliminate it?

[smokeurass]

so wuts the point of the shiflights on the aftermarket tachometeres?

Kevin you said you lowered your shift point when you were stock....would you keep it the same when ur modded, and thats how u can use the shift lights? Or.....can u set the light to turn on in every gear?

[JoeWagon]

Shift lights can be set, or tell you when redline is.

Kevin's modified GSX definately does not have stock shift points. His new turbo should hold boost to 10k rpm, whereas the stock turbo does not hold it to 7000.

[BoOtyChOwDa]

ok well 1st of all, this guy should be slapped for a saying a tip... as if a tip would give any hp gains at all. omg you shouldnt even be driving if you beleieve that to be a mod. tsk tsk tsk. damn, you made me mad... idiots

[kjewer1]

Originally Posted by BoOtyChOwDa

ok well 1st of all, this guy should be slapped for a saying a tip... as if a tip would give any hp gains at all. omg you shouldnt even be driving if you beleieve that to be a mod. tsk tsk tsk. damn, you made me mad... idiots

This is not a good example of a productive post. In fact, I just lost 10 seconds of my life reading it that I will never get back. Not all mods give power. The part is indeed a modification of the stock setup, is it not. Thanks for your contributions to the topic at hand though... Now you made me mad.

Joe, just change power to wheel torque, and it will be correct. Power will remain unchanged at the wheels regardless of gear. Same for motor torque and power, same regardless of gear. What we are concerned with is wheel torque, which is directly tied to acceleration. In fact your acceleration curve will directly follow the wheel torque curve.

The shift light on aftermarket tachs or as a add-on are completely useless if they are not set to the proper RPM.

My shift point is now higher than stock, just a bit. As you move your torque band higher and high, you need to shift higher to exploit it. In fact, if you raise your tq band significantly and still shift at low rpm, you will be slower than you were previously. Unofrtunately on my new setup, even the GT30/40 is nearly maxed out, and I'm still at 20 psi. If I do the math, at 25 psi I will be at the airflow limits of the turbo. Thats why its for sale I will likely be shifting no higher than 8k rpm though regardless of what turbo I run. But it will be weel over 7k now that I dont reach max airflow until about 7200 rpm...

This is a somewhat complicated topic, and everything posted thus far is a gross oversimplification. But its an important subject, and it has a substantial impact on our timeslips.

[smokeurass]

no...but u were saying when you were stock, you first shifted at about 7k rpm, then you dropped it to 6k for 2nd and 3rd gears....

when your modded and all is good, are you shifting at same rpm in each gear? If so, Did u change the gear ratio's?

[kjewer1]

Right. If you look at the gear ratio spread, even with stock torque curve, its in your best interest to take 1st gear to redline. I was comfortable with 7k-7200. Its a big jump to second, so it pays to take first all the way. Then the gears close up a bit. The time it would take that setup to go from 6k to 7k was a waste with the boost having fallen off to 15 psi or less and blowing hot air (since its maxed out). Getting into the next gear at ~5k rpm instead would put more torque to the wheels (roughly a 1k rpm drop from 6k).

When you mod the car you change the torque curve. Specifically, torque doesnt fall off after 6k rpm as badly, beucase you set the car up to make more high rpm torque with bigger turbo, manifold, etc. I now have more torque at 7k rpm than a stock motor will have at its peak, probably by a factor of 2. So my gear ratios are unchanged, but all the extra high rpm torque allows me to make the most of the gear I'm in. No need to shift prematurely because of a setup with a weak top end.

I hope that clears it up, if not let me know.

[BoostedSpyder]

another thread that should get added to the contents...
"10 seconds of my life i will never get back"

[duckydsp]

I have two questions.

Does horsepower meet torque at 5250 or 5650. Wouldn't you want to shift then because you lose torque? Why isn't it the same spot on each gear?

Also, I heard from a reliable source that I should extend my gears. Is he wrong, because from what I understand from the past posts, 95gsxracer shortened his gears and his 1/4 time is a hell of a lot shorter than my friends.