Impreza sti jdm

Hi all,I have recently had my car mapped by Bob Rawle and after the mapping session he gave me a road dyno printout.Just wanted to ask you when is it the best to time to shift to another gear.many thanks

TonyBurns

iTrader: (3)

Depends on your car, normally about 1k below the red line.

Tony

urban

iTrader: (1)

When you can 'feel' the power dropping off.
Assuming its a six speed UK spec, then there's no real point revving it much after 6, best just feed it another gear

G.Mac

iTrader: (2)

Have a look at the graph and see where the torque starts to tail off and change there. Depending on your car and whats been done it prob will be about 6K

ScoobySteve69

iTrader: (13)

That`s also what I read on here recently (6.5 on mine).

banny sti

iTrader: (68)

At the point just after the bhp starts dropping off so you can land back at peak torque

joz8968

iTrader: (13)

Most cars' gearing allows you to get back into the sweet spot of the torque band within, typically, a 1000-2000 rpm drop, upon changing up to the next gear (obviously, depending on the gearing/FD).

So if you change up when the revs are about 2k rpm past the peak torque rpm, then, more often than not, the acceleration is usually 'seamless'.

But things can be further complicated when you factor in the turbo's spooling characteristics - it may be out of kilter with the gearing. I think Performance Car mag, at the time, leveled this criticism at the ST205 (Celica GT4).

ScoobyDoo69

iTrader: (17)

For me it's where I feel the acceleration dropping off massively.

People always says shift at peak power and fall back on peak torque, but you need to remember that even after peak power you still have a lot of power available and a shorter gear than the next one. So you need to know the car, and know when holding on to the gear is only going to lead to slower acceleration than changing up to the next gear.

Impreza sti jdm

Impreza sti jdm

Thanks for all your replies.This is the Road Dyno graph i was given as it might help you 'judge' better.Its in this link as i couldnt find how to upload pics here

https://www.scoobynet.com/members/im...led-22092.html

I am changing gears at 5900rpm and normally when i shift it goes back to 5000rpm and i dont spend more than 2 seconds on a gear.By doing this im finishing the quarter mile in 6th gear as i would have more than 100metres left of it when im in 5th gear@5900rpm.

Thanks.

ScoobyDoo69

iTrader: (17)

Going into 6th on the quarter mile? Have you got a JDM 6 speed with short 5 & 6?

Impreza sti jdm

Yes my car is an Impreza sti JDM 2003.So it has a shorter 4th and 5th i think.

ScoobyDoo69

iTrader: (17)

Shorter 5th and 6th

UK boxes have the same 1-4 but longer 5th-6th.

When I was around the 320ish bhp mark I was crossing the line either on the limiter of 4th or only just into 5th.

Now I'm around 360-370 I cross the line well into 5th, but nowhere near 6th.

Impreza sti jdm

I see.I think to cross the line in 5th i have to hold the gear up to 8000rpm which i dont think it would be wise as much as just shifting to 6th.

scoobiepaul

I think 5th gear will go to about 115/120 mph on my 2001 jdm box on a 13.7 sec run I was only doing 100mph over the line.

Impreza sti jdm

I see approximately 120mph on the speedo when i pass the line.As i said,i think its possible to finish it in 5th gear but i have to rev the engine to about 8000rpm.By looking at the road dyno graph is it the best to shift at around 5900rpm when im on the other gears?

ScoobyDoo69

iTrader: (17)

What sort of times are you running to cross the line near 120mph? I'm sure the JDM 5th must not be near 8000rpm at that speed? I think it has a 1.062 gear ratio which with 225/45/17 tyres would equal roughly 143mph @ 8000rpm.

Impreza sti jdm

My wheels are 18/40/225.I havent yet timed it as im not that much of a fan on launching the car from zero.But from the 'rivals' i raced i assume it will make low 12s.Yes it might be possible to reach those speeds in 5th as when im at 5900rpm im doing about 110mph.But I think it will not keep accelerating as much as to just changing to 6th gear.

ScoobyDoo69

iTrader: (17)

Right.

I will say don't assume here as speedos tell a different story to the speeds you are actually doing, and on the quarter mile you will very unlikely be doing more than around 110mph unless you're around 400bhp. Even then, at 7000rpm you'll be doing around 125+ so I will definitely say hold on to 5th! All in my opinion of course.

I went faster on a 1/2 mile run holding on to 5th to cross the line at 135mph than when I changed into 6th and only managed 131mph, and that was holding on to the gear past my supposed peak power.

Impreza sti jdm

Yes i know what you mean.I think its just a matter of trying different runs.Although im still not certain at what rpm should i shift in 1st-5th gear.

TonyBurns

iTrader: (3)

Set the rev buzzer to 7k rpm, you dont need to go beyond that except to hit 60 in 2nd and for going over the line on a 1/4 mile.
Plus what power are you running?

Tony

Impreza sti jdm

Hi Tony,I have posted the road dyno graph on here earlier today.I think 7000rpm is very high shift point for my setup.thanks

TonyBurns

iTrader: (3)

There is nothing wrong with changing at 7k rpm, these cars have an 8250rpm limit, they are designed to do this.
Sitting in front of me is a copy of a rolling road printout from 2004 when I had my first twin scroll Spec C, power figures are 299bhp/255bhp@wheels, 312lbs of torque on a car with 1800 miles on the clock.
Peak BHP is at 6000rpm when it produces its 299bhp (she was still loosening up), power drops off around 7k rpm.
IF i were to change at 6k rpm then id drop off 2k rpm to the next gear, that puts me down 50BHP on that change, if I carried on till 7k rpm then I would have lost 10bhp, so pushing 290bhp say, changing then drops me down to 275bhp which is a loss of 25 overall.
Set your rev limiter buzzer to 7k rpm, it goes off, you change gear, simples (and ive had 7+ years on these twin scrolls now so know how they drive )

Tony

Impreza sti jdm

Hi Tony thanks for your reply.Can you take a look at the road dyno graph i have posted yesterday?Mine is not a standard 2003 sti jdm so power delivery is different than your graph.Mine makes peak power at 5350rpm.

Shaun

Don't listen to Tony he is full of ****!

Set the buzzer to 6.5k and do a few runs. Do the same to 7k and compare. If the 6.5k don't achieve better times (assuming the starts are equally good or bad lol) vs Tony's 7k suggestion. Don't forget by the time you actually manage to change, I bet you'll be closer to 7k on the 6.5k buzzer and 7.5k on thr 7k buzzer runs.

Also try reving out in 4th because based on your gearing you'll hit 118mph @ 8200rpm. Depending on how slow or quick your changes are, you may save yourself some time here. Then try changing to 5th @ your previous rev points and reving out in 5th. Compare the times.

Whatever you do, don't change to 6th.... 5th will take you to over 150mph and you've got no where near enough power to manage that! lol

Shaun

Trust me..... you'll need a ****load more BHP then you have to be doing 8k in 5th over the line on the 1/4! Unless you're clutch has just gone up the crapper!

johnfelstead

It varies every gear. You can log the acceleration rate in each gear then chose the best point for that gear, i would suspect most people shift too late.

Shaun

It would be interesting to see how much quicker your car is down the 1/4 John..... it should certainly highlight how torque plays a part in acceleration.

johnfelstead

Once off the line top end power would be better for a drag strip as you can keep it in a relatively narrow power band without issue, it's why i dont really care what the drag times are, competition wise whats more impressive is how it does on tight sprint courses that mimic road conditions more.

If you look at my sprint results this year in a full weight car with all the OEM trim still in place, running a full tank of fuel to stop any fuel surge, compared to the other cars in class, it's gives you a good idea of how damn quick my car punches out of the corners.

Shaun

John, you're starting to sound like a certain Fennings/de Banke from 2009. Not that I think there is anything wrong in that.