Skooby53

iTrader: (1)

I know this is probably a really silly question so I apologise before I ask!!

What is the optimum rpm to change gear while making urgent progress?

After my remap I was supplied with a graph showing torque and bhp. Peak torque is 312 ft/lbs at 3750rpm and peak bhp is 281 at 5750rpm. so when is it best to change gear?

Thanks, Martin.

GlesgaKiss

Hi Martin - It totally depends on the car itself. As you say, your's is mapped so will be different to other impreza's. Can you not feel the power easing off as you pass the peak? I only ever change gear by feel. If you're flat out the last think you want to be doing is looking at the rev counter...on the road anyway.

Alan

PantsUK

iTrader: (1)

if you have a nice steady curve you want to change just after the peak (unless it drops straight off) so when you hit the next gear your on the way up to peak again.

Paul at Zen told me this made a big difference to me.

Skooby53

iTrader: (1)

Thanks for the replies, I take your point regarding the rev counter Alan, I try not to look at it while driving. I know what you mean by feeling the power leveling off as well. Since having the car mapped I have at times hooked up some great powerful surges, if you know what I mean. With the car being so much quicker I was just trying to gauge other drivers experiences of their driving style. I really want to get out on the track where I can just concentrate on the driving and not be so restricted on speed, just keeping an eye out for the crazy fiesta drivers!

I also want to make sure I really appreciate what I have before I move on to the next level of modifications. I think there maybe a few drivers who say " I want 350bhp" without truly realising what this additional performance will be like on the open road on a day to day basis.

Thank you again for your input, Martin.

dunx

iTrader: (3)

Try looking at the shape of the torque curve, ideally you want the torque in both gears to be about the same before and after the shift. No point running upto the rev limit if the torque is dropping off.

As std my STI was quickest shifting at 6500 rpm, not hogging 7750 on the limiter.

HTH

DunxC

PantsUK

iTrader: (1)

thats what I was saying ..... just badly

SamUK

iTrader: (1)

Correct me if i am wrong...but does this not mean you need to have you mapped re-looked at as your peak should be towards the end of the rev range..? you care runs out of power at 5750rpm ...

PantsUK

iTrader: (1)

I dont think that's right peak can come at any point but you obviously want power to continue .... unless it just drops straight off in which case probably worth a check out.

dunx

iTrader: (3)

Mine peaked at around 6100 std., but re-mapped peaked up around 6750, but there was little droop as it approached the limiter.

However it is still quicker overall, if I change at 7000 rpm as I "land" in the thick part of the torque curve...

Wish I could post a RR printout with some "guidelines".... Grrrr !

DunxC

Skooby53

iTrader: (1)

Hi guys, the map graph can be viewed by clicking on my 'Plus Profile'. The mapping session was done by Bob Rawle and he spent ages tweaking it, including returning to his garage to change the restrictor pill. As my car is a UK spec car and still has the original up pipe fitted he was really pleased with the results. This was all live mapping as I drove up and down the dual carriage way. I had to back off the throttle just over 6k as open roads don't lend themselves to this kind of driving. Maybe this would explain the sudden drop off?

Skooby53

iTrader: (1)

Just been looking at the specs of the GB270, nice motor. Anyway, the peak torque of 300lb/ft is at 3000rpm and the peak power is 266bhp at 5700rpm. I know this is a 2.5 but wondered if it's different because its been treated to a ppp? Does the mapping make the car more usable by lowering the peak torque and power bands?

dunx

iTrader: (3)

Hello again !

Looking at your graph, I'd suggest that shifting up at 5500 rpm.

If you go up to the red plot at 5500 rpm then move left, you meet the red plot again at 3000 rpm, this at 260 ft.lb, so that's probably (?) quickest.

Depending on gearing, 5000 is about 275 lb.ft. ending up at 3300 rpm, so if that's the "gap" between your gears, then it should be even faster....

Many people can't grasp that my six speed box keeps the gear at peak torque for more of the time, on a friendly "chase" to a club meeting last week, I never went over 5000 rpm, whilst the "young 'uns" were on their rev limiters.... but I still kept up and got 25 mpg at the same time.

HTH

DunxC

swifty.....!

iTrader: (4)

from looking at your power graph your best change would be 5800rpm just after your peak but the best way is to try a few to see what best suits you and the car

Skooby53

iTrader: (1)

Thanks again for your advice, I will give it a go and see what it's like. I'm sure I will get into a familiar pattern now I know the area to change in. There is also a track day coming up at Castle Combe next weekend so I may get time to pop up and have a proper drive. Thanks again for your experienced advice.

The rookie

iTrader: (1)

As torque is multiplied by the gear ratio, the same torque in say third will give about 2/3's the torque at the wheels in second, on that basis you need to hold onto the lower gear longer than is suggested by dunx.

Its a shame the power curve stops at 6K as its no good for telling you how long you need to hang onto a gear until, as their is no real tail off from peak to 6000rpm.

at any given road speed best acceleration is achieved at highest POWER output as the gear ratio means this will give best torque at the wheels.

Simon

PantsUK

iTrader: (1)

?? Thought torque was multiplied by revs to give bhp ???

The rookie

iTrader: (1)

Nearly, for lbft and bhp, power=torquexrpm/5220 (near enough - depending on the variant of 'bhp' you use!) so the two lines cross at that point....

But torque is still multiplied by the overall gear ratio to the wheels,

IF first is 2.85:1 and FDR is 3.5:1 (for easy maths...as 2.85x3.5=10!)

100lbft at the flywheel is multiplied to 285lbft at the gearbox output shaft (i.e. entry into the centre diff on a Subaru), is then multiplied by the FDR to be 1000lbft at the wheels....

So if 3rd is 1.3:1 and second 2.5:1 that same 100lbft is in second 250lbft at the gearbox output shaft and 130lbft in third, so even if torque is a lot less in second at high engine speed its still likely to be higher than torque in third gear at the output shaft.

Simon

Skooby53

iTrader: (1)

Wow, I understood that I do plan on upgrading my original turbo in a while to something like a VF34/35. When I get Bob to remap it I will try and get a better graph and hang on to the redline! Very informative, thank you.

New_scooby_04

iTrader: (4)

That's exactly why the drop is there mate. Mine is exactly the same (see my plus profile) Bob doesn't need you to rev it any higher!

You can see that the car has done the best of its work by about 5500, so I'd be changing up at no higher than 6k personally. I take it you still have the TD04 on there.

Ns04

The rookie

iTrader: (1)

I'd love to know what crystal ball you got that from, the power curve is still pretty much flat at 6krpm (50 rpm before the 'peak' which is an un-natural spike its only 5bhp up on that just before 6K and the peak after that is back to 275bhp!) and could be to 7K for all you know.....

Simon

PantsUK

iTrader: (1)

<D hat on . . .. . . ~

Skooby53

iTrader: (1)

Yep still got the standard TD04 on there and also the standard up pipe! The up pipe will be changed and a sports cat fitted or maybe a total decat. While were at it, when I change the turbo will the standard intercooler be up to the extra power, around 330 I would hope? If not then I guess an sti 8 upgrade would be in order. I know a FMIC would be an option, just don't want to risk MAF damage on a MY99.

Martin.

The rookie

iTrader: (1)

An FMIC won't harm the MAF, its (over) oiled filters on induction kits that are the risk, having said that many cars (like the scoobynet specC project car was) are running over 330bhp on a TMIC with no problems.

Simon

Skooby53

iTrader: (1)

Thanks Simon, I was worried about the fitting of an IK and the problems I have heard regarding increased air flow. This power thing is so damn addictive!