UkLegacyT

my car has the same engine as the earlier impreza with the turbo using the 90 degree angled entry. it has a full 3" mongoose system from the turbo back, it is chipped, and also a pipercross induction kit. power/torque and also boost pressure unknown.

thing is, after my original gearbox broke, i fitted the close ratio box and diffs from a my98 wrx. basically if it is taken to 7000rpm redline in each gear, it only drops back to 5000rpm from one gear to the next. i realise that now it is on boost all the time from 2nd - 5th gear when accelerating hard, and so i dont get the kick that i used to when the boost builds at 3500-4000rpm.
thing is, it still accelerates really quick, but doesnt seem to have the same grunt.

my thought is that as im always above 5000rpm under hard acceleration, this is where the torque starts to drop away, am hence i am missing the highest torque levels present below 5000rpm, resulting in lower grunt?

can anyone answer this?

thanks

ian

UkLegacyT

anyone?....

john banks

Your change up point for maximum performance should be where the power at wheels in the next gear becomes higher than the power at wheels in the present gear or the rev limiter which ever comes first. This usually involves going beyond peak power at wheels unless this climbs all the way to the red line such as on some Honda VTECs or cars with large turbos. Your power at 5000 RPM will be higher than it is at 4000 RPM, so I think you have enhanced performance, by dropping into a higher engine speed after change up.

It is odd though - a car can FEEL very quick going from off boost to full boost and full torque soon thereafter, but would feel smoother and actually be quicker if the acceleration was more constant if you kept it on boos all the time. A change in acceleration such as a progressively increasing force pinning you back in your seat, compared with always being pinned back in your seat.

Some who fit downpipes feel the punch has gone during spool up - it hasn't - its just they started with more so relatively it doesn't feel as dramatic.

Cosie Convert

You never said how your boost is controlled ? I assume it is still by the ECU ?? If so, you will find that the boost has been considerably reduced come 7000 RPM. You may well go quicker by changing up earlier, say 6500 and dropping into the next gear at 4500.
Fitting an aftermarket boost controller (such as a dawes) can help stabilise boost pressure and, if carefully optimised to match your current mods, can produce a worthwhile increase in power throughout the range.
If you can get a run on a rolling road, you can do as John says and work out your optimum shift points from the power curve

cc

Edited to add - Just noticed it's chipped, super-chipped ? I would suggest you get a boost gauge fitted as you may not have any overboost protection

[Edited by Cosie Convert - 2/22/2002 10:14:33 PM]

UkLegacyT

thanks for the reply john. yes, i suppose it could just be a phsycological thing, and is possibly quicker. im going to rolling road it asap aswell, so that i can check if the boost is correctly matched to the fuelling of the chip etc, but i rarely have days off so is difficult to book in.
i actually wanted to make a afr meter of yours when i first saw it (flamin amazing how you made it so cheap) i was considering a meter from demon tweeks (luminition i think?) a while back, but they go for about £110. same thing, just a bit more fancy, but who cares!

p.s. do you have any idea what the turbo is on mine, is it a td05 or something, ive had a look and can see the plate on the compressor housing, but without removing pipework i cant read it.

thanks again

ian

UkLegacyT

oh thanks to you aswell cc, your message hadnt appeared until after id finished the last reply, doh!
the chip is a 'powerchip' from collins performance. the boost is controlled by a bleed valve under the bonnet. after reading recent posts by john banks (above) and also others, i suspect it is just a rip off fuel cut remover?
as for boost level, im buying a boost gauge next week either tues/wed, whenever i get to the store. its something ive been meaning to do, as i havent a clue what it is running at.

thanks

ian

UkLegacyT

just a thought, since mine is a bleed valve (2 way) under the bonnet, could i swap this for a dawes? if so, would it be a better method of controlling the boost? how much is one?

thanks

john banks

Yes. £26 in a group buy. You can get them from www.performanceehxausts.net for a bit more than that.

Also see the DIY FCD thread in drivetrain (see towards the last page for the latest design - we abandoned the original one) for a rather better solution than a Superchip - a fuel cut lifter which combined with a Dawes would be so much better than the usual voltage clamp/bleed valve.

UkLegacyT

thanks again for that john, i will have a look at that thread now.

ian

UkLegacyT

also, just a further point. i originally thought the chip would provide the increased fuelling for increased boost etc. am i right in thinking that the original ecu would do this anyway, i.e. the more air it meters, the more fuel it adds, and that the only difference between the original and 'chipped' ecu is that the fuel cut is raised/removed?

if so, i was ripped off wasnt i.

ian

john banks

If it is like what Superchips do then yes. If you had a proper remap there would be no need for a bleed valve as they would remap boost fuelling and timing.

The £350 or whatever Superchips charge is possibly a bit much for what it is, but my main objection is failure if a hose comes off or the solenoid sticks - resulting in very high boost with no fuel cut. As well as people that decide to run over 25 PSI "because they can" and then wonder why it blows up.

UkLegacyT

yes ive seen plenty of people fit bleed valves to renault 5's etc and keep winding the boost up, then it pops.
im not really sure what a safe bet is with my engine, but am thinking 15/16 psi when set on a rolling road?
the chip probably is like a superchip. i was going to get a superchip, but they cost £411 + fitting !! mine was £250 all in, fitted. still a rip off, but about half the cost of a fitted superchip, and collins performance are a reliable company. but...it still could go bang, you never know.

i have seen many threads on intercoolers, do you have any thoughts on the charge cooler used on my car, as the 'radiator' is behind the grill, so i would have thought that at high speed it may be a saver bet at high speeds?

ian