Boost / RPM Questions

[Adydas]

Right its my turn to put forward a tiny problem to the Toyspeed Circle of smart!!

No matter what setting of boost i choose to run , .5 .7 and .85 bar the car seems to start off with a hiss and a roar ( not littarelly ) and take off till about 4000RPM, where the boost ( sometimes ) tapers off and creeps back down. depending on how high its set depends on how much it drops
ie .5 bar mite go to .42 where at .85 might end up @ .67 @ 7000rpm.

Im useing an Apexi AVCR and tryed playing with all sorts of settings regarding DUTY CYCLE etc how ever unless its on approx 50% duty cycle it just plain wont hit the set boost.

Ive come to a few ideas on things but to save stuffing around replaceing the wrong things in the wrong order if anyones experianced anything simlar or knows help would be much appriciated.

Could it be electric related ie spark plugs and leads? i feel they need doing but this cause this? Is the Actuator stuffed in someway? the turbo going despite its yet proven but apparant rebuild ( have had a play with it regarding play etc feels good for age of car ) or could it be my AVCR settings?

Car is ST165 Toyota Celica Gt-Four useing a Apexi AVCR Boost controller.

[Silent Knight]

Does it drop off in boost in all of the gears as you described above or is it only on a certain gear/gears?

I know this is the obvious but have you checked for any boost leaks? Actuator hoses, T-pieces etc etc?

[Lanius]

Could just be the ebc itself. I have the same unit and apparently they're known for spiking and boost creep. I usually run the duty cycle at 80% and set the boost accordingly.

[Fandango]

Wastegate actuator.. Probably.

[Adydas]

Its in all gears

allmost the higher the gear the worse it gets to.

[Silent Knight]

Have you got a separate boost guage hooked up aswell?

Sounds like a boost leak probably somewhere as you say it increases in upper gears when the load is higher...

[Malcolm]

do you still have factory downpipe/catalytic converter/exhaust?

[EVLGTZ]

yeah to me it sounds like the std actuator aint doing its job. Some types of turbos are reknown for this. I'm not too clued up on the CT series turbos tho so dunno if its common with them.

I used to have similar issues until I went with an external. That combined with EBC gives super reliable and consistent boost levels

[Gadget]

mmm. I can vouch for the AVC-R, I had it (the exact unit) in my supra for near on two years and it behaved brilliantly, after a few problems with the setup, it got up to & held boost bang on.

If your actuator has a lame spring and is being forced open slightly by the boost that could cause your issue...

[Twolitre]

I'd say Malcolms onto it, your exhaust will be too restrictive to support high boost at high rpm, although single entry ct26's are known to crack pretty bad around the wastegate but when you get around to gutting your cat you can look into this at the same time.

[Adydas]

i am planning to replace downpipe etc etc when i get spare cash but atm shocks etc come first..

Cheers that answers all..

i guess its odd that it didnt used to do it only after a tiny bit of doing it..

[sergei]

when you gonna have downpipe off, check the wastegate for cracks, like those:



http://www.gtfours.co.uk/

[Adydas]

are they a cause.. or just something u suggest i loook for..

[Malcolm]

cracks on the wastegate definitely can cause reduced boost when they get big enough, this could possibly be the reason that the problem has come on gradually. Small ones like those pictured wont do much, but when they get bigger they can let air through when the wastegate is closed, leading to improper boost control on behalf of the wastegate.