boost creeping on gear change

Kelly

Kelly

Member +
Firstly my auto has always ran a lil extra boost fine with the hks actuator, but ive since added cat back HKS exhaust and was experiencing boost creep and boost cut. We have wound the actuator down to the point now we are running 10psi steady through the rev range. But as soon as it changes up a gear under hard acceleration it spikes to 12psi and hits boost cut. It doesn't do this when driving and you kick down a gear just when hard accelerating up through the gears and only at the point of gear change.

Put the standard air box back on which help originally with the boost cut, but like said above have now been left with this problem which dont understand as my car 11psi beforehand with none of these probs.

Anyone any insight on why it does this changing gear?
 
Jay

Jay

Admin
It's the same with a manual vehicle Kelly. Boost creep depends a large extent on driving style. Someone planting the accelerator in a stickshift GT will get the same problem (fine under general operation but creeps on extreme throttle).

Problem solving will be the same for all. Restrict the intake and exhaust as required to 'balance' your CT9 again.

I'd imagine the extra flow from the exhaust is the culprit coupled with the colder weather we are getting. A restriction placed in the exhaust should help seeing as the stock airbox isn't.
 
Kelly

Kelly

Member +
well if i wind the actuator down ever more guna be running standard boost all over again. the airbox has helped a little bit but like i said just left me with this on gear change. Would an electronic boost controller solve the problem?
 
Jay

Jay

Admin
Possibly but when I say restrict the exhaust I mean literally just that:

Get a thin strip of metal and place it like a gasket between a join in the exhaust. Cut it so as it is a smaller hole than the exhaust's diameter.

This will increase back pressure and reduce the creep. Might take a little adjusting before you get it perfect but it'll be cheaper than an EBC.
 
Dub-Se7en

Dub-Se7en

Lifer
an EBC probably won't help as the fault isn't with the control of the wastegate, it's more that likely to do with the free-er flowing exhaust syste that is causing the turbo to overboost.

i restricted my air intake and it worked for me, i held 14psi fine. or, as Jay suggested, restrict the exhaust. or better still, get the wastegate ported.
 
ChrisGT

ChrisGT

Member +
Not a bad idea there Jay! Be bloody easy to make up as well...shud've tried that when I put my filter behind the bumper :s
 
Jay

Jay

Admin
I needed to do this on the trackstar. Didn't feel the urge to splash big money out fancified gadgets!
 
Rory

Rory

Lifer
Restricting the Exhaust is the simplist and cost effective solution.
I ran my car like this for about a year, with no problems.
 
Kelly

Kelly

Member +
Right so restrict exhaust or port wastegate? which one is recommended?

cant believe its doing it so much and havent even got de-cat yet.
 
T

Toby@ToyTuning.com

Banned - DO NOT BUY FROM TOYTUNING
Like Jay has mentioned it's a very careful balance, both on intake and exhaust side. Porting will help as well as your increasing the diameter of the w/gate hole which is were the gases are expelled once preset boost limit is reached.

The only problem with porting is that this an already weak part of the CT9 as they crack around here due to the excessive heat the hairdryer produces. A badly cracked w/gate means lack or turbo response as a small amount is being exhausted when you don't want it too.

Again we can port the w/gate if you need, otherwise make a restrictor for the exhaust although you will need to test different restrictions as each car will be different, there is not pre-set amount..

T
 
Kelly

Kelly

Member +
ok well i stil have this prob, nick has wound the actuator down im running 8psi holds steady fine perfect and when the auto changes gear it bangs up to 12psi (im spinning up on gear changes) and the drops back to 8psi holds that fine until gear change.

i have to run at 8psi so when it spikes im below the fuel cut.

I DONT wanna put a restrictor in the exhaust as if i did what would be the point in having exhaust? and i dont wanna port the wastegate as mentioned above it could weaken it.

Im thinking of buying aftermarket goodies like an emanage and actually map the car for the spike and get my boost above 8psi on acceleration. ive been told a boost controller wont help?!
 
GTti

GTti

Member +
A venturi cone in your intake hose should work. Well it did for Scottishcruiser.


and i dont wanna port the wastegate as mentioned above it could weaken it.
Click to expand...

I think thats myth, what consistutes to the cracking is extreme heat (Probably because gasses can't escape through the smaller hole quick enough and become stagnant). Bigger hole, less heat, less cracking?

Surely you can nitrate it after or something (don't know the process), it'll harden the surface after machining though.
 
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Jay

Jay

Admin
One of the myths is that the wastegate area is the point where the fracture starts. This is mainly because it's the only visual indication when looking at a complete CT9.

If you dismantle one you will find the source of the crack further inside the exhaust housing. The fracture starts in there and works it's way out towards the wastegate.

I know it's only a personal opinion (I'm no metalurgy expert) but I feel that the fracturing will be slowed down by a larger mass of metal. It stands to reason that a smaller mass will be at a disadvantage.

Open to debate I suppose.

Kelly you have a choice, either modify to accomodate the extra boost or detune the setup slightly to make it safe and reliable. It depends on your budget and future plans for the car.
 
GTti

GTti

Member +
Perhaps, there was a crack in my RHB5 IHI turbo on the GTti but I don't recall the cracking from inside outwards. The Mazerati spec IHI I now have has a larger wastegate port as stock which is handy.

Who knows, like Jay said I'd just knock the boost down a little if you can.
 
Kelly

Kelly

Member +
i cant knock the boost down anymore im having to run 8psi in order to accomodate for the spike on the gear change which jumps to 12psi. If i run anymore boost then the spike makes me fuel cut.

i'm deffo not going to detune the car, looks like its mod some more :D
 
59bhp

59bhp

Member +
porting the wastegate wont make it any more likley to crack, if anything putting a radius on it will be better for gas flow and the edge will be less likely to absorb the heat. Just dont go mental with it and should be fine.
 
Dave.

Dave.

Member +
on my friends GT we just restricted the intake, similar to dub-se7en's setup on his car before he rebuilt it :)

just some foam/gaffer take around it to make the part it can breath through smaller :)

Its cheap and virtually effortless Kelly, or Jay's idea too, but thats a *little* more effort :)

Dave
 
D

Deano

Banned
Mine creeps up sometimes too hits about 14 psi but doesn't hit fuel cut boosting at 12 psi never heard of an exhaust on a gt causing it to hit fuel cut. Mod some more Kelly upgrade that intercooler lol *jokes*
 
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