Hi peeps

If compressor surge was experienced at 3-4k would this prevent a mapper adding timing and thus loosing mid range torque?

Cheers Ade

 

Pm Jolly Green Monster or any of the competent mappers on here is your best bet, I know a bit about mapping but not enough to answer your question correctly.

 

Thanks for the reply anyway!

 

depends on the severity of the surge..

generally if it is just a noise and you cannot feel it when driving but the boost needle pulses a little then it wont effect the det line / amount of timing that cant be added enough to impact torque.

Generally it occurs in a high gear where the turbo is spooling a lot earlier in the rev range and generally power and torque is measures in 3rd or 4th depending on the gearing so it doesnt normally effect the measured power output but the actually poweroutput in higher gears can be effected.
Also if adjusting to sort the higher gears out then it could effect lower gears too depending on the severity and how it is dialled out (gear dependent boost contorl, rpm boost control etc).

On the other hand if it is bad enough to impact the amount of timnig that can be run on the engine enough to impact torque then you would be feeling it when driving and therefore the boost needs altering so its not surging rather than timing removed, or the inlet alter to remove the surge etc.

Simon

 

Hi Simon,
Thanks for the reply
Yes the surge is noticeable, like you can feel it and hear it.
In what way do you mean to alter the inlet, restrict?
Would altering the inlet restrict power and such like in the higher rev range?

Ade

 

yes, its a play off but usually it can be sorted..

whats the setup?

 

MY03 WRX STI
2.1 stroker
MD321T
Simtek
650cc
RCM pump
FMIC
Headers and up pipe
3" full decat
Intake pipe with air filter in wing
3 bar map sensor

Thanks Ade

 

how much boost is it running?

unusual for the md321T to surge badly or not controllable via the map.

Has it been mapped and then the surge noticed after or was it noticed during mapping and it wasnt possible to dial it out?

inner wing induction can effect it but usually there is a little restriction there which helps.

Do you have a dyno graph? as I presume its been on the dyno and not made the torque you were expecting?

2.1 with AVCS heads on an MD321T should be fairly torquey.

Simon

 

Compressor surge is usually caused by the turbo being able to provide more air than the engine can process at that point in the rev range and particular loading, the surge you feel and hear is caused by a poor relationship between the air delivered and the air accepted, this in itself is a performance restriction and will slow acceleration significantly and can be so bad as to halt acceleration all together in severe cases, to ensure that the turbo provides a flow of air that the engine can deal with you will need to reduce the intake diameter but only by as much as to just make the surging go away and no more, then your turbo intake will be working in harmony with your engine, I think performance lost at the top end (if any) will pail against the gains made in acceleration and mid range by removing the surge.

As an example I setup a Hawk Sti not that long ago and it had all manner of boost issues including boost creep and compressor surge, the surge I sorted by reducing the intake ID, the car was already mapped by Bob Rawle so after all the little issues were ironed out the owner had the car mapped by Bob again and it performed way better right through the range and made way more top end than before.

Cheers Iain

 

Very intesting post, how did you go about reducing the intake diameter?

 

By using an alloy in pipe joiner from forge. The size of which had to be worked out through a bit of testing but the difference it made was well worth the effort.

Cheers Iain

 

Cool thanks

 

Normally surge becomes a problem with aggressive wastegate duty cycles and as Simon has already commented, it is a bit of a trade off because as you reduce the duty cycles you may get lower and later boost particularly in the lower gears where there is less load.
The later ECUs such as the Alcatek new unit have in gear recognition and that can compensate for different requirements in different gears.
If you do not want to reduce duty cycles, applying a constriction shortly before the compressor inlet on the inlet tract is often very effective and with cars running a silicon inlet tract this can be achieved simply by applying a clamp or jubilee clip shortly before the compressor cover. The objective is to increase air velocity and it does not take much of a constriction to achieve this.