fuel cut question

[Koko08]

I wanted to know at what boost level the rvr should cut at... I kept turning up my boost just to find the cut point .. it ended up cutting at 25ish psi is that normal for these cars? Seems abit high

 

[vr401]

Nope, unless you have it chiped?
I would say between 15-17psi it should cut.

 

[Koko08]

Nah no chip

 

[White Knight]

VR401 (Mio) is correct bud. The reasoning for the "between" 15-17psi and not an absolute figure is that the cut is based on airflow that the ECU sees. Mine would cut at around 18-18.5psi but others are different.So I would imagine some boost leaks are occurring somewhere...
Where are you tapping in to measure boost pressure bud?
Seriously though, if you have a stock setup you will blow the engine with continued usage of anything more than 20psi.

 

[evo-gsr]

Nek minute...WTB 4G63T!

 

[White Knight]

Lol, Nek minute...

 

[evo-gsr]

:lol:

 

[Koko08]

I tap my boost gauge with the stock bov pretty much where the intake is... I'm using a 16g turbo td05 550cc injector and walbro 460lph pump( e85 pump) I have bigger injectors just haven't got around it

 

[Koko08]

I do have a 600x300 intercooler 2.5inch piping.. 3inch full turbo back k&n panel filter

 

[Koko08]

Reason for my question is my Audi boost cut around 13psi and I thought that was fair enough but to boost cut at 25+ was confusing the crap out of me I normally run 18psi in my rvr

 

[White Knight]

Fair enough mate, but you're playing with fire over 18psi. Its a matter of when and not if it will go boom.
It is weird that you haven't hit the cut out as yet though.
The 16g will be goingg out of its efficiency range at over 23psi i would imagine as well.
Do a boost leak test, if your reading 25psi at the bov area you likely aren't seeing that at the intake manifold. Tap your boost gauge into one of the vacuum hoses off the intake manifold bro. Far right as you look at it as well.
That way you will see what the engine sees. If that makes sense.
For the time being busy wind it back to below 18psi to be sure.
Cheers mate.

 

[Koko08]

Thanks will do

 

[White Knight]

No probs mate. Different experience from an Audi though I imagine. A lot less refined for a start, lol.

 

[Benzo4gT]

I have an Apexi AVC-R so it only reads in kg/cm^2. While setting it all up it hit 1.8kg/cm^2 (25.6psi) without boost cut..............
I had fixed boost leaks before the install so that eliminates that variable, I also have several HSG ECUs and they all did the same (I was testing ECUs at the same time before socketing them). The only thing that changed was bypassing the OEM boost solenoid to fit the EBC.

Is your boost solenoid hooked up?


I agree with Ian, take it back to 18 and stay in the upper end of the safe zone. I have adjusted the EBC to run 18psi max now as the thought of changing out another engine just about makes me go postal.

 

[White Knight]

^ forgot to ask the question about the boost solenoid.....

 

[grndsm]

Another factor which determines fuel cut is ambient temperature, in the winter, we can see fuel cut as low as 14-15psi! But you guys probably do not need to worry about it

Fuel cut is such an old subject in US, because it was completely removed by all modified ECUs/chips since they late 90's. Why not run one of those chips?

 

[White Knight]

I have an Apexi AVC-R so it only reads in kg/cm^2. While setting it all up it hit 1.8kg/cm^2 (25.6psi) without boost cut..............
I had fixed boost leaks before the install so that eliminates that variable, I also have several HSG ECUs and they all did the same (I was testing ECUs at the same time before socketing them). The only thing that changed was bypassing the OEM boost solenoid to fit the EBC.

Is your boost solenoid hooked up?


I agree with Ian, take it back to 18 and stay in the upper end of the safe zone. I have adjusted the EBC to run 18psi max now as the thought of changing out another engine just about makes me go postal.

Was just thinking about this.... Doesn't the ECU see the volume of air being seen by the way of the MAF? Therefore that would determine the onset of "boost cut"?
Fuel cut defenders intercept the signal from MAF to ECU for this purpose.
I think the factory boost solenoid is used for preventing boost spikes and controls the stock level of boost doesn't it?
Its a moot point I know, but I'm curious nonetheless. Sorry Benny.

 

[Benzo4gT]

You're completely right mate, the MAF is what determines the cut point, but I wonder how the BPS and IAT (as Leon mentioned) factor into the equation. I have taken the honeycomb out of mine, which is a big no no on a Karman Vortex sensor, so I'm wondering if there might be some weird tumble effect happening in the MAF to alter the signals enough to effect the ECU that much.............that's a scary thought.
Is the honeycomb removed in yours boostn?

 

[grndsm]

MAF also measures IAT (Notice how it is one of the values which can be logged?) ECU then crunches all that data and comes up with fuel cut point, but it depends on total airflow value (and not just boost or temperature).

Removing honeycomb was a popular mod, which gave more flow through the MAF, but worsened drivability. Now, people just adapt EVO8/9 MAF or go with speed density (no MAF at all). Another option is to use factory MAF at lower boost/rpm but then switch to speed density at around 450hp (when factory MAF capacity is exceeded). This way, you get the best of all worlds (though you still have to force all that air through the MAF).

 

[penngwyne]

I read a thread like this and realise I still have a lot to learn