COMPRESSOR SURGE IN MY MTNTK AXYS TURBO KIT... AND WHAT TO DO?

tangerine_sky · Jan 11, 2017

I'm not sure how to do that other than verifying that the turbo is holding the same amount of boost as before at full throttle, which is the case.
You have another method of verifying That the CRV is staying closed? At idle since the motor only pulls max -2 InHg I know it's not open then.

mountainhorse · Jan 11, 2017

Nope...Just what you said... make sure it's making the boost it's supposed to under heavy load like you said.

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mountainhorse · Jan 11, 2017

That lack of surge/flutter in your result can only improve the throttle response in my opinion....

With the ultra light spool assembly (gamma Ti turbine) unique to the EFR turbos... surge would stall the spool to a larger degree than, say, a garret or even a custom turbo with an inconel turbine that has more inertia... so, making your turbo run the way it was designed to run can only help your situation.... the low inertia of the EFR spool assy is the big selling point of the EFR's to me.

Thank you for taking the time to bring us along on your 'turbo adventure' and your methodical troubleshooting and solution session !!

Please keep us posted.

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Davajn · Jan 12, 2017

Thanks for this! Going to fix it directly when im getting my kit.

Would you mind taking a picture of the spring that has been cut and measure it?

Peppa · Jan 12, 2017

mountainhorse said:
NIGHT AND DAY!!!

Nice work my friend !!!

Confirming that the CRV is staying closed when it is supposed to... is the task at hand now!

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Is this anything to worry about? Shouldn't the bov stay closed even without a spring as soon as you have boost? Isn't the "closed" chamber surface area bigger then the "open" chamber in the BOV? Spring is only for keeping it closed at idle/off boost operation right? Or do i have it wrong???

tdbaugha · Jan 12, 2017

tangerine_sky said:
I'm not sure how to do that other than verifying that the turbo is holding the same amount of boost as before at full throttle, which is the case.
You have another method of verifying That the CRV is staying closed? At idle since the motor only pulls max -2 InHg I know it's not open then.

And how much boost is that?

Also, in my experience it takes two seconds or so of sustained WOT to reach the MAX boost the spring wastegate will allow.

If you could take it to the mountains and really let it sing that will confirm it's still staying shut

Rosslbz · Jan 12, 2017

Boost pressure is what holds the bov/recirc valve closed when accelerating, building boost. The spring in the bov/recirc valve is to hold the diaphragm shut during peak vac, idle or big deceleration.

mountainhorse · Jan 12, 2017

The nice thing is that it's clear that there was compressor surge before... and the CRV was not operational.... now the CRV is operational, in this application, and no surge.

For those reading that dont know what compressor surge is (aka flutter, chatter)... here is a simplistic video.

<iframe width="900" height="506" src="https://www.youtube.com/embed/FwzUffAuQyc?rel=0" frameborder="0" allowfullscreen></iframe>

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MTNTK · Jan 12, 2017

Compressor Tip Out Flutter

We have done quite a bit of testing with different springs on the Recirculation/BOV valve on the Borg Warner EFR as well as different vacuum locations. We have found lower performance (i.e. slower boost response) when we modify the spring to reduce the tip out flutter. As has been stated in other posts the BOV is operating but the volume of air is larger than it can handle on it's own. The compressor Recirculation/BOV valve on the EFR is only designed to reduce "damaging" flutter and is not a flutter eliminator. The Turbosmart Recirculation type valve probably will not cure the flutter, because the machined hole is small in the EFR compressor housing and is the bottle neck for the air. We have been testing other BOV options and have some RMSHA racers running the new design. No flutter and the impressive sound to go along with. If testing goes well, we may have this as an option for upgrade available in the spring. The good news is, this is still an awesome turbo and we love the way it works!

Rosslbz · Jan 12, 2017

Another factor is elevation, the same motor at 2000' above sea level will not have the same vac reading at 8000' above sea level. This is why most quality built bov/recirc valves have a adj. spring tension set screw. Turbo flutter at these boost levels and volume is 100% avoidable.

mountainhorse · Jan 12, 2017

Agreed

Rosslbz said:
Another factor is elevation, the same motor at 2000' above sea level will not have the same vac reading at 8000' above sea level. This is why most quality built bov/recirc valves have a adj. spring tension set screw. Turbo flutter at these boost levels and volume is 100% avoidable.

I Agree.

Although it might not cause damage in the term that we use the sleds... compressor-surge (AKA 'flutter') is not good and it does detract from inlet flow in ANY turbo...and I believe that as supplied/configured, the CRV in this kit is not functioning at all.... and if so, why even connect it to the vacuum source?

I fact, the CRV on the EFR turbo's is VERY good at managing compressor-surge in chopped-throttle situations.

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Rosslbz · Jan 12, 2017

Also your motor has to produce good vacuum. A vacuum test on the motor is a must if you want everything to work together.

mountainhorse · Jan 12, 2017

MTNTK said:
We have done quite a bit of testing with different springs on the Recirculation/BOV valve on the Borg Warner EFR as well as different vacuum locations.

We have found lower performance (i.e. slower boost response) when we modify the spring to reduce the tip out flutter.

As has been stated in other posts the BOV is operating but the volume of air is larger than it can handle on it's own.

The compressor Recirculation/BOV valve on the EFR is only designed to reduce "damaging" flutter and is not a flutter eliminator.

The Turbosmart Recirculation type valve probably will not cure the flutter, because the machined hole is small in the EFR compressor housing and is the bottle neck for the air.

We have been testing other BOV options and have some RMSHA racers running the new design. No flutter and the impressive sound to go along with.

If testing goes well, we may have this as an option for upgrade available in the spring.

The good news is, this is still an awesome turbo and we love the way it works!

MTNTK... SINCERELY Awesome to have you comment in here !:thumb:

It IS an awesome turbo and your kit is top notch.

It's an Asset to have manufactures on here to discuss their products and help our members and their customers.

Please do NOT take this as bash/criticism.. this is an open discussion where all can present their OPINIONS.

MY 2¢

I've listened to many EFR turbos... and have talked to Borg Directly... as I know you have too... but I remain convinced that the surge is not a good thing in terms of performance on these sleds.... and for most installations of the EFR... the CRV does a great job with surge management.

Borg said that the low vacuum of the two-stroke may not give sufficient to open the CRV as supplied and in such a custom application that very specialized crv springs would need to be used. I find it hard to believe that the same CRV spring used on a twin turbo LS engine or a ecoboost Fiesta RS is optimal for a low vacuum 2 stroke application.

Borg did say that flutter is a performance detractor at any level and that the level of surge shown in the vid should be minimized.

IMO, the CRV is still a clean/compact/efficient way to manage tip-out compressor-surge... it just needs tuning and verification. (which is what I believe tangerine_sky is trying to do here)

I think that the BOV's used by other mfg's turbo-kits also suffer from too stiff of a spring.

Exactly how has the boost response been lowered when you reduced compressor surge?

It will be great to see an update with the CRV in the future.... I think that the integral nature of the EFR CRV is pretty darn cool !

As an "Aside" ... I'd love to see MTNTK build a non adjustable, EFR, non-intercooled AXYS kit that could maintain 17.7 PSI MAP at all altitudes and provide a steady 190 hp to the track throughout the elevation change... the cost would be lower and more people would buy kits IMO.

<iframe width="560" height="315" src="https://www.youtube.com/embed/JNP7EqT3t68?rel=0" frameborder="0" allowfullscreen></iframe>

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Rosslbz · Jan 12, 2017

Does anyone have a pic or diagram of mtntk' s kit? I'd like to see where the bov/recirc valve is mounted and where are they tapped in for the vacuum/boost source.

tangerine_sky · Jan 12, 2017

As mountainhorse said, this thread was in no way meant to bash MTNTK. I think the kit is running awesome, and I wouldn't run any other kit. I just wanted to try to solve a small problem I saw.

I am getting the soft spring for the TS Kompact Dual Port today. I can measure the length of the stock CRV spring that I cut when I install the TS valve. Probably install it after riding tomorrow, assuming I can get it to actuate at a low enough vacuum.

I am going up to the mountains tomorrow (8000'-9000') to test if the stock CRV valve is still functioning properly up there. Theoretically the motor will produce less vacuum at altitude so we'll see how that effects the surging.

I will have more varied riding conditions to test on/off throttle boost response. Then I will determine if I see any negative performance aspect of the modification to the CRV spring.

It's holding 8 psi of boost @ 5000' right now. I have another short clip of it in slo-mo since the camera moves so much in real time it's hard to see the gauge.

<iframe width="560" height="315" src="https://www.youtube.com/embed/tMXY5mjKOKk?rel=0" frameborder="0" allowfullscreen></iframe>

https://www.youtube.com/watch?v=tMXY5mjKOKk

tangerine_sky · Jan 12, 2017

Rosslbz said:
Does anyone have a pic or diagram of mtntk' s kit? I'd like to see where the bov/recirc valve is mounted and where are they tapped in for the vacuum/boost source.

Here are some pics of the reed cage port where the vacuum line is attached and the stock CRV on the EFR turbo.

mountainhorse · Jan 12, 2017

As Ross said above.... the spring is only there for specific reasons.

When the sled is making boost... the vacuum port goes to manifold pressure (boost/charge pressure) which then pushes on the diaphragm... assisting in keeping it closed.

Unless your setup is different from others... I cant see the CRV actually functioning at all on tip in on any of these EFR kits.

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Rosslbz · Jan 12, 2017

My 2$

Tangerine thanks!
I would think vacuum should be pulled from after the reeds," down wind".
The crv right on the compressor housing is different, going back to turbo bikes and cars, I always mounted the bov/recirc valve near the throttle bodies.

tangerine_sky · Jan 12, 2017

JJ_0909 said:
wish I knew the spring silber was using. I'd love to buy a spare and cut it - or just go to something else just to see. How universal are these BOV springs? Could I buy a 2 psi spring from a differen manufacturer and try?

They are not universal in length, diameter, or wire thickness. Doesn't Silber use kPa turbos? You could contact kPa to get a spare spring.

Rosslbz said:
Tangerine thanks!
I would think vacuum should be pulled from after the reeds," down wind".
The crv right on the compressor housing is different, going back to turbo bikes and cars, I always mounted the bov/recirc valve near the throttle bodies.

That would be nice but that's inside the motor.

Rosslbz · Jan 12, 2017

Hah, sure is! Typing before thinking!

COMPRESSOR SURGE IN MY MTNTK AXYS TURBO KIT... AND WHAT TO DO?

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