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

[TreeThrasher]

You get better vac signal on throttle body side of the reeds anyway...pulling vac signal from crankcase you get both vac and pressure as the piston cycles. Reeds cut the pressure cycle off.

I 100% agree with running bov or re circ valve closest to the throttle bodies...unless you are running an inter cooler. Then bov should be between turbo and intercooler to keep from pushing any more charge than necessary through intercooler.

For years I always thought about using two small bov units. One right off the turbo and one in the side of the charge box...back in the carb days I was sure that would be the ticket. Dump the pressure as quick as possible to aid with over fueling in on off on off situations. Never did it, always just using one 50mm unit between turbo and box.

Sled is looking like its working well now!! Sounds good

 

[tangerine_sky]

The charge tubing is so short on the MTNTK kit that the distance from the intercooler to the bov on the compressor housing versus having a BOV in the tube is negligible.

 

[Rosslbz]

You could put one next to the map sensor.

 

[mountainhorse]

With as minuscule as the charge side volume is on most of these sleds, and certainly in the MTNTK... an external BOV just complicates things IMO.

Automobiles have much larger charge side volumes... and this is where most of the 'logic' is derived from by people thinking about turbo sleds... Much of the logic is the same... but there are key features where it does not translate too.

If there were a gain from an external BOV used in conjunction with an EFR turbo with a CRV-block-off... I'd wager it was imperceivable. I think that a NON-functioning CRV blow off system is a performance detractor.


All my OPINION here.


.




.

 

[mountainhorse]

Size matters (charge tract volume that is)

Do I think that putting the BOV next to the Throttle-Bodies on these cars would make a difference ? ?

YES !!​

 

[mountainhorse]

Tiny charge volume.

This one...

I'm not too worried that the CRV is mounted in the compressor housing...as long as it is functioning within the operational conditions of the turbo kit and this 800 CFi.

.

 

[tangerine_sky]

Just got the soft spring for the turbosmart valve. It is supposed to have an actuation range of -13 inHg (Max); -3 inHg (Min) but when I put it on a vacuum gauge on it, the full soft setting just barely starting to open around -13 inHg. Looks like I'd have to cut this spring too in order for the valve to function.

TS gets away with it because idiots like this guy think the compressor surge he's hearing is somehow an "upgrade."

https://youtu.be/Xi3V5VFkwQ0?t=109

 

[mountainhorse]

Those springs look really beefy to me... no wonder the high seat-lift vacuum.

An automobile engine... no problem with that vacuum.. in the normal range... in a 2 smoker twin... DANG !!!



.

 

[Rosslbz]

One more thing that can be a contributing factor to compressor flutter, make sure the vac line itself is big enough. I remember this being and issue I ran into on a street bike. In that picture of the reed cage, that vac/boost source looks small.

 

[mountainhorse]

My thoughts too Ross... From post 33 above.

How big is the hole in the fitting? what is the ID of the hose... and is there any restriction or pinching in the line?

Also wondering what is the ID of the vacuum reference and is it possible that the fitting on the reed side of the TB's is somehow restricted...or maybe has a undersized thru-hole in the fitting (not letting enough volume of air to move through the CRV reference hose??)





.

 

[mountainhorse]

Which begs the question... Is the comment

" It was only pulling -1 to -2 InHg at idle and -3 to -3.5 InHg when chopping the throttle"

A good representation of NORMAL vacuum in an 800 CFi-HO engine?

Has anyone else pulled a vacuum test like this one?









.

 

[tangerine_sky]

My thoughts too Ross... From post 33 above.

How big is the hole in the fitting? what is the ID of the hose... and is there any restriction or pinching in the line?

I'm not sure of the tube diameter off the top of my head, but the hose mates up to the stock CRV without a step down and has the same size nipple in the reed cage. With that being the case,especially considering they use them on cars which pull a lot more vacuum through the same size nipple/tubing with a lot longer hose (volume), I'd assume the tubing size is not an issue.

Also, there are no aggressive bends or pinching in the vacuum hose.

 

[tangerine_sky]

Just FYI the TurboSmart valve is a pos. I originally thought my vacuum pump seals might be leaky but after testing, that is not the case. When I hook up the TS valve to the vacuum pump it immediately starts to leak down rapidly.

I would avoid their products based on this experience. I would not recommend anyone try to run one on the MTNTK kit.

Here's a video demonstrating the valve leaking like a mf.

<iframe width="560" height="315" src="https://www.youtube.com/embed/c2UH65iN78w?rel=0" frameborder="0" allowfullscreen></iframe>

https://www.youtube.com/watch?v=c2UH65iN78w

 

[mountainhorse]

Is the o-ring on the cap still intact?

Thank you for all of the follow ups.


.

 

[sledhead9825]

Is it just me ? Or does it sound less responsive after the spring was cut? Listen to video 1. Don't take me wrong, I am not bashing and maybe its just the way it comes across in the videos.

 

[mountainhorse]

Sounds crisp to me... Waiting to hear back on the ride report though.


.

 

[Davajn]

Is it just me ? Or does it sound less responsive after the spring was cut? Listen to video 1. Don't take me wrong, I am not bashing and maybe its just the way it comes across in the videos.

Only way to be really sure is to datalog runs with std spring and a cut spring. Just hearing and guessing from a videoclip aint accurate.

 

[tangerine_sky]

Ok I rode it up in the mountains for the past 2 days and it seems to be just as responsive if not more so when on/off throttle.

It still has flutter at times but it's about 10X better. The frequency, duration and intensity of the flutter is way lower when it does occur.

Seems to flutter more at 8000'-9000' vs 5000' .
My current theory is that the motor does pull slightly less vacuum as altitude increases.

Also, on all the BOV setup information I've read they tell people to set the spring tension to open the valve right at or just a hair above idle vacuum. This would make sense given the BOV functioned in a lot more situations when I have the spring tension set to actuate at -3 inHg vs the -6.5 inHg the stock spring was set at. So, ideally I'd have a custom spring made that actuated around -2 inHg to completely resolve the compressor surge.

The only downside I see is that it might stay open longer when chopping the throttle, which could cause it to build boost slower once you get back on it. Or if the spring is too soft the CRV will open when pressure is built in the compressor housing (acting on the CRV diaphragm surface) before it reaches the reed cage to equalize.

As soon as the vacuum line is not seeing vacuum and/or begins to build boost again the pressure on either side of the CRV should equalize, and it should seal. It's the time delay between when the pressure begins to build in the compressor housing and when it reaches the reed cage that concerns me.

Only way to be really sure is to datalog runs with std spring and a cut spring. Just hearing and guessing from a videoclip aint accurate.

In hindsight I would have data logged before and after.

 

[mountainhorse]

Nice work Tangerine

Nice !!

Good news ... and compressor-surge is now under control.

With as small of charge-tract as this sled has... lag time of vacuum/pressure signal would be negligible IMO.

Lets see if anyone else goes to the effort that you did... and maybe have a Data logger set to monitor before and after.






.

 

[diamonddave]

With as small of charge-tract as this sled has... lag time of vacuum/pressure signal would be negligible IMO

.

Really? Respectfully I'm not so sure I fully agree especially at higher altitudes??