Help controlling boost

My twincharged car is crazy.

Once the engine gets to around 100kpa/0 inhg my bypass valve shuts and it just goes nuts. Instant 6 psi from charger and the turbo blowing into that creates 20psi compounded boost in a second or two, with next to zero throttle movement. 

Its all or nothing. 

Im using a 38mm external turbo wastegate as a bypass valve. The large diaphragm responds nice to varying vacuum but when vacuum is gone its shut tight and I'm on a rocket! 

Any ideas on what to try to get it to behave? Some sort of drive by wire throttle body? Closes linearly to throttle position.. 

would need to know more about the setup, but a couple of observations.   The supercharger is going to be sucking in the intake side of the turbo generating some velocity before the turbo is even in use.  My first thought is the turbo is too small for this kind of setup, a larger turbo would spool slower.  Ideally, I would think you want the turbo sized in such a way that it is in its peak efficiency as the supercharger efficiency falls off. A turbo too small it going to do exactly what you are talking about.  

The other possibility is that the wastegate is not functioning effectively or the the wastegate bypass path is not large enough.  This might be alleviated by porting the bypass path.  My advise would be to disconnect the external wastegate all together and run it like a "hater pipe" for testing.  That should, theoretically, make the turbo generate a trivial amount of boost.  If you are still getting crazy boost the turbo is too small.  if it becomes more manageable you have a ineffective wastegate setup.  

Wait... just looked at your picture... What turbo is that?  What is the function of the wastegate mounted on the intake side of the turbo? Can you provide a picture of your turbo wastegate setup?  

Isn't "All or nothing" kinda the point of that setup?  If you want it to be civilized, take one of the two blowers off.

air filter > bypass outlet > turbo compressor > W2A IC > supercharger >  FMIC > bypass inlet > throttle body

Turbo is a h1c holset with a large 18cm exhaust housing and a 44mm wastegate.

Charger is an Eaton m62 at 2:1 crank speed

Bypass is a 38mm wastegate with a really weak spring that opens with closed throttle vacuum

I need a valve thats not so on and off.. More progressive if possible..! 

NordicSaab said:

Wait... just looked at your picture... What turbo is that?  What is the function of the wastegate mounted on the intake side of the turbo? Can you provide a picture of your turbo wastegate setup?  

I have 2 wastegates. One as normal on turbo the other is like a BOV.

Wow, OK.  You forgot the kitchen sink. 

The H1C is too small for this kind of setup; an HX40 would make more sense.  Remember the goal of a compound setup is to have the turbo come on as the supercharger is falling off.  Also, Holset turbo are notorious for having wastegate passages that are too small for gasoline setups.  Porting may help your problem. 

I think my advise of disconnecting the wastegate and seeing how it behaves would be my first action.  

Streetwiseguy said:

Isn't "All or nothing" kinda the point of that setup?  If you want it to be civilized, take one of the two blowers off.

The whole point is to compound boost beyond turbine housing back pressure. Which its doing rather nicely!

NordicSaab said:

Wow, OK.  You forgot the kitchen sink. 

The H1C is too small for this kind of setup; an HX40 would make more sense.  Remember the goal of a compound setup is to have the turbo come on as the supercharger is falling off.  Also, Holset turbo are notorious for having wastegate passages that are too small for gasoline setups.  Porting may help your problem. 

I think my advise of disconnecting the wastegate and seeing how it behaves would be my first action.  

 

 

 

I want the 2 adders to work together, once the supercharger is falling off, its getting to the end of its effiency range, then I should spool the turbo into the the near out of puff supercharger? That's gonna get messy!! 

My exhaust turbine doesnt have a wastegate. Im using an external 44mm. You can kinda see it in this pic..

This is the kind of project that I think is REALLY cool. I wish GRM would do more tech articles on things like this. Not every issue but every now and then. 

dean1484 said:

This is the kind of project that I think is REALLY cool. I wish GRM would do more tech arrivals on things like this. Not every issue but every now and then. 

Well I have to be doing something either over complicated, unique or stupid.. Or all 3.

if I could only  control the bypass a bit id be real happy. 

In reply to Craigorypeck :

I'm not sure what you are saying in the above post.  Maybe we need to attack this another way... What are your goals with this setup?  Linear power band? Insane boost?  Insane HP?  

I only know of x2 reasons to build a compound setup: 

1) to even out a power band that utilizes a small supercharger for low end grunt and a big turbo for mid range power 

2) To build big power with very high boost 

I assumed that you were looking for an even power band with a consistent 10-14 PSI.  Is that what you are attempting to accomplish?  

I want to build a car I can daily to work and put down a sub 10 secs at the track... Same as everyone else no!!??

Your option 1 is normally a parallel type system where one adder works until the other takes over and bypasses it.

Im probably in your option 2 catagory with 20psi to start.

Turbo blows into supercharger. Boost is compounded. Both adders work together.. 

I can have my ecu pwm my turbo wastegate solenoid so total boost can be adjusted.. Commute vs competition 

All im trying to do is make it behave. Some sort of electronc bypass valve instead of the mechanical on/off action of the bypass wastegate. 

Ive seen electronic wastegates but those are for internal gates. Are there electronic external wastegates?? 

Couple of things I noticed.

What were your reasons for choosing to set up your twin charger in series as opposed to parallel?

You're using a 38mm waste gate in a non-conventional way, so it might not respond the way you'd like/expect. Also, 38mm is quite small and as such not really an efficient bypass Which may be causing some of your issues. The bypass isn't just there to reduce/remove the boost that the s/c provides, it's also there to bypass the restriction that the s/c becomes once you hit high rpm/high turbo boost. Trying to feed the turbo through an out of puff s/c and a 38mm hose seems counter productive

What size is the inlet and outlet plumbing on the s/c? I'd be looking to run a bypass that is as close to the same size as possible so it can function as it should ie' allowing the s/c to be bypassed as it runs out of steam. 

Turbo sizing is so important when twin charging. To small and it will be boosting to early, to large and your left with a hole in the powerband. Do you know at what point in the rpm range the s/c is dropping off? What point does the turbo start producing useable boost above that of what the s/c can provide?

In reply to Craigorypeck :

Ok, starting to get a clearer understanding. If you are I  the second category or big power/boost. 20psi as a starting point seems to be a good place to start. 

So, when you say "behave" what does that mean? Come on more smooth? Lower base boost? 

Based on your setup, my guess is the turbo spools really soon and hits like a heart attack. A larger turbo would be easier to manage. 

The turbo isn't there to take over from the S/C.  The S/C is a roots blower.  Sized and pullied properly, it's just like a bigger NA engine.  So the turbo feeding into the S/C isn't the hard part here. 

The issue is the bypass valve to keep the supercharger out of the equation at very light throttle.  It sounds like when the bypass closes and lets the blower start working is also when the turbo is starting to spool.  Then once the blower is helping to move more air, the turbo spools and it all comes up really fast. 

I'd be tempted to either try running it without the bypass or to have the bypass close a bit earlier (before 0 psi).  Is the throttle plate before or after the supercharger? 

A more progressive or electronically controlled wastegate solenoid might help:

http://www.minimopar.net/perf/wcv-multi-eepc.html

granted, this can also be controlled by the MegaSquirt with a few minor changes.

That said, a larger turbo probably isn’t a bad idea for this setup.  You’ll still want to have tighter control over the various wastegates or bypass valves (reverse wastegates, essentially)

In reply to daeman :

Your getting the wrong end of the stick i think... Lets pretend this is turbo only and my bypass wastegate is a BOV.. Thats basically it but theres a super charger after the turbo. 

air filter > bypass outlet > turbo compressor > W2A IC > supercharger >  FMIC > bypass inlet > throttle body

Its very simple. I'm not bypassing the super charger at higher revs.. Both adders work together.. im bypassing boost at closed throttle/part throttle events judt like any other boosted setup. Superchargers require a bypass to be open at idle.. Its when the bypass closes i get issues. Like being rammed by a truck from behind! 

The reason for all this is to see what happens when I compound the boost beyond the turbo back pressure...  I have no restriction at the exhaust valve... No residual gasses hanging around. A full cylinder of fresh boost. Less prone to detonation, more ignition timing. I'm running on regular gasoline with no signs of pinging. That in itself is a win imo. 

Plus someone said i couldn't do it.

NordicSaab said:

In reply to Craigorypeck :

Ok, starting to get a clearer understanding. If you are I  the second category or big power/boost. 20psi as a starting point seems to be a good place to start. 

So, when you say "behave" what does that mean? Come on more smooth? Lower base boost? 

Based on your setup, my guess is the turbo spools really soon and hits like a heart attack. A larger turbo would be easier to manage. 

Youre on the right page now smoother transition onto boost. If I'm cruising at say 2700 rpm.. Everything is spinning and reafy to go. As soon as I hit 0 inhg thr bypass closes and all hell breaks loose! 

I enjoy it in a straight line with no traffic.. but this could have me going backwards on a corner easily.

Progressive entry to boost is the target... 

rslifkin said:

The turbo isn't there to take over from the S/C.  The S/C is a roots blower.  Sized and pullied properly, it's just like a bigger NA engine.  So the turbo feeding into the S/C isn't the hard part here. 

The issue is the bypass valve to keep the supercharger out of the equation at very light throttle.  It sounds like when the bypass closes and lets the blower start working is also when the turbo is starting to spool.  Then once the blower is helping to move more air, the turbo spools and it all comes up really fast. 

I'd be tempted to either try running it without the bypass or to have the bypass close a bit earlier (before 0 psi).  Is the throttle plate before or after the supercharger? 

Yeooo! The mans got it.. 

Throttle plate is after supercharger, right on the inlet manifold. See I can be cruising at high rpm and be in a vacuum which keeps the bypass open. But once i get to near zero inhg and the really weak spring in my wastegate overcomes the dwindling vac, everything is spinning fast and ready to go it just ploughs into megaboost in an instant. Its fun.. Don't get me wrong!

I have the largest exhaust turbine I can find for this holset. 18cm.. 

Stefan said:

A more progressive or electronically controlled wastegate solenoid might help:

http://www.minimopar.net/perf/wcv-multi-eepc.html

granted, this can also be controlled by the MegaSquirt with a few minor changes.

That said, a larger turbo probably isn’t a bad idea for this setup.  You’ll still want to have tighter control over the various wastegates or bypass valves (reverse wastegates, essentially)

I have ms3 pro so can control some sort of valve.. Ill have a look at that. Sounds like what I'm after... Thanks!! 

What is controlling the bypass wastegate and what is controlling the actual turbo wastegate?

The turbo shouldn't build any significant boost unless it's own wastegate is shut. I think most wastegates are shut to start and open at some specific boost pressure. Can you use the engine control to keep the turbo wastegate open until a bit after the bypass shuts? Like if bypass shuts as soon as throttle opens 10% can you have the computer hold the wastegate open until throttle hits 25%?

Or maybe it is just as simple as having a small vacuum line or something 'bump' the turbo wastegate open for a moment as the bypass shuts?

I think your setup is doing exactly what it is supposed to be doing. So, that's a win. 

The only solution I can think of is a larger turbo. The H1e is a nice size turbo for a 4 cylinder, but the SC, like stated earlier, is going to make your engine behave like a larger displacement engine. 

I think an HX40 is in your future 

Robbie said:

What is controlling the bypass wastegate and what is controlling the actual turbo wastegate?

The turbo shouldn't build any significant boost unless it's own wastegate is shut. I think most wastegates are shut to start and open at some specific boost pressure. Can you use the engine control to keep the turbo wastegate open until a bit after the bypass shuts? Like if bypass shuts as soon as throttle opens 10% can you have the computer hold the wastegate open until throttle hits 25%?

Or maybe it is just as simple as having a small vacuum line or something 'bump' the turbo wastegate open for a moment as the bypass shuts?

The bypass wastegate is plumbed with MAP to the top side of the diaghphram 

The turbo wastegate is referencing compounded total boost after the supercharger. So it remains shut until I'm hitting desired compounded boost, even though its actually only producing around 12psi. 

I did try running a MAP line to the upper side of the turbo wastegate with no spring installed, and have it work similar to the bypass with bottom side open to atmo.. This worked pretty well as the wastegate remained open until it saw positive pressure to the top of the diaghphram.. Problem is it just keeps on boosting with no cap on final boost made.. That could get messy very quickly!! 

NordicSaab said:

I think your setup is doing exactly what it is supposed to be doing. So, that's a win. 

The only solution I can think of is a larger turbo. The H1e is a nice size turbo for a 4 cylinder, but the SC, like stated earlier, is going to make your engine behave like a larger displacement engine. 

I think an HX40 is in your future 

yes I presume my turbo thinks its attached to a 3.3 - 3.5 liter engine..

I might port around the exhaust turbine housing exit...