Cold-side boost control
 

thought this was interesting; Turbosmart took their electronic straightgate 50mm butterfly wastegate valve and converted it to control boost on the intake cold-side for high power drag racing applications by allowing the turbo to run/hold at max allowable shaft speed and then controlling the boost/flow that the intake manifold sees (electronic BOV that is not simply on/off, controlled boost “leak”) rather than using an exhaust wastegate valve

https://www.turbosmart.com/boostgate50-is-here/

my mind got boosted up and spinning :suspect: and I can possibly see it being applied in other areas as well …
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Folks do this with smaller DBW throttle bodies as well. Mount it on the IC end tank and bleed of excess pressure as necessary.

The obvious issue is over spooling and grenading your turbo. This is the reason it's done on the exhaust side traditionally. You would definitely need to monitor compressor speed.

Usually used to stay on the stable side of surge line on the low flow side of the compressor map while staging drag cars. Massive power loss and temperature issues running the turbo flat out, generally not possible at stall rpm either on auto cars if the turbo is big enough to bother doing it.

^^I get it now, but wasn’t aware of it previously especially for a blow-off valve, per our recent discussion in your own aftermarket BW TT thread.

Though it seems to me a rally style fresh air ALS setup would make more sense. So maybe the FA-ALS pre-dates that method, but was less common then.
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I have like zero real life experience with this haha, but my thinking is this is good for drag racers during staging with throttle on but managing boost for launch. and ALS still might be better for its application of constantly going on during off throttle to keep spool up on turns and braking.

^^particularly for premix applications where the off-throttle fuel cut is turned off and dumping fuel into the manifold - ding-ding-ding

the primary difference being venting it to the turbo manifold rather than dumping to atmosphere. Both require monitoring and controlling turbo shaft speed.

which the advent of the electronic valve version allows finer control of the aggressiveness level wrt turbo durability.

in reality very few people have direct experience with it, and the few who do aren’t blabbing. The basics are easy to locate, but the devilish details are not simply googled up for all to see.
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^^I forgot to mention that the FA-ALS also serves as the BOV, but as with the additional drag style DBW TB, it diverts the intake air to the turbo manifold rather dumping it to atmosphere.

and for anyone possibly not comprehending what instant boost means at every tip of the throttle


RIP Ken Block 🙇‍♂️
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It also means your max flow is 100% dependent on the exhaust housing size, so you'll likely need to run a much larger housing than you would with a traditional wastegate. No problem with a drag car, but not great for everything else.

As soon as you dump boost, you have less exhaust flow, slowing the turbo. I don't think this adds any over-spin issues to the equation.

FA-ALS comes with its own set of challenges, sure is cool though. My favorite anti-lag setup is the Beattie hill climb car, uses a small helicopter turbine hooked up to the hot side to give boost at any RPM even with the engine off :)

Subaru WRC antilag was similar to using a helicopter emergency power unit turbine except it used a pulsejet stage instead of jet turbine in the exhaust between the engine and turbo.

https://cimg1.ibsrv.net/gimg/www.rx7...411d4f0b29.jpg

The rotary would be very well suited for this pulsejet ALS as it can run and make good power at very rich AFRs ( fuel for the pulsejet) with a good enough ignition system.

Can even be used Naturally Aspirated on a rotary as an post pulsejet exhaust ejector/pre pulsejet low pressure exhaust scavenge.


https://cimg4.ibsrv.net/gimg/www.rx7...c402510643.png

yeah, that’s the rocket device, it presents a more difficult control situation. Most have moved away from it to the FA-ALS setup instead for that reason.

mr2peak, I’d suggest you do some more research. The main concern of these devices is to prevent them from going out of control. They’re essentially a self feeding loop and can do that easily without the proper monitoring sensors, controls, and safety strategies in place. The only reason to run a larger housing is for more power at the top end without sacrificing the low end.

The device keeps the turbo spooled up at a certain speed rather than letting it wind down. There’s not much load on it in that scenario, basically it’s free-spooling wrt how much energy it’s being fed. Which greatly reduces the need to rev match when shifting. It’s a bypass throttle body control strategy that removes the engine from between the two.

Think of it this way. You’re braking into a slow corner where the engine might drop down 3,500 rpm at the slowest throttle application point, but the turbo is being kept spooled up as it were at the 6000 rpm point. It only engages there for a short period of time coming out of the corner and then the ALS strategy completely drops out as it if didn’t exist, until the next shift or corner slow down.

It really comes down to how much power you can put down effectively for the application and rule constraints. What you stated above is not entirely accurate. There’s also the launch boost advantage when that’s applicable as well. Which again, the aggressiveness of the system can be adjustable when configured as such. In that regard, a smaller housing may need less compared to a larger housing.

It only maintains a partial loading under certain circumstances depending on the control strategy and mode. The flow capacity of the housing doesn’t enter into it as you suggested.
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rx8 you misunderstood my comment.


Talking about cold-side boost control here


This part is about anti lag

Intake side only wastegating is moronic for 99.9% of applications. Less efficient, more heat generation.

Apart from drag, it could be nice to use as a "pop-off" type valve for safety in overboost if you have a wastegate failure. Would need to be on its own circuit to be useful

Most ECUs cut fuel and/or spark to prevent overboost, I think even a PowerFC can do it. That can accomplish the same goal without adding parts. More parts are more potential points of failure. On a drive-by-wire car, the ECU can close the throttle to avoid overboost. There's a good example posted here: https://www.rx7club.com/link-vi-pec-...ottle-1158807/

And for the fresh-air antilag fans, even if you like the broken-engine misfire sounds you might not like how it affects the maintenance schedule for turbochargers and exhaust manifolds. Antilag is only done on the big-budget rallycar builds, from what I hear it's not something most privateers would be able to afford.

Unless those other safeguards fail, or take too much time to react, or aren't configured properly.

All limiters should be implemented before before the starter solenoid is ever energised. If ecu load sensing fails your engine is gone anyway. If you want a reliable intake side pressure limiter it should be a dumb, single pressure interface (ie only the underside of the valve) relief valve anyhow, not something more complex, if you are scared of runaway boost.

Very few things take effect more quickly than a fuel or spark cut. If the ECU measures manifold pressure slowly or reacts slowly to dangerous conditions, IMHO that's a compelling reason to switch to a better ECU. And if the tuner configures things improperly, IMHO that's a compelling reason to switch to another tuner.

I think the compressor surge situation sounds like a good justification for adding parts to a system, and it might make sense to configure it to be used as another method for avoiding overboost if you've already got the parts installed. But I wouldn't add parts as the primary method of avoiding overboost.

apology for my error mr2peak, wish I could edit that out 😅

it seems to me there are a number of misunderstandings being stated above

perhaps some of you are thinking of the earlier ALS strategies than ran the additional air through the engine rather than the latest fresh air strategies that bypass and remove the engine from the equation to put air directly into the manifold.

and having mentioned it several times, but now another; the aggressiveness can be adjusted and this plays a large role along with many other factors on the durability factor. It can even be streetable and you won’t be lunching on turbos daily.

Running any turbo continuously at or near max allowable shaft speed is going to take it’s eventual toll, but there’s a lot of benefit to having it without pushing the turbo so hard as some top competition rally cars may.
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Those single "dumb" pop-off valves have been used in race series that have a limit on allowable boost. Seems they have been less than reliable, and it's either open, or closed, no actual control. Cold side e-gate gives more control, and could be set up as a separate system. Is it worth it to you? Probably not.

lol no worries

How many forum users are running full chassis methol cars with turbos bigger than the engine that actually need to ride the surge line on the 2 step/launch limiter? Likewise actually running very large turbos on rally cars where a partial throttle stop/bypass and enrich/retard isn't enough to keep it spooled? Very few places you can run old school rally cross spec cars these days.

I live in Thailand nobody is gonna stop you over a massive turbo. Shit, I see pickup trucks with hood dumps on the street on a fairly regular basis.

Just because you live somewhere you can’t do it, doesn’t mean other people have the same restrictions.

But yes, limited application. But, we are the tuner crowd, and we love to push limits

8374 is pretty much right on that surge line, plenty of people here running one

yes, and increasing the shaft speed moves the data point on the map away from the surge zone
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