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DIY Inlet Bypass Anti-Lag? Discuss...

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DIY Inlet Bypass Anti-Lag? Discuss...

Old 10-13-2011, 11:05 PM
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Default DIY Inlet Bypass Anti-Lag? Discuss...

Anybody around here attempted this? Instead of conventional bang-bang style antilag that retards timing and lets additional air into the intake manifold when you are off the throttle, this method uses a valve to bypass air from the turbo compressor right into the exhaust pre-turbine. Then additional fuel is introduced from the engine running rich or from some kind of injector in the exhaust. The exhaust acts as a combustor and spools the turbo like a jet engine. Its much less destructive than bang-bang style antilag. Prodrive has a version of this system aptly named the 'Rocket', which will allow the car to launch at 1800-2200 RPM with 47 PSI!!!! Amazing!

Here is a video of bang-bang:

Here is a video of the inlet bypass system (WATCH THE SUBARUS LAUNCH - the other cars do not use it to the same extent):

I want to get something going on discussing/constructing a functional system like this for a road car, DIY style.

For the valve, a proper large-bore PWM valve would be preferred for adjustable flow, however this is almost definitely out of our budgets. Large 2" bore electrical solenoid valves can be had on ebay for less than $50. They may not be able to be PWM controlled, but an OFF-ON valve can work just fine most likely. As for the piping, your average HMT DIY style hack and slash piping weld job can suffice.

The only real variables here are introducing the additional fuel, controlling it all, and making sure the reaction is taking place before the turbine, and not after it.
Lets address them:
  • Introducing additional fuel: Temporarily running the engine rich (10.5:1) may be enough. For this I would just program a standalone ECU to switch fuel maps when an input is switched. I know, I know, standalones are too rich for your blood. If electrical modification of the injector signal is not possible, fuel pressure can temporarily be boosted, perhaps by some type of solenoid.
    If this is not enough fuel, a suitable injector will need to be used to inject fuel directly into the exhaust, pre-turbine. A nitrous injector and solenoid should work. Ive seen this style anti-lag done by using a standard nitrous nozzle to inject nitrous and fuel straight into the exhaust. It worked well, but the whole point here is to not have to use expensive nitrous.
  • Controlling it all: Rally cars using this system use sophisticated computer control to constantly monitor and change system variables. The valve is PWM controlled, the turbine speed is monitored, among other things. The system will make sure the turbo isn't over-spun and will actuate the valve to command the right boost for all situations. Cheap asses can use a hobbs switch to switch the system off at a predefined boost level. Wired in series with a throttle switch to activate on throttle positions below 10% or so, as well as an enable switch, may work. I would use the standalone ecu to set up a window with TPS and RPM and boost somehow.
  • Making sure the reaction happens at the right spot: Short of serious thermo and fluid dynamics modelling, only testing can really prove this. Should the bypass tube be closer to the manifold or closer to the turbine? Probably as close to the manifold as possible, to give the gas time to combust while travelling at very fast speeds, and also to keep the heat out of the turbine as much as possible. Should the pipe diameter pre-turbine be enlarged for a foot like a chamber to help swirl the gases? Should a spark plug be used to light off the mixture, or will the hot exhaust parts do the job? Should a flame tube be used with an injector and spark plug to emulate a jet engine as much as possible?

Like I said, discuss if you are interested.

Here is an image of the prodrive system utilizing this concept:
There was a source (do not know how reliable) telling me that this system actually used a flame tube pre-turbine to contain the combustion.

Here is the thread of the Buick guy running a giant turbo and using pre-turbine nitrous injection (basically liquid air) to spool it: http://www.theturboforums.com/smf/in...topic=135414.0
Attached Thumbnails DIY Inlet Bypass Anti-Lag? Discuss...-rocket-1.jpg  

Last edited by Bmw5002; 10-13-2011 at 11:24 PM.
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Old 11-29-2013, 07:24 AM
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Dude ! still here ? we have tons to talk about this :P
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Old 11-29-2013, 07:26 AM
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I've bult myself one of these bad boys...i mean 4
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Old 12-25-2018, 05:41 AM
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Hey! Holy cow! Totally forgot about this site, here I am 7 years later, looking into a non-destructive antilag system for my Evo 8.. Started reading this thread, had to double take when I realized I had wrote it!! 😄 What a trip! Yeah so I haven't really looked much into the system after this post, other than discovering the prodrive system was called "hyperbar". I had visions of grandeur, wanting to put this in a street car and having no money. Well here I am with a better budget and a better car, and an actual purpose other than cool factor (road racing). I would love to hear about what you've done to replicate this setup. Let me know! Cheers! 🍻

Originally Posted by vlad_rally View Post
I've bult myself one of these bad boys...i mean 4
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