Anti-lag and ignition timing

[Retracnic]

Over the past few weeks I’ve been developing an anti-lag (or bang-bang if you prefer) system. This is my first attempt at such, so bare with me if you will. The system consists of a stepper motor used to adjust throttle position, a bank of secondary injectors, the ECU and 2 driver selectable toggle switches. Switch A is a 3 position toggle selectable between OFF, AUTO, and MANUAL. In AUTO mode the ALS will engage when certain parameters are met within a specific RPM window. MANUAL engages the ALS on demand regardless of parameters and OFF is self explanatory. SWITCH B is a mode selector between SOFT, NORMAL, and AGGRESSIVE. Ideally this switch will toggle the ECU between the appropriate fuel /spark maps for the desired level of ALS. Which brings me to my problem.

This being my first attempt, I began by pretty much copying an existing aftermarket ALS system. This system employs a flat amount of ignition retard and fuel enrichment. Using the same technique I was able to a get a working system. I would now like to add a bit more finesse to the system. My plan is to tune for the most aggressive mode, then progressively back off for the other 2 modes. My question is this:

For the most aggressive anti-lag setup, roughly how many degrees in crank rotation should I let the charge burn in the cylinder before opening the exhaust valve?

I know I can find this information out through testing, but money is a concern. I would like to go into the next tuning session with a better starting point. Having cooked two turbos and burned through an exhaust manifold so far, the price of this project is mounting. But I must admit, the first time I saw the car speed away, bang into second gear and go CRACKLE-POW!!! I got a big grin on my face, pointed and proudly proclaimed “I made it do that!” Sorry, I’m a geek.

Any advice would be more than appreciated.

Bryan Carter

 

[GregLocock]

Buy an exhaust gas thermocouple! 25 bucks at a rough guess. The more instrumentation you have in your car, the geekier it is. You could even hook it into your ALS.

http://www1.jaycar.com.au/productVi...=&keywords=thermocouple&SPECIAL=&form=KEYWORD

&ProdCodeOnly=&Keyword1=xxxxxxxxxx&Keyword2=xxxxxxxxxx&pageN
umber=&priceMin=&priceMax=&SUBCATID=

Sounds like a fun project, if slightly insane.

Cheers

Greg Locock

 

[Retracnic]

Greg,

We’re already making use of an EGT. The EGT controls the automatic cutoff for the ALS system. But thanks anyway.

As far as the insanity factor goes, I would agree. The vehicle in question is just a test mule, and not intended for racing purposes. A couple of years ago, a few guys set out to develop an aftermarket stand-alone ECU that would offer more flexibility, and easier configuration than current offerings on the market. Somewhere along the way I got roped into the madness. During development one common request we have gotten, from those testing prototypes, is to integrate an anti-lag system. So we’re learning the hard (and expensive) way. Once again, thank you for the advice.


Bryan Carter

 

[grogg]

sounds like fun?
need more info- what size motor and what spec turbo.
how much boost and when you say lag, what rpm is the lag at, and what is max rpm.
is the head modded.

 

[SWTRacing]

Bryan,

Your system sounds interesting. How much ignition retard did you start with in your initial testing? I'm looking for a way to decrease spool time on the starting line. The car is a drag race only car with a transmission brake, so I'm only looking to integrate a simple system into my transbrake button since I'm blowing through a carburetor. I was thinking of a standard retard switch, combined with fuel enrichment. Just looking for a place to start.

Thanks,

Andrew Slater
SWT Racing/Hangar18 Fabrication

http://home.socal.rr.com/swtracing

http://www.hangar18fabrication.com

 

[Retracnic]

SWTRacing,

In our initial tests we used anywhere between 20-25deg of ignition retard. The stepper motor is used to hold the throttlebody open to about 25%. Fuel is enriched by utilizing a dedicated fuel map that is calibrated to run an AFR of about 9:1.

When the ALS is active, the engine ‘idles’ at 2700RPM and makes about .3 bar (or ~4.5 lbs) of boost at idle. When the ECU detects a wide open throttle condition, the ALS is shut off and normal parameters are engaged.

For now, our anti-lag project has been put on hiatus due to mounting costs. If you want to play with an ALS, I would suggest looking into one of the commercially available systems. Also keep the following considerations in mind:

1.Only use an exhaust manifold specifically designed for ALS use. Thin-walled tubular style manifolds will simply burn through. Think log, think cast iron, think really thick.
2.Watch your EGT. Exhaust gas temps will skyrocket while the ALS is in use. In tests we have seen an 800F climb in temperature in a matter of seconds.
3.Finally, get a good deal on turbos. See if your local turbocharger supplier offers a bulk discount. Simply telling him you are thinking of using an ALS will put a smile on his face. Saying ALS is hard on turbos, would be an understatement. “Hey guys! I think it’s working!!” WOOOOSHHH-TWEEET-SCREEEEE! “Hey… what’s that noise?”


After playing with ALS, I have come to a conclusion: Those videos of cars that have the whole exhaust manifold and turbo glowing red hot… is real cool when you’re not the one writing the checks.

Good Luck,

Bryan Carter

 

[ShaunT]

Off the subject of ALS, advancing the cam will reduce spool time. Also, the exhaust valve should opena round the 65-85* BBDC mark. Depending on the desired application, this will put you in the ball park.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

 

[SWTRacing]

Thanks for the info Bryan. I'm not looking for anything sophisticated. I may just pull a few degrees of timing while on the transbrake.

Shaun, thanks for the advice. I currently have my cam advanced 6° (installed on a 108° intake centerline on a 114°LSA). If I recall, exhaust opening is at 56° BBDC.

My plan at this point is to install a good set of rear disc brakes and start spooling in the pre-stage beams. Once I get 1 or 2 psi, I can bump the car into the staged beams, engage the transbrake and got to WOT.

Andrew Slater
SWT Racing/Hangar18 Fabrication

http://home.socal.rr.com/swtracing

http://www.hangar18fabrication.com

 

[Retracnic]

Andrew,

I would not prescribe a true ALS system for drag racing. There is a simple logic to it. Once you know your opponent is running ALS you can screw him coming out of the hole. Since ALS works on a fixed timeline, by delaying or rushing the staging, the other driver can insure that you are off-boost when the tree drops. A local shop campaigned a fairly successful drag Supra equipped with ALS. More than one sharp driver was able to beat them using staging games.

If you are in a class that allows multiple power adders, I would suggest using a modest shot of N2O. Nitrous oxide injection makes for an excellent 'anti-lag in a bottle'.

If you can't run nitrous oxide, then go ahead with your plans to add ignition retard. I would suggest firing the plug about 35-50 degrees before the exhaust valve opens. You'll have to play with it bit to find a good balance between anti-lag effect and EGT. Depending on your cam profile, this can be significant amount of ignition retard. This is going to dump an excessive amount of heat energy into your exhaust. It is likely that your setup will not tolerate this sort of heat for more than a few seconds.

Dropping out the timing alone is more gentle on the turbo, but it gets things really hot and doesn't spool the turbo as fast as a true ALS system. And of course if you're up against a driver who knows his way around, he'll take note of your severely off timing and try to put it to his advantage. Yet another reason N2O can be a superior anti-lag agent where class rules allow it.

Good Luck

Bryan Carter.