Haltech - 13B Flame Tune

Hey everyone,

I’m having a strange issue with injector behavior on overrun/decel on my RX7 FC and I’m trying to understand what exactly is limiting the fuel delivery.

Setup:

• 1987 RX7 FC NA 13B 6-port
• Haltech Nexus R3
• EFI Hardware ITBs
• Racing Beat full exhaust + header
• 4x Bosch EV14 injectors (550cc)
• All 4 injectors running together in a single stage (batch fire)
• Fuel pressure: 2.9 bar
• Dual Wideband + EGT installed
• No decel fuel cut enabled anywhere

Under WOT:

• Lambda around 0.88
• ~24° leading timing
• 10° split
• About 60% injector duty cycle at 7100 rpm

Could you share a copy of your tune and maybe a log for people to see? Going from your description, it could be a multitude of things; the main one that flags for me is that if you are tuning a set of ITB's your should be tuning in Alpha-N.

In the software, open your fuel map and press 'F3' or right-click and select 'table axis setup ' change the MAP value to TPS and reset your axis value to 0%-100% at 5% increments

Thanks for the suggestion.

I'm already tuning the car on TPS (Alpha-N), not MAP. I've attached my latest map and log.

The car runs great in all conditions. The issue only shows up when I try to add excessive fuel during deceleration. Even with large VE changes in that area, injector pulse width stays around 1.7 ms, and decel fuel cut is disabled.

Any ideas what could be limiting the fuel delivery?

The tune you've combined with the log are significantly different with regards to decel VE table and a few other things. I don't particularly care/try to rig a 'flame' tune on any of the race rotaries I support but I can say a few things that certainly aren't doing you any favors:

Your log shows you're at WOT for very short stints and a very low redline, leading me to believe you're not actually generating all that much heat/hot exhaust.

Split - more split = a secondary 'cleanup' ignition event. Yours seems to be at ~20*s on decel.

Timing - again, I don't seek out any sort of flamey pops and bangs but even 10*s is probably advanced enough on a rotary to be a somewhat complete burn on decel.

When driven in anger most high overlap (ported), free flowing and peripheral exhaust port rotaries will do what you're asking for with relatively little fuel to the point where I get annoyed when I can't reduce flames - though maybe leverage the zero demand fuel table to dump fuel rather than reduce.

Thanks, that actually makes a lot of sense.

You're right, the map and log aren't from the exact same revision. I've been experimenting with a few different decel fuel and ignition strategies since taking that log.

The point about split and timing is interesting. I hadn't really considered that my decel timing may still be advanced enough to get a relatively complete burn, especially on a stock port engine. What would you personally consider a reasonable amount of retard on decel before it starts becoming excessive? Are we talking around 0°, a few degrees ATDC, or even further?

Also fair point regarding the engine combination itself. Being a stock 6-port with a 7500 rpm limit, it's obviously not generating the same exhaust energy as a peripheral port race engine. That said, shouldn't I still be able to inject as much fuel as I want if I keep increasing the VE values? That's the part that confuses me. Did you happen to notice anything else in the map that looks unusual or could be contributing to this behavior?

I'll have a closer look at the zero demand fuel table and see what effect that has. Thanks for the input.

As I said, I don't tune for pops, bangs or flames. I tend to run close to the 40s on 'high' vacuum/decel - I've also just noticed you're running TPS as your load axis for ignition angle, I'd certainly swap to MAP there.

Attached are a recent quick and dirty timing maps of a track car that made 300 to the wheels on a set of Dyna Packs I did recently - this is running a big peripheral port with MFR port timing so while I'm not suggesting you run these numbers exactly, you can see that your current map is far from optimized - the difference will be torque peak based on your porting and intake manifold. Generally 25*s at that number and high compression S5 rotors (in my case it was between 7500 and 8500) is a good place to start, with feeding a few degrees in at redline. In your config with lower comp S4 rotors it's entirely possible that you'd want 26-27 at torque peak - probably in the 6k range even with ITBs on a stock port.

You won't really know without a dyno though, its just food for thought.