Discussion and questions related to the course Understand AFR
I work on a Time Attack GTR34 at the moment with HKS 2.8l Step 2 and a Full Race/EFR8374 Turbokit. The Ecu is a Haltech Elite 2500.
This is my first time which we use Nitrous. We fixed a 12kg Nos bottle with a Single Solenoid and a Nozzle before the Nismo Plenum. My plan is to inject the Nitrous from 3500-6600rpm to improve the spool. On MBT i would reduct the nitrous solenoid duty to limited the torque.
Beside the timing retard (basic rule, -2 degree per 50hp),whats is the right AFR target under WOT/Spool with Nitrous...
...with 98 octane pump fuel?
Additional i installed a Wather/Meth system too. My idea was to improve the octane ratio from the E85 under Nitrous conditions and to program a compensation map, RPM vs IAT. As soon the IAT is to high, the pump will start to inject the Wather/Meth.
By the way, it is necesarry to install a Purge Valve if we use Nitrous?
...and sorry about my English, this is not perfect at the moment.
Generally I target the same sort of lambda values with nitrous as I do with a turbo engine. You do need to consider how large a shot you're using though. Just as you'd tune richer for an engine running 25 psi than one running 5 psi, you'd run a richer lambda target with a 200 hp shot compared to a 50 hp shot.
I also find that E85 and pump gas normally work pretty well at very similar lambda targets. In fact often you can choose to tune a little leaner on E85 since the cooling properties of the fuel are so much better. There isn't a specific number that I can give you that will work for every engine and every application but I'd start around 0.80 under full load and test to see what works for your combo.
I'd be very surprised if you will need WMI with E85. E85 has a very high effective octane rating and the cooling properties of the fuel are exceptional.
A purge valve is useful to clear liquid nitrous from the lines before a run. It's not essential but without one you may find that the very first hit may be a little doughy until the lines are cleared.
Thanks for the feedback.
My plan was to run the RB28 between 11.6-11.9 (E85) under WOT @ + - 1.8 bar boost.
About the knock detection, with E85/Nitrous. The last time which i tuned a EVO, i started with 98 pump gas, it was no problem to find MBT and the knock limit with my head phones. Then i switched to E85. At once was very hard to hear the knock limit with my KS4 knock detection (the plex system is already ordered).
Do u have any tips (or other systems) to increase the knock detection with E85?
And make Nitrous the knock detection more hard again?
Assuming you're using a wideband that's scaled for a pump gas stoich (14.7:1) then your target is reasonable. The problem with E85 is that often you won't be able to make the engine knock. From my own experience on an EVO engine with a compression of 8.5:1 and a reasonable sized turbo, you would almost certainly be able to reach MBT without any knock at 1.8 bar of boost. Our 86 with a factory compression ratio of 12.5:1 will still knock on E85 though and it's audible using both the Link G4+ knock block and our Plex Knock Monitor. Ultimately it may just be that you are nowhere near the knock threshold at the boost you're running.
Nitrous is likely to make the engine more prone to knock due to the increase in cylinder pressure but it's really similar to the effect you'd get by running a higher boost target - You'll need less timing to reach MBT and the engine is more likely to knock.
Thanks Simon, a very helpfull answer!