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Running Lean And Severely Down On Power

Super Drager

By Super Drager,
in Engines & Forced Induction

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Super Drager Mentor

Super Drager

Posted
Posted

Hey guys, had my SAFC wired up and took it down to Unique Autosports to have it tuned. On its base run the car only managed a pathetic 120.8rwkw (down almost 11rwkw from its previous) and was leaning out fairly badly, about 13:1AFR on stock maps. SAFC was adjusted to increase fuel by 10% from 3000rpm-5000rpm and 3% at 6000rpm (12.6AFR) and the car gained 2.8rwkw :(. Got the car booked in for a smoke test at Unigroup Engineering to check for vacuum leaks, changed fuel filter today, will drop in a Twin Turbo 300ZX pump and get fuel pressure checked over the weekend. Kinda weird that the car had lost so much power yet still trapped 95-97mph at WSID only 3 weeks beforehand with nothing changed since then. Any other idea's as to why it could be running so lean?

AngryRB Grand Master

AngryRB

Posted
Posted (edited)

would you even feel the difference of 11kw.. could of been some lower octane fuel or the dyno, hows the fuel pump?

definitely need some turbo action to do that beast some justice. :yes: ive driven an NA that was much better than a twin turbo though so make sure its not clapped out.

Edited by SliverS2
Super Drager Mentor

Super Drager

Posted
  • Author
Posted

Its an NA and they usually run 11.5:1AFR stock so 13:1 is a huge difference on a stock ecu. Also i'm currently the 2nd fastest NA 300ZX on Aus300zx so its definately not "clapped out".

mad082 Grand Master

mad082

Posted
Posted

Its an NA and they usually run 11.5:1AFR stock so 13:1 is a huge difference on a stock ecu. Also i'm currently the 2nd fastest NA 300ZX on Aus300zx so its definately not "clapped out".

you should be making more power at 13:1 than 11.5:1 unless it is pinging it's head off and the ecu is backing the timing off

HR32GTS 4DOOR Community Regular

HR32GTS 4DOOR

Posted
Posted

you should be making more power at 13:1 than 11.5:1 unless it is pinging it's head off and the ecu is backing the timing off

This listen to this. You want to be as close to 14.7:1 as you can without pinging and compromising timing.

MBS206 Grand Master

MBS206

Posted
Posted

This listen to this. You want to be as close to 14.7:1 as you can without pinging and compromising timing.

Actually, no you don't.

14.7:1 will provide a perfect stoichiometric burn, ie, all fuel is used, and all oxygen is used.

15.4:1 is a good mixture for cruising on.

12.0 to 12.5:1 has been shown numerous times to be the AFR that an engine will produce it's most torque from.

At 12.5 :1 you can really hammer the timing it and get it producing maximum combustion pressure at top dead centre rather then when running 14.7:1 where it makes maximum combustion pressure after top dead centre.

MBS206 Grand Master

MBS206

Posted
Posted

Its an NA and they usually run 11.5:1AFR stock so 13:1 is a huge difference on a stock ecu. Also i'm currently the 2nd fastest NA 300ZX on Aus300zx so its definately not "clapped out".

If you're running an AFM, clean it with CO Contact cleaner.

Check your air filter too.

Make sure you're running the same oil type as last time (throw in some fresh oil with a fresh filter!)

Check your TPS is set right and sending the correct values.

Check your coolant temp sensor is reading correctly. (voltage VS temperature check)

Pull your injectors and have them cleaned and flow tested.

Have you check your fuel pressure is still good?

Is your cat all okay?

mad082 Grand Master

mad082

Posted
Posted

This listen to this. You want to be as close to 14.7:1 as you can without pinging and compromising timing.

As mbs206 said, you don't want to go as lean as 14.7:1. However, at 13:1 it should still be making good power, but if it is tuned to be at 11.5 then it is probably pinging and the ecu backing the timing off

HR32GTS 4DOOR Community Regular

HR32GTS 4DOOR

Posted
Posted

Actually, no you don't.

14.7:1 will provide a perfect stoichiometric burn, ie, all fuel is used, and all oxygen is used.

15.4:1 is a good mixture for cruising on.

12.0 to 12.5:1 has been shown numerous times to be the AFR that an engine will produce it's most torque from.

At 12.5 :1 you can really hammer the timing it and get it producing maximum combustion pressure at top dead centre rather then when running 14.7:1 where it makes maximum combustion pressure after top dead centre.

hmm this is interesting, I'll have to do some reading on this. Is this for all NA engines or does it noticeably change engine to engine

mad082 Grand Master

mad082

Posted
Posted

that is for most NA engines. to put this into perspective, the stock ecu on the missus SSS pulsar (natro sr20) runs around the high 11:1 mark in the mid section of the rev range and drops to about 11:1 at high rpm. NA's can run a fraction leaner at WOT than turbos can, but not that much.

just like turbos, natro cars still run between 14:1 and 15:1 at cruise via the o2 sensor

MBS206 Grand Master

MBS206

Posted
Posted

hmm this is interesting, I'll have to do some reading on this. Is this for all NA engines or does it noticeably change engine to engine

for petrol piston engines.

Specific engines will change slightly depending on design, but mainly the above.

MBS206 Grand Master

MBS206

Posted
Posted

Ah ok I always thought NA's could run a lot leaner than turbos. I suppose the added compression and timing makes up for that.

You can run it leaner, the difference is, lean is not where the power is made.
KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted

Once you start tuning with an SAFC you will find you want to adjust your timing as well. You could use an SITC if you can find one or if Nistunes work on N/A you would be better to do that.

Super Drager Mentor

Super Drager

Posted
  • Author
Posted (edited)

Few things done, did a dodgy fix on the Vacuum leak till i can sort some stock Intake pipes out and dropped a Twin Turbo 300ZX Pump in yesterday and took it for a quick drive tonight, Injector Duty Cycle was stable(use to get random spikes) and car felt a bit sluggish in comparison to before so i'm guessing the AFR has lowered back to stock(plus the SAFC adding more fuel in) but can't confirm till i get a wideband on there.

Edited by Super Drager

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