Air/Fuel ratio's

[SATO GTS]

does anyone know what the optimal air/fuel ratio's are for a RB25DET running 0.8 to 1.0 bar??

thanks

[blind_elk]

Optimal for any engine is 14.7:1

When you crank in some boost, seems around 12.5:1 is the leanest you should go (factory systems seem to run down around 11:1 or richer)

[fatz]

id jusst burn the thing and get a real car sato

m8

and if i lived in newcastle id by bogan whore and cruze

pete

[Cubes]

On a turbo car its pretty much spot on 12:1.

Any leaner you will notice a drop in power any richer you will also notice a drop in power but also a drop in fuel consumption.

Having a good set of spark's that can ignight the fuel better in leaner conditions also helps with the power/fuel consumption.

i.e Iridiums over coppers.

All in all we are pretty much talking hardly noticible unless you are under 11:1.

Also as a note I run a fuel pressure reg bleed kit to bring the af's in scope.

With the std fuel pump i could tune it well running 1 bar.

I slapped the 910 fuel pump in and i had troubles as the mid range was still the same but the top end became really really rich where as before the std pump started to fall behind with the fuel pressure.

So I lost power up top.

If i tuned the fuel pressure reg to run perfect AF's up top then the mid range was so lean that it would be gutless until 5000rpm and also ping slightly up until then.

This was when I had a std bleed valve on the turbo to make 15psi whcih would drop to 12psi over 5500rpm.

Since I fitted the EBC which now holds 15psi to the red line I can now tune it alot better and with a slight loss in mid range power due to it running ever so slightly lean (no pinging but) nothing like when boost was at 15psi then dropping to 12psi.

Lesson either get a Adj. Fuel Pressure reg and adj. fuel that way if you have troubles with the std pump not handling the high boost.

I'm not sure if the Fuel Pressure reg bleed kit would help fine tune the fuel pressure reg or not though.

Some one with a little bit of knowledge of the fuel pressure reg's would have to shed some light on that one.

[meggala]

joel I dont like the way you have done your fuel pressure bleed its very one dimensional.

for $250 more you could have an s-afc which would give you much better tunabilitiy.

meggala

[Cubes]

Yer it is a little rough but it is cheap and if set up it will gain some economy and power.

I'm not sure how much bleed valves are I think they are around $70-80 not quite sure plus the one way valve another 20 or so thats $100 plus dyno time..

I had Tim do it at RPM as a development type thing when he was first looking in to it.

The SAFC is a very good cheap option but.

[Jay95R33]

Wouldn't a factory computer remap be around the same sort of mark than the S-AFC etc..????

I suppose dyno time could be the killer there.

J

[Cubes]

On a R32 a factory remap is around $500 inc. all dyno time etc..

I just had a look at the turbo smart bleed valve and the cheapest they had was 100 or so..

So the simple cheapo bleeds must be at least half that you would think..

I might do the cold air intake this weekend and slap a nice filter in the std box.

See if it nets me any more RWKW's....

Probably wont but.

[adam 32]

yeh ive been told that peak power is made at 12.66:1 but thats a little lean for the street.

all tuners ive spoken to aim for 11.6-11.8:1 which may still be a little rich but its better than blowing the engine!

[Cubes]

How do these new Iridium IX spark plugs affect the performance of a motor that is running slightly lean as apparently it says that they light the mixture better under lean conditions.

Mine is ever so slightly lean for the first 1000rpm when it comes on to boost like 3k-4k due to the fuel pressure bleed. Tim said that its not a critical area and that it wont hurt it..?!?!

[Grim]

Originally posted by -Joel-

How do these new Iridium IX spark plugs affect the performance of a motor that is running slightly lean as apparently it says that they light the mixture better under lean conditions.

Mine is ever so slightly lean for the first 1000rpm when it comes on to boost like 3k-4k due to the fuel pressure bleed. Tim said that its not a critical area and that it wont hurt it..?!?!

I wouldn't recommend you remap the ECU. At least with a SAFC if you do more mods it's simple to adjust.

I'm running a SAFC and when I got it dyno tuned I still had shit plugs in that were gapped at 1.1mm. Running 12psi it kept missing so i got the SAFC tuned at 10psi and now have an AF ratio of about 12:1. I then put Iridiums in and...wow! Up top there is heaps more power at 12psi.

You dont want it running lean with boost comming on...not good for the engine.

[Cubes]

Yer I know its bad..

Tim keeps saying its not lean enough to do any damage, but who knows sit up a hill at the certian rev where it runs slightly lean with full boost and every thing will get hot and probably burn the crap out of the valves.

[2rismo]

Optimal for any engine is 14.7:1

What absolute crap. As has been mentioned already, different tuners aim for different numbers based on their engine hardware, experience and ultimate goal. Manufacturers (Subaru, Nissan et al) are notorious for releasing cars with ratios dropping at some points to low 11's to safeguard their fickle motors.

In short, get your car tuned by an expert, on a chassis dyno and make sure you have the right hardware to suit your purpose. e.g. S-AFC/pump etc.

Cheers.

[adam 32]

why not remap the ECU?!?!?!

with 256 data points (im pretty sure)

it costs $500 the first time as you have to buy the new ROM, reburn the maps and then epoxy or whatever the ROM onto the board

after that it gets cheaper (around 300) to get another remap

an SAFC costs $500 alone, plus fitting and tuning. in the end the SAFC is only 'tricking' the ECU into thinking there is less/more airflow so is not a long-term solution for a high-powered car