Best A/F ratio for Rb25

[BOOSTD]

Hi all, for those in the know what is the best/Optimal A/F ratio for our skylines? Given no detenation of course. I have been told 12.3:1 is were max power is made on a turbo charged engine however have seen GTR's tuned down to flat 13 and make more power. Are we talking a combination of the best ignition advance curve versus A/F ratio?....ie car X might make more power with slightly richer mixtures and more advanced timing were as car Y will make more power with lean mixtures and a tame timing curve.

Are there any proven ignition timing levels for max power on an RB25 or is it more of a matter of having the timing a couple of points below detenation?

Is there a optimal A/F ratio that has seen the best results in

power?

Peak torque is around 5200-5500rpm, is detenation at this point best controlled by reduced timing or enriched mixtures?

I'm thinking something along the line of "a can of worms"

The reason I ask is because I have an narrow band oxy sensor and meter that I am using on the weekend to check my A/F ratios.

Any advice on road testing and tuning(Power FC) would be greatly appreciated.

[JimX]

I think around 14:1 is the "perfect" mixture, but this will not cater for any variances such as turbulence in the plenum, injectors not flowing *exactly* the amount they're supposed to, etc. That's why cars are usually tuned to around 12:1. 13:1 would be better if you could get it reliably, but it'd be risky if you haven't got everything tuned absolutely perfectly and compensating for temperature.

The "best" mixture depends on the car. Some will show a big jump from 11:1 to 12:1, some will have smaller differences. My car seems happy enough at 11.5:1. The richer you can leave the car, the less likely you are to detonate. My car could run happily all day at over 12:1 during winter, but in summer without anything to compensate for the temperature it would probably ping. That's why my mechanic tuned it to 11.5 or so.

[BOOSTD]

Sydneykid you out there....

11.5 hmmn thats pretty rich

[GTS-t VSPEC]

I have mine tuned for about 12.2 This is as lean as I like to go, just due to variations in the fuel quality.

[BOOSTD]

12.2:1 thanks for that GTST VSPEC

anyone else?

[GTS-t VSPEC]

Obviously it starts off much leaner, we have been able to run 18:1 in closed loop at low load.

[BOOSTD]

Ok

12.2 max load

18:1 min low load

cheers

[GTS-t VSPEC]

Yeah, this only really applies if you have proper management to cope:D

[Steve]

BOOSTD, mine is currently tuned at 12.2:1 on boost. Done at tilbrooks at the beginning of this year, in the morning probably around 25deg C.

In corky bell's book supercharged, it recommends around 13:1 for on boost (above 1psi on the boost guage), down to 14.7: at atmosphere (0 on the boost guage). Idling (20 inches of vacuum) he recommends around 15.5:1. He describes that cruise is at about 10-15 inches vacuum, but doesnt give a recommended ratio, he does however say that it is in between.

He says that the on boost isnt the hard part, the part thorttle at different rpms/loads is 90% of the work and recommends looking at 500rpm increments.

In the book 21st century performance, it describes lean (18:1) cruise mixurues, but this generally requires a good ecu and closed loop as slight increase in load will rapidly increase the requirement for fuel.

[BOOSTD]

Thanks Steve. Did Martin or Mick tune your car? I will find out exactly what my car is doin tonight, both martin and mick have played with my mixtures.

I have the book 21st Century Performance....can't remember how many time I've read it cover to cover.

Any insite on the Ignition side of things??

[Steve]

Sorry I have no idea about the timing, I am pretty sure mine is set to stock (15deg), so I am not sure if they just used stock timing and adj fuel to suit. When it first went on it was running a little advanced, they wound it back as it was pinging pretty bad at about 6200rpm. Dont have any idea what is happening with the ign maps either. Sorry (keep meaning to take a closer look there)

I dont have corky bells book with me at the moment (at work), but I will have a look to see what he says about ign, and post it up this arvo. If you want to borrow it, its a bit thicker than 21st century performance, likewise it definatley requires a few reads to absorb.

I had a thought about the above post too, I am not sure what fuel they were recommending those ratios for (ron), he just stated to start there and add in as needed:)

Martin did the tune.

[BOOSTD]

I would love to borrow that book,might see you if you need borrow the Jack.

[hippy]

hey where do u guys get these books from?? i wanna learn too!!! u nerds!!!

[TomR33]

Try:

http://www.automotivebooks.com.au

or

Book Works in Sydney ph 1800242116

heaps of interesting books there.

[Steve]

Corky bell does mention a bit about ignition. Basically he states that as boost goes up, you need to pull igniton from the off boost maps. Goes on a bit about the differnet factors, such as AF ratios, temperature, octane, etc.

If you like I will give the book to hippy when he picks up the wheels, and he can pass it on:)

Hippy, you are most welcome to borrow when BOOSTD is finished, or there is a motoring book shop in the city on Gouger st ( I think), opposite the markets/cafes. Corky bell also writes a book called Maximum Boost, which is the same price as supercharged, and goes a bit more in to turbo specific applications. Well worth the $100.

[GTS-t VSPEC]

I think it's best to alter the timing than play around with the fuel map. We run mine at 12.2:1 AFR, have a base timing of 20deg, and adjust the timing with the Wolf computer.

[hippy]

100 bucks?? can i get it from a library??

[Steve]

Probably:p

[EnricoPalazzo]

BOOSTD: I have max boost. u can borrow it if u wanna come past.

Call me if u want it urgently

*edited*

[EnricoPalazzo]

Hiep u tight ass, State library has it but u cant borrow it. No one else has it........ Except me muhahaha