cpt_koolbeenz

I have been reading posts and dino charts, trying to get as much info as I can about A/F ratios across RPM and boost ranges. Just got a lot of conflicting bits of info. What should I shoot for when tuning? (Lean in low rpm to get turbo to spool faster? etc.)
Also, does high altitude affect A/F readings?

I plan to run 15-18 PSI on 91 octane (highest I can find).
TIA

dand86951

Chris, you will probably get a lot of different recommendations on this one. the short answer is most will agree a 12.5, or therabouts, is quote ideal for max horsepower. However, from looking at lots of charts rarely do they start at 12.5 and maintain it flat all the way throught the rpm band. Also how lean do you want to run at high rpm is a big question, with a proper sized turbo for high rpm operation in the sweet spot of the compressor map you might be ble to run right at 12.5 without running too high exhaust gas temps.

Another variable is what boost pressure and what octane gas. Lower boost, or higher octane gas and you can run closer to ideal without being too hot. Lots of variables cause this to be a question without one best answer in my opinion. Set some targets that are below ideal, get your car on the dyno with a plan to change the variable you can such as injector pulses etc., fuel pressure, boost and find out what works on your car, with the gas you plan to run.

I think you are correct in that it seems most tuners set the fuel lean in the low end to ge a hotter egt and thus quicker spool. but if you go too radical with this then you could have detonation in the mid rpm when boost spikes up.

The only factor altitude plays is that your compressor has to work harder to make the .8 to .9 bar boost of the stock car and this usually means a higher compressor discharge air temp.

NZ951

Chris, the answer seems easy. Run as lean as you can go, while still making more power (rather not making less), and not kocking. Same with timing, go as far as you can go till you stop making more power and/or when you start knocking. Or is this wrong? Seems to make sense though, I would not go off anyone elses figures, get on the dyno...

cpt_koolbeenz

Good info dand-
That is what I figured/found out for the most part.

NZ-
Yes it seems easy and is with a dyno. But I can't always be on a dyno to tune. I don't intend to take other people's numbers and use them as face value... I just want some insight as to what other people have success with.

Another question-
Is it save to run 15:1 ratios on idle and off-boost conditions? I read it somewhere and wanted to see what you guys thought.

slim_boy_fat

'Dino'....!!!!, you been watching the flintstones?

cpt_koolbeenz

Hahaha OOPS! These antihistamines are getting to me!

rage2

I'll chime in with my setup.

I found my sweet spot to be 12.2 A/F with 18 degrees of timing. Gave me the best power at a reasonable EGT.

rage2

You forgot about EGT's, they have to be monitored when you're fidding around with timing/boost and A/F!

You can make huge amounts of power on pump gas with no knocking, lots of boost, and heavy ignition retard, but you're gonna melt everything starting with the exhaust valves.

cpt_koolbeenz

What boost was that at rage?

Thanks

CBRE

So what boost should I shoot for and be safe at with a k27/6, right now I am at 11.5 A/F with the PLX. I would like to be at 18psi and 12.2 A/F, safe?

NZ951

11.5 seems fat. 12.2 would even be fat if you are not spending a lot of time at 18psi... temps just dont go up that much if its not DE type stuff...

Ski

Best torque from 11.8 - 12.1 ; better hp numbers from 12.3 - 12.5. I've got my Mafterburner set up at 11.8 at the onset of full boost, 12.4 by 6300. Just MHO for me. 15 psi at the moment on street gas.

toddk911

12.5 seems to be the universal number, but then fine tune from that on a dyno/wideband.

Rage, what numbers do you usually seee on the EGT?? How accurate is EGT to wideband??? i.e. 1500 is about 12.5:1 or 1600 is about 13:1??

rage2

12psi 91 octane, 14psi 94 octane.
Depends on timing, fuel octane and condition of motor (any oil in the intake stream?). If there's no knock, and EGT's are reasonable, then it's safe.
How does that work, since hp is directly related to torque (hp = tq * rpm / 5252) . If you make more hp, you're making more torque.
Aim 1550 on the EGT, 1600 is the absolute limit, and only for a short period of time. EGT's go up when you retard timing, goes down when you advance timing. EGT's go up when you lean the mixture (to a point), and goes down when you richen the mixture. There's no universal EGT vs A/F ratio formula, depends on car, timing, fuel, and many other factors.

Ski

Like I said rage, MHO, and it happened to be true setting up my car. One tuner in particular told me this(not LR)...tried it and it worked. The car had better torque numbers a tad more rich, the hp numbers were down about 12, vice a versa'd it and the hp numbers got better, same dyno, same guy operating the car...had a buddy just do his. Hp higher with 12.4-12.6. and torque off 14 ft/lbs from hp. Added fuel to the PB computer and the hp stayed around the same but torque was up 22 ft/lbs.