what afr should i run at idle on a twin turbo 5.3. first turbo build. running terminator x.

 

14.8

 

on my hand held it never goes above 13.8 is that lean or rich

 

the reason i ask is it blows black smoke and acts to rich rich to me. first street race build with fuel injection too. its all new to me

 

i am speaking as in wide band o2 Reading in down pipe. 13.5 Afr is when you are cruising without acceleration. So yes what you just last mentioned is to rich for idle.

edit: 13.8 afr is to rich at idle

 

At WOT you should be at 10.8 - 11.3 afr

 

Depends on idle fuel, idle RPM, sensor location, camshaft overlap, and how it idles. Not every car of ECU or sensor is the same.

 

Idle and Cruise 14.8 to 15.4 to keep plugs clean, reduce carbon deposits, maintain plug longevity and prevent dilution of engine oil with fuel

Need to be sure the wideband can actually read what you think its reading. The number is only as good as your ability to interpret what is really going on. The behavior of the wideband output as you visualize it is just as important as the number itself. It comes with many hours days months years of looking at the same sensor output over time recognize trends and understand what it is telling you, not just the number but the behavior

 

At idle?

 

Topic note: I just changed to a smaller turbo and changed from 4.10 to 3.31 gears, now at the same 16psi of boost on the same boost controller I am now reading 11.8 afr at WOT so I’m having my car retuned because for my engine I feel that is to lean.

 

If it's stock longblock it should idle at 14.3-14.7:1, depending on the ethanol content of the fuel. If it has a cam with a bunch of overlap and a rough idle it will read lean on the wideband. If that's the case just idle it where it runs well and the transition to acceleration is smooth.

 

Is it common to throw that much fuel at turbo street engines? Honest question as I don't play with mod motors or LSs.

The school of thought I come from is that low-load cruise can be as lean as you want it if the engine doesn't respond negatively. Negatively as in misfires, stumbling, knock, etc. I would expect newer engines with aluminum heads and better chambers to tolerate it even better than the archaic iron lump in my Pinto that runs mid/high 14 AFRs at cruise.

10.8:1 is about what my engine runs under load on a stock ECU. The general consensus is that it's excessively rich and was done by Ford largely to keep a wide margin of safety. That, along with an aggressive knock control strategy limited the engine's stock performance a fair bit.

 

Take the 13.5 afr at cruising with a grain of salt as I am speaking as in cruising at 3.5k rpm’s with no added throttle to create acceleration.

The WOT afr part is true. I prefer 11.3 afr at WOT.

At idle my afr goes back and forth from 14.8 to 15.2 afr.

To answer your question, yes it is common to throw that much fuel. I do not tune my own car I use a dyno tuner. There are reasons for needed WOT afr amounts as I am sure you are aware.

Don’t forget the name of the game is engine safety first. Make it rich and safe. Don’t be afraid of psi. Use psi of boost to reach your power goals with the appropriate setup.

If it matters to anyone information wise. I am running a 4.6 aluminator 8.75 compression short block, b heads studded, valve springs, deleted imrc valves, b head intake manifold, single turbo on 16psi boost controlled, pump 93 gas.

When it comes to the street car part, my car is a racecar that lives in a garage barley gets driven and when it does it gets driven on the street.

My factory engine cracked a piston with a vortech supercharger. This is the reason I went with a built aluminator short block.

 

That is on the border of dangerously rich on gasoline. Hope your changing your oil every 2500 miles. It's also not making best power: best power in boost will be somewhere between 11.7 and 12.7 on an F/I application. With modern engine management there is no need to be in the 10s. It seems more normal on carb stuff, and would be fine on a track only vehicle.

We should really be talking lambda numbers. 10.8 would be more normal if you were running something like E20 fuel.

I normally start a boost tune at .78 lambda (11.5:1 gasoline), once everything is dialed in I will creep up on .8 near peak torque and .82-.85 towards peak hp. If your at a strip you can do plug chops and watch MPH to dial it in further.

 

Your welcome wolf man fab!

 

IMO you just can't toss out a "perfect" a/f ratio. To many factors. How many lbs of boost are we talking to start? 1/8 mile? 1/4 mile? Spirited driving? Marine application?

I always targeted 11.2 at 14lbs on my setup. On the dyno it only made 10hp more at 11.8. I richened back to 11.2 for safety margin.

I think most would be surprised to see how rich the oems have programmed. They are worried about warranty returns.

 

Really?


From OEM tune files, read with HpTuners dongle and software:

2020 GT500 peak torque, coolant temp of 160° is .83 lambda (12.2:1 gas scale) .77 (11.3:1) @ peak HP.. that's a very high specific output engine. Doesn't look surprising to me.

2013 roush raptor: Full PE lambda is .82 (12.05:1), this is an aftermarket company boosting stock blocks, and offering a warranty, if anyone has a dog in the fight to keep engines rich they are the ones to do it. .82 is not surprising.

2018 ZL1 PE lambda is .84 ( 12.35:1)

Excessive richness can be dangerous just like excessive leanness can.

 

As soon as those cars get upper and lower pulleys swapped out and dyno tuned those numbers change.

 

That's interesting, especially since that entire post is talking about very specifically about OEM tunes.

Here are some aftermarket tuning examples from well known companies.
5 star, 3.5l Ecoboost, gen 1, 23 PSI: .82Λ
FRPP control pack (for boosted applications) .82Λ
Hennessey ZL1 Exorsist tune (1000hp boosted LS) .80Λ
Diablosport: Dodge redeye with pulleys .80 Λ

Greg Banish in his EFI tuning books recommends boosted AFR in the .82Λ zone.

You don't get progressively richer with more boost. I'm not sure where you got that idea from. Once you hit the fuel ratios that's where you stay.

 

At idle around 14,7 is fine . Always used 11.5-12.0 as a file of thumb at WOT under boost