Fast Intentions "Twin Turbo Kit" is here

Seb@SZ · 08-13-2014, 03:20 PM

Jumping in to clear the "air". When Mike's Z left California it was tuned for high 10s and low 11s. His environment (altitude, pressure, humidity) will attribute to changes in the tune. With that being said 10.5 under WOT on a high compression engine not intended for boost is perfectly safe. On the other hand if your idling and cruising at 10.5:1 AFRs then there is cause for concern!

Another thing to remember is air is 500x times lighter than fuel so when you first hit the throttle you'll see transient fueling enriching quite a bit to account for the huge rush of air entering the cylinders. You may see it dip down but otherwise it will stabilize.

Brand new forced inducted vehicles, for example GTRs, EVO Xs, etc., have a nice soot build up on their tips and the bumpers get "coated" black even after a minor amount of miles. This is with them having two sets of cats on them still. I think Mike's post was taking way out of context and the way it was written makes it sound like something is wrong.

mfeinst · 08-13-2014, 03:31 PM

Quote:

Originally Posted by Seb@SZ

Jumping in to clear the "air". When Mike's Z left California it was tuned for high 10s and low 11s. His environment (altitude, pressure, humidity) will attribute to changes in the tune. With that being said 10.5 under WOT on a high compression engine not intended for boost is perfectly safe. On the other hand if your idling and cruising at 10.5:1 AFRs then there is cause for concern!

Another thing to remember is air is 500x times lighter than fuel so when you first hit the throttle you'll see transient fueling enriching quite a bit to account for the huge rush of air entering the cylinders. You may see it dip down but otherwise it will stabilize.

Brand new forced inducted vehicles, for example GTRs, EVO Xs, etc., have a nice soot build up on their tips and the bumpers get "coated" black even after a minor amount of miles. This is with them having two sets of cats on them still. I think Mike's post was taking way out of context and the way it was written makes it sound like something is wrong.

Correct -- thanks for clearing this up, Seb, and I apologize for any confusion caused. The black coating is nothing new. My Dad's GTR has a similar buildup but not quite as dark, but that is to be expected. Also, the exhaust tips with the Nismo are recessed due to the bumper design, so it's gonna get black faster than a standard Z rear bumper would.

Anyway, the 10.5:1 AFR is a stable reading while under WOT and full boost. Idle is right where it should be: 14's. I'm not concerned in the slightest -- you and the F.I. crew know what you're doing, and I would hardly peg 10.5:1 as off the deep end! That being said, I think 10.7-10.8 would help mileage, but I'm not sure if that's pushing the envelope too much. The tune is definitely rock solid. Another note with mileage, I had my turbo Mazda3 tuned to run mid 15:1s when cruising at highway speeds, which really helped mileage and didn't pose any issues on that particular car, but I don't know the ins and outs of how the Z would handle that.

Any other questions, post up and I'll try to answer them.

P.S. Yeah I took the Z34 PA plate

P.P.S. The F.I. oil cooler setup is incredible! I never top 180, even on 95 degree days. Granted, that isn't track driving, but I was hitting 220 before I made the switch, and that was N/A!

Nixlimited · 08-13-2014, 06:28 PM

Quote:

Originally Posted by mfeinst

That being said, I think 10.7-10.8 would help mileage, but I'm not sure if that's pushing the envelope too much.

I'm not so sure it would. I suspect the majority of your driving is in closed loop cruise fueling mode where you are targeting stoich (14.7:1). You are only going to be getting that rich when under high boost. And if you are under high boost, then there is no point in thinking about fuel mileage.

Now, I have read about people lean tuning for closed loop mode (e.g. 15+:1). That's an interesting idea. It actually works OK from a power output standpoint, but I think the potential issue is the heat. Inevitably, some fuel is not burned, even when targeting stoich, and that fuel is being vaporized and absorbing heat. Take it away and that's more heat the block has to deal with. Not good on a VQ.

1slow370 · 08-13-2014, 07:35 PM

Quote:

Originally Posted by Nixlimited

I'm not so sure it would. I suspect the majority of your driving is in closed loop cruise fueling mode where you are targeting stoich (14.7:1). You are only going to be getting that rich when under high boost. And if you are under high boost, then there is no point in thinking about fuel mileage.

Now, I have read about people lean tuning for closed loop mode (e.g. 15+:1). That's an interesting idea. It actually works OK from a power output standpoint, but I think the potential issue is the heat. Inevitably, some fuel is not burned, even when targeting stoich, and that fuel is being vaporized and absorbing heat. Take it away and that's more heat the block has to deal with. Not good on a VQ.

Thats not how it works but sure.

Nixlimited · 08-14-2014, 09:44 AM

Quote:

Originally Posted by 1slow370

Thats not how it works but sure.

Actually, it is. When I drive my TT Z around, the AFR gauge is almost always reading near 14.7 because most of the time I am not accelerating and moving into a richer area of the fuel map. As for lean tuning cruise mode, just do a google search on that and you will get educated.

But if you think you have a better understanding, please, do enlighten us.

1slow370 · 08-14-2014, 11:17 AM

Quote:

Originally Posted by Nixlimited

Actually, it is. When I drive my TT Z around, the AFR gauge is almost always reading near 14.7 because most of the time I am not accelerating and moving into a richer area of the fuel map. As for lean tuning cruise mode, just do a google search on that and you will get educated.

But if you think you have a better understanding, please, do enlighten us.

Actually it's not how it works, lean fuel mixtures do not make the engine run hotter because there is less fuel vaporizing and sucking heat out of the motor, it is because a lean mixture burns more rapidly which means peak cylinder pressure is reached earlier in the stroke forcing the engine to fight itself while retaining a hotter mixture of gas in the engine for a longer time, in a rich burn situtaion the fuel will still be burning exiting the engine which tends to increase egt's but is not as hard on the engines cooling system. the latent heat of vaporization is less important until you start getting into alcohols and nitro mixes that really can cool the entire top end of the engine just by evaporating.

As for the closed and open loop stuff, what you are suggesting is already in place in the ecu, from the factory the car tapers from the low load sites which are 14.7ish and as load and rpm increase the afr tables drop in the ecu. If tuned properly your tuner should only be adjusting the mid and high range/load sites to keep it rich enough to prevent detonation, the low end only basically needs to be tweaked to fine tuned for changes in maf size. As seb had said in his earlier post if you were running 10.5-1 at idle that wouldn't be a good thing because it shouldn't be doing that. The only other time the low load sites should go richer would be if there is a tip in lean issues that can't be tuned out some other way.

Nixlimited · 08-14-2014, 02:45 PM

Quote:

Originally Posted by 1slow370

Actually it's not how it works, lean fuel mixtures do not make the engine run hotter because there is less fuel vaporizing and sucking heat out of the motor, it is because a lean mixture burns more rapidly which means peak cylinder pressure is reached earlier in the stroke forcing the engine to fight itself while retaining a hotter mixture of gas in the engine for a longer time, in a rich burn situtaion the fuel will still be burning exiting the engine which tends to increase egt's but is not as hard on the engines cooling system. the latent heat of vaporization is less important until you start getting into alcohols and nitro mixes that really can cool the entire top end of the engine just by evaporating.

As for the closed and open loop stuff, what you are suggesting is already in place in the ecu, from the factory the car tapers from the low load sites which are 14.7ish and as load and rpm increase the afr tables drop in the ecu. If tuned properly your tuner should only be adjusting the mid and high range/load sites to keep it rich enough to prevent detonation, the low end only basically needs to be tweaked to fine tuned for changes in maf size. As seb had said in his earlier post if you were running 10.5-1 at idle that wouldn't be a good thing because it shouldn't be doing that. The only other time the low load sites should go richer would be if there is a tip in lean issues that can't be tuned out some other way.

I think we are talking past each other, and not being very accurate. I have only been talking about closed loop mode (i.e. targeting a stoich mixture of 14.7:1).

First, the relationship of flame speed versus AFR is a curve that peaks below 14.7:1 then drops on both ends. So, while moving to a leaner ratio from a very rich ratio will speed up flame speed, that only holds true to a point around 12:5:1. After that, leaner = slower. I was talking about ratios above 14.7:1, where additional air will slow the flame speed down, and not speed it up as you suggest. See, for example, discussion here: Spark Timing Myths Debunked - Spark Timing Myths Explained:: Application Notes ("At about 12.5 to 13 air-fuel-ratio the mixture burns fastest. A leaner mixture than that burns slower.")

Also see the same concept in graph form:

Or here:

As for the lean burn on cruise, the car is targeting 14.7:1 in closed loop, cruise mode from the factory. People have experimented with "lean tuning" i.e. targeting higher than 14.7:1 in closed loop, cruise mode in order to increase fuel efficiency.

For anything under load, I am not about to try to go a bit leaner than what my turner suggests to save some fuel. That extra fuel helps with cooling, which helps with knock prevention. I would rather save my engine.

mfeinst · 08-14-2014, 10:22 AM

Quote:

Originally Posted by Nixlimited

I'm not so sure it would. I suspect the majority of your driving is in closed loop cruise fueling mode where you are targeting stoich (14.7:1). You are only going to be getting that rich when under high boost. And if you are under high boost, then there is no point in thinking about fuel mileage.

Now, I have read about people lean tuning for closed loop mode (e.g. 15+:1). That's an interesting idea. It actually works OK from a power output standpoint, but I think the potential issue is the heat. Inevitably, some fuel is not burned, even when targeting stoich, and that fuel is being vaporized and absorbing heat. Take it away and that's more heat the block has to deal with. Not good on a VQ.

My thinking is more to cut down a tad on in-boost consumption, since there is an incredible volume of air/fuel going through the cylinders in that state and even a few tenths of a point are likely to make a tangible difference. I'd probably go from 1.5mpg to 2.5mpg under load LOL

And on a more serious note, the only thing I really want to adjust is the loudness/drone of the exhaust, which can get tiring. Anyone up for a non-res & 18" res swap out?

08-13-2014, 03:20 PM	#1 (permalink)
Seb@SZ Enthusiast Member Join Date: Jan 2010 Location: Chatsworth Posts: 277 Drives: Zs Rep Power: 26	Jumping in to clear the "air". When Mike's Z left California it was tuned for high 10s and low 11s. His environment (altitude, pressure, humidity) will attribute to changes in the tune. With that being said 10.5 under WOT on a high compression engine not intended for boost is perfectly safe. On the other hand if your idling and cruising at 10.5:1 AFRs then there is cause for concern! Another thing to remember is air is 500x times lighter than fuel so when you first hit the throttle you'll see transient fueling enriching quite a bit to account for the huge rush of air entering the cylinders. You may see it dip down but otherwise it will stabilize. Brand new forced inducted vehicles, for example GTRs, EVO Xs, etc., have a nice soot build up on their tips and the bumpers get "coated" black even after a minor amount of miles. This is with them having two sets of cats on them still. I think Mike's post was taking way out of context and the way it was written makes it sound like something is wrong. __________________ Z Car Specialists www.specialtyz.com Blog http://specialtyz.com/blog/

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