There’s a waiting line to buy the modified Crawford plenum for the 3.5 V6 used on the Z, the G35, and the FX35. This device adds height to the front of the plenum by reshaping the plenum configuration allowing the front cylinders to breath as well as the rears.
Sounds good, and customers reporting to the forum (Fresh Alloy) are very pleased with HP increases in the high teens.
However, what effect does such a mod have on the ECU? When the front cylinders that were running rich due to lack of air volume at high rpm are given the air that they deserve, the entire exhaust flow would reflect this leaner condition. Wouldn’t the O2 sensor be giving the ECU the indication that the fuel mixture needs to be richer. So all cylinders would then run a little richer.
Since there is a positive HP change, I take it that this is not significant, but would it affect economy, carbon buildup, plug life, etc? Is my thinking logical or way off? Any solid technical opinions to add?
Bottom line --- I’d like to get one of these things for the improvement that it offers, but am hesitant if I may be doing some other harm.
Bob
Crawford plenum inquiry
Crafford effect on fuel ratio
No, I do not have headers.
The way I see it, Nissan would design the ECU to provide the correct air-fuel mixture for the leanest of cylinders. Otherwise the leanest cylinders may ping or force the timing correction to try to compensate for ping (power loss). Therefore, when the modified plenum allows all cylinders to enjoy the same volume of fresh air, the front cylinders will run as lean as the rears. That means that all 6 cylinders are now contributing lean exhaust to the O2 sensor who will detect this as an overly lean condition (compared to what it was designed to monitor) in the engine and richen the mixture to all cylinders to compensate. We all know that rich mixture means loss of power, although Crawford and his customers report additional power. So maybe this is insignificant. Or maybe is will do eventual harm such as cause carbon buildups or cause difficulties with emissions testing. Items like cold air kits, improved air filters and headers will affect all cylinders near equally, so that is not the same scenario.
By the way, what's a WOT that Q45tech refers to in his reply?
The way I see it, Nissan would design the ECU to provide the correct air-fuel mixture for the leanest of cylinders. Otherwise the leanest cylinders may ping or force the timing correction to try to compensate for ping (power loss). Therefore, when the modified plenum allows all cylinders to enjoy the same volume of fresh air, the front cylinders will run as lean as the rears. That means that all 6 cylinders are now contributing lean exhaust to the O2 sensor who will detect this as an overly lean condition (compared to what it was designed to monitor) in the engine and richen the mixture to all cylinders to compensate. We all know that rich mixture means loss of power, although Crawford and his customers report additional power. So maybe this is insignificant. Or maybe is will do eventual harm such as cause carbon buildups or cause difficulties with emissions testing. Items like cold air kits, improved air filters and headers will affect all cylinders near equally, so that is not the same scenario.
By the way, what's a WOT that Q45tech refers to in his reply?
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Q45tech
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Nissan and every other manufacturer set the AF ratio excessively rich at WOT [wide open throttle] because rich is safe and you cannot drown the engine with fuel [without going to 5:1 vs 10-11:1 vs 12:1 optimum power ratio vs 14.7 where the cats work.
Any extra air flow [cooler temperature, less restrictive filter, polishing the TB, hogging out the plenum and runners, is allowed for primarily in the fact that the engine may operate at ZERO F when the air may be 7% denser.......than the 70F design point.
The range is really 10% [just to be safe] plus the 10-15% extra rich safety for clogged injectors.In theory if very thing was working perfectly the engine/ fuel system could accomidiate 20-25% more dense air except the combustion temp would rise setting off the knock sensors.
The real question is are we sure that the alleged runners are restrictive..........Nissan has always been perfectionistic in plenum runner design. But maybe they stopped at 6,200 rpm thus the gains above that rpm.
If you had a 10% imbalance in power per cylinder it would show up as a measurable vibration.
Look at it another way you could gain power by leaning the richer runners, also...................as the engines alway run too rich for best peak power!
Easily tested by fooling ecu as to MAF voltage output........build a variable clamp that limits MAF voltage a few tenths {on a Q instead of 4.35 real say 4.25 volts sent to ecu]..........ecu thinks less air so less injector open time...........don't go crazy as the curve is exponential and a 0.1 volt is a lot -- like 6-10% [less air flow] at 6,000 rpm.
Remember when I talked about a BAD MAF reading 0.25 volts too high and the injectors went from 10.0 millisecs to 12.0 millisecs.......at WOT high rpm every 0.1 volt is critical and the ecu resolves the voltage in 0.01 volt steps which get multiplied [raised to the ^3.5 power] in the fuel equation.
Any extra air flow [cooler temperature, less restrictive filter, polishing the TB, hogging out the plenum and runners, is allowed for primarily in the fact that the engine may operate at ZERO F when the air may be 7% denser.......than the 70F design point.
The range is really 10% [just to be safe] plus the 10-15% extra rich safety for clogged injectors.In theory if very thing was working perfectly the engine/ fuel system could accomidiate 20-25% more dense air except the combustion temp would rise setting off the knock sensors.
The real question is are we sure that the alleged runners are restrictive..........Nissan has always been perfectionistic in plenum runner design. But maybe they stopped at 6,200 rpm thus the gains above that rpm.
If you had a 10% imbalance in power per cylinder it would show up as a measurable vibration.
Look at it another way you could gain power by leaning the richer runners, also...................as the engines alway run too rich for best peak power!
Easily tested by fooling ecu as to MAF voltage output........build a variable clamp that limits MAF voltage a few tenths {on a Q instead of 4.35 real say 4.25 volts sent to ecu]..........ecu thinks less air so less injector open time...........don't go crazy as the curve is exponential and a 0.1 volt is a lot -- like 6-10% [less air flow] at 6,000 rpm.
Remember when I talked about a BAD MAF reading 0.25 volts too high and the injectors went from 10.0 millisecs to 12.0 millisecs.......at WOT high rpm every 0.1 volt is critical and the ecu resolves the voltage in 0.01 volt steps which get multiplied [raised to the ^3.5 power] in the fuel equation.
Guys: Thanks so much for the info. Greatly clearified my understandign of the concept. I actually do not have the car to apply this to yet. Will get a G35 of FX35 within a few months. May want to apply the Crawford plenum.
By the way, Greg. What kind of power increases are you getting with the headers? Any downsides to be concerned about.
Thanks again, Bob
By the way, Greg. What kind of power increases are you getting with the headers? Any downsides to be concerned about.
Thanks again, Bob
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AZhitman
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Header gains are averaged over several runs and appear to be as follows (conservative - highest gains eliminated as flukes):
9 hp from 3800-6000 rpms.13 hp / 13 lb/ft @ peak.
Catback was tested seperately and resulted in 9 hp, 10 lb/ft.
Not certain what the combination of the two upgrades would provide.
9 hp from 3800-6000 rpms.13 hp / 13 lb/ft @ peak.
Catback was tested seperately and resulted in 9 hp, 10 lb/ft.
Not certain what the combination of the two upgrades would provide.