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Throttle response or lack of under boost

JDUBU

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Took the car out for a short cruise and I've never really noticed a lag in response to the throttle either when accelerating or more important when letting off. I gave the car a little blip thru 3rd gear and got loose, when I let off it kept pulling longer than Id expect. Any experience with this? It could be a drive by wire tune related or blow off valve delay? Really could be dangerous especially when trying to keep it in my lane. Ill hit up Lund and see what they think as well but curious if anyone else has or had this delayed response.
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engineermike

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I’ve noticed the same on a Whipple setup. It’s not much delay but when pedaling you need response “right now”. The pcm’s initial response is to cut spark timing (fast path) since that happens faster than closing the throttle valve and having to use up the air in the plenum. I wonder if the spark cut isn’t enough when supercharged.
 
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JDUBU

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Yeah it could get sketchy. I know better in the cold air and roads than to get into boost but its been a long winter! There has to be a way to tone this down. Albeit a split second but like you said when peddling "right now" is nice to have.
"
 

engineermike

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The spark torque control is not that easy to follow in the tune. However, I looked at the stock gt, predator, and a couple of other aftermarket sc calibrations. There is something called “spark clip decreasing ramp rate (fast)” that is set to 2.0 in all the coyote calibrations but 10.0 in the predator. Likewise, the “spark clip increasing ramp rate (fast)” is also 2.0 in all coyote calibrations, but 1.2 in the predator. I wonder if this would make it cut spark faster on tip-out.
 
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JDUBU

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In my simpleton mind, it just feels like a delay from the foot pedal module to the throttle body servo. Probably more pronounced with boost but that is what it feels like. Now the spark control parameter your speaking gets over my head a bit but I understand the concept.
 

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engineermike

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The engineers at Ford realized that modulating the throttle is the slowest way to change torque output. Mechanical or electronic, the throttle has to change angles, which can take .1-.2 seconds (~20 engine revolutions). Then, once the throttle is closed, the engine has to use up all the air in the plenum. However, spark timing or fuel cut can reduce or increase torque beginning at the next combustion cycle, which is only 1/4 engine revolutions or .002 seconds response time. When you back out the throttle the spark source changes to “torque control” and spark timing drops before the throttle has time to close. My guess here is that all the tables used to control this spark-controlled torque cut are calibrated for an NA engine and would require some work to get it quicker when flowing 70% more air.
 

Ruiner46

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engineermike, have you tried turning off the gear shift hang in the tune? It was very noticeable on my Whipple car when I had not adjusted my gear ratios yet for my T56 swap. I fixed the ratios and turned this off at the same time, so I'm not sure which fixed it. Before the trans swap, I also had an annoying hang, especially when temps were hot, and at some point in the past I posted a video of it on this forum.

1.PNG
 
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JDUBU

JDUBU

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Makes total sense to me in your explanation. have you ever heard of this parameter being adjusted / tunable? In one aspect I'm glad its not a "problem" unique to my set up but still something being amplified as I add more power and chassis work.
 

engineermike

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Gear shift hang must be a 6r80 or M6 thing. I don’t see it in my or the stock 10r80 Cal.
 

Ruiner46

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Oh sorry, I missed the A10 for both of you. Anyway, I've always wondered if Whipple did something weird to cause the hang in the tune. My car when hot would hang the rpms at idle when I gave it a quick rev.
 

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JDUBU

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I have a Vortech so its not just a Whipple or pd specific quirk.
 

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I just noticed something relevant in my cal. They command a high torque number at wot to make sure it’s always demanding more than the engine can produce, which makes sense. However, at high rpm, as you reduce throttle the torque demand backs off, but you have to get to around 60% pedal for torque demand to fall below torque produced at wot. This might be contributing to the delay in torque reduction response.
 
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I picked up the Velocity Throttle Controller and wow that made a difference.
 

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My cal was commanding 600 ftlb at 50% throttle and 950 at 100%. The engine brake torque was only 650 max. I changed it such that 100% demands 750 ftlb and 90% demands 600. Now when I back off just 10% it starts cutting torque
 

Matthewstorm

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My cal was commanding 600 ftlb at 50% throttle and 950 at 100%. The engine brake torque was only 650 max. I changed it such that 100% demands 750 ftlb and 90% demands 600. Now when I back off just 10% it starts cutting torque
How do you know this?
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