VTEC Question
#1
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Location: Foothill Ranch, CA
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VTEC Question
Has anyone noticed that under full acceleration when the car shifts from 2nd to 3rd it doesn't always stay in VTEC and thats using both sport & sport + mode? I tried shifting myself and letting the car do it which both lead to the same result. The car in question is a 2015 TLX FWD V6 Advance w/AEM CAI and it might be normal but I have an issue with that especially when I noticed the difference in 1/4 mile times. I understand the TLX is not a sports car but I took it to the drag strip a few months ago to see what it would do time wise. My first run of the day I did a 14.5 1/4 mile and that one run it stayed in VTEC but the rest of the runs I did that day the shifts from 2nd to 3rd did not stay in VTEC and my times suffered. When it didnt stay in VTEC I ran 14.7 & 14.8 and I understand launching/60 ft times have alot to do with it but that one miss shift really slows it down. Wondered if anyone else has noticed it and if so do they ignore it or have they brought it up to the dealership? Any thoughts or comments would be appreciated.
Jason
Jason
#3
Moderator
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Originally Posted by Hondanews.com
V6 i-VTEC® with 2-Stage Variable Cylinder Management™ (VCM®)
The TLX SOHC V6 combines Variable Cylinder Management (VCM) with Variable Valve Timing and Lift Electronic Control (i-VTEC®), which changes the lift profile, timing and lift duration of the intake valves. A switching mechanism allows each cylinder to operate with low-rpm valve lift and duration or high-rpm lift and duration. The rear cylinder bank's valve gear closes all intake and exhaust valves to minimize pumping losses while operating in three-cylinder mode.The "intelligent" portion of the system is its ability to vary valve operation based on the driving situation and engine rpm. At low rpm, the i-VTEC® intake valve timing and lift are optimized (low lift, short duration) for increased torque, which allows a wide range of 3-cylinder operation. As engine rpm builds past 5,000 rpm, the i-VTEC® system transitions to a high-lift, long-duration intake cam profile for superior high-rpm engine power.
The TLX SOHC V6 combines Variable Cylinder Management (VCM) with Variable Valve Timing and Lift Electronic Control (i-VTEC®), which changes the lift profile, timing and lift duration of the intake valves. A switching mechanism allows each cylinder to operate with low-rpm valve lift and duration or high-rpm lift and duration. The rear cylinder bank's valve gear closes all intake and exhaust valves to minimize pumping losses while operating in three-cylinder mode.The "intelligent" portion of the system is its ability to vary valve operation based on the driving situation and engine rpm. At low rpm, the i-VTEC® intake valve timing and lift are optimized (low lift, short duration) for increased torque, which allows a wide range of 3-cylinder operation. As engine rpm builds past 5,000 rpm, the i-VTEC® system transitions to a high-lift, long-duration intake cam profile for superior high-rpm engine power.
#5
Instructor
Yea, when I had the AEM CAI, I noticed like a "power drop" when on full throttle. I put back the short ram just for sound lol. you clear see the rpm gauges have a drop.
#6
Team Owner
Honestly, being 0.2s slower can be caused by a whole whack of things. It could even be heat soak from previous runs... a cooler engine will undoubtedly run faster than one creating and sucking in warmer air.
Sounds like the car is just on the verge of hitting (or missing) VTEC when it shifts to the next gear... if anything, sounds like the gear ratios weren't exactly chosen for performance, as Honda would've ensured the car stayed in the VTEC zone otherwise.
Sounds like the car is just on the verge of hitting (or missing) VTEC when it shifts to the next gear... if anything, sounds like the gear ratios weren't exactly chosen for performance, as Honda would've ensured the car stayed in the VTEC zone otherwise.
#7
I believe it is the computer protecting the dog clutches in the transmission. VTEC+Dog Clutch Shift = unnecessary wear.
A quick google brought me to an article, here's an excerpt that might shed a little more light on the technology, although it does not quite point to the 2-3 shift as relaxed.
- Link
A quick google brought me to an article, here's an excerpt that might shed a little more light on the technology, although it does not quite point to the 2-3 shift as relaxed.
Let’s put it all together now. To save space and increase efficiency, the 9HP uses two multi-plate clutch elements, two friction brakes and two electronically synchronized dog clutches. (The 8HP uses two brakes and three multi-plate clutches.) The way the gearsets are arranged inside the case, shifts from 1-2, 2-3, and 3-4 involve only the traditional friction brake and clutch elements. As you would expect, aside from 1st being fairly low and somewhat distant from 2nd, these shifts feel perfectly “normal.” Under hard acceleration there is a momentary reduction in engine torque (courtesy of the computer to reduce clutch wear) and the shift occurs quickly and smoothly. The shift from 4-5 however is different. The transmission has to disengage dog clutch “A” in addition to engaging a friction clutch. This shift takes slightly longer than the 3-4 shift and the car’s computer makes a drastic reduction in torque to prevent wear of the dog teeth. Shifts 5-6 and 6-7 again happen with the only the friction elements at which point we need to disconnect the final dog clutch for gears 8 and 9 so we get the same kind of torque reduction in those shifts. The result is a transmission that has two distinct “feels” to its shifts, one that has only a slight torque reduction (1-2, 2-3, 3-4, 5-6, 6-7, 8-9) and one that has a more “manual transmission” feel where torque is cut severely (4-5 and 7-8).
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#8
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The information is interesting but what I experience is really odd. Under full acceleration it will stay in VTEC in every gear except when shifting from 2-3 gear. However once in a blue moon it will stay in VTEC when going from 2-3 gear and I cannot figure out why. I have watched many youtube videos and it seems everyone has the issue at least from what I can hear in all the videos I have watched. Any more information would be appreciated because as pointless as the issue is it does drive me nuts.
Jason
Jason
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