I hate that 2-3 shift with a passion because of how much the rpms drop with the lockup. When the trans is cold and the converter isn't locking yet, that shift spread is great. Also, I forgot to mention earlier that I have a dod disabler thing plugged in for now until I do the proper delete and tune hopefully next year.
Understading VVT
- Thread starter donjetman
- Start date
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I hate that 2-3 shift with a passion because of how much the rpms drop with the lockup. When the trans is cold and the converter isn't locking yet, that shift spread is great. Also, I forgot to mention earlier that I have a dod disabler thing plugged in for now until I do the proper delete and tune hopefully next year.
The "tune" is worth it's weight in gold.. As far as transmission behavior... You'll get
rid of all the lock up in gears 1-3 (some do 4th too, I don't). Then you can get rid of the
unnecessary clutch slippage in 4th - 6th gears ... If it wasn't such a PITA I'd
do a 6 speed in my older pickup (4l80E w 650 HP) and try it in my MontCarlo SS as
I've really grown to like the 6 speed !!!!
Yeah I am really looking forward to how much better that will make the truck drive plus the extra power from the tune and the bigger cam.
As far as the swap, have you looked into Holley EFI? They now have controllers for the 6 speed autos..
The nice thing about vvt is it gives you options to tune a camshaft to an engine/vehicle, that you don't have with a static cam. You are not only advancing the cam for more torque, then retarding it as rpms increase for more power, you can actually build the cam so that it only works properly in certain positions for a certain applicetion. There is a much bigger difference in average power with a properly designed vvt cam, than there is from taking a normal cam, and advancing and retarding it.
I can absolutely destroy the entire power and torque curve of a stock vvt engine by flipping the normally advanced lower rpm cam position to full restarded, then switching the cam position over to fully advanced by peak power rpm. Much much more so than you ever could by advancing and retarding a standard camshaft.
Just like many other things in history, when something is new, lots of people think the old way is better. I personally love running vvt stuff. The only time I don't use it is when a vehicle has no problem making enough power down low. Lightweight cars like corvettes, vehicles with screw chargers, big strokers (though there is even a place for vvt in a big stroker if it's going in a heavy truck.)
I can absolutely destroy the entire power and torque curve of a stock vvt engine by flipping the normally advanced lower rpm cam position to full restarded, then switching the cam position over to fully advanced by peak power rpm. Much much more so than you ever could by advancing and retarding a standard camshaft.
Just like many other things in history, when something is new, lots of people think the old way is better. I personally love running vvt stuff. The only time I don't use it is when a vehicle has no problem making enough power down low. Lightweight cars like corvettes, vehicles with screw chargers, big strokers (though there is even a place for vvt in a big stroker if it's going in a heavy truck.)
I think you're feeling something else. The VVT system is seamless even in my cammed 6.2L.
Charlie207
Full Access Member
Probably the DoD operating on/off.
swathdiver
Full Access Member
Traditional small block chevrolet engines had peak torque in the 2000 rpm range. Our LS engines are high revving like a European car with their peak torque in the 4000 rpm range. Could this dampen throttle response?
I have seen carbureted LS engines that revved like a SBC.
My 5.3 used to lag off the line at WOT at around where the converter flashed to. It had 3.42 gears then. Now it has 3.73 gears and does not lag anymore at WOT from idle. It just revs fast and faster until it shifts.
From my old racing days, I suspect a free flowing exhaust and maybe a better air intake system would allow the motor to rev more freely as well off idle.
I have seen carbureted LS engines that revved like a SBC.
My 5.3 used to lag off the line at WOT at around where the converter flashed to. It had 3.42 gears then. Now it has 3.73 gears and does not lag anymore at WOT from idle. It just revs fast and faster until it shifts.
From my old racing days, I suspect a free flowing exhaust and maybe a better air intake system would allow the motor to rev more freely as well off idle.
Also keep in mind that vehicles from the time when things were carbed, weighed waaaaay less. A newer camaro has no problem pulling down low at around 4 thousand pounds. A silverado that came stock with a carb, weighed 4 thousand pounds or less. Add an extra 1700 pounds to anything, and it gets sluggish down low, even while adding power. That's a ton of weight, almost 2 seconds in the quarter mile based on weight alone. Just imagine a 1987 c10 leaving the line with 1700 pounds in the box.
There are also issues with the stock tune that keep from giving proper power off the line and down low on truck and suv applications. Do a carb conversion and those issues are deleted. A 6.2 in a denali with a tune will jump hard off the line.
Marky Dissod
Full Access Member
If the peak torque is @ 4000RpM, but it makes over 80% of peak torque by 1000RpM, it's fine.
Obsessing over peak numbers is misleading;
since most engines spend over 90% of their lives under 2500RpM, it'd be more useful to know how much torque the engine makes between 1000RpM & 3000RpM, where it lives.
Biggest things that dampen throttle response are:
lack of displacement - GM replaced Vortec 5.7L with 5.3L, remember? (shrinking the bore tends to move the torque peak higher up the RpM range)
burst knock - this is in the tune, it changes spark timing more slowly than necessary specifically to dampen throttle response ... (there's other stuff of course ...)
87 octane - throttle response and MpG (efficiency per combustion event) improve with 91 or 93 octane, if both sparks table is written for higher octane
axle gearing - before the 8L90, every vehicle GM sold with a V8 was undergeared at the axle(s).
Most GMT800 & GMT900 with 4L60E should have had 4.10 axles instead of 3.73 or 3.42 or 3.23.
Most GMT900 & GMTK2 with 6L80E should have had 3.73 axles instead of 3.42 or 3.23 or 3.08.
