The addition of VVTi seems like more of a non-issue for the 4.7 V8 in our application, tell me if I'm wrong?? Doesn't VVTi benefit you more by adding to your HP at high RPM's? It also flatens the torque curve but were only talken about maybe 10 ft. lbs of torque. To me this is a PR change to cover the fact that Toyota needs to comeout with a 5.6 V8 like Nissan. My 350Z has VVTi and it works in that application because the Z is a high revving sports car with a 6 speed manual transmission that can utilize the VVTi to its advantage. I don't drive my 4.7 V8 any where near the rpm limit and I would doubt any buyer will feel any difference with the addition of VVTi. Matter of fact the complexity of the VVTi is more of a potential downside then the upper end HP is a performance improvement. Please let me know if I am missing something with this VVTi improvement???
VVTi question about the new 4.7 V8
- Thread starter Pitbull
- Start date
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you have got it about right
I agree about not really getting additional power anywhere that is in the typical users operating range. I had an Acura TL that was a pretty quick family car; as long as you were willing to let the VTEC kick in. I realize that VTEC and VVTi are not identical in operation but they are similar in basic theory. How often do you want to do that in an upscale automobile that truly isn't designed for high on-road performance? By the way, I traded my TL in on my LX when the tranny went out at around 15,000 miles.
I was under the impression that the vehicles with VVTi would get some gas mileage relief. Is that not the case?
I was under the impression that the vehicles with VVTi would get some gas mileage relief. Is that not the case?
ok, here's the scoop on the engine change, and these figures are based off the Tundra:
old engine: 245HP, 4 speed tranny, 14 mpg city/18 mpg hwy
new engine: 283 HP, 5 speed tranny, 15 mpg city/19 mpg hwy
the VVTI gives more power across a broader range of the RPM band, not just at higher rpms like the honda, so you are going to see and use the additional power.
jeff
old engine: 245HP, 4 speed tranny, 14 mpg city/18 mpg hwy
new engine: 283 HP, 5 speed tranny, 15 mpg city/19 mpg hwy
the VVTI gives more power across a broader range of the RPM band, not just at higher rpms like the honda, so you are going to see and use the additional power.
jeff
no dyno numbers right now, i'll see what i can find. i agree, the mpg increase is probably due to the 5 speed, that's why i posted that info before somebody called me out on it!
hoser
SILVER Star
Pitbull said:
I'm going to say there is a benefit even in our application. Sure, low rpm torque is the most important but we still regularly exceed 3.5k rpms.
Most manufactures have their version of VVTI and what it does is "OPTIMIZE" low rpm performance/fuel efficiency as well as high rpm performance/efficiency.
A non-VVTI engine is a compromise--a compromise in its valve timing between low and high rpm. Some vehicles can even keep valves shut at low rpm or cruising for better fuel efficiency. Others even turn off cylinders at freeway speed to increase fuel economy.
Valve timing can be based on rpm, throttle, load and can be infinitely variable, not just with two settings.
I'm no expert in this field but how can it not be beneficial?
Jim_Chow
V8_Fan
There are a couple of ways that variable valve timing can be implemented, the most crude being the timing changes at a certain rpm threshold like with Honda's VTEC. You can also have continuous valve timing, where the timing constantly adjusts to throttle/rpm, etc. I think this how BMW does it. So in the latter case, I can see how fuel economy can slightly improve. In the first case, I don't see any difference as long as you keep the rpm's low. I guess they could also set those rpm thresholds lower than that on a sports car.
hoser
SILVER Star
I agree, complexity can sometimes be a downside but have you heard of any problems with a VVTI (or like) system. I've had 4 vehicles with such a system--no problems whatsoever. My 13 year old Acura was one of the first vehicles with variable valve timing and I've never even heard of a problem on the Acura forums.
Even if the sytem failed--it is unlikely that the problem would keep you stranded.
Even if the sytem failed--it is unlikely that the problem would keep you stranded.
toyota has been using VVTI on a number of engines for several years now, and i have not heard of any issues related to it
