Quote:
Originally Posted by pgfpro
I just realized my response to your question never posted.lol
To answer your question, I'm not to sure on the delayed intake valve type engines? LIVC will help with pumping losses, but to what to degree is the question??? Sorry don't have a answer on that one.lol
Very good question though!!!  |
First of all holy smokes 10000 rpm limit on that engine? Nice.
So if you assume that combustion quality is more or less as good as it can be by say 3000rpm, you can find dyno charts for very crazy cammed motors like the 3S-GE with TRD power kit, dyno charts for the 1NZ-FXE and 2ZR-FXE, etc. and infer how much air is being bled off by LIVC based on the specific torque.
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The torque on the 1NZ at 3000 is 105Nm, for a specific torque of 70Nm/L, and at 4000 it's off the chart but if you extrapolate you land somewhere around 115 or 78Nm/L ish. I think the intake cam is something like 280 degrees, but at maximum retarded timing the peak lift happens later than on the 3S example. The stock 3S-GE I would guess has something like a 260* intake cam, which is what you tend to see on a dual-cam-phasing single cam profile engine with that kind of torque curve. The replacement cam is a 296*, but half of the extra duration goes to overlap not delayed valve closure, so if my guesses are right it should have a similar specific torque curve to the 1NZ. The graph seems to show ~160Nm at 4000rpm for 80Nm/L, similar to the 1NZ.
Anyways, 80Nm/L should mean the VE is less than 80% of torque peak since the efficiency should be a little bit higher at that point. The unknown is how much lower that number can go from VVT adjustment, but it looks like you might be able to get in the low 60s at 3000rpm.
I only have my own car to go off of, but Torque reports 30% load on the freeway, 18% at idle, and at freeway speed my engine is at its torque peak (stupid gearing). If the engine only ingested 75% as much air, it seems like I should be able to save 25/70=36% of pumping loss. Taking the hypothetical situation a little further if I ran 18:1 AFRs that would bring the air necessary to produce power up from 30% of peak VE to 36% of peak VE, and so my pumping losses would be reduced by 31/70=44%. If the engine ingested 70% as much air at WOT, the savings increase to more than 50%. Not bad! Bump the compression ratio up to 13-14 and the mpgs should be astonishing. For engines run at really inefficient speeds, LIVC seems like it can help considerably, as each percent torque you lose buys you more than 1% savings in pumping loss while giving you more horsepower at the top end too. I certainly wouldn't mind if my car were as slow as a typical econobox until I rev it past 4.5k if it increased my gas mileage by a lot.