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Discussion Starter · #1 ·
I posted this in the engine section and got no response, maybe this group will have opinions on this?.....:mad:

Here's a question for all the knowlegable gear heads out there....If I could tune my truck via the UNICHIP, etc, to make as much peak HP and Torque at a certain RPM range....say 2300 RPM....wouldn't I theroreticaly get the best milage out of the truck (if it was being driven at this RPM) because is was running at it's best out put for the ammount of gas being put into it? In other words....the engine would be running right on the pipe and never straining while cruising.....which is what I do about 85% of the time.
Whatcha think?

Just curious 'cause I'm thinkin' about doing a custom dyno / UNICHIP tune on this soon!
 

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What you are trying to accomplish is getting your AFR (Air to Fuel Ratio) dead on at 14.7. The unichip might let you do it, but I would suggest otherwise.

Instead use a MAF calibrator from URD. Underdog Racing Development

It will give you a few more ponies/torque but will also optimize air/fuel ratio giving you the best fuel effeciency. You can't really say "peak" power/torque because those numbers are given at different RPM, and that's usually way up higher. You're not going to get better fuel economy running your truck at its peak power/torque point.
 

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Discussion Starter · #3 ·
I was just wondering out loud here......
I know HP and torque don't peak at the same time....I'm just wondering if squeezing out a few more ponies at the right time (meaning cruising RPM) would help mileage? I did a few engine swaps many years ago and one popular one was replacing a dodge 340 or 360 V8 with a 440 V8 (and all necessary drive train) in truck. On every occasion that we did this the customer got a benefit of increased gas mileage......my reasoning was (and still is) that the smaller V8's were terribly underpowered and constantly working their guts out...at high throttle settings....resulting in poor mileage and crappy power. The 440's were barely working! They would maintain the same speed as the smaller V8 at a fraction of the throttle position and always got better mileage and had tons more power.
 

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IMO if you could boost the torque higher in the lower RPM that would help mileage. Many people think that just by gearing up and running a lower RPM at highway speed by larger tires etc. will increase mileage BUT that actually works against you because as you said, a smaller engine now has to work harder to maintain a certain speed. By boosting the torque in the cruising range if possible should improve mileage. One thing I notice with the 4.7 is lack of torque at low RPM, even the VVTi models like mine, but when you stomp on it, THEN it goes like a scalded cat.:D
 

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Discussion Starter · #5 ·
IMO if you could boost the torque higher in the lower RPM that would help mileage. .:D
Yeah.......I agree........I'm thinking the Long Tube Headers that are out ther might be part of the answer....I think SS makes them? I also want to put a lighter / smaller pulley on it.....I know it will lose a tiny bit of inertia from the rotating mass diminishing, but the quicker RPM's might be a help (and fun!:D )
I just found out the other day from a Toyota sales guy (while looking at the 07's) that my 04 DC came with a 5 speed tranny as an option.....I wish I would've known that....mine is only 4 speed. Another gear would help keep the engine in that sweet spot RPM wise.
 

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More hp/torque doesn't mean better gas mileage. Advanced ignition timing under cruise condition will get you better mileage, but increases emissions output and combustion chamber/exhaust gas temps. Some engines will tolerate leaner mixtures with additional timing in order to get better mileage. There are some honda engines that will deal with a 16:1 A/F ratio, but then you're greatly dependent on egr and other tricks to keep those exhaust valves and head gaskets from burning up!

The theory of a vehicle being underpowered and getting worse mileage is true - my wife used to have a 4 cyl jeep wrangler that only got 17 mpg on the freeway, while the 6 cyl wrangler would do much better. This is due to lower rpms at any given throttle position and that is what gives you the best possible mpg.

Toyota runs their engines really lean to begin with, so there's not all that much mpg to gain from tuning. In addition your O2 sensors will keep your engine running at 14.7:1 under closed loop cruise conditions regardless of what you do to the engine tune. I got some good results from an airaid intake and modded exhaust, but not cost effective enough to offset the better mileage IMHO. Things like bigger tires and suspension lifting will negatively impact your mileage much more than you could re-gain with other mods and tuning.
 

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Discussion Starter · #7 ·
Hmmmmmm.......Thanks for the input. I think the only way to alter my IG timing is thru the UNICHIP. I've already experienced too much advance in my old 4Runner (pinged it to death!!) and I don't want to do that to this! I should be receiving the EASE diagnostic software and cable soon, it will be very cool to actually see what is going on in this motor and ECU........Maybe I could lower the overall weight of the truck and gain a little mileage....I know....leave the old lady at home! :D
 

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Well I would love it if I could fit a 440 in my Tundra. I used to have a built to the hilt 460 in an old ford. Oh baby nothing like doing 140mph in a 79 F-250 camper special. Thing cooked. Thank God it stayed together. lol:eek:
 

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interesting thread!

here are some things to consider along the points already made....

first, putting a larger engine in place of a smaller engine may be fixing things like poor gearing, excessive resistance (tire selection, alignment issues, brakes dragging) but may not actually have improved overall efficiency etc. also, with OLDER larger engines, there were no advanced electronic controls to optimize air/fuel. it was just up to the carburator and vacuum advanced timing. in this case, you could "bog" down the engine and it would operate at more efficiency because the throttle butterfly in the carb was more open and that would allow the engine to work against less intake flow resistance. of course, one time putting your foot in it, and you could lose all your gains!

on modern engines, you have he ecu to contend with. it tries to operate as close as possible to balanced air/fuel. you still get some effect from running with the throttle body more open, but the problem here is that you have to use all the power produced. say you want to run your engine at peak efficiency. ok, that may mean running at peak torque rpm (say 3500) with throttle 70% open. now, you have to use ALL the power produced at that point and use it to go forward. so, now you're running 110 mph. that obviously isn't a very fuel efficient speed at which to travel due to aerodynamic drag considerations and speeding ticket overhead.

the one tried and true principle about motors is this: size it right for the condition you need. if your only goal is to drive down the highway at 70 mph at peak efficiency, you need an engine that produces just enough power to accomplish this and does so at it's peak operating efficiency. you may only need about 50 of the 250 horsepower your engine produces to maintain hiway speeds. so, that is one way to fix your efficiency problem.

most truck owners want their engines to produce well in a wider variety of circumstances (towing, around town driving, hauling, hiway cruising, 4-wheeling, etc.) so, you have an engine that is way oversized for simple hiway cruising, but that can produce enough power to do all the other stuff we expect from our trucks.

this is the principle GM and others use by knocking out half the cylinders during hiway driving. it essentially allows them to temporarily resize the engine under certain conditions.

i would look towards other solutions that affect your fuel economy much more than engine rpm. for example: tire selection (width, diameter and rolling resistance), ground skirts, lowering, etc. all will lower wind and rolling resistance which are by far the largest factors in a pickup truck design efficiency when considering hiway speeds.

good luck and let us know if you find any solutions that work well!
 

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Discussion Starter · #11 ·
Wow.......cupidstoy....that's a lot of good info........thanks.
Some of those variables I have already looked at...
Tires.....I went with the Nitto's 'cause they are supposed to have a low rolling resistance......BUT....I did put a larger than stock size on...so I may have ate up any benefits I gained right there!
Ground skirts won't work for me......I'd tear them off the first time I went down my road....
I may get to the long tube headers soon.....and then get the UNICHIP set for them......I just got the EASE OBD II software and cable....I'm really interested in how this thing runs.....what changes it makes on the fly, etc..
And still.....lightening the whole truck up would prolly help.....another reason to leave the wifey at home!!!!:eek:
 
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