MPG, how to improve?

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After removing the roof rack, my MPG went up considerably. I last tank was roughly 12.2 mpg with a mix of city driving and commuting (fun stuff in Northern Virginia with A LOT of start and stop). That being said, I am much more pleased with the 12 mpg in my crappy daily conditions running the a/c, then I was with the 10 mpg with the roof rack. I am looking forward to seeing how it performs on the first road trip. With all of the mods and tires, I am happy with 12/15.
 
has anyone considered ditching the cats off the exhaust system and replacing it with straightpipes for better mpg's?

i have a feeling i'm going to get some slack for this...:popcorn:
 
1meancruiser said:
has anyone considered ditching the cats off the exhaust system and replacing it with straightpipes for better mpg's?

i have a feeling i'm going to get some slack for this...:popcorn:
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I have high flow cats. My factory cats input/output went down to about an inch whereas I now have 2.5inch into a single 3 inch free flowing system. Sounds great, improved performance and economy.

Edit: the sensors had to be extended to suit the performance system I have but I have never had any warning lights. It was installed in 2009 And i posted on here. If you cut out your cats then the two sensors that are gonna complain and put you into limp mode.

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Ditching the cats will likely decrease actual performance by shifting peak torque higher up the rev band. If you also improve the intake you may net out ok since improving both (intake and exhaust) should gain you some power overall. It is difficult to increase power AND retain the low end torque without careful planning (or forced induction).

So, basically it would sound a little different, stink a lot more, and perform a little worse. Not worth it to me but maybe you have different goals.

OTOH with careful planning the 4.7 Is likely good for a lot more power overall. The motor is set up for low end torque and runs out of steam at the high end. If you don't care about the low end you could open up the intake, go to a short-runner plenum, add high rpm optimized equal-length headers with free flow cats, go to a higher capacity fuel injector, and retune the ECU and get maybe 300-320hp. Reground cams after that would probably get you into 350+ territory. It's at least as good a motor as the SBC there are just fewer performance parts available.
 
moooooooo said:
I have high flow cats. My factory cats input/output went down to about an inch whereas I now have 2.5inch into a single 3 inch free flowing system. Sounds great, improved performance and economy.

Edit: the sensors had to be extended to suit the performance system I have but I have never had any warning lights. It was installed in 2009 And i posted on here. If you cut out your cats then the two sensors that are gonna complain and put you into limp mode.

I checked the exhaust system and could not find any sensors beyond the cats. where are these sensors located?
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jOnathN said:
Ditching the cats will likely decrease actual performance by shifting peak torque higher up the rev band. If you also improve the intake you may net out ok since improving both (intake and exhaust) should gain you some power overall. It is difficult to increase power AND retain the low end torque without careful planning (or forced induction).

So, basically it would sound a little different, stink a lot more, and perform a little worse. Not worth it to me but maybe you have different goals.

OTOH with careful planning the 4.7 Is likely good for a lot more power overall. The motor is set up for low end torque and runs out of steam at the high end. If you don't care about the low end you could open up the intake, go to a short-runner plenum, add high rpm optimized equal-length headers with free flow cats, go to a higher capacity fuel injector, and retune the ECU and get maybe 300-320hp. Reground cams after that would probably get you into 350+ territory. It's at least as good a motor as the SBC there are just fewer performance parts available.
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I'm familiar with setting up a motor for low end torque versus hi end. these cats are just a massive impedence on the exhaust, you're still running dual 2" piping into a 2.5" main pipe. Probably the absolute minimum for a 4.7 V8 and, I think, it is hardly considered opening up the exhaust...
 
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I'll take another look, i looked last night and could not find another set after the cats...
 
jOnathN said:
Ditching the cats will likely decrease actual performance by shifting peak torque higher up the rev band. If you also improve the intake you may net out ok since improving both (intake and exhaust) should gain you some power overall. It is difficult to increase power AND retain the low end torque without careful planning (or forced induction).

So, basically it would sound a little different, stink a lot more, and perform a little worse. Not worth it to me but maybe you have different goals.

OTOH with careful planning the 4.7 Is likely good for a lot more power overall. The motor is set up for low end torque and runs out of steam at the high end. If you don't care about the low end you could open up the intake, go to a short-runner plenum, add high rpm optimized equal-length headers with free flow cats, go to a higher capacity fuel injector, and retune the ECU and get maybe 300-320hp. Reground cams after that would probably get you into 350+ territory. It's at least as good a motor as the SBC there are just fewer performance parts available.
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Your quoting out 140-160 horsepower gain with your listed mods... How do think drivability would be affected?
 
RobRed-
I was thinking ~70 hp (235 to 300 or so), not 140-160.

Would be fine on the street although louder. A hair slower off the line but a lot faster from 30mph and for highway passing. It would suck more offroad when you want to idle over something and would stress out the transmission more for towing since you would need to use more pedal to get the load moving. Basically would be better as a car and worse as a truck. :)

I was just speculating based on what you can do with similar displacement Ford and Chevy v8s and a basic understanding of engine tech.

The ideal actually is to use active components so you can have two tuning points, one for low rev and the other for high rev.

E.g.: the later motors use variable valve timing -VVTI - to keep the low end tuning until a certain rpm and then it basically switches the cam to a high rpm profile. Still a mild tune but it ups horsepower from 230 to 270 with basically the same intake and exhaust.

Porsche (and everyone else these days) also use a dual-range intake plenum that switches between short and long runner tuning. I can't think of anyone using dual exhaust tunes...probably too difficult to fit the plumbing in. For intake and exhaust both the goal is to set up a resonance at the target rpm so that the intake side is getting high pressure pulses in time with the intake valve opening (gets more air in) and the exhaust side is getting low pressure pulses in time with the exhaust valve opening (the vacuum helps suck the burned gas out faster).

Anyway, the short of it is that if you make the exhaust bigger it typically changes the resonance to a higher frequency so the exhaust is in tune with a higher rpm.

OTOH something like the DT header is usually designed to enhance the resonance (bigger tubes but longer) at the same (or a nearby) rpm, increasing torque a little.
 
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I have two 06 VVt-i models that get very different mileage.

On mine just got Michelin 285/70-17 AT/2 running at 40/38 rear psi. According to the trip computer I was making 11.4 mpg on a high speed highway run between cities. Probably ran at 3k for over an hour. I have not monkeyed with the suspension at all yet. How do I calculate the deviation % for the larger tires?

I have "0" mods other than tires.
Not running rear seats.
Temperature is between 88-105.

Our other Cruiser has the stock 265/70-17 Michelin LTX that are two years old. The psi is 40/38. I found a broken 4mm air hose...replaced with Gates Hose. Freeway MPG went from 12 to 18 mpg. :) This Cruiser rarely goes over 130km/hr.
 
More MPG? Are you kidding me?

Interesting discussion, here's my $0.02 worth - I stopped checking the mileage on my 1999 after the first few tanks. 12 - 14 mpg. I just fill it up when the gauge hits ever-full. The fuel light comes on consistently at about 300-310 miles, and I plan my trips accordingly.

I'm no Vanderbilt, I knew it was a gas guzzler when I bought it and I really don't care. Its the price you pay for a kick-ass, comfortable off road machine. I keep it garaged and impeccably maintained, and don't use it as a daily driver. There are much more economical vehicles for commuting, I won't bother listing them here.

You knew what you were getting into when you bought it. Want more than 15 mpg? Buy a Tacoma.
 
68lc said:
More MPG? Are you kidding me?
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Congrats, you're getting 12-14. Thats the normal range for most of us.

The OP is getting less than 10. Something is off with numbers that low, even for an LC. He's not asking for 15, he's asking for normal. Nothing wrong with that.
 
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TheFuzz said:
Congrats, you're getting 12-14. Thats the normal range for most of us.

The OP is getting less than 10. Something is off with numbers that low, even for an LC. He's not asking for 15, he's asking for normal. Nothing wrong with that.
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Fair enough but I thought there has been good info in this thread.
The OP needs to take the vehicle to his trusted mechanic and go back to basics. Air filter, fuel filter, spark plugs and coil packs, and check all of the vacuum hoses. As others have mentioned MAF sensor and throttle body cleaning and check your tyre pressures.

Edit: and alternator draw in case you have a battery on its way out meaning your alternator is loaded up more than normal

Sent from my iPhone using IH8MUD
 
I am getting 12+ and am in the normal range after taking the roof rack off.
 
One other thing to consider is the thermostat. Whilst thermostat issues were in older cars from other eras it's still pretty much a thermostat.

What if yours is only slightly dodgy and therefore your temps are slightly higher? Hypothetical I know but it's happened in older vehicles and affects fuel economy.

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watchknut said:
I am getting 12+ and am in the normal range after taking the roof rack off.
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Could it have been your driving style causing the 10mpg previously? I am getting consistent 12-12.5 mpg with the front bumper, sliders, rear bumper, 55 lb drawers and the stock rack

Edit: oops, I did not see that you had an ARB roof rack..might have been the variable which caused the mpg to drop
 
68LC said:
Interesting discussion, here's my $0.02 worth - I stopped checking the mileage on my 1999 after the first few tanks. 12 - 14 mpg. I just fill it up when the gauge hits ever-full. The fuel light comes on consistently at about 300-310 miles, and I plan my trips accordingly.

I'm no Vanderbilt, I knew it was a gas guzzler when I bought it and I really don't care. Its the price you pay for a kick-ass, comfortable off road machine. I keep it garaged and impeccably maintained, and don't use it as a daily driver. There are much more economical vehicles for commuting, I won't bother listing them here.

You knew what you were getting into when you bought it. Want more than 15 mpg? Buy a Tacoma.
Click to expand...

You may not be a vanderbilt but that odor coming from the yellow stuff in your cherios shouldnt put a smile on your face as often as it does. I bet your "daily driver" gets you some attractive looks from strange dudes.
 
DuckLN said:
You may not be a vanderbilt but that odor coming from the yellow stuff in your cherios shouldnt put a smile on your face as often as it does. I bet your "daily driver" gets you some attractive looks from strange dudes.
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fantastic reply. Not. A most uninformative reply and potential bad advertising for ih8mud potential subscribers??


kind regards
peter
 
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