Upgrades For Better Mpg?

jcrome04 · August 31, 2008

fuel additives are a waste. Putting in an extra pint of gasoline will make your tank last longer too! :lol:

Blayd · August 31, 2008

I was doing all this stuff and still getting 13mpg city. Then i changed my thermostat for about $20. (Needle was below half mark)
Now I get 19mpg.

Do what?

LEXUSA · September 11, 2008

My first post as a "hope-to-be-soon-owner" of an LS400.

A faulty thermostat that hangs open will cause two problems. 1, it keeps the ECU in warm up mode which is richer than it needs to be. 2, the engine will not burn the fuel as efficiently and will require more throttle input thusly more consumption.

A K&N will only flow better if the paper filter it is replacing is too small or causes some restriction. This is usually more noticable at higher rpm/throttle openings unless the factory paper filter is large enough to accomodate the engine to begin with. A K&N will flow better per square inch than paper.

Has anyone tried running 89 or 87 octane? If this engine has a knock sensor it should be able to compensate. Premium "Pump" gas is the least thermally efficient fuel you can run. I'd guess that the combustion chamber and compression ratio of the LS is not prone to detonation, the only reason to run higher octane. Premium "pump" gas kills perfomance and efficiency in the process of preventing knock/detonation.

Is there a taller rear gear available? A friggin' Corvette gets mid to low 30mpg highway due to its tall final gearing. 350 to 420 horsepower/torque with no regard for economy. Sure it only weighs around 3,000 lbs but it also only turns in the 1,700rpm range at a 75mph cruise in top gear. What does an LS turn at 75mph?

Vern Dias · September 11, 2008

~2100.

Vern

Blayd · September 11, 2008

Is there a taller rear gear available? A friggin' Corvette gets mid to low 30mpg highway due to its tall final gearing. 350 to 420 horsepower/torque with no regard for economy. Sure it only weighs around 3,000 lbs but it also only turns in the 1,700rpm range at a 75mph cruise in top gear. What does an LS turn at 75mph?

Its more than tall final gearing. Its also very good aerodynamics. And it's very lightweight.

LEXUSA · September 11, 2008

A Corvette's aerodynamics do play a part in the mileage but not the 7-9mpg difference.

The current Corvette is a C6, the C5 started around 99ish. The previous body style that started in 1984 is the C4. A C4 weighs close to 3700lbs, has a little shorter gearing than the C5/C6 and will still get around 30mpg on the highway at reasonable speeds of say 70mph. Gearing is so overlooked on cars that should get better gas mileage, especially those with V-8's that have the torque to turn taller ratios. I bet a big gain in mpg would be had if the rpm could be cut to 1,800 or so at 75mph.

What kinda torque numbers do the later model 400's with the 5-speed auto make? It takes very little hp to cruise but tall gearing takes a decent amount of torque. Is the transmission in an LS similar to a Supra or Truck?

LEXUSA · September 11, 2008

These are just suggestions based on my experience over the years, what I've found that works and what doesn't.

A buddy of mine had an Acura MDX SUV. It got terrible mileage, around 15mpg or so. 3.0L engine I believe but it revved high at highway speeds, mid 2K area as I remember. I know something as simple as a taller gear might sound too easy to be true but the proof is in the results.

lsrxlex · September 19, 2008

These are just suggestions based on my experience over the years, what I've found that works and what doesn't.
A buddy of mine had an Acura MDX SUV. It got terrible mileage, around 15mpg or so. 3.0L engine I believe but it revved high at highway speeds, mid 2K area as I remember. I know something as simple as a taller gear might sound too easy to be true but the proof is in the results.

What do you guys think of this thread at Clublexus.com under "All ls400 owners with bad gas mileage Read This"?

I think they're talking about replacing the Water Temperature Sensor (?).

Thanks.

LEXUSA · September 20, 2008

Was that thread about those not happy with the 25mpg highway or those getting in the mid teens?

If the Temp Sensor is bad and reading low then the engine will stay in warm up mode and run richer. I have a motorcycle that had a problem like this from the factory. Using the correct thermostat and sensor is crucial for an engine to run correctly with fuel injection. FI relies on sensors to adjust it so if they are off, it will be off.

AZ Mike · September 24, 2008

Has anyone tried running 89 or 87 octane? If this engine has a knock sensor it should be able to compensate. Premium "Pump" gas is the least thermally efficient fuel you can run. I'd guess that the combustion chamber and compression ratio of the LS is not prone to detonation, the only reason to run higher octane. Premium "pump" gas kills perfomance and efficiency in the process of preventing knock/detonation.

If the engine is designed for premium fuel, it is because it runs at a higher compression, and the higher octane will prevent predetonation. Yes, sensors in the emissions system can detect pinging, and will attempt to prevent it by adjusting the timing. However, even if it is successful in ping prevention, the engine will operate less efficiently due to the adjustment in timing. So, at worst, you have predetonation, which will cause engine damage over time. At best, you will force your engine to run in a less efficient mode. Is that worth savings of 20 cents per gallon?

LEXUSA · September 24, 2008

You are suggesting that higher octane with more ignition advance is better than using lower octane with less advance. There is a limit to how much advance/!Removed! can be used with good results but I doubt it would take much to run 87 octane. Does an LS400 for sure have a knock sensor?

I'm not advocating the use of 87 octane as a means to saving money. 87 octane is better fuel than 93 and runs more cleanly because it has less additives in it to prevent knock/ping/detonation. I'd love to see what the LS400 combustion chamber looks like. I bet it is very "motorcycle" looking, shallow pentroof design that does not promote knock/ping/detonation with 10:1 compression or a bit more. If so, I can't for the life of me understand why this motor won't run better on 87 octane. I have a Suzuki sportbike with the same displacement per cylinder, 11something:1 compression and loves 87 unless it is really hot outside. It doesn't have a knock sensor, the ECU runs a set advance curve.

jcrome04 · September 25, 2008

the 1UZFE isn't a motorcycle engine...

it's designed to run on premium..... it's a high compression engine...

discussing what octane rating to use is like beating a dead horse....with a broken stick... lol :D

LEXUSA · September 25, 2008

"Premium" is usually recommended by manufacturers as a safety cushion if the engine has any possibility of detonation in the worst of conditions. The only OEM car engines I've ever seen that were "designed" to run on premium are older American designs. Terrible combustion chamber/piston top, poor ignition control, they were designed to detonate.

Please note: I now realize the 1UZFE isn't a motorcycle engine, thanks for pointing that out.

I used to run premium in everthing I owned because I thought it was better fuel.

What is the compression for this engine?

jcrome04 · September 25, 2008

97 is 10.5:1 ...........I believe

LEXUSA · September 25, 2008

Damn, thats up there. This is a motorcycle engine after all. :lol:

The first generation Hayabusa only had 10.5:1 compression, ran best on 87 octane "pump" gas.

johnhoward · September 25, 2008

97 is 10.5:1 ...........I believe

I have to chime in on this... since everyone has changed the subject (kind of).

- I've got a 99 LS

I bought the K and N about 6 months ago. So, the K and N hasn't helped, or hurt my mileage. I have the cleaning kit, and, have since cleaned it once - pretty easy - and, I like NOT having to pay 25$ (mininum) for a new OEM filter every 8 months or so. As far as added power, none extra with the K and N. I think the car intake sounds a bit louder as you accelerate. But, this is the same as the old trick of flipping the carbureutor filter cover over in the good old days - more sound, same or little power increase.

I also have nitrogen filled Mich. tires - while they do seem to stay inflated more consistently - no better milage for me.

I don't really believe in synthetic oils. They are more viscous and will leak much easier in older cars. Look for drips in the garage or drive. Stick with OEM oil and save the bucks, and drips. Some may say their cars don't drip, and they may not, but older milage cars with worn seals are subject to.

2 cents

J

LEXUSA · September 25, 2008

Taller gearing if its available. Something around a 3.90 rear gear would take about 200rpm off of top gear highway cruise.

killerFatty · September 26, 2008

what is the stock rear-end gear ratio and compression for a 93 LS? The 09 LS460 has 11.8:1 compression whis is higher than a 507HP Mercades CLS63 AMG and the same as a 09 porsche 911 carrera S. :D WOW :D

AZ Mike · September 26, 2008

"Premium" is usually recommended by manufacturers as a safety cushion if the engine has any possibility of detonation in the worst of conditions. The only OEM car engines I've ever seen that were "designed" to run on premium are older American designs. Terrible combustion chamber/piston top, poor ignition control, they were designed to detonate.
Please note: I now realize the 1UZFE isn't a motorcycle engine, thanks for pointing that out.

I used to run premium in everthing I owned because I thought it was better fuel.

What is the compression for this engine?

Feel free to use whatever gasoline you like. You obviously are smarter than the Lexus engineers.

As for my car, I am sticking with the owner's manual, which states verbatim: "Select premium unleaded gasoline with an Octane Rating of 91 or higher for optimum engine performance. However, if such premium type cannot be obtained, you may temporarily use unleaded gasoline with an octane rating as low as 87."

My expectation for using lower octane fuel in an engine designed for higher octane fuel is lower fuel economy and lower power at wide open throttle. There are many studies that demonstrate this. In fact, many on this board have tested the fuel economy theory and have proven it in their situations.

Running premium fuel in an engine designed for regular fuel is a proven waste of money. At times, it may mask other problems, but it is much more economical to repair the underlying problem.

LEXUSA · September 26, 2008

Is it that obvious I am smarter than the Lexus engineers? I'll have to tone it down a bit, I get crazy on public forums which encourage discussion and thoughts not mainstream. It has been my experience that most folks don't understand "American Pump Gas". I too used to think there was some benefit to running higher octane other than to preventing knock, but there isn't. But enough of that, seems like most that have tried it in an LS400 have not experienced any improvement.

I believe the rear gear ratio is 4.09 or so. Does the rear ring and pinion in an LS400 also fit other Lexus or Toyota vehicles?

LEXUSA · September 28, 2008

At this juncture I will conceed my faulty reasoning. I assumed the compression would be around 10:1. With the compression at 10.5:1 the factory timing is probably rather mild and for it to !Removed! even further to compensate for 87 octane may put it into the loss of efficiency area.

Retarding timing in crisis situations with turbo set-ups is only for moments at which power and efficiency are way down. This is ok since it saves the engine but if it runs for extended periods it is not good.

Randy&Bonnie · September 28, 2008

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Randy&Bonnie · September 28, 2008

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Randy&Bonnie · September 28, 2008

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HRP · September 29, 2008

Just a comment: In the mid 1950's one of my friends gave me some older (1940's) Popular Science, Popular Mechanics, and Mechanic's Illustrated magazines (all now long gone). I recall reading an article that someone had added an extra smaller fuel tank to his car which he filled with the higher octane gasoline (Hi-Test). The larger one he filled with"regular". He used the higher octane for starting and driving the car around town. He switched (manually) to the regular tank for his highway driving. His reason was that since his engine was not usually subjected to increased acceleration on the highway and at around 45 - 60 mph he saw no need to use the higher octane and noticed no difference in milage with the cheaper lower octane fuel. Of course this was in the days of 3 on the tree, overdrive, oil bath air cleaners, mostly in-line 6's and 8's, and 45-55 mph highway speed limits. With today's technology and $4 plus higher octane fuel, I wonder if that concept would be of value today. Sure wish I'd kept those old magazines.