ADVocate

Any car/truck which uses a turbo does not have a high compression engine. That would blow the cylinder walls out. They use lower compression heads and pistons and let the turbo increase the overall pressure. A standard engine config would have a higher compression rating than the a turbo or supercharged versions.
And even with those factors, the primary difference between the fuel grades is on the Octane rating (and detergent level) which directly couples to performance level. Hence, adding an Octane booster will change the way your engine runs.
I think this thread has deviated into a discussion of ingrained preferences over what grade of fuel to run. And less about the physical results of using regular fuel in this particular truck. We can all find counter statements to reinforce our various viewpoints. I think most people will probably ruin their engines through improper warm up and/ or infrequent oil changes before they muck it up with using improper octane levels. Perhaps to determine if you will get better mileage or appropriate perfromance out of your truck with any fuel, is simply to try it. One thing to consider is that winter fuel is different from summer fuel, with the additives like ethanol and summer's "evaporation inhibitors". So consider that when comparing your results. Me, I don't mind using regular, and I don't think there is a stigma to that. Again, just my POV.

bunka

This seems to be a consistant results with the high performance models as they have the ability to sense poor ingition levels and the car then actual retards the timing. This means that while you can drive it with that fuel, your fuel economy drops SIGNIIFICANTLY more than the price difference between the two types. If you M3 got 22 MPG with premium and it cost $2.50/gallon, you would discover that you fuel economy with the regular probably dropped to about 14MPG while usin gthe $2.20/gallon regulr fuel. A cost savings of approximately 10% and a degradation in fuel economy of around 25%. So, although you can use it (and get poorer performance as you inidicated), the COST issue is that it would not be a wise choice (in that car). Many have found a similar result in reverse witht he GX. It does ":appear" to get beeter performance with premium but this better performance comes at the expense of higher cost (Premium is about 10% more expensive than regular around here) as well as the lower fuel economy (about 5% worse fuel economy with premium).

bunka

I don't beleive that there is a one-for-one with regards to compression and performance. There are a lot of other factors that influence efficency as well as performance (# of value, bore, amount of air the carb provides, etc). Manufacturers can "tune" an engine for differing characteristics. In the case of the Porsche, they tune it to have higher horsepower (see the HP vs. torque figures for a normally aspirated Porsche) whereas the GX is tuned to have greater Torque (for pulling, etc).

looknow12

I'm Dumping my GX.... the second Lexus releases a Hybrid GX. As it is, we are first only 6th in line to get the RX Hybrid. If only it were big enough!

A Hybrid GX would be amazing!

looknow12

Ooops, sorry to change the thread from compression cylinder figures

<VENOM>

bunka
I wondered if in the long run if the regular in an M3 would do more harm then good, the car seemed to run harder like it was trying to make up for the premium by using way more regular, like you said the gas mileage dropped, 50 highway miles it sucked up half a tank.

That car was **** when it came to gas, only 1 gas station was the place it got consistent premium, other smaller stations seemed like the gas was off or it was bad or something, it only got name brand gas but at 2.20+ a gallon when you fill up and the dash lights are blinking, the idle is fluctuating, the car stalls, thats no good, the car avoids those stations, in fact some stations seem like their premium is a mix with the M3, which is F up cause premium comes at a premium, at least 5-10 bucks more a fill up and people are getting gas worse then regular, everytime the M3 got gas and it was running off, the gas was free that was a major pain cause you pull into a major name brand chain and get crap.

Now it only goes to the larger, high traffic Mobils, the smaller stations have way to much questionable gas that is being pumped into the cars, anyone I know that has a premium required performance machine goes to the large stations, the small stations are for the cars that can't feel the difference

GXPrado

Some more reading

http://www.consumerreports.org/main/...East_id=333137

Oh and you guys should try Top Tier gas. I always get Chevron if I can. *Note that Top Tier doesnt mean Premium or high octane.
http://www.toptiergas.com/

<VENOM>

Their is a list of Gas Brands, 1 is the Companies that use Middle East oil and the 2nd is the Brands that don't use Middle East, I can't find it but felt like mentioning it

edit: i looked at the list of the retailers and those are the gas stations who don't use middle east suppliers, damn my area only has Mobil, can't believe thats not top tier

gs400jon

I was just looking at the Toyota press site and took a look at the 2005 GX specs. The fuel requirement calls for 91 octane or higher. Does this agree with the Owners Manual?

http://pressroom.toyota.com/presstxt...05gx470_s2.pdf

If true, some of us have been talking apples and oranges since the 2003/2004 spec calls for 87 octane.

bunka

The HP has been raised in the 2005 model. The way they did this was that they added the variable valve timing function at the higher revs (ala performance cars). This means that a 2005 may benefit more from the use of premium fuel than a 2003/2004 might (at higher revs). However, I believe the 2005 manual still has the same "Vehicle designed to run on regular but use of premium may increase performance..." statement

ADVocate

I think Bunka is correct in his viewpoint on this. From what I understand the higher HP output of the 2005 is more from the computer alorythm adjustments from the factory. It might be possible to do that with the previous model versions (?) if you were able to integrate the newer software. Anyway, most of this thread, which bolsters the use higher octane, is in the perfromance aspect. Not the effiency aspect. I think the fuel economy is stated as a little lower than the previous models. I think the increase in horsepower is simply playing with engine numbers. I could be wrong but I have not read any real difference in the mechanicals of the engine.