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Discussion Starter · #22 ·
My understanding of piston engines is that octane indicates the propensity of a fuel to detonate under pressure. The higher the octane, the higher compression it will tolerate without preignition. I rarely run my car with rpm's sufficient to spool up the turbo, and my 264 cams delay the closure of the intake valve, thereby reducing the compression in the cylinder. Premium fuel existed when this car was new; my 1986 SAAB 9000 Turbo ran better with higher octane fuel but being a 2.0L Turbo the car was almost always using boost.

I filled up my tank this morning. I will be tracking the cost per mile for the next several weeks using 87,89 and 93 octane gas from the same gas station. I will report the results in a separate post.

According to that link I am supposed to use 97 octane gas. My local station has 87, 89 and 93 so I am not sure how to interpret those numbers.
 

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Finaltable, as Chocolate_Cowboy has referenced from the Supra Handbook as per pg. 197.

SPECIFICATIONS
Fuel

Fuel type:
7M-GE engine:
For optimum engine performance, Toyota recommends using premium type unleaded gasoline
with an octane number of 95 or higher (Research Octane Number). If such premium type cannot be obtained, you may use unleaded gasoline with an octane number as low as 91.
7M-GTE engine:
Unleaded gasoline with an octane number of 97 or higher (Research Octane Number).


The RON 97 Octane does coincides with what Wreckless said earlier in the thread, which means PREMIUM fuel is specified.

Also, FWIW. I drive like a putz in my Corolla (Corolla #1), but noticed the car fell flat on its face when ambient temp was > 85*. I started to think about it, and realized the ECU must be running LESS efficient when temps are higher because the ECU is pulling timing due to the 87 Octane and higher intake temps. I switched to 93 octane thinking it would help with knock and improve efficiency I and haven't looked back. I got 6 more mpg and cleaner oil. For all the engine pros here on SF, they may think I'm crazy, but I got longer oil change intervals as per what my ECU was reading. I don't know how exactly, but the ECU knew the oil was cleaner, and it started to get more miles per oil change. I still kept the 87 octane oil change interval for peace of mind. With 93 Octane the ECU was "giving" me 1200 miles difference. Also, the oil that came out for oil changes went from thick and black with 87, to smooth and brown like honey on 93. In my "new" Corolla (Corolla #2), I tested it again. When I switched from 87 to 93, it got 7+mpg more than on 87. Again, the engine is running more efficiently and netting more MPG with a more efficient running engine. Toyota says the Corolla is made to run on 87, but my experience/observation and conclusion is that it is most efficient and optimal with 93 Octane. 93 is the only way to go IMO, even if I'm not driving aggressively.
 

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The stock ecu can hear knock and retard timing on the next cylinder event so it is fast.

I didn't drive my supra to work today but I know that Toyota recommends premium but they do not require it.
 

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Discussion Starter · #25 ·
It turns out I should have just looked in my glove compartment because it is right there on the cover of the owner's manual. 87 is acceptable, higher is recommended for improved vehicle performance.
Font Material property Paper Book Publication


It seems it is perfectly safe for me to continue my test and will not hurt my car to use 87 octane gas.
 

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First things first - that book was published before ethanol/oxygenated gas existed. Octane requirements generally went up across the board because of this. OEM's tuned engines accordingly, but old manuals for old cars are no longer accurate for all the reasons @figgie explained.
Second - you no longer have a stock vehicle. Your driving habits have mitigated a lot of the potential risk, but don't eliminate it.

That does make me wonder how much of the original BHG issues in 7M-GTE's were from people just running 87 octane, especially after Ethanol was added. Occasional mild detonation is a great way to kill a composite HG over the course of 40-50k miles

But given your preferred driving style, It got me thinking about the ideal engine swap for that kind of thing. It's impossible to deny that a MKIII is an excellent long-distance cruiser. I always enjoyed that paired with a shitload of horsepower but the horsepower isn't necessary to enjoy that cruiser aspect of it.

Easy button would seem to be a 1UZ-FE from a SC400 complete with auto trans - reliable as hell, lots of low end torque and easy power without hitting MPG in the shorts, but it also requires premium.

That got me thinking that a 4.0L 1GR-FE and 5AT auto from a 2WD 4Runner or Tacoma would be simply perfect. Lots of low end and midrange torque, good throttle response, insane reliability, drinks 87 octane happily and all day. The 5AT auto would help daily driving/mpg as well.
 
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Discussion Starter · #27 ·
If I ever have to do a complete engine replacement I am leaning toward the 1UZ. I found the guy in New Zealand who has done 20 of these swaps and he sent me a trove of info on it. I have already discussed it with my uncle/mechanic and after reading all the info he says it doesn't sound any worse than what we have already done rebuilding the 7M and replacing the A340. I kind of want to not spend money on the car right now given that I just replaced or rebuilt the entire drivetrain. I didn't know the 1GR was an option. I will look into that as well and appreciate you telling me about it. Next year I will start looking for all the parts needed for a swap and sending them to the shop as I find them. I am only 50 and expect to be at this company, doing this job, for at least another ten years. At 25,000 miles a year I harbor no illusions that this car is not going to need some major work at some point to keep going.
 

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Interesting thought, Wreckless. I've been running 89 octane since my 2nd BHG because the head lost a fair amount. My GE does knock mildly and briefly sometimes when I'm shifting quickly from high revs. I attribute it to the pokey ECU processor not being fast enough to keep up. My 3rd composite gasket died in 60k miles. Surely, the regular mild knock didn't help, but I still completely blame Toyota for a piece of crap gasket.

I will suggest a regular addition of Sta-Bil to keep the stupid ethanol from causing trouble.

And, I've seen a Supra with a 1UZ-FE and it was awesome. Talk about a lot of work, though, including a custom steering rack.
 

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Discussion Starter · #29 ·
First things first - that book was published before ethanol/oxygenated gas existed. Octane requirements generally went up across the board because of this. OEM's tuned engines accordingly, but old manuals for old cars are no longer accurate for all the reasons @figgie explained.
There is a chain of gas stations called Buc-ee's in my region of Texas that sells ethanol free gas at most of its stations. I plan on trying that as one of my options. There is a station very convenient to me on my commute I can use. I just need to make sure I time fill ups because it is halfway between my house and work.
 

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Buc-ee's is a national treasure. I wish they'd build some in NM.


If I ever have to do a complete engine replacement I am leaning toward the 1UZ. I found the guy in New Zealand who has done 20 of these swaps and he sent me a trove of info on it. I have already discussed it with my uncle/mechanic and after reading all the info he says it doesn't sound any worse than what we have already done rebuilding the 7M and replacing the A340. I kind of want to not spend money on the car right now given that I just replaced or rebuilt the entire drivetrain. I didn't know the 1GR was an option. I will look into that as well and appreciate you telling me about it. Next year I will start looking for all the parts needed for a swap and sending them to the shop as I find them. I am only 50 and expect to be at this company, doing this job, for at least another ten years. At 25,000 miles a year I harbor no illusions that this car is not going to need some major work at some point to keep going.
The 1GR is a hypothetical option, I'm not aware of any running MK3 swaps with a 1GR-FE. I do know that 2GR-FSE has been swapped into Toyota Altezza (IS300) and Toyota Soarer (SC300) chassis in Japan, so I'd imagine the 1GR could work though the truck vs car accessories and manifolds and such may change that. So there's some 'pioneering' and figuring out to be done as to how difficult/time consuming it would be to swap effectively. The 1UZ-FE is definitely an easy and straightforward swap, and it does okay on mid-grade gas, but 86-87 octane makes it hate life and I can speak to that having owned an LS400 and SC400 in the past, and I put probably 70k miles on the LS400 in my ownership.
So if you're open to running mid-grade as a minimum, the 1UZ-FE is a drop in proposition if you find an LS400 donor. There's the wiring and all to handle but the engine mounts and trans mounts, trans linkage, gauge cluster, etc are all fairly straightforward to sort out in a MKIII. For your highway mileage, I'd say dropping to a 3.58:1 final drive at the same time as the 1UZ swap would be an excellent call as well, though getting the speedometer accurate would be a little troublesome.

....Now that my brain finally started working, I'd say nix both of those and go with a 2UZ-FE out of a Tundra instead. Similar 4spd auto, but drinks 87 octane all day long and it's torque for days. Similar packaging and swap parts required, one could use the SC400 oil pans and exhaust manifolds on the 2UZ-FE and just sort the rest out from there. It'd weigh a little more being an iron block, but it'd make more torque and drink the cheap gas.

Interesting thought, Wreckless. I've been running 89 octane since my 2nd BHG because the head lost a fair amount. My GE does knock mildly and briefly sometimes when I'm shifting quickly from high revs. I attribute it to the pokey ECU processor not being fast enough to keep up. My 3rd composite gasket died in 60k miles. Surely, the regular mild knock didn't help, but I still completely blame Toyota for a piece of crap gasket.

I will suggest a regular addition of Sta-Bil to keep the stupid ethanol from causing trouble.

And, I've seen a Supra with a 1UZ-FE and it was awesome. Talk about a lot of work, though, including a custom steering rack.
LS400 and GS400 1UZ's are front sump and definitely would not fit a MKIII without lots of changes to the steering etc. But an SC400 1UZ-FE has a rear sump oil pan and much more compact exhaust manifolds, and swapping one of those into a MKIII is very straightforward these days. Basically it's just engine mounts, wiring, and bolt the damn thing in, then finish the exhaust etc.
 
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Discussion Starter · #31 ·
So if you're open to running mid-grade as a minimum, the 1UZ-FE is a drop in proposition if you find an LS400 donor.
I am okay with mid-grade if required. I just don't spend extra if not needed. My $/mile analysis will be educational. It looks like the 4.0 from an SC400 is the way to go so I will start looking for one of those in the not so far future. He said ideally I want the motor, transmission and torque converter straight out of an SC if I can get it.
 

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I've always run 91 octane in my 7M-GTE. Today that price is $4.85 a gallon at my local Chevron. :rolleyes:
 

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Discussion Starter · #33 ·
I've always run 91 octane in my 7M-GTE. Today that price is $4.85 a gallon at my local Chevron. :rolleyes:
Ouch! 87 is $2.79 at Buc-e's. 93 is $3.33. Plus I get $0.10 off per gallon by having a TDECU credit card.
 

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@finaltable I miss Buc-ees! I grew up in Austin and stop by whenever I'm visiting family in TX. No such luck on gas prices here.
 

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Georgia has two Buc-ee's one in the northside of the state and one on the southside of the state
 

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@Wreckless to think my father in-law left us his SC400 he bought new in 93 I think back in 2006. After the daughter graduated HS in 2008 we re-gifted it to another family member in AZ.
 

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Bought my 90 Turbo new and used standard unleaded in it for months or years until a friend suggested I should use Premium for such a fine car. Which I did but since I wasn't heavy footed I didn't notice any difference.

However occasionally it was fun to scare the passengers in the back seat if I didn't warn them I was going to floor it.

That said, I did have the infamous BHG 4 years after purchase, so there's a possibility I did some HG harm. It's still completely stock with whatever HG the dealer put in.
 

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so many limitations on the head gasket and why they blow....

1. factory torque. but hey, its 2021....is there really a 7mge running on a factory HG ? (maybe)
2. unknown history. all it takes is one low coolant event and guess what....maybe you slightly warped it. or maybe it ran hot on one cylinder from a bad injector and heat annalled the exhaust side ....and crushed the head slightly (as in the quake thread on here). maybe the cat plugged and roasted her. who knows
3. its a straight 6. big long head. more prone to problems. like an open deck all aluminum 4cyl vs old school aluminum on iron.

I have been piss pounding a felpro "mls" multi layer aluminum foil with magic 3d printed on holograpic seals gasket. ARP studs, torqued down slowly step by step with someone with 5 mf synapses ... and viola....still holding 15-20 lbs boost on piggy back madness. I built this motor before I was married, 14 years ago, it sat for 8 years (magic assembly lube i tell you) and then I got motivated. so beating it for 6 years now. keep coolant and oil in the engine and the 7m will live. dont detonate with "horse piss" 87 fuel and she will live. RPM's and wide open throttle won't kill it, trust me I am trying
 

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so many limitations on the head gasket and why they blow....

1. factory torque. but hey, its 2021....is there really a 7mge running on a factory HG ? (maybe)
2. unknown history. all it takes is one low coolant event and guess what....maybe you slightly warped it. or maybe it ran hot on one cylinder from a bad injector and heat annalled the exhaust side ....and crushed the head slightly (as in the quake thread on here). maybe the cat plugged and roasted her. who knows
3. its a straight 6. big long head. more prone to problems. like an open deck all aluminum 4cyl vs old school aluminum on iron.

I have been piss pounding a felpro "mls" multi layer aluminum foil with magic 3d printed on holograpic seals gasket. ARP studs, torqued down slowly step by step with someone with 5 mf synapses ... and viola....still holding 15-20 lbs boost on piggy back madness. I built this motor before I was married, 14 years ago, it sat for 8 years (magic assembly lube i tell you) and then I got motivated. so beating it for 6 years now. keep coolant and oil in the engine and the 7m will live. dont detonate with "horse piss" 87 fuel and she will live. RPM's and wide open throttle won't kill it, trust me I am trying
Actually I know the history pretty well. It's a one owner car (mine) and all stock. But back in the day, I could "point-and-pay" and didn't really pay that much attention to what the dealer did for repairs HG-wise. I'll recheck my receipts more closely.
Interesting that your car sat for 8 years. Mine has sat since 2007 because it was burning coolant but passed compression checks etc. The assumption was coolant erosion into the chamber of cylinder (#6?) because exhaust gas was found in the coolant. Was told to keep driving it but I was afraid to so it sat. Big mistake. Now the tranny has issues going into reverse, coolant light is always on no matter how far topped off, etc.
 
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