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Premium Fuel
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Woodmister
- Posts: 230
- Joined: Sat Nov 16, 2002 7:02 am
Premium Fuel
I was wondering if Premium Fuel, the highest octane fuel they sell at gas stations (92/93) really make a difference in my 93 Q45s performance/how it runs? What if I use the lowest octane (87/89)? I know the highest octane is the best, the fastest, and what real dragsters and airplanes use (140ish octane). Im just wondering why the Q needs it. Is it becasue my 4.5L 274 HP ingine smokes my friends Hondas and Acuras Hit me back
Hit me back-
greg_atlanta
- Posts: 1111
- Joined: Tue Jul 23, 2002 4:37 pm
- Car: 2008 G35 Journey Sedan, silver/black (no sunroof), 1992 Q45 (in a past life)
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Woodmister
- Posts: 230
- Joined: Sat Nov 16, 2002 7:02 am
Nothing bothers me I was just wondering. I knew about the knocking, but just wondering what other side affects there are. I dont want or need a Honda. My school is like .2 miles away from my house I can go back and forth from school like 350 times before I need a refill. Im also thinking about getting a small sticker that says "Nice body kit...wanna race?" and put in on the back window.
Probally 700 times, I was doing .5 miles each way, depending on school traffic so 350 saftly
Probally 700 times, I was doing .5 miles each way, depending on school traffic so 350 saftly
Woodmister wrote: My school is like .2 miles away from my house I can go back and forth from school like 350 times before I need a refill.
Your type of use would be considered extreme because your engine never properly warms up if you only drive .2 miles. This leads to harmful accumulations of water in the engine, exhaust system, etc.. You should change your oil accordingly. If you only live .2 miles from your destination, why are you even bothering to drive? Talk about a waste of resources. BTW, knocking is really bad for the engine.
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Woodmister
- Posts: 230
- Joined: Sat Nov 16, 2002 7:02 am
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Woodmister
- Posts: 230
- Joined: Sat Nov 16, 2002 7:02 am
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
"eventually wear out the knock sensors ($800-1000 repair). "
The knocks sensors only fail from overheats [they soften and then crack making an open circuit].
You can always turn the timing back [3-4 degrees less initial advance] losing 10% of power and losing 10% in mileage and burn Regular save $2-$4 a week...............but somehow worrying about $4 week means you are driving the wrong car.
The knocks sensors only fail from overheats [they soften and then crack making an open circuit].
You can always turn the timing back [3-4 degrees less initial advance] losing 10% of power and losing 10% in mileage and burn Regular save $2-$4 a week...............but somehow worrying about $4 week means you are driving the wrong car.
True -- when you don't drive much, you tend to get away for longer periods or time (not more miles) with things like bald tires or abused engines. Here are some general thoughts about the gasoline question.
As the ignition timing backs off, as it must with regular, a greater percentage of the energy released by combustion is rejected as heat (unavailable for propulsion). The excess heat either goes out the exhaust or into the cooling system.
1. Even if your cooling system is 100%, you may be asking for trouble asking it to handle more heat, particularly when the warmer weather returns. Overheats are death to aluminum engines.
2. Passing significantly hotter exhaust by the exhaust valves shortens their life. Cold, hard economics dictates that an older Q usually isn't worth a valve job. Very, very sad, but often true. My assertion here is that running regular gas can endanger the car.
3. If your knock sensors aren't 100% efficient at preventing knock (impossible -- there has to be a knock before it can be detected), some damage will occur to the pistons. If an old Q isn't worth a valve job, it's certainly not worth a piston replacement. Granted, a hole in the piston isn't particularly likely around town, but every ping causes *some* damage.
In addition to making the cooling system's job easier, cooler weather means cooler intake air, and theoretically less chance of ping. Unfortunately, there's no free lunch, because fuels are formulated for the expected temperatures, so the cold air just balances things out. Other tradeoffs exist for other conditions, such as high altitude or oxygenated gas.
It's quite a balancing act. Any motor -- but particularly the Q's motor -- was designed around some assumptions. One of them is 92/93 octane, just like another is that the motor usually operate right-side-up. Screw with any of the engineers' assumptions, and bad things are much more likely to happen.
As the ignition timing backs off, as it must with regular, a greater percentage of the energy released by combustion is rejected as heat (unavailable for propulsion). The excess heat either goes out the exhaust or into the cooling system.
1. Even if your cooling system is 100%, you may be asking for trouble asking it to handle more heat, particularly when the warmer weather returns. Overheats are death to aluminum engines.
2. Passing significantly hotter exhaust by the exhaust valves shortens their life. Cold, hard economics dictates that an older Q usually isn't worth a valve job. Very, very sad, but often true. My assertion here is that running regular gas can endanger the car.
3. If your knock sensors aren't 100% efficient at preventing knock (impossible -- there has to be a knock before it can be detected), some damage will occur to the pistons. If an old Q isn't worth a valve job, it's certainly not worth a piston replacement. Granted, a hole in the piston isn't particularly likely around town, but every ping causes *some* damage.
In addition to making the cooling system's job easier, cooler weather means cooler intake air, and theoretically less chance of ping. Unfortunately, there's no free lunch, because fuels are formulated for the expected temperatures, so the cold air just balances things out. Other tradeoffs exist for other conditions, such as high altitude or oxygenated gas.
It's quite a balancing act. Any motor -- but particularly the Q's motor -- was designed around some assumptions. One of them is 92/93 octane, just like another is that the motor usually operate right-side-up. Screw with any of the engineers' assumptions, and bad things are much more likely to happen.
My wife often puts regular gas in my 91Q and it runs just fine. I always put premium fuel in and really can't notice much of a difference. Mileage is not better with premium. Engine/piston damage can only come from heavy prolonged knocking. Very slight pinging will not cause damage. Not so sure I agree with assertion that "greater percentage of combustion heat is rejected and unavailable for propulsion" as this is technically incorrect. Also, any thoughts on which brand of gasoline has the best additive package. My neighbor works for a testing lab, and he claims that Texaco's System 3's package is the best, with Mobil a close second.
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greg_atlanta
- Posts: 1111
- Joined: Tue Jul 23, 2002 4:37 pm
- Car: 2008 G35 Journey Sedan, silver/black (no sunroof), 1992 Q45 (in a past life)
paintwgn wrote:Also, any thoughts on which brand of gasoline has the best additive package. My neighbor works for a testing lab, and he claims that Texaco's System 3's package is the best, with Mobil a close second.
I've heard Chevron's uses "the most expensive" additives, but that doesn't mean much. Chevron and Texaco are same company now, but not sure if they use the same gas formulation. BP advertises using Amoco fuels (same company).
The general consensus with additives is that regardless of what they use the additives are soooooooo diluted to be almost meaningless. Notice they never claim how many additives are in there.
I think gasoline additives are probably 95% marketing and 5% science. Quality control at individual stations is a lot more important.
Quote »My wife often puts regular gas in my 91Q and it runs just fine. I always put premium fuel in and really can't notice much of a difference. Mileage is not better with premium. [/quote]
Does she put in enough to dilute what's in the tank? For example, does she put in 20 gallons at a time? Or is it more like "I used your car so I put a gallon in"?
Little difference between straight regular and premium in your Q45? Look at some of the other comments here. It's not just me -- there should be quite a difference.
Maybe the base timing is sufficiently retarded that it won't ping with 87 -- that would make it slow all the time, and then no, sadly you wouldn't see any difference between 87 and 93. Ever had the base timing checked? Little or no difference in mileage/performance between 87 and 93 octane in a motor specifically designed for 93 octane, one which backs off on power production to protect itself from low-octane operation?
Unless a person is accustomed to some really fast sedans, this should be about the fastest 4200-lb sedan he or she has ever driven, particularly when the VVT kicks in at 4000 rpm and acceleration becomes vivid.
Quote »Engine/piston damage can only come from heavy prolonged knocking. Very slight pinging will not cause damage. [/quote]
High-speed ping is hard to hear and can melt a piston, particularly an aluminum piston (we're talking about aluminum pistons with no cooling underskirt oil jet), in no time. Call it anecdotal, but I've seen it happen to someone who said "Oh, it's just a little ping." Granted, a light ping around town probably won't cause immediate damage, and I tried to go out of my way to avoid sounding like Chicken Little. Here's my concern -- a little ping is indicative of a problem which may cause damage, given, say a spirited interstate romp. Why would Q45s have two knock sensors? Why are knock sensors universal these days? Even GM finally abandoned their 1980s position that a "little" ping was okay.
Quote »Not so sure I agree with assertion that "greater percentage of combustion heat is rejected and unavailable for propulsion" as this is technically incorrect.[/quote]
Really? Please, disagree! I invite an alternative explanation of what happens when the car "hears" ping and backs off the timing. Energy in the same amount is liberated whether the mixture is ignited at TDC or 20 BTDC. With late timing, you extract less of the liberated energy as propulsion, and it goes somewhere! There may be more accoustic energy in the exhaust, but the rest of it becomes extra heat going out past the exhaust valve or into the water jacket. An IC engine already rejects something like 2/3 of the energy in the fuel as heat. If we de-optimize the timing, why is a little more heat-rejection difficult to believe?
Does she put in enough to dilute what's in the tank? For example, does she put in 20 gallons at a time? Or is it more like "I used your car so I put a gallon in"?
Little difference between straight regular and premium in your Q45? Look at some of the other comments here. It's not just me -- there should be quite a difference.
Maybe the base timing is sufficiently retarded that it won't ping with 87 -- that would make it slow all the time, and then no, sadly you wouldn't see any difference between 87 and 93. Ever had the base timing checked? Little or no difference in mileage/performance between 87 and 93 octane in a motor specifically designed for 93 octane, one which backs off on power production to protect itself from low-octane operation?
Unless a person is accustomed to some really fast sedans, this should be about the fastest 4200-lb sedan he or she has ever driven, particularly when the VVT kicks in at 4000 rpm and acceleration becomes vivid.
Quote »Engine/piston damage can only come from heavy prolonged knocking. Very slight pinging will not cause damage. [/quote]
High-speed ping is hard to hear and can melt a piston, particularly an aluminum piston (we're talking about aluminum pistons with no cooling underskirt oil jet), in no time. Call it anecdotal, but I've seen it happen to someone who said "Oh, it's just a little ping." Granted, a light ping around town probably won't cause immediate damage, and I tried to go out of my way to avoid sounding like Chicken Little. Here's my concern -- a little ping is indicative of a problem which may cause damage, given, say a spirited interstate romp. Why would Q45s have two knock sensors? Why are knock sensors universal these days? Even GM finally abandoned their 1980s position that a "little" ping was okay.
Quote »Not so sure I agree with assertion that "greater percentage of combustion heat is rejected and unavailable for propulsion" as this is technically incorrect.[/quote]
Really? Please, disagree! I invite an alternative explanation of what happens when the car "hears" ping and backs off the timing. Energy in the same amount is liberated whether the mixture is ignited at TDC or 20 BTDC. With late timing, you extract less of the liberated energy as propulsion, and it goes somewhere! There may be more accoustic energy in the exhaust, but the rest of it becomes extra heat going out past the exhaust valve or into the water jacket. An IC engine already rejects something like 2/3 of the energy in the fuel as heat. If we de-optimize the timing, why is a little more heat-rejection difficult to believe?
landtodd wrote:Really? Please, disagree! I invite an alternative explanation of what happens when the car "hears" ping and backs off the timing. Energy in the same amount is liberated whether the mixture is ignited at TDC or 20 BTDC. With late timing, you extract less of the liberated energy as propulsion, and it goes somewhere! There may be more accoustic energy in the exhaust, but the rest of it becomes extra heat going out past the exhaust valve or into the water jacket. An IC engine already rejects something like 2/3 of the energy in the fuel as heat. If we de-optimize the timing, why is a little more heat-rejection difficult to believe?
I've done a lot of monitoring of exhaust gas temperatures and timing while tuning turbocharged cars I've owned, and you can see EGTs go up fast when timing retards. The combustion process starts later, and more heat goes out the exhaust port. Too much timing retard doesn't do good things for exhaust valve/seat life. Whether running 87 octane in a Q45 creates "too much" timing retard is debateable, but it's something to think about at least.
Can you set base timing on the Q45? If so how? Rotating a cam or crank sensor? I don't remember seeing it in the service manual.
I'm pretty sure you can set the base timing by turning the CAS. This must be the reason why the unit's mounting flange uses concentric slots. I think I recall from the old forum that 17 deg BTDC is optimal for power, but that there's a bit more risk in taking it so far, so maybe 16 is a good compromise.