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Discussion Starter #1
In another thread

http://www.honda-pilot.org/forums/showthread.php?s=&threadid=4893&perpage=15&pagenumber=3

It was observed that "Octane has no effect on Horsepower". This is true - all things being equal.

But, if engine timing is adjusted to take advantage of the higher octane, then more horsepower can be produced.

Now, a higher octane fuel, such as premium, can allow an engine to run with the spark advanced more and still not ping. In the old days, this was done by actually changing the rotational position of the distributor. After you did that, you had to buy premium or the engine would ping on hard accelleration.

But, these days, the engine computer controls the timing. So, at long last I come to my question.

If I fill the tank with premium, will the engine computer detect via its sensors that the engine is running differently and advance the timing? If not, then why do they recommend premium for towing? Is that to prevent pinging that might be caused by the increased load and heat?
 

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increased cylinder filling at low RPM's=ping

I think you are right.When you tow,the load causes you to open the throttle plate more(or whatever controls airflow on ECT ig.) ,much more than in low load situations.So,you get better filling at low RPMs.This will increase the pressure in the cyl when the spark ignites the mixture.Since you are at a low RPM,there will be more time for spark travel,and more time for pinging to occur.The increased octane will suppress the pinging,and allow you to run with high torque at low RPMS.Another way around this would be to downshift and run higher RPMs,so you would use more bangs per minute to produce the power you need.This would be less efficient,and noisier.
Well,just my take.The ping detector allows you to run max advance within fuel limits.Increased octane probably will have little or no effect on peak HP(since pinging tends to decrease with higher RPMS,it usually is max,at the torque peak,not the HP peak),but it will effect max power,or max torque at lower RPMS.You might be able to get 70 hp at 2000 rpms with 87 but 75hp at 2000 with 93 octane(these #s are just examples). Charlie.
 

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Let's keep this simple:

To keep it short & sweet -- the part of your post about "increased load & heat" is EXACTLY what the recommendation is for.

The ECU will, however back off the timing when the knock sensor detects ping.

The liklihood of ping would be increased with added load/heat such as caused by towing AND when you are towing the last thing you want is reduced power -- thus the recommendation.

The max advance will NOT get any "further advanced" by using high octane fuel. I highly doubt that there is ANYTHING that the octane rating will do to raise the spark advance programmed into the ECU. In otherwords the "thought process" of the ECU is "run whatever advance I left the factory set at UNLESS ping is detected then dial back..." that is diferent than "determine the ping point by raising advance..."

Makes sense? I hope so...

(this really is not hard stuff -- spark advance is rarely good for more than 5-10 Hp gain or loss anyhow...)
 

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Discussion Starter #4
That's what I figured...

(although a lot of people spend big $ for 5-10hp!)


Hey, we're neighbors, and I used to live in CH!
 

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Re: increased cylinder filling at low RPM's=ping

charlie said:
Well,just my take.The ping detector allows you to run max advance within fuel limits.Increased octane probably will have little or no effect on peak HP(since pinging tends to decrease with higher RPMS,it usually is max,at the torque peak,not the HP peak),but it will effect max power,or max torque at lower RPMS.You might be able to get 70 hp at 2000 rpms with 87 but 75hp at 2000 with 93 octane(these #s are just examples). Charlie.
:rolleyes: if this assumption is correct then you will have exponential gain in this curve up to peak that will lead you to gain in hp and torque? if pre-ignition or pinging is just the reason why you need to use it when towing, the ECU can just retard the timing with 87 octane that 91 or 93 is not necessary. but if they recommend 91 or 93 for towing then you realize gains in hp and torque by doing these albeit minimal increase.
 

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Re: Re: increased cylinder filling at low RPM's=ping

sblvro said:

:rolleyes:
if this assumption is correct then you will have exponential gain in this curve up to peak that will lead you to gain in hp and torque
No, because the gain diminishes as RPM increases. As RPM increases the cylinder fills less efficiently decreasing the peak pressure before combustions reducing the chance for pre-ignition.
Also, as RPM increases the time that the intake change is compressed before proper ignition decreases also decreasing the chance for pre-ignition. So gain at low RPM/open throttle, but no gain at higher RPM.

sblvro said:

:rolleyes:
if pre-ignition or pinging is just the reason why you need to use it when towing, the ECU can just retard the timing with 87 octane that 91 or 93 is not necessary
Nope, because any drop of HP at low RPM/High load will be compensated by the driver by further opening the throttle increasing the severity of the pre-ignition conditions.

sblvro said:

:rolleyes:
but if they recommend 91 or 93 for towing then you realize gains in hp and torque by doing these albeit minimal increase.
High long term loads (like towing) raises the internal combustion chamber temperature much more than short term loads (like acceleration) This also increases the likelihood of pre-ignition given any set of conditions. So when you are towing you may need higher octane gas to MAINTAIN the specified HP of the engine, which it will obtain with regular gas under normal operation.

Now is it my turn to roll my eyes? :2: :rolleyes: :2:
 

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Just guessing that higher octane will allow increased low RPM hp-torque

I am just guessing-based on Honda's recommendation to use higher octane gas when towing-that it will allow higher torque and hp in the lower RPM ranges;and that the higher power levels are obtained from running more advance than 87 octane will allow at these rpms.
Others have pointed out that the increase will be small-maybe a small multiple(1.03 or so),not much-2-4hp or so. Continuing to increase the advance will start to drop the power,no matter what octane you use.
I would also guess that the motor could handle the load-without pinging-with the lower 87 octane,so why does Honda bother to make the suggestion-recommendation?Maybe it would have to handle it by downshifting and running higher RPMS,but it could handle the load with the lower octane.The higher RPMS might give lower MPG's-maybe that is why Honda makes the rec.?The sound would be different also.2000 rpms "sounds" better than 3000 rpms to most folks. .
Oh well,I am trying to read Honda's mind,so... who knows. Charlie
 

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Re: Just guessing that higher octane will allow increased low RPM hp-torque

charlie said:
.....
I would also guess that the motor could handle the load-without pinging-with the lower 87 octane,so why does Honda bother to make the suggestion-recommendation? . . .
Except for the added heat during long term high loads like towing.
Same reason you need the Trans cooler and Steering cooler.
 

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Trust me, this IS correct!

Like I said - try to keep it simple. Don't worry about the RPMs, don't worry about the hp or torque peak. Just remember : if you want to maintaine full power and you are towing you may want to use high octane -- it is the heat/added load...

N_Jay said:


Except for the added heat during long term high loads like towing.
Same reason you need the Trans cooler and Steering cooler.
 

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Honda ECU can only retard timing when ping detected. They will not try to challenge on timing to gain more power. That's why no matter 91/104 gas you put in, your car will only run at default timing. However, say if you put in some year old gas(80 oct), your ECU will retard timing to protect engine.

Then we should be able to run on low octane gas. Yes, but not recommanded. I am not sure if Honda ECU will fine tune timing for your particual fuel, most cars won't do that. They have upto two (some just one) more timing setting to be called safe mode or limp mode. It may not cause ping, while it's not effective neight. That's also why you should put premium gas while tow. It's better not to have ping then run on retarded timing.

The best way to get more power on premium gas other than drop in a race ECU is to adjust CAS sensor(crank angle sensor) to fool ECU and let it think it's on default timing while it's advanced. But then you need to always run on premium gas; once go back to 87.....(ping and retard timing).
 

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I wonder premium has any effect to gas mileage? I hope it hasn't.
I filled premium gas on my first two fill up tanks by using 2 gas coupons from the dealer. My Pilot got 18 - 19 mpg. Same driving condition 75 % city and 25 % highway, I get 16.6 mpg after using regular gas now.
 

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We had this talk a year ago

But I still didn't do anything about the CAS sensor yet. In fact I still don't know where is CAS sensor for our engine
Anyone?:D
 
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