Super to Regular Gas Conversion?

[ichihollow]

like delivering pizzas?

my poor civic... oh well it's getting a timing belt and WP in the next few weeks so what does it matter.

[HCProgramr]

Originally Posted by ichihollow

like delivering pizzas?

my poor civic... oh well it's getting a timing belt and WP in the next few weeks so what does it matter.

Like delivering pizzas. Or commuting 50 miles one way. Or twice-a-month runs to the corporate head office 500 miles away...there are ways that it *can* become noticeable, but they're exceptions and not the rule.

[1992vr4]

I run 91 in my 1g 92 tt..and it doesn't dog at all

[ichihollow]

Originally Posted by 1992vr4

I run 91 in my 1g 92 tt..and it doesn't dog at all

thats the highest octane offered in some areas.

[1992vr4]

yup thats the highest here 91.

[ichihollow]

thats all we had in CO Springs, but on the plus side the lowest octane was 83 which my rx7 loved.

[HCProgramr]

Originally Posted by 1992vr4

I run 91 in my 1g 92 tt..and it doesn't dog at all

I've run 91 before...doesn't hurt it, but I'd rather have the extra point or two just in case.

[J. Fast]

Originally Posted by ichihollow

if 9:1 is perfect and a car runs 10:1 it's high compression, just like 8:1 is low compression. Some one slap me if i step too far off track but the higher the compression generally the higher the burning temp, to counter this higher octane burns more thoroughly which causes a lower burning temp. Keep in mind all gasses have a flash point which drops as pressure increases and rises as it decreases to a point. lower octane fuel has a lower flash point increasing the chance for predet which in a best case scenario bleeds some power in a worst case you start fragmenting your pistons. Want to use lower octane fuel change the pistons and/or heads. By the time you leave the machine shop with the motor back together you'll have spent enough money to buy yet another car that burns cheaper fuel. Your call but if you can't afford the fuel don't drive/own the car.

This is a misconception about why knock occurs in an engine based on octane rating. Although techincally correct this explination is not truly why our engines knock with low octane gas, it has nothing to do with compression in a stock operating range.

From my EFI experience I would say the reason why it's risky to run lower octane fuel is the fuel injectors are controlled by the ECU and lower octane fuel requires more injector pulse than the ECU demands from the engine to produce.

The ECU is constantly translating data from the temp/crank/cam sensor and MAS. From this data it's calculating the the fuel injector pulsewidths (or time of injection to each fuel injector). The ECU decides how long to leave the injector open and when to begin and end the pulse based on the crankshaft position sensor.

The time the ECU has available to inject fuel is a small window limited to the cycle time of the engine (how long it takes to make two revolutions). When the cycle time is translated to the ECU by the crank sensor the fuel injector "on time" is calculated and the ECU calculates the injector duty cycle.

When the ECU sees a specific cycle time and calculates an injector pulse width and duty cycle there is a maximum injector pulse (calculated in miliseconds) that the engine can produce in one "engine cycle" and that's it. Say a maximum of 20ms pulse maximum in a full engine Cycle. With lower octane fuel the ECU calls for a longer pulse width than the engine can produce in a cycle time, say 25ms to compensate for the octane rating.

The ECU may request a longer pulse width than 20ms but the physical speed of the engine dictates the true injector "on time" and "off time." There is no way to majically create a 25ms event evenmore, 101+ % duty cycle in actual injector operation.

Lower octane fuel demands a longer pulsewidth to burn equal or more complete. Unfortunately the engine can not exceed an injector pulse width longer than the cycle time and it runs lean and that is why knock occurs. The knock is caused by imbalanced cylinder filling from an incomplete injector delivery on the intake stroke that runs the car lean which lead to knock and high load catastrophy.

At low loads it is possible to run safely however your car will run like ass and generate Honda Civic like torque.

Jeremy

[ichihollow]

Originally Posted by J. Fast

This is a misconception about why knock occurs in an engine based on octane rating. Although techincally correct this explination is not truly why our engines knock with low octane gas, it has nothing to do with compression in a stock operating range.

From my EFI experience I would say the reason why it's risky to run lower octane fuel is the fuel injectors are controlled by the ECU and lower octane fuel requires more injector pulse than the ECU demands from the engine to produce.

The ECU is constantly translating data from the temp/crank/cam sensor and MAS. From this data it's calculating the the fuel injector pulsewidths (or time of injection to each fuel injector). The ECU decides how long to leave the injector open and when to begin and end the pulse based on the crankshaft position sensor.

The time the ECU has available to inject fuel is a small window limited to the cycle time of the engine (how long it takes to make two revolutions). When the cycle time is translated to the ECU by the crank sensor the fuel injector "on time" is calculated and the ECU calculates the injector duty cycle.

When the ECU sees a specific cycle time and calculates an injector pulse width and duty cycle there is a maximum injector pulse (calculated in miliseconds) that the engine can produce in one "engine cycle" and that's it. Say a maximum of 20ms pulse maximum in a full engine Cycle. With lower octane fuel the ECU calls for a longer pulse width than the engine can produce in a cycle time, say 25ms to compensate for the octane rating.

The ECU may request a longer pulse width than 20ms but the physical speed of the engine dictates the true injector "on time" and "off time." There is no way to majically create a 25ms event evenmore, 101+ % duty cycle in actual injector operation.

Lower octane fuel demands a longer pulsewidth to burn equal or more complete. Unfortunately the engine can not exceed an injector pulse width longer than the cycle time and it runs lean and that is why knock occurs. The knock is caused by imbalanced cylinder filling from an incomplete injector delivery on the intake stroke that runs the car lean which lead to knock and high load catastrophy.

At low loads it is possible to run safely however your car will run like ass and generate Honda Civic like torque.

Jeremy

See i knew there was no way i was 100% right thanks for filling in the holes i didn't know about. Sorry i wasn't able to give a full description that was the limit to what i knew.

[xwire]

Originally Posted by J. Fast

This is a misconception about why knock occurs in an engine based on octane rating. Although techincally correct this explination is not truly why our engines knock with low octane gas, it has nothing to do with compression in a stock operating range.

From my EFI experience I would say the reason why it's risky to run lower octane fuel is the fuel injectors are controlled by the ECU and lower octane fuel requires more injector pulse than the ECU demands from the engine to produce.

The ECU is constantly translating data from the temp/crank/cam sensor and MAS. From this data it's calculating the the fuel injector pulsewidths (or time of injection to each fuel injector). The ECU decides how long to leave the injector open and when to begin and end the pulse based on the crankshaft position sensor.

The time the ECU has available to inject fuel is a small window limited to the cycle time of the engine (how long it takes to make two revolutions). When the cycle time is translated to the ECU by the crank sensor the fuel injector "on time" is calculated and the ECU calculates the injector duty cycle.

When the ECU sees a specific cycle time and calculates an injector pulse width and duty cycle there is a maximum injector pulse (calculated in miliseconds) that the engine can produce in one "engine cycle" and that's it. Say a maximum of 20ms pulse maximum in a full engine Cycle. With lower octane fuel the ECU calls for a longer pulse width than the engine can produce in a cycle time, say 25ms to compensate for the octane rating.

The ECU may request a longer pulse width than 20ms but the physical speed of the engine dictates the true injector "on time" and "off time." There is no way to majically create a 25ms event evenmore, 101+ % duty cycle in actual injector operation.

Lower octane fuel demands a longer pulsewidth to burn equal or more complete. Unfortunately the engine can not exceed an injector pulse width longer than the cycle time and it runs lean and that is why knock occurs. The knock is caused by imbalanced cylinder filling from an incomplete injector delivery on the intake stroke that runs the car lean which lead to knock and high load catastrophy.

At low loads it is possible to run safely however your car will run like ass and generate Honda Civic like torque.

Jeremy

what? no...

your injector plus width would have nothing to do with how complete the burn is...

injector timing maybe some, but ultimately it would come down to IGNITION timing as that is what controls the burn rate in a combustion event when the spark plug fires... before TDC or after

injector plus-width just controls the amount of fuel injected and with lower octane I could see it requiring a little more then higher octane to produce the same amount of power but not enough of a difference to make it knock

and it has everything to do with compression... or more exact cylinder pressure (of which compression plays a major part)

[J. Fast]

In the case of the example I gave, the ECU is calculating 25ms of pulse but by the time the engine cycles, the crank sensor shuts the pulse down at a maximum of 20ms because it must be on "off time" based on where the crank sensor says the engine is positioned and it will automatically cut fuel. The ECU will have no idea that the injector timing event was incomplete and keep calling for 25ms IDC but getting 20ms IDC.

The timing of the engine cycle is fixed, based on engine speed. The timing of the ignition events is controlled in the combustion cycle at a specified crank rotation angle. In our case the ECU looks at the throttle angle calculated by the TPS sensor that is talking with the MAS to calc the airflow, it calcs an injector duty cycle, and the ECU selects an optimum ignition timing to ignite the air fuel mixture. In this case the ECU is calling for a predetermined ignition lead based on the 25ms injector pulse but the engine can only physically produce 20ms of pulse in the engine cycle so it runs lean and knocks.

You also raised a very important point about the relationship between ignition angle and cylinder pressure, xwire. If we were talking about where power and torque are generated then yes, it would be in the cylinders which are generating pressure. Afterall, cylinder pressure is what makes the power and turns the crankshaft. Timing the pressure to the engine's rotation is is a matter of harnessing the expansion pressure of the powerstroke of the engine. The more pressure available thru the powerstroke after TDC, the more rapid the acceleration of the crankshaft.

When you do a an ignition sweep test on a dyno or spark hook test you can detemine where peak torque or optimum torque lie. Through sweep testing it can be determined where the limits of audible knock exist for both ignition advance and ignition retard conditions. In our case pump gas will always audible knock becuse of the imbalance of the air to fuel mixture in the cylinders. With our stock ECU and stock sensors regardless of wether you retard ignition or advance ignition it will almost always audible knock at TPS positions greater than 70% becuase of the air/fuel mixtures imbalance and distance from stoich. The main reason why it's knocking is the ECU is basing the ignition timing lead on a false 25ms reading from the injector timing that's mechnically impossible to achieve.




Jeremy

[xwire]

Originally Posted by J. Fast

In the case of the example I gave, the ECU is calculating 25ms of pulse but by the time the engine cycles, the crank sensor shuts the pulse down at a maximum of 20ms because it must be on "off time" based on where the crank sensor says the engine is positioned and it will automatically cut fuel. The ECU will have no idea that the injector timing event was incomplete and keep calling for 25ms IDC but getting 20ms IDC.
how is the crank sensor shutting anything down? it just provides an input to the ecu that shows crank position, the ECU makes all the adjustments including injector plus-width

The timing of the engine cycle is fixed, based on engine speed. The timing of the ignition events is controlled in the combustion cycle at a specified crank rotation angle. In our case the ECU looks at the throttle angle calculated by the TPS sensor that is talking with the MAS to calc the airflow, it calcs an injector duty cycle, and the ECU selects an optimum ignition timing to ignite the air fuel mixture. In this case the ECU is calling for a predetermined ignition lead based on the 25ms injector pulse but the engine can only physically produce 20ms of pulse in the engine cycle so it runs lean and knocks.

again the tps and maf are inputs to the ecu, from this the ecu calculates airflow and load (from tps, maf and rpm).

You also raised a very important point about the relationship between ignition angle and cylinder pressure, xwire. If we were talking about where power and torque are generated then yes, it would be in the cylinders which are generating pressure. Afterall, cylinder pressure is what makes the power and turns the crankshaft. Timing the pressure to the engine's rotation is is a matter of harnessing the expansion pressure of the powerstroke of the engine. The more pressure available thru the powerstroke after TDC, the more rapid the acceleration of the crankshaft.

not so much where but how to maximize the power output by achieving the highest cylinder pressure the octane of the fuel can support


When you do a an ignition sweep test on a dyno or spark hook test you can detemine where peak torque or optimum torque lie. Through sweep testing it can be determined where the limits of audible knock exist for both ignition advance and ignition retard conditions. In our case pump gas will always audible knock becuse of the imbalance of the air to fuel mixture in the cylinders. With our stock ECU and stock sensors regardless of wether you retard ignition or advance ignition it will almost always audible knock at TPS positions greater than 70% becuase of the air/fuel mixtures imbalance and distance from stoich. The main reason why it's knocking is the ECU is basing the ignition timing lead on a false 25ms reading from the injector timing that's mechnically impossible to achieve.

again why is a false reading?



Jeremy

where are you getting your numbers from? the injector will spray the required time every cycle, now weather or not the intake vale is open to allow said air-fuel mixture to get into the combustion chamber or not is another subject

as far as if the ecu if it requires the injector to spray a 25ms plus it will spray it early (before said intake vale opens) so it can complete it cycle

when it comes to ignition timing that would relate to flame kernel speed (which is determined by octane of fuel, combustion chamber design even piston shape) to much timing and you lose control of the flame kernel and engine damaging "explosions" result

if your picking up "knock" (more then likely pre-ignition) on a dyno there is something not right... on a boosted car you naturally want a fat rich mixture not so much for the power but for the cooling effects of leaving some fuel in the combustion chamber after the power stroke to cool the piston

I know this is not the most technical post but it should get the point across and short of breaking out my technical manuals and posting facts

[i am me n u r u]

Originally Posted by HCProgramr

Good to know you're still out there, Em! Do you and Hans [I think that was his name, the one you were in business with ages ago] still have the shop? I'm gonna need a 60k here in the next year or so [40k to go, but starting year 5], and Ty closed his doors; the only shops in range that I know of are you guys and a dealer.

Getting back on topic:
I can't speak for the DOHCs, but my TT was on 87 when I bought it...and it was an out-and-out dog. I thought sure I'd just spent $5k on a lemon. Sluggish, no enthusiasm, the works.

Thankfully it was on fumes, and there was a Sonoco just up the street. A tank full of 94 and a few miles to work the junk out brought her right back to life; I goosed it coming out of a toll booth, and it was love at first headache. I found out later that the wastegates were disconnected too; the turbos spun up, my head bounced off the rest...then about 3500rpm at full throttle it cut whatever it does to prevent it from running too lean, and my face about bounced off the wheel.

I don't have any experience with the base/ES/RT or base/SL, but on the TTs the good stuff [though I believe the manual calls for 91, not 93, at least on the 1gTT; I'll run 92 in an emergency, such as on fumes and that's the best the station's got, but otherwise I keep it at 93 and up] is absolutely necessary. Personally, I wouldn't risk it even with a DOHC, though I've come to consider that car my first-born.

2 full tanks a month, rounding to 20 gallons on the tank and 20c price differential, is less than $100/year...and that's a lot of driving, 800-1200 miles a month [20-30mpg] unless you're going everywhere at full throttle. Even when I was commuting like crazy right after Katrina, it was 3 tanks a month on a 30c differential; still less than $200 per year difference. I spend more than that per month on food.

A single tank at a 20c differential is $4.00; the 'cheaper gas saves big money' bit of conventional wisdom is an illusion at best. You have to do a LOT of driving at a high price differential to see any meaningful savings from going down a grade.

Yup, we still have the shop! Bigger and better than ever. E-mail or give a call when you're ready to get the work done. ECoppola@gmail.com is my e-mail, and (610) 438-0439 is the shop number.

[J. Fast]

Originally Posted by xwire

where are you getting your numbers from? the injector will spray the required time every cycle, now weather or not the intake vale is open to allow said air-fuel mixture to get into the combustion chamber or not is another subject

as far as if the ecu if it requires the injector to spray a 25ms plus it will spray it early (before said intake vale opens) so it can complete it cycle

when it comes to ignition timing that would relate to flame kernel speed (which is determined by octane of fuel, combustion chamber design even piston shape) to much timing and you lose control of the flame kernel and engine damaging "explosions" result

if your picking up "knock" (more then likely pre-ignition) on a dyno there is something not right... on a boosted car you naturally want a fat rich mixture not so much for the power but for the cooling effects of leaving some fuel in the combustion chamber after the power stroke to cool the piston

I know this is not the most technical post but it should get the point across and short of breaking out my technical manuals and posting facts

There's/are/ can be, a few instances where the ECU is lied to and the injector pulse can be tweaked. 1st case would be when you use an AFC controller and lie to the ecu. Another instance would be when the ecu demands a greater injector delivery than the injectors can supply in the engines two rotation operating cycle. The crank sensor shuts down the injector pulse and superceeds the ECU because it knows the injector can't spray fuel in the cylinder because it's closed.

2nd point we're talkig the same language

3rd point we agree there too


Somtimes, not very often , there can be instances where the ECU demands and calls for more fuel delivery than the engine can provide (101+ injector delivery etc). The various sensors and computers will give it its maximum but it can be short of what the ECU demand is. The sensors only show event timing not entire event completion. It causes a string of chain events based on the ecu thinking its demanded fuel has been injected.

The numbers I'm using are hypothetical illutrations of the condition taking place. They are not the exact numbers.

At one time I also thought you could change the injector time and spray earlier. Spraying early or late is not the cause of the standard pump gas to premium gas problem. Say the cylinder only allows a 20ms window to spray fuel. This is the maximum time available in the injector delivery window. Your demand is 25ms. You could spray it early, you could spray it late, you could spray it perfect. The crank sensor wil only allow you to spray for the maximum injector delivery window, not the ECU demanded window.

I also agree flame spread is important and knock threshhold should be avioded. My point was, no matter which side of the knock threshold you are on, "fat" or "lean", if your ecu is doing it's own thing and demanding injector delivery it can't produce and getting false information from the crank sensor (that the ignition timing event has been completed when it's 5ms short), it will run like ass.

[xwire]

Originally Posted by J. Fast

There's/are/ can be, a few instances where the ECU is lied to and the injector pulse can be tweaked. 1st case would be when you use an AFC controller and lie to the ecu. Another instance would be when the ecu demands a greater injector delivery than the injectors can supply in the engines two rotation operating cycle. The crank sensor shuts down the injector pulse and superceeds the ECU because it knows the injector can't spray fuel in the cylinder because it's closed.

2nd point we're talkig the same language

3rd point we agree there too


Somtimes, not very often , there can be instances where the ECU demands and calls for more fuel delivery than the engine can provide (101+ injector delivery etc). The various sensors and computers will give it its maximum but it can be short of what the ECU demand is. The sensors only show event timing not entire event completion. It causes a string of chain events based on the ecu thinking its demanded fuel has been injected.

The numbers I'm using are hypothetical illutrations of the condition taking place. They are not the exact numbers.

At one time I also thought you could change the injector time and spray earlier. Spraying early or late is not the cause of the standard pump gas to premium gas problem. Say the cylinder only allows a 20ms window to spray fuel. This is the maximum time available in the injector delivery window. Your demand is 25ms. You could spray it early, you could spray it late, you could spray it perfect. The crank sensor wil only allow you to spray for the maximum injector delivery window, not the ECU demanded window.

I also agree flame spread is important and knock threshhold should be avioded. My point was, no matter which side of the knock threshold you are on, "fat" or "lean", if your ecu is doing it's own thing and demanding injector delivery it can't produce and getting false information from the crank sensor (that the ignition timing event has been completed when it's 5ms short), it will run like ass.

how does the crank sensor have any control over the injectors? it doesn't it provides an input to the ECU nothing else... the ECU is the controlling factor

as far as injector duty cycle that is a whole nother subject and has nothing to do with octane of the fuel used, from 87-93 octane the difference in the amount required (injector duty cycle) to make the same power would be negligible at best

I am still lost on how you are coming up with the 5ms short theory? and yes you can get the injector to spray any time you want (esp with a stand alone) it is just better and more fuel efficient to spray right before the intake valve is opened... other wise you are just soaking the back of the valve and not have the injector spray a atomized spray