Air Fuel Ratio under boost Question :
08-01-2002, 01:18 PM
#46
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Man, what an incredible tool! (The wideband I mean 
) If we could come up with a straight ratio or some defined association between octane and knock limit we could take anecdotal evidence like Alan's 19 degree's of advance at 18psi and 93 octane and know within limits what advance you could run at 91 octane, or 104 for that matter. Some of Ross's examples of octane vs. advance show almost no retard for 118 at pretty significant boosts.
) If we could come up with a straight ratio or some defined association between octane and knock limit we could take anecdotal evidence like Alan's 19 degree's of advance at 18psi and 93 octane and know within limits what advance you could run at 91 octane, or 104 for that matter. Some of Ross's examples of octane vs. advance show almost no retard for 118 at pretty significant boosts.
08-01-2002, 02:20 PM
#47
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[quote]Originally posted by Russ Murphy:
<strong>Man, what an incredible tool!</strong><hr></blockquote>
Thanks!
[quote]Originally posted by Russ Murphy:
<strong>(The wideband I mean )</strong><hr></blockquote>
Oh... damn! =)
[quote]Originally posted by Russ Murphy:
<strong>If we could come up with a straight ratio or some defined association between octane and knock limit we could take anecdotal evidence like Alan's 19 degree's of advance at 18psi and 93 octane and know within limits what advance you could run at 91 octane, or 104 for that matter.</strong><hr></blockquote>
I did more tweaking last night, 15psi, 91 octane, 18 degrees total advance with no knock. Any higher boost the knock sensor kicks in and retards down to 16 or 14 total advance depending on the severity. My goal has been met =).
[quote]Originally posted by Russ Murphy:
<strong>Some of Ross's examples of octane vs. advance show almost no retard for 118 at pretty significant boosts.</strong><hr></blockquote>
I'm not surprised at all. I'm going to run pure 103 octane and see how low I can drop the timing to at 25psi.
<strong>Man, what an incredible tool!</strong><hr></blockquote>
Thanks!
[quote]Originally posted by Russ Murphy:
<strong>(The wideband I mean
)</strong><hr></blockquote>Oh... damn! =)
[quote]Originally posted by Russ Murphy:
<strong>If we could come up with a straight ratio or some defined association between octane and knock limit we could take anecdotal evidence like Alan's 19 degree's of advance at 18psi and 93 octane and know within limits what advance you could run at 91 octane, or 104 for that matter.</strong><hr></blockquote>
I did more tweaking last night, 15psi, 91 octane, 18 degrees total advance with no knock. Any higher boost the knock sensor kicks in and retards down to 16 or 14 total advance depending on the severity. My goal has been met =).
[quote]Originally posted by Russ Murphy:
<strong>Some of Ross's examples of octane vs. advance show almost no retard for 118 at pretty significant boosts.</strong><hr></blockquote>
I'm not surprised at all. I'm going to run pure 103 octane and see how low I can drop the timing to at 25psi.
08-03-2002, 11:03 AM
#48
Rennlist Member
Rage,
Don't know if your setup is similar to my Tec3 or not. However, I have found that the GM style knock sensor I am using picks up a lot of engine noise which is not 'knock'. You can see it from a data log. I've never heard any knock or observed any evidence of knock in the engine, used a bore scope to check each cylinder.
With the Tec3 you can set a point for the knock sensor to activate and how much to retard. I've used this feature but the effect was minimal as only a couple of peaks passed the limit I set.
Alan
Don't know if your setup is similar to my Tec3 or not. However, I have found that the GM style knock sensor I am using picks up a lot of engine noise which is not 'knock'. You can see it from a data log. I've never heard any knock or observed any evidence of knock in the engine, used a bore scope to check each cylinder.
With the Tec3 you can set a point for the knock sensor to activate and how much to retard. I've used this feature but the effect was minimal as only a couple of peaks passed the limit I set.
Alan
08-03-2002, 11:29 AM
#49
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RUSS/RAGE, I read that at the point right before knock, you add 3 octane for each additional pound of boost and should be safe. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
08-03-2002, 11:30 AM
#50
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I belive that is also to insure timing stays at the same and those 3 octane will allow no retard by the computer.
08-03-2002, 01:48 PM
#52
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[quote]Originally posted by Alan C.:
<strong>Rage,
Don't know if your setup is similar to my Tec3 or not. However, I have found that the GM style knock sensor I am using picks up a lot of engine noise which is not 'knock'. You can see it from a data log. I've never heard any knock or observed any evidence of knock in the engine, used a bore scope to check each cylinder.
With the Tec3 you can set a point for the knock sensor to activate and how much to retard. I've used this feature but the effect was minimal as only a couple of peaks passed the limit I set.
Alan</strong><hr></blockquote>
Very similar. I got the knock sense limit set perfect now. When it detects knock and retards timing, I can't hear it (a good thing). I put in a 50/50 mix yesterday of 103 octane and 91 octane and turned up the boost, no knock, no ignition retard. So it's GOTTA be working right =).
<strong>Rage,
Don't know if your setup is similar to my Tec3 or not. However, I have found that the GM style knock sensor I am using picks up a lot of engine noise which is not 'knock'. You can see it from a data log. I've never heard any knock or observed any evidence of knock in the engine, used a bore scope to check each cylinder.
With the Tec3 you can set a point for the knock sensor to activate and how much to retard. I've used this feature but the effect was minimal as only a couple of peaks passed the limit I set.
Alan</strong><hr></blockquote>
Very similar. I got the knock sense limit set perfect now. When it detects knock and retards timing, I can't hear it (a good thing). I put in a 50/50 mix yesterday of 103 octane and 91 octane and turned up the boost, no knock, no ignition retard. So it's GOTTA be working right =).
08-03-2002, 01:49 PM
#53
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[quote]Originally posted by David Floyd:
<strong>Rage,
What wide band unit are you using?</strong><hr></blockquote>
The FJO unit with laptop datalogging (http://www.fjoinc.com).
<strong>Rage,
What wide band unit are you using?</strong><hr></blockquote>
The FJO unit with laptop datalogging (http://www.fjoinc.com).
08-03-2002, 11:41 PM
#54
Rennlist Member
Rage,
After you get the fuel and timing right it is amazing the amount of boost you can run on pump gas. I mix 50/50 93 and 115 for the track and have turned it up to 22 psi for a 30 minute run on a 98 degree day. No problems! Plugs look great as does the tail pipe. I've even eliminated the black crud I used to get on the bumper around the tail pipe.
Alan
After you get the fuel and timing right it is amazing the amount of boost you can run on pump gas. I mix 50/50 93 and 115 for the track and have turned it up to 22 psi for a 30 minute run on a 98 degree day. No problems! Plugs look great as does the tail pipe. I've even eliminated the black crud I used to get on the bumper around the tail pipe.
Alan
08-04-2002, 12:37 AM
#55
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[quote]Originally posted by Alan C.:
<strong>Rage,
After you get the fuel and timing right it is amazing the amount of boost you can run on pump gas. I mix 50/50 93 and 115 for the track and have turned it up to 22 psi for a 30 minute run on a 98 degree day. No problems! Plugs look great as does the tail pipe. I've even eliminated the black crud I used to get on the bumper around the tail pipe.
Alan</strong><hr></blockquote>
Yes, I agree. I'm mixing 91 octane with 103 octane right now (97 octane approx) and I'm running 20psi fine. Dialed it up to 22psi today, still fine. 23psi, knock sensor picks up light detonation, ignition dialed back to 16 degrees total advance. I've got my current map set to 18 degree total advance on boost. Not sure of EGT's, but the wideband isn't complaining it's overheating anymore.
I'm getting a centerforce clutch installed next week, the Cup Clutch can't handle the power. Slips like crazy in 3rd and 4th gear at 22psi.
<strong>Rage,
After you get the fuel and timing right it is amazing the amount of boost you can run on pump gas. I mix 50/50 93 and 115 for the track and have turned it up to 22 psi for a 30 minute run on a 98 degree day. No problems! Plugs look great as does the tail pipe. I've even eliminated the black crud I used to get on the bumper around the tail pipe.
Alan</strong><hr></blockquote>
Yes, I agree. I'm mixing 91 octane with 103 octane right now (97 octane approx) and I'm running 20psi fine. Dialed it up to 22psi today, still fine. 23psi, knock sensor picks up light detonation, ignition dialed back to 16 degrees total advance. I've got my current map set to 18 degree total advance on boost. Not sure of EGT's, but the wideband isn't complaining it's overheating anymore.
I'm getting a centerforce clutch installed next week, the Cup Clutch can't handle the power. Slips like crazy in 3rd and 4th gear at 22psi.
08-04-2002, 07:13 PM
#56
Race Director
"Or do our engines have a different advance limit I should be aiming for? Going to do another round of tuning this evening... Danno?? =)"
"Danno!!! Any ideas what the safe total advance is for our engine?"
Rage2, Sorry for the delay, but it's the seemingly simple questions that poses the most difficulty as there are so many variables included. I actually had to do some research on this one and have to admit that a lot of times, the knuckle-dragging big-bore muscle-car hot-rodders actually have quite a bit of empirical testing data that can be carried over to our Porsches.
Gasoline is a complicated mixture. While there may be a link between ignition-timing and octane, there isn't necessarily a correlation between those factors and others such as energy-content or flame-front propagation. Found this quote a petroleum engineer on <a href="http://corner-carvers.com/forums/showthread.php?s=5a8a161fd950f6cf2f3e9df7b7b22f3a&threadid=2240&highligh t=ignition+timing" target="_blank">Corner-Carvers</a>:
[quote]"OK, we're gonna start out with a little gasoline talk. Gasoline is blended from as many as 15-20 refinery streams to meet a set of target specifications. Specs like a distillation curve (D86), Reid Vapor Pressure (RVP), octane, and a host of others that I listed a long time ago in another thread when I was trying to be thorough. Some of these factors, like RVP, change with the season. The gasoline blend changes to meet those different targets. RVP could be as high as 11-13 psi in summer, and as low as 5-6 in winter, while most racing fuels are around 4-5. So it would a fallacy to think of "87 Octane gasoline" as a specific thing- it, and every other level of gasoline, change all the time.
Why does this matter? Because it leads into the next great myth that needs to be debunked. Here's the real truth- OCTANE AND "ENERGY CONTENT" DO NOT CORRELATE. They just don't. That doesn't mean that if you have one gallon of 87 (R+M/2) and one gallon of 93 that the heat of combustion won't be different between them. It just won't vary the same way the next time you try the test. Maybe in the winter the 93 octane will have a higher energy content, and maybe in the summer the 87 will be higher. I always see all these internet generalizations regarding octane and energy- how higher octane fuel burns slower and thus makes less power if you don't need it. Bull****. SOME significantly higher octane fuels are blended in such a fashion as the heat of combustion of the mixture ends up being lower, but its not because of the higher octane. Some non-leaded racing fuel blends fit this bill- their reliance on aromatics and a few other components over branched chain paraffins caused the heat of combustion of the total mixture to be lower vs. a standard gasoline fuel. Because of some data they've seen with very high octane unleaded race fuel, people tend to get this idea that higher octane equals less energy."<hr></blockquote>
Now I don't always like to get too much into the technicality behind the scenes, rather just what gives the best results. What you are aiming for is to have the mixture completely combusted at around 15-20 degrees ATDC. If you have your timing set too far advanced (provided adequate octane to do so), that your mixture is at maximum BMEP before this point, it really does no good because you're just compressing your pistons, rods and crank-journal lengthwise, rather than rotating them. Conversely, if you're mixture is at full pressure after that point, not all of it will be used to power the crank as it will still be burning (at high-RPM) when the exhaust valves opens, dumping your power out the tailpipe. Steve & Todd are right on about this one.
So the optimal ignition timing is found best through experimentation like you've done since every engine is different. A lot of the Mustang guys will run 16-20 degrees advance on an optimized, highly-efficient engine. I think you've found the same optimal setting at around 17-18psi through trial & error. While more boost & less ignition may have gotten you more power, it can be tough on the exhaust valves. Good job!
"Danno!!! Any ideas what the safe total advance is for our engine?"
Rage2, Sorry for the delay, but it's the seemingly simple questions that poses the most difficulty as there are so many variables included. I actually had to do some research on this one and have to admit that a lot of times, the knuckle-dragging big-bore muscle-car hot-rodders actually have quite a bit of empirical testing data that can be carried over to our Porsches.
Gasoline is a complicated mixture. While there may be a link between ignition-timing and octane, there isn't necessarily a correlation between those factors and others such as energy-content or flame-front propagation. Found this quote a petroleum engineer on <a href="http://corner-carvers.com/forums/showthread.php?s=5a8a161fd950f6cf2f3e9df7b7b22f3a&threadid=2240&highligh t=ignition+timing" target="_blank">Corner-Carvers</a>:
[quote]"OK, we're gonna start out with a little gasoline talk. Gasoline is blended from as many as 15-20 refinery streams to meet a set of target specifications. Specs like a distillation curve (D86), Reid Vapor Pressure (RVP), octane, and a host of others that I listed a long time ago in another thread when I was trying to be thorough. Some of these factors, like RVP, change with the season. The gasoline blend changes to meet those different targets. RVP could be as high as 11-13 psi in summer, and as low as 5-6 in winter, while most racing fuels are around 4-5. So it would a fallacy to think of "87 Octane gasoline" as a specific thing- it, and every other level of gasoline, change all the time.
Why does this matter? Because it leads into the next great myth that needs to be debunked. Here's the real truth- OCTANE AND "ENERGY CONTENT" DO NOT CORRELATE. They just don't. That doesn't mean that if you have one gallon of 87 (R+M/2) and one gallon of 93 that the heat of combustion won't be different between them. It just won't vary the same way the next time you try the test. Maybe in the winter the 93 octane will have a higher energy content, and maybe in the summer the 87 will be higher. I always see all these internet generalizations regarding octane and energy- how higher octane fuel burns slower and thus makes less power if you don't need it. Bull****. SOME significantly higher octane fuels are blended in such a fashion as the heat of combustion of the mixture ends up being lower, but its not because of the higher octane. Some non-leaded racing fuel blends fit this bill- their reliance on aromatics and a few other components over branched chain paraffins caused the heat of combustion of the total mixture to be lower vs. a standard gasoline fuel. Because of some data they've seen with very high octane unleaded race fuel, people tend to get this idea that higher octane equals less energy."<hr></blockquote>
Now I don't always like to get too much into the technicality behind the scenes, rather just what gives the best results. What you are aiming for is to have the mixture completely combusted at around 15-20 degrees ATDC. If you have your timing set too far advanced (provided adequate octane to do so), that your mixture is at maximum BMEP before this point, it really does no good because you're just compressing your pistons, rods and crank-journal lengthwise, rather than rotating them. Conversely, if you're mixture is at full pressure after that point, not all of it will be used to power the crank as it will still be burning (at high-RPM) when the exhaust valves opens, dumping your power out the tailpipe. Steve & Todd are right on about this one.
So the optimal ignition timing is found best through experimentation like you've done since every engine is different. A lot of the Mustang guys will run 16-20 degrees advance on an optimized, highly-efficient engine. I think you've found the same optimal setting at around 17-18psi through trial & error. While more boost & less ignition may have gotten you more power, it can be tough on the exhaust valves. Good job!
12-31-2002, 03:35 AM
#57
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hey everyone. I love ur site. Nice cars Everyone. I currently own a volvo. Thinking about buying a porsche, great cars. I moderate the 70 section on <a href="http://www.Volvotuning.com" target="_blank">www.Volvotuning.com</a>
My name one there is 2001_c70_nashville.
Iv been reading all of your posts about timing and the AFR. U guys really seem to know what u are talking about. SO if its not any trouble i really need some help.
Heres what is going on.
Ok i have a 2001 Volvo C70 Turbo.
Im sure ur thinking volvo, they can be Tricked out. I beg to differ
Heres what i have done.
Upsolute ecu upgrade. Took Boost from 10psi to 15psi changed the ingintion timing and everything else.
PiperCross Viper cold air intake
SuperSpring Cat back exuast.
Here is a link to my dyno results. I used 93octane.
<a href="http://forums.volvotuning.com/viewtopic.php?t=664" target="_blank">http://forums.volvotuning.com/viewtopic.php?t=664</a>
STOCK DYNO RESULTS>>> HP 218.6 bhp Torque 227.1 at wheels
NEW RESULTS HP 232.7 bhp Torque 284.0 at wheels
HP at crank 280hp Torque 336 ft-lbs
Now there is something something wrong with the hp gain.. at the crank i didnt even gain 20hp....Now this is Peak Hp..... Low and Mid end was Great ....Around 50+ bhp gain at wheels...But when i start hitting my top end something bad is happening..at top end i only gained 14 bhp.
Now i called Upsolute and talked to them
He said it Knock senor could be going off at top end and or i could be running rich at the top end...This scares me as well as PISSES ME OFF about this.
I am getting Great gains at low and mid end... Now i was thinking... Could i be getting detonation at high rmps and then a knock senor is cutting the power...Could this be due to my RON rating..Also my ignition could be pulling off timing..
U will be able to see what im talking about...... look at 4200 to 4800 .. There is a huge hp gain but then its start leveling off and i gain very little after that....Even my stock runs climbed....The new runs look Too level...SO something is going on....
When i get everything fixed i should see some where in the 250's to 60's bhp ....Thats if something is wrong now which i beielve is.
Also...could it be my Wastegate Or Bov/ resirculator leaking boost..???
I order a 3" Downpipe and race cat also. Havnt put it on yet. Could the reason im getting little power above 5000 cause i cant get enough Gases out. I just orderd a EGT today too.
I know This is kida random, but i think u guys can really help me.
PS.. U guys are getting some crazy Hp and torque gains. Awsome. also not bad on torque at 15psi huh.
thanks guys and get back to me.
Rob
My name one there is 2001_c70_nashville.
Iv been reading all of your posts about timing and the AFR. U guys really seem to know what u are talking about. SO if its not any trouble i really need some help.
Heres what is going on.
Ok i have a 2001 Volvo C70 Turbo.
Im sure ur thinking volvo, they can be Tricked out. I beg to differ
Heres what i have done.
Upsolute ecu upgrade. Took Boost from 10psi to 15psi changed the ingintion timing and everything else.
PiperCross Viper cold air intake
SuperSpring Cat back exuast.
Here is a link to my dyno results. I used 93octane.
<a href="http://forums.volvotuning.com/viewtopic.php?t=664" target="_blank">http://forums.volvotuning.com/viewtopic.php?t=664</a>
STOCK DYNO RESULTS>>> HP 218.6 bhp Torque 227.1 at wheels
NEW RESULTS HP 232.7 bhp Torque 284.0 at wheels
HP at crank 280hp Torque 336 ft-lbs
Now there is something something wrong with the hp gain.. at the crank i didnt even gain 20hp....Now this is Peak Hp..... Low and Mid end was Great ....Around 50+ bhp gain at wheels...But when i start hitting my top end something bad is happening..at top end i only gained 14 bhp.
Now i called Upsolute and talked to them
He said it Knock senor could be going off at top end and or i could be running rich at the top end...This scares me as well as PISSES ME OFF about this.
I am getting Great gains at low and mid end... Now i was thinking... Could i be getting detonation at high rmps and then a knock senor is cutting the power...Could this be due to my RON rating..Also my ignition could be pulling off timing..
U will be able to see what im talking about...... look at 4200 to 4800 .. There is a huge hp gain but then its start leveling off and i gain very little after that....Even my stock runs climbed....The new runs look Too level...SO something is going on....
When i get everything fixed i should see some where in the 250's to 60's bhp ....Thats if something is wrong now which i beielve is.
Also...could it be my Wastegate Or Bov/ resirculator leaking boost..???
I order a 3" Downpipe and race cat also. Havnt put it on yet. Could the reason im getting little power above 5000 cause i cant get enough Gases out. I just orderd a EGT today too.
I know This is kida random, but i think u guys can really help me.
PS.. U guys are getting some crazy Hp and torque gains. Awsome. also not bad on torque at 15psi huh.
thanks guys and get back to me. Rob
12-31-2002, 04:12 AM
#58
Race Director
After having a 944 beaten by a Volvo in that commercial decades ago still has a lot of people harboring some resentment ... heh, heh..
Welcome to the club! <img src="graemlins/wave.gif" border="0" alt="[byebye]" />
Not enough info to process this puzzle. We really need to have a boost-curve and air-fuel ratio curve on those dyno charts.
... heh, heh..Welcome to the club! <img src="graemlins/wave.gif" border="0" alt="[byebye]" />
Not enough info to process this puzzle. We really need to have a boost-curve and air-fuel ratio curve on those dyno charts.
12-31-2002, 06:20 PM
#59
Rennlist Member
Since this topic came up again I thought I'd post a data log from an 18 psi run. Ignore the AF data as this is from the stock O2 sensor. The wide band unit indicated 12.3 - 12.9
Under boost the advance stayed at 20 deg. This was with a Tial gate and a manual boost controller. Pretty flat boost curve which looks the same at 21 psi.
Alan
Under boost the advance stayed at 20 deg. This was with a Tial gate and a manual boost controller. Pretty flat boost curve which looks the same at 21 psi.
Alan
