spark advance and race gas
02-21-2007, 01:01 PM
#1
11 Second Club
Thread Starter
Join Date: Mar 2006
Location: STL BITCH!!!
Posts: 74
Likes: 0
Received 0 Likes
on
0 Posts
spark advance and race gas I was wondering if any one uses a ign. timming controler and runs 100-110octane at the track and then pulls it back for the street. Its something i've been considering, but i don't know how well it will work. Or if the gains will be worth it.
02-21-2007, 01:13 PM
#2
TECH Senior Member
most here likely just make a tune specific to the higher octane fuel, then reflash when done
I know the Grand Prix world is big into using timing controllers (there's an IAT vs Timing table on W-Body's and F-Bodys and Y-Bodys) ... they setup the table so that at different IAT temps, it adds or pulls timing, then you use a potentiometer setup w/the proper resistances to change to different advances or retards
Hardest part is figuring out where the timing should be at, and if you even need 100 octane or higher gasoline... for boosted applications the higher octane helps since you can run more timing but avoid detonation... but for an NA car with decent flowing heads, the increased timing required due to race gas may not help much if any at all
I know the Grand Prix world is big into using timing controllers (there's an IAT vs Timing table on W-Body's and F-Bodys and Y-Bodys) ... they setup the table so that at different IAT temps, it adds or pulls timing, then you use a potentiometer setup w/the proper resistances to change to different advances or retards
Hardest part is figuring out where the timing should be at, and if you even need 100 octane or higher gasoline... for boosted applications the higher octane helps since you can run more timing but avoid detonation... but for an NA car with decent flowing heads, the increased timing required due to race gas may not help much if any at all
02-21-2007, 01:37 PM
#4
TECH Senior Member
more timing doesn't necessarily mean more power... with a set of good flowing heads, you may make the same power running 24* at places as it would running 29* of timing
Higher octane allows you to increase timing further because higher octane fuels are more difficult to ignite... If you were to take a stock car, put 110 octane in it, and then raise the timing way up just under the point of knock, it probably wouldn't see any better (maybe even worse) than that same car running lower timing on 93 octane (in theory, you want to run the lowest octane gas you can at the highest timing that makes power, so if you can make say 400hp with 26* of timing at 6000 RPM on 93 octane, that doesn't automatically mean you will make >400hp with 30* timing and 100 octane... )
The higher octane is more a factor on boosted vehicles (where they can make more power with higher timing, but due to the intake charge temp, 93 octane ignites too easily so they may only be able to run 12*, whereas on higher octane they can run more timing) or high compression (where higher cylinder pressures makes it easier to ignite the fuel charge) ... on a low to mid compression (11.5 or under) LS1 NA, you generally don't need a large octane fuel (93 octane is fine for many, in very hot climates where the intake charge is not dense and is very hot, high octane can help as well) ... but that's not to say you won't get more out of high octane and timing ... the handful of vehicles I've done tuning on didn't gain much if any hp from more timing + higher octane fuel (they ran pretty well on 93 octane at optimal timing)
Higher octane allows you to increase timing further because higher octane fuels are more difficult to ignite... If you were to take a stock car, put 110 octane in it, and then raise the timing way up just under the point of knock, it probably wouldn't see any better (maybe even worse) than that same car running lower timing on 93 octane (in theory, you want to run the lowest octane gas you can at the highest timing that makes power, so if you can make say 400hp with 26* of timing at 6000 RPM on 93 octane, that doesn't automatically mean you will make >400hp with 30* timing and 100 octane... )
The higher octane is more a factor on boosted vehicles (where they can make more power with higher timing, but due to the intake charge temp, 93 octane ignites too easily so they may only be able to run 12*, whereas on higher octane they can run more timing) or high compression (where higher cylinder pressures makes it easier to ignite the fuel charge) ... on a low to mid compression (11.5 or under) LS1 NA, you generally don't need a large octane fuel (93 octane is fine for many, in very hot climates where the intake charge is not dense and is very hot, high octane can help as well) ... but that's not to say you won't get more out of high octane and timing ... the handful of vehicles I've done tuning on didn't gain much if any hp from more timing + higher octane fuel (they ran pretty well on 93 octane at optimal timing)
Last edited by horist; 02-21-2007 at 01:50 PM.
02-21-2007, 01:57 PM
#5
Your thinking of timing and octane are extremely skewed. Horist is absolutely correct. Higher octane can actually reduce power output, since the flame speed will now be slower then typical "pump gas". The most you want to run in an LS1 is about 94-96 octane, depending on your CR. Above that, you will actually start to lose power, regardless of spark advance. Every engine has it's theoretical Max Best Timing (MBT), once you exceed that, you are not gaining any more power, but losing it. LS1 are typically around 26-29, FYI.
Trending Topics
02-23-2007, 09:47 AM
#9
TECH Senior Member
well 2 things
regarding most octane boosters (NOS booster, Octane 104) , when they say it raises octane 5 points, that means if your gas was 93.0 octane, it will become 93.5 octane
Now, in theory if run 89 octane, but can still run timing where you can make peak power, you could potentially make more power (probably a negligable amount but it's possible)
Think of it this way... why do we advance timing? Because we want to create a flame front that causes a controlled explosion EXACTLY when the piston reaches TDC... anytime before this and it's detonation (piston is on the compression stroke moving up, flame front causes boom too early, strain on piston cause we're trying to force it down while it's moving up), if we don't have enough timing, the piston is already on the power stroke when the flame front ignites the mixture .. however if we run really high octane gas, and advance the timing all the heck, it may be timed such that it causes the mixture to go boom exactly at TDC , but by that time the flame front has essentially lost power (it's been moving for so long that some of the heat energy has been absorbed by the metal components and dissipated)
At the same time... you may be thinking "well if i run 10 octane and spark at 1* before TDC then I should have maximum energy to cause the boom" ... but the issue is that such low octane ignites too easily, and the heat inside the cylinder and created during the compression stroke will cause the mixture to go boom before the spark plug fires off (flame front created from compression, kinda how Diesel engines work)
regarding most octane boosters (NOS booster, Octane 104) , when they say it raises octane 5 points, that means if your gas was 93.0 octane, it will become 93.5 octane
Now, in theory if run 89 octane, but can still run timing where you can make peak power, you could potentially make more power (probably a negligable amount but it's possible)
Think of it this way... why do we advance timing? Because we want to create a flame front that causes a controlled explosion EXACTLY when the piston reaches TDC... anytime before this and it's detonation (piston is on the compression stroke moving up, flame front causes boom too early, strain on piston cause we're trying to force it down while it's moving up), if we don't have enough timing, the piston is already on the power stroke when the flame front ignites the mixture .. however if we run really high octane gas, and advance the timing all the heck, it may be timed such that it causes the mixture to go boom exactly at TDC , but by that time the flame front has essentially lost power (it's been moving for so long that some of the heat energy has been absorbed by the metal components and dissipated)
At the same time... you may be thinking "well if i run 10 octane and spark at 1* before TDC then I should have maximum energy to cause the boom" ... but the issue is that such low octane ignites too easily, and the heat inside the cylinder and created during the compression stroke will cause the mixture to go boom before the spark plug fires off (flame front created from compression, kinda how Diesel engines work)
02-23-2007, 02:09 PM
#11
It is all about cylinder pressures, timing increases the pressure inside the combustion chamber by igniting the air/fuel mixture. This pressure needs to start increasing just before TDC. So when the optimum pressure is created, the piston has just crested TDC, this provides the Best Mean Torque. Only during the Best Mean Timing under ideal octane conditions. Of course, we commoners do not have access to that fancy stuff OE's use to find that point. 
If timing is too late (retarded), it will create the high pressure as the piston is going down, which mechanically is creating vacuum (negative pressure). This is opposite of what we want, so the ignition pressure is nullified. Plus it can cause excess heat, as no extra power is being generated but a lot of heat is being absorbed by the engine components. If timing is too soon (advanced), the ignition will start increasing cylinder pressure too soon, and with the piston also increasing pressure from the compression stroke ... BOOM! (aka: knock). The air/fuel mixture begins to self ignite where pressure is high or where the temperature is high (hot spots), much like rasing the CR to 18:1 (example) on an 11:1 engine. 
It is not really that you want the lowest octane, but the most potential power from the fuel. High octanes produce slow increases in cylinder pressures, so unless your engine can increase the pressure fast enough to complement the slow burn, so are just wasting money. Vice versa for low octane (fast burn fuel) ... you do not want the cylinder pressures rising too fast for timing. Each engine has it's theoritical MBT point, finding the best fuel/timing combination to extract the most power is the key.
If timing is too late (retarded), it will create the high pressure as the piston is going down, which mechanically is creating vacuum (negative pressure). This is opposite of what we want, so the ignition pressure is nullified. Plus it can cause excess heat, as no extra power is being generated but a lot of heat is being absorbed by the engine components. If timing is too soon (advanced), the ignition will start increasing cylinder pressure too soon, and with the piston also increasing pressure from the compression stroke ... BOOM! (aka: knock). The air/fuel mixture begins to self ignite where pressure is high or where the temperature is high (hot spots), much like rasing the CR to 18:1 (example) on an 11:1 engine. It is not really that you want the lowest octane, but the most potential power from the fuel. High octanes produce slow increases in cylinder pressures, so unless your engine can increase the pressure fast enough to complement the slow burn, so are just wasting money. Vice versa for low octane (fast burn fuel) ... you do not want the cylinder pressures rising too fast for timing. Each engine has it's theoritical MBT point, finding the best fuel/timing combination to extract the most power is the key.
