Can race gas cause knock?

[Mike70gtx]

I was tuned fairly well with 93 octane and squirting alky. Switched to 108 octane race fuel and made a run and would have to get out of it somewhere in 2nd gear because of knock. I advanced the timing by 2 degrees, it might have helped. Question; with higher octane do I shoot less alky or raise boost (was at 24#'s) or advance timing? All I had to look at was scan master. I now have EGT guage working. Any advice.
P.S. It was a 100 degree day at the track. I thought the race fuel might make up the difference.

 

[chris2316]

i cant believe people use alcohol instead of better gas or more fuel or less timing , but anyways it was 100 temp i personally would of not raced on that hot of a day , thats probably why you were knocking! when you pop a head gasket you will probably use 112 octane and junk the alky!

 

[Mike70gtx]

I think I have been running rich. When I turned the trans plus wot fuel back to 10% lean is when the knock left and I got the 11.9.This was the week before. Would race gas create a richer condition?

 

[2QUIK6]

i cant believe people use alcohol instead of better gas or more fuel or less timing , but anyways it was 100 temp i personally would of not raced on that hot of a day , thats probably why you were knocking! when you pop a head gasket you will probably use 112 octane and junk the alky!

I really don't understand your comments, it has nothing to do with what he's asking. Higher octane is higher octane no matter how you get it, race gas, alky, xylene, propane, etc..and add the extra benefit of alky with its cooling effect, I'd say its better than race gas during the hot summer air. As any head gaskets have been blown with race gas as alky...its all a matter of how the tuner tunes and how far they approach the limit....most of the time a head gasket is blown because the driver does not know how to tune correctly with a scan tool...yeah, usually C116 can be put in the tank and the boost cranked up to 26# and nothing will happen if the fp is cranked up high enough...its is easier with race fuel, but alky is no more dangerous if you know how to tune and have patience.

Ok, on to your question, running excessively rich can cause knock as well. Race gas burns slower, so without the timing advanced, that could cause an overly rich condition. Watch your O2s and EGTs. I see some knock if my O2s get much over 850mv in lower gears, it doesn't seem to mind in 3rd gear.
If have have no knock with 93/alky then why run any race gas unless you want to crank up the boost some more and have run out of alky volume, thats where it will get tricky to tune it appropriately....not as easy as adjusting fp and timing sometimes.

 

[Mike70gtx]

Thanks for the response. That makes sense. I was trying to see how close I could get to a 7.0 index at an outlaw race. I'm sure that day was not the best, but I was on vacation so I had the opportunity. I watched my scanmaster very close and would get out when I saw any knock. I didn't stick around for any finals. I just ran some qualifying runs and then watched the rest of the action. I see you have the trans plus. If I wanted to try (when conditions are better and car tuned good) to get into the 10's, what adjustments would I make with the race gas?

 

[chris2316]

i just think alcohol is used to get people drunk not my g.n , i dont see any of the real fast turbo cars using it bamford, tony o etc! ive been in the tens for 10 years with iron heads ,stock gm build ! and your a/f 11.9 is dangerous ,even a new silverado pick runs 11.4 just to give you a little insight! theres not even a turbo or supercharger on those!

 

[2QUIK6]

Chris, I certainly agree that if you have a full race car, use race gas. For a street machine thats driven alot on the street and run in the 11's or slower then alky is a great alternative if you want to be tuned to the limits all the time, otherwise your wasting a lot of race gas sitting at a traffic light or cruising.
When you're running in the 10's, your probably going to go thru a few headgaskets sooner or later no matter what fuel your running. There's a handful of folks running 10's on pump gas and alky, most have alot of head work to go with that which makes it easier. Alky / methanol injection has come a long way in the last few years and more reliable pumps used. In the early days, pump failure was a main reason for head gasket failure for those that knew how to tune accordingly.

 

[chris2316]

Rob, I Understand What Your Saying , But Mike Sounds Like He Wants To Go 10's ! Its All Good Cant Argue With A Fellow Buick Brother ...later!

 

[2QUIK6]

yeah, didn't see that you were shooting for tens in the original posts.
I would definitely use a mix at least of pure C116 and alky, if you're tuned no with alky, I wouldn't completely take it out of the picture to run that fast, unless you start over with tuning which your entire fuel curve will have to be altered if it was tuned correctly. What chip are you using and was it tailored for alky?
Is your quickest time to date the 11.9 in your sig? If so, thats a huge jump I would not try to accomplish real fast, especially in the TX heat right now.
What timing at WOT and what gears are you currently running?
Any idea where your O2s and EGTs and boost are currently when your getting a little knock?
Its very hard to say what you need to do without a scan tool recording of the pass....if O2s are high and EGTs low when the knock occurs and the boost is maxed out when the knock occurs, then you can raise the boost a little to bring the O2s down and raise the EGTs a bit. If O2s look ok, and EGTs are low, then raise the timing a bit....very little like a degree at a time.
Also, is your SMC alky system a progressive unit? IF so, and the knock occurs before max boost is hit, you may need to adjust the turn on point, and the "initial" amount of alky that is injected.

Remember, before adding alky, make sure your car can run normal 15# boost levels with no alky and no knock on pump gas...heck with that turbo you should be able to handle 18 0r 19# of boost with no knock easily. My GT61 can do 20# with no knock on pump gas no alky before KR occurrs w/CAS V4 IC.

Also, the Trans+ WOT fueling adjustments do nothing unless you have an extender chip, or you are not maxxing out the MAF, but anything over 16# of boost with that 67 turbo should max the MAF.

Hopefully you can make it out to Redline Aug 6th with the DFW Buick club and we can chat more, lots of knowledgable folks are usually there.

 

[Mike70gtx]

My "into the 10's goal" is one my personal goals that I'd like to do,but don't have to. This is my daily driver and loved the feeling of going to the track in street trim with pump gas (alky) and get into the 11's.
I have the SMC dual jet alky, but it's not progressive. It's set to kick on at 12#'s and set at 8 pump speed. I do have the extender extreme chip set at 23/21 degrees. I did the 11.9 at 24#'s boost. Just got the egt guage working and noticed that temps where low and was getting knock (on the sm). (This was after my day at the races with the race gas) Now I'm at 21#'s boost. I turned my fuel pressure back up to 45psi, I think I had it at 42 on the 11.9 run. (I need to start logging my data in a notebook) I leaned it out by 12% and now I have no knock at 21#'s boost. The egt looks like it is right on 1600. It's an autometer guage and that's as far as it goes and I haven't found out if it actually goes past 1600 or pegs out and stops.
I do have turbo link, but the computer is not working right now.

 

[Ormand]

Race gas burns slower

Not true. But this horse has been thoroughly flogged, hard to believe it still comes up. Let me see, I'm going to buy gas for my racing motorcycle, which turns 14,000 rpm. I'll get race gas, which burns slower? Racing fuel has higher octane, which does NOT mean it burns slower. No relationship between burning speed and octane.
Here is a quote from Popular Hot Rodding:
The burn rate of a fuel is a measurement of the time required for complete combustion of the air/fuel mixture. The notion that octane ratings affect the burn rate of fuel is about 180-degrees from reality. Burn rate is a function of several variables, and the two are completely independent, although there is generally a correlation between octane ratings and burn rates.

To give you a good example of this, we contacted Jim Wurth from Sunoco Race Fuels. He explains, "A perfect example is Sunoco Maximal, which is our fastest burning fuel, and coincidentally one of Sunoco’s highest octane fuels at 116 (R+M)/2. A lot of Pro Stock teams rely on Maximal for those sub-seven second runs. When they are turning 9,000rpm or more, the fuel has to burn pretty quickly to achieve complete combustion."

 

[Chris McDade]

I've gotten watered down race fuel before, so you have to be carefull. I put some in my car one time and bumped up the boost and timming and went racing. The car knocked and I couldn't figure out why. I finaly decided the change the fuel and try another 5 gallons. The fuel was no good. I took it back and he gave me my money back.

Just something to check.

Good Luck

 

[2QUIK6]

ok, to get very techincal on the higher octane running slower...that was laymans terms. Its the time it takes to reach complete combustion from the time it is ignited is longer. Once its at complete combustion, its combustion rate is faster then lower octane fuel...but the time it takes to get there is longer.....hence why you can advance the timing so much with C116 compared to 93 octance.
Put in high octane fuel and do not advance the timing, the complete combustion process will be taking place in the exhaust manifold... For those 8 sec and faster cars, when you hear them pull to the line and the exhaust starts popping, its the combustion process taking place in the manifolds because they have retarded the timing extremely in order to heat up the gases in the exhaust to spool the turbo faster.
Its not that it is wrong, its just a spin on words.

 

[Ormand]

No, to get technical, race gas burns faster. The time to complete combustion is SHORTER. That's what is meant by "burns faster". The timing CAN be advanced with race gas, because race gas, by definition, has higher resistance to detonation. That ALLOWS more initial timing, but does not REQUIRE it. If you put in high octane fuel without advancing timing, or increasing boost, you are not getting the most out of the fuel, but it WON'T burn in the exhaust manifolds. Sure, if you're retarding timing significantly to get quick spool, then you can get popping and backfiring, but that's not a fuel issue.
If you try to advance the timing with too low an octane, the pressure will build up to the point where you get detonation. But then, if you use higher octane fuel, you CAN advance the timing to the optimum point. It's not a matter of slower buring fuel REQUIRING more advance, it is, instead, that the higher detonation resistance ALLOWS more advance.

 

[2QUIK6]

k, simple experiment. Put in C116, and watch the O2s and if you have an exhaust gas analyzer like the emissions testers use, watch what happens to the HCs.
Then drain out the C116, refill with 87 octane and observe the O2s and HCs.
Leaving timing the same.

 

[Under Pressure]

my dad could beat up your dad...lol