FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: fryedaddy on November 06, 2017, 06:04:20 PM
-
if you took a strong fe pump gas street engine and put 100% race gas in and planned on running race gas for a while,would you add timing,take out timing,or forget it and leave it where its at.
-
It depends on the combo you're working with. A lot of initial timing might well 'crackle' with marginal gas. Higher octane might well get rid of the crackle and make it possible to properly use the 'more' initial.
Under other conditions it might make very little difference. When you have 'enough' octane, more won't change things.
KS
-
My opinion is that if you make a big jump up in octane, the optimum total ignition timing changes. That is, the optimum timing will increase.
I don't know how to put a number on it, like "for each increase of 5 octane points, add 1 point of timing." I wouldn't do that by any means, as each combination is different.
Sooooo, the easy and safe thing to do would be to leave the timing alone. If it were me, I'd experiment carefully by adding more timing in small increments.
JMO,
paulie
-
I would not change it necessarily. You'd obviously have to experiment. I've noted no difference in performance in timing from 91 pump vs 110 race fuel. Yes it's less prone to detonation but usually a motor likes what it likes. The iron head 351Cs like 38, the AFDs on the dragster like 28. At 11.*:1 I would not test the dragster motor on 91, but all things equal without detonation I'd not expect to change the timing value.
-
im running bbm heads,rpm intake,msd and a comp cam.243 at .050.i have my initial at 14 and total at 32. i was told to set the total at 32 buy a couple members.i have know way of knowing other than test driving.to me it seems to run better at 16 initial and 34 total,but i dont know for sure.
-
Back in the day, Factory heads seemed to run best at 18 initial and 38 total. But that was with Sunoco 260. An un-knowing, inadvertent partial fill with 190 and leaving the station 'on the gas' caused 'crackle' so bad that one piston collapsed the ring lands so drastically that the car turned immediately into a serious smoker. I had to replace the piston/rings on that cylinder.
KS
-
When running 'better' gas, leaving the timing as is can't hurt it.....while bumping up the timing w/o carefully sneaking up on it could.
Perhaps more importantly, how do the plugs look after a hot run on pump gas? If they look good and you don't want to experiment, why not just run pump stuff?
-
I don't think high octane fuel burns the same as low octane fuel. We often act like the only difference is detonation resistance, and nothing else.
-
im not a fan of ethanol. its ten percent at most places.i also noticed my engine will idle on the race gas right away and with the pump gas with ethanol,you have to play with the throttle for a few minutes.
-
So this will be a reply that doesn't help much, be warned, but good discussion
Timing is of course determined by a range of mechanical things in an engine that affect how a flame front travels combined with dynamic stuff that occurs (internal port resonance, overlap/5th cycle stuff, etc) If fuel #1 behaves the same as fuel #2 once ignited, having more octane wouldn't mean the engine wants more (or less) advance
That being said, racers and dyno guys will know this better than me, but I think Paulie is right, it is not an octane issue, it's a fuel burn issue, and I believe that different fuels, even those race fuels with the same octane value, burn completely different and have a different timing requirement for max power.
It'd be interesting to hear from racers and/or dyno guys that have played with different race fuel belnds, however, I am pretty sure it is not the octane rating, but fuel composition and burn that matters.
-
I can tell a storie about that when i was ridind a Triumph Boneville higher comp and
hotter cams. One night i not had enough gas to take me home and the gas stations was closed
The friend i was helping building a racebus filled upp the tank with race gas. It started like normal and
run good on the 98 in the bowls but when i hit the highway i could feel it lost power it was a big difference
The next day i had to kick it several times to start. always started first kick otherwise. It was unresponsiv
i synked the carbs adjusted the mix noting helped checked the ingn.timing nothing helped till i emptied the tank
and filled with 98
-
So this will be a reply that doesn't help much, be warned, but good discussion
It'd be interesting to hear from racers and/or dyno guys that have played with different race fuel belnds, however, I am pretty sure it is not the octane rating, but fuel composition and burn that matters.
This is a misconception that the race fuel mfgs keep trying to surpress - 110 burns like 110 and very much like 93. It's not "faster" or "slower" or any of that other BS you hear in the pits. Highly oxygenated/big octane number fuels - read $$$ gallon - maybe. But your normal leaded race fuel, not so much.
https://www.sunocoracefuels.com/tech-article/beyond-octane
-
what i thought was a simple question turned pretty complicated.with 11-1 compression and bbm heads,should i leave the total at 32 with the race gas,is 34 getting into a too high danger zone.im just trying to maximize power safely.
-
There have been many articles like this one over the year, most of them comes to the same conclusion.
http://www.hotrod.com/articles/fuel-octane-rating-comparison/
Perhaps the Capt Cobrajet him self can tell us his experience beating the ¤¤%%¤ out of all types of FE engines.
-
Yeah, forgot to say when i was in a team campaigning a 71 HEMI Cuda in the late 80-early 90 in A/Sa NHRA legal, at the time when stock class was just that stock, we got the best ET with Shell 98 or 99 pump gas( i dont recall exactly the highest you could get at the gas station anyway ) We elaborated with BP 102 and 105 race gas with different jets and timing and the provider MR. Dolling as i recall, from BP was shaking his head " boys boys it will not do your car any good " and he was sure right. By the way this car was the European record holder for 10 years after race retirement with 10.71 A/Sa NHRA legal until they changed the old stock rules.
-
Anybody know what a gasoline burn curve looks like? That would be burn rate on the left or vertical axis and time (or maybe crank degrees) on the horizontal or bottom axis.
My guess is that rate is not constant. It will start off slow, increasing as the flame spreads, then reach a fairly constant speed until most of the fuel is expended, then fall off again. It might be something like a bell curve with a flat portion on the top?
If that is true, the initial part of the burn would affect how long it is before the mixture reaches its "constant speed". I think this would affect the optimal start of ignition.
Maybe the small difference in starting conditions is too small to make a measurable difference in ignition timing. That's kind of where I was coming from in terms of relating octane and timing.
Also, I once dyno-ed an engine with race gas and the power kept increasing with more timing, up to 45 degrees before I chickened out. I can't remember what octane it was now. Something between 104 and 110. I now have another engine with the exact same heads and it likes 37 degrees total timing with 92 octane gas. There are other differences between the two engines which affect timing, as well. Still the exact same heads, though. I think the timing was accurate both times. Same timing gun and even the same balancer on the engine. So I don't think you can say a certain set of heads always wants the same ignition timing regardless of other factors.
Maybe directly relating octane to timing is not warranted. But surely burn rate, or the average burn rate, varies between different gasolines?
I'm just throwing that out there for discussion.
Flame away! Get it? ;D
-
One thing for sure is, early ignition fights against power.If you have to advance your timing because fuel with higher than necessary octan for a certen engine combo to get maximum power you could lose power. There is so many things with vaporizing, easily burning carbon molecules and how many of them that play a roll how fast a fuels burn rate is besides just octan witch i believe we all understand easily. All to getter its to complicated for me to discuss.
-
Anybody know what a gasoline burn curve looks like? That would be burn rate on the left or vertical axis and time (or maybe crank degrees) on the horizontal or bottom axis.
My guess is that rate is not constant. It will start off slow, increasing as the flame spreads, then reach a fairly constant speed until most of the fuel is expended, then fall off again. It might be something like a bell curve with a flat portion on the top?
If that is true, the initial part of the burn would affect how long it is before the mixture reaches its "constant speed". I think this would affect the optimal start of ignition.
Maybe the small difference in starting conditions is too small to make a measurable difference in ignition timing. That's kind of where I was coming from in terms of relating octane and timing.
Also, I once dyno-ed an engine with race gas and the power kept increasing with more timing, up to 45 degrees before I chickened out. I can't remember what octane it was now. Something between 104 and 110. I now have another engine with the exact same heads and it likes 37 degrees total timing with 92 octane gas. There are other differences between the two engines which affect timing, as well. Still the exact same heads, though. I think the timing was accurate both times. Same timing gun and even the same balancer on the engine. So I don't think you can say a certain set of heads always wants the same ignition timing regardless of other factors.
Maybe directly relating octane to timing is not warranted. But surely burn rate, or the average burn rate, varies between different gasolines?
I'm just throwing that out there for discussion.
Flame away! Get it? ;D
All of those are great questions. And all of those are actually fuel chemistry variables. I had a friend from a pretty good sized gasoline manufacturer try to explain some of this to me a long time ago.
Burn rates, evaporation rates, octane values, and energy content are all somewhat dependent upon each other, but no blanket statement can be made or interpreted from one to the other. As an example, race gas will normal have a high octane to resist self ignition under high cylinder pressures. But it may also have a faster burn rate once lit - - since we have less available time in the combustion cycle to convert the fuel to energy at high RPM. Exactly the opposite of the oft cited urban statement that high octane race fuel burns slower.
-
thanks to everyone who replied.it looks like i will leave it alone.most of that chemistry stuff is over my head.i thought it was a simple question. lol no real reason im going to run the race gas but i dont go over 10 miles on a trip and the price of the better gas is no big deal no more than i drive.last spring i had the gas boiling in the carb problem because of the winter blend pump gas with ethanol .im going to run the 110 whether i need it or not.i was just wondering if i needed to make a timing change or not.
-
All of those are great questions. And all of those are actually fuel chemistry variables. I had a friend from a pretty good sized gasoline manufacturer try to explain some of this to me a long time ago.
Burn rates, evaporation rates, octane values, and energy content are all somewhat dependent upon each other, but no blanket statement can be made or interpreted from one to the other. As an example, race gas will normal have a high octane to resist self ignition under high cylinder pressures. But it may also have a faster burn rate once lit - - since we have less available time in the combustion cycle to convert the fuel to energy at high RPM. Exactly the opposite of the oft cited urban statement that high octane race fuel burns slower.
Thanks, Super-Bear!
I try to throw myself out there as a sacrificial fuel source to promote the combustion of thought. I don't care if I'm wrong as long as me being wrong stimulates someone with more knowledge than me to propagate glorious hp.
I'm going away now. Far away.......... :D
-
I really and truly do not have the answers to fuel chemistry questions.
I was simply fortunate enough to meet somebody who was willing to let me "know that I did not know"....
-
I'll add a couple comments from my experience. Doing experiments on gasoline in the last 1960's , "hi test" burned slower and one could pick up a bit by advancing timing. Our test engine was an old 283 Chevy from the mid 60's. Then along came unleaded and the Clean air act. Gasoline makeup changed significantly. The lighter aromatics were taken out. The burn rates were adjusted by improved refining and changes to the chemical composition. The need to reduce peak temperatures that produced nitrogen oxides that were the major components of smog. As we all know the chemical makeup of gasoline has changed over the years. Today I would imagine the burn rates are tailored for the majority of fuel injected combustion engines on the road and as direct injection is adopted will change again.
-
"know that I did not know"... For me that is one of the more important phrases been working as a technician in nuclear power plants to know when you dont know avoiding mistakes by learning from people that do know and educate your self and then take it from there. Bad enough blowing up a good FE engine but a Atomic station well well. Remember the " dueling" 390 ? when Blair mixed pump with race gas playing it safe with the knew BBM heads and iron CJ heads he sead " He know pretty well wat the CJ heads needs beating on that iron for years " and ended up was it 32 ore 33 ¤ with the BBM.s and 40¤ something with the CJ.s same cam same engine.
Conclusion to your question, if you ask me nobody dont exactly know in your particular case one has to test what your combo likes best .
Like in Blairs case with the 390.s with mixed pump race gas fore me it indicates that you dont have to advanc your timing, so many different dyno shows with modern FE heads that coms in around 32¤ total.
Som one ells my have an another opinion thats fine with me because i just dont exactly know in your case, but you will not hurt your engin without advancing your timing and will not get a core melt down.
-
i am going to leave it in the 32-33 range,i was just wondering because im not going to run winter blend ethanol pump gas in my car any more after the boiling problem last spring. thanks to all