timing-race gas vs pump gas

[fryedaddy]

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.

[cammerfe]

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

[plovett]

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

[Falcon67]

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.

[fryedaddy]

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.

[cammerfe]

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

[machoneman]

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? 

[plovett]

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. 

[fryedaddy]

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.

[My427stang]

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.

[Heo]

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

[Falcon67]

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

[fryedaddy]

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.

[Tobbemek]

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.

[Tobbemek]

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.