Leaded gas purchase...

[Ghoste]

I'm not a chemist so if I am misunderstanding it I hope someone will correct me, but...

A gallon of gasoline has the same amount of latent chemical energy in it no matter the octane level.  Octane is a measure of the fuels anti knock capabilities so if you just add higher octane fuel, it doesn't magically place more energy inside the cylinder.  What it does, is allow you to change certain parameters of the engine such as compression ratio and the spark advance.  These altered parameters allow the engine to operate more efficiently and utilize some more of the otherwise wasted energy that was already in the fuel.  Changing these things without adding a fuel that can operate within those demands forces the engine to operate at a LESS than ideal way.

[1974dodgecharger]

Well I ran out of the good stuff and put in back 91 in the tank and to be honest with you it does run better with octane 100.  She does not 'feel' as sluggish off the line vs the 91 it could all be in my head, but I ran half a tank with 100 and she didnt want to hestitate to just get up and go, but now I ran a quarter tank with 91 and it feels bad I feel the difference between the two.   Then again could be in my head.....

One other thing on a first start of the day I swear I hear knocking with the 91 I always put this off as 'normal' because once she gets up to temp I dont hear it anymore through the day with stop, go, stop, go etc...until I let her sit over night again.  With the 100 I dont hear it upon first start.......

In my head maybe?

[Ghoste]

Not necessarily, your timing and compression may be liking it.  And it would also enjoy the benefits of no ethanol and no oxygenating.

[Cooter]

Without a dyno, impossible to tell.

[1974dodgecharger]

Without a dyno, impossible to tell.

In the end very true...next dyno session will be with octane 91.

[Ghoste]

When is your next session?

[1974dodgecharger]

When is your next session?

Im thinkin vegas iust saw they added a dyno sesson same type of machine.  Plan to upgrade to 850cfm carb.

[Ghoste]

Ah but see, if you are making another physical change then seeing if there is a difference in the fuel is pointless

[1974dodgecharger]

Damn your right fck.....

[Ghoste]

You could take a five gallon can of one of them with you and do your teest then drain the tank, add the other fuel and repeat.

[Calif240]

Didn't see anyone post on here, but if you're looking for a better deal on higher octane, try the local small airport. They should have 100 low-lead, which is allowed for aircraft use. It has lead, but it is illegal to put directly into your car. Take a 5-gallon can and fill it. They shouldn't ask as long as you aren't putting it in your car. If they do, tell them you're putting it in an agricultural or airplane engine that you have at home and are working on. I know 100 low-lead is legal for aircraft and believe it is good for anything not being used on public roads (agricultural and other uses). Can save a bunch of dollars as the gas is usually a dollar cheaper than 100 octane racing gas that is sold at gas stations.
Terry

[Ghoste]

Used to be able to do that here but the local airport will no longer put it in anything but an aircraft.

[Kern Dog]

the lowest octane that you can run WITHOUT detonation will make more power than a real high octane that is not needed.

I agree here. Higher octane gas isn't Viagra, Propecia or Ex lax. If you're not knocking with 87, 89 or 91 octane, the higher octane or leaded gas will make no difference. The leaded fuel does smell different when burned. I like the smell of it.
I ran some 110 in the Charger while trying to eliminate the detonation last year. It stopped the knock and smelled great but D A M N was it ever expensive!

[Windsor]

Just a note that some may not know. Many farmers co-ops that sell fuel, have ethanol free gas. Most that I have seen have them on a separate fuel island set away from the main pumps.

[Ghoste]

Thats ironic.

[Challenger340]

It matters not if it is the most expensive C12 or C16 leaded Racing Fuel... or the cheapest Costco regular 87 Octane Unleaded, it is a BENZENE RING Hydrocarbon... with a Heat Energy potential of approximately 134,000 BTU's per liquid Imperial Gallon(4.54 litres)
that's it... that's all.

EVERYTHING else as it relates to the fuel "quality"... ie; Octane.. research & motor, oxygenation, additives, yada, yada are all about the Combustion conditions present in a specific Engine, as the "BEST" Environment for utilization of a particular fuel.

[Ghoste]

True, but as our specific engines are typically higher performance, it necessarily follows that our combustion chamber conditions more often require a higher quality fuel.

[Challenger340]

True, but as our specific engines are typically higher performance, it necessarily follows that our combustion chamber conditions more often require a higher quality fuel.

A guy would certainly think so... myself as well ?
that said,
we've sure seen some weird results on the Dyno that defy that theory ?

If you go look at some of the HEMI Dyno Sheets I have posted, we've Machined, Built & Dyno'd some 900+hp Pump Gas HEMI's that responded better to so-called poorer quality, bottom of the barrel, NO NAME Fuel.... better power, better egt's, etc., etc., than trying to feed them supposedly HIGHER QUALITY and very expensive Street Fuels ?
All comes down to the "conditions" present in the particular Engine I guess ?
What sometimes SHOULD be better... is not always, and vice-versa.

[Ghoste]

Yeah, I definitely have to concede to your experience there. 

[Cooter]

Hemis don't like to detonate as bad as wedge designs. Read that somewhere like 20 years ago.

[firefighter3931]

Cylinder head chamber shape & design largely influences octane requirements and timing. The more efficient the chamber, the less total timing needed to produce max power. 

This is why the typical hemi makes best power with 32* of total timing. A closed chamber wedge head is usually in the 34-35* range while the most inefficient design being the open chamber iron head is often at 38* and sometimes over 40 depending on the cam and static compression.

Years ago a friend was racing his 440 Cuda wit the typical 10:1 compression, 509 cam, 3500 stall and 4.10 gears using 110 race gas. I told him many times that he was slowing the car down and wasting money but he liked the smell of race gas.  Finally convinced him to run pump gas and it picked up 3mph and dropped 4 tenths.....in the 1/8th mile ! 

When you change fuel it's important to retune the engine properly. The optimal timing/jetting changes with fuel type so you can't simply dump pump gas into a motor that was tuned for race gas and expect it to perform perfectly. 



Ron

[HeavyFuel]

True, but as our specific engines are typically higher performance, it necessarily follows that our combustion chamber conditions more often require a higher quality fuel.

A guy would certainly think so... myself as well ?
that said,
we've sure seen some weird results on the Dyno that defy that theory ?

If you go look at some of the HEMI Dyno Sheets I have posted, we've Machined, Built & Dyno'd some 900+hp Pump Gas HEMI's that responded better to so-called poorer quality, bottom of the barrel, NO NAME Fuel.... better power, better egt's, etc., etc., than trying to feed them supposedly HIGHER QUALITY and very expensive Street Fuels ?
All comes down to the "conditions" present in the particular Engine I guess ?
What sometimes SHOULD be better... is not always, and vice-versa.

So...

I'm understanding you can BUILD an engine to respond well to today's gas by controlling the combustion conditions.  

Would it be safe to say that a pretty much stock engine, that has 60's specs designed for old gas, SHOULD respond to a leaded higher octane fuel?


My stock engine feels kinda like a dog. Especially when listening to old timers talk about how their stock this-or-that used to scorch the hides at will back in the day.  Mine just doesn't seem to have that kind of power, and I'm trying to identify a smoking gun, if there is one.

[Ghoste]

It should, yes but maybe not to the degree you are searching.  Don't get too caught up in older I get faster I was tales.