Gal req before selected fuel comes out the nozzle?

[Cujet]

My high boost Turbo S2000 NEEDS high octane fuel. At the local pumps, 93 octane is dispensed from a "blending pump". Since most people purchase 87 octane, there is, I'm guessing, about a gallon of regular gas in the line/filter and pump. Possibly more than a gallon!

Problem is, my tank is just over 10 gallons capacity. So, I end up putting 8 gallons in. (this is due to modifications, nominal capacity is 13)

I bring a 1 gallon gas can and fill that first. I no longer see the gas change color at the 1 gallon mark. AND, I'm sure each gas station has a different setup.

So, I'm stepping up to a white, 2.5 gallon "race gas" can, so I can more clearly determine how much regular I'm getting.

I know the .gov says you must purchase 3 to 4 gallons to be "sure" the fuel in your tank is the rated octane. That tells me nothing and does not help me determine how much regular I'm getting.

 

[supton]

What about dumping in a can of octane booster and then buying 87 octane? I have never used the stuff, but I wonder if by putting it in first it will have a better chance at better mixing.

 

[Food Scientist]

My math tells me that you are running too tight of tolerance if you NEED 93 octane.

If 1 gallon of 87 octane remains in the line then here is the math:

1 gallon X 87 octane rating = 87 octane points
7 gallons X 93 octane rating = 651 octane points

87+651 = 738 total octane points

738 octane points/8 gallons = 92.25 octane rating

I would think that if your car NEEDS 93 octane gas and 92.25 octane gas won't cut it, then you need to buy E85 or race gas.

 

[Donald]

There are gas dispensers that have 3 hoses and 3 nozzles. Find those.

 

[Padawan]

I think you may be considerably overthinking this. Even if you are getting 1 gallon of 87 in the tank, you're still ending up with 92.25 octane on an 8 gallon fill.

If you are concerned about increasing octane further, you can pump 7.5 gallons and add 0.5 gallons of toluene for a resulting 93.6 octane (assuming your findings of 1 gallon of 87 left in the lines are accurate). Pumping 7 gallons and adding 1 gallon of toluene will bring you to roughly 95 octane.

 

[Brent_G]

Originally Posted By: supton
What about dumping in a can of octane booster and then buying 87 octane? I have never used the stuff, but I wonder if by putting it in first it will have a better chance at better mixing.

From my personal experience with octane booster he would be better off putting the cash down the filler neck. It will raise the octane about as much and save a trip to the store.

 

[javacontour]

Exactly, when it says it raises a volume of fuel X points, what does that mean. For some vendors, that means it raises that volume of of fuel by .X

I.E. if it says it raises 8 gallons by 2 points, you'll go from 87 to 87.2 if you add it to 8 gallons of 87 octane.

https://bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1746544

Originally Posted By: Brent_G
Originally Posted By: supton
What about dumping in a can of octane booster and then buying 87 octane? I have never used the stuff, but I wonder if by putting it in first it will have a better chance at better mixing.

From my personal experience with octane booster he would be better off putting the cash down the filler neck. It will raise the octane about as much and save a trip to the store.

 

[flacoman]

Toluene is your friend.. CHeap and cheerful.

 

[jrustles]

Originally Posted By: Brent_G

From my personal experience with octane booster he would be better off putting the cash down the filler neck. It will raise the octane about as much and save a trip to the store.


lol


Y'know I've had the same issue with blending pumps, but instead my issue is paying premium price for the one gallon/3.85L of regular in the line, and leaving premium in there when I leave. After initially pumping the line clear and getting my high octane, I'll hang the nozzle up and then remove it again whilst selecting regular. Then purge the line out of the remaining premium, replacing it with regular as was presumably thought to be in the hose to begin with. That way, I pay for only what I get-- with the rare chance of there being mid or premium in the line already

Overthinking it? Sure, but why shouldn't we get what we pay for.

 

[Doog]

I have $20 that says every tankful you buy has a slightly different octane content. That number on the pump is just a sticker...if you think the government does anything to ensure refiners make the same blend of fuel you are dreaming. Also, if you think the refiners toss a tank of 87 out to fill a huge tank with 93 your dreaming as well. I run all of my 93 cars and boats on 87...never much difference. Try 87 in your turbo and see what happens. If you don't get a detonation...you are probably getting 90.

 

[javacontour]

The WSJ indicates the API claims it's about 1/3rd of a gallon before you get the octane you desire.

http://online.wsj.com/news/articles/SB122944043385810527

 

[rslifkin]

Originally Posted By: Doog
I have $20 that says every tankful you buy has a slightly different octane content. That number on the pump is just a sticker...if you think the government does anything to ensure refiners make the same blend of fuel you are dreaming. Also, if you think the refiners toss a tank of 87 out to fill a huge tank with 93 your dreaming as well. I run all of my 93 cars and boats on 87...never much difference. Try 87 in your turbo and see what happens. If you don't get a detonation...you are probably getting 90.


There are plenty of things that need 93 that will not survive on 87. With a fairly aggressive tune, a tank of bad 93 will ping in my Jeep (no knock sensor). A tank of 87 would almost certainly lead to killing the motor.

 

[Doog]

Originally Posted By: rslifkin
Originally Posted By: Doog
I have $20 that says every tankful you buy has a slightly different octane content. That number on the pump is just a sticker...if you think the government does anything to ensure refiners make the same blend of fuel you are dreaming. Also, if you think the refiners toss a tank of 87 out to fill a huge tank with 93 your dreaming as well. I run all of my 93 cars and boats on 87...never much difference. Try 87 in your turbo and see what happens. If you don't get a detonation...you are probably getting 90.


There are plenty of things that need 93 that will not survive on 87. With a fairly aggressive tune, a tank of bad 93 will ping in my Jeep (no knock sensor). A tank of 87 would almost certainly lead to killing the motor.


when you get "bad 93" you are probably getting 87 then and your retailer is simply cheating everyone. Like I said. If it detonates dont do it. But you may be surprised. But you have a modified engine which really is moot. I am talking about a stock engine here.

 

[Cujet]

Originally Posted By: Donald
There are gas dispensers that have 3 hoses and 3 nozzles. Find those.


I do remember those. Don't have any local to me.

 

[Cujet]

Originally Posted By: flacoman
Toluene is your friend.. CHeap and cheerful.


Of course, I was one of the original proponents of toluene. As the our IMSA RS turbo Mustang's paddock spot was right next to the turbo F1 guys who were always mixing up a brew. We learned a lot from those guys!

However, it's $15/gal around here. The best street blend I used to make was around 20%, or $60/tank. No thanks.

 

[Cujet]

Originally Posted By: Doog
I have $20 that says every tankful you buy has a slightly different octane content. That number on the pump is just a sticker...if you think the government does anything to ensure refiners make the same blend of fuel you are dreaming. Also, if you think the refiners toss a tank of 87 out to fill a huge tank with 93 your dreaming as well. I run all of my 93 cars and boats on 87...never much difference. Try 87 in your turbo and see what happens. If you don't get a detonation...you are probably getting 90.


Man is that ever true! I log "knock" events. It's clear that the fuel differs from fill to fill.

However, the S2000 is a very highly modified car. Running 19.5 pounds boost and making 407RWHP. It's clearly better (fewer knock events) when I put the first gallon in the jerry jug.

 

[Brent_G]

Originally Posted By: Doog
I have $20 that says every tankful you buy has a slightly different octane content. That number on the pump is just a sticker...if you think the government does anything to ensure refiners make the same blend of fuel you are dreaming. Also, if you think the refiners toss a tank of 87 out to fill a huge tank with 93 your dreaming as well. I run all of my 93 cars and boats on 87...never much difference. Try 87 in your turbo and see what happens. If you don't get a detonation...you are probably getting 90.


Doing this with a modified engine, especially forced induction, is a very very quick way to add a new window in the block/oil pan. Going lean and detonation WILL make you have a very very expensive day.

 

[RF Overlord]

Originally Posted By: Brent_G
Originally Posted By: supton
What about dumping in a can of octane booster and then buying 87 octane?
From my personal experience with octane booster he would be better off putting the cash down the filler neck. It will raise the octane about as much and save a trip to the store.
Originally Posted By: javacontour
Exactly, when it says it raises a volume of fuel X points, what does that mean. For some vendors, that means it raises that volume of of fuel by .X

I.E. if it says it raises 8 gallons by 2 points, you'll go from 87 to 87.2 if you add it to 8 gallons of 87 octane.
Agreed. OTC "Octane Boost" products are worthless. All they do for my '68 Buick Gran Sport is foul the plugs.

I can't speak for adding toluene as I've never tried it, but I have heard sufficient anecdotal evidence that it could have some value.

 

[SHOZ]

Benzene works great if you can get it for boosting the octane

But toluene is easy to find.

 

[Brent_G]

Cujet what octane do you require approximately? You could always blend in some 100 octane race gas to ease your mind. We do that with one of our cars and it works great.