# 1968 GTO Fuel Tank Size/capacity



## gtovett (Jun 13, 2007)

I can't find the size of the stock fuel tank anywhere. Wat is its capacity? Any help is much appreciated.


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## 68greengoat (Sep 15, 2005)

21.5 gallons.......


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## gtovett (Jun 13, 2007)

Interesting figure. I was surprised that no website that sells replacements lists the size.


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## 68greengoat (Sep 15, 2005)

I found that info from 2 different published sources. Maybe the 1/2 gal goes up the tube. Or maybe, a 21 gal actually holds 21.5 gals. Who knows. I'm assuming you can find a 21 gal? I would go with that. No one will ever check the capacity of your tank....


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## Rukee (Feb 8, 2007)

I think both are right. The tank holds 21.5 gal, but when filling you can only get 21 gals to allow room for expantion due to heat of the day or whatnot.


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## gtovett (Jun 13, 2007)

The reason I ask is that I am adding a mixture to the fuel and while it doesn't need to be exact I need to know when I am at 17 gallons of fuel. The ratio is 17:1. So depending on the temperature outside the capacity range is 21-21.5 gallons I suppose. 

A oil company chemist told me when you add 1 gallon of toluene to 17 gallons of 91 octane unleaded fuel the octane rating increases to 113. I've done it 4 times now over the last few months and there is a BIG difference.


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## jetstang (Nov 5, 2008)

That is so cool. I am so wanting to try some mystery octane boost. I have heard Acetone, mothballs and others. I don't need 110 octane, so can I quarter it and get 97 Octane? I am worried about it drying out lines and messing up the carb.


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## 66tempestGT (Nov 28, 2009)

why not mix it in another container then pour it in mixed. 113 seems like overkill. why not just half it. still over 100.


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## jetstang (Nov 5, 2008)

OK, per this article I found it looks like the NOS octane boost worked better than Toluene. But, that was 12 ounces compared to your gallon. If I'm reading it right, the NOS raised the Octane to 93, while the Toluene raised to 91.4, if that is what AKI means.
0503Ec Techboost Chart2 Photo


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## Rukee (Feb 8, 2007)

Too bad it's not street legal.


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## 66tempestGT (Nov 28, 2009)

this is a good read http://www.gtoforum.com/f50/octane-booster-question-24717/?highlight=octane+boost


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## 68greengoat (Sep 15, 2005)

I was just told by two different mechanics not to use a octane boost products. They say it can screw up your carb, don't remember if they said it could either soften or eat away diaphrams, rubber hose and dislodge coatings inside a gas tank plugging up the carb. Sounds like it's nasty stuff..... Last fall I used a fair amount, 16oz bottle per tank. Changed plugs this spring and they were red. The red color can be caused by fuel additives according to Chilton. Right now I have all kinds of carb problems. Hasn't been torn down yet to see if it's plugged up and with what. But..................


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## gtovett (Jun 13, 2007)

My preferred method would be to pre-mix it in a different container but I just don't have the facilities to do so where I live. 
I'm not entirely sure that I'm achieving 113 octane but I notice a SIGNIFICANT increase in power and a complete lack of hesitation when I use the toluene. 
Whats the significance of "street legal"? I'm just not sure why it matters.


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## 66tempestGT (Nov 28, 2009)

im with you about the street legal thing. i just was thinking you could mix it in a couple of 5 gallon gas cans. not a 20 gallon container.


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## dhinnah (Apr 12, 2010)

You can also buy aviation gasoline (avgas NOT jet fuel!) and mix it to get the desired octane. It is called 100 octane low-lead, but if measured like car gas it is 115 octane. Mixed 50/50 with regular gas, you get about 102 octane. It does have some lead in it.


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## andreasue (Dec 7, 2010)

gtovett said:


> I can't find the size of the stock fuel tank anywhere. Wat is its capacity? Any help is much appreciated.


For future reference you might find this helpful to you i am using this in my car. This is also compatible with 1969-1970 Pontiac GTO Fuel - Spectra - 24 Gallons / 91 Liters, Steel. The dimension is 37-1/4 x 30 x 6-3/4 in. This is already with hanger assembly but too bad it doesn't have any included seals and vent pipe. i think i just bought it for $450 but that is already 8 months ago i am not really updated with its current price today. Cheers.


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## dimitri (Feb 13, 2009)

I have a 68 GTO. I am looking at my owners manual that came with the car. It shows for the capacity:

U.S. 26.5 gal
Imperial 21.75 gal


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## Eric Animal (Oct 28, 2007)

jetstang said:


> That is so cool. I am so wanting to try some mystery octane boost. I have heard Acetone, mothballs and others. I don't need 110 octane, so can I quarter it and get 97 Octane? I am worried about it drying out lines and messing up the carb.


Mothballs are Bu!!sh!t.....so is Acetone as per aviation mechanics who are in the know. Don't do it!!!!!!!!!!!!!!


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## geeteeohguy (Feb 2, 2008)

First off, I have earlier GTO's. but I've nevber been able to get more than 19 fallons in the tank. Is anyone out there able to get more than 21 gallons in their tank? For real? Also, I too have been doing the Octane Detective role, and found out that racing fuel is up to 30% toululene. Problem is, it's $20 per gallon here. The Australians seem to use a lot of it, as I think it's cheaper "down under". I've been using Kemco's TEL130 in the '65, and it works (because it's tetraethyl lead) but it is not street legal. It is about $20 per quart, but one quart will "do" two full tanks of fuel. My good friend locally has just finished his '67, and is running 110 leaded that is $9.79 per gallon. His 10.75 iron headed engine loves it, and apperently is "scary fast". My next move is to visit the airport and see if I can get ahold of the 100 LL that's available for $4.85 per gallon...that's barely $1 more per gallon than the 91 octane crap we get here at the pump. I used to use 104+ and 108+ and my car pinged and the plugs fouled with bright yellow and red fuzz. Never again.


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