100 Octane with 12:5:1 340??

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emnestor

emnestor

emnestor
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I have a 340 with 12:5:1 comp street car. What are the opinions about 100 octane gas ? Do you think it is sufficient? We have a couple of ststions in our area that sell 100 and 108 octane fuel and I have been experimenting with mixtures etc... I have run this motor a few times on 93 pump gas and have never experienced any knocking or pinging.
 
My motor has the same compression and I mix high test 98 octane with 112 race fuel.
 
Not great. It spark knocks if I do not run race fuel. I am putting about 5 gallons of race fuel in each tank of fuel which means to work well. What are you running your timing at?
 
110 Octane only... you built a race motor, or at least high compression... now you have to deal lol... if you cant deal then put thicker head gaskets on it...
 
So let me get this straight, you are calling it a street car when you can not roll into any gas station and fill it up? So you never venture beyond a half tank away from home? Or do you carry fuel cans in the trunk?
 
inkjunkie said:
So let me get this straight, you are calling it a street car when you can not roll into any gas station and fill it up? So you never venture beyond a half tank away from home? Or do you carry fuel cans in the trunk?
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That would be correct. Is that a problem?
 
you best bet would to find out the availability of E85 in your area and convert the car to run on it...Will be cheaper in the long run.

E85 is 105 octane.

http://www.raceone85.com/
 
I would LOVE to do that but it is not available in Canada. If it does become available I will run it for sure. What kind of cost am I looking at to convert?
 
1968dartman said:
I would LOVE to do that but it is not available in Canada. If it does become available I will run it for sure. What kind of cost am I looking at to convert?
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The cost isn't high to convert but you do need to burn more.

Your cruising range off one tank full will be significantly less. That's the big thing I don't like about E85. Someone needs to come up with a 30 gallon fuel tank for an a-body.
 
1968FormulaS340 said:
The cost isn't high to convert but you do need to burn more.

Your cruising range off one tank full will be significantly less. That's the big thing I don't like about E85. Someone needs to come up with a 30 gallon fuel tank for an a-body.
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just have to have a flat trunk floor.... may do one for my 73 swinger
 
Why not run water methanol injection and not worry about octane ratings? Expensive to invest but cheaper in the long run.
 
E85 is like a program for a macintosh computer. It works AWESOME... for a hand full of people.

I'm still a fan, but I want a car set up for flex, which is out of the question with a carb. You'd have to run an O2 controlled electronic fuel injection and timing, with injectors that didn't hit static on the high end, but ran good on the low end for low octane.

Flex is the way to get some great drivability + high octane, but almost not worth it.

100 should be fine in a 12.5:1 if you have a good quench and blueprint your dist.
 
Y2K era,California. Ran a 11.7 to one,Edelbrock headed 340,on 91 with TK7 additive. Good for street driving.Race night,rolled out race gas.(N20). Car had 4:57's, 4800 stall converter. The gear,and high stall,let the engine "float". Deep gears,and good stall,reduce the load on the engine.Efficient? No.Less engine load,less possibilities,of detonation. Not mine,helped with assembly.
 
emenstor if your car runs on the 93 dont mess with the others too much octane will slow it down and its exspensive. It smells good. If you dont need the high octance dont run it. Lots of guys think they need it but actually dont.
 
If you have aluminum heads and more than a thumper type cam, 100 will work. You would need at least a 3000 stall converter. I have a 10.5:1 , 2500 stall, 3.23 gears and run 12.35 with full exhaust on 91 octane. LOL
 
emnestor said:
I have a 340 with 12:5:1 comp street car. What are the opinions about 100 octane gas ? Do you think it is sufficient? We have a couple of ststions in our area that sell 100 and 108 octane fuel and I have been experimenting with mixtures etc... I have run this motor a few times on 93 pump gas and have never experienced any knocking or pinging.
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I,m guessing when you added the 93 octane it mixed with what you had in the tank already(100-108).Running a 12.5-1 engine on straight 93,your engine isn,t gonna last to long.As suggested,I would put a thicker head gasket on it to lower your compression.It will give you more life from your engine and piece of mind.JMO.:D
 
Wow! back from vacation and there is a wealth of info here.
well, I have a 4 speed and no worries about stall. Comp cam XE294H,250/256 110 degrees. Yes it is a full blown race motor, but I am fortunate to have a station nearby that sells 110 and 100 right from the pump. I admit its a bit ridiculous for the street but Damn its fun to drive. I have other cars for cruising. I keep a little 110 at home for when Im running low. I happened to run it just a few brief times on 93 and it ran just fine ie... no Knocks etc. Just curious about others experiences
 
My motor is 12.5 and I run pump gas on the street. The trick a lot of over lap in the cam. high stall and low ratio gears ,410 and up. Also run it a tad rich. As long as you don put a load on the motor your fine. My car does not hook up on the street at all so it never loads.
 
Has anyone here swapped over to aluminum heads but kept their high compression? Did it allow you to run on 93 octane?
 
emnestor said:
I have a 340 with 12:5:1 comp street car.

I have run this motor a few times on 93 pump gas and have never experienced any knocking or pinging.
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That's because static compression isn't the end all be all in fuel requirements. Timing (static, curve, and total) Carberation, weight of car, gears, transmission,camshaft and cranking compression all affect this.
 
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