What fuel should I run in my 340?

[Promark]

What do you guys run in your car?
I'm currently running 91. And some ppl r telling me that it's making my car idle bad

 

[1970Duster]

Depends on your compression ratio.

 

[1968FormulaS340]

91 should be fine as long as you don't have detonation.


As mentioned in your other thread. Check all the normal stuff.

•Plugs
•Wires
•Cap
•Rotor
•Timing
•Carb Tuning
•Vacuum Leaks


But even if all that is good some cars will still not be happy with the winter blends (that has been my experience anyway).

 

[Promark]

Ok when you say wires. Your talking bout the spark plug wires that run from distributor to spark plugs?

 

[1968FormulaS340]

Ok when you say wires. Your talking bout the spark plug wires that run from distributor to spark plugs?

Yes

 

[Promark]

Ok I'm going to replace these cuz the headers have burned them up a bit Do u guys really think the wires could b the source of the problems. I've had to reclamp some

 

[pettybludart]

I run 94 Sunoco in my cars with stroked engines.It all depends on your compression.Make sure cyl 5 and 7 plug wires are seperated good.These 2 are common for spark jumping,causing it to run bad.Good luck.

P.S I use asbestos sleeves over my plug boots,great for hedders too.
View attachment car pics 66 Dart 172.jpg

 

[1968FormulaS340]

Ok I'm going to replace these cuz the headers have burned them up a bit Do u guys really think the wires could b the source of the problems. I've had to reclamp some

Burnt up plug wires can make your car run bad or not at all. They also need to be installed in the correct order or it will run like a turd or not at all.

Please post any questions you may have about putting the plug wires on.

Take some pics of the burnt areas of the old ones too if you can.

 

[abodyjoe]

hell i run 89 octane in my 360..

 

[1968FormulaS340]

hell i run 89 octane in my 360..

Yup..... You only need what you need. Beyond that you are just handing out money for nothing.

 

[3406pk]

The gas octane should not affect the idle quality. The octane level controls or limits the detonation at acceleration or high load. As stated in formulaS340 reply look for plug wires, vacuum leaks, and timing. Also check check vacuum at idle to see if it varies a lot; could be valve leak or misfire. Also if the idle setting of carb is too rich, it will idle bad but drive good.

 

[green1]

Depends on the compression; pulling apart my old 70 Duster that I got back from the ex-wife- she had been using 89 in it. 10.5 factory advertised. #6 had the top of the piston broke off, exposing the top ring. Detonation.

 

[dodge freak]

Is the intake exhaust heat blocked off or running an Air gap intake? In cool weather the plugs can foul out. Fuel needs heat to burn, carbs are different than FI. Racing or hot summer weather heat isn't needed, in the winter on the street its a big help.

Plug wires wear out also, they need to be replaced after so long. If you have a spare carb you could swap carbs, this gas can loosen up crud and plug up the idle passages

Once running right you should not really feel the octane at idle.

 

[Promark]

Well I'm gonna switch up my gas for 1 tank
But im also gonna replace the wires

Does anyone have any recommendations for plug wires?

 

[Burntorange70]

What is the CR? I run 91 in my 70 340. Would think 87 is fine for a low CR 72+.

 

[Promark]

What is cr. I'm a noob

 

[66340SEDAN]

CR = Compression ratio

 

[66340SEDAN]

I run 92 pump gas-non oxyiginated type from BP. I have run 91 before and it pings a bit when I hammer on it, 92 doesn't do it. Sometimes I will run some 110 mixed with 92 thru it, runs great. I have fueled up at Super America gas stations before with my Valiant and my car always runs shitty on their fuel, one time it died a block away right after fueling, when I finally got it started it ran very rough for awhile, thought something was really wrong. The next day I filled it up the rest of the way with some better fuel and it ran fine. BTW, I have a 72 340 with a 9.31 compression ratio.

 

[Promark]

How can I findout what is my compression ratio?

 

[70aarcuda]

my 73 340 Duster is happy on 87 octane these days.

 

[1970Duster]

How many CCs are your heads and how close does the top of the piston come to the end of the block (where the heads bolt on).

 

[Tony Fields]

87 octane works just fine for me......Dished pistons down in the hole

 

[Promark]

My car is shutting off at every light! Fml. I'm changing the wires now the car runs horrible on 87 it feels like performance went down and it's shaking Alot. The car was fine last week well not this bad

 

[Promark]

Tony fields what type of wires are those

 

[Tony Fields]

Tony fields what type of wires are those

MSD....my complete ignition system is MSD including the dist.