MAX. CYLINDER PRESSURE

[360DARTGTS]

I HAVE A 360 WITH A CYL. PRESSURE OF 175#. WHAT IS THE MIN. OCTANE I CAN RUN? I KNOW I NEED TO ADD OCTANE BOOST WHAT WORKS THE BEST?

[Dart]

You are around 10.5 to 1.

You will need to mix gas (premium with race or aviation).

[Tony W]

Well, it depends on how well your tuning is and if the carb is jetted properly, etc. Generally 165 psi is about max for pump premium 92-94. I have seen small blocks run premium pump without a problem at 175 psi(without turning back the timing) but this is not the norm. I also think these were "quench" motors. Looks like you will probably have to mix fuel. What combo do you have(heads, pistons, cam, etc.)?

[360DARTGTS]

I AM RUNNING THE M.P. HIGH COMPRESSION SHORT BLOCK WITH PORTED "J"HEADS, HEADERS, 4 SPEED, 750 VAC SEC. CARB. 3.91 REAR, M1 INTAKE (DUAL PLANE). I KNOW THE PISTONS ARE HYPEREUTETICS SO MAYBE I'LL GET BY WITH JUST SOME OCTANE BOOSTER AND PREMIUM GAS... WHAT DO YOU THINK? ANY RESPONSE WOULD BE GREAT.

I HAVE A FEW FRIENDS THAT ARE WORKING ON THEIR CARS AND I'M THE ONLY ONE WITH A SMALL BLOCK AND I NEED TO GIVE THEM A RUN FOR THEIR MONEY. THEY HAVE 440+6 70 'RUNNERS AND ONE HAS A PRETTY STOCK '69 383 'RUNNER WITH THE EXCEPTION OF CAM WHICH HAS AROUND A 228 DUR. @ 50 CAM.

DOES ANYONE HAVE ANY EXPERIENCE WITH A SIMILAR COMBO FOR A 360? WHAT CAN I EXPECT FROM THIS ENGINE AND CAR? IT'S IN A '69 GTS.

MOPAR TO YA GUYS!!!!!!!!

[Brian_wo]

Originally posted by Dart:
You are around 10.5 to 1.

You will need to mix gas (premium with race or aviation).

Tell me how you know this from the info stated because I know of no way for anyone to know this,my cranking pressure is 165 and I have a little over 11:1 but my cam bleeds off cylinder pressure.

[This message has been edited by Brian_wo (edited May 26, 2000).]

[451boy]

My 499 motor has a compression ratio right at 9:1 but cranks 185 psi. It runs fine on pump gas.

[chrisfly]

I have to agree with brian_wo. There is no way of knowing what compression ratio is by knowing the cylinder pressure. Every cam bleeds off cylinder pressure differently. I have built a 440 with 10.02:1 and i have 180 psi. this is with a hughes 223/230 540/550 cam. they tell me it will run fine on pump gas. I will find this out shortly. engine goes in car in about 3 weeks. Hope this helps, just my 2 cents

[toolman]

I've seen stated in a Mopar magazine that premium is maxed out at around 165 cranking pressure. But location may play a part in where the gas was purchased,California gas sux worse than other places, also how lean or rich the carb is set. What you need may depend on your particular car and not anyone elses. Listen for pinging for sure! At part throttle it's more prevelant. Also, I think you are going to embarrass the heck out of your friends, or at least gain alot of respect for your smallblock!

[bemiller]

I'm not sure what gas is costing where you live but around here its $2.25 for premium gas. Why even bother when racing gas is only $3.00 per gallon. Save the headache and run the gooood stuff.

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Check out http://www.donet.com/bemiller/ and let me know what you think!!

[ChristianCuda]

bemiller I wish Race gas here was $3.00/gal Here 105 is $5.00/gal and 110 $10.00/gal

Most people here mix AVGas and Premium. But then Premium here is $1.85/gal right now.

I wonder if we could get the same benifits with AVGAS and Regular??

Christian

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68 'Cuda 383 Formula S recreation
Working on adding EFI
69 'Cuda Race Parts Car
76 Duster 273 recent transplant
95 Neon 2.0 SOHC best of 16.96
84 Dodge Ram D50 transplanting 360

[Thunderstruck]

My turbo 2.2 pumps out 150 psi, not even close to 9:1 let alone 10 or more to 1. So you can't equate cranking cylinder pressure to compression ratio other than the very general statement that in otherwise IDENTICAL motors the one with the higher cranking pressure will have a higher compression ratio. By identical I mean same cam, stroke, headgasket, rockers, etc.

What's the max you can run on pump gas? I don't know. But I run a nominal 9:1 318 on 89 octane. A rule of thumb is take the octane rating, stick a decimal point between the two numbers and that's your max compression ratio. It's conservative but most rules of thumb are.

Steve

[T748]

ChristianCuda-if you need a formula to figure your octane from mixing octanes here it is;say you mix 9 gallons 110 and 9 gallons 92. 9 gallons X 92=828. 9 gallons X 110=990.add both=1818. devide by total number of gallons 18=101 octane.12 gallons of 110 and 7 gallons of 87 would get you 101.5 octane.

[440 Jim]

These race gas prices caught my interest. At Maryland International Raceway (MIR), 110 octane is $3.75/gallon and 114 octane is $3.95/gallon. A local Mobil station sells CAM2 110 for $3.75 also. Of course they say you have to pump it into a jug or the car must be on a trailer...



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440 Jim
E-Body Fish