Is there a way to determine what octane gas you would need by the compression you are creating? I know as the compression goes up the octane must also.

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2006 Jeep Commander
2013 Chrysler 200

1964 Valiant 4 Door
1965 Plymouth Barracuda
1967 Chevy Camaro

Not by compression alone. You have to also take the cam overlap into account. A wider grind verse a narrow grind, (106 vs 112).
With a lot of cam overlap you can bleed off a high compression engine. It's a balance between the two....
Doc will say, calculate your DCR.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Ted lined it out really well. A DCR calculator will help determine whether it will be best for turbo duty or needing some of that diesel fuel...

There are some online and some that are down loadable. typically they are geared toward a V-8, and the slant depending on a couple of factors can be a little more tolerable on the fuel needed based on the head, compression, timing, car/drivetrain, etc...

Typically the rule of thumb with the DCR calculator up to 8:1 DCR is 87-regular, mid-8's are 89-plus fuel, and 9:1 is super and more than that starts into the race gas only category....I can say that if you use the calculator as a tool to subjectively work out the engine component combination you can do some 'interesting' things. In my example I built a 10.3:1 static CR engine, which most 'over the counter guys' would say needs super 'or else'... using the DCR I set the cam up to deliver a low 8:1 DCR...this allowed me to dial a little less timing on my distributor and daily drive on 87 with little impact on mpg, go to the track : add 5 gallons of super and dial back in the 2 degrees and drop a little time...time to go back to work reset it and save the .30/gal...

http://cochise.uia.net/pkelley2/DynamicCR.html

The URL above has a nice read, and is an OK downloadable calculator...when head scratching a build, I will dream it up in Dyno2000 then to make sure that the numbers aren't 'fantasy' (i.e. short cam/lots of cylinder pressure/lots of power...DCR says needs jet fuel...), I run it through the DCR calculator and if too high for the intent I go back and tweak the build or stick but allow some room for 'fudge factor' as nothing is perfect.

-D.Idiot

You have to find what cam your going to run, then useing a dynamic compression calculator find what your static compression needs to be to get a max of around 8.5 DCR for 93 pump gas, and at 8.5 you may be flirting with disaster if timing or fuel is off, 8.0 would be safer for a street driver. If you add boost you will need to figure that in also, some of the calculators have that built in to them, or you can run methenol injection, spark retard, intercooler, or all the above

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Check page one of the link for Doc's guidelines for fuel needed

http://slantsix.org/forum/viewtopic.php ... +groupings

Rick

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Well I can give you some information to hopefully help. I am using the

Oregon Cam Grinder 791 Cam.

Intake Open: 11 BTDC
Intake Close: 39 ABDC
Exhaust Open: 47 BTDC
Exhaust Close: 3 ATDC

Felpro Gasket
Compressed: .036
Uncompressed: .041
Piston Opening: 3.520

Combustion Chamber: 48cc per cylinder

Cylinder Bore: 3.440

Cylinder top to Deck height: .071

Rod Length: 6.669

Stroke: 4.125

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2006 Jeep Commander
2013 Chrysler 200

1964 Valiant 4 Door
1965 Plymouth Barracuda
1967 Chevy Camaro

These are .050 numbers of your card correct? The calculator needs actual numbers to work with, have you installed and degreed the cam for the actual Intake close event?

The calculator also states that given your numbers you have about a 10.73:1 SCR engine...

-D.Idiot

Yes this is at .050. I have not degreed the cam yet. The machine work is being finished up this week. The number I provided is what my machinist and slantsix.org has worked out.

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2006 Jeep Commander
2013 Chrysler 200

1964 Valiant 4 Door
1965 Plymouth Barracuda
1967 Chevy Camaro

Since it's unknown as to what you are going to degree the cam in at, and since OCG only provides their durations in .050 and .020 settings the guess work on you build now puts the Static at 10.66-10.73...taking a guess on the DCR based on my experiences with that cam and this compression range...

Puts your DCR at 8.2:1 if you install the cam straight up (no advance or retard), and can be up to 8.68:1 if you advance the cam 4 degrees or had it ground with that advance....that starts into the high end of needing super and a little more 'gumption' in the tank...

-D.Idiot

Thankfully it's not an 11:1-12:1 motor where a few hundreths really is a make or break on the compression calcs.

Well I was planning on following the indications from OCG and install it 4 degrees advanced. I am looking to squeeze as much as I can.

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2006 Jeep Commander
2013 Chrysler 200

1964 Valiant 4 Door
1965 Plymouth Barracuda
1967 Chevy Camaro

If my run through on the calculator checks and you do this at 8.68:1 DCR, you will be super all the time and dial back the timing unless spiking with race gas...if you compromise in the mid range you can get away with running 92 all the time.

Better check to see what you can afford, this high up, you cut back to lower octane or low quality gas and things will suffer.

FYI.

-D.idiot

Thank you I appreciate the info. I don't drive her everyday and truthfully my Hemi Charger uses super also so I am used to the prices unfortunately.

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2006 Jeep Commander
2013 Chrysler 200

1964 Valiant 4 Door
1965 Plymouth Barracuda
1967 Chevy Camaro

These days, buying high octane is no big deal. Usually, premium is 30 cents more than 87 octane, which is about 7-8% of the cost of the gas. I build all my stuff to run premium. Back when I started driving in 1988 it was about $1.00 for 87 and $1.20 for premium, so it was a bigger deal (20%).

Lou

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Home of Slant6-powered fun machines since 1988

Good point Lou.

By the way Lou I signed up for SCCA and hoping to have my first race 3rd week of April. Machinist has been SLAMMED and I am the kind of guy that likes to use that to my financial benefit.

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2006 Jeep Commander
2013 Chrysler 200

1964 Valiant 4 Door
1965 Plymouth Barracuda
1967 Chevy Camaro

What kind of race? Do you mean with your Barracuda? If so, what class?

Thanks, Lou

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Home of Slant6-powered fun machines since 1988