Hello all,

I've come to the "Mopar-Side" and purchased my first Mopar; a 1969 Plymouth Roadrunner 496CI.


The reason for this post is to see if there is a member who can help me with my compression ratio dilemma.


The former owner of the car told me that he's pretty sure the CR is 13:1 and he used a fuel additive to ensure there is no detonation.The cars engine was originally a 440 but has been recently stroked to 496. I don't plan on ******* the car at all, but when I decide to give it a bit of gas I don't want to hear any pinging.


What I'd like to find out is what type of octane rating should I put into the gas tank to keep it above and beyond detonation? Or can I retard the engine or something else...?

Other information that might be useful in finding this out:

I live just above sea level (less than 100')
The summers can be hot around 105 degrees on some days but usually are mid-high 90's
The transmission is a built 727 reverse manual valve with a 4500 Art Howe converter
Dana 60 Rear End with 4:10 gears
I plan on driving the car once, maybe twice a month, on a weekend in good weather from city to city (less than 50 miles round trip)

Lastly, there is a 76 Gas station that sells 100 Octane that I will be filling the tank up with. If I fill up with the type of gas will it be a sufficient octane rating? I don't know the CC of the heads or intake/exhaust info or I'd include those figures.

Please let me know if there is anything else that might be needed that I can get you.

Thanks in advance!

 

110 octane racing gas. Pull the plugs and do a compression test ! May run on 100 Or you can retard the timing some

 

Welcome aboard to.

 

inri -

Like TV said. You do have options.

100 Octane may work, try it.
If you get pinging under moderate load, try retarding the timing.
If the timing + 100 oct doesn't do it and the gas gets too expensive (it will), consider a water injection system. Back the the day Edelbrock made one (I still have it too) and these days the hot name is "Snow". It's an old, like WWII old, technology but does work.

Archer

 

welcome to the forum

 

Sometime they put alcohol in the windshield washer bottle and plumbed it into the air cleaner with a holley jet to adjust flow
Check the NOS parts for a spray bar if you want to get fancy

 

Welcome to the Forum.... Be sure to check out the Mopar of the Month contest....

 

Welcome!

 

Welcome to our forums

 

Watch out for my Buddy (Harry) He lives up in Sac.... HE loves to cruise that town....

Here he was cruising around SO-CAL at Fontana Raceway or (AutoClubRaceway)

 

too much cr for a street car

 

Naaaaaaaaaaaa....

 

:welcome2:

 

Another option ? Depending on what heads you have ? A switch to large chamber Eddelbrock heads may work

 

If its a true 13.1.0 CR motor... Your going to need a little more than that to run that dog on...
Check the octane at the pump. You will find it is not a true 100....
Your going to need around 113 Octane rating to get around a 107 True Octane rated fuel.
What is needed in the know department is "Was the engine" built to run on Pump Fuel? If the answer to that is NO. Then a higher Octane fuel must be used.
If that is the case... Go with a VP-110 Fuel.
Head over to Sac. Raceway and pick some up if you cant find any.

 

 

It sounds like it is going to cost alot to take a Sunday cruise in this car...That CR is ok for the track but not so good for the street esp.with Ethanol fuel...Premium fuel hear is 92 octane and $4.09 a gallon and that doesnt last long in a car that gets at best 10mpg....Hope it comes down before the season starts...Bill

 

INRI,
Well how are thing going..?????? Any progress or are you still penciling it together?
What the update for us here.....
Hope all is well?

 

see there, ask the right people youll get great answers. glad your here. IMHO. a race engine is more likely to detonate at high RPM than low RPM. am i right Bob?

 

It will detonate at higher RPM's you just won't hear it...

 

Hi Bob,

I'm still taking it apart! LOL I did pick up a 1000lb engine stand recently. So I'm good for any future engine build. Engine cherry - check, engine stand- check.

I sent out the heads to be ported and was called back two days later by the shipping company that there was a little oil residue found in one of the heads when they were packing them. So they asked me to come down and pick it up and get it cleaned. Then I get to drop it back off and have it shipped!! They told me that when I dropped it off that it would be shipped in two days....

I've been selling alot of the old engine parts to help with the rebuild costs. Cast iron pump, pulleys, old distributor, 830 holley carb etc..

I do have a lot of what I would like on paper. BIG CUBES AND LOTS OF POWER

To be serious though, I do have a lot of what I'd like on an excel spreadsheet that includes part, description, cost, and location (website or catalog). What I'm sold on is going with a roller cam and roller lifters, perhaps Jesel. I've read that moving away from the needle type bearing lifters is like a cure for cancer.

Taking more time than I'd like, but that's probably because the weather is getting warm up here and the family would rather we go to the water slides than purchase a carb?! Crazy huh?

 

Yup. I can't hear anything other than the engine's exhaust in or outside the car. The rebuild will be less than 11:1 and probably closer to 10.5:1.

 

Sounds like a great plan coming together. Cant wait to see what you do? Also cant wait to see a vid's and pictures of how it comes out....
Thats one Fine looking ride...

Keep us posted

 

Sold the '69 block with crank, pistons, rods, oil pan etc. today. All this $$ will help with the build!

 

I'm Smelling a 572.....

 

LOL! Man that would be sweet! I'd love a nice AA572MW (All Aluminum 572 Max Wedge)
Afraid I'd have to take out a personal loan for one of those...