I am going to rebuild a 71 340 w/10.5:1 comp pistons keeping everything else basically stock.  2 of my local machine shops are against running 10.5:1 unless aluminum heads are used.  They say 94 octane isn't enough and they discourage octane boosters.  They suggest taking it down to 9:1.  Looking for advise/experiences from other 10.5:1 drivers.   Thx  

I have run 10.5 in several engines, and never had a problem running 93-octane fuel. Several of our participants in the 2007 Amsoil/Mopar Muscle Engine Challenge were running cast heads, with AT LEAST that much compression without fail. Schurbon Racing Engines--one of the participants in 07, posts and replies here a lot, and he was one of the guys with cast heads. I'm sure he'll chime in.  

Sorry, there is no point in running 10.5/1 compression on todays gas. The only way you can do it is to back off the timing or run a ridiculous amount of duration and that is defeating the purpose of the higher compression motor.
9.5 speed-pros are the perfect solution, you can run Sunoco 94 without a problem and the engine will make tons of power.
This is what I run with a built 360 with LA heads, puts 447 hp. to the crank, is a ton of fun and gets about 18 mpg.  

I have a 70 340 bored out 40 over  with X heads and run this thing on 93,octane gas and have never had a problem. I can actually be in 4th gear with the tach reading about 900-1000 and it will go, I certainly cant floor it but it will go. I have never heard a ping from the engine.  

Same here, 10.5, x heads, 284 solid cam, 34*total timing, no problems.  

Great, we got two guys that say it'll work, but one can't floor it at 900 rpm, so whats the point of owning a 340 if you can't floor it anytime all the time!  

OH...
I can floor it @ 900 rpm but it accelerates a lil slower than usual.....
BECAUSE IT'S IN 4TH, like the example your refering to.
Now if your hearing that he can't floor it in 4th @ 900 rpm cause it detonates well thats that would be to bad, but still not the case with my 340, I can floor it anytime.  

I was refering to bob challenger mr. 4 speed valiant, since he commented he couldn't floor it at 900 rpm.
Lets see mr. 4 speed, your the guy that runs with out any vac. advance is that correct?
And I believe bob is the guy who runs around without a thermostat.  

Yep  

I thought so, it sounds like you guys have a bandaid for just about anything.  

Hey, no big. If you can run one and improve your gas mileage then sweet.
But it has nothing to do with performance/racing or my MSD pro billet. [joke]
I ran one on a mopar distributor setup and had to crank it down to like 8* [34*+8*=42*]
Reason being that upon sharp acceleration from a cruise it pinged & LOUD so Problem fixed, however the difference mileage wise was... well... who the hell cares I'm not doing this for mileage I'm doing this to go fast and just about everything I've done to my motor was to do so and if mileage is a byproduct of any of that I've done to it then hey cool....... other wise it's a fist full of dollars down the filler neck and black stripes out the parking lot.  

Nice, you already answered the mans question, you can't run the proper timing as I suggested because the vehicle will ping due to the 10.5/1 compression, this is the reason he needs to listen to his machine shop and install the 9.5 slugs as i suggested.
People on the street do drive with more than two positions of the gas pedal, and if they can get a huge increase in mileage by setting the car up properly than why wouldn't they. Besides why wouldn't you run a vac. unit on the street if you get the same performance with or without it, plus you get 5-8 more miles per gallon. Its kind of a no brainer isn't it?  

Vacuum advance is for you, not me.
The right timing? where did you mention your opinion of the proper timing?
A sb MOPAR with the right amount of compression only needs 30*-34* performance wise period. That means with every thing dialed comp, cam , chamber's shape, ect that's all the timing they need to run proper and if it runs with more well you should of put the right compression in it.
Ever put KB hypers in any MOPAR SB?
Ever read their recommendations for timing?
They recommend using only about 32* IF THE MOTORS SET UP RIGHT= compression?
Every motor I ever put more timing in then that was because it had low cylinder pressure weather it low comp pistons, too much cam, ect
You know high compression does more than just raise the cylinder pressure and increase the octane requirements It gets the piston closer to the valve and basically the closer the piston to valve the faster that signal is transmitted initiating flow sooner & pulling harder.
11.2 in a 451 on the street w/iron 915 +87 pump gas 28*initial & 35*total hows that sound? scary?  It hauls ass!  

I think you guys have made my point quit clear, for a street car you cannot run 10.5 compression unless your willing to sacrifice fuel economy and driveabilty by altering the engines timing and operating temp.  

Wow didn't mean to offend anyone. Just saying what works for me. I run 10.5 and get decent gas mileage and in a car like that I dont really care too much about the mileage as with most performance since its just a weekend driver.The timing is set to 36 full advance, starts immediately, and runs fantastic. Can you tell me that most of the guys cars out there with the modifications are set to factory specs.OK so I pulled my therm out, still runs about normal,its damn hot down here in FL. I think using the word altering is a bit much. Why would I ever want to floor it in forth gear whats the point, thats why I have gears. My point was that I could be in forth gear and still push down on the gas and go, not to floor it, and thats pretty damn good by any .ones standards.But I did not mean to offend anyone.