Comp. ratio/ pump gas
 

I have a 68/69 460 out of a Lincoln Continental that the books say has a 10.5-1 compression ratio. I fear she wont run on todays gas:( What ratio do you guys run and what grade of fuel do you run? Ive heard that the early heads will tolerate more compression than most other motors, but is this pushing my luck? Ill use dished pistons if I have to. I do plan to polish up the chambers to eliminate "Hot spots". What do you all think?

Nathan

Comp. ratio/ pump gas
 

Nobody knows, huh?

Nathan

Comp. ratio/ pump gas
 

I've heard 9:1 or 9.5:1 on pump gas with iron heads and about a point higher with aluminum heads. Also with the older heads you should have hardened exhaust valve seats installed.

Comp. ratio/ pump gas
 

Nathan, ive never dealt with higher compression on a big block ford, but a friend of mine was running ~10.4 to one on a 70's chevy 400. he had serious pinging problems even with 93 octane. big power was there but in order to protect the engine he had to back the timing waaay down and in return lost a ton of power. if he sets the timing to where he gets no pings AT ALL he has trouble getting one tire to spin off the line. if he sets it even half way as advanced as it should be to be getting peak power, he can break the tire lose off the line and smoke it. hes tried octane booster and it is a LITTLE bit of a help, but in his case it was hardly enough to make it worth it. i would personally try to keep any street motor under 10 to 1....the best would be between 9 and 9.5 i would think.

Comp. ratio/ pump gas
 

Premium fuel in Canada runs at 91 octane, considering the fuel for this engine required 98 , I tell everyone to find a friend who has a in , with somebody who sells AV-Gas (112 octane)at a decent price.

Dennis

Comp. ratio/ pump gas
 

well you can probally run thicker head gaskets for fix. another thing to try is run a distributor out of a 351(( modified )). they will drop right in a big block. you will have to run a different cap set-up. the one advantage is you can adjust your vacuum advance to compensate for spark knock. drop in the dist. set your timing say at 14 deg. and drive it around, if you get a spark knock get a 1/8 allen wrench. pull off the vacuum hose at the dist. there is a allen head fitting inside the vacuum advance. slide in the allen wrench and adjust by turning the wrench (( cc )) counter-clockwise about a 1/2 turn at a time and drive again. you might need to re-adjust your timing again. you should do this until the spark knock goes away. it does work.... C.J.

Comp. ratio/ pump gas
 

Thanks guys. I havent had the decks checked yet, but I did find a KB piston with a 22cc dish thats supposed to give a 9.9 CR. With some chamber polishing this should go down a little (as long as the deck and heads dont need to be milled).

Nathan

Comp. ratio/ pump gas
 

Cobrajet, do all 351M's have the adjustable vaccum advance? and if so, that would mean all 400's have that too right?

Comp. ratio/ pump gas
 

If you run those dished pistons, and get a thick head gasket, you should be around 9.7:1.. That should be alright with 92 octane gas. Lots of houses manufacture head gaskets up to .040" thicker than normal.. you figure, .040" OFF a head raised the CR by what, about 3 points? add that back ,and your CR drops.
Also, if you have the interest, those combustion chambers can be ground , and that will drop the CR even more, by however much you need. Good luck!!

J/.c

1965 Ford Galaxie 500 (okay, so not quite a truck)
460/C6 transplant @ 389hp/491 lb.ft.
14.29@103.8, 13-14 mpg heheheheheh

Comp. ratio/ pump gas
 

that i don't know,, the 351m dist. is for a 1977 application. you can try and see when you go to the auto parts store, take along a 1/8 inch. allen wrench and stick it inside to see. it might be the same. i looked in there book and tried about 10 different 429/460 vacuum advances and none of them are adjustable. then i remembered the 351's.. ....

Comp. ratio/ pump gas
 

An answer for the original question. I have a stock early 460 w/10.5 comp. runs fine on 93 octane. I also use a lead substitute because it has the original valves and seats.

Comp. ratio/ pump gas
 

>An answer for the original question.
>I have a stock early
>460 w/10.5 comp. runs fine
>on 93 octane. I also
>use a lead substitute because
>it has the original valves
>and seats.


Huh? good to know! Im still going to get it a little lower, though.

You can get an adjustable vac. advance from the aftermarket, might be easier than searching the yards.

Thanks again
Nathan

Comp. ratio/ pump gas
 

I don't think anyone mentioned this yet so let me throw a turd in the pool. If the engine is a 69 and assuming Canada has Unleaded only gas(I could be wrong) like in the US, you may have problems over time with valve seat recession and other problems related to the lack of lead in the gas. I am pretty sure most engines from about 71 and older did not have the hardened seats necessary to survive unleaded gas.

You may have to use a lead substitute which can get expensive if you drive much or a better solution is to have hardened valve seats installed. This will be expensive since in effect if is a valve job with new parts thrown in.

Just thought you should consider this issue, if you do not have access to leaded gas.

Good Luck,

Jim Henderson

Comp. ratio/ pump gas
 

Jim, Im at the home plate with the rebuild on this motor so new hardend seats are in the plans along with new SS valves, which brings up another querry. The heads currently have the "small" 2.08/1.66 valves. Would it be worth installing the next size bigger valves? This will be a tow motor, not a racer!

Good advise anyway, Jim, thanks.

Nathan

Comp. ratio/ pump gas
 

stock valves will work just fine... save the extra cash for filling up your tank ............. c.j.