SalikDDD

well i just got a 4160-c holley 600cfm carb, a performer rpm intake manifold , a comp 268 cam , tri y's and some other things. the question is, i understand the engine is 9.3:1 compression - would installing thinner head gaskets raise compression, and if so how low can i go as i do not want to get the stock heads milled.

67mustang302

Depends on how thick the head gaskets are you have now, but you might be able to get it up to like 9.5:1, and it'll have tighter quench, so you'll get more compression AND more detonation resistance, the best of both worlds. Just get GOOD head gaskets, that aren't stupid thick and don't worry too much about compression, it's doubtful a gasket thickness change is gonna make more than a few tenths difference

cmanf

Having the stock heads checked for true deck is a good idea.
Even factory ones can warp over the years.
A lil off the head then have the block decked is a great seal and does bump up your compression.
I think on my 289 I built 10 years ago gt40 heads were dead flat no cutting and the block I had decked .10
.30 over forged pistons
It gave it a 10-1 if I remember correctly.

my77stang

if your going to pull heads dont put those back on. i understand most people dont have boatloads of cash, but GT40 / early 351w heads can be got for cheap and will add a respectable amount of horsepower.

otherwise, leave the heads on there - its not worth pulling out to install a thinner gasket.

SalikDDD

well i was considering the 351 heads as i can get rebuilt E5/E7's for like 150.00 but then i cannot use my Tri Y headers with them, correct? and i also heard the compression drops which will lower the power and make the 351's not even worth it to put on? i apologize for being a moron but i don't wanna go driving around with 2 boat anchors on my engine if that's the case :/

or are they the d00e heads that i need to find? from the 69-71s ?

SalikDDD

we have a yard here with tons of older fords with 351's , 302's and such - what are some casting #'s or vehicles i should look for that have a better head on them that will let me use the hydraulic cam and are better then the 289 stock. ? thanks guys

JMD

With iron heads and your cam selection IMO 9.3 is pretty close to right, the cam might let you get away with closer to10 to 1, but IMO 9.3 should be ok. Just FYI the same setup with aluminum heads would get you about another numeric point....

I am baseing this on what we did with the 408, we are running atouch more than 11 to 1, with quite a bit more cam and aluminum heads with no detonation issues on 92 gas. (at 4,000 ft elevation)

Colorado_Mustang

If you're replacing the heads, you need to keep track of the combustion chamber size. Since you said 289, I'm guessing you have a 53 or 56 cc head, which is hard to find in the aftermarket. Many newer heads are above 60cc, which will make a large difference on the compression ratio.


FYI, the octane ratings for gasoline are adjusted at the pump. 91 octane fuel at stations residing at 5280 is not the same fuel that is 91 octane at sea level...and is likely less than 87 octane. This is why your car manual says to use a certain octane fuel no matter what elevation you're at...at least the newer owner's manuals will say that.