Join Date: Mar 2007
Location: Fort Worth, Texas
Re: 390 2v to 4v Conversion
390 2bbl and 4bbl heads are the same. In fact, non-Hiperf 352, 390, 410, and non CJ 428 heads are all the same. For example: C6AE-R heads can be found stock on any of those engines from a 1966 or 1967 (no 352 in 67) model year vehicle regardless of 2bbl or 4bbl. Most FE heads run in the low-mid 70's cc range. The big difference in most Hiperf heads was port and valve sizes.
The difference in compression between stock 2bbl and 4bbl 390's is the pistons. Stock 2bbl pistons have a large circular dish to reduce compression. So to properly convert an H code to a Z code, new pistons would be in order in addition to intake swaps.
But as stated above, when you get into 10:1 compression and up, you're more likely to run into detonation issues. A better plan of attack to get more power from your stock 2v is to leave compression where it is (9.5:1 ain't bad) and concentrate on breathing. A 4bbl carb and modern aluminum intake (not the 60's stock iron piece) will get more air in. A set of headers to replace the abysmal stock log manifold will do you more good than anything by letting much more air out. And cleaning up the head ports from casting flash along with a good port match will let your stock heads breathe better. Or if you can afford it, get the Edelbrock aluminum heads. To capitalize on your improved breathing, get a new cam with a bit more lift and duration. Stock FE cams are pretty small, and a new cam in the .500" / 274* range will really wake up your engine and be very streetable.
With the mods above, your former 2bbl engine will make more power than the stock 10:1 Z code 4bbl did from the factory and still run happily on pump gas.
1964 Galaxie 500 4dr 289, 1967 Galaxie 500 fastback 460, 1968 Fairlane 500 302
1969 Montego MX 410, 1971 F100 400, 1979 F250 400
Last edited by Tex; 06-28-2011 at 11:27 AM.