220BR

It was easy on my boat. A removable engine cover (ie no front bulkhead) makes it easy. You don't have to remove the oil pan, only drop the front lip enough to get the timing cover back in. I jsut removed the first 5-8 screws on each side (and front) and loosened the rest

rchevelle71

That is what I thought, I have done this several times with success on cars, but didnt want to sound like a hack on OSO, figured I would let someone else post it first, Just kiddin, good to hear, I think this is the route I will go since it is halfway apart anyway, and Florida seems to be a "little" too cold for boatin' lately anyway. Thanks for the info.

BAD-HABIT

The Swap is a simple 40hp increase. With no other changes. You will need to change the intake. Carb and disrtibutor can stay.... I did the swap. If you are going to change the cam just make sure you keep the lift to under .490 otherwise you will need to change the springs....You can get the heads new and complete from Salee performance pretty cheap. As far as compression ratio with the heads you can run up to 9.5-1 pretty safely with the vortec heads. Keep the quench around .25 and you will be fine. The stock Mercruiser motors that use the Vortecs heads run 9-1. You will want to keep the Timing under 32degrees...
Also if you are dressing up the motor valve covers are hard to find..... Here's my 355 vortec. Im pushing about 375hp at 5200......

BH

220BR

Huh?

traviss

just helping...only flat top pistons can be run with vortecs, cause if you used a dome piston, the dome hits the heart shaped point in the Combustion chamber.

Correct me If i am wrong, but "quench" head to piston clearance should .035" minimum! I used these heads on a stock block with a shim .015" gasket. had .040" quench.

my .02

rchevelle71

UMMMMMM,

I kinda know what your sayin, BUT I have no clue what pistons are inside the stock 1992 5.7 non mag??? I am assuming Flat top, as far as Valve covers, I will just paint the stock ones, and put em back on, I am not into the flash, as much as a few extra MPH. Long story , but lets just say one side of my motor got a little HOT, (somehow water flow got restricted to one manifold, after disassebly, water was gettin to the manifold, but not out the other side?????) I know the manifold is bad, but I am afraid I may have caused a little damage to the head also, so if I am gonna replace, why not VORTEC, and if I got the intake, and heads off, I might as well throw a stick in it!!!!!

220BR

If its a 1992 Merc 5.7L (350) its like mine ('92 5.7L lo rise intake with Q-jet), and has flat top pistons with 4 valve reliefs cut into them (about -3cc, maybe -7, can't remember). The only other piston Merc used on pre-vortec SBC was a dished piston, but I'll bet you don't have them.

What travis said. Deck should be +0.025 so add a .018" shim gasket for a quench of .043 and you're set. Just make sure your static compression is ok. I seem to recall my calculation showed 64cc vortecs with .043 quench put me above 10:1 static compression.

rchevelle71

Thanks,

sounds good, I am gonna look further into it after the Holidays.

jaroot

when i replaced cylinder heads i quickly blueprinted a couple of my bores for static compression calculations... 1997 250hp 5.7 2V. my motor has the dished pistons which measured 13 cc. the highest point on the piston at TDC (indicated) was 0.024 inches down from the deck (depth mic).

utilizing a 0.015 shim head gasket i end up with a quench distance of .039 inches... distance is good but piston style is bad... if you are gonna use high turbulance heart shaped chambers the flat tops or (better yet) a D-dish quench style piston are the best. the dished piston accomplishes very little in the quench scenario.

these measurements with a 64 cc combustion chamber yield 9.39:1 static compression ratio on a 4 inch bore 3.48 inch stroke motor (350 chevy).

on the camshaft front, GM has been doing factory roller cams since about 1987... if the motor uses a flat tappet be aware that the block MAY already be machined to accept a roller camshaft thrust plate, spider and lifter tiebars so that you CAN run a roller... these parts are pretty easy to come by.

rchevelle71

Again, good advice, anyone got a set of heads collecting dust???? Intake also?????? Holley 650???????