Trollin

The 331 will fit alot better in the 302 block. The 347 will have to be clearanced. Thankfully we drive fords and not chevys. If we drove chevys we would have issues with clearing the cam. (High deck height for the win!) The bottom of each cylinder will have to be ground to clear the connecting rod bolts. I have clearanced a few blocks myself prior to getting the block bored and honed. So you figure out where it will hit, mark it, grind it then send it to get bored and honed. Or for a couple hundred bucks they will do it for you for your own insurance.

Basically the 331 will be easier. The 331 will have less problems dealing with heat. The 331 has better rod angles and compression height (I think probe makes a kit for a 347 with a better compression height dont quote me on it tho). Less grinding.

The 347 will be alot more work and money. The 347's have been known to have problems with heat (I have had first hand experiance). You may be looking into cooling system upgrades to help. I would be waiting at a red light for 2-3 mins, and I would watch my mechanical coolant temp gauge slowly climb with the stock w/pump, rad, the whole bit. BUT the 347 will offer you higher performance gains..

There is always a compromise.

AdderMk2

interesting opinions. Luckily, they are all completely wrong. I have a stock pump, rad and fan. My car can sit all day long and never overheat. Maybe the person who built and tuned your car did something wrong. Saying that a 347 will have heat problems is like saying that a 306 will do it as well.

Jeez! we all better stick to stock bore!

Thanks for coming over here and talking out of you ***.

Venomantidote95

Well the main thing pending rod design you will have to clearance the skirts also. As for the heat issue lol I have stock cooling system and never once overheated and I drive my 347 daily! Next???? Everything depends on the person doing the hard parts right and they really arent that hard.

tinman

Grinding the relief in the bottoms of the cylinders is no big deal.
Mustang ranch, Riverside, Calif. sells a template like tool for doing this for about $40.
Takes about 10m minutes to mark and another 10 minutes to do the grinding.
What over heating problems?
I've run 302's out to +060 with stroker kits and have never had a problem.
I live/race in Arizona whre if you are going to have a heating problem you'll notice it right away. I run the old time Moroso cog belt electric drive to the water pump and still don't have any problems.

Venomantidote95

You can use either a 5.4 or 5.315 rods either is fine you just have a oil ring spacer with the 1.09 piston for the 5.4 rod. Its no big deal either way! If your just mainly going n/a max you cubes!

Trollin

I had roughly 11.5:1 compression ratio. Keep in mind. I didnt do the flat-top two valvereliefs like most do I had big domes.

Venomantidote95

When did CR become a matter of this thread? Mines 10.3 not that it matters.

tinman

Even with 11.5 compression you shouldn't be seeing an overheating problem.
Is the cooling system working ok, I think not.
Are you running the engine super lean? That can cause overheating........

89stang1

Comp Cam NX274HR custom grind cam .550/.570 im very happy with it great power and sound is sick!!!!!

Five-0stangs1987

I'm looking for help with my 347 I'm new to the site and don't know where to go to get help on here anybody help me with my problem or show me where to go to get help