306 to 347?

[badandy73]

My 306 is going back to the builder under warranty due to an oil consumption issue. They're going to tear it down to the block to investigate what's going on; put new bearings in it, rings, go through the heads, etc. Had the discussion with them about squeezing some more power out of it and for around $1500- 2k they said they could put a stroker kit in it. Originally came dyno'd at 367hp/ 374 ft-lbs... has plenty of pep to it, but wanting more without running into reliability issues.

Running it in a 'driver' with 33's, C4 and 4.11's. Mostly street driven, hwy, etc. Have thought about going to a 4R70W at some point down the road; running the explorer front dress, so would have to get the damper rebalanced to 28oz, get a new flexplate, etc. Want it to still be reliable, run cool on hot summer days and be able to take it on longer trips for bronco events around the state.

Don't want to go the 351 route, as I'm already tied to the 302/ 5.0 block and would like to keep my hydroboost setup intact without having to go to an angled bracket, etc. Would it be worth the extra $$ to make the jump to 415 hp/ 415 ft-lbs.?

 

[MonsterBIlly]

I totally recommend it. Upu will not regret it. Ypu need to make sure ypu have enough head on it. Usually a 302/306 willnhave a 165 or 175 cc head. They will work fine for a 331 or 347 as well. Your total HP depending on cam will vary a lot. To maximize your Hp 185cc head in general is better. However with a smaller flowing head like a 165 you wont quite hit as high HP but your torque will benefit, which is what you want with a Bronco. I say got for it.
I currently have a 347 in my 66 mustang. It dynoed at 410 hp and 455ftlbs. It destroys tires with no effert. It would rip in a Bronco as well. CI =s torque a d thats what heavier rigs with bigger tires like.
You may want to post up a little more info as to what heads you have and what cam.
But I say go for it. Otherwise you may regret it.

 

[Broncobowsher]

347s tend to be short lived engines that tend to turn into oil burners. I've never liked the ring package they have to use. Not a fan of the steep rod angles either. I know there are lots of fans of them. I often wonder how many don't know the biggest power gains were in the good heads, some compression and not the bottom end?

I like the 331 (3.25" stroke) better. There is a little more room for a better ring package. The rods are not trying to go through the cylinder walls as much since the rod angles are a bit less. Avoids having to notch the cylinder walls for the rods which is nice as the pistons are not falling out the bottom of the bores as much either. Piston skirts don't do much support if they are not touching anything below the bore in the crankcase.

But it is your money, spend it as you like.

 

[badandy73]

Thanks for the input fellas.

Heads on the 306 are 60cc and specs for the 347 show a different part number but same chamber size. 2.02" (190cc) intake/1.60" (60cc) exhaust on the 306 heads vs. 2.02" (190cc) intake/ 1.60" (65cc) exhaust for the 347.

They don't list an option for a 331, so it'd be either leave it as a 306, or make the jump to 347. Reliability and longevity are definitely top of the list and don't want to spend the extra dough if it's not going to last. Just considering my options since I'm starting from scratch.

 

[Tiko433]

Can’t speak for longevity… but can say I love the torque and power.