SB Ford - 331 vs 347?

Ford experts:

Was looking around on JEGS site at crate engines for the heck of it. What exactly is a 347 and a 331? I realize both of these probably started out as 302s, but what has been done to increase the capacity?

Also the 331 has a claimed 500 hp and the 347 around 360. 331 has a 7,000+ redline...and of course alot more expensive.


*Edit*
Oops sorry, wrong category...but its made of metal so close enough

a 331 is a 4 +.030 bore with a 1/4 '' stroke, same as a 327 chevy bored .030 over. the 347 will be a bored and stoked 302.It uses a cleveland crank cut down to 3.4 and special rods. Makes for a more specialized eng. a 351 w is 4'' bore x a 3.5 stroke. I would prefer a 331, unless you just want more.

When I built the engine for my 27 I debated 331 vs 347, and everything I read said the 331 was the way to go. The extra stroke of the 347 puts the pistons on an odd angle at the bottom of such a long stroke and can cause premature wear and blowby. So, I went with a SCAT 331 setup. Scat said you might also have to grind some metal off of the lower cylinders to clear the crank with the 347.

I would like to say it is as dependable and smooth as the 306 I ran in my 27 for years, but I can't. I have some "stroker noise" from the pistons being moved around.........they are extremely short and rock in the bores. I have also been having a small drip out of the rear seal. I have replaced it twice and have a different one being delivered tomorrow.

That is the down side. The upside is that this thing just makes some serious HP, probably the fastest street car I have owned, 2nd gear is just brutal.
So, my advice is, build the 331. Believe me, it will make all the HP you need.

Don

donsrods said:

I have some "stroker noise" from the pistons being moved around.........they are extremely short and rock in the bores.

Click to expand...

Interesting - I've never heard that term before. Is that similar to piston slap? Does it sound like a knock? Does that create a problem with premature ring or bore wear?

One day I would love to build something like yours. I love a high-rpm smaller displacement screamer. I'm not even hugely concerned with high hp but I do want it to rev and sound evil.

Yeah, I had discussions with both Scat and Keith Black Pistons and they say some strokers are noisier than others, that is just the way it is. The pistons in these stroker kits are about half as long as a regular 302 piston, with one of the rings going through a machined area where the pin goes. SInce there is very little height and a long stroke, the piston gets pulled sideways a little as the rod pulls it to one side going down and pushes it to the other side going up. I think wear over time might be an issue as well. Just the price we pay for HP.

I am not totally sure if all the noise I am having is piston noise though, some of it may be coming from my roller rockers. I have adjusted them the way I always do, take the play out and turn one half more on the polylock. But Harland Sharp, who make the rockers, now tell me to go 3/4 turn because of the aggressive cam I am running. I am going to do that when I put the motor back together this time. As it is, with the headers capped it sounds like a sewing machine ticking away, sort of like an engine with some bad lifters.

But I can't tell you how hard this thing pulls through the gears. The 302 always moved the light T pretty well, but this thing feels so much different. A friend on another forum did a desktop dyno for me, and he came up with 424 HP at the flywheel. Now I understand why all those little Fox Mustangs are turning such good times at the strip.

Don

2 cents

First off the 500 horsepower they are claiming isn't the same 500 horsepower as of old.
many different ways to measure hp...
At the rear wheels, at the flywheel, net, gross, and the most liberal braggy way is to calculate hp from the btu of fuel burned.

What is accepted as a standard is net horsepower at the flywheel. this is the horsepower you can use minus the power that it takes to run the engine.
A chassis dyno is really only an accurate comparison if the engines being compared are run in the same vehicle or if your comparing the engine to itself in different states of tune.
Every drive train drags an engine down differently.
Now if everyone running on the chassis dyno has a mustang... then it's accurate. if one guy has a stang and the other guy has a 3//4 ton pickup it isn't going to figgure out right. at least I don't think so.
it might be possible to measure resistance as the drivetrain decelerates and make a correction in the numbers

They run the engine on a dyno and simply measure how much water it can pump. hp is a measure of work done in a given amount of time. torque is the mechanical force measured in foot/pounds of the power used to do the work.
the first way to measure horsepower was like a vertical tractor pull for horses. they just set up an elevator... a rope, a pulley and a weight and measured how fast the horse could pull the weight to the top.
the pull of gravity is an acceleration..the same physics as what an engine fights against to make the car speed up faster only applied in a different direction.

Gravitational acceleration, linear acceleration, centipedal acceleration...
Through acceleration, energy is converted into inertia. inertia is mass in motion, deceleration converts inertia back into energy.
it's a logical conversion. In reality matter IS energy E=MC^2 and mass and inertia are interchangeable. the only thing you are converting is your calculation of the energy as it exhibits different actions.
In rocket science just the act of spinning a rocket increases it's inertial mass without increasing it's weight and it will go farther and higher into orbit on a given amount of fuel than will a non-spinning rocket... proven fact...research Von Braun's orbital anomaly and the work of Dr Bruce DePalma. If you think I'm blowing your mind...Torsion field physics will really blow your mind.
back to the 331...

A low powered engine that has the capability to spin really fast naturally will do more work in a given time allotment (if it can pull the load and spin up)than a powerful engine that isn't fully loaded and can't get out of it's own way.

1-1.5 horsepower per cubic inch is not unreasonable to expect out of a well built street engine but I highly doubt those 800 horsepower small blocks with a mail order chrome kit and intake running small tube headers, 600 cfm carbs and flat tappet cams..."I spent $2,000 so I must have like...a gazillion horsepower lol"

My buddy had a clean 91ho mustang. He picked up a brand new 331 for it with a new tremec off a guy needed the cash for $2k. it had trick flow manifold and edelbrock (i think) mass air sensor big cam and oversized injectors.
it would pull the wheels off the ground both in first and grabbing second.

Then he was unemployed and he needed the money and best money he could get at the time was $4500 for the car

The man is right a 331 can make more than enough