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Discussion Starter · #1 ·
I NEED HELP, this is my first attempt at fixing up an old car, it is 1970 mustang fastback, and I dropped of the 302 to get completely rebuilt! The engine has not been touched in 20 years so nothing will be saved but the block... My question, what is the better stroker kit for my needs 331 or 347? I would like to drive the car 4-5 days a week during the summer with enough HP to dust any blue haired kid in rice burner. There does not appear to be a consistent answer out there, I have tried to read as many articles and forums I can find to no avail. Any advice on a good set of heads and intake would also be very much appreciated! Thank you!!!
 

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what are youre goals as far as quarter mile times cuz usually a mid 14 second/95MPH car would get the job done as far as just smoking ricers and such. What do you wanna run? INCLUDING TRAP SPEEDS. also i think a 351 would be a cheaper way to go,it weighs just a bit more but allows you to go 400+ cubic inches when fast starts feeling slow.LOL
 

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The general though is that the 347 will make more power but the 331 will last longer.The 302 can easily be made to smoke ricer's if that's your only goal.
 

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347, AFR 185, and a Performer RPM. Get all the cubes you can. They cost the same.

There are plenty of production engines out that have a worse rod stroke ratio than the 347. Those engines last well over 100,000 miles.
 

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I agree that it is hard to get a straight answer regarding the 331/347 question. My research would agree with the other reply that a 331=more reliable and a 347=more power. This doesn't mean that a 331 won't make good power or that a 347 couldn't be a reliable engine.

I also am fixing up a '70 fastback as my first restoration and it has a tired stock 302 2V in it. I have considered just about everything from a stock cheapy rebuild to a 408 stroker monster. After consideration I plan to build a either a 302 or 331. I ruled out the 347 because the added power isn't worth any reliability issues since the '70 is for street use only. I also ruled out the 351/393/408 idea because of expense and excess. It would require many new parts and ultimately I think it could be too much engine for my car and goals.

Ultimately, your choice will depend on your goals and your wallet.
 

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Discussion Starter · #6 ·
I have no goals for the quarter; my main purpose is for street use and would only take it to the track for the heck of it. I do have a 351 but decided to use the 302 to keep the car as close to original as possible. Money will not be an issue as I want to do it right this time and not regret anything by cutting a corner and saving a couple hundred bucks. I am now thinking about going fuel injection, I have heard that is a great way to increase HP. M22ss I have some extra parts if your looking for anything let me know I may be able to help you out.
 

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fuel injection does not add horsepower, but it does add unecessary complexity and expense, if thats what you're after. Fuel injection has become so trendy that it has lost all appeal to me. If going with forced induction, then yeah, fuel injection serves a purpose. And no offense, but a 70 sportsroof, orginally with 302, doesn't have much value to lose by switching engines. I think a mild 351 will suit all your needs and can be done properly without spending a fortune., while probably adding value to your car. Heck, you could stroke it to 400+ cubic inches, slap a 302 2V decal on the orginal air cleaner, and 98% of people would belive it was a stock 302.
 

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Some very good points here by indigo 66.If you don't already have a bunch of parts for the 289/302 block the 351 is a very easy swap using the same mounts and transmission.Even a lot of ford guys have trouble telling a 351W from a 302 when its in the car with all the accesories on it.
 

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You want to keep the car as original as possible? Is there something rare about a '70 fastback with a 302? It is a great looking body style! Sleeper?

I don't see why you wouldn't build a mild 408 stroker since you have the 351 block. Is fuel economy a concern? Won't cost much more to build at all if you go 351 based stroker.

Never heard of anyone with a 351 stroker that wished they had stayed with the 331-347. Have heard many wish they would have just gone with a 408 when they have a 331-347.
 

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If it were me,...I would go with the 331 over the 347. Why? Because the 347 will have a little more power at low RPM, BUT... as the revs get higher the 331 will actually make more power than the 347. And more reliable power. As RPM increases the frictional loses increase dramatically on the 347. Just better rod ratio with the 331. That's just my take on it. I am building a 331 as we speak.
 

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Discussion Starter · #11 ·
Indigo No offence taken as I stated this is a new hobby for me so I truly appreciate your honesty. I have not purchased any “engine” parts for the 302 yet! The transmission and rear-end need to be upgraded or replaced regardless of the engine I use. What are the stroker kit options for a 351?
 

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393 and 408 are the most common, but there are other options. A 393 is the cheapest to build. You'll need a stroker crank, but you can re-use the stock rods, and just use 302 pistons. The 408, 418, 427, etc would require aftermarket crank, rods, and pistons, which all add to the cost. I'm no expert on strokers so I'll put an end to my input on the matter, lol. Remember that the bigger cubes will require a good flowing set of heads, so add in ~$1200 for the usuals, TFS, AFR, Edelbrock. The more you spend on the engine, the more you'll have to spend on the rest of the drivetrain, like a beefed up transmission, stronger torque converter or clutch, possibly swap to a 9" rear, 31 spline axles, locker, good tires, big fuel system, big radiator, big headers/exhaust. It all compounds on itself and the dollars add up real quick. Watch what you're getting into. A mild 351 can make some real good power, but don't build it to be so powerful that you can't afford all the supporting parts.
 

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you dont need better flowing heads on a bigger engine. Itll still make more power,might bring down the rpms a tad but it would still make more HP AND have a broader power band
 

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On 2006-03-28 11:23, coolreed wrote:
If it were me,...I would go with the 331 over the 347. Why? Because the 347 will have a little more power at low RPM, BUT... as the revs get higher the 331 will actually make more power than the 347. And more reliable power. As RPM increases the frictional loses increase dramatically on the 347. Just better rod ratio with the 331. That's just my take on it. I am building a 331 as we speak.
This is not true to the extent that you state. Is the rod ratio worse in a 347? Yes. Is it bad to the point of making the engine have a short life and loose power due to excess side wall loading. No. A 347 will have the potential to make more power at ALL rpms due to the fact that it can move more air.

Look at all the "terrible" rod ratios in production cars past and present. They still go well over 100,000 miles with ease.

<font size=-1>[ This Message was edited by: 289nate on 3/29/06 3:36am ]</font>
 

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It's not just the rod ratio. Alot of the 347 pistons have the rings over the edge of the wrist pin due to the very short piston height to squeeze in the extra stroke.
 

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On 2006-03-28 12:31, bluelightning302 wrote:
you dont need better flowing heads on a bigger engine. Itll still make more power,might bring down the rpms a tad but it would still make more HP AND have a broader power band
you're kidding right? The factory heads aren't even adequate on a stock 302. Who builds a 393/408 with stock heads, so it runs out of breath at 3500 rpm? Its a Mustang, not a F350.


<font size=-1>[ This Message was edited by: indigo66 on 3/29/06 4:01am ]</font>
 

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One of the magazines did a test a few years back and put many different heads on a FPP 392W stroker. They tested it with stock 302 heads for a baseline. I think it was just more for kicks. The motor made great power for those heads. I think that was the point Bluelightning was trying to make. If you have crappy heads you can still put a big motor under them and make good power (for the heads). Put the right heads on when you have the money.

You are very right on the fact that whatever motor you build you will need a car that can handle it.

Some 347's have the ring intersecting the pin. On those about 85% of people who've I've heard from say they see no extra oil consumption at all. The other 14% seem to think it is barely noticeable. Then there is that one percent that feel it's excessive. Think the 14 and especially 1% may have problems not related as much to the intersecting ring but more so due to improper break in and/or assembly. Just what I've read and heard from people I trust.
 

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yes thats all i was trying to say. i wasnt saying "you dont need better heads just build a bigger displacement engine with stock heads" i just said,just because its a bigger displacement engine,it doesnt make it a MUST to have a better heads, youll still make more horsepower
 

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nhekkers,
There's a lot of information posted on this one. The real question is: what do you want? A 347 has more power potential for torque, by virtue of the additional cubic inches. A 331 runs slightly less torque, but can easily match the HP output of a 347 with an adjustment to the combination. The overlooked point is, a 306 (302 bored .030) can produce an equal amount of horsepower, although it runs short on torque on the low-end torque (about 65’ lbs at 2K RPM). My advise, be ware of random advise that comes from “I’ve heard or I read an article about…” Go see someone that builds performance engines professionally (not a buy the simply bolts on parts) and you’ll discover that combination is the most important factor (for both longevity and total performance); you’ll end up with more Energy Per Cubic Inch in the RPM range that suits your diving needs. Engine combination simply means, matching the cylinder head flow (all data points from .100” lift through maximum lift of your camshaft and area under the flow curve), camshaft specifications (lift, duration, lobe separation, degree, etc), intake design, complete exhaust system design, compression ration, etc… The goal is to produce 100% volumetric efficiency from your air-pump that we affectionately call a Ford V8.

I have a 306 that I toiled over for several months (and mass amounts of data) to dial in the correct combination for my 1965 street car. The combination achieves 100% VM efficiency at 6K RPM. At the flywheel, the engine produces 451HP at 6500rpm and 397’ lbs of torque at 5000rpm (294’lbs at 2K RPM). Here’s the kicker… with less than 10.1 to1 compression ratio! …but I had to design the camshaft.

Good luck, DP
 
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