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Discussion Starter · #1 ·
I will be starting my rebuild on the '70 this week and wonder what kind of difference in horepower/torque there would be between an identically prepared 306 and 331. I will be using Windsor Jr heads, an Edelbrock F4B intake and headers/X-pipe exhaust either way. Carb and cam will depend on the stroker option but nothing to wild. I am not looking for any exact numbers just some rough estimates. Believe it or not my engine builder thinks that I might be happy enough with just a nice 306! He said it would be plenty of engine to spin the tires and have fun. I'm sure it would be better than the seven cylinders I have now!
 

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Horsepower not much difference at all. On my combo I lost 6hp going to 331 but the cam is the key thats where you can gain it back. The real difference is in torque it is the whole reason to stroke a small block. Your engine builder may very well be right. We would need more info like expected HP and TQ on what drivetrain and its intended use.
 

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He's right, you would likely be happy with just a 306. However, you'd be much happier with a 331 lol. It's like 'Hmm...should I just make power? Or...should I make MORE power?' For me too much is just a little less than enough!

On to the specific question, with your mild mods, you can look forward to roughly 15% increase in power with the 331, if you cam it correctly. You wouldn't have to go overboard on the cam, just make sure you give it as much room to breathe as you would the 306. A correctly jetted 750cfm carb would work well on either motor.

Hope that helps!

Cris

(edit) This also assumes the same compression. You can safely add a bit of compression, not too much, but some. More cubic inches are a bit more tolerant as far as octane goes. And yes, as said above, you'll gain torque either way, but the cam's what wll be required to let you increase your horsepower.

C

<font size=-1>[ This Message was edited by: Is1BadFord on 3/26/06 12:56am ]</font>
 

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Figure your going to make about 1.2 HP per cubic inch and roughly the same for torque. This is a rough estimate, but a reasonable one. I'll give you an example. I have a friend with a 289 with a 294S cam and ported Ford heads. I have a 331 with 282S cam and ported ford heads. Compression is just about the same for both...10:1 for the 289 and 9.8:1 for the 331. We both put down 335 RWHP, but his torque is 292 and mine was 337. The extra stroke probably has a lot to do with the higher torque. My peak HP was at 6400 while his is around 6000...interesting since he has a bigger cam, but his intake is a dual quad while mine is a weiand stealth dual plane which will make a difference in power curves. He got really good peak HP out of that 289.

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Tracy Blackford: Corona, Ca
'65 FB Mustang 331 with 282S cam, fully preped 351W heads. T5z and 3.50 9" posi. 335 [email protected] RPM


<font size=-1>[ This Message was edited by: blkfrd on 3/26/06 1:54am ]</font>
 

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Discussion Starter · #6 ·
My car is intended for street use only. As far as expected HP/TQ I don't know. My drivetrain consists of a toploader 4-speed and 8 inch rear with 3.00 gears. I am thinking to change the gears to 3.25 or 3.50 for a little added pep.
 

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On 2006-03-25 10:53, blkfrd wrote:
I'll give you an example. I have a friend with a 289 with a 294S cam and ported Ford heads. I have a 331 with 282S cam and ported ford heads. Compression is just about the same for both...10:1 for the 289 and 9.8:1 for the 331. We both put down 335 RWHP, but his torque is 292 and mine was 337. The extra stroke probably has a lot to do with the higher torque. My peak HP was at 6400 while his is around 6000...interesting since he has a bigger cam, but his intake is a dual quad while mine is a weiand stealth dual plane which will make a difference in power curves. He got really good peak HP out of that 289.
There are other factors at work here. With 42 more ci and a smaller duration cam your peaks should be 500-700 rpm lower than his, not higher. Your engine should've made more power and torque everywhere in the rpm range until you reached the heads flow limit.
 

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We did up the compression from 10.7 to 12.2 but with the same heads cam etc we went from 471 hp and 385 tq with the 306 to 535 hp and 429 tq with the 331 peak hp/tq rpms stayed the same on both engines... cant wait to try it out!
 

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62 falcon is that rwhp or fwhp? By the way that falcon is "AWSOME"

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<font size=-1>[ This Message was edited by: 347LX on 3/26/06 8:18pm ]</font>
 

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All else being equal, the 331 will not produce much more power than a 306... unless the original 306 combo was to big for 306ci to start with. However, it will be at a lower rpm with increased torque.

I'd say the falcon above didn't have enough cylinder pressure for its big camshaft. Much of that increase probably came from an increase in compression ratio.

If the airflow path can handle the extra flow, increasing the cam duration around 5 degrees will spin the 331 up to the same rpm range as the 306, and provide significantly more power.

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302 4-speed 289 heads, 10.63 @ 129.3
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220


<font size=-1>[ This Message was edited by: n2omike on 3/26/06 10:26pm ]</font>
 

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On 2006-03-25 20:01, 62Falcon wrote:
We did up the compression from 10.7 to 12.2 but with the same heads cam etc we went from 471 hp and 385 tq with the 306 to 535 hp and 429 tq with the 331 peak hp/tq rpms stayed the same on both engines... cant wait to try it out!
Holy s**t
 

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On 2006-03-25 19:19, 1 Bad 88 GT wrote:
On 2006-03-25 10:53, blkfrd wrote:
I'll give you an example. I have a friend with a 289 with a 294S cam and ported Ford heads. I have a 331 with 282S cam and ported ford heads. Compression is just about the same for both...10:1 for the 289 and 9.8:1 for the 331. We both put down 335 RWHP, but his torque is 292 and mine was 337. The extra stroke probably has a lot to do with the higher torque. My peak HP was at 6400 while his is around 6000...interesting since he has a bigger cam, but his intake is a dual quad while mine is a weiand stealth dual plane which will make a difference in power curves. He got really good peak HP out of that 289.
There are other factors at work here. With 42 more ci and a smaller duration cam your peaks should be 500-700 rpm lower than his, not higher. Your engine should've made more power and torque everywhere in the rpm range until you reached the heads flow limit.
That's basically a re-statement of what I tried to say in my post. There are other factors...he has a bigger cam and he has very different carburation and manifold than mine. If I dwell further, he has an 8" rear and I have a 9" rear which tends to use up more HP. I'm just trying to provide an example, but I also provided a few caveats with it since our engines are not set up exactly the same.

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Tracy Blackford: Corona, Ca
'65 FB Mustang 331 with 282S cam, fully preped 351W heads. T5z and 3.50 9" posi. 335 [email protected] RPM




<font size=-1>[ This Message was edited by: blkfrd on 3/27/06 12:23am ]</font>
 

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You can make good power with a 302. But a bigger engine will make more power. The combo must be optimized for the bore and stroke,

<font size=-1>[ This Message was edited by: fastback.brian on 3/27/06 4:38am ]</font>
 

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First off...I love big motors. However, I firmly believe that smaller motors will make more horsepower, per cubic inch, than large motors. But, if unhindered by artifical restrictions, which could include rpm limits (due to component weight, matereial stress, costs), mileage or any number of other variables, the larger motor will produce higher overall power and, usually, longivity.

Torque has a very close relationship, based on rpm, to engine size. If you look back a few years, this was the basic difference in thinking that seperated European engine design vs. American engine design. Ameican engineers or manufacturing executives (who know which made the decision?)...shose to use lightly stress large motors, European builders went with smaller, highly stressed motors.

this was, my opinion, the foundation for Hot Rodding. Think about it, a 2 liter motor making 200 horsepower is pretty much at its limit. While an Ameican V-8, at 300, 350 or 400 cubic inches at 200 horsepower is loafing. Add in the fact that most of our blocks were way over-built, early small block weigh as much, sometimes more than modern "thin-wall" cast big blocks.

All that to say, the same thing...given free choice, a bigger engine can produce more overall horsepower, when outfitted with similar equipment as a smaller motor. The trade off, there is always a trade off, is the smaller motor will need to either rev higher and/or trade off driviablity. Again, looking at history; a 400 cu engine didn't need to worry about being in its optimum power band, having a boat load of torque from 2-3000 rpm on up, most american engines were more than capable of useing a 2-speed automatic or 3-speed manual to move huge cars. European, smaller engines needed 4-speed or better transmission to keep their engines in the sweet spot.

This is a good debate but there is still an obvious answer, bigger is better, until you run into build, racing class, weight or material restictions.

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<font size=-1>[ This Message was edited by: Beoweolf on 3/27/06 9:14am ]</font>
 
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