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Which Heads
I have a 347 stoker and 48 idf's both on order.
The cam i plan on using: http://www.compperformancegroupstore...WeberCamshafts This car want see much track use, 99% street driving. I orginaly was thinking AFR 185 but someone told me this. "48 IDF's have a barrel diamter of 48mm. Which equals 1.89". If you put 2.02 valves under them, your performance will stink. Stick with the smaller ports and valves, and you'll do a lot better. The key here is that you don't have a common plenum, and that makes all the differance." So he was recommending the smaller 165's I wanted to get some other people's thoughts. |
Suggest you don't get just "other " people's opinions but get the opinion of the guy that wrote the book on Webers for Cobras as he did all of the work on setting up his Cobra - not other types of cars. You should talk to Jim Inglese - only!!!!
He can be found at his website and contact info. http://www.jiminglese.com/index.html I guarantee you will not be sorry that you followed his advice. |
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The ideal induction tract has one throat per cylinder with the throttle valve equal to the inlet valve diameter. The choke (venturi) should equal the smallest diameter just under the valve seat. 85% is considered the correct choke to valve diameter relationship. |
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If the intake valves are larger than your carb barrell or ports, you'll lose intake velocity just above the valve. The air will slow down, the chamber will not fill properly, and the fuel will come out of suspension and puddle. You'll have no low end power. Been there, done that. |
I think I'd go with the 165's as well, unless your looking for max flow at max rpm. But if that was the case, max flow, then you could consider Twisted Wedge or Blue Thunder or a number of other heads for ultimate all out performance. But you can't beat AFR for the best flow at low to mid range rpm and there close to max flow of the competitors at the high rpm end. 165's should be perfect for this application for the best throttle response on the street.
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I am running a 331 Ford small block with a Comp cams 282S cam, AFR 185 heads, and 48 IDA's with 40mm chokes. Runs like a scalded cat.
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What's your torque curve look like?
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I am running a 351W with 48 IDAs, custom ground Comp cam (fairly mild) and AFR 185 heads. TQ at 3000rpm is 468 and peaks at 496 at 4000. At 5200 I am still pulling right at 468 and 390 at 6000. That was before I re-jetted the carbs. I haven’t had it back on the dyno since, but it “feels like” it pulls even harder now.
I do know this: It will produce more power than I can get to the pavement without boiling the 315x35x17 Goodyear F1’s attached to the rear axles! Gun Doc |
Running 48 IDF's, 40,5mm chokes and 2.02 valves on Vic Jr heads. No issues whatsoever.
Yes, size on valves and aperture diameter is of concern regarding crab/ choke size. But, would you see a difference in Hp @8000 rpm on these heads VS a set of AFR185's or 165's? In case so- which direction would the change go? Another matter is low and middle RPM torque/ Hp differences. I would predict that the drop in performence because too large valve appertures would be seen here because of less speed and hence less mixing and droplets forming. |
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Sounds like the difference between a single plane and a dual plane intake. The single will "run like a scalded cat" and make more high rpm horses. But the dual plane will have better throttle response, better low rpm power and feel better on the street.
Depending on the intakes (or heads in this case) perhaps the difference will be very marginal on the street and difficult to tell the difference between the two. Plenty of guys say their single plane intake works just fine on the street, others swear the dual plane is the ticket... |
It kinda depends on the size of the engine too. For an example, a Super Victor intake would make a 289 behave a lot differently than a 363ci Dart based stroker. In the same token, 185cc heads on a 302 would be a different story than 185cc heads on a 347.
When selecting a head, it's best to aim for the highest flow with the smallest port volume. This helps keep the velocity up. Due to the light weight, a Cobra can get away with a little more radical-ness than the normal street rod. Cams can be a little bigger, heads can be a little bigger, etc. AFR 185's run absolutely great on a 331/347 though. The AFR heads have great low/mid lift flow as well as the peak lift flow. They really make a good product and I use them every chance I get. |
Velocity is the key word here.
Should not the first question be: "At what RPM will this engine normally play....most of the time? Then design/build around that. Happy Motoring! |
Not running webers - maybe further down the road!! But my 331 KC stroker was built with AFR 165's - and dynod on the stand at 446 hp at 6000 rpm. On the chassis dyno it put down 326 HP to the rear wheels. Smaller valves than the Twisted Wedge .. but greater overall flow due to higher velocity. I'm told velocity = improved fuel air mix and power.
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i would use the 185's and get a cam (made) specifically for the application, very important.
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