Not worth it on a NA application, unless you're planning on turning 7,000+ RPM.
whats the combo?
you would definitly benifit from the boxed upper. Just because your not revving the motor past 7k dosent mean it wouldnt help, that GT40 is gonna be a bottleneck
My advice to you would be to sell that GT40 intake, you could get decent money for it and buy a better flowing intake, your motor sounds pretty stout, get an RPM II, Victor5.0, Systemax II, or a Trick flow R-series.
Also some box uppers require aftermarket fuel rail to work. Not sure about the downs, but the TFS one does.
I was always under the impression that a systemax would bolt right on to my 351. I hear GREAT things about that intake, but I have always ruled it out due to the motor being 351 based? I have heard great things about the Trick Flow R-series, but my car is never raced and I enjoy having as much streetable torque as possible. Would that intake take a little grunt out of my bottom end? A little is fine as guess, but a lot would not be in my best interest. Thanks for the advice thus far bud!
The R is by no means a race only intake, my car is snappy as shiiiiit with the R-intake, its all about the combo, the camshaft has more to do with losing the low end than the intake.
My tuner actually reccomended using the box upper because power was falling off at 5800, but the tq curve on my motor is pretty flat, there is a pic of my dyno sheet in my progress thread.
If you do go with the R intake do yourself a favor and get the 90mm opening in the upper. The 75mm uses a longer bolt through the center of the air path in the intake, with the 90mm uppers, it uses a stud and the opening in CNC milled, much better product, even if you use a 70mm TB, the design is just smarter with the larger opening.
That sounds like good advice, I would have probably picked the 75mm opening thinking the 90 was over kill, but that makes total sense. Another subject...my cam is an old b303, i know its old tech, but it works for me due to me not being a racer. My car is a street car and I love street torque with good response and snap. Could you advise me on a nice cam to go with a TFS R intake (in the near future) Your combo sounds great! NA, snappy, bustin out mid 11's ALL DAY!!! What cam would you recommend to bring this 357 into the 21st century? Thanks again for the info......Coupes Rock!
Save the box intake for an engine with pressurized induction or one that runs circle tracks above 5500 RPM all the time. In this case, it won't make any difference how many cubic inches you have, a good flowing long runner intake manifold will outperform a box intake on a street driven car.
What makes for good street response is long runners. The longer runners produce more torque at lower RPM which is right were a street driven car lives most of the time. Box intakes have very short runners, so they give away more low end torque than the pick up from better flow characteristics.
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