What to do with modified intake?

[TJinSA]

I ask this in the lounge, because there's been two heavy handed modifications on this intake.  One is more cosmetic, but the other could affect how the intake performs.  I hope to better canvas the group's expertise / opinion across spectrums.

BACKGROUND:  Found S2MS SBF COBRA intake on eBay advertised as reproduction.  Looking at photos, I'm convinced it's a modified original, but hard to see if it's what I'm looking for to restore 6S296 to semi-concours.  Intake arrives, and it is indeed an original, has all the other correct hallmarks, but with two issues.

COBRA NAMEPLATE:  I was looking for a rectangular nameplate, but this one has been ground on for distributor clearance.


     QUESTION 1: Do you:
          1)  weld it back up and whittle it down to shape, OR
          2)  Just go with it, if the car's not in judged concours, no one will notice it anyway.

CARB TO MANIFOLD PORTS:  Someone followed up act 1 with milling out the individual barb bore holes to one open, gaping hole.  i intend to put a Paxton on the car, but the question is effect on either carburator or Paxton ...


          QUESTIONS 2+:  Do you:
          1) Go with it, but ease over the sharp edges inside the plenum. OR
          2)  HOLY CRAP COWBOY, that needs to at least have a divider plate between the two planes, that just kills performance.

Or I guess one last question is it just wall art, and expensive lesson?

[Greg]

Tom,

The cosmetic cutting of the Cobra is minor and as you said, could be welded and shaped to make look right.  The more concerning factor is the milled intake ports to a single plane.  The issue is the "scavaging effect" of the now heavily modified intake.  IMO, I would continue the search for a non-modified intake (at least regarding the intake plane) as I have a concern that you will never get the engine to a happy AFR for all cylinders and it will stumble (causing for an unhappy owner).  Better to do it right the first time as the ole saying goes than to have it in the car and then have to fix it.  Others may have a different experience but that is my 2 cents worth. 

Greg

[gt350hr]

     TJ  The opened plenum will have a positive effect when used with the Paxton blower. I tested things like that 50 years ago when I was drag racing with a Paxton. The extent of that mod "without" the Paxton is questionable and would probably benefit from adding a center divider like repop COBRA intakes have. BUT since you are "force feeding" your engine with the Paxton , the modification "actually" helps power production. I eventually went to a single plane "back then" for more improvement. Pressurized air changes everything so you can leave the manifold as is , no need to do additional smoothing as suggested.
   The stuff I did back then got me over 500 hp when SAI rated the engine at 390.
          Randy

[TJinSA]

Greg, Randy. Thank you both for your insightful feedback, as all your points cycled my head, I needed the practical experience to know the point one design transitioned performance characteristics toward, if at all, to the other.  I look forward to all other feedback the group may share.

Very best regards,
Tom Kubler

[shelbydoug]

An Offe 360 is a lot like that. I ran one for a while. It was ok off idle and had a terriffic top end better then the Cobra. The Cobra did have more torque off of idle but not a lot. Just felt a little crisper.

This manifold would probably very good on a big cube small block.

[sg66]

I picked this up back in the 80's and still run it today. I can't comment on what you give up for low end torque because at the time I also built the motor with the larger Motorsport cam .512 I / .536 E  bigger valves 1.94" / 1.60" replaced a 715 with a 650 double pumper and some other things.  A few years later I switched to a 5 speed so losing any low end torque didn't mean much as I can easily light up the tires in 1st if I'm already driving 10 MPH and floor it. The motor runs great at 7k when I decide to go there. Also running a 3:89 locker FWIW

[gt350hr]

  The early Cobra ( small letter) intake has smaller runners than the later large letter manifold and it would respond favorably to the plenum modification you have. I would like to caution those who offer advice based off of reading magazines. "Most" of the information on modifications to intakes is centered around GM products , not Fords. "Generalizing" that information over to a Ford intake/engine is not a good thing to do as Ford port layout and manifold runners are VERY different than a GM "siamese port" style head. The same can be said for the oft quoted Smokey Yunick comment about connecting rod length. It applies to specific situations on a small block Chevy. Building "EVERY" engine with the longest rod possible will result in some very poorly performing engines.
    Randy

[shelbydoug]

Super Ford did some dyno testing on Ford intakes with modifications and I believe a manifold with the entire plenum divider eliminated like this.

I'm thinking that it may have been on the Blue Thunder Cleveland intakes but that may have been in the early '90s.

I agree that any intake modifications need data, i.e., dyno testing to determine the results.
The problem here though is that once you remove too much materials it's difficult to go back.

I leave that all to someone with a lot of time and a stack of intakes they can afford to turn into junk.