Various Intake mods

My intake modifications
My "fix" to finally install the JDM intake supplied with this B16A2 engine involved both relieving the cross-member and eventually realigning the intake.

Rather than attempt to source a manifold that may work, I decided to use what I had.

Initially I was unable to install the manifold completely and could only see the obvious fouling between the cross-member and the intake runners.

At first, I started by modifying the bulkhead cross-member, as I considered this would be relatively simple compared to cutting and re-welding the intake manifold. However any cut out section must be replaced with a part that is able to transfer loads back to the original structure without causing local deformation under load. Since I was about to remove a section of the cross-member that carries among other things, transverse load, it had to be a reinforcement with sufficient strength to resist buckling.

With this in mind I made a flat template in cardboard to see if what I thought was required could actually be physically made considering the bend radius being used.

Once the dimensions were established, I fabricated the same shape from a single piece of 16 SWG steel. When installed it completely fills the cut out portion of the cross-member. It was MIG welded inside and out.

This mod did result in clearing the manifold runners, however once the manifold was put in place it still did not have any clearance between the back of the intake plenum and the bulkhead possibly due to the cars original manufacture.

At this time all my interior wiring, relays, ecu, brake masters, and dash was completed, which meant the cutting required would basically alter the complete bulkhead shape and also require more modification to the wiring and dash. After months of work getting to this stage, I did not want to go this route.

Therefore to exhaust all the possibilities at hand, I decided to try to angle the original intake. If the engine operation was affected, I always had a fallback, although not one that I really wanted to contemplate.

I spent some time measuring and made a bulkhead to engine intake drawing to determine how much angle on the intake was actually required for positive clearance.

I was also in the fortunate position to have access to professional aerospace welding personnel who are no strangers to working with cast aluminum.

On inspecting the intake runners I noted that there was a cross-section that held the same diameter over a short length. I figured if the runners were angle cut at these precise points there would be minimal effect to the tract length or the cross-section.

With my trusty hacksaw I cut the manifold at the chosen locations and hand filed the angles on the lower runner portions without removing any more material from the base of each cut line. No more material was removed from upper side of the plenum runners other than a general deburr. The amount of material removed from the lower runners across their face was less than 0.125 inches.

I chamfered the edges of all the manifold runners for good weld penetration made a jig fixture to hold everything in place during the welding process.

Once it was welded up, the interior of the manifold was hand blended to remove any overlap or weld between the upper and lower sections. In fact this operation was very successful in that very little effort was required to achieve a smooth transition between the two parts because of the small change made.

I realize it can be argued that I have altered the original intake performance, yet without using sophisticated flow measuring equipment, it would be very hard to prove. Add to this, that this is a cast manifold which is made in bulk for all Honda cars, and as such the manufacturing tolerances cannot be so held so tight that any deviation from the original design would end up affecting the engine performance and operation to such a degree that it becomes a liability for the consumer.

Given this sad truth, any batch of stock manifolds will not produce identical results on the same engine, they will all work (within a +/- tolerance) and who here can categorically say that a 1.5 degree angle change to the plenum is a detriment, no change, or possibly an improvement.

From a purely personal perspective, I cannot see or feel any effect on the engine performance or its operation. Basically gas mileage with a stock diff is 40+ and it pulls like a freight train to 8K.

Looking back on this particular mod, I suppose I could have chosen to buy another manifold, but my gut feeling was knowing British Leyland and their lack of build quality, it could turn out to be a turkey shoot, on the other hand I enjoyed this opportunity to experiment and have what I consider to be a successful conclusion.

It could also be thought that the cross-member mod was completely unnecessary when in my case it was. I elected to make the angle to the intake the minimum amount required to have bulkhead clearance. If the intake only is modified, I suspect that the angle required would have to be somewhat greater. And the end results I could not comment on.

The other change worth noting in this diatribe is the TPS rotation of 180 degrees. This was made to clear the cannon connector with the bulkhead interference. It is very simple to accomplish and the unit still performs its original function as was intended.
  1. 1 flat template
  2. 2 mockup1
  3. 3 mockup2
  4. 4 crossmember cut out
  5. 5 intake cut 1
  6. 6 intake cut 2
  7. 7 cutout1
  8. 8 intake after welding 1
  9. 9 intake after welding 2
  10. 10 result1
  11. 11 reversed tps
  12. 12 weld and relief
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