As many of you are aware, I recently pulled the intake on #007. My rationale for doing so was twofold. First, although not actually leaking oil, both the front and rear of the intake showed signs of oil "dampness" or residue. Second, after reading several threads on various internet sites, reviewing an article in the October '96 issue of Corvette Fever, and exchanging e-mails with folks on the Grand Sport and GS Registry mail lists, I decided it would be worthwhile to do some limited port matching of the intake manifold to the cylinder heads.

I describe the porting as limited because I really only matched the roof of the port. Fully matching the port would require cylinder head port work. This will occur when I have the heads and intake manifold CNC'd in the future.

Intake Removal....In my opinion, removal of the intake was quite straight forward. It took me less than 90 minutes. The fact that I've bypassed the throttle body (TB) (relative to coolant) was an added "plus" in that I did not have to concern myself with disconnecting coolant lines. The LT4 intake is "dry"...ie no coolant flows through it. This means you don't have to drain any coolant, nor worry about it seeping in the block and heads when you dislodge the intake.

The procedure is pretty straight forward....I disconnected the intake duct work between TB and the air filter. I then began unplugging the various wires and the few vacuum hoses the LT4 has. FWIW, the most difficult connector to get to was the one that goes to the crankshaft position sensor (CPS) as you have to pop it loose by feel. It also has a small loom which secures the CPS wiring to a bracket, but again...a little patience and it's easily freed.

After unplugging all the connectors and lines, remove the studs that secure the wiring harnesses to each side of the intake and move the wiring out of the way. I used my shop vac and a small brush to insure there was no debris which could potentially fall into the lifter valley upon intake removal. Next remove the MAP sensor, and the 4 bolts which secure the fuel rail to the intake which allowed be to lift the injectors/fuel rail out of the way. I left the injector/fuel rail assembly connected to the fuel lines and let them lay on the coolant fill reservoir. With those things completed, I removed the AIR pipe that connects to the passenger exhaust manifold (header in my case) and to the rear of the intake. Note....there's a "hidden" 14mm bolt that secures the AIR bracket to the rear of the passenger cylinder head. Simply loosen this bolt...the "bracket" is slotted and will slide free. Now remove the nut from the stud that secure the coolant pipe to the passenger side (front) of the intake. Next, remove the throttle cable from the TB and the guide bracket. Remove the throttle cable bracket that's bolted to the drivers side of the intake. Lastly, remove the TB. With all this complete, you can remove the intake bolts and lift it free.

Porting....After removing the intake, I used a Dremel tool to cut the old intake gaskets to the shape of the cylinder head port. Because the gasket overlaps into the port, there's an easy to follow build-up of carbon on the gasket.

Once the gasket was cut to fit, I laid it into place on the intake manifold and marked the area of material to be removed. The amount of material is quite significant...0.250"

With the intake manifold marked and my trusty Dremel tool at my side, I began porting. I used the Dremel to open the port to the rough shape. I then used small half-round and ignition files to do the final material removal. I errored on the side of caution, leaving ~1/16" material. More material can always be removed, but it's difficult to put it back (not to mention quite expensive). I estimate that I spent 30-45 minutes per port. Even with the pattern clearly marked, I checked my progress versus my gasket "template" several times per port.

Clean-up and Reassembly....With the port work done, clean-up is next. I first cleaned the block and cylinder heads of all gasket and RTV debris. It's important to have a shop towel or rag in the lifter valley to catch the excess material. For extra safety, I also stuff rags in the ports as well. I paid particular attention to the end seal area. When the were clean, I cleaned them again. I use Ditzler wax and grease remover as a final wipe. This product is used a a final prep before painting and leaves no residue like some lacquer thinners. It's expensive, but worth the price in my opinion.

After cleaning the block and heads I turned my attention to the intake manifold. Obviously, after porting there are a lot of metal chips. I first sprayed the intake with brake parts cleaner, both inside and outside, as well as into all the various passages and fittings. Next, I washed it down with soap and water and also scrubbed inside and out with an old toothbrush. I then took it to the car wash and used a high pressure sprayer for a final rinse.

Reassembly is the reverse of the above using new gaskets. For gaskets there are two alternatives. Use the production gasket (p/n 12528884) which blocks the ports and would require modification or use the LT4 gasket from the GM Performance Parts catalog (p/n 12367777) which does not block the ports. I choose the "77" gaskets for ease of assembly. I purchased them via Worldparts.com from Hutton Chevrolet in Memphis, TN for ~$16 each ("77" gaskets are sold in quantities of one for some strange reason). Shipping was free, and I had them the next day.

The trick to a long term, oil leak free intake is to let the engine sit 24-48 hours prior to starting. This lets the RTV fully cure before hot oil is splashed on it from the inside. I believe this is a step that many dealers fail to adhere to and the oil leak returns 6-8 months later. After allowing enough time to elapse, I started the engine and checked for loose vacuum lines, connectors, etc.

Driving impressions....After the engine was fully warmed, it was time for some "testing". For now, SOTP will have to suffice until I can make some G-Tech runs. SOTP, there's no change until 5000rpm. Above 5000rpm, I believe the engine to be stronger. In fact, where the LT4 horsepower typically begines falling off (~6000rpm), the drop off is noticeably non-existent. Low rpm operation has not been affected. Cold start performance and idle qualities are also the same as before.

For $32 and a little bit of time, I feel this is a mod that's well worth the time on a slightly modified motor such as mine. For stock motors, I suspect the change would be less noticeable. None the less, the little things begin to add up and when this is combined with a free flowing cat-back exhaust, headers, 52mm thottle body, etc, I believe it's beneficial.