DIY Top End Porting
 

Going to port my intake plenum and injector housings on my 1992 ZR1. The plan is to open up the plenum and IH's to 36mm. I will also port match the heads (on the car) to the new 36mm openings. The primaries are smaller than the secondaries at the heads. The primaries also have very large injector bosses that can be significantly reduced in size as the o-ring for the injector is located high in the boss. The smaller primary diameter coupled with the large boss greatly restricts the flow when compared to the secondary port. (See my poor man's flow bench below). I will post my pre-porting flow numbers shortly along with test conditions. One thing I observed is the secondary port injector o-ring seal is at the bottom on the injector. The new FIC injectors I am using seat a tad deeper into the boss placing the o-ring very close the end of the boss inside the port (see pic below) which means I will need to steer clear of that area when porting only doing some mild smoothing with with a flap wheel.

Still on the fence regarding removing the secondary butterflies.

Be careful..... I hope you have experience porting. It's not as easy as it seems on the surface and often times less is more. These are expensive parts too. I know I've considered buying extra injector and an upper plenum, but I would likely send them out to be ported by one of the two recommended ZR-1 shops. That will probably be the extent of any mods along with full length headers.

I echo Anthony's comments. I know that even Marc Haibeck once ported an intake slightly too thin and the result was breaching an oil passage. Didn't know it until it was on the car for a little while. Costly for him to pull the engine again and replace the part under warranty. And he does a couple a week, for many years. Strongly suggest you send the parts out to Marc Haibeck (ZR-1Specialist) or someone else with considerable experience. You will also need a tune (chip) tailored specifically to what you do (porting, headers, larger throttle bodies, etc.) and probably larger throttle bodies, which Marc can provide. Unless you have done a lot of porting and tuning, I would suggest that at least you talk to someone who is experienced with these issues on the ZR-1 before attempting it.

Also, I am a big supporter of removing the secondary system. Had Mark do it when he did my 510 package. Removes a lot of unneeded complexity under the plenum. I seem to have had vacuum leaks in both my Z's at one time or another. But if you do that, you must get your chip reprogrammed for it, as both injectors need to be set to run at 50% flow rate at low speeds instead of one injector running all the time then before secondaries activate. It also means you can't run in "Normal" key off mode because that would turn off the secondary injectors and you would run to lean. But good luck with the project--it will result in a big performance improvement.--Bob

I have ported and port matched intake plenums before but have never done heads. I plan on having Marc do the chip and open up the TB to 63mm. I port matched some badly shifted IH ports to the heads on my 95ZR1. It will likely take a while but I have most of the tools including micrometers and calipers to track wall thickness including a 36mm gauge ball.

JB weld.

That will fix a breach....if one should happen. :thumbs:

Nice diy setup. What are you using to move the air? I thought about doing something like that, but before i knew it, I had just ported mine. To avoid the trouble with the thin spots, you could just do 34-35mm passages- that's still quite a bit more airflow than the stock casting shape.

One thing I would request is mock up an unported cylinder head port that is not tapered. Many examples of good gains even with port mismatch with the injector housing hole being a couple of mm larger than the intake port on the top of the head. if the airflow isn't that much different, then it may support the argument to not go through the trouble to touch the head with a grinder unless you are going to fully port everything.

If I touch the heads it will be to just match. I did the same on my 95 (see attached before and after picture). The dyno HP gains were only about 4hp.

Good to know it was at least measurable. I was able to port match my 8 primary head entries in about 6 hours as I recall. Not so much time, but prep and care to not drop chips into the works. I had to turn the crank 8 times as I did it with valves closed, oily rags, and a special vacuum cleaner attachment I made out of a narrow straw type of tube I had.

Good for you!

Can you give us some more information on your setup?

Used a piece of 2" PVC and 6" PVC connected by a "T". I think it is 6".....will check tomorrow. Using RTV, glued a plastic lid to the bottom of the T and a piece of Masonite to the top with a 40mm hole (approx). Stuck some 2" wide weather stripping on top of the masonite. The flow source comes from a shop vacuum. That thing with dial is a rheostat (I used this to control the vacuum speed/flow in lieu of a valve or some type of vacuum relief hole in which to control the static test pressure). I have 1/8" npt barbed hose fitting mounted in the 6" section about half way down from the top. This is where the static pressure is measured. This is what the flow source is adjusted to maintain. A pitot tube is mounted in the 2" section and it measures the velocity pressure. Knowing this and the cross sectional area of the PVC, one can calculate the approximate cfm. I use a digital manometer for the measurements but water filled homemade manometers can also be used. My manometer only has a 5"water gauge range so I must adjust my test pressure/vacuum to work within this range.

On a 90 you can remove the primary injector boss entirely.

Port match the primary IH - with the head ports. Then "cone" the head port; 36.x @ the entry of the heads (primary) to the stock dimensions (33.x mm) near the valve guide, taking care to keep the walls of the runner straight (or run the risk of veering into oil or the water jacket).

Coupled with TB porting to 63mm and headers and a dyno tune, I estimate my RWHP would have been just north of 400, had I dynoed it at that stage.

Just the "short" version. Completing the "full montie" (head porting and tune) is worth another 20-25 . Pete's cams are good for about another 25 at the wheels. That should leave you in the range of 440+ or so @ the wheels. The full "FBI" treatment by Mark or Pete and 450+ @ the wheels. is a well established recipe for a stock-bottom LT5.

Just sayin...

My 1995 does 400 at the wheels minus the head porting and cams. I would love to add cams but not willing to pull the engine at this time for that car.

It appears that most of the primary boss can be removed from a 92 as well.

As I recall Marc welded the aluminum then machined it down again more carefully. Although he may have just trashed the piece and used another. Senior memory issues. :ack: --Bob

One shouldn't have trouble with breaching (water or oil) if just doing a "top-end" porting; port matching especially. You don't remove enough metal along the ports to get in trouble (e.g., 36mm ± at the entrance to the head, and tapered to blend with the stock opening, just as you reach the injector boss(es). CORRECTION! Make that VALVE boss(es) rather than injector boss(es):hide:

Where I got into some trouble (that had to be welded/re-shaped) was later when opening the entire length of the head runners to 36+mm. Some core-shift occurs when the heads are cast, and the oil and water regions are not always where they should be - especially the water. But, as Marc Haibeck once told me: "If you don't break into the water jacket at least once (while cutting), you aren't trying hard enough!" (Marc has a welder he sends any goofs to that is a wizard with aluminum runners!)

My plan was to open up to 36mm throughout the length of the primary and secondary IH ports and then match the head port similar to what I did on my 95. On the heads I only went in about 0.5" or so deep and tapered to stock (primaries only).

The secondary head ports were fine but the primaries are in the area of 32mm. It would seem to me by not fully porting the IH, that would diminish the gain? I know just by removing the injector boss in the primary will likely gain a good bit of flow improvement. The secondaries may just require a mild chamfer in the head.

I established the baseline flows for the injector housing and intake plenum. The IH primary measured at approx. 57cfm (avg) and the secondaries measured 79cfm (avg). This represents a 38% increase in flow between the two. All the plenum ports were in the area of 79cfm (with TB removed). Standard conditions were assumed and test pressure was held at a constant -6"wg. These values are intended to be approximations and used for "apples-to-apples" before and after comparison only.

The pic below shows how large the primary IH port boss is. Reduction of this alone should have a significant impact on primary flow.

:lurk:

Below you will see the flow data for the plenum and IH Ports. This data is approximate and intended for comparison only.

Started to port the plenum yesterday. Already learned a few things. Keep the burr shaft length as short as possible to get the job done. A longer burr is harder to control. Also recommend when performing work if you are using a grinder that has the ability to lock in the "ON' position to not use that feature if you are in an area or holding position that may promote tool binding or kick back. Once the burr starts to bounce around inside the bore it can be nearly impossible to regain control without withdrawing the burr which can cause damage to the walls on the way out. I am considering a foot pedal to eliminate hand fatigue by holding unlatched switch in the ON possible and to quickly get the power OFF when needed.

Keep the speed as slow as possible.

I managed to get the gauge ball fairly deep into the bore but find it impossible to get much further into the 90 degree bend. A ball shaped burr might help get a little further into the turn.

I found the back lighting the bore with a flashlight helped me to see the contact points when checking with the ball. I need to figure something out that will allow me to do this on the IH's.

I think removing the septum in the plenum and doing a partial siamese into the IH would provide some extra flow but LOTs extra grinding.

You definitely need a ball burr on a longer shaft to get around the plenum corner. I could have probably done better on mine in retrospect (as I spent more time with the I/H's). That said, it seems the top plenum flows better than the i/h's stock so with no injector hump and other odd geometries, maybe it will be less work to achieve the flow you need to match the other part.

I would maybe take a trip to horrible freight or check ebay for a good used air grinder with a rubber grip coating so you won't freeze your hand. I chose to use the air compressor at work over the weekend to save my neighbors from having to hear it run for hours on end.