I have a Holley single plane high rise oval port multipoint EFI intake. Going by the coloring of my plugs, it looks like I'm getting uneven air distribution. The four corner cylinders, 1, 7, 2, & 8, are darker than the others. #7 is by far the worst. I had to do a lot of grinding on the intake to get the ports to match my heads. It had the small peanut oval ports to start with. I thought I did a good job blending as far up the runners as I could. Maybe the intake flowed poorly to begin with, I don't know.

Can an intake be ported like heads can to get all 8 runners to flow the same?

Merc marine on its HP series engines stagger jetted the carbs on older engines. What you are seeing is common.

Can it be corrected?

BBC has 2 intake ports, short and long, in the heads then we have the intake runners thesmselves that are different. Air travels in pulses. Intake track tuning requires specific lengths to tune to. Yes it can be corrected but the $$$'s it will take will not warrant the result that you may or may not be after. Many ignition systems now allow you to time each individual cylinder. 1,2,7,8 may have 36 degrees total and 3,4,5,6 may have 36 degrees total. In some OEM head limited classes I do cams that feature 2 intake lobes. 1 for the short runners and 1 for the long runners. The opening and closing events, duration, and centerlines are "in tune" to what the engine needs.

In your case with EFI if the software allows you to tune each cylinder then yes. If not, again it will be expensive.

Would a tunnel ram based intake manifold improve this situation? I am thinking about a configuration with a larger common plenum on top. True it would not change the port lengths in the head. But it would tend to at least equalize the lengths in the intake manifold.

The Accel Stealth I have appears to include some design features towards this end including individual runner ram pipes inside the plenum with slightly different lengths.

The problem most likely is the "SINGLE PLANE INTAKE" you don't have any control over runner length... The "STAGER JETTING" mentioned was used on "DUAL PLANE" intake manifolds where the runners were closer in length. The stager jetting would help fine tune the fuel air mixture getting to the various cylinders.

I did a substantial amount of testing on BBC EFI intake 3-4 years ago. I saw what you are seeing and several of the reasons why. Some reasons are different from a carbureted induction system and some are similar. Most never think of this.

There are both air and fuel issues, but the problem is they vary depending on many factors, RPM, throttle opening, cam design and intake design.

People assume that iwth EFI this is all even and that isn't always the case.

Things that affect it as I found during this particular testing and ever since pay attention to is:

- Throttle body design, with a 4 bbl style throttle body, the best design IMO is a center dump, non-progressive piece. If the throttle body doesn't distribute air evenly, you will have uneven airflow front and back. Even with a fairly large plenum.
- Cam and intake, what happens with more overlap, and this is most prevalent at high vacuum and moderate RPM is that one cylinder may rob from another cylinder's fuel. The intake design really contributes to this. A single plane is worst. I did some cutaways with intake with strobe lights and saw this. I'm impressed Steve mentioned a tunnel ram. I did some testing with tunnel ram style intake and this greatly reduced the cylinder robbing. I run a tunnel ram on my BB with twin 4 bbl air valves, not because of any "look", but because I saw this to have the best air distribution and fuel characteristics.

Cylinder to cylinder fueling can't really help with this too much with EFI IMO because this is very dynamic and changes with load and RPM.

This may sound very bad, but the good new is at WOT the a/f distibution was almost perfect which is most important for engine life, and for the most part this is impercepable with how the engine runs. Most people see it with the plugs if at all.

I did this testing with a wideband O2 sensor in each cylinder.

If anyone thinks a carb is better, I've seen a lot of 8 cylinder A/F charts from carbs and it is terrifying. There is a ton that affects this and it has other variable other than mentioned above for EFI. At WOT if the high and low is 2 pts variance, that is VERY good from what I have seen (IE on hole at 12:1 and one at 14:1) and have seen 5++ pts at WOT. At part throttle I've seen this vary over 8 pts (one hole at 9-10:1 and one at 18:1). Trust me when I say there are thousands of engines running out there with cylinders with an A/F that are supposed to "melt" that hole ie 14-17:1 at WOT. But they don't.

I believe this is one of the reasons nitrous can really keep killing just several holes with carbs and I know several people that switch to EFI and dry nitrous and the engine is a lot more reliable.

You can measure the average A/F in one bank, and with EFI at WOT, this is pretty safe, but with a carbureted system, you really have to watch as you can end up with really lean individual cylinders.