Inliners International Forums General Discussion Engines Mixing Lump and Non Lump Ports and Other Head Stuf

Hi All

I am trying to think just inside the wall of the of the box.

We know that the head and manifold pairing is not the best in the world for fuel distribution. That being written has anyone tried to manipulate the heads and/or exhaust to try and even out the fuel distribution?

Below I would like to throw out some examples to see if anyone has tried these, what the result was, and if not, would it even be worth trying? I am not looking for more power, per se, but more consistent distribution across the cylinders.

1. A head with stock valves on 3/4 and oversized valves on 1/2 and 5/6.

2. A head with stock valves on 3/4 and oversized valves on pair 1/2 and 5/6. Then with slightly larger valves on one of the 2 outside pairs to compensate for charge stealing.

3. A head with 3/4 intake port bolt boss left in and the intake ports 1/2 and 5/6 have the bolt boss removed

4. A head with 3/4 intake port bolt boss cutout and the intake ports 1/2 and 5/6 have the boss cut out and lump ported.

5. Changed the lengths and/or diameter of the header primaries for the outside cylinders to improving scavenging. Or the center port to reduce scavenging as compared to the outside pairs.

6. Any combination of the above.

There are many more combinations but you get what I am trying to do.

Any input would be greatly appreciated.

Thanks,
Rick

The 3 port pairs are only similar, not identical.

The intake differences:
1-2 has 240° 480° 240° firing order separation
3-4 has an even 360° 360° interval
5-6 is 480° 240°; the same irregular interval as 1-2 but with the inner/outer sequence reversed

The exhaust differences:
1 is an individual port with a 720° rotation
2-3 has 240° 480° 240° firing order separation
4-5 is 480° 240°; the same irregular interval as 2-3 but with the inner/outer sequence reversed
6 is an individual port with a 720° rotation

This will be very complicated with minimal results, L6 siamese engines have been popular for over 100 years.

I follow the reasoning but I am skeptical about the efficacy of such changes. The imbalances in your hypothetical will certainly change the flow-rates into certain ports and/or into certain cylinders sharing a port. But to panic’s point the charge stealing is a function of valve events – so restricting flow into a ‘stealing’ cylinder will just richen the stolen charge; and easing the flow into a ‘robbed’ cylinder will lean out what is left with even more air flow.

As for selectively de-scavenging the exhaust (another interesting thought exercise) – the result will be exhaust gas left in the cylinder (reducing VE). If combined with restricted flow into a ‘robbing’ cylinder the mixture simply becomes even richer with CO and CO2 left over from the last Otto cycle.

Complicated with minimal results. But fun to ponder.

One reason why the center pair of cylinders does not always run richer in an L6 is that the long rotation delay for the 1-2 and 5-6 pair produces a stronger vacuum signal than the "balanced" 3-4. Jaguar compensated for this in the XK-E with slightly richer jetting in the 3-4 SU.