Dual Plane Exhaust Manifold.

[GJM85]

 

I've been staring at this exhaust manifold for some time now. It's a piece of K series engine history that, in my opinion has been a wee bit ignored. And for several good reasons.

1. It's attached to the intake as they all are. And that's wee bit shite!

2. It's cast iron and prone to cracking.

3. They're not tube headers and that's not cool now is it?

 

But I'll say they're just as good as most tube headers for few reasons. The majority of K series extractor manifolds are 4-1 pipe combinations with unequal length runners despite being advertised as tuned length. This negates exhaust scavenging in the collector because the negative pressure waves created by each runner expelling gas are not effectively timed or tuned.

 

The dual plane manifold is in one sense a 4-2-1 manifold where cylinder 1 & 4 are linked into a single 1 1/4" pipe & cylinder 2 & 3 are linked. These 2 pipes then join at a collector some distance from the manifold. At this point scavenging does occur because the negative pressure waves are balanced out through the lengths of the secondary runners.

 

4-1 headers are ideal in high performance applications where runner length is equal and scavenging occurs in a single collector and as close to the head as pressure waves will allow. This improves performance in the mid to top end.

 

4-2-1 headers should use equal length runners between 1-4 & 2-3, then again between the secondary runners. The distance between the primary and secondary collectors splits the low pressure waves and increases performance in the lower to mid range. This is where the dual plane exhaust manifold come in.

 

I've looked at the manifold in many different frames of mind. Twin turbos? Full dual exhaust straight through maybe?

 

It's pretty well designed for what it is, although the 2-3 runners join just 3 inches from the head and the 1st runner is 12 inches long and runner #4 is 9 inches long. This difference is countered in the length of the secondary runners. 1-4 being a bit shorter at the second collector.

All in all this manifold has my vote and I believe it to be just as effective as most off the shelf extractors? I think I'm going to use it on my big 5k build. Unless I can get a set of Colby's

 

Edited September 18, 2014 by GJM85

[altezzaclub]

I reckon it depends on how well the first pipes blend into the second.

 

The OD looks larger on the casting, so what are the IDs like? The casting walls will be thicker than the pipes. Does it give good smooth flow right down to the collector?

 

I didn't know they were prone to cracking, but having cracked a set of extractors and seen Pintara R31 castings crack, some do and some don't. I will admit I tossed my stock manifold in the corner without ever considering using it with the other mods.

[GJM85]

I haven't separated the secondaries from the manifold yet but the 2-3 section seems to blend quite well down into the secondary pipe. There does seems to be the possibility of porting and fitting larger secondaries.

 

The 2-3 runners are straight forward and open. The 1-4 runners seems to open up slightly after the flange. But just like the intake, larger exhaust runners doesn't necessarily mean better flow. As long as there isn't any obstruction and casting smooth, hot gas will naturally flow towards cooler lower pressure areas in the exhaust. Usually the exit.