Tri Y header pipe order for Nissan V8 1-8-7-3-6-5-4-2

[Rob-bb]

Hi, the Nissan V8's have this firing order 1-8-7-3-6-5-4-2

What is the best way to connect the primary pipes in the Tri-y setup? And if you could explain why that would help me learn a thing or two as well

[BLSTIC]

You want the 90-degree-separation cylinders to join in the second Y not the first. This results in a simple side with two side by side Y and a lower Y, and a complex side where pipes need to cross each other to make the first join.

90 degree separation between exhaust results in a ~5% VE loss for that cylinder at moderate to high rpm by pushing a blowdown pulse (EVO) into a cylinder on overlap. Ptuomov has a good thread on this in the advanced forum.

Long tube headers eliminate that by having a long enough pipe that the pulse can't make it in time. A properly designed Tri-y can help by disrupting waves so that the blowdown pulse is weak by the time it gets to the overlap cylinder. "Exhausted" has threads that hint at this

[BLSTIC]

Note 7-3 are 90 degrees apart and not adjoining cylinders. You can have a simple side. 2-4 are adjoining, so you'd need to cross over and join 2-6 and 4-8 instead

[Rob-bb]

Note 7-3 are 90 degrees apart and not adjoining cylinders. You can have a simple side. 2-4 are adjoining, so you'd need to cross over and join 2-6 and 4-8 instead

Are you saying 1 and 3, 5 and 7, and on the other side 2 and 6, 4 and 8, as the pairs to to be joined at the first y? Like in my crude drawing

So some are more than 90 degrees apart at the second y, that's ok, but we don't want 90 degrees apart at first y, is that correct?

[BLSTIC]

Yes that's about it. Ideally the 90 degree ports wouldn't join for a long time, like with long-tube headers. Or you cross two cylinders from each bank over to the other collector (crossover headers) to make 180-degree grouping for everything. But unfortunately 90-degree interference isn't the only design criteria.

There's also another school of thought like what Ford did and have the 90 degree cylinders join by *shortest* possible pipework and alter the cam timing. Not really sure how that works, but they did it.

Or there's the Z-06 route where they have 4 pipes dump into a comparatively huge volume that basically negates wave tuning. Apparently tipping out the baby (tuned length) with the bathwater (blowdown interference) was the way to get power when a compact manifold was necessary for the cat converters. Probably also worth a thought. Look at "log manifold lessons" post by Calvin (Exhausted) for a similar thing.

[Rob-bb]

Probably also worth a thought. Look at "log manifold lessons" post by Calvin (Exhausted) for a similar thing.

haha, I am going to all this trouble to get rid of my log manifolds, I don't dare read something that might tell me they are good

[BLSTIC]

"Log" in name only. Not many logs have stepped long radius primary runners identical to best practice pro-stock for the first handful of inches into a 5" pipe (IIRC, it was really big)