Don Terrill’s Speed-Talk

A 6-1 design is simpler, easier to route, lighter and has less surface area to lose heat to than a 6-2.

The 6-2 would allow for 120* spacing between exhaust pulses, and the use of an h/x pipe.

Seeking the broadest curve possible, is there an actual advantage to the 6-2, or is it far outweighed by the weight?

MrWOT wrote:A 6-1 design is simpler, easier to route, lighter and has less surface area to lose heat to than a 6-2.

The 6-2 would allow for 120* spacing between exhaust pulses, and the use of an h/x pipe.

Seeking the broadest curve possible, is there an actual advantage to the 6-2, or is it far outweighed by the weight?

I have no input other than I'd like to know myself as I've never seen a clear cut answer

I think it depends where the power band is. On a 800ci pro stock you'll see 2-2-1. On a 500ci they don't vary to far off the conventional header.

Anyone have a photo or link to a 6-3-1 header? I'd love to see it.

An inline six works out as two 120-degree triples. You treat 1-2-3 and 4-5-6 as separate groups.

An even-firing three is as simple as headers get - just pull the three pipes together at some convenient point and run the exhaust out. No collector necessary, since there's no overlap between cylinders until the exhaust duration goes over 240 degrees.

dwilliams wrote:An inline six works out as two 120-degree triples. You treat 1-2-3 and 4-5-6 as separate groups.

An even-firing three is as simple as headers get - just pull the three pipes together at some convenient point and run the exhaust out. No collector necessary, since there's no overlap between cylinders until the exhaust duration goes over 240 degrees.

+1

The 240° separation is a great advantage when working on inline 3s and 6s. Inline engines are more sensitive to primary length and pulse interaction than V engine designs, where collector length sensitivity is more of an issue.

This separation also makes tuning intake systems easier, and very effective.

Fitting 2 separate 3-1 headers, running dual exhaust and setting collector length with a termination box has advantages that need to be considered.

I usually use 6-2-1. Do not see the need to go 6-3-1 as they are still even pulsing and heavier and more mass to fit. It does depend though, I suppose there are situations where it would be harder to package the 3into1 collectors.
I also keep the primary lengths less than 2/3rds of total OAL. Even shorter for drag stuff.

Well, guess I'll pipemax for 6 cyl and zoomies then, termbox and exhaust separately. Great input all

strokersix wrote: ↑Sat Jan 24, 2009 6:36 pm Anyone have a photo or link to a 6-3-1 header? I'd love to see it.

Factory fitted to 84-86 Holden VK Commodore with EFI option.

Circlotron wrote: ↑Sat Nov 07, 2020 11:42 pm Factory fitted to 84-86 Holden VK Commodore with EFI option.

Thanks for sharing.
About 2years ago i built my own header/extractor (here in south africa its being called " branches ") wanted to do 6-2-1 but my luck at that time i could not find 3into1 collectors locally, so then came the idea of doing 6-3-1 but still needed a 3into 1 collector, and space not that much so i made a 6into1 but the shape is not round, made it rectangular. Building an unique collector, being a pita but got it done, not one of my best attempts of building my own.
Chevy inline six in an opel a2 senator, which is very close to the holden vk commodore, just that it uses a steering box with draglinks instead of rack system like the holden. So space not that much with chevy bellhousing getting in the way.
I see they use very long primaries,
mine less than half that lenght so there is only one pipe going inbetween draglink and bellhousing.
Works great for space constraints but at low cruising rpm 1500-2000rpm doing 60-80kph it sounds like a damn subaru with that constant misfire popping.
Changed back to std log manifold cleared that. (I'm not very fond of a boxer sound) as for performance, normal driving there is no difference, above 4000rpm it does help if engine is cammed.

Chevy freak.

Found another, aftermarket this time. For same motor retrofitted to earlier car that originally had earlier 9-port head. https://genieheaders.com.au/listings/ht-hz-gen099e/ Usually feeding 3 cyls to each pipe excites a resonance in the entire length of the pipe, making it really bark at mid rpms. I wonder what a *triple* exhaust out the back would have sounded like?

Circlotron wrote: ↑Sun Nov 08, 2020 5:49 am I wonder what a *triple* exhaust out the back would have sounded like?

Haven't tried that one, but it can be done just to confuse some people. Or maybe 6 singles , 3 per side. really confuse them all

Have done the dual setup, no balancing between them it sounds the same as my essex (english) v6 in my cortina.

Chevyfreak.

In the vast majority of cases the 6 - 2 -1 set up, split 1 2 3 - 4 5 6, has been proven to work the most capably

I'm sure someone can dredge up a exception, but it doesn't disprove the rule

Keep the pipe sizes, especially the primaries, on the conservative side

6-3 not only joins pairs with uneven firing order, but different order depending on which pair.
1 & 2 are 240-480-240, 3 & 4 are 360-360, 5 & 6 are 480-240-480

Ok ..... the assumption being a 153624 firing order, which is the most common .......