Le Mans headers

[SMA390]

I recently read an article about a guy who purchased a 70 mustang that had an original 67 427 Lemans motor in it. In the article it talked about the #3 and #7 header tube crossing over to opposite collectors. So cylinder 1,2,7,4 on one side and 5,6,3,8 on the other . Anyone ever heard of doing that ? What would be the purpose?

[BattlestarGalactic]

You used to be able to buy headers like that for cars.  Not sure if anyone still makes them?

I'm sure it has to do with exhaust pulses and scavenging.  They are very cumbersome, hang low and likely fell out of favor with most guys.

[GerryP]

You can still buy them.  Yes, the theory is to create a balance in the exhaust pulses.  It does work, but it's more of a throttle on the floor racin' deal.  You don't see that advantage on a corked up street car crusin' for burgers.

https://www.jegs.com/i/Doug's+Headers/776/D627/10002/-1?gclid=CjwKCAjwo4mIBhBsEiwAKgzXOMVKdf3H4F6lKXI2_lKkbL7uPWY8WR_YuU3UvFRRYdXkg585-btwgRoC6g4QAvD_BwE

[machoneman]

Most of those header designs offered minimal, if any real advantage, over more conventional (read: non-cross over) headers in street cars at least. The low hanging pipes were awful on street cars as noted. Keep in mind too that mufflered street cars, by definition, most often do kill of hp compared to open pipes.....meaning any small advantage of trick exhaust headers is often lost. 

Somewhat related, long ago (and far away!) Mickey Thompson offered his Super Scavenger headers where the pipes (no cross over) ended up dumping into a really long box-like tube collector. The idea was that, IIRC, the equal length tubes flow evened out, inside the long collector, the exhaust pulses. A buddy had a set for his SBC '61 Vette but never installed them.

https://www.pinterest.com/pin/569846159071038878/

Come to find out years later, this header design on a dyno test, as with may others, offered mainly bragging rights as opposed to hp!

[thatdarncat]

Like Gerry said, Doug’s Headers still makes a cross over design. Other brands in the past had them too, with different configurations.

[GerryP]

...dumping into a really long box-like tube collector. ...
Come to find out years later, this header design on a dyno test, as with may others, offered mainly bragging rights as opposed to hp!

It actually is pretty smart design since it does correlate to theory.  That kind of specialized engineering usually requires a really specific, very narrowly defined combination to bear fruit.  In line with that, one of the most important features of a header is the collector since that is a critical design component for good scavenging even on a street exhaust.  The one problem I have with most shorty headers is the very short, abrupt collector.  There are some long tube headers, Headman for one, that use that very short collector. 

Most "performance" parts are mainly marketing.  Not that headers, cams, and pistons don't work.  They do.  But there's a lot of consumer arm twisting going on with the sale.  That is true to this day.  How many "cold air intakes" get sold to those Honda Civic owners?

[WerbyFord]

Those headers cross over 4 and 8.
I dont think that solves anything, you still have 90 and 180 and 270 pulses.

We had a similar pair, 63-64 Galaxie, 3 and 7 cross over.
Same thing - NOT 180 headers, but more to obtain equal length.
We never ran these, didnt want to cut the car (still have it), sold em in 1978 For $100 new.
Bought a whole 6v setup with polished T-bird air cleaner with the money for $120.
Sold that too. Sold too much.

I'm not that keen on equal length unless you want a high, narrow peak at a given RPM. Fine, maybe even better, if the peaks spread out a little ie different lengths.

The shorties & short collectors dont offer much. We made that mistake at the Dirty D, just dropped the pipes & ran. Loud, but it really wanted a long "collector" on the end of the shorty iron, eg 2.5" diameter best. I think this was known even back in the early 60s - ALL the lengths matter, and way-too-short doesnt help much.

[Stangman]

Thats why they used to play around with collector extensions

[machoneman]

Thats why they used to play around with collector extensions

Hey, drag guys still do. Works only on open headers though. Start with a long bolt-on or slip-on collector. Draw a wide horizontal mark on each one with a colored wax pencil or yellow crayon, Make a few runs (tune s/b be pretty much right on before starting this test) and see where the burn mark ends. Cut off the tubing after the mark and you'll have the correct length collector.   

[Ranch]

I don't think The cross under design make the setup any lower.  Now the 1-2 & 5-6 tubes dropping down under the control arms really hindered ground clearance.  Which is why I keep my stance up ala 60/70/s look, I clear most normal stuff cept if I bottom out my suspension.  By he way, my cross under tubes are 3 & 7, I don't know who makes them, I've had them 50 years.