Gains from fitting 4 branch extractor?

[MJH2454]

I read a lot about BHP gains from simply fitting a four branch manifold and K&N filters, in the real world is this true, I hear 10 BHP from some sources.

Can you still get these gains without fitting a noisy, to me, straight through system?

1300 Spitfire MKIV, 

[Wagger]

The 'Expert' is in hospital. (PeteL).

The intake needs to be cool, so do not allow hot air from the exhaust to be sucked into the inlet manifold. Exhausts are almost a 'Black Art'. It depends upon a pressure balance, so a Big Bore exhaust is not necessarily any advantage.

Also, cast iron manifolds absorb the sound better than separate pipes. Lagging them can negate any advantage gained.

I messed around with exhausts on my motor cycles. Long term all that I gained was tinnitus and hearing damage.

[JohnD]

Tubular manifolds can improve performance by enabling better extraction of exhaust gases from the cylinder at the end of the cycle.   They do this when the exhaust valve opens and a pressure wave exits.    All waves have positive and negative components, and if the wave can be persuaded to attend the exhaust valve in the negative phase then, in effect, the exhaust is 'sucked out'!   Such a manifold may have various names, "Extractor", "Interference" or "Scavenger".

Any such wave will be reflected back up the primary at a junction, so that if the length of the primary is chosen correctly, then the reflected wave will arrive back at the exhaust valve in negative phase,  at a certain engine speed, and only at that speed.    So any benefit will occur at that speed and in a diminishing range around it.

Six cylinder engines are, in effect two three-cylinder engines on the same crank.   Their pistons move in pairs with their ignitions 360 degrees out of phase.    EG, when No.1 is at TDC on the firing stroke, the No.6 is at TDC between the end of one cycle and the beginning of the next.    If the exhaust primaries are connected together in pairs, 6-1, 5-2, 4-3, then the reflected wave will travel up the other pair and  benefit that exhaust valve as it opens, and because it needs only to affect the paired cylinder half a cycle away, the primary may be relatively short at 17".   The manifold must be of the "6-3-1" type, and will induce a benificial 'scavenge' in the 3.5-4.5K rev-range

Four cylinder engines do not have this pairing.      Some seek to copy the six style:

 but this is futile.

A 4-1 pattern can be helpful, but the rev-range in which there is a benefit is much higher than for a six, at 6K+, unless excessively long primaries are used.     Rimmers sell a long-primary manifold for fours:

 but IMHO, this it is only helpful for highly tuned competition use, and won't show any benefit on the road. 

John

[Puglet1]

Wagger. “I messed around with exhausts on my motor cycles. Long term all that I gained was tinnitus and hearing damage.” 😂

[Pete Lewis]

2 hours ago, Wagger said:

The 'Expert' is in hospital. (PeteL).

Ha  Om Back,   no expert on this but stick to the triumph basics well tried and tested 

as soon as you dive into must have mods expect the headaches to start

I have  hate of KN and you choose how to get the fueling right ( never) to match the loss of intake vacuum 

tubulars are as said just noisy compared to a cast manifold  and make more under bonnet temperatures you dont need 

best well left alone and juts have a happy drive with what you have , without a dyno to measure whats going on you can spend ££££ and get just a headache 

Pete

[Wagger]

JohnD gave a very comprehensive answer. Brilliant!

Some Ford engines have a different firing order for their 'Fours'. 1-2-4-3 instead of  1-3-4-2 That would mess it up again.

Subura and VW flat fours differ in this respect too. One broken inlet valve spring could stop any intake happening at all on a single carb manifold.

On my bikes, a two into one (Siamese system) gave the best result for a single carburetor. Twin exhaust was better for twin carbs. Then balance pipes were fitted both sides, so it was really a long learning curve.

Megaphones and the term 'On Song' come to mind. Lovely until I went deaf!

[Wagger]

8 minutes ago, Pete Lewis said:

Ha  Om Back,   no expert on this but stick to the triumph basics well tried and tested 

as soon as you dive into must have mods expect the headaches to start

I have  hate of KN and you choose how to get the fueling right ( never) to match the loss of intake vacuum 

tubulars are as said just noisy compared to a cast manifold  and make more under bonnet temperatures you dont need 

best well left alone and juts have a happy drive with what you have , without a dyno to measure whats going on you can spend ££££ and get just a headache 

Pete

Welcome back PeteL.

I remember seeing a 3.8 Jag 'E' type at Brighton Speed Trials in 1966. (The Philbee Jag). Six carb intakes and six exhausts of equal length exitting to the left side. Phenomenal noise (no silencers) approaching 6000 rpm and completing the standing start kilometre in about 23 secs. Those were the days.

[MJH2454]

3 hours ago, Pete Lewis said:

Ha  Om Back,   no expert on this but stick to the triumph basics well tried and tested 

as soon as you dive into must have mods expect the headaches to start

I have  hate of KN and you choose how to get the fueling right ( never) to match the loss of intake vacuum 

tubulars are as said just noisy compared to a cast manifold  and make more under bonnet temperatures you dont need 

best well left alone and juts have a happy drive with what you have , without a dyno to measure whats going on you can spend ££££ and get just a headache 

Pete

Think this is about the best advice to receive and act on, sort of where I was going but nice to have wise words in confirmation.

[ahebron]

17 hours ago, Pete Lewis said:

Ha  Om Back,   no expert on this but stick to the triumph basics well tried and tested 

as soon as you dive into must have mods expect the headaches to start

I have  hate of KN and you choose how to get the fueling right ( never) to match the loss of intake vacuum 

tubulars are as said just noisy compared to a cast manifold  and make more under bonnet temperatures you dont need 

best well left alone and juts have a happy drive with what you have , without a dyno to measure whats going on you can spend ££££ and get just a headache 

Pete

With you on this on Pete especially the K&Ns or their ilk.
I do not know how a filter of a certain size can get more air through without bigger holes, bigger holes means bigger dirt.
The number of cars with K&N filters stuffed into an engine bay with no coldair box staggers me and the owners proudly show them off as power mods.
Hockey stick exhaust manifolds I am curious about though. 
I assume they are mainly like that for space reasons as I cannot see them extracting gases efficiently.
But I might be very wrong

Edited May 22, 2023 by ahebron

[JohnD]

"Hockey stick"?  Like this 

See my post above.

John

[PeteH]

Anyone out there old enough to remember the Ford 6`s of the 1950`s? the Exhaust was litterally nothing more in effect, than a pipe with holes bolted to the side of the block into which all 6 pot`s exhausted?.

Pete.

[JohnD]

To be honest, the Triumph version isn't much better than the Ford 'log'.

[PeteH]

8 hours ago, JohnD said:

To be honest, the Triumph version isn't much better than the Ford 'log'.

Often Refered to as a "hockey stick". :- https://www.ebay.co.uk/itm/Hockey-stick-exhaust-manifold-for-Ford-Zephyr-and-Zodiac-Mk-I-II-and-some-III-/295652198099?_ul=UK&mkcid=1&mkrid=710-53481-19255-0&campid=5338703918&toolid=20006%26customid%3Ds%3AGS%3Bgc%3ACjwKCAjwpayjBhAnEiwA-7ena42X3SHJ4Kbt9HoItdK-1FcIXVltjkJLNnaWuHnSdIQnuCeBm5TotRoCm84QAvD_BwE%3Bpt%3A1%3Bchoc%3A2&customid=s%3AGS%3Bgc%3ACjwKCAjwpayjBhAnEiwA-7ena42X3SHJ4Kbt9HoItdK-1FcIXVltjkJLNnaWuHnSdIQnuCeBm5TotRoCm84QAvD_BwE%3Bpt%3A1%3Bchoc%3A1&nma=true&si=SPuP87QfRJIfBhaD33Kt1IRr5ys%3D&orig_cvip=true&nordt=true&rt=nc&_trksid=p2047675.l2557

I had "loan" of a Zodiac Convertible, in the 60`s, while mate was seconded to the far East (RAF). It had an "Aquaplane" conversion and tripple carbs; which did actually make a noticable difference, in the "traffic light grand prix". (And was one hell of a "pulling" machine with the Ladies). Allegedly, many of the Zepher`s supplied to Plod at the time where so converted?.

Back when, we got more improvement by "gas flowing" inlet manifolds, and rarely got too bothered with exhaust.

Pete