Exhaust Manifolds for Twin Cam

[jbcollier]

Now that's a very nicely designed system fro the street.  Well worth the price.

[literarymadness]

Here is a good article of equal vs unequal length headers and 4:1 vs 4:2:1 merge collectors.  It is written about a Subaru but the principles are the same.

https://www.comeanddriveit.com/engine/equal-vs-unequal-length-exhaust-manifolds

[4173R]

Thanks for the info Glen.

I will contact them.

[BDA]

'madness got me thinking about design theory for headers. I remember reading a book about it when I was racing and in engineering school. A brief look at the article he pointed to seemed like it might be geared for turbos or even Subaru flat engines. I say that because I remember that one of the design goals was to match the low pressure of the pulse from one runner to help scavenge the exhaust gasses in another runner. This is one reason why headers are designed for an rpm range and on a straight four, that would require equal length primary runners. V and flat motors are more complicated because the low pressure in one primary tube that is needed to help scavenge the exhaust gasses of another primary tube (or combustion chamber) could be on the other side of the motor which would require one or more primary runners on one side of the motor to connect to runners on the other side! Of course this is not only dependent on motor configuration (flat or V) but also the firing order which depends on the crank for an engine with a dizzy ignition. Before I get any further past my real understanding, I found this article that explains some of this (https://www.onallcylinders.com/2015/10/30/header-theory-part-1-looking-at-the-science-behind-exhaust-header-tuning/ and https://www.onallcylinders.com/2015/11/27/header-theory-part-2-tuning-header-collectors-for-optimum-performance/). These would probably interesting reading for someone more interested what goes into header design.

[literarymadness]

Both articles agreed that it is best to get as close to equal length as possible.  I have r.d. headers currently (actually pfreen's old headers) But now I am reconsidering getting one's that are equal length.

[Pfreen]

Kelvedon (https://kelvedonlotus.co.uk/ )in England also sells headers.  I don’t know anything about them.  They cost £446.  I have bought parts from them with no problems.

[jbcollier]

If you are interested in this topic may I suggest you read the bibles:

Scientific Design of Exhaust and Intake Systems
Philip H Smith

Four-Stroke Performance Tuning
A Graham Bell

From recent yahoo/io posts:

4-1 systems are very effective over a relatively narrow range.  They also have a strong “anti-tuned” frequency which causes “reversion”.  This works well in a highly tuned engine where the cam is also tuned to a similar range — though it makes for a “peaky" engine.

4-2-1 systems do not give as large a hit at the tuned rpm but they provide a significantly broader effective rpm range and suffer much less from reversion.

Again, all from dim memory.

Right now I’m struggling with reversion (also known as megaphone-itus) on one of my bikes.  I have a beautiful pipe with a 2° taper that works very, very well.  Hardly any reversion and great power.  Unfortunately, the exhaust volume is so low that it is noisy, very noisy.  How does a 140+ db at full chat sound?  Glorious but setting off car alarms is the norm not the exception.  I also have a 4° tapered pipe with the same top end and much, much quieter due to the larger volume.  But it has a simply massive hole a few thousand rpm below peak — like shut it off and park it massive.

All that is why I was very careful when I built my Europa’s exhaust.  I use a Banks 4-1, yes, but I situated the muffler sideways for a longer main pipe and, so I can fit a very large, though still free-flow, muffler.  Add a relatively unrestricted short super-trapp as an outlet, and my exhaust is both free-flowing and quiet.  I also deliberately did not match the tuned frequencies of the header and the cam.  This broadens the power band significantly.  I have a really fat mid-range (mostly cam) with a nice top rpm hit at 6000 (mostly pipe).  Ultimate hp is modest compared to theoretical but it makes for a great street engine.

-----

If you are interested in engine tuning I also recommend Cycle World’s Kevin Cameron.  His columns are collected in "Top Dead Center" vol 1 and 2.  Even more fascinating is his book “Classic Motorcycle Race Engines”.  It covers the history of engine design at the same time as you examine in detail race engines from the 20s on up.  Every wonder why engines originally had such long strokes?  Why some engines have twin spark plugs?  What are the advantages and disadvantages of forged and cast pistons?  It’s all there in a detailed but easy to read style.

[Fotog]

I have R&D headers currently (actually pfreen's old headers) But now I am reconsidering getting one's that are equal length.

For what it's worth, I think that's "R.D.", as in "Raymond D." Psulkowski, proprietor of RD Enterprises, rather than R&D.

[literarymadness]

I stand corrected.  I should know better because I certainly have accumulated enough r.d. enterprises, ltd invoices over the last few years (plus phone calls).  Oh well!

[TheKid#9]

Hey guys,

Well my cast iron manifold has a small crack in it and I think its time to get a new header system. I like the stainless steel that SJ has but shipping it over here compared to Rays Mild Steel header system has me thinking, is it really worth it? Any of you guys have a used one laying around?

I will purchase one of the two above soon, just not sure which one but I am leaning towards Rays because of the shipping costs.
Thanks,

[BDA]

Hey Kid!

First, I would check with Dave Bean to see if they have stainless headers.

As for the actual headers, my experiences may or may not directly translate to you but they may be helpful.
You should know that one stainless steel is not necessarily as stainless as another. Unfortunately, I don't know which alloy to point you to but it might be worth asking about that when you shop around.

An option you might want to be aware of is ceramic coating. It can be applied to any header and provides cooler engine compartment temperatures, corrosion resistance, and a nice look. Here is one place that does it: https://www.jet-hot.com. There are also rattle can and brush on ceramic coatings. I have no first hand knowledge about either but I don't think I would bother with a rattle can.

[TheKid#9]

Gave Dave Bean a call and they do not have SS headers anymore, just the mild steel.

[BDA]

Bummer!

That wouldn't wouldn't let shipping from England dissuade you. It's probably quicker and more economical than you expect.

As an alternate supplier, I just checked with Lotus Supplies and they have a nice setup including muffler that looks pretty reasonable (https://www.lotus-supplies.com/part-category/exhaust/twincam/page/2/). Lotus Supplies is probably best contacted by phone. I have no specific knowledge about either of these headers but looking at the pictures, it would not surprise me to find out that SJ gets theirs from Lotus Supplies. I know both companies to be reputable and I would not hesitate dealing with either of them but it may turn out that because of the Wuhan flu, you may not have a choice of supplier.

[MRN I J]

I found the Phillip Smith book very old fashioned whereas A Graham Bell updates his Four-Stroke Performance Tuning regularly, V4 has been out for 10 years now & has plenty of BTCC engine info of the early 90s whereby the engine control was 8500rpm to limit hp to around 300bhp from 2ltrs /122 CI otherwise it could have been 330/350 bhp or more.

Bell has interesting theories on exhaust primary unequal lengths & anti-reversion mismatches, the latter I have dyno tested on one & used on 50 + engines, although I knew about them from Vizard's A series engines & the guy who used to port our heads was an ex Cosworth cyl head guy, from DFVs through Sierra's & J series Opel's 
 

[jbcollier]

I do a lot of 2 stroke work.  Mild steel is easier to fabricate and less likely to crack with vibration.  It will corrode but you can ceramic coat it to help stop that.  Stainless looks super cool polished but is more likely to crack with vibration.  I dob'y mind SS for pipes but for headers with a tight curves and a lot of welds, I prefer ceramic coated mild steel.  YMMV.

In any header, I look first at the flange that mounts to the head.  It should be thick, very thick.  Next I check that it lines up with the mounting holes properly and I match the ports.  I then send it out and get the flange surface ground.  Works like a charm, no leaks.