Exhaust Manifolds

[stuarthardy]

I am approaching re-uniting the car and engine after a 20 year restoration (don't ask). Right now I am wondering whether to stick with the standard exhaust manifolds, which are unused and already fitted, or to fit a 6 branch manifold.

If a 6 branch is the favoured option then which one and what exhaust system to use? Car is a 3.8 coupe with largely standard Rob Beere built engine and SU's although I may change to Webers at some point. I'm also concerned about additional heat soak and excessive noise.

Advice appreciated.

Regards
Stuart

[piman]

Hello Stuart,

this is something I've been thinking about, but I can't say I'm impressed with the manifolds illustrated in the club magazine. One manufacturer claims quality but the variation in primary pipe length is huge, the other has very long primaries which just don't look right.
The other question I have asked on the forum if anyone knows or has tried a 6 - 3 - 1or 2 set up.
this pairing of primaries works well on the Triumph 6 cylinder engine. I understand that style is used in Australia but I've never seen it here.
Have you spoken to Rob Beere?

Unless you plan to race your car, I would stick with S.U.'s, more flexibility and equal power until high in the rev range, looks apart S.U.'s are a better carburettor for general use.

Alec

[stuarthardy]

I just dug out my copy of Des Hamill's book on tuning the XK engine and he makes some interesting observations on exhausts. Not least of which is that XK engines seem to be able to tolerate all sorts of variations of exhaust without too much ill effect. In fact, the large bore systems only seem to be effective at more than 5500 rpm.

Using Hamill's terminology, we are probably better off using tubular manifolds with 45mm (1 3/4")primary pipes and no bigger than 50mm (2") mains. There seems to be no stated preference between 6 into 1 and 6 into 2 into 1 headers other than the latter are usually easier to accommodate. Primary pipe length matching is not that critical either, within a couple of inches.

I was hoping for a flood of suggestions and opinions from people who have done this before but it seems that the excessive bulletin board down time has driven traffic away. Can anybody else see that tumbleweed gently drifting across their screen?

Regards
Stuart

[piman]

Hello Stuart,

yes it is quiet here isn't it.

I'll keep looking, but I have some time as I'm occupied with a couple of other more pressing projects.

Good luck.

Alec

[DaveK]

Alec,

When E-Type fabs were producing the 6 branch manifold and exhaust both in st. st. I bought one of each for my car. No excessive noise or heat from either the exhaust or the manifold.
Most people who know the E-Type will say that the cast manifold is very hard to improve on except for looks.
The st. st long branch manifold of course discolours very quickly and you have to be very careful on to let oil drip on them.

E-type fabs no longer produce the manifolds or exhaust they sold the business to Classic fabs who now produce exactly the same item and the workmanship is also very good.

If I had to buy another system then without doubt that is the one I would go for.
Haywood and Scot also produce a long branch manifold but the welding is hideous, looks like its been stick welded rather than TIG.

Prices are around £1200 for the long branch manifold and exhaust from Classic fabs which might focus you on which direction you might go in. I would expect Haywood and Scot to be around the same.

I originally bought a st. st sports exhaust from a very well known supplier before I even got the car on the road one of the welds split, the radius of the exit pipes were not the same and trying to fit the downpipes from the original manifold was very difficult. I have a friend who also bought the same system and had similar if not worse problems.
I won't mention the company on the website since they advertise with the JEC but if you would like to know drop me a PM.

Dave

[piman]

Hello Dave,

thanks for the reply, it's for a Mk 2 by the way but that doesn't alter the interest I have in finding a good design. I plan to fabricate my own but I'm still very interested in the branching in pairs rather than threes. As I said earlier this is common in Australia for XK engines.

Alec

[stuarthardy]

A sad endictment of progress on my project but I still haven't moved forward on this. Has anybody got any words of wisdom to add?

Stuart

[nick320]

Words of wisdom: Leave the standard manifold on, get your car back on the road, and stop dithering about !

Nick

[stuarthardy]

Thanks mate!

[nick320]

If I am allowed to mention another website, look for threads on the E-type forum, e.g.

http://etypeuk.com/forum/viewtopic.php?t=287

where exhaust options are discussed extensively.

Nick

[piman]

Hello Nick.

quite an interesting post but as I mentioned elswhere in the forum I'm amazed at the different manifolds and their huge differences in primary length. Even with the Classic fabs manifolds shown there is noticeable variation in primary length from one cylinder to the other. I'm also rather intrigued by the authors obsession with having no visible welds, as that has no bearing on manifold performance.
Although a different engine, the now accepted performance manifold for the Triumph six is to pair the primaries rather than triple them as has been conventional manifold design for sixes, with a noticeable gain in power. Apparently a common design for XK Jaguars in Australia. Philip H. Smith's book on induction and exhaust design shows another six cylinder engine (Tatra) with is style of dual primary configuration.

Alec

[stuarthardy]

Hey, some discussions at last.

Interestingly, my 6 cylinder rear-engined car has a 6-4-2 exhaust arrangement. I think firing order has quite a lot to do with configuration.

I think Dave's article is rather well put together and the classic fabs manifolds do look good. I especially like the way the manifold to head interface has shaped the pipes to match the exhaust ports, this has to help to maintain the speed of the exhaust gases at lower revs. Also means the tolerances on the construction of the manifold are tighter meaning the results are more consistent.

Not much discussion about primary lengths. I'm off to read Des Hamill's book again.

Stuart

[piman]

Hello Stuart,

"Interestingly, my 6 cylinder rear-engined car has a 6-4-2 exhaust arrangement. I think firing order has quite a lot to do with configuration."

That and physical engine configuration, it's impossible in the confines of most engine bays to run a 6-3-1 or 2, and would, in any case, give extremely long primaries.

"I especially like the way the manifold to head interface has shaped the pipes to match the exhaust ports,"

I can't imagine doing it any other way!
From Smith's book he suggests the manifold section should be about 1\8" larger than the port to reduce surface friction, but I've never seen any manifold following that theory?

Alec