Extractor manifolds

[simonjrwinter]

I'm looking to buy a stainless extractor manifold to compliment my head tweak.

I don't need anything tooooo radical, and I'd like to retain the rest of the two pipe/single box standard type stainless system I already have as well as the throttle linkage.

Any recommendations/pictures?

Thanks

Simon

[Richard Crawley]

Simon

The Phoenix manifold is one of the best you can get. I have one & run it through a standard SS rear box, mainly because I wanted to retain the original 6 sound; you do sacrifice a little of the power though!

 

When you order you manifold, you also need to order a ‘Y’ adaptor, this splits the single pipe back into 2 & picks up on the 1st set of double pipes so fits the standard system.

[lee]

Don't Phoenix make two types?

 

One being 6-2-1? which I think is the one to have......or should that be 6-3-1 ?

[Tom Fremont]

I've got the type which consists of (2) 3-into1 pipes which then nest together, either going thence into the stock dual pipe exhaust or, as in my case, into a "Y" which feeds a large bore single pipe exhaust.

 

In Simon's case, perhaps a 6-into-1 is better so as to tie all ports together ( if briefly ) to effect the famous 6-pulse extractor behavior recommended by experts.

 

One thing to consider is the space requirements; removal/refitting of the starter on my TR250 was barely possible with my version. Other systems are known to make it impossible altogether

[john.r.davies]

6-to-1 only works at unfeasibly high revs for a six cylinder - without steel everything.

6-3-1 most effective

6-2-1 NBG.

 

Just MHO.

 

JOhn

[JohnC]

Has anyone done any comparative dyno tests on the various manifolds? There's certainly a weight of opinion on this forum that the 6:3:1 is the best, but I've seen no data. I'd be interested in how much better it is than the standard and vs the 6:2. There's also the issue of what cam you're running vs the exhaust setup, not to mention the fuelling.

 

For Simon's situation, i.e. wanting to retain the twin system back from the manifold, a 6:2 may be the best compromise. When I fitted one 15 years ago, it seemed to me that there was a noticeable improvement over the standard manifold, but then I would think that, wouldn't I?

 

Having said that, I'd view choosing the manifold based on the rest of the system as the tail wagging the dog!

 

FWIW, I have the same exhaust system as Tom (as far as I can tell): Two separate 3:1 manifolds feeding a Y piece into a 2.5" single pipe with a transverse straight-through silencer. Access to the starter is, as Tom says, very tight. I've never tried to remove the starter, but access to the electrical connections is bad enough! On the performance front, I don't pretend to have a well-tuned engine, as it has a hot cam in an unmodified head, and the PI setup is definitely not right yet. Even so at the last dyno test it was putting out 114bhp and 131lb.ft at the rear wheels. The sound on the other hand is glorious

 

John

[Roger H]

The 6/3/1 has been found to be the best for all but the highest revving race engines. Many custom-made systems which are built to achieve the best results have to be modified to be commercially viable for manufacturers. The modifications reduce the performance from the ideal butt allow mass production and installation across a range of models using the same engine bur with different engine bay layouts.

 

I spoke to Simon (the MD) of the Phoenix Exhausts on this very matter. http://www.phoenixexhausts.co.uk

They had their 6/3/1 manifold dyno tested in Germany and it gives a 'bolt on' 13bhp extra. The thing is, that their design is NOT the most efficient you can get (it has unequal primaries), but is commercially the best (for them and most of us!). They were faced with pressure to provide a system that would suit a range of Triumphs and some comprimises were necessary. Even so, their system is hailed by many as being one of the best around. A custom made set would give better results, but is big $$$.

 

Unless you are in the seriously high rev range all the time, our straight sixes benefit most from an 'interference' type manifold which scavenges gases from the exhaust stoke even when inlet mixture is starting to enter the cylinder. There is a magic length for the primary pipes when fabricating a manifold (20", with the first 3" straight). This length is determined by the wave pattern so that when exhaust pulses from cylinders (firing 180° apart) the end of one pulse co-incides with the beginning of the next and so on. The shock wave of the exhaust pulse creates a negative pressure (rarefaction/suction) behind it, which assists the following pulse along...etc etc. Unfortunately limited space in the engine bay makes it tricky (but not impossible) to do.

 

Bottom line is, that if you look at a commercially produced manifold for street and occasinal track use, ensure that A: it is a 6/3/1 and B: that they are connecting 1/6, 2/5 and 3/4 ports and C: try to get the primary pipes are as equal in length as you can get.

 

Many (seemingly US based) aftermarket 'twin' systems are 6 into 2 at the manifold. They separate the exhaust pulses into two parallel streams and do not allow for any resonance which creates the desired 'suction' effect. This is the reason for a drop in power. Two branches of three combining into two does not work as the firing sequence in a straight six does not promote continuous flow.

 

The TR's factory twin system was used in conjunction with a cast iron manifold which had a resonant cavity just above the flange. This cavity allowed the exhaust pulses to interact to form a more continuous stream of gas (a short 'header' of sorts). There is nothing wrong with a twin system, so long as there is a chance to combine the pulses into a continuous single flow before the gases are then split into two. (My twin system with standard factory cast iron manifold gave 119hp (SAE corrected) at the rear wheels).

[Guest andythompson]

Roger has pretty much summed it up...

 

The worst POSSIBLE set up (apologies to those who might have it) is a 6-2-2 extractor with the standard exhaust and no link pipe. Standard would be far preferable.

 

Don't get confused by the terminology , just make sure the pipes join like in the photo

[Red 6]

Perhaps i can contribute to Simons enquiry.

 

Recently i swapped a tubular manifold (moss type) connected to twin pipes and twin boxes, which had performed well for 10 years or so on my uprated 250. The sound was the traditional twin box cackle.

 

I upgraded to a phoenix "big bore" 6/3/1 system and the results were a substantial improvement in mid range power delivery, the cackle was gone thank god and a pleasing thrumble appeared in its place. When driving the car is almost silent except when the foot is planted when it sounds las a big British sports car should.

 

Other benefits are that ther whole system locates by a single strap as it exits the car and the manifold slips into place without hitting anything which means installation is a doddle. Oh yes and it does not knock on the chassis.

 

I am very pleased with it.

 

I also have several other race/pulse type manifolds with different length primaries which i used on my 6 race car. As Roger mentioned when your engine revs to to 8k you need to optimise the manifold to those conditions and in general those manifolds tend to be push fit and leak gas like billieo! (so you can get them off quickly)

 

Simon if you would like to see apicture of the phoenix manifold in place i will be happy to send you one

 

Tom.

[lee]

Just checked and I do have the 6-3-1 phoenix. After running it for a couple of years with the Y piece into twin sports exhaust I changed to the single Phoenix pipe all the way through........Sounds awesome.

 

However I did notice that when I originally offered the Manifold up to the Head whilst on the bench that the port entries on the manifold were not particularly clean and smooth.... there was a certain overlap on the flanges.

 

By the way if anyone wants a redundant sports system with Y piece it's yours for a drink.

 

lee

[rob wilsher]

As the topic of exhaust manifolds have come up I'd like to mention a recent MOT observation/query on my car.

 

The MOT guy noticed that the Y piece was not clamped or welded to the single big bore pipe which leads to the box. It just rested in place with plenty of overlap. The pipe was not cut so I guess a clamp wouldn't have worked anyway. He thought it was odd but passed it anyway. He did mention however that if it did catch and dislodge then pole-vaulting could be quite hairy.

 

Maybe the joint should be telescopic but I doubt it. Any thoughts????

 

Rob

[Richard Crawley]

Hi Rob,

 

At the risk of stating the obvious - why not cut and clamp ? Maybe someone forgot to do that in the past ?

 

Cheers,

 

Alec

 

I'd agree; I would certainly be unhappy with a road system that didn't have clamps fitted.

 

 

PS. Alec, you seem to be a late bird rather like me!

[Roger H]

This is a response to a post by Tom on Stephane's thread (TR6 from France) which I felt maybe better dealt with here.

 

QUOTE: "Looks like the 2x ( 3-into-1 ) exhaust manifold going into a dual outlet system"

 

Tom - from what is visible in his picture, I believe that Stephane's manifold is actually a 6 into 1 (race) type. I had one of these from Racetorations UK which had long primaries. Strictly speaking, 2 sets of 3 pipes did gather into two, but immediately then combined into a single pipe collector (only an inch between the two for fitting clamps). This is done for a couple of reasons, firstly for ease of manufacture, and secondly for some flexibilty in the fitting. I suspect that Stephane's system is actually a 6/1 which then splits into two pipes for twin mufflers. The undesireable 6/2/1 which was mentioned in this thread has shorter primaries, approximately half the length of Stephane's, which combine into two pipes of similar length to the primary pipes. These then rake back and either feed two separate pipes to twin rear mufflers, or combine into a single pipe under that starter motor. It is this type of system which is worse than the original factory cast-iron manifold. Unfortunately I do not have a picture to post but if one comes to hand I will do so. I will query Stephane on his thread as to the system he has.

[Tom Fremont]

Strictly speaking, 2 sets of 3 pipes did gather into two, but immediately then combined into a single pipe collector (only an inch between the two for fitting clamps).

 

This sounds like what I've got ( from Racetorations ) - your post is somewhat reassuring as I can't imagine them supplying anything horrible considering their reputation. My system's two manifold pipes sit one atop the other, and yes, mine employs a short "Y" to combine into a single large bore exhaust. This style does allow clamping of all joints, a feature not evident in the type depicted in Andy Thompson's photo above.

 

Further to Jean's concern about proximity to the starter ( featured elsewhere ) I did have mine ceramic coated, which is claimed to reduce heat transfer considerably.

[JohnC]

I'm particularly interested in the discussion of the 'NBG', 'undesirable' version of the 6:2:1 manifold, as I'm pretty sure that's what I have. The collector boxes (if that's the correct term) are about half way down the vertical section of the primaries in Stephane's pic. I think it's a Triumphtune TT1200, but I could be wrong.

 

Anyway, I still have the original (cast iron) manifold and downpipes, and I have toyed with the idea of swapping back, hence my question about whether anyone has any reasonably quantified comparative data. Next on my tuning agenda is another dyno session to see what effect my latest PI tweaks have had, but after that I may do the swap just for giggles & test again (yes I know my PI tune will be out again). If anyone has already done this it would save me the effort. Frankly it's barely worth swapping if it's only going to make a couple of bhp difference either way.

 

I know the 6:3:1 has an excellent reputation, but it ain't free, and my NBG/undesirable 6:2:1 and cast iron versions are. Hence my beast doesn't have a shiny new manifold in its immediate future. Hopefully it will end up with the best of a bad lot, rather than the worst!

 

So, does anyone have any data?

 

Cheers,

John

[Guest andythompson]

The system I posted a photo of is an old Mike Randall system (Mike the Pipe) which was effectively a race system (hence slip joints) and made back in the eighties when Gareth Thomas and co. were spouting the virtues of the configuration whilst the mainstream suppliers (Moss/ Triumphtune) all sold versions of what was originally the SAH 6-2-1.

 

John C.. if your 6-2-1 has the collector into 1 then back into twin it will be giving better top end power than a standard manifold thanks to a less restricted exhaust port but unfortunately the interference issue in the midrange doesn't help torque.. this issue gets worse as the cam duration increases so modified engines can really suffer in the 3000 -4500 band..

 

The works had a lot of problems particularly tuning the rally 2000's because they stuck with a cast iron 6-2-2 set up and found they lost a lot of torque with long duration cams... if you study some early SAH cam profiles they are all lift and bugger all duration....if only they knew.... The 6-3-1 manifold really helps torque with a long duration cam

 

I helped build the engine in Jimmy Elliotts (CSCC) Mk1 2.5 PI before I knew some of these secrets. It has a 357 SAH cam and the 6-2-1 and the hole of torque feels like "turbo lag" until it "comes on cam" at about 4300 revs

 

This surge of torque and hence steep rise in BHP at these revs make you think it has a really wild cam but infact running 6-3-1 manifold in an otherwise similar spec car gives a lovely smooth progressive increase in power... the idle is still a little lumpy but you have no real gaps in the torque curve..It can actually 'feel' slower but is in fact far more flexible and suited to the torque characteristics of the long stroke 2.5

[rob wilsher]

Additional thought on Rob's exhaust.

 

A couple of years back I came up with a chap who had a 2.5PI engined TVR, and the new fancy exhaust system rattled, banged and resonated. Hence he'd unclamped the manifold to main pipe joint, which reduced the problem considerably. My thought was to insert a section of the flexible 'concertina' type pipe as on my Rover 800 frontpipe. A scrapyard provided the necessary, hacksawed off for a couple of quid. End of problem, the system just needed a bit of flexibility, not surprising when you looked at the movement on the engine mounts !!

 

Most exhaust manufacturers have a modest choice of 'off the shelf' sections for custom installations, which doubtless includes lengths of flexi pipe. I've usually found an answer in the Bosal catalogue.

 

Cheers,

 

Alec

 

Alec, thanks for this info.

 

I think some ammount of flexibility between anything fixed at front and rear of a car is sensible. I remember my first 6 was very unpleasant to drive until I discovered that the sliding spline on the propshaft had seized solid. What a difference that made when it was freed and greased.

 

Thanks

 

Rob

[Roger H]

which is claimed to reduce heat transfer considerably.

 

Tom, the proof of the pudding..... ....I had mine coated as they were made from mild steel - I don't know what they used: they would not let me into the factory!! - all I know is that I can touch the manifold (albeit briefly) after a good thrashing.