The E-Type Forum - Produced in association with the E-Type Club

[Heuer]

After testing my car on both a rolling road and using a Road Dyno it was pretty apparent I had a huge dip in torque at about 2,500 rpm. Andrew Turvey at CMC reckoned this was due to the outlet manifolds (headers) being too wide which meant the gases were not reaching a high enough speed to exit the system cleanly. At high revs this is not a problem but below 3k rpm it most certainly is. Unfortunately this is the very part of the rev range that is used for normal motoring and also at the start of the band used for an overtaking maneuver. CMC's suggestion was to fit the standard E-Type cast manifold feeding into a big bore exhaust which would have the effect of accelerating the gases as they were squeezed out. Only downside would be a reduction in bhp at the top end. I decided to investigate further and found Classicfabs. My problem:



Based in Girvan on the Scottish west coast, Classicfabs produce manifolds to the design developed by Uryk at E-Type Fabs, makers of the ultimate E-Type frames. Uryk spent a great deal of time and research on a new type of manifold but unfortunately as production started his machinist had a heart attack and he was unable to continue production. Classicfabs bought the designs and tooling. I met with Ian Stewart who makes the manifolds, pipes and silencers using some pretty special equipment including a CNC mandrel tube bender. The concept was to have a manifold with no visible welds, to improve the transfer of exhaust gases to produce more power and eliminate the torque dip exhibited by all the current big bore systems. We booked into the local Wildings hotel and restaurant on Ian's recommendation - good accommodation and superb food.

I turned up at Classicfabs the following morning having already ordered a full manifold. I decided to visit Classicfabs for a number of reasons apart from wanting to see how the manifolds were made. My plan was to keep my existing plain steel exhaust for the moment and run the new manifolds into it. This meant Ian had to do some cutting and fitting to the old system in a way that would let me install their full stainless exhaust system when I was ready without further modification. Installation of the manifolds is also a two man job and does require access to some garage equipment. It involves removing the old manifolds, the alternator, alternator bracket, engine mount and mount bracket, loosening the other engine mount and stabiliser. This allows the engine to be tilted slightly to allow the new manifolds to clear the torsion bar. They went in relatively painlessly and whilst I was putting the car back together Ian started work on modifying my existing silencers to accept the manifolds. With hindsight I should have ordered the entire system as it is beautifully made. You can also have a choice of removable venturis. Leave them out, fit the standard venturis for greater back pressure or the 'Swiss' venturis designed to run quieter (mandatory for Switzerland it seems). Ian also took me through the production process demonstrating each machine. To give you an idea, the three into one collector cup at the bottom of the manifold each take two hours to produce, such is the attention to detail:

Computer controlled mandrel pipe bending machine in background:



Here is an example of another vendors manifold. Spot the welding?




My old manifolds were of a similar design in plain steel:



Here is the Classicfabs manifold - no visible weld, thinner pipes:



The art does not stop at the manifold, here are their E-Type resonators:



All systems are fitted up on their in house 'jig' - an E-Type engine - to ensure proper fit and maximum ground clearance. Serpentine seems the appropriate word:



On my car:



After completing the install it was off for a blast around the deserted Scottish roads and boy has it made a difference. There is smooth power delivery right through the rev range with no apparent dip in torque and the sound is fantastic. I asked Ian what made his manifolds different in terms of performance. His analogy was "try blowing up a balloon through a two inch pipe!". All the others go for the 'big bore manifold' approach whereas the truth is - small is beautiful.

Classicfabs make short and long manifolds to order as well as supplying their complete polished stainless steel systems. Normally they do not get involved in fitting (I paid for Ian's time and assistance). Classicfabs will be exhibiting at the Goodwood XK60 event if you want a closer look. Highly recommended. http://www.classicfabs.co.uk/

I will post a Road Dyno graph tomorrow as given we have just driven 300 miles back I think both we and the car deserve a rest, a beer and a curry.

[Car-Nut]

David,

An interesting article they certainly look better than what you have taken off and obviously you are please with the new performance....

Do you ever stop spending on your E youve just had new wheels

[Heuer]

Clive

Work in progress! Had this site been around nine years ago I would have been able to get straight to the good bits without going through the learning curve. My pain is your gain. Will add the manifold picture to my sig.

[MarkE]

They are works of art. David. How on earth do they do welding like that?!

Now, remember what CMC said...S/S manifolds have to be wrapped or you'll burn the paint on the bonnet

How could you cover those up?

Mark

[Heuer]

Mark

The pipes are formed into the oblong shape an a special machine. They are passed through the flange and tack welded on the inside. The flanges are then put on a planishing machine to dress the weld. The clever bit is the flanges have a groove around the pipe which is then filled with weld and dressed. All welding is done on the inside of the flange with nitrogen extraction technology to ensure there are no failures and weld does not go any further than desired.

The pipes do not stay shiny very long as stainless steel discolors with heat. Ideally they turn a sort of bronze colour but you have to be careful not to rev the engine when cold otherwise they will 'blue'. Not a problem in terms of performance but the look may not be to everyones liking. There is no real way of removing the blueing short of proper machine polishing so covering them up with DEI exhaust wrap is no great loss. Also the exhaust wrap should increase gas temperature helping extraction.

After 300 miles of hard driving, engine cold:



For some reason the two front pipes have 'blued' whilst the others have 'bronzed' suggesting they are running hotter than the other four. Need to check on that - maybe the mixture on the front carb.

I made up my own shield to protect the frame as the paint was bubbling with my old manifold. I suggested to Ian he might like to offer a ready made plate with his manifolds. He already provides a heat reflection plate to protect the alternator as you can see. A revised dipstick bracket is also included.

[Heuer]

Just did a quick Road Dyno run in less than ideal conditions - too much traffic, everyone seems to have left work early. I will do another run later this evening when it is quieter and cooler (to get a fair comparison of the first run).

Run with big bore manifold:



Run with Classicfabs manifold:



It is fairly obvious the torque dip has reduced and, more importantly, now happens earlier - 255lb/ft @ 2,200 rpm compared with 245lb/ft @ 2,600 rpm. The horsepower curve is also more linear and I have in excess of 255lb/ft from 1,500rpm up to 5,400rpm peaking with 350lb/ft @ 3200 rpm. Differences on the dyno may seem small but on the road the change is quite dramatic. As a benchmark my Porsche 993 Carrera2 Varioram produces a peak of 251lb/ft @ 5,000rpm.

In summary

a) Big bore manifolds will work wonders on a race car where revs are maintained above 3k. Performance will be compromised below that especially under normal road conditions.

b) For an unmodified XK engine standard E-Type manifolds coupled with a big bore exhaust will give the best balance of power, tractability and sound.

c) On modified XK engines (aka 'fast road' spec - gas flowed, bigger valves, high lift cam) the Classicfabs manifold will give excellent and balanced performance. Recommendation confirmed.

Edit: After several more runs the results were very much consistent with the above graph each time.

[Car-Nut]

[Heuer]

Ian Stewart has contacted me to say he has developed a new rectangular section pipe to go between the silencer and the resonator. One problem with big bore exhausts is the reduction in ground clearance as the pipe curves under the IRS. Becomes quite a problem if you have two people, luggage and an uneven road or speed bump even in a otherwise standard car. With settled suspension and lower profile tyres the situation is exacerbated. I suggested to Ian he might want to think about making the pipe flatter or rectangular in section and despite the manufacturing problems he has found a solution. The trick is not to compromise the cross sectional area which would impact gas flow. Ian reckons his new design improves ground clearance by 20mm. Here is a picture of the mock up:


The flat to round adapter:


Also here are examples of the optional venturis that can be fitted to the manifold side of the silencers. The venturi on the left can be inserted to reduce resonance in the silencer - it speeds up the gases and is the recommended standard fitment. The venturi on the right is the 'Swiss' version, named after the country with strict noise limits rather than Gruyère cheese. Although it has the same cross sectional area as the 'swamped' venturi it causes the gases to alter direction, create turbulence and improves the silencers effect significantly. The end is closed off except for a 10mm hole. Classic Fabs can supply either (or both if you want to experiment) to suit your requirements:


Obviously one type only is fitted to the manifold side of the silencers.

[Heuer]

ClassicFabs exhaust system with the 'flat' inter pipes to improve ground clearance ready for dispatch (3.8 system with the longer resonators):

Cost is approximately £750 for silencer system including fitting kit. Manifolds are extra, obviously.

[Moeregaard]

That's almost too pretty to put under the car!

[Heuer]

Just had an update from Ian Stewart at ClassicFabs on what he is working on. This is one of his systems for a Lightweight. The primaries are 41" long!



Ian will be at Stoneleigh so drop by and say hello. He is a regular visitor to the Forum so he will no doubt know most of you.

[HarryW]

You may recall Jenks' comment on exhausts "..the tell tale symptoms of hard usage were scratches and graunches along the underside of the twin central silencers, while the tail pipes under the rear suspension would be flattened." p.80 of 'Jaguar E Type' Science following function

[Heuer]

Ian Stewart of ClassicFabs has just sent me this:

"Hi David, hope your well, keep up the stern work you do, the information on the Forum is first class, The Bible ! I have enclosed a photo for you, the picture of the equipment on the table is part of an order for a racing E-Type, the bore is 2 1/4" all the way through even the tailpipes. This is the first one I have made this bore, being for a race car it does not get polished, but I think it just looks the biz. The other system is for a racing D-Type, regards Ian."

[falcon3]

I have to say that ClassicFabs exhausts do look really good.

Just re-reading the remarks of Harry W and Jenks's views on exhausts.

Page 56 of Jenks' "Jaguar E-Type" gives his views on the rear silencers "The first of these tail pipes fell off at 100 mph and skated up an Autobahn, and the other one was rusted through and ready to part company, so I threw it away and made up two straight-through pipes from the main silencers. There was no noticeable change in the exhaust note."

I still run the car with the straight-through pipes and I disagree with Jenks as I think the car sounds better this way.



Perhaps ClassicFabs would like to offer this set up as an option.

[Heuer]

Roger

They will make up anything your heart desires so if yours get damaged or fall off Ian will quickly be able to make a set to meet your needs. A lot of his stuff is bespoke.