exhaust headers

[bengalcharlie]

hi,

I have been looking through the archives to find some info about headers and the overall consensus seems to be that you can improve on the original system.
I do not pretend to know much about exhaust systems, but I do know that bigger is not always better.
the mean reason that big bore exhausts not always produce good results has to do with the gas flow speed.
if the pipe bore is too big, the gas flow speed will drop and as a result the vacium created in the cylinder drawing in a fresh air/fuel misture won't be enough to fill the cylinder to an optimal level.
so my question is what is the ideal header for a standard/mildly tuned stromberg engine?
If someone could also advice me what the ideal lenght of the primary and secondary pipes are? Am I right to assume that the longer these pipes are you lose low end torque but gain high end power???
does anyone have experience with the system sold by Ray from Rdent.com?
It looks good but the pipe diameters are standard.
cheers
Robin

[GrUmPyBoDgEr]

Hi Robin,

you've placed some concise & specific questions but I think that knowledge on the tuning of Stromberg engines will be limited to only a few members.
It may pay you to ask QED those questions, they do know Stromberg as well as Weber engines.
Other tuners will probably be more specialised in only Weber competition engines.
Considering you are so far from GB, QED may well offer you answers to your questions without pressurizing you into buying their parts.
More broadly speaking, the dimensions for a Weber engined manifold should be more than usable for a Stromberg engine, after all the firing order is the same.

Now if you wanted info' about the manifold dimensions for a 2 liter Zetec I could have given you the answers you need now

Good luck
john

[mikealdren]

Robin,
You've raised a few points and it's a complicated topic but to start things off:
The exhaust size shouldn't make too much difference to the intake. As long as the exhaust stroke has scavenged well enough, the cylinder should be empty and apart from a bit of overlap, the exhaust valves will be shut during the intake stroke.

The usual aim is to keep the pipes the same length and this is more important for smooth running than that actual length. After this, avoid sharp bends and any abrupt changes of diameter (e.g. match the pipe to the head). On the intake, you want some turbulence to give a good mix, on the exhaust you want a smooth (laminar) flow for optimum gas flow.

I wouldn't have thought that too large a bore would be a problem, in fact I would expect that straight venting to the outside world with no exhaust pipe would give excellent results and this would be an infinite diameter.

For manufacturers, there are issues of tuning pipe lengths and size to avoid resonances at different flows for both noise and performance. Then there is the issue of the optimum points for hanging the pipes, try to hang from the vibration nodes which move with frequency!

Ok, more input from those with more experience than me!
Mike

[jrwiseman]

Hi Robin

I have the header available from Ray. I do not have any dyno numbers associated with
the before and after, but I can tell you that the difference between the original cast exhaust
manifold and the very small diameter exhaust that was on the car originally, and the
header and a 2 inch diameter exhaust with a supertrapp at the end is considerable

I also used some of DEI's header wrap to help keep temperature somewhat under control
which made a huge difference in under bonnet temps.

Installing the header was painful. In the end I had to relieve the frame a bit to get
the header to fit in. This was on an S2 with Weber head. Once on the car however, I have had no issues
with it and Ray is always great to deal with.

Overall a good improvement performance wise. I believe Dave Bean has/had a header
that will go in without frame clearancing if that is critical to you.

take care
John

[collins_dan]

I have always used Ray's header on my Cosworth L2 cammed stromberg S4, so can't provide a comparison. I can say that everything runs smoothly, but these headers are a real challenge to remove. I was planning to have them ceramic coated to reduce the engine compartment/driver's footwell temperatures, but it would have involved releasing both engine mounts, removing carbs and a lot of gymnastics with the engine, so have opted to hold on that project. Dan

[Galwaylotus]

Both tube diameter and length are important for achieving the correct gas flow. As was stated earlier to get the best out of an engine you need to get the proper flow through the head and this includes the scavenging effect. Intake and exhaust must be considered as part of one system. Making changes on one side affects the other. David Vizard has done a lot of work on this. In addition, Keith Calver has written quite a bit on how it affects the BMC A-series engine as in a Mini. Too large a diameter slows down the exhaust gases and has a negative effect on scavenging and the overall flow through the engine. I'm afraid that while I understand the concepts involved, I've never done the calculations so I defer to those who have (see above).

[ceejay]

Exhaust headers, a very complex subject when you get into it.

Having decided to replace (Fabricating a new systems) the old
system thats been on my twin cam for the past 27 years, there
is considerable amount of new technology available now to read
& learn about the subject.

The subject covers sequential and non sequential arrangement
of pipes which affects the timing of the pulses and the effects
on scavenging.

Primary & secondary pipe length & the tube diameter has quite
a bearing on where max torque will develop in the rev range.

There are discussions about the effects of reversion of exhaust gas flow,
(A brief moment where exhaust gas is sucked back into the cylinder)

Merge collectors for the primary and secondary pipes can have
quite an influence on the performance of the whole system.

The links below make for interesting reading on the subject of
exhaust header design, the ford focus link is a particularly good read.

http://www.focusfanatics.com/forum/show ... hp?t=93157

http://tom.marshall.tripod.com/exhaust.html

But when it's all said and done, installing headers on a road
going engine will certainly help the performance, but you cant expect to
gain the results that you would expect of a custom design header
system for a full race engine.

[bengalcharlie]

Many thanks for all your valuable advice and articles about this subject.
based on the information provided and my use of my elan plus two as a road car I have decided to order the headers form Rdent.com. They look good, have sligtly larger bores than standard and I am confident it will do the trick. Thank you Dan and John for sharing your experiences with Ray's header system. suppose you can say that unless you develop a system on a performance test bed you will never now whcih system is optimum for your engine.
I will try to give a further update once the headers are on the car if some of you are interested?
Cheers
Robin

[Tahoe]

Installing the header was painful. In the end I had to relieve the frame a bit to get
the header to fit in. This was on an S2 with Weber head. Once on the car however, I have had no issues
with it and Ray is always great to deal with.

Do you think this is still an issue with the Spyder frame with the removable cross member? I'm trying to decide between Ray's header and Dave Beans header at the momment. Dave Beans is SS, more expensive, but with a little larger bore with a slip fit to a 2 inch exahaust.

,Russ

[GrUmPyBoDgEr]

Installing the header was painful. In the end I had to relieve the frame a bit to get
the header to fit in. This was on an S2 with Weber head. Once on the car however, I have had no issues
with it and Ray is always great to deal with.

Do you think this is still an issue with the Spyder frame with the removable cross member? I'm trying to decide between Ray's header and Dave Beans header at the momment. Dave Beans is SS, more expensive, but with a little larger bore with a slip fit to a 2 inch exahaust.

,Russ

One of the benefits of the Spyder tubular frame is that it offers more space between the engine & frame than the original Lotus frame.
This will permit a much "fatter" manifold to be fitted.
The removable cross member may help things but I think that the engine mount is the biggest obstacle when fitting any make of manifold.
Quite often it is necessary to support the engine in some way & remove the engine mount completely to facilitate fitting of the manifold.

Cheers
John

[Jeff@Jae]

Headers for the Twin Cam is quite a subject for discussion but there are a few things I've learned.
Header primary size, the best for road cars is a 1.5" OD primary and if you'll remember that was the standard on the MK1 Lotus Cortinas. They had excellent road manners with a very nice powerband and they are quite a bit heavier than an Elan. They were also listed as having 108HP versus the Elan and 105HP in some publications. The more the engine is modified the greater that difference will be. The usual 1-3/8" primary size found on Elan headers sold is OK but not a very big difference, if at all, over the twin outlet cast iron S/E type exhaust manifold. Of course anything is better than the early single outlet cast iron manifold of S1/S2 type.
Design. For anything but an all out race car a 4 into 2 into 1 has the very best results in scavange of the exhaust and a wider power band. Equal length is nice but secondary to primary pipe size and the 4-2-1 design. Close is good enough in terms of equal length. A well designed header will make the car fell like it has a lighter flywheel in terms of engine response.
I prefer mild steel headers with a ceramic heat barrier coating inside and out over a stainless steel version for heat radiation issues and overall appearance.

[rgh0]

Have a look at the Burns Stainless site technical section for a lot of good information on header design and fabrication.

http://www.burnsstainless.com/techarticles.aspx

cheers
Rohan

[Galwaylotus]

Headers for the Twin Cam is quite a subject for discussion but there are a few things I've learned.
Header primary size, the best for road cars is a 1.5" OD primary and if you'll remember that was the standard on the MK1 Lotus Cortinas. They had excellent road manners with a very nice powerband and they are quite a bit heavier than an Elan. They were also listed as having 108HP versus the Elan and 105HP in some publications. The more the engine is modified the greater that difference will be. The usual 1-3/8" primary size found on Elan headers sold is OK but not a very big difference, if at all, over the twin outlet cast iron S/E type exhaust manifold. Of course anything is better than the early single outlet cast iron manifold of S1/S2 type.
Design. For anything but an all out race car a 4 into 2 into 1 has the very best results in scavange of the exhaust and a wider power band. Equal length is nice but secondary to primary pipe size and the 4-2-1 design. Close is good enough in terms of equal length. A well designed header will make the car fell like it has a lighter flywheel in terms of engine response.
I prefer mild steel headers with a ceramic heat barrier coating inside and out over a stainless steel version for heat radiation issues and overall appearance.

That's a 19% difference in cross-sectional area.

[john.p.clegg]

"the best for road cars is a 1.5" OD primary"

Hate to be pedantic here but is this supposed to be ID,if not,what about the header wall thickness?

John

[Galwaylotus]

"the best for road cars is a 1.5" OD primary"

Hate to be pedantic here but is this supposed to be ID,if not,what about the header wall thickness?

John

Good point. Missed that the first time around.
I assume he meant I.D. as the O.D. would be meaningless except for fit considerations.