Exhausts For Our Cars
By Karl Schluter (Low Zep)
So its exhaust time is it? This article is merely a
guide of what I have learnt the hard way on my own Zephyrs, Zodiac’s, in-line
6’s, V6’s and V8’s. It’s mainly to do with DIY, ie: making it yourself. The job
sounds bigger below than it really is, remember you can do it in stages. If you
pay a shop to do it, make sure they clearly understand what you expect, ask to
view cars they have done for others (ask other car people who did their
headers/extractors and exhaust systems and if you can look over their cars).
First up is consider safety, you need the car off the
ground if not on a hoist (lucky you if you have access to one!). So a good jack
and at least 4 axle stands are needed. NEVER trust a jack no matter how new,
whatever rating etc. Remember it’s your life you are playing with. I like to
remove the rear wheels if running a full exhaust so I can then use the two
wheels under each side of the car as a back up. Having a helper or someone to
check on you is handy too. Overkill? Not if you drop the car on yourself, or
get over come with welding gases. Watch welding near the fuel tank or fuel
lines, I lower the exhaust away from the car to weld these sections.
Do use correct eye protection when both welding and
when cutting or grinding pipe and wear earmuffs too.
A note at the end of the job when letting the car off
high set jack stands, do it in stages! I have had a car come off a trolley jack
once while lowering it after removing the jack stands!
If you are using a electrical type welder (mig/tig), remove or unplug any
ignition boxes or computer type instruments as a welder can spike or put a
voltage surge through these items. Some go as far as to remove the box/item
from the car completely, the choice is yours. Just unhooking the battery is not
often enough. Always connect the earth cable as close to the weld area as you
can, as this will help safe guard electronics too.
Right lets start with what you want. I don’t know of
any company currently offering complete Zephyr/Zodiac/Consul off the shelf
exhaust systems, but that doesn’t mean they are not out there. Often asking at
a club meeting/get together or on a web-site forum is one way to locate a
supplier.
If the car is running a mostly stock drive train then
a stock type exhaust system is fine. However if a bigger than stock cam,
increased carburation, a re-power or other performance modifications have been
done then a stock system may well choke the engine. One test is to install a
copper line (like an unused oil pressure gauge copper line) with a low psi
(0-10 psi or so) pressure gauge and plumb it in between the exhaust manifold
and the first muffler, closer to the latter is best. Any reading above 2-3psi
is too restrictive for a performance engine.
At the very least I suggest headers or extractors (now
referred to as headers in this article). Headers replace the stock cast iron or
hockey stick type exhaust manifold. These leak less and are a very worth while
item to aid in both performance and mpg. Capri V6 Essex powered car headers are
listed as fitting the MklV cars and are still sold
today too.
Coby is the NZ Company making and selling headers for our
cars (they supply mufflers too):
Coby Performance Exhausts
21 Euclid Avenue
Saint Andrews
Hamilton City
Waikato 3200
PO Box 10438
Te Rapa
Hamilton 3241
Phone (07) 8491765
fax (07) 8491765
Cell (021) 978208
Email orders@cobyexhausts.co.nz
Plus we have
contacts in our FAQ/part supplier’s section that may be able to help as well.
The system on the in-line 6 engine comprises of the front 3 primary pipes
leading into one collector, the rear 3 ports also leading into one collector
and then from these two collectors, two larger pipes travel down to the bell
housing area and into one final collector.
I have had in-line 6 headers which had the 3 primaries
going into a single 2” pipe that then ran the full length of the car with one
muffler on each pipe as well, the other 3 primaries running the same to the
back of the car. This does away with the lower 2 into 1 section.
If you cannot locate a set of headers, fear not, any
good shop or yourself can fabricate them. The in-line 4-6 or V6-V8 engine lends
its self to DIY as the lay out (photo above) is simple with a lot of engine bay
room. Any good shop could make a set up for you.
The only tricky part for the in-line 4 and 6 engines
is the “inserts” referred to as D blocks (by its side profile) photo above,
that go between the head and the exhaust primary tubes flange on the factory
in-line engines. These are often sold from the suppliers of the headers for
these engines.
A local engineering shop could also machine these in
alloy, if you give them the full diameter of the curve on the outside of the
exhaust port. Or lend them a cylinder head to measure from.
Solid alloy bar can be brought in different diameters
so whatever material fills the curve in the exhaust port will do. Machine a
flat side that is about 5-8mm proud of the heads side profile (so the flange of
the header tube does not tighten again the heads cast iron side). The D block
only has to be as wide as the primary flange. Then machine a port opening in
this tube that is 2mm overall larger than the heads port size. You want both
the D block you have (or are making) and the header primary tube and flange
port hole to be slightly larger than the exhaust port in the head, this helps
stop reversion. What’s that? If you run a performance cam often the last burnt
exhaust mix can be partly sucked back into the combustion chamber due to cam design.
Some cams are worse than others are. Having the port in the head slightly
smaller than the header tube helps keep this to a minimum.
Notes on D blocks: I have seen the D blocks made of
brass so they could be gas welded to the primary flange, that’s not a bad idea
as it can stop the problem of them slipping out sideways which can happen.
Pinning them in place to the flange is also a solution to this problem. I
always used a product called “Maniseal” to help seal
the D blocks.
One other note I’ll add to the in-line engine cars is
if fitting headers, a good idea in colder climates is to cut a short section of
exhaust tubing that fits the area left under the factory alloy intake manifold.
Cap the tubes ends with two frost plugs by welding them inside the tube ends
and install it in the area under the intake where the factory hockey stick ran,
this helps heat the lower half of the intake manifold.
A note on
header wrap-DON’T use it! Unless you are running a turbo and are after every
last HP, I can’t recommend its use. Header wrap causes the exhaust tubing to
break down in a rather short time. Instead use a coating method mentioned
further down below like Jet coat or HPC, they can often coat the inside as well
as the outside of headers which can really drop the heat in your engine bay and
keep heat inside the tubing where it aids performance in some cases.
Some use the size and length of the primary pipes to
change the range of power in the rev range etc. As mentioned try to have the
primary inside diameter (ID) a few millimetres bigger than the exhaust port in
the head. On some engines a primary tube may go right to the main collector
near the transmission or bell housing, on others the pipes are stepped into a
bigger size tube before the collector. The primaries each go between 8”-14” long
before ending into the first collector and then onward (and up a size or two in
pipe ID) down to the bell housing area or rearward of it at the last collector.
While we could
go into working out the lengths of primaries etc in detail for a chosen rev
range, cam type etc, often its just a matter of what will fit the best in the
chosen room you have! I’ll explain my reasoning behind this: Remember how
everyone tried to get each primary pipe the same length? Well its since been
shown the because of the extra pipe bends needed to achieve header primary
pipes of the same length, that the flow rates between the primary pipes will differ
because the extra bends end up restricting the flow compared to the next
primary pipe. So like I said, do a tidy job and get the lay out of the primary
pipes looking as uniform as you can, but don’t stress on it!
Often you are restricted by the store brought exhaust
collectors and headers that you will be able to buy locally. Do view and study
the photos of the headers we have above. Also study sets in magazines, the net
and what you can see on cars at displays or hanging up in exhaust shops.
I know first hand that even performance exhaust shops
have to work within the restrictions they are faced with regarding room etc.
This is were I bring my next point in, doing it your self or getting a shop to
do it.
Here are notes on doing it your self:
I had before never used a gas welding set for longer
than 5 minutes but I rented a set, and away I went! There are many great guides
on the net to learn from, once you set the bottles up, chose the right gas
torch tip, and adjust the flame correctly – away you go! Practise on clean off
cuts first then check how far your weld penetrated by cutting the weld open.
A 4” hand
grinder is handy, and/or a bench grinder. Some use tin snips to trim two
joining pipe sections so they fit better. A file is handy and a wire brush too.
Make sure to use clean pipe or at least clean pipe ends. This makes for a
better weld. I use a marker pen to put a mark on adjoining sections of pipe so
I know how to line them up before tack welding them together. Another trick is
to use mini G clamps or hose clamps to hold pipes together. You can drill holes
in the wider hose clamp bands to spot weld through them too!
Wear the correct clothing (cotton is good) and have a
fire extinguisher handy regardless of the welder type. Don’t gas weld over
concrete, use a steel table/plate or some axle stands. A good vice to hold a
pipe while you weld it way from anything flammable is best.
I brought pipe
U bends, 2 mufflers (one for each pipe) and 6 exhaust hangers (to hang/mount
everything under the car) plus some straight pipe sections and went to it. Some
engineering supply places will sell you a 5-metre length of tubing at a very
good price. Often they have a drop saw so you can cut the pipe to fit in your
car to take home (or take a hacksaw with you).
I got the pipes to go/point where I wanted, to look
the way I wanted, and every thing cleared. I remember the set of headers I had
made for a V6 powered Mklll Zodiac years ago by a
“professional” shop. They looked horrible and the first time I used the hand
brake, the lever on the engine cross-member jammed between the primary pipes!
Do you save any money doing it yourself? Maybe, mostly
on labour if you plan what you are doing. If renting a welder do things like
getting the car jacked up on stands and the old exhaust out before picking the
welding set up. Then the welder is used the complete time you have it, doing
things like that you can save even more money.
I brought extra pre bent U bends and returned what I
didn’t use for a refund. Buying pre-bent U bends means you can section them to
point a pipe wherever you like. It will flow better than a bend made on the
spot by a pipe bender that is done at the exhaust shop, those type of bends
often crimp the pipe a small amount.
Some exhaust shops that make complete systems may have
the more expensive mandel pipe-bending machine that
does not crimp pipe bends down, ask if you are pricing at a shop that maybe
making your exhaust system.
I know I got a huge amount of satisfaction doing my
own exhaust. If you are running a V8 you have a choice of the Tri Y design or
the 4 into one type of header. The Tri Y is rarely used today, it was well
known as the design on the Shelby Mustang cars, it can also often fit better in
a tight engine bay. The pipes are linked according to firing order so differ
from one side of the engine to the other. If interested contact me at avocalea@xtra.co.nz and I can give more details. These are
more of a mid range power type of header.
At the header end next to the bell housing or gearbox,
its possible to tune the headers for the best collector length, make the bottom
collector 3” diameter for a modified engine or 4” for bigger cube V8 engines
(over 300ci). First have the open length of the collector 15” to 20 “ long,
draw a chalk line the full length of the collector and now for the fun bit: (on
a private road of course!) Take the car for a run at varying high RPM. The
chalk line will burn off along the side of the collector at a certain point,
this is the best place to cut the collector(s) to add a flange and reducer to
the remaining exhaust system. I mostly use pre made collector flanges, Paul Garton in the UK can supply most flanges whether to match
the cylinder head of your choice or any type of collector:
Most exhaust
shops can supply collector and common engine header flanges or take a cylinder
head/ drawing to an engineering shop near you for them to cut a flange out, the
thicker the flange the less it can warp and leak.
For those of you installing an Air fuel sensor, I
recommend the boss/retaining nut for the sensor be welded half way up the side
of the collector near the bell housing, close to the start of the collector.
Where the two into one collector on the 4-6 in-line
engines sits next to the bell housing/gearbox area, add a strap off the bell
housing cover bolts or the gear box extension housing area to the collector
flange(s). This helps to better support the weight of the headers.
Right coatings: I would recommend a coating like Jet
coat or HPC over Ceramic coatings as the latter can chip. The Jet coat (a number
of companies do different versions under different names) can handle a scratch
yet not rust, it’s a sort of self healing surface. Australia and NZ both have
companies that do this coating method, use the net or yellow pages to find
where they are located, the same if you are overseas based. I myself go for the old trusty VHT in a spray
can!
First make sure you have no leaks in the headers
then file and sand the welds, be careful not to file a flat spot, use your
fingers to feel high areas that will show through once the coating is on. I use
sandpaper to finish. Then I wipe the header(s) down with thinners and keep my
fingers off the outside surfaces.
I hang the
headers by a wire on the cloths line (it pays to send the wife/girl friend out
for the day!) then let the sun heat them a bit or even use a heat gun, I then
start painting by following the directions on the spray can exactly. There are
other hi-temp paints in spray cans out there but I find VHT lasts the best. The
headers may smoke on engine start up!
If running a V6 or V8 it also pays again to add a
brace near the lower collector area to the bell housing.
I made my exhaust system so that I could run an open
system at the drags. I could unhook it at the collector flanges and move the
rear half of the exhaust to one side of the front flange and re-bolt it up to
hold it safe up under the car. On leaving you simply re-align the collector
flanges so the exhaust is closed and legal again. I recommend you closely
monitor jetting, as you may have to jet richer to run an open system. Take a
spark plug reading at the end of the first run without letting the car idle, if
the plug is more white the tan, jet two sizes up. If the car on the first run
misfires or won’t rev out then you are running very lean and I would not run
the rest of the run under full power until you re-jet otherwise you may risk
engine damage. If you design a good system, extra performance from unhooking
the exhaust should be nil.
Once past the front collectors, if running a V6 or V8,
adding a cross over pipe can add mid range power or at the least reduce the
overall sound by a few decibels. Use a tube the same size as the main exhaust system
tubing or go down a size. Placement in not critical, as close to the collectors
as possible is best but think of when its time to remove the transmission etc.
If you place it 6” or 150mm back from the front drive shaft universal it could
double as a part drive shaft loop for safety.
For a good 6 cylinder, one 2.5” pipe has ample flow.
Twin 2” pipes are nice sounding and worth installing of course too.
For a V8 or large capacity V6 I would use 2.5” pipes x
2, any bigger can be very tight over the diff. The larger the diameter the pipe
the deeper the note, 2.5” is very nice sounding!
One thing to watch for is the bend up over the diff, it
can straighten out as it heats up! I found this out the hard way: With
everything being tight for room under the car, once the bent section of exhaust
tubing over the diff heated up, the bend straightened out which caused the
tubing to knock underneath the car until I readjusted it! Hence I suggest no
bigger than 2.5”-3” pipe if going over the diff.
I had to off set my hand brake cables because of the muffler
size and placement but even with tube shocks, a panhard
bar and its locating frame plus the electric fuel pump, I managed to fit the
twin 2.5 “ pipes over the diff in my Mklll. I do know
of a shop refusing to do jobs like this, if you find that, go elsewhere. After
all some of our cars came from the factory with twin pipes!
Now onto
lowered cars, the question is over or under the rear differential? I think
“over” is just more professional but yes it’s more work.
If you run the
exhaust under the cars diff, a handy tip is to weld studs to the rear most exhaust
hangers top mountings. These studs can go through drilled holes in the
boot/trunk floor so that butterfly nuts can be screwed on to them. That way you
can undo the butterfly nuts by hand to drop the rear exhaust if you need to
jack up the rear of the car for a flat tyre etc.
Again I do
think if you can run it over the diff…Do it.
I allow at
least 2” or 50mm between the floor and any exhaust tubing. I also try and get
more room around mufflers as heat can build up in them more. I use at least 3
hangers to tie the exhaust pipe on each side of the car, I weld the lower part
of the strap to the exhaust tubing so there’s no U clamp bolt ends to catch on
things.
Clamp the muffler on as they often rot out first and
clamping them on also allows you to reposition the exhaust if need be after
installation.
Regarding mufflers, there is a lot of hype on the
“bullet” glass-pack type, which is restrictive by design. Few believe this,
they look down the muffler, see daylight and figure, hey its straight through,
there must be no restriction! However the exhaust sound in these mufflers is
made quieter by the reversing of sound ways/pulses inside to cancel out certain
tones, ie the back pressure created in these mufflers is what quietens the
sound. This level of created back pressure is high, plus the sound reducing is
not that great. Reversing them does nothing better than making them louder.
You are better to go with a common parts store type
Oval 3 chamber type muffler. These, like the factory fitted type they are
designed to replace, often reduce noise with less back pressure.
A note on flow
bench testing of mufflers, I have seen tests done on mufflers that pit one
muffler against the other using a flow bench more commonly used to test flow
cylinder heads. This is a complete waste of time. The hot exhaust gases pulses
though a muffler, and at different pressures, temperatures and speeds, backward
and forward so a flow bench can not show what a given muffler may do on any set
engine. Far too many variables come into it
I alway spend a good amount of time under the car
working out the best place for mufflers and where to run the exhaust. Keep away
from brake and fuel lines as at the least you can get vapour locks in your fuel
lines and at the worse brake problems. Do consider a simple alloy shield to
cover sensitive items from heat. Inside the car you can install heat proof matting
that make it more comfortable in summer (take it from me your feet can get nice
and toasty in a V8 Mklll). I like to install mufflers
towards the rear end of the car where exhaust gases have slowed down. Under the
rear seat area of the floor pan is a good place as is either side of the fuel
tank. With the exhaust system sitting on stands, blocks, or tied up under the
car with welding wire, I check that I am happy with how it runs under the car,
then I do the final welding. It can pay to stop and look now and again as
things move!
Keep a safe 2” or 50mm distance between the tank, fuel
/brake lines and the mufflers if you can, plus weld these exhaust sections off
the car that are near the fuel tank to be safe. (I prefer to lower this section
down to safely weld it).
Installing a fuel cell type of fuel tank in the boot
of some modified cars can open up room for mufflers at the rear of the car too.
Do set the rear exhaust pipe(s) to run square out the rear of the car. Having
the pipes pointing down a small amount can help drain condensation from them.
However it can cause them to jam in the ground on lowered cars when reversing!
My exhaust tips point up a fraction. I also run the pipes at least 100mm-4”
pass the rear bumper. I am a firm believer this is best for most cars as
otherwise fumes can creep into the car even at speed, these fumes are odour
less but can kill. Some areas have laws on the placement of the rear outlet of
the exhaust(s) relevant to the farthermost rear door too.
A tidy exhaust that is tucked up under the car is a
nice way to finish off a car build.
Disclaimer: The advice
and guidelines given in these articles are given in good faith. The owners
and managers of the Galeforce Zephyr site will
take no responsibility for any injuries or loss sustained while carrying
out the described tasks and procedures or any consequences arising.
Please read the Safety First Article
Why not
do an Article on your Pride and Joy and have it featured on the home
page or spend an hour doing a technical article about anything you have
done or know of to do with these cars
We need more information for this site, to make it bigger and
better. Any information on these cars will be gratefully accepted. Paint Codes,
Colour Charts, Technical Information, Articles out of a book or Magazine you
might have, Scanned copies of Advertisements, We will accept just about
anything at all to do with these cars. It might seem trivial to you,
but could be information someone has been after for years. Email
anything at all to Karl
Enjoy
the Site