Terry Thompson Wrote...
>If I swap out my exhaust manifold for a header, (and thereby lose the
>EGR valve) does the dizzy need to be modified for a mechanical advance?
>
>Also, would using an electronic ignition have any effect on this?
>
>Terry L. Thompson
>'76 Spit 1500 (with older Dizzy)
>Maryland
This one is dicey!!
With all the talk about overheating spitfires, perhaps we should discuss
exactly
what the EGR valve does before throwing it away!
As Emissions got stricter, the mixture got leaner throughout the driving
range.
In order to combat the reduced CO2 in the leaner exhaust, the ignition
timing was altered to adjust the length of time that the mixture burns in
the combustion chamber. Leaner mixtures burn slower than richer ones.
As this lean mixture is still burning when the exhaust valve opens, the
overall timing was retarded to reduce valve burning. This is the reason that
most EGR equipped spits have a vacuum retard or have a double acting unit.
Since the lean mixture also burns hotter producing lots of NOx. a small
amount of exhaust gas was directed into the intake manifold to reduce the
combustion temperature. This effectively lowers the engine operating
temperature without altering the mixture.
If you simply remove (or disconnect) the EGR without making any other
changes, several things will happen.
1 - You will fail the emissions test in California and British Columbia
(required to be there!)
2 - Your engine will run warmer due to the higher combustion temperatures
3 - You run the risk of burning the exhaust valve seats out of your car
4 - You won't get any performance gains (or not as much as you might think
you should)
5 - Your engine will likely ping or knock because the octane is no longer
high enough
6 - Your spark plugs wont last very long
My suggestions:
A - If you want to run a header, have a muffler shop install an EGR port in
the header (or get one for CA)
and use the EGR
B - Since the header allows the engine to breath better, have the
distributor recurved, or install the
vacuum unit from a 75-76 Federal (double acting) (8 BTDC Static)
C - If you really don't want the EGR, and your emission laws allow it, use a
distributor from the 71-74 Mk IV
Spitfire, along with the carburettor, etc. and Use these settings.
What I did on my 80 - (Which I sold, unfortunately!)
The EGR was installed in the header and connected correctly.
Installed an insulated sheet between the intake manifold and the header
(large!)
I used a double acting vacuum unit, on a modified 1974 distributor
(electronic)
Disconnected the air pump rail, and injected the air directly into the cat
Replaced the cat with an aftermarket (Ford) with a air inlet pipe
Anti-run-on valve disconnected (because it failed, not because it wasn't
useful)
All venting pipes were intact
Added K&N Filter to the stock Stromberg 150 CD4T
Opened the Air inlet, and used a thermostatic door from a Ford routed in
front of the Rad
Closed off the lower space between the radiator and the chassis (2"
space???)
- Result - very reliable car, with lots of power which passed the emissions
test and failed
the inspection until I showed them where everything was.
- Would I do it again? Except for the header, yes. The header was more a
pain than anything. It required
too much work to get it fitted and to protect the carb. The OEM system
works well and if you make sure
the cat works, you won't have any problem. Remember - reliability is the
key to a fun car.
Remember, the main difference between the US and UK spec was emissions, and
Most of this was due to the ignition timing.
As an aside the other useless emissions parts explained:
- The catalytic converter burns the unburned exhaust gas
- The air pump allows the catalytic converter to work correctly (check where
it puts the air!)
- The anti-run-on valve was used because the timing was too far retarded at
idle most of the time
- The vacuum advance was eliminated because the advance couldn't be used and
keep the car cool
- The thermostat temp was raised to 180F, with a change to the sender
- The radiator on US spec cars was larger than UK equivalents
- The viscous fan was only to reduce noise and help with power robbing of
the engine
- The electronic ignition was needed to eliminate timing drift for emissions
- The Automatic choke was used to stop people from pulling out the choke for
more power.
(There is a note in my service manual about the 1/2 - 3/4 temp guage on
75-77 spits. The factory used a different sender, and subsequently the guage
reads high. Not a problem if you use the older sender)
Wayne Burton
1963 Triumph Spitfire4
1966 Triumph 2000
1954 Austin A40
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