Quote:
Originally Posted by California98Civic
Agreed, but I don't have much in terms of skills and experience yet. I'm getting there. Out of curiostiy and for future reference, what hardware would you use for such a build?
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I've used different things ranging from parts from air-cleaner housings in junk yards (thermac valves), to plumbing and HVAC valves from the hardware stores, to cable operated exhaust cutouts.
I just found this image quickly. You can find them MUCH cheaper than this out outlets like J.C Whitney.
Mr Gasket 5424 Exhaust CutOuts w cable
Well, this one is smaller and a little cheaper, but I still wouldn't pay that much. You might find one second hand but unused.
Shinnfu Cast-Iron Exhaust Cutout - JCWhitney
the valves inside these things are just crude bent flaps and they don't seal as is, but are easy to modify to seal for use with intake air.
The factory thermacs can be handy because you can use vacuum to control which air source you use, which handily coincides with engine loading. I've used them, but I prefer not to have the "mix" of air temps that you get with certain vacuum levels. They also require physical modification to plumb with round tubing.
I'm always keeping an eye out when I'm in hardware stores for something like this to pop up as well, and it's unusually rare I see something worth getting. It has been a long time, but if I see something good in the near future I will post it. The valves I use I acquired almost 20 years ago and they haven't worn out so I just keep using the same ones on different vehicles. Two of them are the cable operated cast-iron cutouts from J.C Whitney, but were much cheaper back then.
I don't know if you are aware of this, but there are also heat-riser valves you can install in your exhaust to control backpressure.
They were originally used by the factory to increase exhaust flow through the exhaust crossover in the intake manifold of V8 engines. This same crossover passage that quickly warms up the intake manifold was also what fed the EGR system, though the heat-riser was used mostly for idle warm-up, and not to increase EGR flow.
As you can imagine an increase in backpressure can have several effects that you could possibly utilize to increase MPG. How, and how much all depends on the individual set-up and how it is tuned.
On an older carbureted engine an increase in backpressure reduces air through the system which reduces fuel metering at the carb. Obviously it cuts a significant amount of power output, but many driving situations would not need the power, so user discretion would be needed.
On a newer vehicle the effect would be similar (reduced air throughput), but the amount of EGR delivery would be increased if you are running EGR. If no EGR system, it would still increase the amount of self-EGR, which is a result of incomplete combustion evacuation of the chamber.
Your resultant fuel trims and MPG could be monitored with a Scangauge while you determine how much to move the valve for certain driving conditions. You certainly wouldn't want to close the valve off too much or you could damage the engine in a similar fashion to what happens when a CAT converter fails, breaks, and clogs the exhaust.
The heat riser valve normally mounted between the exhaust manifold and the down-pipe. In factory form it was used in conjunction with the thermac valve on the air-cleaner housing to speed up the warm-up process after a cold start. On a V8 engine the valve was only on one exhaust manifold and forced extra exhaust flow through the intake manifold and out the other side's exhaust. With a single bank engine you might wish to use an EGR bypass to route excess pressure back into the exhaust pipe if you want to use the heat-riser to speed up your warm-up. That would assume your EGR passage runs through your intake manifold. Some do not.
My Focus has a plastic intake manifold and has no EGR passages inside it besides the EGR delivery tube. My CAT is mounted on the front of the engine immediately after the exhaust manifold, and so that is were I built my heat-stove for the WAI.
Here's the heat-riser valve:
http://www.hamiltonmanufacturing.ca/hrv.htm