WAI/CAI switching and snorkel size
 

Following advice on this forum about WAIs and CAIs I redesigned mine, and I am already considering another rebuild.

The photo below is of my new set-up. All the stuff was either stock or laying around my garage (so cheap and easy). The pipe running from the airbox toward the head is the WAI and the other, running down toward the transmission on your left is the "CAI". When I plug the CAI air comes in through the WAI, plug the WAI and it comes in through the CAI. And I can reset the stock setting in about 1 minute (for smog check). I just tested the effectiveness today. With the car thoroughly warmed and running for 15 miles I ran the WAI, then CAI, the WAI settings ABA:

A=89.7, B=82.1, A=94.3 (degrees fahrenheit)

So I am happy. Today was only mildly warm (in the 60s).

Question: I think I may be reducing the effectiveness of this mod for FE by restricting the airflow with a slightly smaller than stock diameter snorkel. The stock setup seems to be a little under 2" diameter and the piping I use is 1.5" diameter. Anybody think this could be significantly counterproductive since the WAI is supposed to save on pumping losses as well as help fuel atomization a little?

those are some impressive numbers.

I don't think the smaller pipe should make much difference. As hypermilers we don't push our engines to the limit and there shouldn't be a problem with supplying enough air to the engine. You could do a comparison if you have some wider pipe laying around.

The factory air duct is sized for WOT for passing power.
If you're cruising with your TPS between 15% and 20% then the actual cross section area of the air tube you need is very small. Unless you need to make full power at WOT, then you do not have a problem there with size.

I've always ran my WAI to the exhaust manifold , to either the factory heat-stove or one that I made. After a few minutes of driving typical temps for the WAI are between 120*F and 160*F for mine.

What are those numbers you posted exactly?


IMO the best set up is using a cockpit controlled diverter valve to switch between WAI and CAI.

Thanks. That makes sense.

That's what I will do in the end with the WAI portion again. This was just for proof of concept.

Sorry... it's degrees F. I'll go edit it ...

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?

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.

http://repairguide.autozone.com/znet...52800b144a.jpg

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
http://performanceparts.com/performa...asket_5424.jpg

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