Deceleration vacuum? valve

[sc2dave]

I want to install a valve that opens during deceleration to reduce fuel usage.This will be for an 86 toyota 22r,carbed. If you've done this,what did you use?

[downinit25i]

i haven't done it myself, but I'm trying to understand your idea. If you want to reduce the vacuum right after letting off the throttle quickly then I know you can look at the Chevy AIR system. That redirected the forced air from the catalytic converter to the intake after a hard let up to prevent backfiring due to the overly rich condition created. It might not be too hard to adapt to what you want to do.

I think your basic set up would be a small valve normally closed which is sized correctly to open at the engine vacuum you've decided is correct. When it opens, have it plumbed through some kind of fixed choke or small line to the clean side of the air filter. This would lean out your mixture, since you are basically bypassing the carb, but since under these conditions you normally pull too much fuel you may end up equaling out if you design carefully. If you overdo it you may lean out too much and have to deal with those issues.

[lunarhighway]

isn't this a bit what en EGR valve does?

[dcb]

I've had motorcycles that had a decel valve, was integral with the carburetor. Might be easier to swap in fuel injection if you cannot find a carb that does what you want.

[downinit25i]

Yes it's very similar to EGR, which closes at idle to block exhaust gas flow to the manifold. It opens under partial load, and closes again at full throttle.

[sc2dave]

On another note, i do have the egr bolted on,but i need to figure out how it can be hooked up very basically. It's for the same engine. All other smog stuff has been stripped off.What determines when the egr valve opens?

[downinit25i]

The egr opens based on manifold vacuum, and on many cars there is also a solenoid which closes the valve after a cold start. Some cars are set up to open on exhaust backpressure, but I thik the vacuum type is more common.

[sc2dave]

Originally Posted by downinit25i

The egr opens based on manifold vacuum

so it goes connected to any manifold vacuum source?this should also raise my mileage too?

[downinit25i]

Well there are different systems but the basic concept is the same. I'll explain the system I know the best, which is a mid 80's small block chevy.

There is one vacuum source coming from the underside of the carburetor, which sees manifold vacuum. This goes to a solenoid, which can cut off vacuum when cold. The vacuum then goes to the top of the EGR valve. The valve is normally closed, but when a vacuum is pulled on the diaphragm the valve opens. When that happens it opens a flow path for the exhaust gases to enter a second port to the manifold, to be sucked into the cylinders again. The flow is regulated by the size of the opening and flow characteristics, it isn't really modulated.

[bgd73]

I was going to use the egr valve on my little boxer, as locally, be it pulp mills or whatver, the egr is equivalent to a chemical suicide for the car and driver..I disconnect these right away...

also a carbed engine, japanese.. alot of similar between the 22r function because of the year and CARB paranoid unthunk weirdo engineering of the 1970s and 80s..

in injection what you are trying to do is bypass.

to make it work natural, by its own vacuum.. this needs thought. I do not have that correct... but there must be a way.

you could also add a large resonator chamber about a foot after the catalyst convertor.. this acts perfectly as a backwards air bypass, cylinders getting satisfied through their own exhaust. My own mileage lept into the 30s after making my own out of a hollowed glasspack, but keeping the steel innards.

on four cyls, about 18inch is perfect, the two foot is too big.. and only 20 bucks. be sure packing is removed if you try it. the hollow chamber is the trick...