RXJIM

iTrader: (3)

Hello, I’m finishing up the emissions removal on my 85 S. I’ve got the block off plates coming and the rats nest removed. Although I have a few questions.

You can call it a shutter valve, coasting valve, or get technical and call it the flapper in the intake manifold. From what I read through searching this site, the FSM and inspection of the part, this thing closes on deceleration under vacuum to save fuel. I’m wondering how much fuel will it save if you leave it in tact, are we talking less than 1 MPG, or something more significant? Is it worth the flow obstruction? Is it as easy as putting a vacuum line on it, or do you need the solenoid to operate properly?

Thanks,

RXJIM

iTrader: (3)

The good doctor answered all my questions.

Thank you sir,
RXJIM

ray green

iTrader: (14)

Good Doctor, please tell me too, I was just doing the same thing today, a nice one here in NE GA. And I want the best gas mileage possible.

Ray

FirebirdSlayer666

iTrader: (3)

It was like 4% more efficient under decceleration, but that's only if it is functioning properly. Once it goes it's just a big vacuum leak and a headache.

RXJIM

iTrader: (3)

This is what he sold me via pm.

FirebirdSlayer666

iTrader: (3)

Yeah Doc has it pretty good there. Once you start hearing it honk, it's time to plug her up

ray green

iTrader: (14)

So if I remove my emissions (ie rat's nest) I will loose the shutter valve and as a result the car will have about 4% poorer full efficiency when decelerating?

If so, that could add up to a significant difference in gas mileage.

Does anybody know if any of the other rat's nest-dependent "emissions" features also significantly improve gas mileage?

Thanks, I'm trying to decide if rats are good or not before I remove them.

Ray

FirebirdSlayer666

iTrader: (3)

I honestly don't think it would be enough to make a real noticable difference

trochoid

iTrader: (6)

I doubt if it will be a 4% savings and that would be on decel only. If one simply pushed in the clutch on decel, more fuel would be saved at the cost of more brake wear.

As far as fuel mileage difference w/wo the rats nest, it would be minimal at best and hard to accurately document. Biggest savings would come from removing the air pump and cat, then adding a pre-silencer that has better flow. Even then, it won't be much.

ray green

iTrader: (14)

I can accurately document it, I have been getting 23-24 with the rat's nest and air pump installed but no cat, just a presilencer. If I remove the rat's nest and air pump, I can again accurately measure my gas mileage under the same usage (the 110 mile daily commute). It sounds like I shouldn't expect much change, I just hope it doesn't get worse or the whole effort would be a waste of time, and money.

Another question, can you remove the air pump and other emissions components but keep the shutter valve, since it sounds like the shutter valve might have some effect on gas mileage and maybe even performance, like reducing back firing by cutting off the gas on deceleration?

If the shutter valve is regulated by the emissions computer, I can see this might not work, but if it is simply operated off the vacuum, I don't see why it wouldn't work normally even without the rest of the emissions stuff.

Thanks
Ray