Evap/Emissions System Question

[infernosg]

I have a custom intake manifold that only has two ports for vacuum sources. One for each rotor and they're independent. The rear is the brake booster source and the front is for the FPR and MAP sensor. The charcoal canister and oil catch can are vented to the atmosphere. These should be connected to a vacuum source. I thought it was best to keep the brake booster source separate so I'd be hooking the canister and catch can up to only one rotor. They'd also be on the same "signal" as the FPR and MAP. Would this cause any issues? Should I even bother?

[RETed]

First, having the vacuum source deep into the runner on a single rotors will induce pulsations due to the physics of the running motor...
It's a question if this is significant or not.

If your MAP sensor is damped, then this would not matter too much.
For very sensitive MAP sensors (or signals), this can cause headaches.

FPR's are not as important, but don't be surprised to see pulsations of + or - 5 to 10psi in some cases - verify by monitoring fuel pressure.
The effects can be minimized by the tune - tuning slightly rich will "fix" this.

If you want a more stable vacuum source / signal, you really need to run a plenum...
This is why most intake manifolds have a (collected) plenum - to minimize all the weird pulsation in the intake tract.
If this is not possible, you can cheat and run a vacuum manifold, which acts like a mini plenum by collecting multiple source of vacuum into a single space; be careful with such a system, as making things "too big" can cause more pulsations in the system!

Your brakes might be perfectly fine drawing off just one rotor - this goes into brake performance theory, but that's a whole 'nother ball of wax!


-Ted

-Ted

[t_g_farrell]

Just vent the charcoal and oil catch into your air intake somewhere. That way it will just
suck the vapors into the intake. No need for extra vacuum connections. Thats how most
PCV systems are connected.

[infernosg]

I have restrictors in the MAP and FPR lines to minimize the pulses you described. With ITBs and a large street port getting a stable MAP signal is difficult enough.

I have a small vacuum block for the FPR and MAP. It has extra ports to add in the second rotor, brake booster, charcoal canister, and oil catch can. I thought I read something somewhere that said you should keep the brake booster separate as it can cause vacuum fluctuations when the brakes are applied.

Would I want to have everything hooked up to one source? It's not a turbo car so there should never be positive pressure but I'm hesitant to have the FPR and MAP in the same circuit as the oil catch can and charcoal canister. Is this an issue? This is not a DD/road car so I'm not concerned with emissions. If there's no value I'd just assume vent the oil catch can to the air and delete the charcoal canister.

Originally Posted by t_g_farrell

Just vent the charcoal and oil catch into your air intake somewhere. That way it will just
suck the vapors into the intake. No need for extra vacuum connections. Thats how most
PCV systems are connected.

That's my main question. My current setup would draw the catch can and canister vapors into only one rotor. If that's an issue I can merge my vacuum setup but then I have the brake booster, MAP sensor, FPR, oil catch can, and charcoal canister all in the same "circuit." If that's not an issue - great! That all being said if there's no value added to applying vacuum to the charcoal canister and catch can (i.e. make them work better) I'd just assume delete the canister and vent the catch can. It's not a DD or really even a road car so I don't care about emissions/smell.

[infernosg]

So a simple check into the FSM answers one of my questions. Connecting the charcoal canister directly to the intake seems like a bad idea since I no longer have the purge control valve. I have two options: (1) leave the canister in the car and cap the nipple that used to go to the bottom of the oil filler neck or (2) delete it altogether. Is the reactive charcoal still working after nearly 30 years?

So the only question that remains is whether or not it's a bad idea to have the vacuum source for the oil catch can tied to a single rotor or to the same "circuit" as the FPR, MAP sensor, and brake booster.

[RETed]

I don't think we can all give you a definite answer without having the set-up in front of us...

Only way to confirm is to test it yourself...
Run a (cheap) pressure / vacuum gauge and put it inline (T?) into all the branches and see how bad the fluctuations are.
Brakes should not be that big of a deal, since minimal fluctuations are not going to change the braking performance that much.
Also, very few functions of the engine depend on deep vacuum under throttle lift, so I don't see how this will effect the performance of the engine significantly in the first place.

If you don't have to worry about emissions, then just run all that crap open-air - you just gotta deal with the fumes smell every now and then.


-Ted

[infernosg]

I've come to the conclusion I can't properly connect the charcoal canister and oil catch can to a vacuum source without a purge control value. Connecting them straight to the intake manifold applies the most vacuum at idle, which isn't ideal. So for now the catch can and the canister will be vented to the atmosphere. The only question l have left is if the canister serves any value if it's vented or of it's no different from having no canister at all.

[RETed]

The primary function of the charcoal canister is to contain the fumes from the gas tank.
Due to current, modern (fuel system) emissions rules / laws, even vapors from the fuel tank are not supposed to escape into the atmosphere...including under conditions such as filling gas into the gas tank.
Ideally, when you fill gas, the incoming gasoline displaces air space / vapor in the gas tank...
Where does that all go when you fill the gas tank?
It's supposed to be captured by the charcoal canister and associated emissions components.

The secondary function is also to let the air space / vapor displace without backing out and up the filler neck.
Most gasoline pumps have a back-pressure safety shut-off that stops the pump when it senses too much back-pressure - i.e. when the gas tank gets full.
If you didn't have this charcoal canister system to handle the displacement, it would make it a tough time trying to fill your gas tank from most gasoline pumps nowadays...

Venting is to atmosphere works perfectly fine...
Like I said before, if you have no worries about emissions, then just vent it.


-Ted

[infernosg]

Yep, the canister stores air and fuel vapor from the fuel tank until it's sucked into the engine through the purge control valve. The gas tank vents through the "check-and-cut" valve. If the canister will cut down on the gas vapor vented to the atmosphere I'll keep it since I don't want a fire hazard in the garage. If not, it's a waste of weight and I'll remove everything back to the check-and-cut valve.