Nop

Hi!

1970 Cutlass Supreme, 350/350, no EGR, no air breather box vacuum stuff at all - Just a carb, power brakes, a TH350 and a distributor...

I have been reading about ported/manifold vacuum and the vac system for days now, I slowly start getting a headache! I need some help and guidance of the more experienced folks here, please have a looksie:

While everything works, some of my vac hoses are brittle and need replacement, routing is somewhat strange and I want to add an additional large 1/2 NPT sender for my water temp gage - This 1/2 NPT sender is fixed to the gage's copper line, no other sender is possible and I can't reach the passenger side location, has to go to the left of the engine.

I have a decent vacuum at the moment, measured at the vac ball outlet to the dash I get:

~00 Hg when off
~16 Hg idle after start, cold with choke
~18 Hg idle when warmed up
~20 Hg for a short time after revving when rpms go down to idle

Doesn't look too bad from what I have read.

My current setup is as follows:



Details of my TVS-Switch:

D: Should be distributor, T-ed to carb ("C")
C: Should be carb, is carb (rear connector) and T-ed to "D"
M: Should be manifold, is manifold and transmission modulator

The plan:

I want to get rid of the TVS switch (I don't think I'll need it here, no 30 mile city drives with hundreds of red light stops,
no 100° summer months) and move the idiot light temp sender (X) to the pass. side with a longer cable and fit my mechanical
water temp sender with a non-extensible copper hose/pipe at "X".

"X" and "T" both are 1/2 NPT, right?

Brakes:

Large hose from larger "C" connector in manifold. OK?

Transmission:

Now coming from manifold "D" connector, magically T-ed on TVS switch, going to Transmission modulator pipe. I have read "The vacuum line for the vacuum modulator is connected directly to a vacuum port on the intake manifold."

I'll get rid of the T and connect the transmission to manifold vacuum "D" directly. OK?

Distributor:

Now hooked up to the driver side carb outlet, I guess(!) that's ported vacuum?

Without TVS switch, there seems to be a little war as if to use ported or manifold vacuum. I'd like to go with manifold vacuum. Simply hook it up to the unused "A" connector the shortest way?

Note to myself: Close connector on carb!

Vacuum ball:

A/C controls are working. Ball stays at "B", new hose only. OK?

Summary:

* Manifold A: To distributor
* Manifold B: To ball, to A/V controls
* Manifold C: To brakes
* Manifold D: To Transmission
* Close carb connector that was used for distributor
* Move idiot light temp sender to passenger side ("T"), longer cable
* Add mechanical water temp gauge to driver side ("X") with copper hose

Does that seem OK? Did I miss something? Bear with me, I only had 4 hours of sleep last night...

MDchanic

Yes.

- Eric

MDchanic

To elaborate slightly, remember that the TVS is only there to allow the car to run with its timing at idle retarded because the vacuum advance is connected to ported vacuum (which is zero at idle).
If you are planning to run the advance on manifold vacuum, the TVS serves absolutely no purpose.

Other than that, I really have nothing to add. You can connect any of those hoses to any manifold port that looks good to you, and it will work fine.

- Eric

Nop

Yes, I remember that I'll have to check & set idle rpm, check & set ignition advance again after "moving".

Thank you, Sir.

joe_padavano

This comes up a lot, and compared to say, the vacuum plumbing on a 307, this is not complicated.

First, ports A, B, C, and D are all manifold vacuum and are equivalent.

Second, the ported vs. manifold vacuum issue for vacuum advance has been debated since the 1960s with no resolution yet. You might as well debate whether the toilet paper comes off the front or the back of the roll. Bottom line is that you should try both and use the one that lets the engine run better. Personally, I always use straight manifold vacuum for this reason. If you do run ported vacuum, you should use some sort of thermal vacuum switch to switch the advance to full manifold vacuum if the engine starts to overheat.

Third, your car should have Transmission Controlled Spark, though in 1970 the TCS solenoid was separate from the TVS. It appears from your drawing that it's already been removed. No problem.

Fourth, the trans should run off of manifold vacuum, which is how you have it connected currently.

Fifth, the vacuum ball is the reservoir for the vacuum operated HVAC flapper doors, and should also run off of manifold vacuum, which is how you have it.

You haven't shown PCV, but I assume you have that connected to the port at the base of the carb.

Your stock intake only has two ports in the coolant crossover, so you can either run two senders or one sender and the TVS (if you retain ported vacuum for the advance). You cannot tee coolant senders as they have to be in flowing coolant for an accurate reading.

Fun71

Why would you modify the ignition advance based on where you connect the vacuum advance? Leave the initial advance alone and adjust the idle speed only.

joe_padavano

Because ported vacuum does not provide any vac advance at idle, but manifold vacuum does. If you set the initial timing for a ported vac connection, you may get part throttle pinging if you then switch to manifold vacuum without changing the initial timing.

Nop

Use the search, Luke! I already read and learned a lot, as I wrote, but somehow I needed a final confirmation of some things.

Yes, I was thinking about the physical shortest ways with my "plan".

Seen that. Had a short trip to chevelles.net but came back here rather quick: 2 guys, 3 opinions...

I think that's the path I'll take, too.

Ooops - already "fixed" that. No strict emission tests here with historic cars, another thing that won't fail as it's removed.

Ah, forgot that. Still there, but hooked up OK, new hoses and done.

That's the original reason for looking to free the TVS hole for my sending bulb and getting rid of the three-branch TVS tree.

Learned that too, already.

Plus: Screwing around 2-stroke engines for 25 years makes you check ignition stuff at least three times after fiddling around with anything even close to ignition...

Thank you again!

Fun71

But then you would have less total mechanical advance (and potentially reduced WOT power output) due to reducing the initial setting.