russell-t

1963 Cutlass with 215 v8. Had a low restriction turbo muffler with duel

outlets installed on my cutlass and I'm noticing that the car seems to use

a lot of gas during normal cruising around. The crossover pipe from the engine

to the muffler was left in place,creating a single inlet into the muffler and

a duel outlet out of it.Exhaust shop suggested this to to hide the pipes.

The carb is a small bore Rochester 4bbl that has been reworked 3 times

to get it to run right. Don't know if it is original to the car. The engine has

a mild cam upgrade from stock.

Do I need a more restrictive exhaust system? Timing advance? (set at

approx.7 BTDC)., or some carburetor work? I don't know exact gas milage

but burning through a 1/4 tank of gas in about 30 miles seems like a lot

to me.

oldcutlass

How do you know it was a 1/4 tank? Gas gauges react differently due to the contours of the tank. It may fall really fast from full to 3/4 and then hang there for a long time because the float level does not drop near as fast.

Next question would be have you looked at your plugs to see if your engine is running rich? Does the exhaust smell like it's running rich? What is your dwell set to? Is your vacuum advance hooked up and functioning? There are many things that effects fuel economy.

joe_padavano

Unless your two exhaust pipes are shooting at each other, they are DUAL exhausts...

You never want a MORE restrictive exhaust system, and unless the pipe from the crossover to the muffler is larger than stock, the muffler is pretty much irrelevant as far as restriction is concerned.

What you DO need is a properly tuned carb. If you have reduced backpressure, you may need to richen the carb slightly. More likely is that your 4GC carb is not running correctly. I rebuild all my own carbs, and the 4GC on my 62 215 was just impossible to get running correctly. I don't usually use aftermarket carbs, but I did bolt on a 500 CFM E-brock. The car runs great, but I did have to fabricate a throttle valve linkage replacement for the Roto-5 trans.

By the way, on my 62, I kept the stock Y-pipe and adapted a cat-back pipe from a third-gen Camaro that was 2.5". Only minor mods were required to get it to fit in the stock location next to the driveshaft. I did not want to run separate dual pipes under the car due to the reduced ground clearance. I used a Magnaflow single-in, dual-out muffler, also designed for a Camaro, with fabricated tailpipes that exit behind the rear wheels. Here are some photos:

https://classicoldsmobile.com/forums...ting-work.html

russell-t

To oldscutlass...Checked the dwell and found that it was set at about

26 degrees.Reset it to 30 and reset timing to 7 degrees BTDC.

Checked the vacuum advance and discovered that I had NO vacuum

advance at idle. 2 hours later after removing the carb and tearing it down,

blowing out the passage,(in picture) I reinstalled the carb on the car. I

STILL have no vacuum advance.(with vacuum gauge attached to the

carb.

When revving the engine I saw a vacuum reading on the gauge.When

returned to idle,the reading goes away. What's going on here?

The car seems to run fine,and I've been driving it this way for almost

2 years.

Is this normal for an OLDS 215 V8? Any other car I've owned always had

vacuum advance at idle,that would DECREASE when the engine was revved

up.

MDchanic

What's going on is called "ported vacuum."
The vacuum barb goes to a point just above the throttle plates, so that when the throttle plates are closed (idle), the port sees no vacuum, but as the throttle plates begin to open, the vacuum is transmitted (so to speak) to the port.
This allows for no vacuum advance at idle, but full advance just a bit above, which improves drivability in some cars (it can also reduce NOx emissions, but its presence on your pre-emissions carb is evidence against the commonly-made claim that it was designed for that purpose).



Are you quite certain about this?
It is the opposite of how vacuum advance, and manifold vacuum in general, works.
Increasing revs, without a load on the engine, should increase vacuum, not decrease it.

I've never heard of a car with a vacuum setup like this.

- Eric

joe_padavano

Are YOU sure, Eric? Manifold vacuum is a function of RPM and throttle position, but more heavily weighted to throttle position. As the throttle opens, the manifold absolute pressure gets closer and closer to atmospheric, meaning the vacuum level decreases with increased throttle position. Manifold vacuum is highest with closed throttle blades and goes down from there. I'm guessing that what the OP is talking about is opening the throttle with the car in neutral and watching the vacuum gauge. Under those conditions, he is correct, manifold vacuum will decrease as the throttle opens (and RPMs will also go up).

MDchanic

Reasonably. That's why I specified no load.

Sure, if you whack it open, the vacuum will fall, but if you just crack the throttle, it will go up, not indefinitely, but usually to a point a bit higher than at idle (at least mine always did).

I agree, as the throttle plates open, the "demand" for air is more readily "satisfied," and the vacuum level decreases, but if the throttle is maintained just open enough, vacuum should remain high.

Now, of course, I'll have to go out to my car (once I've got the radiator fixed) and see if I'm right, or if I just imagined the whole thing. If I'm wrong, I'll post back.

All of that being said, it doesn't affect the function of the OP's ported vacuum.

- Eric

garys 68

Is the centrifugal advance working correctly?

russell-t

To Garys68...When doing the timing check using the light,revving the engine

up(vac advance hose disconnected and plugged)caused the timing mark

move up from it's base position. I feel that this is an indication that my

centrifugical advance setup is working properly.

russell-t

To MDchanic......After reading all posts and rereading my own OP, I realize

that I have made a mistake with one of my descriptions.(Always had

vacuum advance at idle,but would DECREASE as engine was revved up).

This sentence needs to be changed.To read.....Any other car I've ever had

always had vacuum advance at idle,(with vac advance hose connected).

When removing the hose and plugging it....TIMING would DECREASE with

vacuum source removed. RPM's would also drop.

As Joe P states that the vacuum gauge reading will drop as the

throttle is opened is true.

I am going to put a vacuum gauge on the engine and see how high

a reading I get when I open the throttle,and at what point the vacuum

begins to drop back down. It sounds as though my engine is designed to

run with ported vacuum.

russell-t

Just thought about this question....Why do some engines have their

timing degree markers on the right side,and some(like my 215 V8) on the

left side? (when facing engine from the front of the car)

MDchanic

Ported vacuum advance should work exactly as you describe, Russell.

The ported / direct vacuum debate (argument?) is never ending, but the bottom line is that you should set it up whichever way runs best for your car.

A vast number of cars, since at least the 1940s (I won't say "most cars," because someone will come back with exact numbers) were designed to use ported vacuum, and others were not. Regardless of the original design, though, you may find that a different way works best for you, especially if parts of the engine are different from the way they were originally set up (such as a different cam).
You already know that it runs well for you on ported vacuum, and it is completely reasonable for you to try it on direct vacuum and see whether it runs better.
Your 215 is not one of the "workhorses" that everyone else modifies, so there may not be a lot of information out there about what sort of set-up has worked best for other people.

- Eric

joe_padavano

Usually the timing tab is located in an area that can be seen even with all factory available accessories installed. One classic example is the 1964 Olds 330 vs. all later Olds V8s. 64 has the one-year-only water pump with the inlet on the driver's side, so the timing tab is on the passenger side. The balancer is obviously marked differently from others as well.

russell-t

To MDchanic...This morning I switched my vacuum advance from the

ported outlet at the front of the carb to full manifold vacuum at the rear

of the carb. The full manifold port pulls approx 15 vacuum on the gauge.

This setup has improved the drivability and idle is smoother.Had to lower

idle speed from 900 rpm to 600 after changing to full manifold vacuum.

I feel that this change will improve gas mileage,and it seems to have

better performance.

To Joe...Thanks for the reply on timing tabs.Glad to know that it has

no influence on how the car runs.

joe_padavano

Assuming the timing tab and balancer mark are a matched set (ie, don't use a 64 330 balancer on a later Olds motor), the location of the tab has no affect on how the engine runs.

As for ported vs. manifold vacuum for vacuum advance, a quick Google search will find heated discussion by fanatics of each type all over the web, often approaching religious fervor. I personally prefer simple manifold vacuum, but ultimately use whichever makes the engine run best.

MDchanic

Sounds good.

I have no idea how the 215s were set up originally (Joe knows), but if it runs better, that's what matters.

Let us know what happens with the mileage.

- Eric

russell-t

After 3 months of cruizing around with this vacuum advance setup

(manifold vacuum) the car is running much better in all the rpm ranges.

Although I've not tried to measure gas mileage exactly,it is improved too.

It,s great when somthing so simple can change so much.

oldcutlass

Glad to hear it's all better. As Joe said, very heated discussions on ported vs manifold vacuum. You won't realize any real performance increases by changing it, you will realize lower idle temps and a smoother engine idle. Some like it and some don't.

MDchanic

Glad you got it sorted out! Sometimes you just have to mess around with stuff until you finally get it right.

- Eric