Vacuum reading on 318 @ 62 MPH cruise = 19 inches - is that normal / expected?

[67CBodyGuy]

Drove my '67 Monaco with rebuilt 318 circa 1987 (Ontario ReMan) on the highway today, first time at highway speeds in 25 years. This after complete front-stub R&R, all new front suspension. I was nervous, hoping I didn't forget a bolt somewhere. I'm guessing the engine has maybe 9 or 10k miles on it total since the rebuild. Carb is china clone BBD (got this 2 years ago, to replace the Carter). Might be the "Super-6" carb.

I was watching a vacuum guage while driving. 93 octane. Ground is flat here, I can drive for miles in a straight line. Turned around and went back - direction didn't matter. Steady foot, 62 mph (100 kph), gauge was solid 19 inches. At 20 the guage reads deceleration. This looks good to me - but is it crazy good?

 

[remytherat]

That’s normal.

Smaller cam, higher rpm, more intake restriction, and lighter load all mean higher vacuum

 

[1WildRT]

Yup, normal..

 

[PROSTOCKTOM]

That's really good. Power brakes should be really happy. I am lucky if I make 13 inches on my rowdy ride.

Tom

 

[Dana67Dart]

I was watching a vacuum guage while driving. 93 octane. Ground is flat here, I can drive for miles in a straight line. Turned around and went back - direction didn't matter. Steady foot, 62 mph (100 kph), gauge was solid 19 inches

Next time floor it at 62mph and report back the vacuum!

 

[mbaird]

93 octane in a stock 318 ? Is that needed ?

 

[67CBodyGuy]

I have it set for idle timing 10 btdc, I don't know what the all-in advance is, but I believe I hear pinging on the low-grade 87 octane (10% ethanol) we have here. All grades here have 10% or so they say.

 

[413]

Find a hill and coast down it, tell us the vacuum hen.

 

[67CBodyGuy]

Find a hill and coast down it, tell us the vacuum hen.

In gear?
It'll go way over 20.

 

[halifaxhops]

bet in reverse it would go -20?

 

[Dana67Dart]

bet in reverse it would go -20?

 

[Dana67Dart]

I have it set for idle timing 10 btdc, I don't know what the all-in advance is

I was using my laptop code reader on my 96 Jeep GC with 318 (5.2). The idle advance is 17 BUT.... it is computer controlled so I'm sure it is much lower during cranking. No idea what the max timing is .

IMHO 10 btc is a nice compromise but if you get pinging you might want to either limit the max or back off 5 and see what that does.

Do the testing when the tank is almost empty and put in 1/4 tank of 87. That way if it pings you can fill it with 93 and be ok.


I'm at 5000 foot elevation and out grades of fuel are lower due to less air pressure

My 2006 3.3 Dodge Grand Caravan requires 87, 85 and it pings.


Side note:
Our local gas station has 85,87,91

The price for 85 is 3.10 per gallon
The price for 87 is 3.60 per gallon
The price for 91 is 3.95 per gallon

But if you look at the average of 85 and 91 it's 88 that's close enough to 87.

If you mix your own 50% 85 and 50% 91 the price per gallon is 3.53


Not enough to be worth the hassle but very interesting

Me

 

[RustyRatRod]

I'd be happy with 19".

 

[Dartswinger70]

Ported Manifold or Venturi vacuum?

 

[67CBodyGuy]

Ported Manifold or Venturi vacuum?

Ported off the carb, the small brass pipe coming off the throttle plate:

The other 2 larger pipes off the back of the throttle plate, one is capped, the other goes to PCV. Front large pipe is also capped. Large pipe coming off the box above the bowl is open. Brake booster comes off a port on the intake.

 

[4spdragtop]

Cool tag!

Ported off the carb, the small brass pipe coming off the throttle plate:


View attachment 1716427411

The other 2 larger pipes off the back of the throttle plate, one is capped, the other goes to PCV. Front large pipe is also capped. Large pipe coming off the box above the bowl is open. Brake booster comes off a port on the intake.

View attachment 1716427414

View attachment 1716427415

View attachment 1716427416

 

[413]

I was using my laptop code reader on my 96 Jeep GC with 318 (5.2). The idle advance is 17 BUT.... it is computer controlled so I'm sure it is much lower during cranking. No idea what the max timing is .

IMHO 10 btc is a nice compromise but if you get pinging you might want to either limit the max or back off 5 and see what that does.

Do the testing when the tank is almost empty and put in 1/4 tank of 87. That way if it pings you can fill it with 93 and be ok.


I'm at 5000 foot elevation and out grades of fuel are lower due to less air pressure

My 2006 3.3 Dodge Grand Caravan requires 87, 85 and it pings.


Side note:
Our local gas station has 85,87,91

The price for 85 is 3.10 per gallon
The price for 87 is 3.60 per gallon
The price for 91 is 3.95 per gallon

But if you look at the average of 85 and 91 it's 88 that's close enough to 87.

If you mix your own 50% 85 and 50% 91 the price per gallon is 3.53


Not enough to be worth the hassle but very interesting

Me

I have a car that will ping on regular. If I mix 50/50 with super, no ping. If I buy the middle grade it pings just like straight regular. You are better off mixing it yourself.

Turns out the procedure is the drivers put their leftovers on the mid grade tank, and since they sell way more regular then the mid grade tank gets more regular put in! Another bad deal for consumers.

 

[CFD244]

I have a car that will ping on regular. If I mix 50/50 with super, no ping. If I buy the middle grade it pings just like straight regular. You are better off mixing it yourself.

Turns out the procedure is the drivers put their leftovers on the mid grade tank, and since they sell way more regular then the mid grade tank gets more regular put in! Another bad deal for consumers.

Hmm..I always thought that the pump did the mixing. You learn something new every day.

 

[RustyRatRod]

I have a car that will ping on regular. If I mix 50/50 with super, no ping. If I buy the middle grade it pings just like straight regular. You are better off mixing it yourself.

Turns out the procedure is the drivers put their leftovers on the mid grade tank, and since they sell way more regular then the mid grade tank gets more regular put in! Another bad deal for consumers.

I hope they don't mess around with the ethanol free like that.

 

[413]

Hmm..I always thought that the pump did the mixing. You learn something new every day.

That's why I looked into it, the middle fuel was exactly like the regular. Pinging same rate.

 

[413]

I hope they don't mess around with the ethanol free like that.

I've found some stations selling alcohol gas in the ethanol free pumps, dirty rats.

 

[AJ/FormS]

The trick is to recurve your distributor, so it meets all the needs of the engine.

As it is;
IIRC the factory Base timing was TDC, to maybe 5advance tops. That means from the factory, the distributor would have had 30/35 in it, which means at 10A the total could be as much as 40/45*.
The VA might have 13>17 in it, for a cruising total of say 57/62*
So, that's a pretty good number, if a little high. Fuel-economy should be exceptional.
But the Power-Timing, and Part-Throttle Timing is all wrong, and so, it pings; which is detonation, which your 318 can only survive for a very short time, before damage occurs. It's a good thing your terrain is dead flat.
There's a good chance that with a well-fitting recurve, you can run low-octane full-time.

 

[Ricks70Duster340]

I've found some stations selling alcohol gas in the ethanol pumps, dirty rats.

You mean they sell alcohol gas in the "ethanol free pumps"?

 

[Dana67Dart]

That's why I looked into it, the middle fuel was exactly like the regular. Pinging same rate

I would bring that to the attention of the gas station AND the local authority on fuel consumer affairs - weights and measures? You know the people who put tags on pumps saying the pump is delivering the correct amount of fuel

That is theft from the consumer and not anything that the average person can check for.

 

[67CBodyGuy]

The trick is to recurve your distributor, so it meets all the needs of the engine.

As it is;
IIRC the factory Base timing was TDC, to maybe 5advance tops. That means from the factory, the distributor would have had 30/35 in it, which means at 10A the total could be as much as 40/45*.
The VA might have 13>17 in it, for a cruising total of say 57/62*
So, that's a pretty good number, if a little high. Fuel-economy should be exceptional.
But the Power-Timing, and Part-Throttle Timing is all wrong, and so, it pings; which is detonation, which your 318 can only survive for a very short time, before damage occurs. It's a good thing your terrain is dead flat.
There's a good chance that with a well-fitting recurve, you can run low-octane full-time.

That's why I put 93 in the tank, I didn't want to take a chance on causing too much ping. I'll check the timing with dial-back gun maybe tommorrow. I assume it will tell me what the total advance is going to be if I rev the engine.

This car was dormant for 20 years until the fall of 2022. Have maybe put on 20 miles on the car, slow inner-city driving. The plugs weren't happy - pretty black. After this run yesterday 50-60 miles on the highway, I pulled a couple today and looked at them. Very clean and white again. RN14YC.