Author Topic: 1773-1976 Eldorado V8's and fuel type  (Read 657 times)

Offline Seachange01

  • Posts: 19
  • Name: Alan James Beaumont
1773-1976 Eldorado V8's and fuel type
« on: April 26, 2017, 07:05:13 PM »
Hi guys,
Just a question to see what gas all of you guys with a similar car to be are using.
In the couple of weeks I have had my 74 Eldo, I have been using High Octane (91) gas.
Is this considered the right thing/the best thing to use on these?
Mine is obviously not fuel injected, but I am just curious to see what others with similar Eldo's are using.
Thanks,
Alan

Offline The Tassie Devil(le)

  • Administrator
  • Posts: 7296
    • CLC Member
      CLC Member #18992
  • Name: Bruce Reynolds
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #1 on: April 26, 2017, 07:09:24 PM »
On my '72, I was using plain Unleaded petrol.   The same should be for the later ones.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
(Past President Modified Chapter)

Offline WTL

  • Posts: 79
  • Name: W. Love
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #2 on: April 26, 2017, 07:39:45 PM »
Whale oil for the 18th century Eldorados, steam for the 19th century ones. 

My 69 barely pings on 93, but they did lower compression and I understand the mid 70 cars were far more forgiving. 

Offline 35-709

  • Posts: 2749
  • The most valuable antique is an old friend.
    • CLC Member
      CLC Member #4719
  • Name: G. Newcombe
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #3 on: April 26, 2017, 08:16:22 PM »
I use regular in my '71 and '73.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold
1950 Jaguar Mark V Saloon resto-mod

Offline Carl Fielding

  • Posts: 344
    • CLC Member
      CLC Member #10797
  • Name: Carl Fielding
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #4 on: April 26, 2017, 08:31:52 PM »
Detonation is very hard on engines. It occurs before you can hear it. By the time it "barely pings" it is no longer detonation. The technical term for this condition is "SEVERE detonation". Modern 93 octane gasoline is inadequate for most old 10:1 or 10.5:1 compression engines. I believe I have written about running my '70 CDV on 100 or 110 octane gasoline available in L.A. What a difference ! You must not run high manifold pressure in pre '71 Cads using modern pump gasoline. Keep your foot out of it. By all means continue to use 91-93 octane gasoline in your low compression post 1970 Cadillac. It is cheaper , and is easier on your engine , and you can use full throttle any time under any conditions. Oh , wait a minute. Did I say "CHEAPER" ? Huh ? Hmmmmm. Let's see. Pump price might be 5 - 10 percent higher. Could you get 5 - 10 percent better gas mileage ? Maybe under certain conditions. Very slow , light throttle , probably not. Higher speeds ,higher manifold pressure , probably. Road and Track mag tested this back in the late '50s or early '60s in a large sample of cars. All , save one , got better mileage on the high octane. The reverse was true with the VW they ran. "VWs" , as old Cadillac Carl used to say , " ain't Cadillacs". Cheaper ? Hey , it's easier on your engine. What's that worth ?   - Carl

Offline Scot Minesinger

  • Posts: 4209
    • CLC Member
      CLC Member #20543
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #5 on: April 26, 2017, 08:51:27 PM »
Alan,

Continue to use the 91 and higher octane "premium unleaded" in your Cadillac.  That is what I use on any Cadillac that runs on pump gas unless it is 80's or newer that were designed for regular unleaded.  Carl is right, when you hear a slight ping that is bad, and why take a chance.

Enjoy your Cadillac!
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Offline WTL

  • Posts: 79
  • Name: W. Love
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #6 on: April 26, 2017, 09:21:39 PM »
It would be great if I had easier access to something higher than 93.  I'm running stock timing, with full manifold vacuum.  Tried in the past using commercial additives, maybe they help a bit...but not convinced its a huge jump (think I heard .07 octane point per tank).  Looked into toulene and other home brews (even mothballs  ::)) - they all have seem to have real downsides, not to mention questionable effectiveness.  Spent a night reading about running a bit of E85 mixed in with the 93.  Just a little freaked out generally about what it will do to the system, and also thinking it would necessitate tuning the carb a little differently. 

I don't want to carry a barrel of race fuel around with me.   I just really wish there were a few pumps that had 95.  Just a little edge.  As is, I just try to really stay off the pedal, especially on hills. 

(not trying to hijack your thread, Seachange)....

Offline 7gen

  • Posts: 173
  • Name: K. Reynolds
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #7 on: April 26, 2017, 09:43:52 PM »
I don't know what the manual for 1974 states, but in my owner's manual for 1976, it states that Research Octane Number 91 unleaded gas should be used.

Research Octane 91 is the same as (R+M)/2 of 87. That's regular unleaded gas at the pump.

Research Octane 96 is the same as (R+M)/2 of 91. That's premium unleaded gas at the pump.

I use 87 octane but I can understand using premium as a rule to avoid any chance of a problem.

I believe the compression ratio on the engine went down from 10.1 in 1970 to 8.5 in 1971 which I think means that different octane recommendations would be in effect for the lower compression engines, all other things being equal. My 1976 is an 8.5 compression and it takes regular 87 octane pump gas. A 1974 is an 8.25 compression and the manual likely recommends 91 RON as well but I don't know.

That's the numbers but each car is unique and might need different octane from what is recommended in the manual. For example, my first car was a 1977 Mercury Grand Marquis  with a 402 engine. This engine had a compression ratio of 8 and the manual recommended 87 octane at the pump but it pinged on 87 and I had to run premium. All depends on the car. The manual can't tell you what your individual car needs - the car tells you that.
« Last Edit: April 26, 2017, 10:24:08 PM by 7gen »

Offline Carl Fielding

  • Posts: 344
    • CLC Member
      CLC Member #10797
  • Name: Carl Fielding
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #8 on: April 26, 2017, 09:57:58 PM »
WTL : What are the downsides to Toluene ?  - CC

Offline WTL

  • Posts: 79
  • Name: W. Love
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #9 on: April 26, 2017, 10:56:26 PM »
Too many people suggested that it was a carcinogen, so my concern is either exposure upon dumping some in the tank, or breathing whatever fumes it produces after combustion.  Not that other additives, or indeed todays pump gas (or the leaded gas of 1969) is much better. 

Offline Eric DeVirgilis CLC# 8621

  • Posts: 3797
    • CLC Member
      CLC Member #8621
  • Name: Eric DeVirgilis
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #10 on: April 27, 2017, 08:44:37 AM »
Whale oil for the 18th century Eldorados, steam for the 19th century ones. 

My 69 barely pings on 93, but they did lower compression and I understand the mid 70 cars were far more forgiving.

Ben Franklin's was a hybrid: Whale oil or lightning.  :o
A Cadillac Motorcar is a Possession for Which There is no Acceptable Substitute

Offline EAM 17806

  • Posts: 359
  • GOD Bless America - Love It or Leave It For Good!
    • CLC Member
      CLC Member #17806
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #11 on: April 27, 2017, 11:56:12 AM »
I don't know what the manual for 1974 states, but in my owner's manual for 1976, it states that Research Octane Number 91 unleaded gas should be used.

Research Octane 91 is the same as (R+M)/2 of 87. That's regular unleaded gas at the pump.

Research Octane 96 is the same as (R+M)/2 of 91. That's premium unleaded gas at the pump.

I use 87 octane but I can understand using premium as a rule to avoid any chance of a problem.

I believe the compression ratio on the engine went down from 10.1 in 1970 to 8.5 in 1971 which I think means that different octane recommendations would be in effect for the lower compression engines, all other things being equal. My 1976 is an 8.5 compression and it takes regular 87 octane pump gas. A 1974 is an 8.25 compression and the manual likely recommends 91 RON as well but I don't know.

That's the numbers but each car is unique and might need different octane from what is recommended in the manual. For example, my first car was a 1977 Mercury Grand Marquis  with a 402 engine. This engine had a compression ratio of 8 and the manual recommended 87 octane at the pump but it pinged on 87 and I had to run premium. All depends on the car. The manual can't tell you what your individual car needs - the car tells you that.
  You are correct, the 1976 devilles manual suggests we use regular unleaded gas in our 500cu engines, and I assume that applies to the 75 years too since that was the year GM began with catalytic converters. I've been using regular gas since Feb 1977 in my 76 and made sure the timing was right on 6 degrees before top dead center; if the timing is not correct I don't care what octane gas you use you will get some pinging. Be sure the timing is on the money and use regular (87 octane) gas and your 75 and 76 should run very well.  EAM
Ev Marabian

1976 Cadillac Coupe DeVille, 1989 Chevrolet Caprice Classic

Offline bcroe

  • Posts: 2016
    • CLC Member
      CLC Member #14630
1773-1976 Eldorado V8's and fuel type
« Reply #12 on: April 27, 2017, 06:24:47 PM »
WTL : What are the downsides to Toluene ?  - CC 

That tetra-eythel-lead is extremely poisonous stuff by itself; I wouldn't want to
be messing with it.  I suppose they used a lot of it, plus super refining during
the war; by the end our fighters were running on 130 octane. 

Ping can be caused by carbon buildup in an engine not used as hard as mine;
can be removed with the water treatment.  And a loose timing chain about
drove me crazy with pinging 3 decades ago, till I figured out the problem. 
Getting a tight chain is better than premium.  Bruce Roe

Offline 7gen

  • Posts: 173
  • Name: K. Reynolds
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #13 on: April 27, 2017, 06:39:14 PM »
The "water treatment"? What is that?

Offline Dan LeBlanc

  • Administrator
  • Posts: 3522
    • CLC Member
      CLC Member #27657
  • Name: Dan LeBlanc
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #14 on: April 27, 2017, 07:04:42 PM »
Google Italian tune-up and you'll have your answer.
Dan LeBlanc - CLC # 27657
1970 DeVille Convertible
1953 Series 62 Sedan (Parts Car)
1953 Fleetwood (Project Car)
2004 Deville

Offline Carl Fielding

  • Posts: 344
    • CLC Member
      CLC Member #10797
  • Name: Carl Fielding
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #15 on: April 28, 2017, 04:14:52 AM »
High BMEP on takeoff during the heyday of the great recips of aviation required Anti Detonation Injection (ADI). A 50/50 mix of water and alcohol was used. The high specific heat of water in the mix cooled the temp of the charge as it changed state from liquid to gas. Sometimes you could see the carbon mess blown out in the exhaust at the right moment. We were taught that the alcohol played no part in suppressing detonation. It was said to be simply antifreeze , for obvious reasons. I have read that the methanol DID contribute somewhat. I cannot pass judgement on this. But I did use an Edelbrock Vara-jection water injection system on one of my Cads. This was a very long time ago. I wonder what the thinking on such systems is now. Anyone ?   - Carl

Offline The Tassie Devil(le)

  • Administrator
  • Posts: 7296
    • CLC Member
      CLC Member #18992
  • Name: Bruce Reynolds
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #16 on: April 28, 2017, 07:18:38 AM »
I also used an Edelbrock Vara-jection unit on my 1937 Chevrolet Hot Rod that was powered by a 12.5 to 1 427 L88 Chev, bored out to 440.   It used to consume a Gallon of water every 100 miles, but no hint of pre-ignition.

Wish I had kept it as I could use it on my '72 Eldorado to replace having to use a bottle of Octane Booster every time I fill her up.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
(Past President Modified Chapter)

Offline EAM 17806

  • Posts: 359
  • GOD Bless America - Love It or Leave It For Good!
    • CLC Member
      CLC Member #17806
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #17 on: October 12, 2017, 02:46:46 PM »
  You are correct, the 1976 devilles manual suggests we use regular unleaded gas in our 500cu engines, and I assume that applies to the 75 years too since that was the year GM began with catalytic converters. I've been using regular gas since Feb 1977 in my 76 and made sure the timing was right on 6 degrees before top dead center; if the timing is not correct I don't care what octane gas you use you will get some pinging. Be sure the timing is on the money and use regular (87 octane) gas and your 75 and 76 should run very well.  The major oil companies state use the grade the car manufacturer report in the car's owner's manual; higher octane is a waste of funds because that specific car does not require it.  Be certain, again, the timing is on the money and if it is then you better look elsewhere, not with higher octane, unless you have an abundance of cash to waste.  EAM
« Last Edit: October 16, 2017, 12:35:21 PM by EAM 17806 »
Ev Marabian

1976 Cadillac Coupe DeVille, 1989 Chevrolet Caprice Classic

Offline "Cadillac Kid" Greg Surfas 15364

  • Posts: 2751
    • CLC Member
      CLC Member #15364
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #18 on: October 12, 2017, 02:52:32 PM »
Carl
I believe the over Boostwith water/methanol injection was the "war emergency" throttle setting.
Greg Surfas
« Last Edit: October 12, 2017, 06:52:24 PM by "Cadillac Kid" Greg Surfas 15364 »
Cadillac Kid-Greg Surfas
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Offline The Tassie Devil(le)

  • Administrator
  • Posts: 7296
    • CLC Member
      CLC Member #18992
  • Name: Bruce Reynolds
Re: 1773-1976 Eldorado V8's and fuel type
« Reply #19 on: October 12, 2017, 05:29:44 PM »
I used Water Injection with great effect in my road car when running 12.5 - 1 compression.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
(Past President Modified Chapter)