1960s Fuel Grade Recommendation for '67 DeVille

[CadConvert67]

While this topic may have been covered previously, my question is what grade fuel is recommended for running in the 429 in my '67 DeVille convertible?  Local options include 91 recreational gas but if on the road may not be available.  Thanks for any direction.

[64\/54Cadillacking]

The 429, as well as other Cadillac engines from this era require premium fuel as they are high compression engines. 91 is barely adequate for these motors since when these cars were new, they required at least 100+ octane ratings in order to run very smooth at original timing specs.

I've never tried using 87 since I don't want to risk pre-detonation in my 64 Cad.

[V63]

As a frequent and gratuitous participant of the forum here, now labeled a "moocher" ...please consider the source:

I notice that Lucas fuel additive reports their product is also an anti pinging formula. As well as upper cylinder top lubricant. I just paid $35 for a gallon and treats 10 gallons with 3 oz.

I'll try it! Will advise!

[Cadillac Jack 82]

We only get 91 here in AZ.  Lead additive plus that works fine but I wish I could get my hands on avgas

[TJ Hopland]

Local options include 91 recreational gas but if on the road may not be available

Most places the premium option with the note on it is non ethanol which is a good thing for an old car especially if it doesn't get used a lot.  The definition of recreational usually includes classic cars too. 

If the pump says 'off road' is when you have a problem because 'off road' fuel doesn't have the road taxes on it.  Diesel is often sold that way but I don't think I have ever heard of gas except in the case of aviation gas.       

[badpoints]

You should be fine with 91 octane.

[CadConvert67]

Thank you for the feedback and recommendations!

[CadConvert67]

One reply addressed the "on the road" comment in my question.  To clarify, locally I have the option of buying 91 rec gas which has no ethanol but when I'm away from my home area, that may not be an option.  Thanks to all who addressed my question.

[Gabe Davis]

I have the option of buying 91 rec gas which has no ethanol but when I'm away from my home area, that may not be an option.

Check out the Pure Gas app. It shows you the location of gas stations with ethanol free gas in your current location or anywhere on a map. I found a gas station near my house that I never would have thought they'd had ethanol free 91.

https://apps.apple.com/us/app/pure-gas/id454559068

Then throw a little VP Madditive in there. I use the "off-road" version in my '59 as it has TEL in it.


https://vpracingfuels.com/product/octane-booster-vp-octanium/?c=367&;

It made a massive difference in how smooth the idle is on my car. And helps keep the valve seats happy.

[Jeff Rosansky CLC #28373]

I run standard mid- grade with a little Marvel's. She does just fine.
Jeff R

[Clewisiii]

Tried looking into the Pure Gas app. I cannot download it because it is for an older version of Android

[jaxops]

We only get 91 here in AZ.  Lead additive plus that works fine but I wish I could get my hands on avgas

Don't use AVGAS!!  Just my opinion but adding Seafoam for the ethanol, and an octane booster is probably your best bet.

[Jeff Rosansky CLC #28373]

Don't use AVGAS!!

May I ask; Why not?

Jeff R

[TJ Hopland]

One reason would be the lack of road tax. I believe most states its $1000 minimum fine or $10 per gallon which ever is greater.  I don't think there are typically swat teams in the bushes around airports looking for this but its still something to consider.

Its also a hassle since in most cases you can't just drive up and swipe your card.  Then the cost, right now in the USA looks like its about $6.50 average vs $3.30 for regular and what $4.50 for non ethanol premium?    

["Cadillac Kid" Greg Surfas 15364]

Aside from the legal issues, AV Gas is going to UL 94. There are other characteristics that detract from it's being appropriate for automotive use such as lower vapor pressure, etc.   guess we are fortunate here in Texas (and many other states) that we have 93 octane pumps. I ran that for 20 years in my 66 (10.7:1 CR) and fro just going to the track or drive in it works well for my "hot rod" 73.
Greg Surfas