old car octane

[9Trac]

I own a 2002 ST but this is about my 1971 Ford LTD convertible with a 400 cid and 2 bbl carb. For years I have been using 93 octane gas but with prices where they are I was wondering if it could tolerate 87 octane. I've never done anything to the valve seats. I guess I could go on and try it to see but I don't think I'd want to risk doing damage to the engine.



Thanks for any help. By the way, the car is for sale, located in the Jacksonville FL area.

 

[Travis Munday]

The compression ratio of the engine may be too high to safely run lower octane gas. The gas will predetonate and cause pinging and may cause further engine damage, so I woudln't really suggest dropping all the way to 87; 89 or 91 it might could take better.



I've actaully got a question for you now, for my project car I'm using the brake system from a '71 LTD, master cylinder, booster, and complete front spindles with calipers and rotors. Well, I'm missing the passenger side rotor and backing plate, and I haven't been able to find a place online that sells them cheap, you know of a place? I haven't checked all the junkyards around me, but they are mostly later models so I'm not holding out hope.

 

[TRACket Paul]

You'll need to maintain the octane level for the engine or damage will result to the valves/valve seats or pistons.

You can add octane booster to the 87 octane gas which may or may save you some money. Do you know what the actual octane requirement is for it? 93 seems a little high for a 2 barrel carburetor.

 

[Bill Cooksley]

I think you will find that the 400 will run just fine on the 87 gas. I just looked in the book its only 168 hp and has a comp ratio of 8:4 to 1 go for it reg. will be good have fun. Bill

 

[Shawn Hennessy]

#9 Trac

I've never done anything to the valve seats. I guess I could go on and try it to see but I don't think I'd want to risk doing damage to the engine.

It isn't the octane that is at issue with the valve seats. The concern is around unleaded gas....but not in your application.



Unless you're drag racing, pulling a heavy load constantly (i.e., a truck towing a trailer) or something similar that puts a lot of RPM's and a lot of heat (like where the exhaust starts to get red, running lean EPA-style mixtures), there is no big problem running unleaded in an engine without special (i.e. hardened) valve seats.



If you were running high compression or a blower...that scenario might push you into the territory where hardened seats are needed.



Like Tiger says, the pingin/predetonation is the issue with lower octane. I remember dudes buying octane boost and adding it to their 87 octane at fill-up. It seemed to be about the same in cost at that time, as premium gas.

 

[Fred]

Retard the timing if it spark knocks. As far as the valve seats go, I always thought it was the lead that gas no longer has that cushioned them. Thus old heads being reworked getting new stainless steel seats. (I think)

 

[Gavin Allan]

1971 and later vehicles were made to run on unleaded gas (even though it wasn't that popular until 1975, when catalytic converters were required).



An LTD probably did not require high-octane fuel. Usually, it was the exotics, sports cars, or luxury cars that required premium.

 

[Johnny O]

Since it's a 2 bbl engine, it will run fine on 87 unleaded. Like Gavin said, starting in 1971 most cars (and all GM's) were tuned to run lower octane unleaded although a few still had high compression (some hi-perf Fords and Mopars). By 1972 the party was over and everybody had lower c.r.'s.

 

[Ben Poche]

if it is stock it will run fine

 

[Phil Frady]

You probably won't be able to tell the difference.

It's low compression and low fuel delivery, you would hardly notice.