I just got (about a week ago) a '67 Delta 88 with a 425 and 2-bbl. The owner's manual, which was still with the car, says to use regular fuel for the low compression 425 with 2-bbl and premium for the high compression. How can I tell whether I have the high compression or low compression 425?

Also, in this day and age, is it still necessary to use premium fuel if it was required back in 1967? Not that I'm averse to doing so. It's just that gasoline is considerably different now than it was 42 years ago, and some of the qualities of premium fuel that made it necessary in 1967 might be present in regular fuel now. Also, these cars took leaded fuel, and that hasn't been around for going on 30 years now, yet we put it in and drive these cars without thinking twice about it. Clearly it would seem that whatever the lead did to protect the valve seats in cars back then is present in today's unleaded fuels in some other form.


Thanks.

 

It is most likely a low compression engine because of the two barrel, but honestly who knows what has been done with it over time. I believe the only way to actually tell is to take off the heads and look at the pistons. You might be able to look in the spark plug hole and see if the pistons have a small or large dish. Try running it on regular and see if it has any pinging, if so, get high octane.

 

Thanks. It's just funny because it says this in the owner's manual, and I doubt the owner's manual would expect the average owner to remove the heads and look at the pistons just to find out what kind of fuel to use. Maybe it originally said on the window sticker, but that certainly couldn't be expected to survive and always be kept with the car if it was later sold or traded in. It would seem that that there would be an easy way for the casual owner to find out. Perhaps the label on the air cleaner, which says "ultra high compression," except mine doesn't because it has the wrong air cleaner. But maybe not.

More importantly is what you said. By now, after 42 years and 129,000 miles, who knows what's been done to this engine and what's been run through it. I figure I will use regular as long as it doesn't knock and not worry about it.

 

That's not true, you don't have to remove the heads to tell. On the passenger side head on the front is a machined pad thyat should have a stamped number. This is the engine unit number. The prefix/suffix letter/s should tell you which you have as listed in the '67 Chassis Service Manual.
Post the digits and we'll translate them for you.

 

If HC the gas cap if original should say premium fuel only. If original air cleaner is there is should be orange/red and say ultra high compression. I think still in '67 the standard engine in the delta was a 2bbl HC 425. To get the best performance out of the car use premium fuel as it will help eliminate pinging and timing can be set close to or to factory specs.

 

First, to answer wmachine, the only numbers I could find were two that were cast into the engine. One is directly behind the water pump and says 389244D, with the "D" much larger than the numbers. From what I've read elsewhere, this says that it's a 425. Does it tell anything further?

The other number, which I've not been able to determine what it means, is above the other just to the driver's side of where the upper radiator hose attaches to the engine. That number is 397357.


But Oldsmaniac had the answer. I don't know why it didn't occur to me to check the gas cap as that would be something that would be expected to survive and be readily accessible. So I went and looked at it. The good news is that it is the original, 42-year-old gas cap. The bad news is that it is the original, 42-year-old gas cap.

In other words, it was there but it was covered with 42 years of crud. A quick treatment with a wire brush, though, revealed all, and it most certainly says "PREMIUM FUEL ONLY." So I guess that answer's that. Thanks to all.

I notice that it also says "NOT VENTED." But it has to be vented somehow in order that air can get in to replace the gasoline as it's drawn out, otherwise a vacuum would develop, and the fuel would be increasingly harder to pump out. Also, the gas cap would become more difficult to remove. Am I correct here? So what does "NOT VENTED" mean?

Just because one can these days, I took pictures of the cap before and after, and those are below.

 

The tanks are otherwise vented. When caps are down low and could slosh/leak gas, they are unvented and the tank has other vents built into it, just not through the cap.
Easy with the wire brush on that cap! Those premium fuel caps are worth some money!

 

I thought of this the moment I did it! But I plan to keep this one on the car, behind the license plate, doing its job, and where it will never be seen. (Do judges pull down the license plate and check this sort of thing at car shows?)


Thanks for the info about the venting.

 

Oh lord, someone swapped ON a 2 bbl manifold and carb?
Is there some sort of chain that permanently locks that cap to the vehicle? It sure is much easier to change a gas cap than to change the manifold and carb, no matter if it was 1967, 87, or 2007.

If my memory serves me right, the 2 bbl cars had 9:1 compression, and that WILL require you to run premium fuel from today's swill pump.
A true premium fuel engine will rattle on anything from today's pumps if tuned to stock specifications.
If my statement is off, I am sure to hear it now.
Jim

 

Not necessarily, if I understand what you're getting at. According to the owner's manual, at least, one combination that was possible to get on this car was a high-compression 425 with a 2-bbl carb. That combination is listed on the page that shows what kind of fuel to use in the vehicle. That page shows three possible combinations: the one I just listed, low-compression with a 2-bbl carb, and high-compression wth 4-bbl. The two high-compression versions were to take premium fuel, the other regular.

 

The standard engine was a 2bbl high compression as already mentioned. A 2bbl in the mid sixties does not equate to a low compression engine.

 

Okay, let's talk specifics for '67 425s
Super Rocket V8, 2-bbl, 9.0 comp, 300 hp
Super Rocket V8 H.C., 2-bbl, 10.25 comp, 310 hp
Super Rocket V8 H.C., 4-bbl, 10.25 comp, 365 hp
Starfire V8, 4-bbl, 10.5 comp, 375 hp
Toronado Rocket V8, 4-bbl, 10.5 comp, 385 hp

All except the first one are considered "high compression".