Technical What Kind of Gas Chevy Small Block?

Have 29 Model A street rod with Chevy small block. Unfortunately no real info on build. Would it be good ideal to use non-ethanol gas or some other kind of gas?

How could I identify engine?

Thanks.

 

If you look on the front of the block, just in front of the passenger side cylinder head, it should be stamped with some letters/numbers, which might help identify it. But it's pretty common for folks who are putting engines in hot rods, to change stuff inside the engine.

But as for which gas to use...regular unleaded works for most cars, and the alcohol in it isn't an issue if you don't leave the car sitting for months at a time. If you do leave it sitting, it would be good to add a stabilizer. If it will sit for more than a few months, you might want to drain the fuel, including what's in the carb. If you can get non-alcohol gas, you could use it instead. It's less prone to absorbing moisture.

If the engine "knocks" or "pings" with 87 octane, you could try 91 or 93 octane. This would be an issue if the engine has relatively high compression ratio.

 

A few pictures would be good. Seeing how it is set up would give some idea of what the original builder might have had in mind.

As for octane need, the first step is to make sure that the timing is set correctly. We've all seen engines with the initial timing advance cranked way up, where it should not be.

 

Mmmostly what squirrel said.

BUT, with a good stabilizer, ethanol fuel can last...a while. I've got one car that mostly sits lately. In almost 11 months, both the battery and the fuel were up to the task, without help. I turned on the fuel pump, filled the carburetor, a coupla pumps of the throttle and with a pull on the toggle switch, the engine came to life. Ran just fine on old...but...Sta-Bil...added to the fuel, kept in if properly running condition.

Note, that any...engine that sits for more than a coupla days, needs an electric fuel pump to fill (re-fill !) the carburetor. The carburetor WILL be, or mostly be dry of fuel. Todays oxygenated gas...just does that. Alcohol evaporates quickly.

Mike

 

The climate difference between the midwest and the southwest, means that you probably need to get some opinions from folks from your area....

 

If you have the older design SBC heads with small combustion chambers and domed pistons, you probably have a compression ratio that wants higher octane fuel. They also like a lot of ignition advance due to the shape of the chamber and piston dome, and the need to allow the flame front travel across the piston dome to maximize the combustion.

If you have flat top pistons with the larger combustion chambers.......I agree with squirrel.....

 

My 54 Chevy was good on our E10 unleaded mix. Same stuff my daily Subie runs. 87 Octane. You would probably be fine with this. Only way to know is to look inside.

My Touring ran E10, E15 and we even experimented with E85 which is 85% ethanol. My fuel system was set up for alky, most cars are not.

 

We run 87 in everything, but also live at 4500 ft elevation. I put 93 in my Chevy II before I race it when I'm "back east".

 

We don't even have 93 (or 94) out this way, just 91. It's 87, 89, or 91, unless you are at the track, or the supplier.

There are a number of guys running air/water intercoolers under 6-71's and 8-71's out here, so they can push the boost up, and not run spendy and hard-to-find race gas.

I might do the same.

 

In any case, irrespective of octane requirement, if your gasoline is E10, it has a different stoichiometric ratio than straight gasoline.

Straight gasoline is standardized for complete combustion at 14.7-parts air to 1-part fuel.

E10 is 14.2:1.

It does not sound like a lot, but if you are using that fuel, and have the means to tune for it, it will increase efficiency.

Higher efficiency. means both better mileage AND more power!

 

Same here. And in the mountains of the Rockies, lots of places only have 85-89 at the pump.

 

Does it idle smooth, or does it "lope"? That is also a clue as to what might have been changed inside the engine.

 

Engine " could" be rebuilder dish pistons with 76 cc heads , & about 7.5 :1 CR , with one of those well known poser cams , either trial & error testing or tear it down ......... Or just speculate ..LOL

 

I have only ever seen 85 in Central and South America.

I have only crossed the Rockies on a motorcycle, and that was a long time ago.

 

you need to get out more

 

Sounds like a good idea, but I have no time.