Gasoline requirements?

[Florida_Orange]

In this video the Boss 351 owner states that he had to "de-tune" the engine so that it could run on unleaded gasoline. A thought that has never occurred to me before because I don't yet own my dream car. Will a 71-73 mustang run on modern gasoline? If not, what issues will I have to address when I purchase my car? If they will run on modern gas, what is this guy referring to?

Video: https://www.youtube.com/watch?v=qvyNLGGd91k

 

[CZ-75]

there are 2 issues with modern gasoline:

First is Ethanol. Most of our gas now has 15% Ethanol. Ethanol will eat away at older rubber seals and fittings, which will cause issues in older carbeuraters. Newer ones, however (like if you buy a new Holly or Edelbrock, etc.) are built with rubber/plastics that Ethanol will not harm.

Second is compression ratio. In days of old, lead was added to gas to keep engines from pinging. When lead was removed, engines were built with lower comression ratios so they wouldn't ping even without the lead added to the gas.

Low compression generally means lower power. So... engines today, with higher compression ratios require higher octane gas, which also help keep engines from pinging.

compressions of about 11:1 and higher require high octane fuel, and also may not be able to advance their timing as far as might otherwise possible. Advancing the timing can increase power, but ti also increases the likelihood of pinging.

 

[jbojo]

In this video the Boss 351 owner states that he had to "de-tune" the engine so that it could run on unleaded gasoline. A thought that has never occurred to me before because I don't yet own my dream car. Will a 71-73 mustang run on modern gasoline? If not, what issues will I have to address when I purchase my car? If they will run on modern gas, what is this guy referring to?

Video: https://www.youtube.com/watch?v=qvyNLGGd91k

The Boss motor was around 11.5 : 1 compression so it would have a hard time with todays gas. The motors with 10.0 : 1 and below should be ok with todays gas. I have 10.5 : 1 running 92 octane and it ran fine. If I do get pinging i'll have to add octane booster to fix that but I don't anticipate having to do that. It is recommended that the exhaust valve seats should be changed to a hardened seat with unleaded fuel with some saying it's not necessary. If you rebuild the motor change those seats then.

BTW, I heard that the lead in gas actually provided a cushion for the valve seat when the valve slams shut as well as raising the fuel octane for the higher compression.

 

[Kit Sullivan]

Yes, the lead "salts" did provide a cushion of sorts to the valves. The BOSS 351 engine was a sky-high 11.7/1 compression ratio, requiring 101-octane gasoline when new.

10.5/1 is about the upper limit that can be used with today's 93-octane swill.

If done correctly, a BOSS 351 engine could be converted to lower compression and with hardened valve seats so that it could live happily on 93-octane...and it could be done without losing any performance or power.

The word "detune" I think is used improperly in a lot of cases.

My 71 429 CJ, which ran 11.3/1 when new has had a lot of internal mods: 10.5/1 compression now, modern cam, valves and springs, worked heads and manifolds, etc...

It produces significantly more power than it did stock, runs on pump gas, and gets better mileage.

I would not consider that "detuned", just modified.

 

[Jeff73Mach1]

I'm running 11.5 to 1 Compression in a 393 4v Cleveland stroker and it neither pings nor detonates on Premium unleaded. It can be done.

My distributor was recurved to reduce total advance. I have the power valves pulled from the carb and the jets were increased in size (I'm running a Holley 850 DP) THis was necessary as the lopey idle and low vacuum of the Lunati Solid Roller Long duration cam was just too much for any power valve to work properly at all engine speeds. I have an HEI distributor and my plugs are gapped at .045. I did add a idle solenoid that allows the throttle plates to fully close when the key is off

I guess I'm detuned as I start off with my timing at 12 degrees and it maxes out at around 32 degrees. My power level is roughly 150% of a Boss 351.

So what I am saying is you can often run on crappy gas if you take the time to make a few changes. I think the most important three changes are having the distributor recurved for less total advance, improving the ignition performance with a pertronix or other higher voltage than stock system, and spending some time on the carburetor to make ure it is dialed in to the engine.

 

[jbojo]

I'm running 11.5 to 1 Compression in a 393 4v Cleveland stroker and it neither pings nor detonates on Premium unleaded. It can be done.

My distributor was recurved to reduce total advance. I have the power valves pulled from the carb and the jets were increased in size (I'm running a Holley 850 DP) THis was necessary as the lopey idle and low vacuum of the Lunati Solid Roller Long duration cam was just too much for any power valve to work properly at all engine speeds. I have an HEI distributor and my plugs are gapped at .045. I did add a idle solenoid that allows the throttle plates to fully close when the key is off

I guess I'm detuned as I start off with my timing at 12 degrees and it maxes out at around 32 degrees. My power level is roughly 150% of a Boss 351.

So what I am saying is you can often run on crappy gas if you take the time to make a few changes. I think the most important three changes are having the distributor recurved for less total advance, improving the ignition performance with a pertronix or other higher voltage than stock system, and spending some time on the carburetor to make ure it is dialed in to the engine.

Not to hijack this thread but I do have a question about the timing aspect. I plan to lockout the advance on the distributor and allow the EFI computer to control the timing. What is your opinion on this? the control module should optimize the timing based on engine reqmts correct?

thx

 

[Jeff73Mach1]

absolutely! I'm not big into the EFI world, but that is one of the advantages of the computer control. You can adjust timing curves on the computer to suit engine needs. Also the computer can retard upon starting and can have multiple advance profiles for tailoring the ignition timing to your specific needs.