regular or unleaded gas

[thelonewolf]

 My. Manual for  my 71 Apollo  says  regular gas. Only. Does that mean  I should u   put  lead additive  in the. Unleaded gasoline.   I no this. Probly a weird question but.  I thought I ask. 

[Elandan2]

The lead additive will help protect your valves and valve seats.  When the switch was made to unleaded gas, the manufacturers began hardening the valve seats and putting in sodium cooled or hardened valves to compensate for the lack of lead in the fuel.  If the engine has been rebuilt, it may have had hardened (stellite) valve seats put in so it can run unleaded gas.  If you don't know if that has been done, the safest thing to do is put in the additive.  Rick

[thelonewolf]

Thank you rick. As I am new at this. And  I am thinking I bit off more then I can chew.  But so far. Its been a real  good experience so far alot of cussing  and alot sweat and a few tears. And lots of cash.

[ClydesdaleKevin]

If I remember correctly, you can also use spacers under the heads to lower the compression ratio, and then run any gas you want without additives...but if you go through the labor of removing the heads anyway, you can have the valves and valve seats replaced with hardened ones while you are at it.

Kev

[DRMousseau]

The issues of unleaded fuel are far less today than it was in the mid-70s. With poor substitutes then available, and the dramatically reduced octane, high-compression engines like yours, really suffered. Most notably was valve head and valve seat wear, and the only real solution then was to lower compression. This was done by either a piston change or the "quick and dirty" added head gasket. It also was necessary to retard ignition timing to prevent damaging spark knock. All these combined to greatly reduce the horsepower efficiency those big-8's were capable of.

Specially hardened valve seats were designed to overcome these issues, as were filled valves, to reduce wear and were made available for replacement. But lower compression and retarded spark were still necessary until the advancements of better additive technology and ethanol became common. The improved qualities and higher octane of modern gasoline formulas have allowed older unmodified, high-compression engines to again come to life with little concern of the damage we were once worried of.

IF,... you have engine knock under load or pinging, in ANY engine, then corrective actions should be taken. Either reduce ignition timing a bit, use a higher octane fuel, or improve fuel octane with the addition of available after-market fuel additives and lead substitutes. I'm not sure you easily find any "tet-lead" fuel additives, but if true leaded fuel were your option, you would probably be in violation of current laws forbidding it's use.

You should have no concerns today, of todays available fuel being used in your older RV engine. Any damage to your early 70's engine due to unleaded fuel, was likely suffered long ago when the original owners may have used it inadvertently or because leaded fuel was becoming increasing difficult to find shortly after they bought it. But nothing to worry of if there is no current issues with your engine today.

[Rickf1985]

The 71 318 was not a high compression engine. It was designed to run regular gas. The hype about unleaded gas ruining valves and seats is mostly just that, hype. Unless you are running a high lift, long duration flat tappet cam then the valves will live a reasonably long life even with unleaded gas. High lift long duration cams bring the valve down hard and fast and combined with high RPM that will recess the seats into the head. Compression has nothing to do with running unleaded gasoline. Modern engines run 10.5:1 all the time. Granted, the timing is controlled by computer so it is constantly on the edge but the lead in the fuel has nothing to do with compression or preignition. Octane has everything to do with it and the high octane gas is still available. None of the engines in these motor homes are high compression engines.

[MotorPro]

A 71 does not have hardened seat . Under load like climbing a hill in a motor home is the worst case for valve seats.  I have had customers bring me heads where the valve was over 3/8" deep in the head. You have 2 choices, have the exhaust seats replaced with hard seats or run lead additive. Octane has nothing to do with this.

[ClydesdaleKevin]

If it was me, I'd just run it using the cheapest gas until you had a problem, and then just replace the engine with an 80's 318...and chances are, you won't have any problems anyway.

Kev

[Rickf1985]

You will not need to replace the engine, just the heads or have them reworked. The 318 itself will last damn near forever.

[M & J]

What Rick said.

[Oz]

Here's a simple chart to put that into perspective...

[DRMousseau]

Yup,... like Rick stated, it's all "mostly hype" today, that stemmed from the serious early problems of unleaded conversion. Without a good substitute for the buffering and octane that lead provided, most all engines suffered serious damage if action wasn't immediately taken. I too have seen valve seats seriously eaten away. Knocking, pinging, and extremely high temps in the exhaust valve, caused a sort of particle "spot welding" of the seat to the valve. That particle would blow out the exhaust and pick up more from the seat, literally "eating" the valve seat away. Most notable symptoms were loss of power, backfiring and leaky valves. The high temps also caused weakened valve heads that occasionally broke and caused SERIOUS piston, cylinder, and head damage.

That period of time in the early-70's, when this was most problematic, was also a time of increasing fuel costs and less traveling in gas guzzling motorhomes due to the "73 gas crisis". If your "classic" survived thru this period, and endured the following decades, it likely suffered little damage. If it instead was driven and used heavily during this time, then it was likely seriously damaged requiring at least a top-end rebuild and probably had the cooler filled valves and hardened seats installed at sometime.

So if it's running today, and has been since whenever,... then there's really no need to worry none.
Now IF,... you have something that hasn't been run for a couple decades, chances are it jus might have been retired early because of the damage that affected performance, and someone jus couldn't afford a rebuild since then. It kinda makes me wonder about some low mileage early 70's classic that's been sittin in storage for 30+yrs. When was it parked?? Why was it parked?? Why hasn't it been used since??? Yes,... probably needs a rebuild in spite of low mileage.

[Rickf1985]

Here's a simple chart to put that into perspective...

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