If you're just "driving" it you should be fine, most 71's had slightly harder seats as the Mfr's. knew unleaded was coming. Not as hard as later 70's engines but you should still be OK in a driver. If you have any concerns throw a bottle of "Instead 'O' Lead in it every so often. I ran a stock '62 Impala 283 on 87 Octane 10% Ethanol for 10 years with no ill affects. If it's in something that's going to be worked hard that's another story.
Old racers trick. Put a small bottle of 2 cycle oil in the tank, won't smoke and it lubes the valves which is the main problem.
I've run non-hardened seats on unleaded for years w/o any issues. I know folks will say it will wear your exhaust seats, but I've not had any problems - *knock on wood*
I'm with Ernie on this. Never had a problem. Back when I was a young guy, the BEST gas all the old farts would buy was Amoco White Gas which had NO LEAD. In the 50's and 60's. Splain that. . Frank
Well...the truth of the matter is you can pull the head, install hardened seats and beat up your valves. OR, you can leave it alone and beat up your seats. The choice is yours, but in the end neither is a real concern. Run regular 87 octane unleaded and don't worry about it. I might only go another 100 thousand miles before it croaks, but when it dies, it probably won't be from the valves or seats. Good luck, -Abone.
It should run fine. I had a new 71 Ford and I was told it could run on the "low lead" that was the sign of things to come. I imagine that most people who had them kept on driving them once the lead was gone completely. Of course back then "regular" was 94 octane, athough they changed the rating system it was suposed to be the same as the 87 that they sell now.
You can also pick up some lead additive at your local parts store. I've done this for many old engines,
I've been driving nothing but old cars since I got my license (87). I only knew of one place in my area that still had leaded gas, and would occasionaly put it in untill they stopped selling it in about 89, but really I never ran anything but unleaded. Just filled up my 62 on the cheapest crap I can get about 1 hour ago. Never had a problem yet.
Just run it if you are really that worried use the additive. One of the main reasons seats Or valves get beat-up is the guide is worn out. My 72 250 had a compression of over 12-1 ran it for the better part of 17yrs as a daily driver and i ran nothing but the LcheapO 87 octang. It would start with a bump of the key but always had to load the clutch to shut it down. NO Pings no dents nicks Nothing in the pistons I can even show you photos. But when ever i took it to the track I ran 110 And I never had any valve Or seat issues. Oh and did i forget to say it had a cam with a 583/607 lift. So i have to agree with most here Run it and just use a additive now and then. just my2cents.
Uhhhh... hmmm... I have to call bullshit on this... real 12:1 and 87 do not mix, at least not with the cylinder heads on a 250, way to innefficient. I doubt you could even fuck with the timing enough to make it pull it's own weight. Sorry, I'm not buying...
I ran a stone stock 56 Buick 322 on regular gas for 5 years 90 MPH from Meridian, MS to the Indiana state line and back once no additives never had a problem.
The Nailheads are great for this, they have pretty low spring pressure and high nickle content in the castings. Another pice of advice, don't ever try and put hardened seats in a Nailhead, more often than not there will be a head ruined. water passages are to close....
If you do a valve job then put in the hard seats. I built a 72 Ford 300-6 and didn't put in hard seats. In 20,000 miles the seats were so pounded out that it couldn't be fixed and I had about 20 hours time into porting. I am presently running a tired assed 1970 390 engine that hasn't been apart, maybe ever. I have put 35,000 on the leaky old pig since I got it and it still runs out good. Bottom line is that there is residual lead in the seats for a looong time after you quit using it, grind that out and it's a different story.
I've got a non-HAMB '71 Olds Cutlass convert with the Olds 350 with over 100k on the clock and I've been driving it for the last 30 years or so on unleaded - runs just fine.
I don't know what the head pressure is on a 12 :1 but i had a 2 stroke with 190 lbs that would run on 94. It would also depend on elevation , a 12:1 set up in Denver is about 10:1
My understanding with the old engines is if they were run with the lead for 40,000, 50,000, 70,000 miles, enough lead collects on the valves and seats that you're fine to run without it basically for the remaining life of the motor. But if you were to do a valve job on that same motor, running it without lead will ruin the seats or the valves in a hurry - because you've ground it all away and now it has none. And certainly all of the already well-worn lead-gas motors I've run on unleaded have been fine with it. I had one car that was down a tad on one cylinder, compression wise, but it still always ran great and I never took it apart to see if it had a bad ring or a bad valve.
Hey zman That motor was built with a 307 12-1 Pistons were fly cut .225 to clear the valves the Head was a 194 with 1.84's intake 1.6 exhaust 583/607 lift cam the CCs on that head was 59cc . The compression was Over 12.5-1 When I gave GlenSelf the CCs on the head and the dome on the Piston he figured The Motor was Pushing somewhere between 13.9 to 15-1 compression Block was not Zero deck so I wasn't 100% the CCs of the Block with the Dome. On the track the motor would only make 3-4 passes befor it would blow the head gasket. These motors will hold just a little over 12-1 with out O ringing the Block 13-1 and up the blocks need to be O ringed. But anyway here is a Pick of the piston dome and you will see No marks in the dome.
Could be an illusion based on the pic, but those pistons look like they're down in the hole quite a bit - if you didnt account for this in the CR calculation, you may be a bit off. What's the cranking pressure? That gives a more accurate impression than static CR anyway... Al or Fe heads?
In that photo the pistons were not top dead I had the head off to replace that gasket and to have the head shaved because when it blew the gasket it put a .010 groove in the head. the motor was built back in 84 so honestly i do not remember. I took that motor out about 4yrs ago for a New build(fresh L6 250) studed this build compression should be right at 13-1 Zero deck to the pistons Reused the same pistons but had them floated, fire slotted & remilled for the New cam 691/680 lift 269/272 duration lobe center is 105
Octane requirement is dependent on the actual dynamic compression ratio,which considers the cam.Being that a hi performance cam usually lowers cranking compression.And just as important ,head combustion chamber design and how resistant that design is to detonation.Generally,a small combustion chamber is less likely to cause detonation that a large chamber. The 302 GMC inline 6 I run in my 37 Chevy truck farmer hot rod has large chambers,112 cc's after a moderate mill job.The measured compression ratio is 9.3 with a moderate duration cam with fast lift rates.The cranking compression is 165 psi on the third stroke of the gauge.With total timing and the timing advance curve set for best power and throttle response,this engine is marginal on 91 octane unleaded.Depending on outside temperate and so on ,it may tend to detonate under full load,not a good thing.Pinging at part throttle is generally no problem,but under load,it can turn pistons and bearings to shit.93 octane is readily availabe around this area,so no problem. On the valve seat,I've been told that after years of running,the seat become hardened so to speak from the valve action on the seat.But once ya cut new valves,seat errosion can occur.But all engines are different,some will have an issue,some not. When I do a head,especially an old one,I have the seats replaced if possible to restore the valve head position for best performance.
Something else too on factory "hardened seats" Unless they are stellite inserts like the flathead mil-spec Power Wagons the first time you grind them, the induction hardness is gone and they will be soft as butter. I have put heads on off of a junkyard engine that had not been cut, that didn't have any valve recession, and just took a look see at whether they were leaking with some kerosene. They will last longer than if you did a valve job on them if you plan to run unleaded. The induction hardness is only skin deep. And the embedded lead works well too, unleaded is really dry. I have a 352 with a set of used induction hardened later heads that I had on the shelf that were good and tight in the guides, and had a good pattern on the valves. They work really well. The engine has some blow by from the bores anyway, but it runs like a striped-assed ape on 89 at right at 9.5:1. Will they sink? It depends, load is the worst. When those valves get cherry hot they are going to anneal the seat unless it has resistance to heat in it. Lead or induction hardening are all you will get unless you go to inserts.
It's the material the seats are made from.Each time the red hot exhaust valve closes it "micro welds' the seat to the valve.After thousands of cycles the seat errodes,at least in theory.Valve seats used as replacements are made of a metal that resists this welding. The lead in gas helped conduct heat from the hot valve head to the seat where the heat was carried away by the coolant.This limited seat damage on hard working engines. Back in the 40-50's valve jobs weren't uncommon at 50K miles.Older engines usually had richer fuel mixtures keeping valves cooler.
Over here, when they took away leaded petrol -a few years ago - and all that was available is now unleaded, we were... and still are, able to purchase a "shot" at the petrol station to add to your tank when you fill it. The "shot" is a small syringe (bout the size of your little finger) and it basically consists of Kerosine, which lubes the valve seats. Give that a go.
I've got a just-under-the-wire HAMB '64 Olds Cutlass, and it has the stock High Compression 10.25:1 330 cu. in. motor. Been running premium (91 Octane here in Southern California) in it since the first day I purchased it some 10 years ago. After the first few months of owning the Olds, I upgraded to the Pertronix ignition and recurved the distributor. It pinged all day long no matter how much I messed with the timing. Dealt with that for years, and was certain it was the engine's timing. I was wrong... I finally pulled the damn system out some 5 years back and went back to geniune old school GM points, recurved the distributor back to where it originally was, and I rarely have a problem now. Now 79K on the original odometer.
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