This is a question for you pro engine builders out there. It is not boat related, but has been bothering me for awhile.

I have a '70 Corvette with a 350/350 engine, 11:1 compression. It was obviously designed before unleaded gas came into being. I was always told that it would be necessary to change the valve seats in order to run unleaded gas, something about the lubricating qualities of lead. I even got quotes from a number of machine shops who perform this change. It occurs to me, however, that we all ran Amoco unleaded high test at that time with no adverse effects. Is this a scam by the machine shops?

Very interested in your response! Thanx,
Seamate

YOUR right amaco was used inthe 70's no problem ,,right?
Its becaused then as now they use other things than lead to
lube the seats ,ect ,,,,the primary thing lead did was keep those 10 and 11 to 1 motors from knocking !

I one ran a Volvo 170 AQ 3.0 l line 6, with triple solexes carbs, in an old Glastron V184. I had a head problem, and used a junkyard automotive head, with cast iron valve seats.

All was well for a season or so, then the boat became really hard starting when hot..an old timer suggested the valves were too tight..solid lifter rig..they were..the clearance had gone away, as the valves had pounded their way into the un- hardened valve seats.

When I tore down the head the wear was quite apparent. I had Stellite seats installed, and ran the boat sucessfully for many a year with no further trouble.

My understanding is that the lead , in addition to boosting octane, provides a solid film lubricant that cushions the valve closing..sounds like bull**** to me..but all the unleaded motors today do have hardened seats.

An engineer buddy tells me that the lead is super corrosive, and the unleaded fuel is a major reason engines last a lot longer these days..I think it has a lot to do with CNC machined parts and better QC leading to better fits.

FWIW, Dave

PS, here is a pic (taken right before I fell thru) of my boating "grounds" Casco Bay Maine.. a salt water bay..who needs a boat when it is 8 degrees!

Hardened valve seats are not a scam. But some motors are much more prone to seat wear than others. Since your 350 probably runs pretty rich it will not wear the seats as much. Lead is a lubricant along with being an octane booster. The only place it is really needed is on the valve seats-especially the exhaust because of the heat. There are numerous reasons why engines seem to last longer now. They burn cleaner, oil dilutes less, less deposits, closer tolerances, better materials(like hardened valve seats ) better machine and assembly techniques. It all adds up to a better quality, more efficient powerplant.

Too bad all the new transmissions suck .........

Oh, and the Amoco was "Low Lead" not "No Lead", still had some in there.

Back in the mid 80's we had a pair of Merc 330hp 454" engines in a 1979 Scarab that we wanted to upgrade. The heads they were using back then were the GM oval port "049" castings which is a very GOOD head. We had the heads bowl/pocket ported and installed the larger intake (2.19) and exhaust (1.88) STAINLESS STEEL valves. After running them for one season we had to take the engines out and bore the bottom ends. When we removed the heads the we quickly noticed how the stainless valves had BEATEN the seats down on the exhaust side---if I am remembering correctly. We couldn't help but notice how the valves we sunken within the combustion chambers. Honestly, I cannot remember if it was on the intake side or the exhaust side. Anyway, we obviously had to have hardend seats installed.

Seamate,
It probably comes down to how much you use it. Two years ago I sold a 64 Chevelle SS 300/327 4 speed. Owned it for 10 years but only put MAYBE 500 miles a year on it , sometimes not even that. Never had a problem with it .
I have seen daily drivers with sunken enhaust seats after 50/60,000 miles , and marine use is far more abusive than any car will see.
I also had a BB Chevelle new in 1970 and ran Amoco exclusively and never had a valve related problem in 5 years and 85,000 miles.
If your Vette is a toy that sees minimal use , I wouldn't worry about it. Besides , @11:1 you'll need premium anyway , so just use Amoco

Oh yeah , I also used Amoco premium in my 64 Chevelle , because although it looked factory stock , it had a 365hp cam and the heads were ported , polished and shaved a bit. Boy did that black little sucker run good .