unleaded vs. leaded for '67 straight 6

[Lefty&Son]

Hi Guys,

First, thanks to Rod for answering my previous VIN question. Not sure about this board...others I've used don't want to "waste" posts with thank yous...anyway...THANKS!

Second - I've got 2 differing opinions of gassing up my "new" 1967 GMC - NO WAY can you put in unleaded, and You can if you're not going on long trips. The second guy mentioned some additive (Marvel Oil?) that I could add.

I am soooo new to this, scared to damage anything. What do you all think? Any opinions would be greatly appreciated.

Thanks,
Lefty

[CPNE]

We like thank you's.

My opinion is the second. Drive it but don't drive it hard. You can always put in lead substitutes if you want. I don't have any first hand experience with them however.

BTW, welcome, and where in MA are you?

[O'l Buck]

When rebuilt the 330 in my cutlass, the machinist said it would be ok with the original valve seats as long as I wasn't going to race it much. I went ahead and put new valve seats in it anyway because the old ones were a little pitted and it got all new valves too.

[BtnkBndt]

I've had differing opinions on this too. I have a 67 283 PO told me the engine builder he used said to use lead additive. Have a friend who works for one of the big engine houses here in town said the same. He says the seals, seats or guides, can't remember exactly sorry should have paid more attention, need the additive for lubrication. Also said it was expensive to rework the heads for different ones.

I saw on another post somewhere, I think it was LonghornMan who said you could use 305 heads on a 283 to resolve this. Maybe later model 6 heads would work for you.

I had it saved! Heres the quote (Thank you LonghornMan):

305 heads are an awsome low buck upgrade to any Chevy small block under 307 cubic inch. Just the hardened exhaust seats for unleaded fuel makes them worth the hassle.

I'm definitely lookin into the swap.

[palallin]

I've had the hardened seats installed in two or three sets of heads. In no case was it a particularly expensive mod.

[tom hand]

Just drive it and don't worry about it. It will shorten valve life somewhat, but not enough to lose any sleep over. When ever the motor needs a rebuild, deal with it then.

[Lefty&Son]

Awesome - thanks for the info everyone...

CPNE - I live in Devens, which was the old Army Fort Devens - grew up in Reading.

[Professor]

If you are going to do some work on the internals later, then drive it as is. Using unleaded with older heads will shorten their life. But, if you plan on re-doing the heads later anyway, you can put hardened seats in them then.
Older heads had softer metal in the valve seats; the lead in the gas acted as a cushion between the valve face and the head. When the lead was phased out of the gas, heads had to have hardened seats to maintain any level of durability. Proper seating of the exhaust valves through metal-to-metal contact is a primary method of cooling the valve face/head, preventing it from overheating.
I did not put hardened seats in a set of sb 69 heads when I had them off, thinking that I would do it later on a major build-up. They did not last as long as I thought they would. The seat went on 1 or 2 valves, the valve could no longer seat/seal properly, it got hot and the extra heat consequently took out the valve guide. This made the lack of proper valve seating/sealing even worse, causing even more heating and wear of the guide. Then followed a loss of compression and a noticeable sound from the engine. When I pulled the valve covers, there was a lot of oil that had "coked" up on those valves, rockers, and springs. I pulled the heads and put in new guides and hardened seats.

[our64]

My street rod has a 71 350, with a mild cam and 4 barrel. The valve seats were designed to have leaded fuel. I now have 15,000 miles on its since I put it in the rod. It had 70,000 miles when I put it in. I used lead additive on occasion, but can;t get it anymore. Its been running great for years. City and Highway. Yes someday the seats will be damaged from the lack of lead, but its been trouble free now..

[Longhorn Man]

If you are able to find some lead additive...or a lead substitute, then run it. It will indeed make your engine last longer...at least the valve seats anyways.
The federal gov did research on this when unleaded was being phased out (all there equipment back then was designed to run on leaded) and there research said that the most wear is when you rev past 3000 RPM. Not a big deal in a car, but many of our trucks scream at or above 3000 as soon as you hit the on ramp to the freeway.
As my quote sid above, late model 305 heads are great for a 283/307 small block. If you have an inline and want later heads, I can't help...but some one here could.