Do I need lead substitute?

[64Deluxe]

Hello all, long-time nose-arounder, first time posting on here. A quick thanks to everyone on this forum for all the useful insight and knowledge I’ve gotten!

I recently purchased a 1975 Chevrolet C-30 Dually, 454/SM465 truck. The truck has 92,000 original miles and the motor has never been rebuilt; truck makes solid power and runs like a top.

Now, I also have 2 other squarebody Chevrolets, a 1979 C-20 Suburban with a 454, and a 1985 K-5 with a 305. The fuel gauges on these two trucks clearly states “unleaded fuel only”. However, the C-30 simply says “fuel”.

I understand that emissions standards were different on larger trucks like the C-30, it has minimal emissions equipment and no catalytic converters to speak of, just a simple factory dual exhaust setup. I am wondering if I should be using any sort of a lead substitute in the fuel of this truck.

If I understand correctly, this truck has a pretty tame compression ratio from the factory, around 8:1 or so, it’s a workhorse motor. I run 87 octane gas in it with no pinging or misfires to speak of, and it seems to run well; my concern lies more in the area of the truck being old enough to not have hardened valve seats. Should I be using any sort of fuel additive or lead substitute on this truck? Thank you all!

 

[Exhaustgases]

I wouldn't.

 

[Opelman]

I wouldn't either. A friend was running it in a genset powered by a Willys flat 4. We ran it loaded for 10-12 a day on engine show weekends. It developed an odd cold start knock that a teardown could not identify or repair. It only went away with discontinuing the additive. Chevy cars were unleaded required by 75, yours most likely is also but isn't labeled as such as trucks didn't have cat converters yet.

 

[Trav]

Hello all, long-time nose-arounder, first time posting on here. A quick thanks to everyone on this forum for all the useful insight and knowledge I’ve gotten!

I recently purchased a 1975 Chevrolet C-30 Dually, 454/SM465 truck. The truck has 92,000 original miles and the motor has never been rebuilt; truck makes solid power and runs like a top.

Now, I also have 2 other squarebody Chevrolets, a 1979 C-20 Suburban with a 454, and a 1985 K-5 with a 305. The fuel gauges on these two trucks clearly states “unleaded fuel only”. However, the C-30 simply says “fuel”.

I understand that emissions standards were different on larger trucks like the C-30, it has minimal emissions equipment and no catalytic converters to speak of, just a simple factory dual exhaust setup. I am wondering if I should be using any sort of a lead substitute in the fuel of this truck.

If I understand correctly, this truck has a pretty tame compression ratio from the factory, around 8:1 or so, it’s a workhorse motor. I run 87 octane gas in it with no pinging or misfires to speak of, and it seems to run well; my concern lies more in the area of the truck being old enough to not have hardened valve seats. Should I be using any sort of fuel additive or lead substitute on this truck? Thank you all!

View attachment 257857

Look in the owners manual, it may say something like this..

All General Motors engines from 1972 on up were designed to run on unleaded fuel.

 

[zrxkawboy]

I would think that by '75, they would have hardened exhaust valve seats.

 

[RDY4WAR]

That year has hardened valve seats so no. Honestly, I don't think it's all that necessary with older (pre-72) engines either. I've run quite a few 50s and 60s engines on unleaded pump gas (including E10 with carbs), some of them pushed pretty hard, without any related issues. The valve seats have shown no signs of erosion or abnormal wear. Only one showed excessive wear with poor sealing but that one also suffered from valve bounce. (stock springs weren't happy at 6000 rpm)

 

[wlk]

I had a 75/76', can't remember which, c10 w the 5.7l and never did the 3 years I owned it. Love the truck, my c10 was a single cab with the same paint scheme. Miss that old truck, it was a great truck.

 

[joekingcorvette]

I had a 1973 Chevrolet pickup back in the day and I just ran regular unleaded gas without any problems. That's a nice big truck!

 

[barryh]

The thing to take into account with unleaded fuel causing valve seat erosion is that it's temperature related. The micro welding that causes the erosion is going to be much worse on an engine that's used at sustained high revs and load. If that's not your thing, there may be very little if any erosion taking place. I still have the original cast iron seats on my old motorcycle and there is no measurable sign at all of valve recession taking placed as evidenced by valve clearances that don't change between services. If and when I do see the clearances closing up I'll know it's time to act.

 

[emmett442]

That year has hardened valve seats so no. Honestly, I don't think it's all that necessary with older (pre-72) engines either. I've run quite a few 50s and 60s engines on unleaded pump gas (including E10 with carbs), some of them pushed pretty hard, without any related issues. The valve seats have shown no signs of erosion or abnormal wear. Only one showed excessive wear with poor sealing but that one also suffered from valve bounce. (stock springs weren't happy at 6000 rpm)

All of this.

 

[Astro14]

I would think that by '75, they would have hardened exhaust valve seats.

They do. By 1975, it was common. Everyone knew lead was going away, so, engines were built to run on both.

 

[64Deluxe]

Got it! I’ll avoid the additives. Thank you so much everybody!

 

[64Deluxe]

Look in the owners manual, it may say something like this..

The owners manual actually doesn’t mention anything about leaded/unleaded fuel that I could find, I read it bumper to bumper.

 

[64Deluxe]

I had a 75/76', can't remember which, c10 w the 5.7l and never did the 3 years I owned it. Love the truck, my c10 was a single cab with the same paint scheme. Miss that old truck, it was a great truck.

They’re great trucks! My suburban actually matches the C30, I love the blue/white.

 

[wlk]

They’re great trucks! My suburban actually matches the C30, I love the blue/white.

View attachment 257906

Sweet ride!!

 

[Opelman]

That year has hardened valve seats so no. Honestly, I don't think it's all that necessary with older (pre-72) engines either. I've run quite a few 50s and 60s engines on unleaded pump gas (including E10 with carbs), some of them pushed pretty hard, without any related issues. The valve seats have shown no signs of erosion or abnormal wear. Only one showed excessive wear with poor sealing but that one also suffered from valve bounce. (stock springs weren't happy at 6000 rpm)

Most older engines do well on unleaded, only one I've seen with serious seat recession was on a 70 383 Mopar.

 

[Exhaustgases]

Leaded gas caused more valve problems than not.

 

[Sumboodie]

Never thought about it, I've got some pre 70s equipment.

 

[ChrisMU]

1971 and newer GMs had hardened valve seats, ‘72 and newer for Ford/AMC/Chrysler. 87 octane should be fine, especially with the low compression of the smog era engines. However, my dad had a well-used winter beater 1985 Caprice that ran much better on 89, brand didn’t matter. Half-ton trucks didn’t require cats or unleaded gas until 1978 or 79. It was later for the bigger trucks, like the C-30. That would explain why there’s no mention of unleaded gas in the manual or on the truck.

 

[ElectroMechanoMan]

I’ve never had any issues running unleaded gas in engines as old as a 1934 Chevy, 1938 Farmall A, a 1938 Allis Chalmers B, and a 1965 Farmall 656. The 656 did burn a valve, but I don’t believe it was due to fuel. It was more due to a lot of hours. Don’t beat your truck and you won’t have any problems.