I have a question about purist originality from you good Corvette folk. I am a car nut, and have worked on cars for 30 years, but my knowledge lies with weird British stuff and some old USA iron, but less with Vettes.

I have a friend that wants to sell his numbers matching '69 427 with 4-spd and side pipes. It has not been converted to run on unleaded. He wants me to work on getting it ready for sale.

I know that with most cars, converting to unleaded means replacing the valve seats and guides with bronze and hardened respectively. Does that hold true for this engine as well? It goes without saying that new valves and springs are required with the swap.

Second--How does the Vette community (read: whoever is willing to pay the most for this car) feel about modifying a numbers-matching car in this way? Is it a Pure-originality vs. Practicality contest?

British-car people in general...and yes, even many purists...usually don't complain about unleaded converts because MGs, Triumphs and whatnot are usually driver cars. In other words, the owners are usually so happy they got the car running they can't wait to drive it as far as they can before the next breakdown and don't want to carry a leaky bottle of lead additive.

What's the word among you?

Andy

 

In a word, no. There's no evidence that valve seat recession occurs on older Corvettes. The vast majority have never been converted, nor do they need to be. There's no need for lead additives for any reason also. Pump gas of the correct octane, and you're all set.

 

The mythical valve recession. The reality is that these engines don't need any alterations to run on unleaded pump gas. I've been running my cars both big and small blocks for years with no issues. No hardened valve seats and no valve recession in any of my cars.

 

There is no conversion required. If that 427 engine has higher compression ratio than 9.5:1 (I believe that all '69 427 engines were over 10:1), then you will need to detune the engine so that it will run on today's premium fuel or you'll need to add an octane booster to the fuel tank at fill up's.

 

The comments above are correct.

I'm an SAE member, and I get all the technical info generated by the society. Back when the unleaded gas/valve recession issue came to light, a lot of testing was done to evaluate the problem. The results are as follows:

In passenger cars and light duty trucks driven in "normal" use, there is no valve seat recession or erosion when using unleaded gas in pre-1971 engines (1971 saw the advent of induction-hardened seats). If a pre-1971 engine is run on unleaded gas and used for extensive heavy pulling (pulling loaded horse trailers up long mountain passes at wide open throttle for extensive duration), the pre-'71 heads can see more rapid seat wear than the post-71 heads. Brief WOT operations, such as 1/4-mile activity, has no effect on seat wear.

So to fix the unleaded gas problem, simply stop pulling your horse trailer with your Corvette...

Lars

 

So what fuel has he been burning since leaded gas was phased out in the mid 90's?

 

He bought the car about 8 years ago, and has only put 4k on it. He said that he did some research and was told that he would be fine if he just filled it with premium unleaded.

You all have addressed the issue of the seats, but what about the valve guides? I realize that most of what I'm basing this on is British cars and may not translate to big iron, but from what I understand, the lead was originally an octane booster as well as a lubricant for the valves. Is this not an issue with the Vette? We have to replace the British cars' guides with bronze to compensate for the loss of lubricant.

 

Also no problem on these cars. No issue.

 

There is a show on TV called Wheeler Dealers were 2 guys buy, fix up and resell so old English cars and in 2 episodes they pulled the head to have inserts installed saying that now the cars could run on unleaded fuel so it must be more of a problem with those old English cars then with the Chevys.

 

His research is correct.