Unleaded Gas and Un-Hardened Valve Seats

[bobs66440]

I found some threads on this subject but they were almost 10 years old...sooo... I would like to get an updated opinion. 

Is it necessary to have hardened valve seats on 906 heads ('69) while using unleaded fuel with limited mileage (1000-1500 miles per year). And, will a lead substitute/additive help?

Thanks!   

[Chryco Psycho]

yes , the exhaust valve can get extremely hot in the middle of the exhaust flow when the engine is working hard , so when it closes it tends to weld to the seat ripping out metal when it is opened again , conversly  the intake sits against the head & is cooled by the surrounding metal so hardened seats on the intake side are not as critical .

[bobs66440]

yes , the exhaust valve can get extremely hot in the middle of the exhaust flow when the engine is working hard , so when it closes it tends to weld to the seat ripping out metal when it is opened again , conversly  the intake sits against the head & is cooled by the surrounding metal so hardened seats on the intake side are not as critical .

Will it help to use an additive?

[Chryco Psycho]

it would depend if the additive leaves a film between the valve & seat to prevent the welding

[bobs66440]

it would depend if the additive leaves a film between the valve & seat to prevent the welding

Thanks!  Can you recommend one? 

[pentastar426]

Interesting. My shortblock was just assembled by a very reputable engine builder familiar with 60's and 70's heads and valvetrains. I brought up this issue with him. He said it is thought that unhardened seats account for about a 10% reduction in valve and cylinder head life. He asked me "how much are you gonna drive this car anyway?" I honestly had to admit that if I put 3000 miles a year on it I would be surprised. " So you got 30 years of engine life here, minus 10%. "When you are 80, are you gonna care?"
I told him not to bother with the hardened seats. I will probably use some kind of additive anyways.

[A383Wing]

still got the original engine in the cream 66 and the Metropolitan...no hardened seats in those heads...still running strong...no additive either

Bryan

[RallyeMike]

Well, here is some real life experience: I ran 906 unhardened heads on my 71 440 in the 74 Rallye for from 1987 to 2010. I only put 10,000 miles on the car. I went to take off the 906's before I sold the car (because I had ported them) and the exhausts seats were so bad they had to be chucked. I never ran "Instead O Lead" for the last 5 years that I owned it and nothing prior.

[elacruze]

It really depends on how hot the exhaust valves get. My '68 pickup has the original engine (which has no signs of service) and at 95k miles the idle is noticeably uneven but it still runs great.

If you load the engine hard, like drag racing, high road speeds, or towing you subject the valves to higher heat. Same with high RPMs-the valve has less time to cool on the seat and higher temps to go with that.

If you only putter around town with the occasional first gear short tire squeal, you probably won't ever notice the difference. Nobody had to have the heads on granny's car redone due to exhaust valve deterioration.

Also, consider your build. Rich mixtures and late ignition timing heat up the entire exhaust due to incomplete burn while contained in the cylinder-the burn is completed in the exhaust port/tract. Keeping proper tune extends life of course.

I had a set of 906 heads that I had installed hard exhaust seats, and I didn't like how thin the casting was afterwards. I've heard that they're prone to cracking if the seats are not installed perfectly, or if there is too much core shift.

So the question is, 'would I install hard seats on my own'? Yes I would if necessary due to seat wear. No if no pitting is present. A 'lead replacement' additive works ok, if not as well as lead-also you can still find leaded fuel at most small airports, although you must specify-not all aviation fuel is leaded nor high-octane. Certainly, I'd install high quality stainless exhaust valves too, which are more heat resistant and harder than 'stock'.

[histoy]

If you're concerned about the seats, CD2 makes an inexpensive replacement lead additive for off road vehicles.  You just add a few ounces to each fill-up.   I've purchased it at Farm & Fleet stores.