1968 Eldorado W/hardened Valve Seats

[Forgiven1989]

I talked to a guy this past weekend that knew a lot about old Cadillacs.  He told me that if my 68 Eldorado was a California car and had a pollution air pump on the motor, that it also was designed to burn unleaded gas and was designed with hardened valve seats.  Does anyone know if that is the truth?  Thanks.

[The Tassie Devil(le)]

The Cadillac heads can handle unleaded petrol as the valve seats are hardened, but these engines really have too high a compression ratio for straight unleaded petrol.

Unleaded Premium yes, but not the basic stuff.

Bruce.

[TJ Hopland]

1968 was the first year for that engine so it was a 'brand new' design.   You would think they knew it was coming by that time.   I believe they advertised it as 'million mile' tested.

I don't know that they had hardened seats but they were high nickel castings, much higher quality than say a typical Ford or Chev.   The 472/500/425 family of engines have always been and still are somewhat popular among the 'hot rod' crowd and even in those circles you never hear about installing seats or having issues with them.

Seems like the owners / service manuals said that it was alright to use low or no lead fuels fairly early on.   I know 73 said that but seems like even earlier years said it too.  I don't have any early manuals myself but for some reason I am thinking maybe as early as 69 it was mentioned.   

Same head casting numbers were used 68-73.  74 was a 'new' design head.  71-73 to meet the new corporate mandate for lower compression ratios they just put very large dishes in the pistons.  The 74-76 design had a larger chamber that allowed them to go with a more typical piston.    In theory a 71 or newer should run fine on 'regular' unleaded.    68-70 because of the higher compression ratio should run on 'premium' unleaded.    It was not till the 1990's with computer controls that they were able get compression ratios above about 9:1 that would run on regular.  The 68-70's were in the 10:1 range.   71-80's compression was around 8.5:1.   

[Dave Shepherd]

Keep in mind only the exh.seats need to be hardened, something to think about if redoing heads on a pre-hardened seat head.

[Forgiven1989]

Thanks for the info.