# Hardened valve seats



## 68GTO4004Spd (Jun 19, 2008)

My engine builder says he wants to put hardened valve seats in the heads because todays gas doesn't have lead in it. A guy I work with that used to build pro-stock drag racing engines says that BOP used more nickel than Chevy and that it's not necessary. I need some expert opinions, Mr. P-body where you at man.


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## Mr. P-Body (Jan 20, 2011)

Relax, dude, I'm "here"... -

Both statements are purely "myth and superstition". It is true, "hard' seats came about right before unleaded gas. In '72, GM began "induction hardening" exhaust seats. That was the year EGR was to be "debuted". Well, certain car companies (NOT GM) weren't "ready" for their EGR program yet, so the feds "moved" it to '73. The extreme heat of the diluted "artificially lean" mixture made exhaust temps high enough to start deterorating the seats. We heard the same about bronze guides in the '70s. Yes, you HAD to use bronze guides with unleaded fuel.... NOT!

Lots of "stories" about "high nickel" content of blocks and heads. Chevy guys REALLY run with that one. I've never seen an engineering paper or sufficient Brinell testing to agree or disagree. It is true, Pontiac heads didn't have near the "recession" problem Chevys did in the late '70s. I believe that to be more related to the superior design and machine work with the Pontiac. 

Our "rule of thumb" here is that if the original seats are still "in place" and not beat up, and the car is not going to see a lot of low-speed "work" (towing, lugging up hills, etc.), "hard" seats aren't necessary. Make the seat itself .090-.100" wide, with a 15 deg. "top" angle and "bump" it with a 70 for the throat.

In the case the seats ARE to be replaced, use SBI part no. SB-1812-5. It has a slightly smaller ID than the -1 (the book recommended). You can "profile" the seat to flow better over the original "straight" type.

Jim


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## 68GTO4004Spd (Jun 19, 2008)

Hey thanks for the quick reply. Is there a down side to putting hard seats in? I heard one guy say that you could get a "leaker", whatever that means.


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## pontiac (Mar 6, 2011)

seat can dislodge or worse, machine shop can cut head wrong for seat and make head worthless.


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## geeteeohguy (Feb 2, 2008)

I had a new seat drop out in a VW I once had. Destroyed the head. Lucky I didn't grenade the engine. I would have been better off leaving it be...


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