Hardened valve seats for iron heads; worth it or not?

Are your heads prepared for unleaded petrol?

  • yes

    Votes: 12 60.0%
  • no

    Votes: 5 25.0%
  • don't know

    Votes: 3 15.0%

  • Total voters
    20
A few points: Spark Plug heat range -- in brands other than NGK, a higher heat range number relates to "hotter" plug, lower numbers just the opposite. NGK goes backward to this orientation, with smaller numbers being hotter. "Hotter" relates to the amount of combustion heat which the spark plug dissipates or transfers to the cyl head, which means that a "hot" plug is phyisically hotter in the spark plug tip area whereas a "colder" plug will be physically cooler. Which is why an "oil burner" will get hotter plugs before a "non-fouler" attachment is needed. Oil intrusion, for example, can come "up" from the rings area or "down" from the valve guide area.

Exhaust valve size -- The larger exhaust valves have more to do with "flow" past the exhaust valve seat, NOT exhaust system back pressure. Putting more flow into an existing system might even INCREASE back pressure in the system, unless the system is similarly upgraded (i.e., single to dual, or mufflers with more flow). Exhaust system "pressure" is usually minimal at cruise conditions, but increases quickly in "kickdown" at then at WOT situations. The issue becomes how good the cylinder is ridden of the per-cycle exhaust gases and a fresh charge enters during the overlap period. The smaller exhaust valve can possibly increase residual EGR as much as a smaller intake valve might, with the end result being that either the exhaust can't get out or more clean air might not be able to get in.

In more recent times, the issues of flow are important at ALL valve lifts, not just at .500" lift. Especially at .200" lifts to get things started. Then, notice that current high compression engines might well open the intake valve a bit later, for less physical charge, then compress it more. Which means the total .050" duration might be a bit less than what it might have been years ago but power is still very high, still with a 550rpm idle in gear that is smooth (which can relate to both intake/exhaust manifold designs and EFI). Combustion and manifold flow dynamics have been well-evolved over the past 60 years.

Sorry for the diverson.
CBODY67
 
A few points: Spark Plug heat range --
....
Combustion and manifold flow dynamics have been well-evolved over the past 60 years.

Sorry for the diverson.
CBODY67

Te absolvum! I sit enlightened and better informed as I prepare to go into this. Looked over the old heads this afternoon, as one of the bags I had on it broke down with the extreme heat here. Wiped the slight bit of rust off using WD40 to displace any moisture remaining on it, tthen rebagged and moved it indoors for now. These heads look damned GOOD given their age and use. I think they can be made very serviceable with minimal effort. No beaten seats, very little crap on valve surfaces. My 2' aluminum ruler lays nice and true on the inner, cylinder sides of them. Think I'll clean off a work area, get a bigger and better spring compressor, and finish tearing these down for a flux bath and sonic test..... In a pinch, I'd probably be able to bolt these on and make them work as they are. Don't want to do that here.
 
Regardless of head casting the rebuild cost will be the same so do hardened valve seats.
Keep in mind the 915's will increase compression which will increase the chances of detonation on todays corn fed gas.
I personally prefer the 452 heads that already have hardened seats.
With a good 3 angle valve job and with some porting and gasket matching they will flow better than the 915 and no ping.
I have 452's on a 66 300 383 with a 68 301 cast intake. Works great!
View attachment 472501

VERY NICE engine compartment BTW! The 452 is rather like a latter day (mid-late 70s)906 isn't it? (I have those too.) IFF I NEED to QUICKLY burnish some heads and bolt them on, I'll use the 452s. I like the way my older 383 behaves though, even with the 516 heads, which is why I shopped for the 915s.
 
VERY NICE engine compartment BTW! The 452 is rather like a latter day (mid-late 70s)906 isn't it? (I have those too.) IFF I NEED to QUICKLY burnish some heads and bolt them on, I'll use the 452s. I like the way my older 383 behaves though, even with the 516 heads, which is why I shopped for the 915s.
Yes tbe 452 have same size valves as 906.
What power you lose in the .2 compression ratio you can gain back by recurving the distributor and set timing to work with todays gas along with correct heat rang spark plugs.
With dual exhaust the 66 300 managed 18MPG when we drove it to Carlisle in 2016.
Lots of torque and good passing gear power.
 
Yes tbe 452 have same size valves as 906.
What power you lose in the .2 compression ratio you can gain back by recurving the distributor and set timing to work with todays gas along with correct heat rang spark plugs.
With dual exhaust the 66 300 managed 18MPG when we drove it to Carlisle in 2016.
Lots of torque and good passing gear power.

OK, that's good to know. I got 14 MPG out of Mathilda on the interstate as she was in 2016 when I had to haul a crew of 4 large men up to Coolidge from Tucson for the Election, so there IS room for improvement. Alas, I VERY SELDOM get ANY highway driving with that car. MONTHS go by before I ca put it on the road for more than a mile or 2. Now, do you use an 11" converter with that machine? I noticed I picked up a mpg when I went to dual exhaust last summer. THAT certainly helps, hence my worry over back pressure! IDK if I want headers, though maybe HP manifolds would be worthwhile..... She DOES romp nicely with the passing kickdown now!
 
OK, that's good to know. I got 14 MPG out of Mathilda on the interstate as she was in 2016 when I had to haul a crew of 4 large men up to Coolidge from Tucson for the Election, so there IS room for improvement. Alas, I VERY SELDOM get ANY highway driving with that car. MONTHS go by before I ca put it on the road for more than a mile or 2. Now, do you use an 11" converter with that machine? I noticed I picked up a mpg when I went to dual exhaust last summer. THAT certainly helps, hence my worry over back pressure! IDK if I want headers, though maybe HP manifolds would be worthwhile..... She DOES romp nicely with the passing kickdown now!
The 66 has stock convertor and cam.
With the 2.76 gears lucky to get 12 mpg in the city, with 10 average. But really dont care about milage just a reference since I dont trust the gas guage ..lol
 
The 66 has stock convertor and cam.
With the 2.76 gears lucky to get 12 mpg in the city, with 10 average. But really dont care about milage just a reference since I dont trust the gas guage ..lol

Your city mileage identical w mine. It averages 10.5 mpg after all said and done. I THOUGHT I had a 2.76 rear end, but after washing off the tag thoroughly, it shows 2.93! Not much difference in the differential tho. Reckon they were short of the usual ring n pinions when they put mine together on the Line yrs ago....
 
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