MarkP...please, help?

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MarkP":3r9ty2c2 said:
...My 200 starts to create slight spark port advance when the timing is +12 degrees and the idle is 800 RPM. Dropping the idle to 600 RPM then makes the spark port vacuum just barely disappear. At this time, I have 12+26(dist)+22(vacuum) degrees for a total of 60 degrees, with 9.2:1 compression, and I get 24 MPG hiway/20 city. (This improved my MPG from 14/16 without the vacuum advance.) There is no ping, even on the cheapest gas. Throttle response is very crisp, too!

This is the fourth post I've read referring to the original factory compression, or close to it, of 9.2:1 and still being able to use 87 or lower grade gasoline. What gives? Please, someone enlighten me!

Is the cylinder head able to dissipate heat quicker than what most are lead to believe? If so, does anyone know the limitations for "regular" grade gasoline (assuming all likeness of 87 octane is achievable)?

I understand aluminum dissipates heat much quicker than cast iron but I was under the impression that with a CR of 9:1 is pushing for regular grade unleaded gasoline.



-Chris
 
Howdy Chris:

While I'm not Mark, I can tell you that Mark lives in Colorado at about 5,000 ft elevation. That is one factor. There are others to. Thinner air at higher elevations allows for more advance and leaner A/F ratio.

I'm sure Mark will be along soon to give you the rest of the details.

Adios, David
 
Chris,

How about hearing from the other co-author? In 65, 66, 67 and 68 Ford advertised a 9.2 compression on the 200. The key being the word advertised. Just 'cause they advertise something doesn't mean that it is true. Madison Ave Advertisers are in the business to SELL. They don't necessarily tell the facts.

Ford MASS PRODUCED our lovely little sixes to make them the most money, not to necessarily for us to have exact specs. A little slop in the deck height, A little slop in the piston height, A little slop in the combustion chamber size, A little slop in the head gasket thickness, adds up to a lot of slop and an 8.5 to 1 compression.

All of this is why we try to gently preach to measure everything, and then to deck the block and mill the head to either achieve factory specs or even to up the ante just a bit.

The wedge head design that Ford gave us is inherently ping resistant - IF the quench area (the distance between the top of the piston and the surface of the head) is .020 or less.

My brother Dave told you right in that we need to know what Mark did to his engine. Mark may have also polished the valve faces, polished the combustion chambers, and smoothed any sharp edges. All of which will help control flame travel and dissapating heat. He may also have a hotter cam which holds the valves open longer so compression doesn't start to build up until they close. That's why when you read the cam specs, they will recommend some high compression ratio to go with their hotter cams. He may be exceptionally lucky and stumbled across that engine that didn't have sloppy clearances.

You are right about the Aluminum head dissapating heat better. That's also why they load those Alum heads with pretty polished stainless steel valves - they dissapate heat better.

I like the way you are thinking here. Read about what Hot Rod and Car Craft are doing to their 500 cubic yard V/8s; figure out why they are doing it; and apply the idea to our little sixes. While we can't have aluminum heads, we can polish valves and get some tight clearances.

In the 200 I am currently running, I have a 9.7 compression and use 18 degrees initial advance on 89 octane gasahol with no audible ping. I have the pistons sticking out of their bores .006 inch to compensate for a .040 thick gasket. and everything is polished, and a clifford cam. So far, it lives. This past summer, I drove it to Idaho 1200 one way, Wisconsin twice 500 one way, and to Kansas City 750 one way, plus numerous short jaunts. So after approx 8000 miles I'm almost ready to say it is reliable. And now I have the cold of winter to dream up a new concotion to screw it up.

BUT - in my experiments to find out what works and what breaks, I have cracked a cylinder wall, cracked a piston, snapped a rocker arm shaft in half, blown up cluthes and ... well... wrecked some otherwise perfectly good FoMoCo parts.

Beng a little conserative with your mods will save lots of broken parts.

Good Luck
 
Thanks guys! I always valve and reflect heavily on your thoughts and ideas. Your experience is a true, tried and trustworthy investment.

Thanks again.



-Chris
 
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