Have somewhat of a dilemma w/ the 440 in my dad's road runner.
Basic specs...440 + .040", Ross flattops .005" down from 0 deck.
509/292 purpleshaft, 1 7/8" headers, 6 pack induction, 906 heads w/ mild porting, .040" head gasket.

It pings under load in hot weather w/ pump 93 gas in it. In cool weather the thing runs GREAT. You have to lug it to get it to ping...it is a 4 speed. Obviously the hotter it gets, the worse it is.

I have a set of ready to bolt on, mildly ported, big valve set of closed chamber 915 iron heads sitting on the shelf. I'd love to throw them on this car and gain some grunt, but I know it will raise the compression a decent amount. I have not CC'd them, but they are close to factory specs...minimal clean up cut on the decks.

So will the gain in compression be offset by the gain in quench as far as it tolerating pump gas? I'd hate to put them on and find out I need to mix some race fuel in it to drive it hard.
What do yall think?

1 step colder plug should fix it.

What's your timing at

I've pulled the timing back to 35° and that helped. The car is driveable like it is, just can't lug it in hot weather.

I want to put the closed chamber heads on to gain power, but not sure if it'll be a spark rattling nightmare if I do.

what compression ratio increase are you looking at?
10.3 to 11.1 or so??

It's about 9.9:1 right now. Should be 10.8:1 or better w/ the closed chamber heads, but it'll have good quench.

That is a good question. Best bet is aluminum 75cc heads but probably not in the cards. Colder plugs will make a difference.

160 degree thermostat and cold air intake. Check spark plug heat range too, maybe a step cooler plug as mentioned.

I'd just run some octane boost in the hot weather, maybe pull another degree or two out of it, maybe try slowing the advance down a bit.

It has no quench now, so you could lower the cr a little with a thicker gasket(and not lose any quench benefit cuz you don't have any now) which should help some.

I would not be confident that combo with 10.8cr and quench would be ping free.

I am not interested in working w/ the 906 heads anymore. A little less timing and/or colder plugs and it'll be fine like that.
I'm wondering if the better quench of the closed chamber heads will be offset by the higher compression making it even less pump gas friendly?

Different heads aren't in the equation. This motor will be replaced by a 540" hemi whenever I get around to assembling it.

OK, so I'd gain power but you think I'd probably be worse off than I am now as far as pinging.

I'm not sure on the cast iron head and higher compression is going to ping less. The bigger valve may help get a better mixture in and the squish will help a tad. It's something I would try. It's just labor and you are not staying with the combo for ever. I say try it.

I saw this in two real similar 360 motors. One was a 9:1 with no quench and one was a 10:1 motor with quench, both motors had X heads.

The 9:1 motor had trouble on hot days like you speak of. The 10:1 quench motor was fine and was able to run a few more degrees of timing.

The biggest difference was on the track, the quench motor performed much better. I don't recall the difference but it was almost one second and several MPH faster than the non quench motor was.

This was a long time ago but both motors were pretty close. Both guys worked at the same machine shop so there was lots of consistencies between the builds, the biggest difference being the piston choice and attention to quench.

I built a quench 340 around the same time with iron heads that was a little over 10:1 and ran fine on pump gas.

Being a street car do you have the vacume advance hook up? If not do you know what the timing is doing at the RPM it is pinging at when lugging it? The ignition timing, spark plug heat range and manifold inlet temps. will determine when it pings, cool things down on any of those three and it probally won't ping anymore
I had a 21 ft inborad/outdrive plesure boat with a 8.5 to 1 compression ratio SB Chey 356 C.I. with irn heads, it would ping a little at the lower elevations we used it at, not up higher on the same gas. I change the spark plugs from RJ12YC to J11Y and that stop the pinging
I wouldn't, and don't, run more then 9.5 to 1 compression on pump gas on the street with a iron headed motor, quench or no quench

I think I may try these heads anyway...just to see.

The timing is locked out. The car has a vintage air AC system...the lines are real close to the distributor and wouldn't clear the vacuum pod on the first distributor I had in it. So I put one in that's locked out w/ no pod on it. One of those things that became temporarily permanent. Been that way ever since we put it together back in 2007 or so.

You might want to unlock the distributor and put a curve in it that has 16 to 18 degrees at idle and up to 2000 RPM and then slowly ramp the rest of the timing so it has 34 to 36 degrees total timing by 3000 RPM

Yeah, get some dynamic timing going in this thing and swap the heads.

Chip, what's the cranking compression on the thing now? Where is you initial timing set at, and which advance springs are you running? Or, when does you mechanical timing come in?

It may be as easy as running stronger advance springs to delay the timing until the engine builds some higher rpm.

I think the white head gaskets that 440 source sells are .050 gaskets. Not sure about that but they were really nice head gaskets that I always ran on my BB. I would swap heads

I don't think it will live on pump gas with the closed chambered heads.

Whats the cam installed at... back it off a couple
degrees so it would have less compression(the piston
would be higher in the cyl).. if your like the rest
of us we tend to advance them at least 4* or more for
more low end

I had a 451 low deck with kb quench dome pistons and 452 heads a 223 230 at 50 cam that had 10.6 compression. It ran on pump gas on all but the hottest days. When the weather was 90+ I would add 2-3 gallons race gas. Quench was .038

I ran 10.2.1 iron headed 451 with a 284xe juice cam for 16 years no issue with an auto and loose converter. Swapped to a manual and ping city. Colder plugs and 33 total quieted it down but lost power for sure.

I would use different gaskets & shoot for .035" quench (to get EFFICIENT quench). & precision measuring as in my exp listed gasket thicknesses (compressed and uncompressed) can be a mile off (10-15 tho is a mile off). But on the Q at hand I ain't optomistic on avoiding quench (gas is crap & getting worse). post what you go with & how it turns out

That locked distributor isn't doing you any favors for either combo on a hi-compression street car.

If it was me and the heads are on the shelf ready to go, I'm picking a head gasket that gives me the tightest quench and still keeps the piston from smacking the head and going for it.

It already rattles so if there is no improvement on that front you're out a set of gaskets and some time but with quench you might be able to tune around it and gain a few ponies to boot.

Kevin

I agree with changing to a distributor you can set up with less initial, and ramp in total to match the motor. Also, anything you can do to cool the intake charge will help, obviously. Since you plan on a better motor soon, you might as well just work with the 906 heads for now, unless you want to know just how much the closed chamber heads will change things.

lets see... timing backed off a little helped. So if you had a curve to the timing you could take out as much as you want at that problem rpm/area. problem solved....with the closed chamber heads just my

Chip it can't be any worse than it is... do it ...

I did a KB quench piston motor for a friend a number of years ago, it was an identical build as another KB piston motor another friend had , the only difference was one motor had the quench number at no more than .045, the other motor was .050 plus.

The tight motor had 10.3 compression, the loose one was 9.5. The tight motor ran fine on 93 octane from the pump, the 9.5 motor would ping if the owner ran anything lower than 93, i would have expected 89 to be ok.