[helmerrock]

I am putting together a 400 and have some questions on quench. Currently planning on using a set of 061 heads. These are big valve and CC at 79-80. Installed screw in studs. These heads have almost no quench pad area. I'm planning on flat top pistons and zero deck. So will zero decking make any difference since the quench pad is almost nothing? Will the lack of quench make this motor more prone to detonation? Compression calculates at 9.8 at zero deck or 9.6 if I leave the pistons .01 in the hole. Cam choice is 2802 but subject to change. Goal is a ping free pump gas engine. Looking for advice on quench factor.

[Tom Vaught]

.010" change on that head is not going to do much as far as quench goes.
Not sure how you are coming up with your math. Use this calculator:

http://www.wallaceracing.com/cr_test2.php

I come up with 9.3 to 1 on a standard bore deal and a 3.75 stroke.

Tom V.

[steve25]

With the 061 heads chamber you will need more octane then would be associated with any similar compression run in any other D port head.

[Cliff R]

Regardless of chamber design try to establish very tight quench.

Steve may be onto something with that chamber design.

Many years ago I built a 460 Ford that had heads with very similar combustion chambers and it was extremely octane sensitive. Never really knew why because it was pretty low compression and very well chosen camshaft (towing application). It should have been fine on 87 octane pump fuel but we found that it required very conservative timing settings or it would ping everywhere, even at very light throttle openings and very light load.

That engine still led a long life and made PLENTY of power for what they were doing with it, we just couldn't run much timing on it anyplace and had to keep good fuel in it as well......Cliff

[HWYSTR455]

Originally Posted by steve25

With the 061 heads chamber you will need more octane then would be associated with any similar compression run in any other D port head.

Can you elaborate on that for me please Steve? Would like to understand the basis of that statement? Like, for what, to produce the same amount of power, or to reduce det compared to a chamber with a pad?

Think there's more to it than just the chamber design (as it pertains to the pad). Like, if this were a requirement, why then is the hemi head so successful?

I've had engines with no quench pad chambers and no issues with det. Personal experience. I've had engines with pistons in the hole that were successful. There are other makes, a number of them, with no pads in the chambers, which are/were successful. So to say it's going to ping like a pig without quench I believe is an incorrect blanket statement.

Now, I would agree that most likely, a chamber with a tight/aggressive quench pad would probably make more power, or be more efficient. Now by how much more I'm not sure, but doubt it would make for a pass/fail situation.

.

[steve25]

Many folks make the big mistake of comparing these 061 chambers to theRAII and RA4 chambers and they react to timing and cylinder pressure levels way different!

The only thing they have in common with these other heads is the reduced valve to piston clearance due to the one common thing the 061s have with these other heads, that being a shollower chamber .

The best thing you can do when running these 061 heads is to use a long threaded plug with a extended tip to fire off the burn more in the center of the chamber in terms of both left and right plus up and down!

To do this the new plug needs to start one full head range colder than stock and all of the unused threads sticking out into the chamber need to be rounded over as to make for glowing knock making hot spots.

Hemi heads have no quench yes, but the plug is always at the top of the chamber where the opposing distantance to the chamber walls is the smallest, and many Hemi heads run two plugs!

Look at the distance the plug hole is in the 061 heads to the nearest or average chamber wall.

The tightest packing of fuel and air mixture is far on the shallow side of the chamber and this is what you want the spark to light off first, yet it is the most distant chamber area from the plug!

This is why modern Heart shaped chamber work so well, as just due to the Exh valve being smaller makes that side of the chamber smaller and then add to that the plug is then angled to that side of the chamber too boot!

[jonmachota78]

Very interesting stuff there. By looking at the picture, Would an exteded plug be at risk off hitting the intake valve?

[steve25]

They may need to be shimmed , so yes that needs to be checked.

[Cliff R]

Mopar also did a combustion chamber revision to their excellent big block wedge cylinder heads in 1968, the "906" castings.

I drove and raced a 440 powered Roadrunner for a quite a few years using those heads. I'm sure they were on the same track as Pontiac with the 061 and later "open chamber" designs.

They increased the quench area by opening up the chambers considerably compared to early designs. Although this does help with breathing and emissions, it certainly doesn't help everyplace.

Way back then we ran into running hot/overheating issues, and they were for sure more octane sensitive than the earlier closed chamber versions. WAY back then I didn't give it much thought, we just tuned the engines accordingly and never looked back. These days I pay closer attention to such things when selecting cylinder heads for any particular engine build......Cliff

[HWYSTR455]

906 casting were desirable, and still are today. Lots of folks run them even now. Friends in high school had many fast combos based off those casting, some in the 10s, and that was late 70s, early 80s. Guys that owned a shop used to buy retired Sox & Martin cars, and bet drivetrain parts were shuffled back & forth for street duty.

Personally, if I were to do a Mopar these days, I'd use aluminum heads. The Indy ones are killer.

I still think the original poster would be fine on his direction, and don't feel in this case quench would make much of a difference on that combo. I say go for it.

.

[Cliff R]

Agreed, the 061 castings have worked very well even though they are kind of an "odd-ball" deal.

Back when I raced 440's the head of choice was the 1967 440 closed chamber casting 915 (nearly as I can remember), followed very closely by the later 906 "open chamber" heads.

Both are still highly sought after today, although I do agree they are obsolete in every area compared to the Indy heads......Cliff

[HWYSTR455]

The 512ci stroker kits are based on a 4.25 stroke, very similar to the Pontiac combos. The 528 is based off a 4.375 stroke, the 541 on the 4.50 stroke. Yeah. And all are long rod combos.

They make 5 different aluminum heads, and believe they still have the hemi heads that bolt on the 440 block.

I am brand-loyal, and lean towards Pontiacs. But....

.

[steve25]

I think Pontiac may have based the RA4 Intake ports on the Mopar castings with that tail coming down the back of the valve bowl off the rear of the guide, Pontiac just did a better job and got 234 or so cfm to the 906 castings 215 cfm!
What heck Mopar was thinking in regards to some of there Exh ports when they already had a Hemi under there belt makes for a lot of questions!

[Cliff R]

I really try not to be brand specific with these things, but I did drive and race Mopar's for a number of years.

The blocks are tough as nails, with extensive support well below the crankshaft centerline.

They didn't even know what a cast crankshaft was until the 1970's when compression ratios went into the toilette and power with it. (Before someone points it out there were a few cast cranks used in the 1960's, but most of their stuff was forged, even on the lower performance engines).

ALL of their B and RB engines(prior to 1971) not only had forged crankshafts, but they had very strong forged rods to go with them.

They are all oversquare, with very large bores and short strokes.

The oiling system is superb, and the oil pump is mounted on the outside of the block for easy access.

The cylinder heads are excellent as noted, and they really didn't start closing down the port size until 1971 and after.

They were also very generous with the good parts. The only real difference between the 440 that powered a 1969 station wagon and a GTX was the camshaft, valve springs, carburetor and exhaust manifolds, unless you had the tri-power option, then it got stronger connecting rods, better pistons and timing set.

What this meant or means to the Mopar crowd is that there were PLENTY of the good engines made and they were readily available at any salvage yard and even now at swap meets decades later.

Pontiac made some pretty good stuff, but as we all know they really didn't have decent rods until the 455 Super Duty engines, and the blocks have very little support, even the good 4 bolt main (with few exceptions) ones in the lifter area.

The better heads are rare as hens teeth as well, but a good note there is that the aftermarket stepped up so we now have plenty of good offerings available.......Cliff

[steve25]

I don't think that the deep skirt on those RB motors bought them much added strength ( just more weight ) when we are taking about the intended usage of the motor, but if we are taking about the Ford FE series motors and there cross bolted mains, now that's a different deal!
The external oil pump has it good and bad points though.

Good, easy replacement and pressure adjustment.

Bad , the pump unlike the Pontiac that sits in the oil and is in effect self priming, must suck oil up a good long distance!

Let's not forget that every other manufacture had to go to into different block designs at a given point for added cid, yet the Pontiac block was so well conceived that such a thing never had to take place to get the motor 58% larger , from 287 to 455 cid, and even then with only some 20 added pounds in weight!!!