Technical Enlarging SBC Combustion Chambers?

Just drill some shallow holes in your pistons.

 

Well heck. I think I’ve been convinced. This car won’t be driven daily, so running mid grade or premium if needed would/should take care of any potential issues.
Thanks all.

 

Or turn that distributor clockwise until that ping ping ping stops lol

 

The old guys that passed along their engine building secrets to me used to say that on a 4-inch bore, 10cc's account for about one-point of static compression.

To get rid of a half-point, 5cc's would need to go.

Cut a 3.5" diameter pocket in the top of the piston, to the depth of 0.0317", and 5cc's are gone.

 

Just finished a std.bore 350, 9.0:1 comp. With the 268h cam , LSA 110, intake valve closes at 60 degrees ABDC. Dynamic comp. will be about 7.5:1. Will run 91 octane pump gas. Your old 64 cc heads were milled, cc them so you have a base line for volume, you can radius the quench pad ( flat area of combustion chamber) towards valves to gain a couple CC's, or if you go with a thicker head gasket you may exceed the recommend quench spec. of . 040", since the ZZ4 pistons may be.020/.025" from top of block. With a .015" gasket, that total gives you the the quench "space". Your engine did not come with a cam , if you don't want to buy cc equipment, take the heads to machine shop and have them check the volume, and look for cracks, since they are known for that, pick their brain for cam selection regarding compression, apparently you put the old pioneer 350 reman aside, ZZ4 is a excellent choice done correctly.

 

By the way, no such thing as reverse milling, get correct info from the pro's at the machine shop.

 

Two out of three of my OT cars require premium gas. That said, I really have to wonder about anyone who would spend the extra money for a ZZ4 short block and then fuss about not being able to run Joe cheap regular. Unless you are used to backing up to the farm gas pump on the place.

Still unless actually CC the heads you won't know what you have and then as mentioned a bit of bowl cleanup to unshroud the valves would probably work to drop it.

 

Not true, we reverse mill all the time. Simple process to add lost material. Saved a lot of scrap parts that way. Works on the same principle as our de-hone machine that saves oversize cylinders.
We also have an under drill service for holes that were drilled too large.
I’m looking into adding a re-thread service for stripped nuts and bolts.
You need to find a new machine shop.

 

What Does Reversing Mill Mean?
A reversing mill is a rolling mill in which the workpiece is passed forward and backward through a pair of rolls.

The reversing mill is so named because the steel runs back and forth between the rollers, reducing the thickness incrementally with each pass. A reversing mill can be used to reduce material to gauge. Reversing mill plants are preferable for rolling silicon steels and other special grades.

Reversing mills are also known as reversing cold rolling mills.
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This process seems to reduce thickness instead of adding.
Can you explain reverse milling ?
The procedure and how it is accomplished , to cylinder head or block?
Is it some kind of Electro welding of small Metal, iron, alloy dust added to surface & bonded.

 

This will help quite a few

 

Ask to see their hardware bin.

 

Hi Mike.
I asked Kerry and he said 1st choice is Cometic gaskets like the turbo crowd use (they are reusable)
Next choice is to open the chambers by de-shrouding the valves.
And the other method is to "sink" the valves into the chamber.
Cheers Mimi

 

You need to realize that not every post is serious and informative… Some are intentionally comedic.

 

Thanks for all the replies. Seems that ZZ4 is not available, at least with the places that I’m familiar with the names that I’ve dealt with in the past.
I think I’ll go with plan b. And start looking at some shops around the area, ask some questions, get a sense of what kinda work they do.
There’s a reason I wanted a quality block to bolt stuff onto and into and get on down the road.
I thought I had my current short block ready a month or so back, but we all got put on an extra shift, and working a n overnight shift, doesn’t leave much time or ambition to to go driving around, etc. I also had some concerns with the prep work I did on it talking to a few friends. So the hunt for a “mail order” part was on that I could bolt things in and on to.
Oh well. Next thread I start will be along the lines of “excellent shops near me”?

 

We all know someone who knows someone who knows someone. Somebody somewhere near you is going to take that dinosaur early SBC out and go the dreaded LS direction. I'm sure some welcome funding will net you a good deal on a perfectly used castaway engine, short block, long block, or some combination. Sometimes we get so encased in plan A we forget the other 25 letters. Merry Christmas...

 

I've got a bucket of nuts and bolts that I'll send your way, this changes everything! I knew it was a good idea to save them all these years!

 

why not go to a open chamber head? like a 882, already has hardened seats and unshrouded valves.

 

If you choose to run the higher compression, polish the chambers and piston tops to chrome like finish. The ultra smooth surface reflects heat and keeps any carbon from building up that could cause hot spots. Take all sharp edges off in the chamber and on the pistons for the same hot spot reasons. With the right timing, lighter weight car, and gearing, you can get away with it. Lugging the car around with overdrive could be a problem.

 

I don't like this idea. The layer of carbon that forms on a piston is a barrier to heat related damages that can occur. To see how this works heat up a bare piece of steel and something painted. Takes way longer to get the painted gig red hot, the carbon of the burnt paint makes a hella badass layer. In the Grumpy Jenkins How to Hot Rod SBCs he tells how they coated piston tops in VHT to carbon up faster and get to their race tune settings faster. He was right. 2 strokes also need a carbon layer of you're gonna lean on em. A polished combustion chamber gone too far can cause or support vapor separation as well. Smooth, not polished. Only exhaust benefits from polishing, but we all may be getting over our skis a bit. Worth a mention tho.

 

I thought this was a Hotrod site, lol. 7 to 1 won't pull a fat girl off a tri-cycle. No offense fat girls.

 

Could you safely retard the timing of the current cam a few degrees and expect it to reduce some of the risk of detonation, at least at lower RPMs?

 

I'm puzzled how 9.6:1 c.r. would ever be an issue? I am running 10.5:1 with iron heads on one of my cars, and that is a problem even with premium crap gas today. But my '39 is 9.5:1 and even on regular grade unleaded gas it doesn't ping or have any issues.

 

In order for me to try and answer this question I first need to know what your understanding of quench is.

Here is the reason I am making this statement. Please do not be offended. Quench is the distance from the top of the piston to the head face. It has nothing to do with the combustion chambers. If you are running dished pistons that would be measured from that little ring of material around the edge of the piston.

 

Yes, that I know. It’s kind of a moot point now that the short block I was looking at isn’t available anymore that I can tell. But it had true flat too pistons with 4 valve reliefs which was going to change the CR from 9.1 to 9.6 (if memory serves). Although gas prices have lowered over the past month or so, it will probably be back to 5 bucks a gallon (we were over 6 for a spell) in the spring/summer. The quest to keep the CR down was for that reason. Why spend the extra 20cents for Midgard or 40 cents for premium if I don’t have to?
You’d tell me I was nuts if I showed you my cost of living vs my W2, but I’ve always been so tight I squeak under the right circumstances

 

When you mentioned came across ZZ4 short block I thought perhaps you purchased one, my mistake.

 

Don't mess up those heads; it's just not necessary. I have .003-.004" deck clearance on my 327 +.040 and milled .020 off the heads with .040" thick Cometic head gaskets. I think the static C.R. figured out to about 10.2:1. I calculated that you should be at about 9.5:1 on that ZZ 350 with stock deck clearance,.040" head gasket, 4 valve reliefs and 64cc chambers. If you use ANY mild hydraulic lifter cam you could probably run mid grade gas..... because your dynamic CR will be much less . Probably 1/2 point less. IIRC the period Chevy steel shim head gaskets were only .016" compressed. .016" plus .025" would make .041" quench.

 

I was raised in the Bay Area and have lived there off and on through out my adult life. I don't live here for the weather, this is where I can afford to live.

If you keep your quench tight that will effectively lower your octane requirement. Also if you CC your heads you will probably find that your 64CC heads are not all that small match your combustion chambers to the largest one. radius any sharp edges. Make it run as cool as possible, there are some tricks to that. Efficient cooling system, run it a little fat, efficient exhaust all help with that. if you keep it cool you also reduce your fuel requirement.

You'll get it worked out.

 

Just get a pair of thicker head gaskets, and choose a cam that will bleed-off a bit of dynamic compression.

If you can, get aluminum heads. The heat transfer can be better, keeping chambers cooler.