Thread: Coolant in cylinders; fresh 400 sbc build

Tweet

I think all of you are doing a great thing trying to help this guy out. There's a lot to learn and that's all he's trying to do.
I agree he needs the proper heads for the job. He's learning and so am I.
Thanks. It's nice to see someone help.

Well…. It’s what we all want to do – help others. Sometimes it’s hard because we all tend to have our own ideas about what is the “best way” to do something. I know I do – however; when it comes to engine building, I listen up to Jerry, Pat, Tech and some others here as they’re a storehouse of knowledge brought about by a lot of years of hands-on experience. I’ve built my share, but I’m not a machinist and I want to keep learning until the day they lay me to rest.

Ask me how I know about steam holes and 400 SBC? Been down that road because I thought, “those tiny little holes can’t possibly be that important…” Well, let me tell you – they are! The machinist I was working with was gracious and gave me a “Heat and the Siamese Cylinder Block 101” lesson after hours in his shop and then he and I found a solid set of cores and he showed me the correct way to drill holes. You don’t soon forget those experiences and hopefully, when people come to CHR and have questions they’ll realize there is a lot of smart men (and brilliant women too - Barb!) who are passionate about what they know. Listen up, process the responses and make a decision. We’ll always support someone who wants to learn. Know-it-alls, eh –not so much.

Ok, the squish is .041" THe piston clearance is greater than .030" my largest filer gauge is .030 and it slides freely. these are also dished pistons

In case you didn't know, you can stack feeler gauge blades one on top of the other to make any thickness you want. How did you arrive at 0.041 squish? Squish is the piston deck height plus the gasket thickness.

Originally Posted by techinspector1

In case you didn't know, you can stack feeler gauge blades one on top of the other to make any thickness you want. How did you arrive at 0.041 squish? Squish is the piston deck height plus the gasket thickness.

Thought it was just the thickness of the gasket. Deck height is .036 so that makes squish .077

Piston clearance????/how did you measure that???I know you said feeler guage but how?????

Originally Posted by jerry clayton

Piston clearance????/how did you measure that???I know you said feeler guage but how?????

Jerry, you must have a lot on your mind today because I know that sometime in the past 50 years of hot rodding, you've checked piston deck height with feeler gauges and a steel rule. I explained to this OP how to do it in post #45 and he is reporting back, saying that he has a squish dimension of 0.077" (0.036" piston deck height and 0.041" compressed gasket thickness).

Originally Posted by Bigbzc

Thought it was just the thickness of the gasket. Deck height is .036 so that makes squish .077

Do you understand that 0.077" is pretty much unacceptable and that it needs to be between 0.035" and 0.045"?

Originally Posted by techinspector1

Do you understand that 0.077" is pretty much unacceptable and that it needs to be between 0.035" and 0.045"?

I'll try to measure it again. It is in the truck so it makes it very hard to measure. However, the thickness of my gasket after being torqued down (compressed) is .041" which according to your specs isn't giving me much to work with and I know there is more than .004 deck hight. Maybe we are misunderstanding each other somewhere?

OK Tech

I reread it---I was taking it that he checked piston to wall like above the ring land--I've had people do that before not understanding that the pistons are much smaller up there than the skirts.
Have a good week end

Jerry

Originally Posted by Bigbzc

I'll try to measure it again. Maybe we are misunderstanding each other somewhere?

Perhaps. Let me go through it for you. When you assemble a motor, you want a flat part of the piston crown to come up against the underside of the cylinder head with just enough clearance to squeeze out the fuel/air mixture from that area and "jet" it across the chamber just as the plug is firing. This creates turbulence in the chamber and homogenizes the mixture to prevent rich and lean pockets where the mixture would burn inconsistently. Tests have shown that this tight "squish" dimension (0.035" to 0.045" including piston deck height and compressed gasket thickness) will allow the motor to operate without detonation on lesser quality fuels than a motor with a wider squish or no squish at all, as in the case of the '72 Ford D2VE cylinder heads. Ford had to drop the static compression ratio down into the 7's to prevent detonation on that motor. Needless to say, they only used that head for one year. The following year, they cast up the D3VE heads, using +/-95cc chambers and a squish pad. The clearance is just enough to prevent a piston to head collision at high engine speeds. You are setting the clearance cold with the motor at rest, but at speed, the crank flexes a little, the rod stretches a little and the piston compression height gets a little taller from the heat of combustion. David Vizard has done exhaustive experiments with the SBC and reports that he experienced contact between the piston and head at around 0.026" squish.

The best piston configuration you can use is a flat-top with valve reliefs cut into the crown. Next best, if you need to lower SCR, is to use a D-cup piston that has a generous squish pad on the piston opposite the chamber side. Either of these designs will make the best squish.

Look closely at this piston crown, the one at the top where it starts off "For budget or stock-style rebuilds". You can see that there is insufficient material on the crown to mate up with the underside of the head. The piston is cut into a "dished" configuration with no squish pad. I would not use this piston on a demolition derby car, much less a daily driver.
Sealed Power Cast Pistons - SummitRacing.com
Here's another example of a piston with no squish pad....
Sealed Power Z536NP - Sealed Power Cast Pistons - Overview - SummitRacing.com
Here's an example of a piston with a D-cup. See the nice squish pad on the left of the piston in the photo?
Keith Black/KB Pistons KB138-030 - Keith Black KB Performance Pistons - Overview - SummitRacing.com
And you don't have to spend a lot of money to get pistons that will work. Here's a flat-top for a 350 that has the proper 1.560" compression height and also a generous squish pad for under 100 bucks for the set ot 8. That is a deal!
http://www.summitracing.com/parts/SUM-17350-30/

Now, here's the way it works. The block deck height on a SBC is nominally 9.025" from the centerline of the main bearing bore to the decks where the heads bolt on. When choosing parts, you try to put together the tallest stack you can that will fit into that space. Let's use a 350 to keep it simple. The stroke is 3.480", so the crank radius is half of that, or 1.740". The rod is 5.703" center to center and the piston has a compression distance (centerline of the wrist pin to the flat crown of the piston) of 1.560". Added together, we find a "stack" dimension of 9.003. Fitting this stack into a virgin block where the decks have never been cut produces a piston deck height dimension of 0.022". If we know the decks of the block and the decks of the heads are good and flat, we can use a 0.016" compressed thickness shim head gasket and reach a squish dimension of 0.038" (0.022"+ 0.016"). You can't use these shim gaskets with aluminum heads though, so you must cut the block decks to reduce the block deck height so you can use a thicker gasket to prevent brinelling the aluminum.
So, in summation, you could use a 0.022" piston deck height with a 0.016" gasket or you could use a 10105117 GM composition gasket that compresses to 0.028" together with a piston deck height of 0.010" or you could use a 0.039" gasket with a zero piston deck height (you have to cut the block decks 0.022" in this case).

Well, as I have said over and over, that the bottom end including the pistons is stock and that is the way I plan to leave it. This means that the pistons are dished, just the way they come from the factory. Now your telling me that this will not work which is why I'm getting confused on what you are asking of me. I do not plan on racing this engine and am not seeking 500 hp out of it. At most, it will be used to tow my rock crawler.

it will work fine with the right heads find a set that are not screwed all up drill them for steam holes . bolt them on run it use a good RV cam .as for the stock re build i used cast pistons and deck them . i trim the deck to get better squish and the stock deck can be off and a bad finsh. i done many cast piston engine s for stock to very mild use .i seen one thing i will add stop using them phucking 3m wheels on flat parts engine deck intake heads less you want some thing not flat when done them small wheels remove metal. 80 grit long boad stick it paper on a long board works better if your not milling

Excellent post explaining squish and the relationships between the pieces, Tech. I really enjoy reading and learning more about these things from your experience base, and you're a good writer.
The one thing that jumped out at me is the gasket thickness - it seems that you could pick up ten to fifteen thousandths by using a thinner gasket, getting you down into the .055 to .060 range. Pat, you mentioned a long board and some 80 grit. Would it be possible to keep things flat and take off another .010 to .015 with elbow grease? Too much risk of getting it crooked? Just wondering after reading both yours and Tech's posts. May not be worth the risk for a basic stock rebuild where the decision has been made that the lower end is not being touched (no new pistons).

Very Interesting post humm!!!