Checking Total Cylinder volume

[John Nechiporchik]

OK, Because the tech section is a little slow (Winter doldrums), I'll use this opportunity to keep you guys busy.
If a car is summoned to the barn for teardown, What is the process for tech determining the correct total volume (CC'S) to compare your results to.
Example, my LT-1 specs call for 51.9cc combustion chamber, .047 compressed gasket, .015 in the hole for the piston. Also, my piston has 4 valve reliefs with no spec for volume.
Do they account for the overbore and the gasket bore size when calculating your specific volume number? Then I assume the process is to check your specific parts to compare to that number.
I'm trying to learn /understand the process in order to comply with the requirement.
Looking for a little "schooling" here.
There are a few good calculators on-line to do the math given the appropriate data. Just need to be sure I understand how tech develops the target number.
Anyone know the valve relief volume? Per notch or per cylinder???

Thanks,
John

[Dwight Southerland]

They really don't check total cylinder volume. They will measure a combution chamber volume, piston to deck at TDC, overbore (measured above the ring travel), stroke, and head gasket thickness in several places. The tech sheet specs for gasket and deck will be added together and should be less than or equal to the sum of the measurements of those items on your engine. If you have a Super Stock engine, they may or may not measure the piston to meet spec for dish or dome volume. On a Stock engine, they look for accepted piston identification or OEM piston id for correct application, assuming that an accepted piston will be correct for dish or dome volume.

[Adger Smith]

To add to Dwight's post Head gaskets are measures (By Wesley) in all there places between the cylinder bores in the center.. then averaged for the final gasket thickness number. At EMC I was taught by Wesley to push the oil out of the rod bearing (push down on piston top) and bring the piston to TDC and measure the deck along the C/L of the wrist pin (front to back). Avg the numbers if they are different. I would bet all the methods he uses at EMC are what NHRA tech uses or should use. Good info on Dwights post. Been there done that, AYE!

[Adger Smith]

OH! I just had a flash..of memories.. Remember when you are measuring that Temperature variations can make some changes in the numbers you get.
I remember on real hot days we would hit the carb for a while with a Dry Ice extinguisher to cool it to make sure it passed on the size. Most of the time hot and cold heads measure different too. I've got some interesting stories about Temps. Best one was .001 on a hot spacer that almost threw out a top name team at EMC. I said "Almost" Remember that one R.J.? :~) I bet there are a lot of Tech stories out there!!

[Dwight Southerland]

A lot of tech stories . . . Yeah!

Adger pointed out a couple of fine points of the tech process that you need to know. Once you start measuring stuff yourself, you will soon see that all those details of procedure will make a difference in the data. The fact that the .001"-.002" boundary layer oil film can make a difference in stroke measurement or that piston rock in the cylinder due to rotation around the pin will make a difference in deck clearance or that head gaskets do not compress evenly. Also, some procedures are applicable to some measurements and not others. (You can average the thickness of a head gasket but not the deck height or bore or stroke.) The detail of the procedures that have been developed over the years are to get accurate measurements and not allow for either the tech person or the builder-owner to fudge. If you are doing the engine building for yourself, it is always good to get a mind set to allow some cushion in specs so that you do not put yourself in a possible situation where you would fail a tech inspection. There are enough variables in a teardown event that fretting over that last couple of thousandths or cc's are not worth it. Even if you use precise measuring instruments regularly, getting repeatable measurements exactly is a challenge. The old rule books had a paragraph with instructions encouraging racers to allow at least .002" on critical measurements and .3cc on volume measurements. That's good advice.

Of course, you can always gamble the odds that you won't be torn down . . .

[Ed Wright]

Back when my hair was still brown, I was fast, setting records, and getting torn down a lot, I learned to use .002" more deck and an extra half a cc to make tear downs go much easier. Ran no slower.

[John Nechiporchik]

Ed, Adger, Dwight,
Thanks for the lessons based on your practical experience. Your feedback, along with a few private messages I received are helping me generate a great "punchlist" of items to check during this process.
Interestingly, I am checking the critical dimensions/volumes as I go thru the dis-assembly process so I have a good baseline as to where everything is at now.
As a starting point, I have found the heads to be very conservatively within spec. Also, the old gasket plus in the hole deck numbers also are way conservative.
So, my winter science project continues.
Thanks to all of you for your continued support. I'm sure I'll be seeking additional advice as the project progresses.
BTW Ed, I represent the youth movement in "Stock" as I'm only 62 yrs. young.(LOL)

John

[Adger Smith]

John, thanks for making us look old... LOL!

[PJ305]

I could be wrong, but I always thought deck height & head gasket had to be greater than or equal to the specs listed.

[Adger Smith]

You can now add the two numbers for a total. Your block can be shorter as long as the head gasket is thicker and more than makes up the difference in the total number. Conversely you can have a thinner head gasket than the spec and have the piston farther in the hole. It is the total number of the two that is relevant. But, If the spec calls for "in the hole" the piston must be at zero or in the hole. It can't be above. That is unless that is one of the NHRA moving tech targets that has recently changed .