Summit got my deck bridge, dial indicator, and other goodies here early so here it goes. Think of this a detective work. If I had this short block built by an engine builder myself I would have a build sheet that would tell me all of the clearances and measurements I need. I don't have that, so I must figure it out myself. The point of all of this outside of checking the condition of the block in general is to get the measurements I need to start piecing the top end together.

Phase 1

Scope: Inspect short block in greater detail, clean, disassemble rod cap and bearing to check for wear.

This is a picture of the back of the camshaft.



I was given cam specs of 232/234 duration @.050, .610"/.617" lift on a 113 LSA based on the owners memory. This photo tells me a few things. The LSA is actually 114+2 meaning it has 2 degrees of advance ground in. The 114 LSA will reduce overlap improving idle quality and it will broaden the torque curve as compared to a lower LSA which will make more peak power, with more overlap and a thumpier idle. By all accounts this engine and head combo has a VERY wide, smooth torque curve. The AFR 225 heads and this small duration cam on a 383 should give that kind of result. The second thing the photo tells me is the lobe numbers. I looked them up in Comp's master catalog and they are XE-R lobes on the intake and exhaust. 3732R and 3734R are the numbers we are looking at. These are very aggressive lobes. They pick up off the seat very fast and slam the valve back down equally as fast. They are about as aggressive as you can get for an LS1 from Comp. They will make really good power with a sacrifice in spring life, valve guide wear, and valve seat wear. This engine was built in 2008 and it was not destined to be a daily driver. Back then this is how you made power. There are other lobes out there, like the Endurance lobe proprietary to EPS that can make nearly as much power (maybe 5-8hp less in this combo) with double the spring life and far less valvetrain noise. Finding out this thing is on XE-R lobes has me seriously considering a replacement.

Let's calculate the overlap of this cam. I don't have a cam card so I don't know the seat to seat durations for REAL overlap, but I do have .050" lift durations. This will give us an idea of where it's at.

((Intake duration + Exhaust duration)/2) - (LSA*2)

232+234=466
466/2=233
114*2=228
233-228=5

So we have 5° of overlap at .050" lift. I personally put anything under 8 degrees in my "Daily Driver" category. Everyone is different. The extra cubes and smooth airflow of the AFR's should give this engine plenty of power down low. That's why you usually see bigger cams in bigger engines. They can sacrifice the low end power loss. 5 degrees in a 383 should drive nearly like stock after a good tune.



Next up, figuring out the piston valve relief volume. The pictures were deceiving. After looking this thing over on the stand the valve reliefs are not as big as I thought. It has Arias pistons which aren't common in the LS world but they are really high quality. I was going to CC the reliefs myself but I lucked out. After removing the windage tray I was able to see a 6 digit serial number on the underside of the piston. A quick call to Arias and they were able to look that number up. They keep a build profile of every order, even the shelf pistons, and they all get their own unique serial number. That's pretty cool. They are -3.1cc reliefs. That is going to be a big help later on.


Engine pr0n



The carbon deposits on the pistons were extremely light. They wiped perfectly clean with a little alcohol and a paper towel. That is a good sign that this thing didn't idle too much, good fuel was used, the tune was good, and it was driven hard.

Yikes! more on this later

It's time to flip it over and remove the windage tray. This engine has ARP main studs installed so there is a flange nut on the back side of the windage tray. On the stuck setup this would be a bolt. The tray is spaced down with washer to clear the stroker crank. That is something important to remember to put back or you will be pulling the engine again.





I pulled 2 of the ARP 8740 rod bolts and removed the rod cap. The bearing looks good for 14k miles and a lot of track passes. The crank looks perfect.

Time to CC the heads the poor man's way. This isn't as accurate as a graduated cylinder or burette but it will work for what I need to do. I don't need an exact measurement. +/- 1cc is good enough.







The pictures are pretty self explanatory.

8x10 lexan sheet with a small hole drilled in it
some sort of light grease, I used dielectric grease since it cleans up easier and I had it on hand. Lots of people use vaseline. This is used to gently seal the lexan to the head surface
A spark plug of the same family as the one you will be using, I used an NGK TR55
Food coloring
Alcohol or any other solvent with a low viscosity
graduated cylinder, berette, or in my case a 60cc syringe and 12cc syringe with 16 ga needles from Tractor supply

I couldn't get my hands on a syringe big enough to do it in 1 go so I had to use 2. These heads shipped as 65cc chambers and he said he had them milled .005" to clean them up which should put them at 64cc or pretty close. So I filled up my 60cc syringe and my 12cc syringe.

Fill er' up




I should mention I used a little permatex teflon thread sealer on the spark plug threads and I packed a thin layer of grease around the valves to make sure there were no leaks.

I came up with exactly 64cc of fluid. Now we have 2 parts of the puzzle. Valve relief volume and combustion chamber volume.

is it strange that im excited about this?

Now on to the next step. We are going to measure piston to deck height. With the right tools this is pretty damn simple. People fuck it up every day which is amazing.

The summit box came in, and the packer got confused by the ARP fastener assembly lube, Redline break in oil additive, and redline assembly lube. They packed an extra 4oz container of redline assembly lube. Cool deal, it's $10 a jar. It's pretty new stuff and I like it a lot. It's a paste instead of a liquid and it doesn't contain any solids like moly or ptfe so it won't clog filters and oil passages. It also doesn't run or drip. It quickly dissolves into the engine oil once the engine is running and leaves behind some phosphorus and ZDDP.

Other things in the box- 1" dial indicator with magnetic stand, Proform magnetic deck bridge, and Comp checker springs (for measuring pushrod length later on)




Ok, so why is piston to deck height important? Visualize a piston traveling up the bore... wait... I'll show you one




Look at a piston that has traveled up the bore. It is at top dead center. That is the highest point in the piston's stroke. Now picture the head sitting on top of the block deck. In order to determine how thick of a head gasket we are required to run at a minimum to keep the piston from striking the head we need to know how far the piston comes out of the hole. The piston's position relative to the block deck is the piston to deck height. It can be a negative number or a positive number or it can be 0. A stock LS1 has it's piston coming out of the hole by about .005". Most rebuilt performance engines have their piston to deck height set at 0, or level. This is called a 0 deck. In some cases the piston can be in the hole, or below the deck. Given the 3.905" bore of this 383, .001" up or down on the piston to deck height will greatly effect the static compression ratio of the engine.

There is another VERY overlooked measurement that most shade tree mechanics have no clue about. They think the function of head gasket thickness is to adjust the final static compression ratio up or down. The other measurement is called "Quench" or "Squish". When the piston compresses it's cylinder's volume of air all the way to top dead center that air and fuel is pushed into the combustion chamber. It also fills the area between the cylinder head quench pad (flat surface) and the piston. This area changes volume based on piston to deck height, gasket thickness, and gasket bore. Every type of engine has a little different ideal quench. For an LSX it is recommended to set it somewhere between .032" and .045" with an ideal target of .035"-.040". This is the distance from the top of the piston to the bottom side of the head. There are some other factors to keep in mind when setting quench. As the engine heats up, parts expand. An aluminum LS1 block will grow as much as .010" from cold to hot. An iron block will grow a couple thousandths at most. The steel connecting rod and crank do not grow as much as the block. So when the engine is at operating temp, your quench distance will be larger than when you measured it cold. It is prudent to set an aluminum block on the tight side, allowing for that growth. The other thing to keep in mind is the rod actually stretches several thousandths at high RPM. Horsepower and cylinder pressure only put a fraction of the force on a connecting rod that the physical force of starting and stopping the piston does. I forget the formulas, but it is an exponential thing. The force applied to the rod at TDC as it stops the piston at 7000RPM is several times that same force at 5000RPM. So we have to leave a buffer zone for rod stretch since I will be turning this thing at least 6600RPM even though it's a 383. That is where the golden zone of .032-.045 comes from.

Beyond contacting the head, the quench measurement is an important factor in how the engine runs. The tighter the quench, the higher the detonation resistance. With tighter quench, you can run more timing. The combustion process itself actually runs cooler as well. Keep this in mind when you hear someone saying they are going to replace their stock head gasket with an .060 or .070" gasket to lower the compression before installing a turbo or supercharger. They may lower the compression a half point but they really didn't pick up any detonation resistance because they fucked up their quench.


So back to piston to deck height measurements... In the picture above you see I have zeroed out my dial indicator on the deck surface itself. After that, you want to make sure you have found TDC. Placing the deck bridge over the center of the piston, rotate the crank until the dial indicator just stops moving. That is true TDC. Now we can measure. You want to measure the piston to deck height at the top of the piston, the center, and the bottom. You want to do this again after rocking the piston all the way to the top side of the bore. It will move back and forth a few thousandths. In a build like this with a 2618 alloy piston the piston to wall clearance should be set at about .003-.004". That clearance is your piston rock. It will make quite a big difference in the measurement. So you measure with the piston up, then your rock it down and measure again.


Sorry for the blurry pictures. An LS1 is an aluminum block with iron sleeves. The magnets on the deck bridge have very little steel to hang on to so I had to hold it in place as a precaution.

So here are the measurements I got:

With the piston up in the bore

Top- -.008"
Middle- .008"
Bottom- .021"

With the piston on the down side of the bore

Top- .021"
Middle- .006"
Bottom- -.007

Unnecessarily I tried to center the piston as best as I could and I got .009,.008,.006 top to bottom. I'm no machinist but I have pretty good attention to detail and in my mind I can use those numbers to double check my other measurements.

So now we average out both sets of measurements with the piston rocked.

Top-.013
Middle-.007
Bottom-.014

That is good. The top and bottom numbers are almost identical. Everything averages out to .007" piston to deck height. This is actually puzzling. The shop that built the engine seems to have decked it, but not all the way down to 0. With the 6.200" rod, 4" stroke, and piston height it ended up with a touch higher piston to deck height than stock. That isn't bad, it's actually conducive to making power, but it is something that needs to be taken into account. If I had thrown on a .040" cometic head gasket without measuring I would have had .033-.032" quench. That is on the tight side but it would work. Now I'm going to take this measurement and plug it in a compression ratio calculator and see where I come out with a few different gasket options.

Brb

No, you should be thoroughly enthused.


With a stock GM .054 compressed MLS gasket that measures 3.910 on the bore it would have 11.3:1 compression and the quench would be .047"

With an .040" cometic with a 3.910 bore it would have 11.67:1 and the quench would be .033".


I was shooting for 11.5:1 and I like the idea of the cometic but .033" quench is tight. I'll consult the guy that designed the heads about this when I talk to him about lifters and pushrods as well as the possibility of swapping the cam.




Good detective work today... Now I'm going for a drive before it gets dark. It was 80° today!