Deciding between 1.08 and 1.33mm deck height......?
 

With my 3.2 to 3.4 single-plug on 91 Octane (California) build, I am getting ready to install the cylinders and pistons, but it seems I have two choices:

A deck height of 1.08mm (.50mm shim) or a deck height of 1.33mm (.75mm shim).

I am not yet sure that I will have the desired valve clearance with a 1.08mm deck height, but I will have sufficient piston-to-head clearance.

I am running stock gears. I will also be running the A/C in the summer (so higher temp intake charge). Factory HE's, cat delete and a sport muffler.

With the 964 cams, Max Moritz style (10.3:1) pistons, chamfered heads, and my measured head volumes, this will give me:

With 1.08mm deck height:
Static CR: 10.15:1
DCR: 8.6:1

With 1.33mm deck height:
Static CR: 9.87:1
DCR: 8.37:1

I plan to have Steve Wong make me a chip.

I was planning on going with the 1.33mm deck height, but now I am concerned that I will be giving up critical quench, and have read that although decreasing the CR will help with detonation issues, reducing quench can increase the potential for detonation, and negatively affect efficiency/power.

I understand that many builders recommend 1.25mm to 1.50mm deck height for a street car, but Bruce Anderson's book mentions to shoot for 1.1 to 1.25mm, I believe. Perhaps it was different with the older style heads?

If I end up with sufficient valve to piston clearance at 1.08mm deck height, should I go with it?

I also need to figure out which way the Supertec head stud washers should be installed- I am assuming that the side of the washer with the tapered hole goes "down" towards the head...?

Any input appreciated,

Dave

Also, I found a better/repeatable method of measuring the deck height using some things I had laying around...

http://forums.pelicanparts.com/uploa...1756699086.jpg
http://forums.pelicanparts.com/uploa...1756699086.jpg

I like your idea for measuring the deck height. (why didn't I think of that!!)
The surface of the cylinder sealing surface is very slightly tapered tho... prob not enough to really make much of a diff.

Where do you get 0.75 base gaskets? I could use some of those!

Well, that explains why the Stomski tool wasn’t stable by itself- it tended to “rock” slightly, and so I had to “choose" which side I was going firmly press down on…. When zeroing and measuring.

Now that I know that the cylinder top is tapered, I will need to do this all over again! Perhaps this will not be a valid method to measure deck height… The “feet” of the tool ride along the outside edge of the cyl, and the dial indicator point sits on the very inside edge of the cyl for zero, then a slight move to drop it onto the piston edge. Now I am thinking this is a hinky method? IDK

I guess this explains why Bruce Anderson’s book provides another method- using blocks with the dial indicator and taking measurements off of the center of the piston.

.75mm gaskets: For the 3.2 I could not find them anywhere….so I am prepared to stack a .50 and a .25 to get there, if necessary.

I vote for 1.08 mm . From my experience , a bigger deck height will have a negative effect with engine performance . If you are concerned about the CR , machine the piston tops .

Regarding deck height... I've struggled with getting repeatable measurements using depth end of calipers. Decided to spend the time and make a plate to mount to next to cylinder and use dial indicator. Four 1/2" drive sockets worked well under the plate (all were withing about 0.005" height). Deck height measurement was repeatable within 0.001" to 0.002". I also found that you do need to put some force on the cylinder to get it seated. Using those little cuts of green hose on the plate did not work well enough which is why there's metal spacers on cylinder with piston. Deck height reduced by 0.005" when pushed down harder.

http://forums.pelicanparts.com/uploa...1756832893.jpg

That is a nice solution…

Are you referring to the nut, or the washer?

Washer- the washer is different on each side- one side has a conical ID (hole)

The washers with the Supertec head stud kits vary over the years. Some are flat but the latest kits have a chamfer on the inside of the hole.
That chamfer goes towards the head to compensate for any issues previous washers may have caused. If the surface has an excessive anomaly, a clean up cut is suggested.

Thanks Henry!

Whenever you are building a moderately tuned street engine I always recommend erring on the side of caution.
Fuel quality can vary greatly and detonation is the death knell for these little Hemi engines. Slight compression increases produce very little performance but with head temps at risk (hot days, AC on, or just spirited driving) detonation looms ever-present.
We also have to consider the Green Squirrels targeting octane to reduce classic car viability, we may find ourselves dealing with less than stellar octane numbers. If changing your engines compression becomes necessary, it is a major job.
Deck heights approaching .060" (1.5mm) you will have no issues with performance.

I really appreciate everyone”s input- thank you.

Richey, I have that devil on my shoulder wanting the smaller deck height, but I am still very green with these engines, and will very likely wuss out this time around….

Henry, thank you for sharing your knowledge on this subject!

Mine originally came in at .85-.9mm. Thicker base gaskets took it out to 1.1-1.15mm. Runs strong with 10.2:1 CR. 1.5 seems a bit much.