I need some help with a CR calculation. I am looking at getting Wiseco HD pistons for a E-85 setup. I want a CR of 10.5:1
This is the the spec of the pistons:

CR height: 1.378
Dish: 4.3cc
evo 9 gasket
Piston to Deck clearance -0.3

According to the specsheet it should have 10:1 CR, but when I calculate it I get 10.66. Am I doing it wrong? Could somebody please check.
Link to the pistons: https://www.wiseco.com/Catalogs/Spor.../MiniMitsu.pdf partnumber: K656M85

 

I got 10.46:1 using the eagle calculator.

I used 43cc head volume, 0.042 gasket (stock IX), -4.3cc dish, but it comes out at zero deck not down the hole as you showed.

 

i thought the 9 gasket was something like .052"? also what kind of head work? my ported heads came out to 48cc's.

 

His is a stock head, the gasket I forgot the IX had the extra layer. I think 042 is the VIII, we use 051 for all our builds and custom piston orders.

 

Aaron do you use a 9 gasket on a evo 8 ?

 

I know that this is an extremely newb question, but I am wondering where in these calculations an increase in bore size is taken into account. Would't one need to factor in any increase in bore diameter since I imagine that we are talking about overbore piston sizes which would increase swept cylinder volume in comparison to stock capacity?

 

We use stock VIII gaskets most of the time on VIII or IX. Depending on the build and power though we make adjustments as needed. Being that we do a lot of 2.4s right now we havent really revisited the 2.0L headgasket for awhile. I have several though running 44psi on the stock VIII gasket. All of our custom pistons are ordered assuming we use an 0.051 gasket (more or less the IX I see).

 

The dish should be -4.5cc, I put the wrong numbers in the first post. And you are right it is zero deck. Still my numbers is different. I got 10.33.

I use metric btw.

Number of cylinders 4
Cylinder block bore diameter 85 mm
Cylinder block deck height 229 mm
Crankshaft stroke 88 mm
Cylinder head combustion chamber volume 43 cc
Piston Dish or Dome -4.5 cc
Piston Compression height 35 mm
Rod length 150 mm
Compressed headgasket thickness 1.06 mm
Total milled and decked block and head 0 mm

I thought the VIII gasket was 0.026 and the IX 0.042??? Anyone can confirm this?

 

I'll measure one out in the shop later

 

Sorry to dig this up but I just bought these to use in my evo3 (same thing as the dsm 7bolt motor)

Issue is that what ever cr you guy get I will get half a point less due to the 47cc combustion chamber.

With a 1.3mm head gasket I get around 9.5:1. Which I might add is a far cry from 10.5:1.

A 10.5:1 piston for me should be 11:1 for you guys.

I intend to call wiseco in a bit to get some clarification. I could have gotten the 10:1 je's damn it