Change of piston spec

After purchasing the cosworth pistons, I got an email to explain that the suppliers didn't have any. So after waiting a few days for a refund, I did a bit of reading up on materials and compressions ration.

I decided to go with Manley Forged pistons with an CR of 8.5:1. With a minor head gasket change in thickness, you can tweek the exact Compression ratio you want. 

After looking up the measurements and dimensions of the pistons, I went to this site "Click here" 

and this allowed me to enter the piston and block dimensions and get an approximate Compression ratio. Naturally everything will be correctly measured once the parts are being assembled but all things being equal, it gives you a good way to dial in the spec of the engine. This means you can have a nice low compression engine, which means more boost and less knock! Also, you can add timing safely and not worry about blowing the things to pieces when giving it the right boot!

Its also worth noting that the Manley pistons are of 2618 alloy, the same as many other high performance brand. Why Manely? Again, its like anything in engineering....its a compromise between performance, reliability and PRICE. They were nearly 200 GBP cheaper than other pistons of the same material. They are also a respected brand, and seeing as Im not building an E85 hot rod, they will give a nice street spec engine. 

Here are the specs below:

Manley Sport Compact - Platinum Series Lightweight Pistons: Manley pistons are machined of high strength 2618 material. Each design is lightweight yet robust enough to deliver long service life. Perfect ring groove to skirt squareness is achieved through our unique "one fixturing" manufacturing method that assures maximum horsepower. Round wire locks, tool steel wrist pins, and rings are included with every set at no additional charge.

*Forging*
* 2618 alloy for maximum high temperature strength and fatigue resistance. 

*Attributes*
* "Contour forgings" provide the optimum balance between strength and weight with no grain-interrupting internal milling.
* Proprietary multi-step top ring groove machining process assures optimum control of the groove's size, geometry, flatness, and finish.
* All final turning is performed in one fixturing resulting in complete squareness of rings to the cylinder wall.
* Federal Form-Scan gauging validates ideal skirt indexing to pinhole and skirt-to-skirt polarity.
* Value - added features such as a pressure balance groove included in all series.
* Precise pinhole machining results in an exact compression distance as well as precise lock ring groove spacing, size, and concentricity. 

Manley Sport Compact Platinum series pistons come complete with pistons, rings, pins, and locks
Part Number: 612000C-4
Notes: Platinum Series Lightweight Pistons; Set of 4; Includes Ringset Part # 46995-4
Manufacturer: Manley 
Dome Volume: -22cc
Stroke: 79mm
Bore: 99.5mm (STD)
Comp Distance: 1.209"
Piston Type: Dish
Weight: 417g
Rod Length: 5.141"mm
Comp Ratio: 8.5:1
Cylinder Head: 51cc