Ordered a set of wiseo pistons for my b18c5 they were listed as 11.8:1-12.25:1 but when I did the calculation on zeal they show as givin me 10.99:1 can anyone explain why this is. Pistons are K566M815

 

The compressed thickness of an OEM 3 layer on my measurement was .023


Zeal isnt exact either.. it gives an estimate.

 

https://honda-tech.com/forums/all-motor-naturally-aspirated-44/diy-compression-ratio-calculation-2476094/

Use this. Only way to do a B20V properly too.

 

Still got under 11:1 using that way

 

^^

than thats your CR with those pistons.

If you want more, then mill the head and/or use a 2 layer

 

Those Wiseco piston compression ratings are for a stock 94-01 B18C. As soon as you change anything from the stock measurments your compression is going to change. Plugging in the B18C5/B16 head to the formula adds 1.1cc volume and drops compression.

Also the compression height that you plugged into the calculator isn't exactly what Wiseco spec'd for those pistons. Should be 30.1mm

When I plug in everything that you have posted in your picture above including 456 elev. I get 11.25:1, 11.34:1 w/0.023 HG thickness. The more precise you can be with your measurements the closer you will be to your approximate compression ratio.

 

I was hoping to get a c.r of between 11.8:1 to 12:1 because I want to run buddy club spec iv cams. Will that be possible with decking the block or milling the head or am I going to run into problems with the piston touching the head or p2v contact or am I best of going with different pistons.

 

If you just ordered them. Why not call up the shop and swap out those K566M815 pistons for a set of K593M815 with an 8.25cc dome? They would put you in the 11.8 - 12:1 range.

You are still going to have to measure the piston to valve clearances when using a 12.3mm lift camshaft.

 

Before you do anything else measure your deck height, and cc your chambers. The numbers that most piston manufacturers use are based of a "virgin" set up and have changed drastically over the years due to people tinkering with them. Certain factors are easy, like rod lengths, stroke,bore, and dome cc, but head cc changes with valvejobs , chamber work, and milling.

 

^^

I didnt say anything about that because the OP posted .001 on the head decking. So I was under the impression it was a virgin head.

 

There was no head work done on the engine just .001 off the block think I going to be using a virgin block I have anyway and im swaping the pistons for the 8.25cc dome was talking to the shop I got them and they have no problem changing them.

 

Yeah I hear ya unfortunately we always hear that its a virgin and once we measure it out ,that is usually not the case. Id say 1 out of 10 virgins are actually virgins and we see a lot of builds come through the door so it just became common practice to never believe their word and just check it anyway.

 

Wow really? What was the part number of that gasket? When I measured my OEM GE bored head gasket for a B18C it measured .027" with head studs @ 70 ftlbs

OP, you have to setup the calculator exactly how its specified in the catalog. Fortunately Wiseco tells you all this data upfront unlike some of their competitors. Double check the head chamber volume they are calculating the compression with and the rod length.

 

Yeah that's why I mentioned that Wiseco's compression numbers for those particular pistons are based on a stock 94-01 B18C w/41.5cc combustion chamber.

OP, you should pick up a 60cc syringe from the drug store and measure the volume of your combustion chamber. Easily done with the head off the engine.

Take your syringe and fill it with light weight engine oil or alcohol w/foodcolouring . Put the head upside down, combustion chamber side up, on a level work area and squirt the oil into the chamber until it is level with the surface of the gasket surface. Subtract the amount of oil that remains in the syringe from your original amount and that is a close volume of your combustion chamber.

There are much more elaborate ways of doing it using a plexiglass cover and sealer along with a scientifically graduated cylinder. I find this way works just fine for calculating the volume with little to no investment or fabrication required.

 

Thos was the OEM B20 gasket. ARP's to 80lbs.