need someone whos good with calculating CR, 11:1 B20 w/ B17 crank/head?

[94tegRS]

ok, I have a B20 shortblock sitting in my garage right now. it has JE 11:1 pistons in it and when I got them crower told me that the B16 head would bump it to between 11.2 and 11.3:1, Im assuming the B17 head will raise it a bit as well. I am going to have a B17 pretty soon, cuz im buying a 2nd gen GSR, and I hope to finally finish my CRVTEC when I sell my hatch. cuz now Ill have the ecu/dist/head/close ratio tranny/harness, everything but dowels/oil lines/plug.

I also have a nice condition IHI RBH5 I think turbo from a old probe GT turbo. no end play, no nicks in the compressor wheels, spins very freely. I kinda wanted to get some use out of it.

so what CR would this combo yeild?

B20 block
JE 11:1 pistons
B17 crank (also what length the rods compared to the B20's?)
B17 head

I wanna lower the compression to where 7 lbs of boost would be safe, I wouldnt throw the boost at it til I could afford the S200/tuning though so it wont be relying on just a rising rate FMU.

I have a feeling though it wont change much though, at least not enough to really justify destroking it in "hopes" of boosting it in the future.

what would that be, about 1.9 something? Id do it myself but dont know the B17's stroke.

[whtteg]

Ok so here is what we know:
B20B rod length is 137mm and the stroke is 89mm.
B20 head CC's not sure.

B17 rod length is 132mm and the stroke is 81.4mm
B17's head CC's 42.7 same as the B16 head.

Ok so you are going to use a 132mm crank and you have a 211.84mm deck height so you are going to need approx. a 140.8mm rod, which will have to be custom. This is based on assuming the JE pistons are made for the B20B/Z motor. The calculations are as follows: Deck height = stroke/2 + rod length + piston compression heigth + stock deck clearance.
Now lets fill in the values.
211.84 - 81.4/2 - 29.97- 0.37 = 140.8 mm this is the length of rod needed to use the stock compression heigth pistons with the B17 crank ina B20 block.

Now it has been a long time sense I have done this so it could be a little off, and the measurements that I was using could be a little off as well, but the formula is correct.

Now the rod length is out of the way so lets move onto the C/R.
You are starting out with an 11:1 static compression ratio, and you are using a head with a smaller head CC value so you will be increasing the CR. But to correctly calculate the CR we will need the specs on the cams you are going to be using. This is called Dynamic CR, it is what you need to go buy, not static CR. Here is a link to a Dynamic CR calculator http://www.rbracing-rsr.com/comprAdvHD.htm you can covert mm to in by dividing mm by 25.4. ie: 81mm/25.4= 3.19in. But you will need all of the correct info for your build before you can calculate the Dynamic CR. The only thing I am unsure of is the rod length needed to run the B17 crank.
So here is a number I came up with using the JE 11:1 pistons and the stock rods and stroke of the B20B and Crower 62404 cams : 10.16:1.

Basically I don't think you will be boosting that motor with much success, the cylinder walls are way too weak to hold cylinder pressures that would result from boost and those pistons, and the Dynamic CR I came up with is using wild N/A cams you would want a shorter duration intake cam and this would result in a higher Dynamic CR. If you want to boost it get new pistons.

Now displacement on the setup you listed would net you somewhere in the 1850-1860cc range.

Hope this helps more than it may confuse, just let me know if you need somthing explained in more detail.

[94tegRS]

alright that idea is ditched, I dont wanna drop my 2 liter to about the displacement of the B18 with a lower CR that still wont let me boost. if I get new pistons I am gonna go with 9.5 maybe 10:1's and have it bored/sleeved since #4 has some nasty grooves from the wrist pin taking a stroll into the wall. so i might even have it sleeved at 87mm for a 2.1L since I need custom pistons anyways.

at least from crower JE's are only 9, 10.5, 12.5:1 so Id need to apy the 100 dollar custom charge anyways.

might have it just resleeved to 84 though since I got pistons with only about 1500 miles on them and then Id probably just go with the ITR exhaust, CTR intake cam