Ok so after speaking with multiple tuners/builders I can't seem to come up with a fit answer here. I am in the process of building a high compression ls/vtec. According to a compression calculator I used recently I got a static compression ratio of 12.4:1, seems kind of high. Just want to clarify on exactly what compression I will be working with here. Maybe I am just comp calculator dumb

Rundown:

Gsr head base - Ported/polished/3 angle valve job/shaved 0.010"
Ferrea SS valves
Supertech valve springs/retainers

B18B1 base - Decked 0.010'' and bored to 81.5 mm
81.5 mm USDM ITR spec pistons w/ new rings
3 layer headgasket

Cc's of displacement - 1857

 

You really found it necessary to list all that $hit....really? You couldn't just list the pertinent details?

I hope to God your head wasn't shaved 0.1"...if it was, it's junk.

12.4:1 sounds right. IDK why you think it sounds high....

Calculators are just for an estimation. If you want an EXACT calculation, you're going to have to do some work....CC the combustion chambers and the pistons and do the math.

 

Thanks for the input..

 

why do you fill thats hi for the set up your using usdm p73 pistons witch have something like a 3.64 dome ls crank and rods 89mm stroke and your running a GSR head witch started with something like 41.60 CC volume and u milled it down .010 that should be right + the 81.5 bore bumps it up a tad bit

 

So, your head CC's are?, your gasket cc's are?, your cyl. +.- cc's are? Your cyl. displacement is? That is the only way to know. A NGK 06 VS an 10 spark plug changes your compression ratio, when you figure that out reply. Same as stock VS Ferrea valves or Supertec.

 

I won't know the head cc's, or gasket cc's, or cylinder numbers for now since the motor is currently in the machine shop getting the bottom end balanced. The cylinder displacement is 1857

 

Well then, take them the head and have them CC it and calc your final compression ratio.

 

10 thou off a GSR head has to be cc'd...it starts off as 42.7cc and reduces from there but not lineraly because of the way the chamber is shaped...BTW the ITR/B16A does reduce linearly as an FYI.

12.4 doesnt sound too far off from milling off 20thous in total between the head and the block (including flat faced ferrea valves) and 0.5mm overbore.

 

The first part of your 2 verses threw me off a bit? Call me a newb in the whole head discussion thing but I know the gsr head is square port as oppose to the circle port of the itr/b16 making it a bit more favorable for the all motor application that is why i sourced one, alot cheaper than itr.

 

thats correct, so if you mill 10thous from the b16a/itr head you can simply use the volume formula for a cylinder to calculate the cc amount to deduct from the original 43.xx cc that the stock itr/b16a volume is...but because you have the squareport gsr head you cannot use that cylindrical formula to calc the cc to deduct from milling the gsr head by 10 thous...

 

Ahhh now we see eye to eye lol..so how would one go about doing such with a gsr head? I am sorry for the newb questions, I want to learn correct, not hearsay.

 

The best, most accurate way, as Cheetah told you, is to have the chambers CC'd with all the stuff in place that you're going to use (spark plugs, valves, etc).

 

Ok. Thank you.