10.9 84.5mm GSR Arias Flatop pistons + Itr head + supertech "domed" valves (turbo version with inverted dome) = Lower then 10.1 compression??

I know someone must know, any help would be greatly appreicated...

 

You would need to post a lot more information for help, like volume of of the Arias flat tops (including valve reliefs), thickness of the head gasket, 87.2mm stroke?, Chamber volume, height of the piston in the bore, etc.
Usually a flat top piston will normally give you about 10-1 compression ratio, however.

 

I would tell u to go to c-speedracing.com and use the calculator but the site is down right now. Anyways, I thought a ITR head on a GSR would lower compression about 3-4 points? So it should be about 10.5:1

 

84.5mm bore
87.2 stroke
10.9 compression gsr flat top pistons
stock head gasket
itr head with supertech turbo valves.

 

i pluged it in and came out with 10.03

 

How did you plug it in without knowing piston dome, dish or valve relief volume or knowing how deep in the hole is your piston?
I guessed at some of your numbers and came up with 10.5-1 but it could be higher if your head has been milled. What ever it is, it is too high for safe turbo use anyway.

 

i pluged it into the compression calulator, using the Dome CC.. It has to be lower, due to the turbo valves, im assuming.. lower then 10.03

http://www.ariaspistons.com/sportacura.htm

 

BTW, SuperTech turbo valves have the same volume as stock oem valves.

 

Arias flat top pistons have a -3CC valve relief, that combined with a stock chamber ITR head, stock headgasket, and a piston .020 in the hole would give you 9.6:1 compression. .010 in the hole = 9.84:1 compression, and at zero deck would give you 10.08:1 compression. I don't have a clue what the dish size is on the supertech valves, but guessing and saying it's 2CC's combined for all 4 valves it would drop your compression at .020, .010, and zeo deck to 9.30:1, 9.51:1, and 9.73:1 respectively.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by earl &raquo;</TD></TR><TR><TD CLASS="quote">BTW, SuperTech turbo valves have the same volume as stock oem valves.</TD></TR></TABLE>

they are exact?? from what full race told me, they drop it a few points :/

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chip &raquo;</TD></TR><TR><TD CLASS="quote">Arias flat top pistons have a -3CC valve relief, that combined with a stock chamber ITR head, stock headgasket, and a piston .020 in the hole would give you 9.6:1 compression. .010 in the hole = 9.84:1 compression, and at zero deck would give you 10.08:1 compression. I don't have a clue what the dish size is on the supertech valves, but guessing and saying it's 2CC's combined for all 4 valves it would drop your compression at .020, .010, and zeo deck to 9.30:1, 9.51:1, and 9.73:1 respectively.</TD></TR></TABLE>

Dead on Jordo

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 0x64 &raquo;</TD></TR><TR><TD CLASS="quote">

Dead on Jordo </TD></TR></TABLE>

so i should have 9.3:1 compression??

if thats the case then damn, thats a major drop in what they rate it for..
9.3:1 would be pretty perfect.

 

Your best bet, IMHO, would be to make a plate to CC your chambers out of plexiglass, then you don't have to guess around with the size of the dish on the supertech valves.

 

I would definitely cc the chamber. Those valves look like they've had the seats sunk into the head a little.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by IN VTEC &raquo;</TD></TR><TR><TD CLASS="quote">I would definitely cc the chamber. Those valves look like they've had the seats sunk into the head a little.</TD></TR></TABLE>

What exactly does this mean?? sunk a little?

 

When the seating angle gets cut into the valve seat and the backcut on the valve, it puts the valve higher up into the head. It's just a question of how much.

 

So basically what you would want to do is take a head gasket, trace the cylinder bolt pattern onto a sheet of paper, or even right onto the plexiglass, then cut out the cylinder head bolt holes into the plexiglass, then drill a small hole in the center of the plexiglass for the water to enter. Get a Buret from somewhere (go to a local high school, ask them where they get them) it's basically a graduated cylinder with a valve on the bottom that measures the amount of liquid you're pouring out of the buret. Fill up the combustion chamber right up to the plexiglass, look at what it says on your buret, and that will tell you how much water your combustion chamber holds.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by IN VTEC &raquo;</TD></TR><TR><TD CLASS="quote">When the seating angle gets cut into the valve seat and the backcut on the valve, it puts the valve higher up into the head. It's just a question of how much.</TD></TR></TABLE>
is this bad?

 

Not always a bad thing, but like everything else, you have limits. It can give you a little more piston-to-valve clearance and retainer-to-valve seal clearance if you're running really big cams.

It can also change valve stem install height, valve spring install height, and maybe some other things that a head porter could tell you. There might be a possibility of shrouding the valves.

 

im running stock cams.. think ill have a problem?

 

I'm guessing that you're around 10.2:1. Using the specs from the Arias website. The supertech valves are the same as stock, but those are Skunk High Comp valves. An entire set of those valves will net you an increase of about 2 tenths of a compression point, so I'm guessing 1 tenth since you are combining the two. The head may have been milled, so I added a tenth for that also. I think that its gonna be a little high for a daily driven boosted car.