LQ4/LQ9 Static Compression Ratio Discussion
#1
LQ4/LQ9 Static Compression Ratio Discussion
Hey all, I've got a bare LQ4 block and I've been weighing options for quite sometime on what route to go with from a rotating assembly standpoint. After looking into the more traditional 402/408 route, I ran across the 413cu TSP rotating assembly.
My concern is in regard to compression ratio. To get the CR to 11.75 I had to calculate it with a -15cc piston and .051 head gasket (see below). I will be running e85 with this setup, but if for some reason I can't get e85 sometime down the line, I want to make sure that I wont be stuck with race gas. Does this CR seem doable on a LQ4 block with forged rotating assembly.
LSx Compression Calculator
Bore 4.005 Cyl. Volume BDC Engine Cu. In.
Stroke 4.1 56.4559520358 cu. in. 413.21
Rod Length 6.125 Cyl. Volume TDC Rod/Stroke Ratio
Piston Comp. Height 1.11 4.8049410195 cu. in. 1.493902439
Piston Dome cc -14 Compression Ratio
Head Comb. Chamber cc 63.5 11.75 :1
Head Gasket Thickness 0.051 Piston - Deck (Piston in/out of hole inches)
Block Deck Height 9.24 0.045 in.
Cylinders 8 Quench
0.006
mm in mm -> in in -> mm
0 0
My concern is in regard to compression ratio. To get the CR to 11.75 I had to calculate it with a -15cc piston and .051 head gasket (see below). I will be running e85 with this setup, but if for some reason I can't get e85 sometime down the line, I want to make sure that I wont be stuck with race gas. Does this CR seem doable on a LQ4 block with forged rotating assembly.
LSx Compression Calculator
Bore 4.005 Cyl. Volume BDC Engine Cu. In.
Stroke 4.1 56.4559520358 cu. in. 413.21
Rod Length 6.125 Cyl. Volume TDC Rod/Stroke Ratio
Piston Comp. Height 1.11 4.8049410195 cu. in. 1.493902439
Piston Dome cc -14 Compression Ratio
Head Comb. Chamber cc 63.5 11.75 :1
Head Gasket Thickness 0.051 Piston - Deck (Piston in/out of hole inches)
Block Deck Height 9.24 0.045 in.
Cylinders 8 Quench
0.006
mm in mm -> in in -> mm
0 0
#3
So from that information the piston is out of the hole .006" and the Quench is .045"? That is about right however I'm not a big fan of dished pistons, and -14cc is quite a bit, I let some moron spec a rotating assembly for me long ago and he put some -13cc pistons in it that sucked. I have them on the shelf, can't even sell them as no one wants them, might end up in a turbo motor eventually.
A rotating assembly that has a large dish in the piston screams to me "DON'T DO IT!" You get the proper compression ratio through other means, not by using pistons like that.
#4
So from that information the piston is out of the hole .006" and the Quench is .045"? That is about right however I'm not a big fan of dished pistons, and -14cc is quite a bit, I let some moron spec a rotating assembly for me long ago and he put some -13cc pistons in it that sucked. I have them on the shelf, can't even sell them as no one wants them, might end up in a turbo motor eventually.
A rotating assembly that has a large dish in the piston screams to me "DON'T DO IT!" You get the proper compression ratio through other means, not by using pistons like that.
A rotating assembly that has a large dish in the piston screams to me "DON'T DO IT!" You get the proper compression ratio through other means, not by using pistons like that.
#5
TECH Regular
iTrader: (17)
Ran 11.5 to 1 in my 370 on 93 octane with 28* of timing. Daily driver. Just use your cam to get the compression ratio down for the street. I ran the COMP 231/239 614/624 114+2 to get my ratio to 8.8 to 1. Made 504rwhp with L92 heads.. Good luck.
I was using Diamond pop-up's with non-milled L92's.
I was using Diamond pop-up's with non-milled L92's.
#7
The compression calculator Im using indicates to use a negative value for a dished piston. I double checked this by entering it as a positive valve, and the compression ratio went up.
*corrected after noice's post
Last edited by zman1; 10-18-2011 at 11:03 PM.
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#8
Hmmm sounds like you said that backwards or have it backwards. Enter it both ways, the higher compression result tells you that it is a dome piston, dish piston is the lower result.
#9
Yeah, I said it backwards, ugg ... the guy above had me all confused. But the fact is that most manufacturers are using a negative value to indicate a dished piston, which is contrary to what bww said.