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

 

Anybody see any issues with these figures on pump gas 93 or e85?

 

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.

 

Im pretty sure I see your point. Part of the issue is I dont know exactly what an acceptable CR is for these engines on pump gas is. Even-though I will run e85, I prefer it more as a security blanket so to speak. Basically Im trying to make a set of heads with a 63.5cc CC work, and it seems to be what is causing the compression concerns. Maybe I need to acquire some LS3 heads or something.

 

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.

 

If you used negative 14 cc's in your calculations, then you Are figuring it for a domed piston not dished.

 

"Note that clearance volume does not take into account any pop-up domes or sunken-in dishes on the head of the piston. These configurations also increase or decrease volume in the combustion chamber and affect the compression ratio. The manufacturer's catalog will list the displacement in cubic centimeters of the dishes or domes on the piston, but we've found that it's not consistent whether they express the cc's of a dish as a positive or a negative number."

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

 

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.

 

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.