dustin

So, I go measure the JE 9.0:1 pistons and they have the same compression distance as stock LS pistons from the top of the wrist pin to the top of the piston. The only difference is that the GSR pistons have a dish top... aka lower compression.

Now all of you fine folks told me that the 9.0:1 GSR pistons should yield 9.3-9.4:1 in an LS motor... ?

Ideas?

Dustin

Mikex25

that would be great on lowing the compression of a LS block you don't get that much of a lag since your right in between the 9.0 mark and 9.5 mark.

Blown90hatcH

Now measure the quench area of the head....see any diff to make up for the dish pistons?

Jason

dustin

Well, I am comparing stock LS pistons to 9.0:1 JE GSR pistons. If the GSR pistons result in higher compression in the LS motor than the stock pistons, I would expect there to be more distance between the top of the wrist pin and the top of the piston than w/ the stock LS pistons (since the GSR pistons are dish)

Dustin

Blown90hatcH

Okay...so you measured the distance between the wrist pin and the edge of the piston or to the center of the dish portion? This distance might be the same, but if the quench area/volume is smaller on the LS, the compression is going to be higher.

dustin

All I am saying is, the distance from the wrist pin to the edge of the piston is the same on both pistons... but the stock LS pistons are flat and the GSRs are dish... there is obviously a crater taken out of the GSR pistons and the LS pistons are flat... which seems to me to mean that the GSR pistons will create lower compression than if I used LS pistons in the block.

ArizonaTurbo

Yes, you will have lower for 2 reasons:

1. Quench area for teh LS head
2. Pistons
The factory LS pistons are Flat top pistons correct? If you would replace the stock cast LS pistons with Flat top JE B18A/B pistons, you would have the same exact CR, correct.

Regardless of the fact that the pistons you have are for the B18C1, they are dished for 9.0:1 CR in a B18C1.

These same pistons would be an even lower CR because of the quench area on your LS head! You will net even a lower CR with those pistons since you have an LS head. I am guessing an 8.8:1 CR if you use those pistons!

dustin

It is my understanding that the GSR has a more head volume than the LS, so if I were to put stock GSR pistons in an LS, the compression should go up.

Dustin

HX_Guy

The GSR has less combustion chamber space then the LS

GSR = 41.7cc
LS = 45cc

EDIT:




By looking at the specs, OEM GSR pistons in a LS engine will raise the compression beyond the stock LS 9.2:1 CR.


[Modified by HX_Guy, 3:29 PM 11/13/2001]

dustin

Hrm, so why would anyone try to tell me that the GSR 9.0:1 pistons would yield 9.3-9.4:1 in an LS? 3 or 4 people even concurred.

Dustin

HX_Guy

Dustin, do you have the dime displacment of these GSR 9.0:1 pistons?

I can figure out the compression ratio of these pistons in an LS.

dustin

I do, but I cannot find the paper.

HX_Guy

I found the info on Crower's webpage...so here we go...

Swept Volume: (81 / 2)^2 x pi x 89.0mm / 1000 x 4 = 1834.4671
Piston Dome Displacement: -9.300cc x 4 = -37.200
Combustion chamber volume: 45.000 x 4 = 180.000
Headgasket volume (incl. piston to deck height) - (81 / 2)^2 x pi x 1.524/ 1000 x 4 = 31.1799(0.030" + 0.030" = 1.524mm)

Compression Ratio = (volume at BDC) / (volume at TDC) =

(Swept Volume - Piston Dome Displ. + Comb. Chamber volume + Headgasket volume (incl. piston to deck height)) / (Comb. Chamber volume + Headgasket volume (incl. piston to deck height) - Piston dome displacement)

= 2082.847 / 248.3799 = 8.38:1 Compression!!!!

So, those 9.0:1 GSR pistons in a LS engine would gibe you a 8.38:1 CR

dustin

Hehe. Hrm, so I guess it is time to get some more pistons then Anyone want a set of 9.0:1 GSR JE pistons w/ rings and pins, unused?

Dustin

HX_Guy

What compression ratio are you looking for Dustin?

dustin

I want to end up with stock compression JE pistons in my LS and stock compression JE pistons in my GSR.

I have one set of GSR 9.0:1 Pistons.. and I guess they do not help my situation any

Dustin

HX_Guy

You can start milling