?why 4VR pistons in new LS7?

[Jack]

I'm drooling over the photos & info about the new LS7/ZO6/MY2005 vette... and I've been looking at a photo of the new LS7's piston. It has 4 (four) valve reliefs.

I understand the new LS7 has 2 (two) valves per cylinder and the motors are hand-assembled by specialists.

It's been and is still common to employ 4VR pistons ... one part number will usually fit all eight cylinders and they're almost impossible to install wrong ... but they're not typically optimized for power-efficiency.

I'm wondering why LS7 designers have chosen a 4VR piston for a big buck, very hi-po motor that's assembled in low-volume work cells by specialists?

Also ... has anyone gotten new LS7 specs for blocks' deck height, rods' length and pistons' compression distance?
JACK:gap

 

[c4c5specialist]

HI there,
.591 lift on the valves and 11.1 to 1 compression made the VR necessary.
Allthebest, c4c5

 

[Aurora40]

HI there,
.591 lift on the valves and 11.1 to 1 compression made the VR necessary.
Allthebest, c4c5

I think what he meant was why doesn't it just have 2 valve reliefs instead of 4.

 

[Jack]

I think what he meant was why doesn't it just have 2 valve reliefs instead of 4.

Precisely.
JACK:gap

 

[c4c5specialist]

HI there,
The engine is still a mass produced part and thus why make 2 sets of pistons.
Cost, is the only reason that I can think of.
Allthebest, c4c5

 

[Jack]

Purported LS7 production rate about 30/day through 15 subassembly stations at new Performance Build Center in Wixom MI. Thirty motors a day seems rather low volume to me.

First, lemme make it clear that I have NO experience disassembling or assembling any LSx motors. I'm trying to understand what's out there and what's changed.

Unlike Gen I sbc motors, seems both Gen III & Gen IV sbc have entirely different valve layout ... seems Gen III&IV valve train is NOT siamesed on center cylinders. Seems Gen III&IV valve layout is [IE-IE-IE-IE] ... like a big block chevy.

Old Gen I sbc is different, it's [EI-IE-EI-IE].

So, based SOLELY on valve layout, Gen IV sbc shouldn't need 2 different pistons if it had only 2VR. But ... IF it has offset piston pin bosses ... it would require 2 different pistons. Regardless, in such a specialized expensive hipo motor with very limited production, it seems odd to have 4VR pistons ... even if it meant needing 2 different pistons. I'm not certain, but seem to recall that some of the old Gen I high compression motors employed 2 different OE pistons.

Also, from LS7 exploded pics I've seen, there appears to be a gerotor type oil pump located within the front cover and driven by crank snout ... seems to have a dual stack of gerotors just inside cover behind damper pulley. I dunno if other LSx motors have oil pump similarly located or not?
JACK:gap

 

[Dave C. '04 Z06]

Be careful assuming the cut-aways you're see are actual LS-7 cut-aways or just an LS-2 cutaway with the rail covers re-done.


My guess is that no one has seen an LS-7 yet, so perhaps there are no accurate cut-away photos yet?

Maybe it does have 2VR pistons. The LS-1/6 have an oil pump that runs off the crank in the front.



-Dave C. '04 Z06