I roadrace a C6 Vette and needed a new LS3 for it. The first combo I put together:

- L92 longblock (4.065 bore), refreshed with changes below:
- LS3 intake valves
- Full stage 1 exhaust only port
- Chamber ported/polished to lay down the bump
- competition valve job
- decked the heads (62.4cc)
- stock bottom end (376ci) with deep eyebrows in the stock pistons (-2.3cc)
- 11.21 compression
- 0 deck on the pistons (flush)
- 93 octane pump gas
- BTR custom roadrace cam, springs, pushrods
- Cam: 23x/24x, almost 600 lift, 111+4, HUC lobes
- Stock LS3 TB and intake (untouched)
- 16lb race clutch and flywheel
- ARE Stage 1 Dry Sump oiling system
- LG Super Pro 1 7/8 headers to 3" ‘X’ and dual 3" out the back (no cats or mufflers).
- 27 degrees total timing and high 12’s AFR.
Car has stock 3.42 Z06 rear gears and trans.

This engine dyno’d at 505rwhp (SAE) and 480tq. You can find that post on this site if you look. Unfortunately a stock rod bolt let go and it destroyed the engine shortly after the tune.

Round 2:
- Forged LS3 shortblock, 4.080 bore so 379ci and a heavier rotating assembly
- -3.5cc valve reliefs in flat top forged pistons
- FRH Stage 1 LS3 heads, (full intake/exhaust/chamber porting)
- 11.0 compression
- Pistons 7/1000 out
- 266cc volume intake vs. 255cc stock.
- Cometic head gasket 4.085 x.040 compressed height this time just to shrink some of the extra chamber volume of the new heads.
- EVERYTHING else the same down to the shop/tuner/dyno/cam/TB/Intake/Exhaust/CAI.

Results:
522rwhp before beingfully broken in. Detuned it to 23 degrees of timing and 11.5:1 AFR and the attached dyno shows those numbers. My racing organization requires all dyno pulls be with 28psi minimum rear tire pressure and the car up to full operating temps so none of these are glory pulls.

Summary:
It gained ~ 11rwhp and 7rwtq from 5500RPM and up but on 4 degrees less timing and running a lot richer. It showed 17rwhp gains on one pull at 27 degrees but was quickly detuned as the engine was still breaking in and the tuner was being conservative due to all the bad luck I’ve experienced with stock and/or used parts. Unfortunately my luck persisted and this engine too is now coming out (block has cracks). All the guts will be transferred to a brand new LS3 block bored 4.080 so hopefully a perfect repeat just like the second attempt.

Exhaust Ported vs FRH Stage 1 dyno by Filistin01, on Flickr

 

Nice results! Does it feel any different?

 

Damn, that's some shitty luck. I hope the third time works out for ya.

 

I would like to see what it would do fully tuned aka max timing and correct fueling.

As it stands, those gains seem to be very weak and only at the high end of the RPM band.

I'd expect that out of a mild 6.0 build...but on the correct bore and with a decent cam that's no bueno.

 

I think the only place a larger intake port (266cc) is going to see gains is in the top end, do you really think in a .15 over 6.2 it's going to pick up much below 5K? I don't think its a stretch to expect that fully broken in it will make 525rwhp and 485tq. It is a prime candidate for intake/tb upgrades at this point, that would probably help the numbers if I needed more power.

 

Pretty impressive for stock intake/TB! Sorry to hear about the bad luck though...

Looking forward to updates

 

Any chance you have or plan to measure the intake & exhaust runner volumes on the new heads? I'd also be interested in the runner lengths.