LS1-450

iTrader: (33)

Have seen threads where guys have gone up into the high 8's DCR on 93 Octane. If you have gone above 8.6 DCR please note what was experienced.

Planning to up ours to 8.82 & can reduce if necessary (adjustable timing set & 2 piece cover). Have run up to 8.6 in the past without issue. SCR will be 11.65...reduced down from 12.0.

AFR 205 heads, 4.030"/.040 Cometics, stock LS6 cubes. Quench is excellent. We ran 29* @ max TQ & 32* after & up to 6800 RPM through carb w/ no pre-detonation. Plan on similar w/ modded set up. Can log A/F ratio & have headphones/mic to listen for knock. So, we will be able to safely dial it in.

Darth_V8r

iTrader: (4)

I'm at 8.7 now. Peak power at 24 degrees advance vs 27. Had some KR initially in the off idle range but was able to get rid of it. Peak Tq timing is 22 advanced.

Exidous

iTrader: (11)

8.96:1 with a really tight quench... About. 033". I have not tuned the wot yet but have not seen any knock yet. I am on RON 98 gas. Roughly equal to ron/mon93.

Cam is smallish. 225/227-114+4 mamo top. Tony expects around 26-28 peak.

What's your quench at? Probably the same as mine.... You'll be fine.

redtan

iTrader: (5)

I've done 8.9, wouldn't do it again.

Had to really tone down the timing across the board way to much and still had quite a bit of KR.

Exidous

iTrader: (11)

Hopefully I don't have too many issues with kr.... Well see when I get home in November.

Exidous

iTrader: (11)

.033" quench not gasket. I am using .040" cometics. Pistons avg .007 proud.

I have the Mamo220's milled to 60cc. Should have about as good a quench as you can get.

Camaro99SS

iTrader: (4)

My combo was ~8.9 DCR and ran fine on 93 octane. Peak timing was 26 degrees, and it even ran find on 28 but no additional power. Air/fuel was also 13-13.2:1 for the dyno pulls.

Two things making this possible IMO were the welded chambers enabling some extra metal for AI to reshape them into a more defined hearth shape and tighter quench. It was at 0.033" with the 0.040" gaskets. If not for these mine would have been a KR bomb.


Jason

Exidous

iTrader: (11)

Sounds like my setup. If I do have issues I can just get a cam with a different intake valve event....(bigger bwahahaha)

Darth_V8r

iTrader: (4)

you would greatly benefit from later IVC and earlier EVO. If you go 45 degrees on IVC, you'll still have 8.5-8.6 DCR, less chance of detonating, and more power.

You could either keep your durations and go wider LSA, or keep the overlap and open up duration. I would go option 2 personally.

JakeFusion

iTrader: (7)

I'd aim for 8.5:1 ~ 8.7:1... but I'd keep overall compression around 11.5:1. That still matters.

LS1-450

iTrader: (33)

We can retard cam & get it lower. Figured w/ the quench surface area on the AFR heads coupled w/ the tight quench height, could get away w/ 8.8:1. No?

Exidous

iTrader: (11)

Yea if I reduced the 4° advance (hexadjust) down to 2° I'd be at about 8.8:1. Straight up would get me about 8.65:1 and probably carry a little better up top but I'll wait to see how it does as is. Hopefully I can leave it as is and keep as much midrange as possible...

blk00ss

iTrader: (66)

I just figured mine up and came up with 8.07:1

Seems pretty low considering I have 12:1 SCR. Guess it could explain why it wasn't showing any detonation with 28* of timing on pump gas.

redtan

iTrader: (5)

You can get away with it yes.

That's exactly what I did, going from 8.9 that was tough to tune down to 8.7 with 11.5 SCR. It feels just as snappy, but tuning is much easier. I can play around with timing and not worry about pinging all time.

Darth_V8r

iTrader: (4)

How are you doing this? Are you swapping cam? cam and heads? head gasket?

LS1-450

iTrader: (33)

This is key & seems to be the point missed by people using stock heads. There is more quench surface area on aftermarket heads & the added area is typically shaped to enhance quench. It's not only about using a thinner head gasket.

It would be helpful for everyone to include which heads are being used when noting their DCR related experiences.

Another small detail that can help is spark plug indexing.

JimMueller

iTrader: (9)

So I should be fine with these planned future changes?

LS3 heads (~69cc stock) milled to 62.5cc, Cometic .045x4.080 gasket, flat-top piston .011 above the deck, 5cc valve reliefs, 4.07 bore, 6.125 stroke, advertised IVC should be near 68. I come up with SCR ~11.3, DCR ~8.8, quench .034 (cold) unless I'm missing something. Each degree I change the IVC moves the DCR by 8/10th's. No plans on spark plug indexing, I thought that was hype except for extremely high compression?

redtan

iTrader: (5)

Yes new cam and smaller chambers, but the biggest difference is in the lobe design. It's a significantly less aggresive lobe (at 0.006) and lowers DCR.

Exidous

iTrader: (11)

That's probably part of my "problem" if it shows up. I'm running LXL on int and exh.

.006 275 277 .612 .614
.050 225 227

114LSA
110ICL

I'm curious if retarding the cam 2-4 degrees would provide a noticeable shift in power. A 114ICL would net me about 8.65DCR.

LS1-450

iTrader: (33)

If you're being told that indexing makes more power; then, yes it's hype. Indexing is simply a small detail used to ensure that the spark is positioned where it has the best chance of producing the most efficient burn.