JakeFusion

iTrader: (7)

Are you sure you don't have -15cc dished pistons and 72cc heads? That'd put your SCR down below a stock LS1 and with that cam... ugh, very low DCR.

Patrick G

iTrader: (14)

With cranking compression over 200psi, his DCR would have to be in the 8s.

98Z28CobraKiller

iTrader: (17)

Flat top pistons and 72cc heads milled to 65cc. Should yield about a 11:1 compression. I checked the heads to make sure that they were milled by getting some 72cc head dimensions from Tony Mamo.

Patrick, I thought that you said that this is about what I should be seeing.

NEVRLIFT

That sounds like much higher than 11:1. My uncle is around the same compression with 70cc heads and -4cc pistons on his 402. What head gaskets are you using?

98Z28CobraKiller

iTrader: (17)

Stock 6.0 MLS

98Z28CobraKiller

iTrader: (17)

Sorry the pistons are -6cc dish.

98Z28CobraKiller

iTrader: (17)

Here are my guts:
4.000" Eagle 4340 forged steel crankshaft, balanced to rotating assembly
4.000" Ross 2618 forged alloy pistons with -6.00cc dish (includes new rings and full-float pins)
11:1 compression ratio (nominal; ultimate compression ratio will depend upon heads and gaskets used)
6.125" Eagle H-beam rods
Intake flow up to 304 CFM at .500 lift, 320 CFM at .600 lift @ 28” of H2O.
Exhaust flow up to 250 CFM at .600 lift @ 28” of H2O (using 1-7/8 inch exhaust pipe).
AFR 225cc heads with 65cc combustion chamber.
CNC ported intake and exhaust ports, and combustion chambers.
2.080 intake, 1.600 exhaust standard length valves.
3-angle radiused valve job.
7° titanium retainers and valve locks.
1.290 inch double springs, 135 lbs seat, .600 inch maximum lift.
.596”/250º int. .596”/246º exh. camshaft.

pkincy

iTrader: (1)

Whoa, whoa, guys. I too have 42#ers in my 402 but I am not ready to say that is what is causing the problem until I see a log that shows the injectors hitting 100% duty cycle at say 3500 rpm which is where this motor starts laying down.

And I will bet that they are not locked open at 3500 rpm. So there is something else going on. The 42s will be a nice addition but I have never hit over 60% DC with mine so that is probably not the biggest problem. (I am at 384 rwhp/344 rwtq with a smaller cam than this, but probably better heads).

And was the cam degreed when it was moved one tooth???

BTW, the leakdown test is really not at all hard to do, but you do need the leakdown kit and the compressor. But once you get the sparkplug out, you can work on the degreeing also.

Perry

NEVRLIFT

I hope those numbers are 4xx instead of what you posted. I will assume that it was a typo.

pkincy

iTrader: (1)

Wow, that is way higher than 11 to 1. I calculated I wanted 76cc in the compression area. And I used 72 cc heads, the gasket area, and 2 cc valve reliefs to get to what I calculate as 10.8:1.

You better run a CR calculator on that. No wonder it is detonating.

Perry

pkincy

iTrader: (1)

Yup a typo. At my age the eyes and the mind go first <g>

And that is what comes by having a couple of LT1 383s also. You forget how much power our cars make.

Perry

pkincy

iTrader: (1)

If you are running a Cometic 0.051 gasket and truly have flat tops at 0.008 out of the cylinder you are running 12.13:1 CR with 65 cc heads.

If you have a thinner gasket (very possible) you are well above 12:1.

Try a tank of race gas and redyno and see what happens.

Perry

pkincy

iTrader: (1)

I see that you are running 6 cc valve reliefs. So you have 11.7:1 with a 0.040 thick head gasket if your pistons are 0.01 out of the hole.

Perry

Chuck Harmon

Guys,

I have the same block-head combo as CobraKiller and I do not have any detonation even on the 91 octane fuel we have in Kalifornia. And I still don't believe stock injector size is a problem at anything under 5500rpm with this motor. I made 400# of torque at 2500 rpm, 490# by 5000rpm. CobraKiller isn't there yet. But he will, and then some!

Chuck

p.s. I may be off base considering I am comparing my stock LS6 injectors against whatever ones CobraKiller may be using. Stock LS1 injectors would probably cause the motor to fall flat on its face well before the 5,000 rpm range.

NEVRLIFT

This thing seems to be stumping everyone. We've dicussed timing, tuning, fuel, compression and more but there's gotta be something else.

Chuck Harmon

Have you checked your Hydrosilator? I saw a special a couple years ago about when cars go bad. The Hydrolsilator, a little know device installed in every car starting with those made by Henry Ford can cause very bad things to happen. You may find more information under the topic "pogoe carburation-injection systems"

Chuck

98Z28CobraKiller

iTrader: (17)

I'm pretty sure that the stock 6.0 head gasket is .060.

98Z28CobraKiller

iTrader: (17)

Ok , I started off with stock 98 injectors (28#). I went on the dyno 1 tooth off and major detonation. I fixed the one tooth off and changed to stock LS6 injectors. Still lots of detonation. Backed the timimg way off and now the detonation is gone and it feels stronger. Still haven't started messing with the commanded AFR. I think that it is at like 1.18 across the table commanded. I am getting close with the VE Table but when my new injectors arrive(tomorrow), I imagine that I will have to retune the table anyways. Just with the VE Table semi dialed in, I am starting to hit spark table scan cells in the .94 area. I did a scan on the injector duty cycle and I am hitting 118% at 6K RPM . So I wont do that again. Belive me that I had done scans before with the other problems and the highest duty cycle I had seen was like 93%. These are all good signs I think. I think that once I get some better fuel control, I should be doing better. Once I dial in the AFR I hope to be flying.

98Z28CobraKiller

iTrader: (17)

That's just what we needed, some out of the box thinking.

JakeFusion

iTrader: (7)

Doh. I was thinking he was still down in the 110-120 range. I kickass at reading comprehension!