outkast6991

iTrader: (34)

I'm trying to track down a kr issue I'm having and I'm starting to think it compression related. I've used an online calculator and I'm coming up with 11.2 scr and 9.0 dcr. my setup is

stock lq9 with .060 flycuts on both valves
stock ls2 head gaskets
pistons measured at .008 above deck
63cc 243's (measured)

valve events are

7 btdc / 49abdc (intake)
53 bbdc / 11 atdc (exhaust)

all numbers are at .050

I'm running on 93 at all times and my timing in the affected area's is pretty low (22ish). I'm starting to think the 9.0 dcr (if correct) is part of the issue. Any help is appreciated

batboy

iTrader: (6)

You might be a little high on your static CR calculations. Any idea what your valve relief volume? My guess you're at 10.8 or 10.9 CR.

What cam is this? Most of the dynamic calculators I use require cam specs at .006" not .050". I think your dynamic CR calculations are a bit high.

Try reducing timing a bit more and see if that helps your KR. You might be getting false knock. Does it only happen when you first accelerate or do you see it during WOT? During the middle of a WOT run is bad.

outkast6991

iTrader: (34)

Kr is starts between 3600-4000rpm and stays through the pull. I have one of the better tuners out there acting as a mentor for me. Reducing the timing isn't showing signs of help. I'm actually starting to think its a false condition due to solid motor mounts. I'm ordering poly's to rule it out. I really just wanted to see if my calculations were close and I'm not dealing with a compression issue. The cam is from Bauer, no idea as to volume of the fly cuts but they are .060 deep and stock sized

batboy

iTrader: (6)

KR staying throughout the pull is definitely cause for great concern. I'd probably inspect the spark plugs and look for signs of detonation.

So the cam is a custom grind and you have no cam card? Just looking at other cams with similar specs, I think your dynamic CR is below 8.5, so unless you got a bad tank of gasoline, you should be ok there.

You situation sucks. Hope you get things figured out.

outkast6991

iTrader: (34)

Cam is a custom but I have the card from comp. I just had the heads of and neither the heads/valves or pistons/ plugs show any signs of knock

batboy

iTrader: (6)

Does the card list advertised specs (at .004" or .006")? Hope you don't have a lifter collapsing or a rod knocking.

outkast6991

iTrader: (34)

motor is dead silent as far as valve train noise. i'll try to post the card

outkast6991

iTrader: (34)

the only numbers at .006 on the Comp card are duration 289 int 306 ex

batboy

iTrader: (6)

Ok, I found a dynamic calculator that can use .050 specs if you add 15 degrees. I just guessed -3 or -4 for valve relief volume since we don't know for sure. But, dynamic CR should be around 8.6-8.7 or so.

outkast6991

iTrader: (34)

Sounds like the one I used and came up with 9.0. I didn't input the valve reliefs though

Grr

iTrader: (2)

Cam from your numbers is

.050
236/244 111+0

IVO 7 btdc
IVC 49abdc
EVO 53 bbdc
EVC 11 atdc


.006 289/306 111+0

IVO is 33.5 ° BTDC
IVC is 75.5 ° ABDC
EVO is 84.0 ° ATDC
EVC is 42.0 ° BBDC
Overlap is 75.5 °

Static compression ratio of 11.2:1.
Effective stroke is 2.52 inches.
Your dynamic compression ratio is 8.09:1 .
Your dynamic cranking pressure is 161.30 PSI.

outkast6991

iTrader: (34)

Wow your duration is almost dead on the advertised on the card. It reads 236/245 and it degree'd in at 110. Your 8.0 is pretty far from my 9.0. Lol. It your is correct I'm thinking it can't be compression related

batboy

iTrader: (6)

Probably not CR related if your ABDC is 75.5 degrees. I was using 69-70 to do the calculations. Can you get a few gallons of high octane racing fuel? If you still knock with that, then no.

Grr

iTrader: (2)

Pull the plugs and look for a lean cyl, could be one injector that is off from the others. pull ALL of the plugs and look at them really well.

Otherwise pull timing back to 18 and see if it goes away, if it does not it is most certainly false. Some setups such as mine dont like timing and I only run around 24* FWIW

outkast6991

iTrader: (34)

I still had it with 18* through that area. That's why we are leaning towards a false condition. The heads were inspected by a knowledgable guy and showed no signs of knock. Locks were good,valves showed no heat either. I just wanted to make sure I didn't miss something with the scr/dcr because it was setup but someone else. Thanks for all the help. Poly mounts will be in next week and I'll pull another log