Fei

I know this is stupid question to ask seeing as you need a data log to give me any real answers BUT...

I just got my engine running. le1 heads, KB 5cc flat tops, .022 in th hole .026 compressed VR head gasket, CC306 cam.

I get crazy detonation at WOT on 92 gas. I pulled 4 degrees across the board and that helped some but I really don't want to pull anymore and make the thing a dog.

I can only get a scan at idle seeing that I don't have a laptop right now. So what I would like is some suggestions on possible causes of such bad detonation. I guess I'm really wondering if I went with too much compression for pump gas.

Injuneer

What year is the LT1 engine? Does it use the unvented Opti with the splined drive shaft? If so, are you sure you got the splines aligned correctly? Is the knock sensor still functional in the tune?

Fei

it is splined but (I know they all say it) certainly straight. No miss or anything like that. It's a 94 lt-1. I know I need to dyno tune it but i've been playng with tunercat to get the thing drivable in the mean time. I might just break down and do an internet tune until then.

I'm keep getting code 42. that's why I asked about the knock sensor in the previous post BUT I get knock count when I scan it. So I'm not sure.

It's running great except for that knock. I only get audible knock at full throttle in 3rd or higher. I can rip through 1st and 2nd no sound. I'm sure I'm still getting knock though.

Sometimes it will knock right on start up then smooth out. I can hear a lug then starts up and runs. This is thing that has me worried as for having too high of comp.

Injuneer

DTC 42 is not related to the knock sensor. Its for a short in the ignition control system. Do you possibly mean DTC 43? That would indicate a faulty knock sensor, and you would have almost continuous knock retard. Knock count is not generated by the knock sensor. Its the result of the PCM identifying operating conditions that it feels will cause detonation. But it doesn't act on the increasing knock count unless the knock sensor has been active.

Do you see any knock retard at all? The stock tuning alllows the PCM to pull out up to 15* of advance to eliminate knock. The fact that you can hear the knock indicates either the knock retard system has been altered in the PCM by limiting the maximum amount of knock retard, or eliminated completely, or you have massive detonation and pulling 15* (or whatever the tuner set the max retard to) isn't enough to eliminate it.

Did you ever actually calculate the static and dymanic compression ratios?

95Blackhawk

Wondering the same thing.

Just as an FYI, I run 32* at WOT on my car in the upper rpm's. What is your timing in WOT right now? Did you confirm you are getting knock other places other than WOT?

Do you know for sure that your AFR is correct at WOT? Maybe you are going lean.

FryedClutch

i wouldnt think that your compression would be too high.
with out knowing the combustion chamber size and gasket bore i can only guess your static is between 11.2 and 11.9:1. with the 306 cam on a 383 11.7:1 static gives a dynamic of 8.6 - 8.7:1 which is slightly high for 93 octane.
but with alluminum heads and reverse flow cooling it should still be allright. it is pushing it a bit but i wouldnt think you would be having the issues you are
how hot is itrunning?
is there a possibility that the coolant system wasnt properly bled and there are air pockets causing the the combustion chambers to prdetonate because they are too hot

im just throwing ideas out there but it could be lots of little things

Fei

I didn't CC the heads :-/ but if I go with 54 CC heads, which is almost impossible seeing that stock was 54 and most of those turn out to be 56 and these are le1's but have been surfaced, I get 9.08 dynamic and 12.30 static. 58CC heads gives 8.61 and 11.64. So I'm somewhere in between that.

So I just checked out the spark vs. rpm vs. map and the timing was super high. low 40's for a lot of it. I scaled everything down so nothing was more than 35. Added a little fuel in the wot table and that eliminated the audible knock.

I will need to get a laptop to dig any further into this but that is a little comforting to know it can run.

FryedClutch

what are you using for your head gasket bore diameter ?
because if your piston is sitting .022 in the hole it shouldnt be that high

marshall93z

Your compression ratio math doesn't sound right.




Mine has audible knock before the knock sensors pick it up.

FryedClutch

the only way i calculated your compression that high was if it was 0 decked and the head gasket bore was 4.030

Fei

that's using a dcr calc I got off this site.

pistons 4.040
gasket .026
clearance .022
head gasket bore 4.100
Advertised intake close 73
effective stroke 2.49


and I just re ran the numbers and they were way off. I must have mistyped. huh. well they range from 8.57-8.16 DCR 11.55-10.98 SCR and that is in no way too high

Guest47904

Stroke is not 2.49

FryedClutch

thats what he is using to calculate dynamic not static