detonation

[hellrico]

Hi
Long time follower, first time posting.
My engine was built base on some post I've read over here.

I come to a dead-end and need advise.
Truck 2WD 1993 Ramcharger
Engine:
408 magnum engine with OOTB Eddy head.
Barrel intake. stock throttle body for now.
Cast 1993 exhaust manifold.
12 CR static,
210 PSI cylinder pressure, done cold, good battery, no plug and no intake.
.055 quench. flat top, piston .015 above block and.070 head gasket.
intake valve close 35 ABDC
195 thermostat, will put 175 shortly.
Megasquirt MS3Pro
GM coil over plug
2 knock sensor
ICOM injector, DEKA blue injector with D5 tips. plastic hose spread liquid phase LPG at about 1 inche from intake valve
fuel pump is 45 PSI over return line pressure
44 total ADV at 2600
15.5 AFR.

Engine is running fine, cruise around fine, but above 2800 and TPS 45%, I hear it faintly detonate and knock sensor capture it as well.

I have those injector size number from Icom, but, don't know the actual unit. CC/Min, L/Min, etc. If you know, it might help me program the ECU.

What may cause detonation? What do I miss?
Any guidance would be appreciate.
I can post Megalogger, VE table and Timing table later,
Thanks

[Tom68]

Sounds like too much ignition timing if the knock sensor can catch it and stop it, if the knock sensor retards but doesn't stop it then you have several things to look at, intake air temp, type of engine oil being used, may need an oil that doesn't use calcium as a detergent. etc etc.

[storm]

Hi
Long time follower, first time posting.
My engine was built base on some post I've read over here.

I come to a dead-end and need advise.
Truck 2WD 1993 Ramcharger
Engine:
408 magnum engine with OOTB Eddy head.
Barrel intake. stock throttle body for now.
Cast 1993 exhaust manifold.
12 CR static,
210 PSI cylinder pressure, done cold, good battery, no plug and no intake.
.055 quench. flat top, piston .015 above block and.070 head gasket.
intake valve close 35 ABDC
195 thermostat, will put 175 shortly.
Megasquirt MS3Pro
GM coil over plug
2 knock sensor
ICOM injector, DEKA blue injector with D5 tips. plastic hose spread liquid phase LPG at about 1 inche from intake valve
fuel pump is 45 PSI over return line pressure
44 total ADV at 2600
15.5 AFR.

Engine is running fine, cruise around fine, but above 2800 and TPS 45%, I hear it faintly detonate and knock sensor capture it as well.

I have those injector size number from Icom, but, don't know the actual unit. CC/Min, L/Min, etc. If you know, it might help me program the ECU.

What may cause detonation? What do I miss?
Any guidance would be appreciate.
I can post Megalogger, VE table and Timing table later,
Thanks

Don't take offence but you have a seriously mismatched vehicle there. The engine sounds like a weapon, even though the cam information lacks detail, and would love something like a Barracuda.
You have a heavy truck which will labour the engine and you're running 12-1 compression. Even with alloy heads that is pushing the boundaries alot with the timing you have. The generic starting point of 14=14+14=42 and that is on a regular compression engine. IN general the higher the compression the lower the timing.
"intake valve close 35 ABDC" doesn't really tell us much. What are the full cam specs? what duration do you have at .002 and .050 lift on both intake and exhaust? what are your lca and/or lsa?

I'd start with taking 5 degrees out of your timing map at any area where detontation occurs. Why 5 degrees? if you can hear it you are already 2 degrees further than a quality knock sensor will pick up. Try the smoothing function in TunerStudio after you take that out to get the timing map smooth and help with drivability. Take it for a drive and add 1 degree (at the most) at a time until you get detonation on your logs or the engines responsiveness becomes sluggish. When you see any sign of detonation take 2 degrees out and leave it at that. You must give your engine some room simply because a heavy vehicle makes the engine stay on the load point for much longer than a light vehicle. The longer it is detonating the more likely damage will occur.

[hellrico]

Thanks,
Will retard until no further Knock. thanks

The magnum head were crack between valve seat, and there was a special at Mancini for set of fully assembled eddy head for 1300$. Thought that aluminium head would help.
Do not want to build a racing machine, but would like to squeeze as much as possible of the advantage of using LPG and the ''while we area at it'' of rebuilding an engine.
My intend is longevity, I want to do 300K with it. It will pull camping trailer(amoung other trailer). Body is super clean.
This is a LONG term project. We do not need the truck right now, but will become our main vehicule next year.

Dana 70 3.54 (from a Dodge 92 D250) is under rebuilt and will change front wheel hub to 8 studs as well.
I have a spare 46RH that i will prepup as winter project.
Cam is CRS XR268HR-10
@.05 lift 218 and exh 224
lobe sep 110

Engine is freshly build, so still purple oil in in.
Air intake temp is there, but unhook in megasquirt yet.
Thanks

[storm]

Good quality LPG has an octane rating of 105-110 which is ideal for 11-1 compression ratio, alloy heads can afford another full point. The thing is the higher the comp ratio the more critical the timing is. If you get a load of LPG that has alot of Butane in it the octane goes down so if you are already on the edge of detonation with your timing the lower octane will make you engine detonate as soon as you load it up.

Air temp is vitally important so I recommend you connect it up and set it up in TunerStudio as soon as possible.

Nice cam, did you notice in the Comp Cams catalogue that it was designed for 9-1 compression? I like roller cams they allow better breathing. The combination of your compression ratio and this cam is why your cranking pressures are so high and by extension why you're getting detonation with your timing set at 44 degrees.

You'll be able to tune it out with the timing adjustments. If you can grab a screenshot of your timing map I'd be interested in seeing it, also a log screen with the point of detonation shown.