chevy1500z71

alright, a little info on the vehicle first, its a pickup truck with a 355 small block, flat tops and 76cc chamber dart heads, around 9:1 compression, 10spi with a Whipple supercharger(non inter-cooled) i run 93 octane and methanol injection, running an 850cfm tbi w/ 80# injectors with the 7427 ecm.

iv been fighting a bad low rpm/high gear knock retard with a massive power loss ever since i swapped out the auto for a manual. the truck is an animal at wide open, it runs great at full throttle, but when when i accelerate lightly from a red light i get 8 degrees of knock retard which turns the motor into a real dog, the knock count is always aroun 195 once its warmed up. if i wind the motor up to around 2500 it runs better because im reducing load, the vacuum is increasing, and my timing goes up, but when i try and just drive normally its a dog, every time i shift a gear it bogs down and struggles through the gear. when i disable knock retard it seems to run ALOT better, but i feel like im still just making the motor fight through a knock, just with more timing. the truck has a manual trans and i feel like i can feel when the motor knocks through the stick. what im wondering is if im feeling a "knock" through the stick, or if im just feeling the motor breaking up, because the knock retard puts me down to 7 degrees of timing, making the air fuel ratio drop into the high 10s.

looking over my last data log i can see that upon starting the truck, the knock counts are around 50, once it warms up they are up to 190 and it pretty much stays right around 200, peeking at around 250 towards the end. its got a 160 t-stat and it runs at around 170 degrees lately in the summer heat of Florida.

i feel like the motor really cant be knocking, being that its reading 190 knock counts at 1600rpms witht he timing at 13 degrees, then the timing drops to 7 degrees with the knock retard and it still read high knock counts. is it really even possible that im knocking at 7 degree of timing at as low as 1400 rpms with a fairly low compression motor on 93 octane and not making any boost, it makes me wonder if i should put any trust into this knock sensor or if i have a false knock issue from valvetrain harmonics, header leak, ect? the headers are surely leakers, $150 cheapies, my cam is pretty high lift, flat tappet, and stamped rockers.

should i be worried or should i do away with knock retard and move on, i can remove the knock retard and still maintain burst knock for rapid throttle movement. my bigest thing is that i really can feel the motor kncokign when im holding on to the stick, should i disregard this?

xch3no2

Check the plugs for evidence, tiny peppering.

No mention of blm's or afr's, that will help.

chevy1500z71

ill pull a plug tomorrow and post a pic of it

the tune is a little rough around the edges, it idles around 17:1, really light pedal/slow speed it stays around 15-16:1. under acceleration it stays around 13, then drops to around 12 as you near 0 vacuum, wot sticks around 11.5:1

chevy1500z71

alright, i got some pics. its at the bottom of the post.

today the motor started to miss, sounds like its down a cylinder on the left side, this has happened before, but only after going a long time on old plugs that have been through many tuning sessions and are full of carbon. its odd that this is happening only a few weeks after a new distributor, coil, wires, plugs, i did keep the old cap and rotor that was about 8,000 miles old, maybe it needs inspection. the condition goes away as the load decreases, if i keep the rpms up and the vacuum low there is no problem, if the vacuum drops and the rpms are lower then 2200 the motor just starts to miss, the best description is it basically sounds and feels like mud truck that has just been swamped out, like its got wet plug wires or water under the cap, that sort of feeling.

anyway i finally pulled a plug today, i definitely think the motor is knocking. i just don't know what to do? im thinking the motor is just slap full of carbon, but i have methanol injection. im thinking about seafoaming it and putting a set of cr41ts plugs in gapped to .25 instead of my current cr42ts at .35, maybe it will help... or would a hotter plug help a low rpm/high gear knock? i dont know, i need some input on this one.




when shining a flashlight inside it its dark on the inside, runs a little rich.

RBob

iTrader: (1)

My take is that you are borderline too rich with too much spark timing. This is what gives plugs that gray color. It is a little difficult to tell as the plugs have also been cruised on.

Start by pulling timing , then work on the fuel.

RBob.

chevy1500z71

i can run a stock timing table and have the same problem, the issue isnt a timing problem. what do you think about the heat range? do you think im having a real knock issue based off of the plugs or is the motor just breaking up from too much fuel.

iv got a new tune written up. it has less fuel and less timing. ill try it out but im sure it wont resolve my problem. i still need to get the truck running on all 8 before i load up a new tune anyway.

RBob

iTrader: (1)

For heat range, I run the coldest plug that doesn't foul. You mentioned Dart heads, are they cast iron? If aluminum then different plugs are required.

As for detonation, it is hard to tell from the pictures. The plugs have a lot of build up which also doesn't help. Put a couple of new plugs in and drive it where the problem is (high load, low RPM. Keep out of WOT.

Then pull the plugs and check them.

RBob.

chevy1500z71

alright, ill do that and post back. ill get some new plugs and a can of sea foam.

the heads are iron, the blower is non inter cooled, and its 100 degrees outside, im getting a pretty hot intake charge. my knock problem is right before the methanol is spraying.

i have been keeping out of wot, although, the problem is non existent at wide open, i can run 20 degrees of timing or 32 degrees at wide open and get little-no knock count, any knock count would just be false knock from leaky headers or noisy valve train. iv been trying to get the rpms up and the methanol spraying to try and blow the carbon out of it but its obliviously not helping. i cant ever hear a knock with my exhaust system but i really can feel every time it knocks if i just hold my hand on the stick, my home made short throw is all solid, no isolator, so i feel everything through it lol.

as for gaping the plugs, i know tha gap wont really do anything for my problems as far as knocking goes, but wouldn't a tighter gap help prevent premature fouling? iv had these plugs in the truck for literally 300 or so miles. heres a thought, while a colder plug may be the correct way to resolve a knock problem, maybe its not the case here. my plugs are fouling so fast i have to think that i need to go up a heat range, maybe my plugs are too cold, not getting a full burn, and contributing to alot of carbon build up which leads to pre-ignition? am i way off here or could i be on to something?