I'd like to hear what people think about running colder plugs for knock problems and what other side-effects this can have.

I was having a knock problem with my vortec l98 setup. I was running R44LTS plugs. I tried making the mixture richer (running wideband), removed almost all of the advance, put in a new knock sensor and could not get rid of the knock retard.

I tried cooler heat range plugs (R42LTS) and I never get knock - even when I am running too much timing and I am too lean but didn't think much of it. Took the car to the dyno last week and the car peaked at only 4400 RPM (230 rwhp) and I expected another 1000 RPM and another 50hp.

I am wondering if this could have to do with the plugs/heat range and if I was better off with the 44 plugs and maybe there was some other underying problem with the knock.

any opinions?

My mods: zz4 cam, AS&M runners, modified vortec heads, headers, bigger TB, all port matched.

 

With spark plugs it is best to run the coldest possible that doesn't foul.

A plug that is too hot usually causes pre-ignition. This is different from detonation but the knock system can still pick up pre-ignition and report knock counts.

What did the previous plugs (the 44's) look like after being run for a while?

RBob.

 

With a conservative tune, colder plugs may reduce WOT a small bit on the order of 5 - 10 hp at most. With an aggressive tune, the colder plugs can show a 5 - 10 hp gain. It's usually a small percentage of your total power.

Unless you did controlled back-to-back testing and retesting with the plug swap, I wouldn't assume the plugs were completely responsible.
While cold plugs can reduce detonation and tendancy to spark-knock, they cannot eliminate all spark-knock. They also wouldn't kill 50 hp unless they were misfiring because of cracks or fouling.

A plug swap will not change the shape of your power curve or make it peak at a different point.

Hopefully you know that SBC1 engines have always had a problem with the #5 & #7 cylinders crossfiring when under load. Reducing the SA will not solve this problem as it is usually caused by the plug wires being ran too close together.

One cylinder overheating will have the same effect of spark-knock that is difficult to eliminate. It could be caused by clogged passages in the cooling system, a fuel distribution problem in the intake manifold, or an injector that is falling behind in flow.

Slop in the bottom end of a high mileage engine or piston slap can also cause knocking that is relately unaffected by SA.

 

The 44 Plugs and the 42 plugs both looked fine however they had less than 500 miles on them.

I do not know if the knock the computer detected was preignition, detonation, or some other noise... BUT I have NO KNOCK whatsoever just by going from 44 to 42 plugs... if that helps! I always got knock when I got on it with the 44s but I can't even make it knock with the 42s.

No I didn't know about the crossfiring problem but the knock is gone and sounds like the power difference is minimal from 44s and 42s so I should probably just stick with the 42s - still need to figure out why my power is down though.

Also, I have a 50k L98 and I think it's pretty healthy. I have another set of injectors maybe I can swap them in and see if there's a difference although both sets were supposedly flow-matched.

thanks for the info...