Justhereforinfo

iTrader: (2)

I recently swapped out set of flowtech headers with no cats, to a set of Kooks with cats. During the swap i changed plugs from a tr55 (3951) gapped at .60 to a tr6 (4177) gapped at .40. I was told there was a tsb and these are the new preferred plugs from GM. Is this true?

Now i'm noticing a flatspot in the powerband. at around 3400 rpms, the rpms seem to tak longer to rise then they used to.

I can understand losing a few hp due to the cats, but this seems unusual. I would say its down a good 20-30 hp, judging from the butt dyno.

Should I switch back to the tr55? Its only like $20... Or is it from the cats?

LilJayV10

iTrader: (39)

Use TR5 for the smaller gap.

TR55 come pregapped larger.

The TSB talks about gap, not the plug itself, but it's been a while since I've read it.

TR6 are a colder plug.

spawne32

iTrader: (2)

should always run the widest gap possible without risking spark blow out, which is usually relatively easy with an NA engine that is mostly stock.

vettenuts

iTrader: (4)

Doubt its the plugs. Have you looked at any Kooks dyno curves, some headers produce less mid-range torque. Not sure that's what you feel or if the new headers threw off the tuning. Plugs would only be an issue if you foul one.

I swapped out my QTP Tri-Y headers for a well known brand of 4 to 1 headers and felt the mid-range torque loss immediately. Dyno curves confirmed this and the QTP's went right back on the car. I was surprised as was the vendor I bought them from.

MuhThugga

TR6 plugs are gapped at .035 and are one heat range colder. You want the TR5, which should be gapped at .045.

Justhereforinfo

iTrader: (2)

Truck ran great with the tr5s and the stock gap (thought it was .60) with the other headers and no cats. Didnt see a need to retune it going from stock exhuast to the flowtechs, but if this is the new powerband, it needs a retune for sure. I really hope its not the $600 kooks catted mid pipe.

I'll try a new set of tr5s tonight. If that doesnt work, i guess i will have to log some data and try to retune this thing myself.