I'm doing a disaterous LT1 4L60E swap into a K5 Blazer and have had nothing but trouble from the setup. I had the engine rebuilt by a machine shop and the transmission is almost new but my problem is that every time I get on the gas, at a certain RPM it makes a loud clacking noise. On top of that, it doesn't seem to have any power. My old 350 with 165 horses did a lot better than what this thing is doing now. Any ideas on what the problem might be? Wiring? A sensor?

 

i'd double check ur plugs and the optispark
it can cause tons of problems

 

plugs are brand new. Opti... I don't even want think about that. That thing was the worst idea in history. I'll replace it if I have to but I think it's somwthing else.

 

sounds like someone has some knock???
is it high rpms?
may be signs of spun bearing(s)

 

On an brand new rebuild????

 

'clacking' is usually loose valves.. Check those...did you adjust em? rebuilt may not be adjusted correctly...

 

rockers?

hey its definatly possible
1 bad bearing clearance

 

maybe u switched few wires around on the opti?? double check that

 

Spark plug wires?

 

yea

 

It's not a constant clacking noise. It's just at a high RPM when I step on it, or even rev it parked. That's the sound, and it doesn't have any power.

 

you didn't put regular in it did you?

 

I have that same noise and I have no Idea what it is!!!!!!!!!!!!!!!
My power seems to be fine but then again there could have been something wrong the whole time and can't tell there is something wrong....oh ya and the noise seems to move around from left to right from the engine bay

 

Yeah, I did put in regular. Could that be part of the problem?....Or all of the problem?

 

I dont know about all of the problem, but im willing to be it could be part of it. My car runs like crap on regular.

Aaron