hey guys,
so I have a new build 350 in my blazer, it ran great for about three months. after that it started clicking or tapping in the engine, come to find out some of the rocker arms come loose, so I readjusted them. after that it ran fine for a couple of weeks and then the sound started up again. this time I thought two of the lifters had gone bad because when you adjust them the engine would not change even when you tightned them. you could only hear this noise when you applied the gas when going down the road, at idle it sounded fine. so I replaced the lifters, now it clicks all the time, even with the valves sit. this is driving me nuts, anybody have any ideas?

 

Did you check all of your push rods to make sure that none were bent?

 

yeah i checked them when i pulled the intake off to change the lifters. also i forgot to note on here that when you adjust the valves on cylinder 4 it makes this woshing sound, kinda like air excaping or something. and now the sound is back to where you can only hear it when stepping on the gas, at idle or rolling down a hill off the gas you cannot hear it.

 

hmmm possibly spark knock sound??? just throwing it out there, seeing its only happening when your hitting the throttle, and not at idle or anything like that.

just trying to help narrow it down

Ck1500

 

thanks. I looked up some of the things that can cause spark knock, and a lot of them is posable. like lean mixture, timing, vaccum leak, and some others. now I've got a edelbrock 650 cfm carb, 1406 i think, and its the one that was made for lean ECO. cars. so I'm wondering if the carb is to small. it worked fine on my stock 350, but the new 350 is bored .30 over, with a .442 lifted cam, hooked headers, edelbrock mufflers, and some other PERF. parts. so anybody think this carb is just not big enough for this engine? I've been thinking of getting one of those thunder series 750 carbs from edelbrock.

 

Based on the cfm chart, at 100% volumetric efficiency (most engines are at 85%) a 355 cu in engine at 5500 rpm max will need 595 cfm at redline (525 cfm at 85%). Your performance parts have little to do with cfm, rather fuel requirements. You will probably need to order their jet kit and spend a day tuning. I've used the 1406 in big block application with good results. FYI the 1406 is 600 cfm not a 650 cfm, Edelbrock only makes a 650 in the Thunder series.

If the valves are adjusted right and the motor runs good other than the noise, it sounds like spark knock caused by too much timing. If the timing is correct it is in the valvetrain or camshaft.