I have a 355 that i swapped in my car. It feels fine under 3500 rpm and doesnt smoke even on hard acc. but when i take it up to 4000+ it feels rough and lets out some kind bluish smoke. Can someone tell me what the problem is??

 

How many miles on the motor????Sounds like rings to me....

 

Sounds like it's running rich, but you didn't say what induction system you're running so not sure what you should do about it.

If it's carb w/ a Quadrajet, make sure the secondary air valve spring tension is set right and the vacuum dashpot is working correctly. If it's carb w/ a Holley, post back with info...mechanical or vacuum secondaries?

If it's TPI check your fuel pressure and verify you're running the right MEMCAL and injectors for your new engine. Next step beyond that is to borrow a scantool or set up a laptop so you can read ALDL data while the problem is happening.

If it's TBI, no clue...my only experience w/ TBI is replacing it with TPI.

 

If it was running rich, wouldn't the problem be worse at lower RPM's?

 

Sure, but it could be she's flooding when the secondaries are coming in (If it's a carb). However you would see Black smoke(fuel), not so much blueish(oil).

If your swaped engine is kinda new with low miles, than your rings are not quite seated yet. The smoke is not as visible when your cruising around, as when your getting up to into the higher RPM's.

Ron

 

Depends on the cause, especially so if it's a carb. The secondaries open at a certain throttle position, so the primaries could be dialed in fine and it would run great until the secondaries open...then things would go rich.

Quadrajets are really bad about this if the spring tension on the air valve butterflies is loose, the'll open early and dump gas down the secondaries. They don't use a traditional venturi like Holleys do, so misadjustments show up much worse.

 

Bums me out when people post a problem, then just let it die without an update...oh well Ive learned something from this post. Thanks guys!

 

Yeah, I wonder some times...did the guy just say "oh well" and drive the car off a cliff? I suppose some people show up expecting a step-by-step procedure on how to fix their problem, and get disappointed when there's actual thinking involved.