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Old 10-01-2010, 12:14 AM
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sbc 350 twin turbo (Knocking)

I have recently built a sbc 350 and put twin turbos on it. Dummy me i only built the top end and shortly after installing it, it had excessive crank case pressure. I was so eager to drive it before summer was over that I ignored it and drove the car anyways. Initially it had more power than i had ever felt. As the crankcase pressure worsened I started to lose power. I then went and got a boost timing master and got no more power at all. The motor ran fine with absolutely no noise until just a week or two ago(other than the pressure), but then it started to tap just a little. Once again, stupid me, i kept pushing it until just tonight i went to go for a ride and it was tapping a little louder than usual. After a slight rev to about 1700rpm it started knocking and knocking hard. I instantly curdled my boxers and shut it down. I have over 14k in this set up over the past 3 mons and i am in diar need of help. Please tell me the knocking is fixable.

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Old 10-01-2010, 12:29 AM
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Like a tap tap noise, or a deep thunk noise? If it's the latter I bet you toasted a bearing somewere.
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Old 10-01-2010, 12:34 AM
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From the sound of it you've hurt it bad - rod bearing, wrist pin, or piston. First mistake was not getting the Boost Timing Master on it from day one - it isn't used to get more power, it is used to prevent too much ignition timing causing detonation and hurting the engine. The BTM retards timing in relation to rising boost to prevent engine damage, and that is all it is made for.

If you are lucky it could just be something bent or broken or come loose in the valvetrain, so cross your fingers and look there first.

It was a real mistake to push it hard without the BTM.

Are you using a blow-off valve, and what psi is it set at?? How many pounds of boost are you running??

Might help to give us a rundown of all the parts used in the engine, compression ratio, etc.
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Old 10-01-2010, 12:42 AM
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regret. tear/tear/tear

I am using a blow off valve and intercooler. The compression ratio, i was told, is about 8.5:1. The waste gates are standard with the kit i got and open at eight psi. The engine initially had a faint tap tap for around the last 150 miles and tonight went to an extremely loud KNOCK,KNOCK, loud enough that i think i could physically feel it. My number one question is, is there any way that it could have destroyed my extremely expensive heads, roller rockers, block, or new cam. I've made peace with rebuilding hte bottom end already. I just would like some piece of mind in knowing i don't have to start all over.
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Old 10-01-2010, 12:49 AM
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what exactly happens when an engine starts to knock, the rods, pistons, etc. do what. Sorry to sound so ignorant but i simply had the motor built and paid the bill. Though I did all the work in the car itself i have but a clue as to how the engine works and what can happen to them.
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Old 10-01-2010, 12:52 AM
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The rods could be bent or have the pins/berings screwed up, holes elongated, the main bearings could have spun or worn through, the crank could be toasted. pistons could have the pin holes turned into oblongs or torn up. could have a bent valve or pushrod, messed up cam, rockers could have come loose and are hitting something. It it was detonateing and is still detonateing it could have blown a hole in a piston or melted the rings/pistons.

Those are all worst case possibilitys.

Last edited by TireTracks; 10-01-2010 at 12:57 AM.
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Old 01-12-2011, 10:34 PM
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knocking found!

I finally got the engine out and apart and found that i hit detonation. I burned a whole in the number three piston. Some of the debris was smacking into the head making the knocking noise. The heads are off to be fixed @ midwest head repair and i have bought a forged scat crank, forged scat connecting rods, and srp forged dish pistons along with some cereamic rings. The block is going .030 over and I am going to push the turbos up to 12psi and see what shakes out. Wish me luck. Tire tracks is the winner!!! It would have had to be the worst case scenario.
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Old 01-12-2011, 10:41 PM
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Wish I had the kind of money your spending. What kind of car is this in?
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Old 01-12-2011, 10:41 PM
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Knocking found!

I have a question about the fuel feed into my sbc setup. I am using a holley 650cfm and edelbrock mechanical fuel pump. When the car was running and i was dragging light to light it would shut off about eighty when punched from a stand still. I am just wondering if it is possible that i was sucking the carb dry and forcing a lean condition, thus putting me into detonation. Is this possible??? If so, what can be done???
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Old 01-12-2011, 10:42 PM
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Knocking found!

1984 Monte carlo ss. Wish i never got into it for as much as i have. I took the body off, blasted and zinc plated the frame and underbody, then rino lined the whole underneath. I have well over 14,000 in it and the freakin thing is in pieces in my garage.
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Old 01-12-2011, 11:56 PM
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lack of fuel???

I have a question about the fuel feed into my sbc setup. I am using a holley 650cfm and edelbrock mechanical fuel pump. When the car was running and i was dragging light to light it would shut off about eighty when punched from a stand still. I am just wondering if it is possible that i was sucking the carb dry and forcing a lean condition, thus putting me into detonation. Is this possible??? If so, what can be done???
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