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1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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Discussion Starter · #1 · (Edited)
I did try a search but nothing narrowed down IMO, 489 10.77:1 comp., Broke in on dyno and 5-6 pulls to 589.? HP & 600.6 TQ and has about 10 road miles, I put new M&H Race Master DR 275/50r17" so I took it for a short drive to see if it would stay straight, from a 15-20 mph roll I punched it long enough to see if it would stay straight maybe 2-3 sec then let off, went around a couple blocks and back to the garage, well now when I start the car it has a loud pop/bang out the exh. then once it warms up it's not so noticeable but doesn't sound right, cam is a Lunati 231/239 110 lsa .600 lift hyd roller, Howards Max Effort (Gatorman) roller lifters, Brodix RR R port 294 115 cc W/CNC option, AED 1,000 carb, So Where would you guys Start looking???
 

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I'd start with the timing. It's possible the distributor wasn't fully tight. Could have spun a little the first time you ripped it in the car, with all the vibrations and such.

I'd also pop the valve covers of and re-check all the rockers / valve lash. Make sure nothin loosened up on ya.
 

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489 10.77:1 comp., Broke in on dyno and 5-6 pulls to 589.? HP & 600.6 TQ and has about 10 road miles, I put new M&H Race Master DR 275/50r17" so I took it for a short drive to see if it would stay straight, from a 15-20 mph roll I punched it long enough to see if it would stay straight maybe 2-3 sec then let off, went around a couple blocks and back to the garage, well now when I start the car it has a loud pop/bang out the exh. then once it warms up it's not so noticeable but doesn't sound right, cam is a Lunati 231/239 110 lsa .600 lift hyd roller, Howards Max Effort (Gatorman) roller lifters, Brodix RR R port 294 115 cc W/CNC option, AED 1,000 carb, So Where would you guys Start looking???
Check to make sure the distributor didn’t come loose and rotate on you.
 
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1969 El Camino SS396
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Has the distributor moved? How is the distributor gear? Pull the valve covers and check the rockers.
 

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1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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9,305 Posts
Discussion Starter · #5 ·
I'll check the dist. first if it's OK I'll pull the plugs, bolt the 3 bolt crank turning socket on and start checking lift with a mag base dial indicator at each rocker arm...but was hoping to Not have to do that, think a spark plug could cause it? I already changed the iron gear that came on the Pertronix Flame Thrower III to a Nitrided? gear from Straub Tech.
 

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1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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9,305 Posts
Discussion Starter · #7 ·
Hum that's too simple :oops: LOL But I'll check EDIT I'm going back to the car tomorrow after work then I'll post what I find, or don't find
 

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If your distributor is moving on you, everything else is a wild goose chase.
After confirming your plug wires are all on, I'd start by seeing if you can move the distributor by hand or not....and then check the timing.
 

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Start with the basics. Pull the valve covers off and just check for the obvious. Don't want to keep troubleshooting if you have a broken spring or something, but then go for Burnt wire, broken plug, etc. Yes I did have a bad plug that would pop going down the track. Then you can check the timing, and look for vacuum leaks.
 

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1966 Chevelle SS396
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Distributor is the quickest place to start. As was already mentioned, see if it's loose enough to turn without much effort.
 

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Check easiest thing to hardest thing in that order .
Signed
The Master of the obvious

Does it backfire when you first fire it up cold ?
 

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Agree with everyone else. Check timing.
 
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Check your plugs, I had a new set of AC plugs that I ran a couple of races ago and the car was not doing well, messed around with it for half the day. Swapped in the 2 year old plugs and the car ran perfect, pulled to 7K again cleanly.
 

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Lift the hood at night, or make it dark somehow, and with the hood open look for a light show coming off the wires to a ground source. You might be able to hear a pak, pak, pak sound too.
 

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1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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9,305 Posts
Discussion Starter · #18 ·
I didn't watch the tach as I was kind of expecting the car to get sideways but it didn't, my guess would be low 5,000 but I really don't think it even broke the tires loose, I'm starting to think the dist moved pretty quick, the dist has an adjustable digital rev limiter but the backfire clears up after warming up..?
 

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Have you retorqued the intake? Could be adding to other items.
 

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1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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9,305 Posts
Discussion Starter · #20 ·
I'll check the intake bolts too, engine builder put it on with gray silicone at the China walls but I don't know if anything is on the gaskets, the back fire goes away after a couple min of warming up and turns to a miss so maybe plugs?
 
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